Abstracted/indexed

Warm conveyor belts (WCBs) are important cloud and precipitation producing airstreams in extratropical cyclones. By combining satellite observations with model data from a new reanalysis dataset, this study provides detailed observational insight into the vertical cloud structure of WCBs. We find that the reanalyses essentially capture the observed cloud pattern, but the observations reveal many mesoscale structures not resolved by the temporally and spatially much coarser-resolution model data.

The study presents the first results from the airborne RASTA observations measured during North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX). Our combined Eulerian-Lagrangian analysis found three types of organized convection (frontal, banded and mid-level) in the warm conveyor belt of the Stalactite cyclone. It suggests that a dynamical linkage between these organized convective ascents and the mesoscale negative PV bands found in their vicinity.

In this paper, we investigate air-sea interaction by looking at the relationship between spatial variability in surface heat flux and air temperature. We observe that their interaction characterizes different stages of storm evolution thus providing a new perspective on the role played by air-sea heat exchange.

This study addresses the origin and impacts of a source of large-scale atmospheric waves in the lower stratosphere, which has not been examined before. This wave source is caused by interactions of waves of smaller scales. Here we show that as it lies in the lower stratosphere, this wave source can precede extreme events in the stratosphere and that such events can then lead to a robust response of the tropospheric weather patterns several weeks later (potential for long-term forecasting).

This study explores the relationship between the North Atlantic Oscillation and the winter climate of eastern North America using reanalysis data. Results show that negative phases are linked with an increase of frequency of winter storms developing on the east coast of the United States, resulting in much heavier snowfall over the eastern United States. On the contrary, an increase of cyclone activity over southeastern Canada results in heavier precipitation and snowfall during positive phases.

Our study focuses on the impact of topographic structures such as Himalayas and Rocky mountains, so-called orographic gravity-wave hotspots. These hotspots play an important role in the dynamics of the middle atmosphere, in particular in the lower stratosphere. We study intermittency and zonally asymmetric character of these hotspots and their effects on the upper stratosphere and mesosphere using a new detection method in various modeling and observational datasets.

To understand better the factors that impact the weather in North America, this study explores the influence of El Niño-Southern Oscillation on wintertime surface air temperature variability using reanalysis data. Results show that La Niña enhances subseasonal variability over western North America by amplifying the baroclinic conversion of energy from the winter-mean circulation to subseasonal eddies. Changes in the vertical structure of these eddies are crucial for this amplification.

Most precipitation over Europe is linked to low-pressure systems, cold fronts, warm fronts, or high-pressure systems. Based on a massive computer simulation able to resolve thunderstorms, we quantify in detail how much precipