the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 May 2021
A 25-year climatology of low-tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica
Abstract. A 25-year set of daily radiosonde data was used to investigate temperature and humidity inversions at Neumayer Station, coastal Dronning Maud Land, Antarctica. For the first time, inversions were studied differentiating between different synoptic conditions and different height levels. It was shown that, generally, inversions occurred on the majority (78 %) of the days, with simultaneous occurrence of humidity and temperature inversions being observed on approximately two thirds of all days. Multiple inversions are common in all seasons for both weather conditions, however, typically occur more frequently under cyclonic conditions. The seasonality of inversion occurrence and features, i.e. inversions strength, depth and vertical gradients, was analysed statistically. Different formation mechanisms depending on inversion levels and prevailing weather situations are related to typical annual courses of certain inversion features. Winter maxima were found for the features that are mostly connected to the temperature close to the surface, which is mainly a result of the negative energy balance, thus influencing surface-based inversions. At the second level, both temperature and humidity inversions are often caused by advection of comparably warm and moist air masses related to the passage of cyclones and their frontal systems. Thus maxima in several inversion features are found in spring and fall, when cyclonic activity is strongest. Monthly mean profiles of humidity and temperature inversions reveal that elevated inversions are often obscured in average profiles due to large variations in inversion height and depth.
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RC1: 'Comment on wcd-2021-22', Anonymous Referee #1, 11 May 2021
The manuscript “A 25-year climatology of low-tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica” addresses temperature and humidity inversions at Neumayer Station in Antarctica. The study aims to connect inversion properties to synoptic weather conditions, and to study inversions on different height levels. Investigation of both temperature and humidity inversions at a single station provides an opportunity to analyse inversion properties, their connection to prevailing weather conditions and affecting physical processes in detail, but unfortunately this study fails to go deep enough in those analyses. Although the manuscript is in many aspects well prepared, it has serious problems related to methods.
- My main concern is that the concept of the manuscript is based on division between “cyclonic” and “non-cyclonic” conditions at the station, defined from the synop weather codes. In practice, these weather codes used tell whether there is/has been precipitation or not. They do not indicate anything about circulation, and they should not be referred as cyclonic/non-cyclonic. If the authors want to classify circulation, they should use reanalysis/numerical model pressure fields for that or at least utilize more the wind direction information (which is also available from radiosoundings). As far as I understand the classification made in this manuscript, it practically only separates precipitation events from non-precipitation events. This leads to my second serious concern: what is the motivation to study inversion characteristics in precipitation events, when we know that radiative cooling, which is largely controlled by clouds, subsidence and horizontal advection are the main factors affecting the inversion properties? Clouds and advection can occur without precipitation. Radiative cooling, both at the surface and on the cloud tops, is almost neglected in this study (including the Introduction section), even if it is the main mechanism behind the temperature inversions. Specific humidity inversions close to the surface are largely affected by this radiative cooling, and saturation takes place in the lowermost cold layer and leads to specific humidity inversions. Formation mechanisms of inversions are not adequately taken into account in the analyses, and the authors do not utilize what is known about inversions in the other polar region, i.e. Arctic.
- Interpretation of the results is not deep in the manuscript, and it is mostly at the level of a “data report”. The data analyses made do not really provide support for physical interpretation, especially because they do not give reliable estimates of the synoptic conditions/atmospheric circulation. The abstract the Discussion/conclusions section should be able to convince a reader that this manuscript has provided some new valuable results, but unfortunately this value is not clearly visible in the current version of the manuscript.
- I have two suggestions to the authors: (1) if you want to define the states based on circulation (cyclonic/non-cyclonic), define the weather states based on reanalysis/numerical model fields, and utilize those data also to address advection, or (2) if you want to limit the study to observational data, utilize more comprehensively the wind speed/direction information of radiosondes, cloud cover observations and surface radiation observations (if available). Instead of dividing the data between precipitation/non-precipitation cases, divide the data based on cloud conditions (which are known to have a large impact on the inversions), radiative fluxes at the surface, and wind direction.
Citation: https://doi.org/10.5194/wcd-2021-22-RC1 -
CC1: 'Reply on RC1', Elisabeth Schlosser, 11 May 2021
We thank Referee #1 for the fast review with helpful comments. We will provide a detailed answer when both/all reviews are available, but would like to briefly comment on the referee’s comments right now.
We realize that we failed to sufficiently explain our method to define the different weather conditions. Different from the Arctic, weather and climate at Antarctic coastal stations is strongly influenced by the circumpolar trough, a climatological low pressure area that results from a number of cyclones that regularly develop and move eastwards above the Polar Ocean. Weather at Neumayer thus has a fairly “binary” character: either overcast conditions with precipitation (and or blowing/drifting snow) and high wind speeds from easterly to NNEly directions related to a cyclone passing in the north of the base, or, between two cyclones, fair weather conditions with south to southwesterly winds and low cloudiness.
Thus a classification based on model pressure fields, wind direction or cloudiness, as the referee suggests, would basically lead to the same results as our classification based on SYNOP observations. We will add this information in the revised version of the manuscript.
We agree that clouds or warm air advection without precipitation can be very important in the formation or destruction of inversions, however, this is more important in the interior of the Antarctic continent and negligible at Neumayer. (cloudiness would be a difficult variable anyway as there are no eye observations at night and, during the polar night, observation of clouds is difficult and not reliable.)
At Neumayer, as we state in our study, the cyclones (that bring precipitation) are very important for the formation of elevated inversions since they are usually associated with advection of relatively warm and humid air masses.
We also stated that surface based humidity inversions are caused by deposition of hoar frost which is caused by radiative cooling. Arctic and coastal Antarctic conditions are very different, and there are clearly more studies available for the Arctic than for the Antarctic.
We would like to stress that our study is the first in Antarctica to investigate humidity and temperature inversions at different levels and for different weather conditions and by far for the longest time period (25 years). Seasonality of various inversion features were studied in detail and their relationships with each other and different formation mechanisms were discussed.
As we state in the conclusion, more detailed studies including the surface energy balance and advection terms from models are recommended, but beyond the scope of our study. In particular, the formation and destruction of inversions could be studied with the abundance of data available at Neumayer, but this would be better done in numerous case studies than for a complete 25-yr data set.
So, we will use the suggestions of the referee to improve our introduction and methods section, including a more detailed comparison with Arctic conditions and the revised version of the manuscript will clarify all these points. (T.Silva and E. Schlosser)
Citation: https://doi.org/10.5194/wcd-2021-22-CC1 -
AC1: 'Reply on RC1', Tiago Silva, 20 Aug 2021
We thank RC1 for the fast review with helpful comments. We will now answer to all single points:
- My main concern is that the concept of the manuscript is based on division between “cyclonic” and “non-cyclonic” conditions at the station, defined from the SYNOP weather codes. In practice, these weather codes used tell whether there is/has been precipitation or not.
This point was also of concern for RC2, and we realize that we have to explain our choice of definition and terms in more detail. “Cyclonic vs. non-cyclonic” has not been our first try, but we came to the conclusion that it describes our defined synoptic situation as closely as possible. “Precipitation vs. non-precipitation”, as the RC2 states, too, is difficult because diamond dust is also precipitation, but definitely falls into the non-cyclonic class. Also, “fair weather” vs. “bad/stormy weather” is not a good choice since fog would not belong to the bad weather category while it is not exactly what one would call fair weather. Non-cyclonic conditions would not occur when the area is under the influence of low pressure (except for a short transition period, we discussed this difficulty already in the original text).
- They do not indicate anything about circulation, and they should not be referred as cyclonic/non-cyclonic. If the authors want to classify circulation, they should use reanalysis/numerical model pressure fields for that or at least utilize more the wind direction information (which is also available from radiosoundings). As far as I understand the classification made in this manuscript, it practically only separates precipitation events from non-precipitation events.
Different from the Arctic, weather and climate at Antarctic coastal stations is strongly influenced by the circumpolar trough, a climatological low-pressure area that results from several cyclones that regularly develop and move eastwards above the Polar Ocean. Weather at Neumayer thus has a fairly “binary” character: either overcast conditions with precipitation (and or blowing/drifting snow) and high wind speeds from easterly to NNEly directions related to a cyclone passing in the north of the base, or, between two cyclones, fair weather conditions with south to southwesterly winds and low cloudiness. This knowledge comes from personal experience (ES has wintered at Neumayer and lived in the area for almost 2 years) and is also confirmed in the literature (e.g. König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006, König-Langlo et al., 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. VOL. 103, NO. D9, PAGES 10,935-10,946).
Thus, a classification based on model pressure fields, wind direction or cloudiness, as the referee suggests, would basically lead to the same results as our classification based on SYNOP observations. We added this information in the revised version of the manuscript.- This leads to my second serious concern: what is the motivation to study inversion characteristics in precipitation events, when we know that radiative cooling, which is largely controlled by clouds, subsidence and horizontal advection are the main factors affecting the inversion properties? Clouds and advection can occur without precipitation. Radiative cooling, both at the surface and on the cloud tops, is almost neglected in this study (including the Introduction section), even if it is the main mechanism behind the temperature inversions. Specific humidity inversions close to the surface are largely affected by this radiative cooling, and saturation takes place in the lowermost cold layer and leads to specific humidity inversions.
The original motivation for the study of Antarctic inversions stems from ice core studies, where paleotemperatures are derived from stable water isotopes of the ice. The stable isotope ratio of the ice is the result of a complex precipitation history (isotopic fractionation during evaporation and condensation processes), and the derived temperature mainly represents the condensation temperature of the last precipitation. The relationship between surface temperature, condensation temperature and temperature at the top of the inversion is still a fairly unknown subject. For the deep ice cores in the interior of Antarctica, which yield information about the last 800,000 years, of course, the surface-based inversions are most important, and about half of the precipitation falls in the form of diamond dust. However, there are also cores close to the coast (e.g. Law Dome, e.g. Souney et al., 2002) and also the interior cores get precipitation related to warming events with advection of relatively warm and moist air from lower latitudes at higher levels.
Different from many deep drilling locations, Neumayer Station has an abundance of meteorological data and thus was chosen for the presented study for a first climatology of temperature and humidity inversions. In a second publication that also includes the inland station Dome C, a deep drilling location, we will present a more elaborated study of the relationship between condensation temperature, surface temperature and temperature at the top of the inversion, which has been used as approximation to the condensation temperature in ice core studies for many years, simply due to lack of better knowledge. We had mentioned the ice core related motivation already in the original version but elaborate it in more detail in the revised manuscript.We agree that clouds or warm air advection without precipitation can be very important in the formation or destruction of inversions, however, this is more important in the interior of the Antarctic continent (e.g. Hirasawa et al., 2000) and of minor importance at Neumayer. Cloudiness would be a difficult variable as there are no eye observations at night and, during the polar night, observation of clouds is difficult and not reliable.
At Neumayer, as we state in our study, the cyclones (that bring precipitation) are very important for the formation of elevated inversions since they are usually associated with advection of relatively warm and humid air masses.
We also stated that surface-based humidity inversions are caused by deposition of hoar frost which is caused by radiative cooling. Arctic and coastal Antarctic conditions are very different, and there are clearly more studies available for the Arctic than for the Antarctic.
We would like to stress that our study is the first in Antarctica to investigate humidity and temperature inversions at different levels and for different weather conditions and by far for the longest time period (25 years). Seasonality of various inversion features were studied in detail and their relationships with each other, and different formation mechanisms were discussed.
As we state in the conclusion, more detailed studies including the surface energy balance and advection terms from models are recommended, but beyond the scope of our study. In particular, the formation and destruction of inversions could be studied with the abundance of data available at Neumayer, but this would be better done in numerous case studies than for a complete 25-yr data set.- Formation mechanisms of inversions are not adequately taken into account in the analyses, and the authors do not utilize what is known about inversions in the other polar region, i.e. Arctic.
We used the suggestions of the referee to improve our introduction and Data and Methods sections, including a more detailed comparison with Arctic conditions. In particular, we stressed the differences between Arctic and coastal Antarctic climate that also would lead to different classifications of synoptic situations for a study of inversions in the Arctic. Also, the highly complex interactions between surface inversions, elevated inversions, and low-level clouds and the involved long-wave radiation fluxes are very important in the Arctic, but only of minor importance at Antarctic coastal stations due to the vastly different climatic/synoptic conditions.
- Interpretation of the results is not deep in the manuscript, and it is mostly at the level of a “data report”. The data analyses made do not really provide support for physical interpretation, especially because they do not give reliable estimates of the synoptic conditions/atmospheric circulation. The abstract the Discussion/conclusions section should be able to convince a reader that this manuscript has provided some new valuable results, but unfortunately this value is not clearly visible in the current version of the manuscript.
The study was mainly planned as a climatology. It covers the longest time period of radiosonde measurements used in a study of inversions in Antarctica, at least to our knowledge. We explain the synoptic conditions and our choice of definition in more detail in the Data and Methods section now, based on a more elaborated introduction about weather conditions at a coastal Antarctic station and the differences to Arctic conditions. We also added a new Figure (Fig. 15) for a more thorough discussion of the composite temperature and humidity profiles including the vertical wind profile.
- I have two suggestions to the authors: (1) if you want to define the states based on circulation (cyclonic/non-cyclonic), define the weather states based on reanalysis/numerical model fields, and utilize those data also to address advection, or (2) if you want to limit the study to observational data, utilize more comprehensively the wind speed/direction information of radiosondes, cloud cover observations and surface radiation observations (if available). Instead of dividing the data between precipitation/non-precipitation cases, divide the data based on cloud conditions (which are known to have a large impact on the inversions), radiative fluxes at the surface, and wind direction.
Neumayer weather conditions are strongly determined by cyclonic activity in the circumpolar trough. The weather is characterized by cyclones passing from west to east with the general westerly flow, with anticyclonic conditions for shorter or longer periods between two cyclones. The semi-annual oscillation can lead to longer anticyclonic periods in summer and winter when the trough and thus the position of the frontal zone moves northwards. This is also indicated by the main wind directions. For the majority of the time Neumayer Station experiences relatively strong easterly, to ENEly winds, related to the clockwise rotation of the passing cyclones. Weaker winds from southerly or SWly directions prevail under high pressure. We add a figure of the mean Neumayer wind direction in the supplemental material. Also, clouds are of much less importance for inversions at Neumayer than at Arctic or interior Antarctic stations. A study by Hirasawa et al. (2000) showed that at Dome Fuji, advection of relatively warm and moist air lead to formation of low clouds, which were not sufficient to produce precipitation but increased downward longwave radiation, which, together with increased wind speed destroyed the prevailing inversion. At Neumayer, the increased wind speeds, thus turbulence associated with an approaching cyclone remove an inversion very quickly.
We explained our definition of the two-weather situation typical at Neumayer in more detail in the Data and Methods section and also gave more general information about the climate of Neumayer as an Antarctic coastal station in contrast to interior Antarctica or most Arctic stations in the introduction.References:
Hirasawa, N., H. Nakamura, and T. Yamanouchi, 2000. Abrupt changes in the meteorological conditions observed at an inland Antarctic station in association with wintertime blocking. Geophys. Res. Lett., Vol. 27 No. 13, 1911/1914.
König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006.
König-Langlo, G., King, J. C., and P. Pettré, 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. ,Vol. 103, NO. D9, 10,935-10,946).
Citation: https://doi.org/10.5194/wcd-2021-22-AC1
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RC2: 'Comment on wcd-2021-22', Anonymous Referee #2, 13 Jul 2021
Review of “A 25-year climatology of low-tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica” by Silva and Schlosser
This is a very well written paper that presents a 25 year climatology of temperature and humidity inversions at Neumayer station. Temperature inversions are important for their role in limiting vertical mixing while humidity inversions are important in cloud processes as well as being associated with atmospheric rivers. This comprehensive study of the climatology of these features will be of interest to the Antarctic and polar meteorology communities and can serve as a model for similar studies at other locations. I do have some larger (major) comments that I believe will improve this manuscript as well as a few minor comments. I find that this manuscript will be suitable for publication in Weather and Climate Dynamics after some revisions.
Major comments
I am not convinced that using the terms cyclonic and non-cyclonic is truly accurate given the way that the synoptic weather observations are used to define these two weather types. While the conditions used to identify the cyclonic type most likely occur during periods of low pressure that may not always be the case. Similarly, the non-cyclonic conditions could occur when the station is under the influence of an area of low pressure. I suggest renaming these two synoptic classifications - maybe precipitating and non-precipitation would be more accurate (although this is problematic due to the inclusion of diamond dust in the current non-cyclonic category, which I think is appropriate). But, I do think this better reflects the distinction between the two synoptic categories being used for this work.
I have some concern about the use of a fixed humidity threshold to define humidity inversions. Given the strong dependence of absolute humidity on temperature it will be much harder to meet the humidity threshold for a humidity inversion in colder conditions (aloft or in winter). It might be better to define a humidity inversion threshold as a percentage of the humidity at the inversion base or top instead.
The inversion composite figures are interesting but it may be better to create these composites using a varying height scale rather than one fixed relative to sea level. Specifically, it might make sense to create composites with the 0 height taken as the inversion base. In this way varying heights of inversion will not “smear” the inversions in the composite and a more robust signal of the inversions and their relationship to wind is likely to be seen. I would also suggest using the temperature (or humidity) at the inversion base as the 0 value so that variability in the value of temperature or humidity can be removed from the composites. Taken together these two changes should produce much more robust composites.
Minor comments
Line 5: What “both” refers to in this sentence is unclear. I assume it is cyclonic and non-cyclonic conditions, but please clarify this text or explain what two synoptic classifications are being presented in this work before this sentence.
Figure 1: It would be useful to also indicate what percent of all possible days in each month during the study period the total radiosonde count for each month represents. This could be listed below the monthly radiosonde count at the top line of this figure.
Section 2.5: It would be good to indicate the typical vertical resolution of the sounding data either here or when the radiosonde data is first introduced. This impacts what depth inversions can be reasonably identified. It might also be worthwhile to discuss why the BSRN radiosonde data is used rather than IGRA data here rather than in the discussion section.
Line 172: It would be useful to more explicitly state how the 5 point moving average profile is used. The text states that this moving average profile is used to detect the inversion base and top positions. Is this done for both absolute humidity and temperature profiles? Also, are the top and bottom inversion values of humidity and temperature taken from the unsmoothed profile data or do these values also come from the moving average profile?
Figure 4 and all similar figures: Please indicate what the boxes, whiskers and open circle symbols indicate in the figure caption. The figure caption should fully explain what is plotted in each figure without the reader needing to refer to the main text for this information.
Paragraph starting at line 299: The change in humidity gradient across the three height ranges and seasonally is driven by changes in the magnitude of absolute humidity as a function of temperature. It is not surprising that gradients are smaller at upper levels or in winter where colder, and thus drier, in an absolute sense, conditions, occur. This point should be made when discussing Figure 10.
Citation: https://doi.org/10.5194/wcd-2021-22-RC2 -
AC2: 'Reply on RC2', Tiago Silva, 20 Aug 2021
We would like to thank RC2 for the thorough review and constructive comments. In the following we address them point by point:
- I am not convinced that using the terms cyclonic and non-cyclonic is truly accurate given the way that the synoptic weather observations are used to define these two weather types. While the conditions used to identify the cyclonic type most likely occur during periods of low pressure that may not always be the case. Similarly, the non-cyclonic conditions could occur when the station is under the influence of an area of low pressure. I suggest renaming these two synoptic classifications - maybe precipitating and non-precipitation would be more accurate (although this is problematic due to the inclusion of diamond dust in the current non-cyclonic category, which I think is appropriate). But I do think this better reflects the distinction between the two synoptic categories being used for this work.
This point was also of concern for RC1 and we realize that we have to explain our choice of definition and terms in more detail. “Cyclonic vs. non-cyclonic” was not our first try, but we came to the conclusion that it describes our defined synoptic situation as closely as possible. “Precipitation vs. non-precipitation”, as the referee states, too, is difficult because diamond dust is also precipitation, but definitely falls into the non-cyclonic class. Also, “fair weather” vs. “bad/stormy weather” is not a good choice since fog would not belong to the bad weather category while it is not exactly what one would call fair weather. Non-cyclonic conditions would not occur when the area is under the influence of low pressure (except for a short transition period, we discussed this difficulty already in the original text).
Neumayer weather conditions are strongly determined by cyclonic activity in the circumpolar trough. The weather is characterized by cyclones passing from west to east with the general westerly flow, with anticyclonic conditions for shorter or longer periods between two cyclones. The semi-annual oscillation can lead to longer anticyclonic periods in summer and winter when the trough and thus the position of the frontal zone moves northwards. This is also indicated by the main wind directions. For the majority of the time Neumayer Station experiences relatively strong easterly, to ENEly winds, related to the clockwise rotation of the passing cyclones. The center of the cyclones is always north of the coast since the topography (increasing elevation) blocks further southward movements of the low-pressure systems. Weaker winds from southerly or SWly directions prevail under high pressure. We add a figure of the mean Neumayer wind direction in the supplemental material (Fig. S1). Also, clouds are of much less importance for inversions at Neumayer than at Arctic or interior Antarctic stations. A study by Hirasawa et al. (2000) showed that at Dome Fuji, advection of relatively warm and moist air lead to formation of low clouds, which were not sufficient to produce precipitation but increased downward longwave radiation, which, together with increased wind speed destroyed the prevailing inversion. At Neumayer, the increased wind speeds, thus turbulence associated with an approaching cyclone remove an inversion very quickly.
We explained our definition of the two-weather situation typical at Neumayer in more detail in the Data and Methods section and also gave more general information about the climate of Neumayer as an Antarctic coastal station in contrast to interior Antarctica or most Arctic stations in the introduction.- I have some concern about the use of a fixed humidity threshold to define humidity inversions. Given the strong dependence of absolute humidity on temperature it will be much harder to meet the humidity threshold for a humidity inversion in colder conditions (aloft or in winter). It might be better to define a humidity inversion threshold as a percentage of the humidity at the inversion base or top instead.
We found that the use of absolute values of specific humidity to define inversions has been widely used in similar studies, mainly in the Arctic (e.g., Devasthale et al. 2011, Kilpeläinen et al. 2012, Vihma et al. 2011), but also in the Antarctic (Nygård et al. 2013). We thus assume that it is an accepted method for studies of humidity inversions.
Concerning lower humidity in colder seasons or at higher levels: Saturation vapor pressure is a function of temperature, and this usually leads to lower absolute humidity when the temperature is lower. However, this is only part of the story. First of all, we do not always have saturated conditions, and more important, warm air advection in winter can lead to temperatures similar to the temperatures of warmer seasons, even summer, so the humidity should be not necessarily lower, particularly since at Neumayer warm air advection usually means advection of moisture, too. Only southerly winds bring dryer air, but those are generally cold. We added these considerations in the paper (Section 2.5 and Discussion of Fig. 10).- The inversion composite figures are interesting but it may be better to create these composites using a varying height scale rather than one fixed relative to sea level. Specifically, it might make sense to create composites with the 0 height taken as the inversion base. In this way varying heights of inversion will not “smear” the inversions in the composite and a more robust signal of the inversions and their relationship to wind is likely to be seen. I would also suggest using the temperature (or humidity) at the inversion base as the 0 value so that variability in the value of temperature or humidity can be removed from the composites. Taken together these two changes should produce much more robust composites.
We thank the referee for this constructive suggestion. We created new figures with normalized height and temperature (humidity) axes for both surface based and 2nd/level inversions. Furthermore, we included the profiles for surface-based inversions under non-cyclonic conditions (Fig. 15a) and for 2nd-level inversions under cyclonic conditions (Fig. 15b) in the main manuscript and kept the original Figures 11-14 in order to be able to show the entire height profile. In Fig 15 we discuss change of wind direction and speed with height within the inversion. All figures with normalized axes including a short discussion are found in the supplemental material (Fig. S4-S7).
- Line 5: What “both” refers to in this sentence is unclear. I assume it is cyclonic and non-cyclonic conditions, but please clarify this text or explain what two synoptic classifications are being presented in this work before this sentence.
We agree that this formulation was not exact, and we corrected this in the abstract.
- Figure 1: It would be useful to also indicate what percent of all possible days in each month during the study period the total radiosonde count for each month represents. This could be listed below the monthly radiosonde count at the top line of this figure.
We fully agree, and we added this information in Figure 1.
- Section 2.5: It would be good to indicate the typical vertical resolution of the sounding data either here or when the radiosonde data is first introduced. This impacts what depth inversions can be reasonably identified. It might also be worthwhile to discuss why the BSRN radiosonde data is used rather than IGRA data here rather than in the discussion section.
This is also a good suggestion, which we followed. We changed the text in the Data and Methods Section accordingly. Given the 25-year period, three types of radiosondes were used where the latest version has always higher vertical resolution than the previous. Moreover, the weather conditions severity can also affect the vertical resolution. One of a few IGRA corrections during the quality control procedure is the removal of pressure levels where relative humidity is exceeded 100% with respect to ice. Supersaturation is remarkably important to account when making analysis over polar areas. Here, we add a figure with arbitrary dates comparing BSRN with IGRA data:
However, a statistical analysis of differences among upper air sounding archives due to distinct quality control procedures and associated impacts on inversion detection go beyond the scope of our study.
- Line 172: It would be useful to more explicitly state how the 5 point moving average profile is used. The text states that this moving average profile is used to detect the inversion base and top positions. Is this done for both absolute humidity and temperature profiles? Also, are the top and bottom inversion values of humidity and temperature taken from the unsmoothed profile data or do these values also come from the moving average profile?
Exactly. We wrote this in the manuscript already but tried to change the formulation to make it better understandable for first reading.
- Figure 4 and all similar figures: Please indicate what the boxes, whiskers and open circle symbols indicate in the figure caption. The figure caption should fully explain what is plotted in each figure without the reader needing to refer to the main text for this information.
Principally we agree that figure captions should have the full explanation of the figure. We tried to follow this request, but it turns out that adding the (same) explanation to all figure captions for Fig. 4-Fig. 10 would reduce the size of the figures if we wanted to keep the caption on the same page as the figure. This would also reduce the legibility of the figures. Thus, for practical reasons, we gave the full explanation of the box plots only in the first Figure where box plots occur (Fig. 4). (You will notice that here the page number gets aligned with the caption already. The layout done by the journal might have a reduced figure size.) We would like to avoid having this for all box plots. In the following Figure captions, we refer to this explanation in caption of Fig. 4. We hope that this will be sufficient, also taking into account that box plots are actually textbook knowledge.
- Paragraph starting at line 299: The change in humidity gradient across the three height ranges and seasonally is driven by changes in the magnitude of absolute humidity as a function of temperature. It is not surprising that gradients are smaller at upper levels or in winter where colder, and thus drier, in an absolute sense, conditions, occur. This point should be made when discussing Figure 10.
As stated above, it is true that saturation vapor pressure is a function of temperature, and this usually leads to lower absolute humidity when the temperature is lower. However, we do not always have saturated conditions, and more important, warm air advection in winter can lead to temperatures similar to the temperatures of warmer seasons, even summer, so the humidity should be not necessarily lower, particularly since at Neumayer warm air advection usually means advection of moisture, too. Only southerly winds bring dryer air, but those are generally cold. We added these points in the discussion of Fig. 10., also referring to the revised Section 2.5.
References:
Devasthale, A., Sedlar, J., and Tjernström, M, 2011.: Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes, Atmospheric Chemistry and Physics, 11, 9813–9823, https://doi.org/10.5194/acp-11-9813-2011Hirasawa, N., H. Nakamura, and T. Yamanouchi, 2000. Abrupt changes in the meteorological conditions observed at an inland Antarctic station in association with wintertime blocking. Geophys. Res. Lett., Vol. 27 No. 13, 1911/1914.
Kilpeläinen, T., Vihma, T., Manninen, M., Sjöblom, A., Jakobson, E., Palo, T., and Maturilli, M., 2012: Modelling the vertical structure of the atmospheric boundary layer over Arctic fjords in Svalbard, Quarterly Journal of the Royal Meteorological Society, 138, 1867–1883, https://doi.org/10.1002/qj.1914
König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006.
König-Langlo, G., King, J. C., and P. Pettré, 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. ,Vol. 103, NO. D9, 10,935-10,946).
Nygård, T., Valkonen, T., and Vihma, T. 2013: Antarctic low-tropospheric humidity inversions: 10-yr climatology, Journal of Climate, 26, 5205–5219, https://doi.org/10.1175/JCLI-D-12-00446.1
Vihma, T., Kilpeläinen, T., Manninen, M., Sjöblom, A., Jakobson, E., Palo, T., Jaagus, J., and Maturilli, M, 2011.: Characteristics
590 of temperature and humidity inversions and low-level jets over Svalbard fjords in spring, Advances in Meteorology, 2011,
https://doi.org/10.1155/2011/486807Citation: https://doi.org/10.5194/wcd-2021-22-AC2
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AC2: 'Reply on RC2', Tiago Silva, 20 Aug 2021
Status: closed
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RC1: 'Comment on wcd-2021-22', Anonymous Referee #1, 11 May 2021
The manuscript “A 25-year climatology of low-tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica” addresses temperature and humidity inversions at Neumayer Station in Antarctica. The study aims to connect inversion properties to synoptic weather conditions, and to study inversions on different height levels. Investigation of both temperature and humidity inversions at a single station provides an opportunity to analyse inversion properties, their connection to prevailing weather conditions and affecting physical processes in detail, but unfortunately this study fails to go deep enough in those analyses. Although the manuscript is in many aspects well prepared, it has serious problems related to methods.
- My main concern is that the concept of the manuscript is based on division between “cyclonic” and “non-cyclonic” conditions at the station, defined from the synop weather codes. In practice, these weather codes used tell whether there is/has been precipitation or not. They do not indicate anything about circulation, and they should not be referred as cyclonic/non-cyclonic. If the authors want to classify circulation, they should use reanalysis/numerical model pressure fields for that or at least utilize more the wind direction information (which is also available from radiosoundings). As far as I understand the classification made in this manuscript, it practically only separates precipitation events from non-precipitation events. This leads to my second serious concern: what is the motivation to study inversion characteristics in precipitation events, when we know that radiative cooling, which is largely controlled by clouds, subsidence and horizontal advection are the main factors affecting the inversion properties? Clouds and advection can occur without precipitation. Radiative cooling, both at the surface and on the cloud tops, is almost neglected in this study (including the Introduction section), even if it is the main mechanism behind the temperature inversions. Specific humidity inversions close to the surface are largely affected by this radiative cooling, and saturation takes place in the lowermost cold layer and leads to specific humidity inversions. Formation mechanisms of inversions are not adequately taken into account in the analyses, and the authors do not utilize what is known about inversions in the other polar region, i.e. Arctic.
- Interpretation of the results is not deep in the manuscript, and it is mostly at the level of a “data report”. The data analyses made do not really provide support for physical interpretation, especially because they do not give reliable estimates of the synoptic conditions/atmospheric circulation. The abstract the Discussion/conclusions section should be able to convince a reader that this manuscript has provided some new valuable results, but unfortunately this value is not clearly visible in the current version of the manuscript.
- I have two suggestions to the authors: (1) if you want to define the states based on circulation (cyclonic/non-cyclonic), define the weather states based on reanalysis/numerical model fields, and utilize those data also to address advection, or (2) if you want to limit the study to observational data, utilize more comprehensively the wind speed/direction information of radiosondes, cloud cover observations and surface radiation observations (if available). Instead of dividing the data between precipitation/non-precipitation cases, divide the data based on cloud conditions (which are known to have a large impact on the inversions), radiative fluxes at the surface, and wind direction.
Citation: https://doi.org/10.5194/wcd-2021-22-RC1 -
CC1: 'Reply on RC1', Elisabeth Schlosser, 11 May 2021
We thank Referee #1 for the fast review with helpful comments. We will provide a detailed answer when both/all reviews are available, but would like to briefly comment on the referee’s comments right now.
We realize that we failed to sufficiently explain our method to define the different weather conditions. Different from the Arctic, weather and climate at Antarctic coastal stations is strongly influenced by the circumpolar trough, a climatological low pressure area that results from a number of cyclones that regularly develop and move eastwards above the Polar Ocean. Weather at Neumayer thus has a fairly “binary” character: either overcast conditions with precipitation (and or blowing/drifting snow) and high wind speeds from easterly to NNEly directions related to a cyclone passing in the north of the base, or, between two cyclones, fair weather conditions with south to southwesterly winds and low cloudiness.
Thus a classification based on model pressure fields, wind direction or cloudiness, as the referee suggests, would basically lead to the same results as our classification based on SYNOP observations. We will add this information in the revised version of the manuscript.
We agree that clouds or warm air advection without precipitation can be very important in the formation or destruction of inversions, however, this is more important in the interior of the Antarctic continent and negligible at Neumayer. (cloudiness would be a difficult variable anyway as there are no eye observations at night and, during the polar night, observation of clouds is difficult and not reliable.)
At Neumayer, as we state in our study, the cyclones (that bring precipitation) are very important for the formation of elevated inversions since they are usually associated with advection of relatively warm and humid air masses.
We also stated that surface based humidity inversions are caused by deposition of hoar frost which is caused by radiative cooling. Arctic and coastal Antarctic conditions are very different, and there are clearly more studies available for the Arctic than for the Antarctic.
We would like to stress that our study is the first in Antarctica to investigate humidity and temperature inversions at different levels and for different weather conditions and by far for the longest time period (25 years). Seasonality of various inversion features were studied in detail and their relationships with each other and different formation mechanisms were discussed.
As we state in the conclusion, more detailed studies including the surface energy balance and advection terms from models are recommended, but beyond the scope of our study. In particular, the formation and destruction of inversions could be studied with the abundance of data available at Neumayer, but this would be better done in numerous case studies than for a complete 25-yr data set.
So, we will use the suggestions of the referee to improve our introduction and methods section, including a more detailed comparison with Arctic conditions and the revised version of the manuscript will clarify all these points. (T.Silva and E. Schlosser)
Citation: https://doi.org/10.5194/wcd-2021-22-CC1 -
AC1: 'Reply on RC1', Tiago Silva, 20 Aug 2021
We thank RC1 for the fast review with helpful comments. We will now answer to all single points:
- My main concern is that the concept of the manuscript is based on division between “cyclonic” and “non-cyclonic” conditions at the station, defined from the SYNOP weather codes. In practice, these weather codes used tell whether there is/has been precipitation or not.
This point was also of concern for RC2, and we realize that we have to explain our choice of definition and terms in more detail. “Cyclonic vs. non-cyclonic” has not been our first try, but we came to the conclusion that it describes our defined synoptic situation as closely as possible. “Precipitation vs. non-precipitation”, as the RC2 states, too, is difficult because diamond dust is also precipitation, but definitely falls into the non-cyclonic class. Also, “fair weather” vs. “bad/stormy weather” is not a good choice since fog would not belong to the bad weather category while it is not exactly what one would call fair weather. Non-cyclonic conditions would not occur when the area is under the influence of low pressure (except for a short transition period, we discussed this difficulty already in the original text).
- They do not indicate anything about circulation, and they should not be referred as cyclonic/non-cyclonic. If the authors want to classify circulation, they should use reanalysis/numerical model pressure fields for that or at least utilize more the wind direction information (which is also available from radiosoundings). As far as I understand the classification made in this manuscript, it practically only separates precipitation events from non-precipitation events.
Different from the Arctic, weather and climate at Antarctic coastal stations is strongly influenced by the circumpolar trough, a climatological low-pressure area that results from several cyclones that regularly develop and move eastwards above the Polar Ocean. Weather at Neumayer thus has a fairly “binary” character: either overcast conditions with precipitation (and or blowing/drifting snow) and high wind speeds from easterly to NNEly directions related to a cyclone passing in the north of the base, or, between two cyclones, fair weather conditions with south to southwesterly winds and low cloudiness. This knowledge comes from personal experience (ES has wintered at Neumayer and lived in the area for almost 2 years) and is also confirmed in the literature (e.g. König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006, König-Langlo et al., 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. VOL. 103, NO. D9, PAGES 10,935-10,946).
Thus, a classification based on model pressure fields, wind direction or cloudiness, as the referee suggests, would basically lead to the same results as our classification based on SYNOP observations. We added this information in the revised version of the manuscript.- This leads to my second serious concern: what is the motivation to study inversion characteristics in precipitation events, when we know that radiative cooling, which is largely controlled by clouds, subsidence and horizontal advection are the main factors affecting the inversion properties? Clouds and advection can occur without precipitation. Radiative cooling, both at the surface and on the cloud tops, is almost neglected in this study (including the Introduction section), even if it is the main mechanism behind the temperature inversions. Specific humidity inversions close to the surface are largely affected by this radiative cooling, and saturation takes place in the lowermost cold layer and leads to specific humidity inversions.
The original motivation for the study of Antarctic inversions stems from ice core studies, where paleotemperatures are derived from stable water isotopes of the ice. The stable isotope ratio of the ice is the result of a complex precipitation history (isotopic fractionation during evaporation and condensation processes), and the derived temperature mainly represents the condensation temperature of the last precipitation. The relationship between surface temperature, condensation temperature and temperature at the top of the inversion is still a fairly unknown subject. For the deep ice cores in the interior of Antarctica, which yield information about the last 800,000 years, of course, the surface-based inversions are most important, and about half of the precipitation falls in the form of diamond dust. However, there are also cores close to the coast (e.g. Law Dome, e.g. Souney et al., 2002) and also the interior cores get precipitation related to warming events with advection of relatively warm and moist air from lower latitudes at higher levels.
Different from many deep drilling locations, Neumayer Station has an abundance of meteorological data and thus was chosen for the presented study for a first climatology of temperature and humidity inversions. In a second publication that also includes the inland station Dome C, a deep drilling location, we will present a more elaborated study of the relationship between condensation temperature, surface temperature and temperature at the top of the inversion, which has been used as approximation to the condensation temperature in ice core studies for many years, simply due to lack of better knowledge. We had mentioned the ice core related motivation already in the original version but elaborate it in more detail in the revised manuscript.We agree that clouds or warm air advection without precipitation can be very important in the formation or destruction of inversions, however, this is more important in the interior of the Antarctic continent (e.g. Hirasawa et al., 2000) and of minor importance at Neumayer. Cloudiness would be a difficult variable as there are no eye observations at night and, during the polar night, observation of clouds is difficult and not reliable.
At Neumayer, as we state in our study, the cyclones (that bring precipitation) are very important for the formation of elevated inversions since they are usually associated with advection of relatively warm and humid air masses.
We also stated that surface-based humidity inversions are caused by deposition of hoar frost which is caused by radiative cooling. Arctic and coastal Antarctic conditions are very different, and there are clearly more studies available for the Arctic than for the Antarctic.
We would like to stress that our study is the first in Antarctica to investigate humidity and temperature inversions at different levels and for different weather conditions and by far for the longest time period (25 years). Seasonality of various inversion features were studied in detail and their relationships with each other, and different formation mechanisms were discussed.
As we state in the conclusion, more detailed studies including the surface energy balance and advection terms from models are recommended, but beyond the scope of our study. In particular, the formation and destruction of inversions could be studied with the abundance of data available at Neumayer, but this would be better done in numerous case studies than for a complete 25-yr data set.- Formation mechanisms of inversions are not adequately taken into account in the analyses, and the authors do not utilize what is known about inversions in the other polar region, i.e. Arctic.
We used the suggestions of the referee to improve our introduction and Data and Methods sections, including a more detailed comparison with Arctic conditions. In particular, we stressed the differences between Arctic and coastal Antarctic climate that also would lead to different classifications of synoptic situations for a study of inversions in the Arctic. Also, the highly complex interactions between surface inversions, elevated inversions, and low-level clouds and the involved long-wave radiation fluxes are very important in the Arctic, but only of minor importance at Antarctic coastal stations due to the vastly different climatic/synoptic conditions.
- Interpretation of the results is not deep in the manuscript, and it is mostly at the level of a “data report”. The data analyses made do not really provide support for physical interpretation, especially because they do not give reliable estimates of the synoptic conditions/atmospheric circulation. The abstract the Discussion/conclusions section should be able to convince a reader that this manuscript has provided some new valuable results, but unfortunately this value is not clearly visible in the current version of the manuscript.
The study was mainly planned as a climatology. It covers the longest time period of radiosonde measurements used in a study of inversions in Antarctica, at least to our knowledge. We explain the synoptic conditions and our choice of definition in more detail in the Data and Methods section now, based on a more elaborated introduction about weather conditions at a coastal Antarctic station and the differences to Arctic conditions. We also added a new Figure (Fig. 15) for a more thorough discussion of the composite temperature and humidity profiles including the vertical wind profile.
- I have two suggestions to the authors: (1) if you want to define the states based on circulation (cyclonic/non-cyclonic), define the weather states based on reanalysis/numerical model fields, and utilize those data also to address advection, or (2) if you want to limit the study to observational data, utilize more comprehensively the wind speed/direction information of radiosondes, cloud cover observations and surface radiation observations (if available). Instead of dividing the data between precipitation/non-precipitation cases, divide the data based on cloud conditions (which are known to have a large impact on the inversions), radiative fluxes at the surface, and wind direction.
Neumayer weather conditions are strongly determined by cyclonic activity in the circumpolar trough. The weather is characterized by cyclones passing from west to east with the general westerly flow, with anticyclonic conditions for shorter or longer periods between two cyclones. The semi-annual oscillation can lead to longer anticyclonic periods in summer and winter when the trough and thus the position of the frontal zone moves northwards. This is also indicated by the main wind directions. For the majority of the time Neumayer Station experiences relatively strong easterly, to ENEly winds, related to the clockwise rotation of the passing cyclones. Weaker winds from southerly or SWly directions prevail under high pressure. We add a figure of the mean Neumayer wind direction in the supplemental material. Also, clouds are of much less importance for inversions at Neumayer than at Arctic or interior Antarctic stations. A study by Hirasawa et al. (2000) showed that at Dome Fuji, advection of relatively warm and moist air lead to formation of low clouds, which were not sufficient to produce precipitation but increased downward longwave radiation, which, together with increased wind speed destroyed the prevailing inversion. At Neumayer, the increased wind speeds, thus turbulence associated with an approaching cyclone remove an inversion very quickly.
We explained our definition of the two-weather situation typical at Neumayer in more detail in the Data and Methods section and also gave more general information about the climate of Neumayer as an Antarctic coastal station in contrast to interior Antarctica or most Arctic stations in the introduction.References:
Hirasawa, N., H. Nakamura, and T. Yamanouchi, 2000. Abrupt changes in the meteorological conditions observed at an inland Antarctic station in association with wintertime blocking. Geophys. Res. Lett., Vol. 27 No. 13, 1911/1914.
König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006.
König-Langlo, G., King, J. C., and P. Pettré, 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. ,Vol. 103, NO. D9, 10,935-10,946).
Citation: https://doi.org/10.5194/wcd-2021-22-AC1
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RC2: 'Comment on wcd-2021-22', Anonymous Referee #2, 13 Jul 2021
Review of “A 25-year climatology of low-tropospheric temperature and humidity inversions for contrasting synoptic regimes at Neumayer Station, Antarctica” by Silva and Schlosser
This is a very well written paper that presents a 25 year climatology of temperature and humidity inversions at Neumayer station. Temperature inversions are important for their role in limiting vertical mixing while humidity inversions are important in cloud processes as well as being associated with atmospheric rivers. This comprehensive study of the climatology of these features will be of interest to the Antarctic and polar meteorology communities and can serve as a model for similar studies at other locations. I do have some larger (major) comments that I believe will improve this manuscript as well as a few minor comments. I find that this manuscript will be suitable for publication in Weather and Climate Dynamics after some revisions.
Major comments
I am not convinced that using the terms cyclonic and non-cyclonic is truly accurate given the way that the synoptic weather observations are used to define these two weather types. While the conditions used to identify the cyclonic type most likely occur during periods of low pressure that may not always be the case. Similarly, the non-cyclonic conditions could occur when the station is under the influence of an area of low pressure. I suggest renaming these two synoptic classifications - maybe precipitating and non-precipitation would be more accurate (although this is problematic due to the inclusion of diamond dust in the current non-cyclonic category, which I think is appropriate). But, I do think this better reflects the distinction between the two synoptic categories being used for this work.
I have some concern about the use of a fixed humidity threshold to define humidity inversions. Given the strong dependence of absolute humidity on temperature it will be much harder to meet the humidity threshold for a humidity inversion in colder conditions (aloft or in winter). It might be better to define a humidity inversion threshold as a percentage of the humidity at the inversion base or top instead.
The inversion composite figures are interesting but it may be better to create these composites using a varying height scale rather than one fixed relative to sea level. Specifically, it might make sense to create composites with the 0 height taken as the inversion base. In this way varying heights of inversion will not “smear” the inversions in the composite and a more robust signal of the inversions and their relationship to wind is likely to be seen. I would also suggest using the temperature (or humidity) at the inversion base as the 0 value so that variability in the value of temperature or humidity can be removed from the composites. Taken together these two changes should produce much more robust composites.
Minor comments
Line 5: What “both” refers to in this sentence is unclear. I assume it is cyclonic and non-cyclonic conditions, but please clarify this text or explain what two synoptic classifications are being presented in this work before this sentence.
Figure 1: It would be useful to also indicate what percent of all possible days in each month during the study period the total radiosonde count for each month represents. This could be listed below the monthly radiosonde count at the top line of this figure.
Section 2.5: It would be good to indicate the typical vertical resolution of the sounding data either here or when the radiosonde data is first introduced. This impacts what depth inversions can be reasonably identified. It might also be worthwhile to discuss why the BSRN radiosonde data is used rather than IGRA data here rather than in the discussion section.
Line 172: It would be useful to more explicitly state how the 5 point moving average profile is used. The text states that this moving average profile is used to detect the inversion base and top positions. Is this done for both absolute humidity and temperature profiles? Also, are the top and bottom inversion values of humidity and temperature taken from the unsmoothed profile data or do these values also come from the moving average profile?
Figure 4 and all similar figures: Please indicate what the boxes, whiskers and open circle symbols indicate in the figure caption. The figure caption should fully explain what is plotted in each figure without the reader needing to refer to the main text for this information.
Paragraph starting at line 299: The change in humidity gradient across the three height ranges and seasonally is driven by changes in the magnitude of absolute humidity as a function of temperature. It is not surprising that gradients are smaller at upper levels or in winter where colder, and thus drier, in an absolute sense, conditions, occur. This point should be made when discussing Figure 10.
Citation: https://doi.org/10.5194/wcd-2021-22-RC2 -
AC2: 'Reply on RC2', Tiago Silva, 20 Aug 2021
We would like to thank RC2 for the thorough review and constructive comments. In the following we address them point by point:
- I am not convinced that using the terms cyclonic and non-cyclonic is truly accurate given the way that the synoptic weather observations are used to define these two weather types. While the conditions used to identify the cyclonic type most likely occur during periods of low pressure that may not always be the case. Similarly, the non-cyclonic conditions could occur when the station is under the influence of an area of low pressure. I suggest renaming these two synoptic classifications - maybe precipitating and non-precipitation would be more accurate (although this is problematic due to the inclusion of diamond dust in the current non-cyclonic category, which I think is appropriate). But I do think this better reflects the distinction between the two synoptic categories being used for this work.
This point was also of concern for RC1 and we realize that we have to explain our choice of definition and terms in more detail. “Cyclonic vs. non-cyclonic” was not our first try, but we came to the conclusion that it describes our defined synoptic situation as closely as possible. “Precipitation vs. non-precipitation”, as the referee states, too, is difficult because diamond dust is also precipitation, but definitely falls into the non-cyclonic class. Also, “fair weather” vs. “bad/stormy weather” is not a good choice since fog would not belong to the bad weather category while it is not exactly what one would call fair weather. Non-cyclonic conditions would not occur when the area is under the influence of low pressure (except for a short transition period, we discussed this difficulty already in the original text).
Neumayer weather conditions are strongly determined by cyclonic activity in the circumpolar trough. The weather is characterized by cyclones passing from west to east with the general westerly flow, with anticyclonic conditions for shorter or longer periods between two cyclones. The semi-annual oscillation can lead to longer anticyclonic periods in summer and winter when the trough and thus the position of the frontal zone moves northwards. This is also indicated by the main wind directions. For the majority of the time Neumayer Station experiences relatively strong easterly, to ENEly winds, related to the clockwise rotation of the passing cyclones. The center of the cyclones is always north of the coast since the topography (increasing elevation) blocks further southward movements of the low-pressure systems. Weaker winds from southerly or SWly directions prevail under high pressure. We add a figure of the mean Neumayer wind direction in the supplemental material (Fig. S1). Also, clouds are of much less importance for inversions at Neumayer than at Arctic or interior Antarctic stations. A study by Hirasawa et al. (2000) showed that at Dome Fuji, advection of relatively warm and moist air lead to formation of low clouds, which were not sufficient to produce precipitation but increased downward longwave radiation, which, together with increased wind speed destroyed the prevailing inversion. At Neumayer, the increased wind speeds, thus turbulence associated with an approaching cyclone remove an inversion very quickly.
We explained our definition of the two-weather situation typical at Neumayer in more detail in the Data and Methods section and also gave more general information about the climate of Neumayer as an Antarctic coastal station in contrast to interior Antarctica or most Arctic stations in the introduction.- I have some concern about the use of a fixed humidity threshold to define humidity inversions. Given the strong dependence of absolute humidity on temperature it will be much harder to meet the humidity threshold for a humidity inversion in colder conditions (aloft or in winter). It might be better to define a humidity inversion threshold as a percentage of the humidity at the inversion base or top instead.
We found that the use of absolute values of specific humidity to define inversions has been widely used in similar studies, mainly in the Arctic (e.g., Devasthale et al. 2011, Kilpeläinen et al. 2012, Vihma et al. 2011), but also in the Antarctic (Nygård et al. 2013). We thus assume that it is an accepted method for studies of humidity inversions.
Concerning lower humidity in colder seasons or at higher levels: Saturation vapor pressure is a function of temperature, and this usually leads to lower absolute humidity when the temperature is lower. However, this is only part of the story. First of all, we do not always have saturated conditions, and more important, warm air advection in winter can lead to temperatures similar to the temperatures of warmer seasons, even summer, so the humidity should be not necessarily lower, particularly since at Neumayer warm air advection usually means advection of moisture, too. Only southerly winds bring dryer air, but those are generally cold. We added these considerations in the paper (Section 2.5 and Discussion of Fig. 10).- The inversion composite figures are interesting but it may be better to create these composites using a varying height scale rather than one fixed relative to sea level. Specifically, it might make sense to create composites with the 0 height taken as the inversion base. In this way varying heights of inversion will not “smear” the inversions in the composite and a more robust signal of the inversions and their relationship to wind is likely to be seen. I would also suggest using the temperature (or humidity) at the inversion base as the 0 value so that variability in the value of temperature or humidity can be removed from the composites. Taken together these two changes should produce much more robust composites.
We thank the referee for this constructive suggestion. We created new figures with normalized height and temperature (humidity) axes for both surface based and 2nd/level inversions. Furthermore, we included the profiles for surface-based inversions under non-cyclonic conditions (Fig. 15a) and for 2nd-level inversions under cyclonic conditions (Fig. 15b) in the main manuscript and kept the original Figures 11-14 in order to be able to show the entire height profile. In Fig 15 we discuss change of wind direction and speed with height within the inversion. All figures with normalized axes including a short discussion are found in the supplemental material (Fig. S4-S7).
- Line 5: What “both” refers to in this sentence is unclear. I assume it is cyclonic and non-cyclonic conditions, but please clarify this text or explain what two synoptic classifications are being presented in this work before this sentence.
We agree that this formulation was not exact, and we corrected this in the abstract.
- Figure 1: It would be useful to also indicate what percent of all possible days in each month during the study period the total radiosonde count for each month represents. This could be listed below the monthly radiosonde count at the top line of this figure.
We fully agree, and we added this information in Figure 1.
- Section 2.5: It would be good to indicate the typical vertical resolution of the sounding data either here or when the radiosonde data is first introduced. This impacts what depth inversions can be reasonably identified. It might also be worthwhile to discuss why the BSRN radiosonde data is used rather than IGRA data here rather than in the discussion section.
This is also a good suggestion, which we followed. We changed the text in the Data and Methods Section accordingly. Given the 25-year period, three types of radiosondes were used where the latest version has always higher vertical resolution than the previous. Moreover, the weather conditions severity can also affect the vertical resolution. One of a few IGRA corrections during the quality control procedure is the removal of pressure levels where relative humidity is exceeded 100% with respect to ice. Supersaturation is remarkably important to account when making analysis over polar areas. Here, we add a figure with arbitrary dates comparing BSRN with IGRA data:
However, a statistical analysis of differences among upper air sounding archives due to distinct quality control procedures and associated impacts on inversion detection go beyond the scope of our study.
- Line 172: It would be useful to more explicitly state how the 5 point moving average profile is used. The text states that this moving average profile is used to detect the inversion base and top positions. Is this done for both absolute humidity and temperature profiles? Also, are the top and bottom inversion values of humidity and temperature taken from the unsmoothed profile data or do these values also come from the moving average profile?
Exactly. We wrote this in the manuscript already but tried to change the formulation to make it better understandable for first reading.
- Figure 4 and all similar figures: Please indicate what the boxes, whiskers and open circle symbols indicate in the figure caption. The figure caption should fully explain what is plotted in each figure without the reader needing to refer to the main text for this information.
Principally we agree that figure captions should have the full explanation of the figure. We tried to follow this request, but it turns out that adding the (same) explanation to all figure captions for Fig. 4-Fig. 10 would reduce the size of the figures if we wanted to keep the caption on the same page as the figure. This would also reduce the legibility of the figures. Thus, for practical reasons, we gave the full explanation of the box plots only in the first Figure where box plots occur (Fig. 4). (You will notice that here the page number gets aligned with the caption already. The layout done by the journal might have a reduced figure size.) We would like to avoid having this for all box plots. In the following Figure captions, we refer to this explanation in caption of Fig. 4. We hope that this will be sufficient, also taking into account that box plots are actually textbook knowledge.
- Paragraph starting at line 299: The change in humidity gradient across the three height ranges and seasonally is driven by changes in the magnitude of absolute humidity as a function of temperature. It is not surprising that gradients are smaller at upper levels or in winter where colder, and thus drier, in an absolute sense, conditions, occur. This point should be made when discussing Figure 10.
As stated above, it is true that saturation vapor pressure is a function of temperature, and this usually leads to lower absolute humidity when the temperature is lower. However, we do not always have saturated conditions, and more important, warm air advection in winter can lead to temperatures similar to the temperatures of warmer seasons, even summer, so the humidity should be not necessarily lower, particularly since at Neumayer warm air advection usually means advection of moisture, too. Only southerly winds bring dryer air, but those are generally cold. We added these points in the discussion of Fig. 10., also referring to the revised Section 2.5.
References:
Devasthale, A., Sedlar, J., and Tjernström, M, 2011.: Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes, Atmospheric Chemistry and Physics, 11, 9813–9823, https://doi.org/10.5194/acp-11-9813-2011Hirasawa, N., H. Nakamura, and T. Yamanouchi, 2000. Abrupt changes in the meteorological conditions observed at an inland Antarctic station in association with wintertime blocking. Geophys. Res. Lett., Vol. 27 No. 13, 1911/1914.
Kilpeläinen, T., Vihma, T., Manninen, M., Sjöblom, A., Jakobson, E., Palo, T., and Maturilli, M., 2012: Modelling the vertical structure of the atmospheric boundary layer over Arctic fjords in Svalbard, Quarterly Journal of the Royal Meteorological Society, 138, 1867–1883, https://doi.org/10.1002/qj.1914
König-Langlo and Loose, 2007: The Meteorological Observatory at Neumayer Stations (GvN and NM-II) Antarctica. Polarforschung 76 (1-2), 25 – 38, 2006.
König-Langlo, G., King, J. C., and P. Pettré, 1998: Climatology of the three coastal Antarctic stations Dumont d’urville, Neumayer, and Halley. J. Geeophys. Res. ,Vol. 103, NO. D9, 10,935-10,946).
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https://doi.org/10.1155/2011/486807Citation: https://doi.org/10.5194/wcd-2021-22-AC2
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AC2: 'Reply on RC2', Tiago Silva, 20 Aug 2021
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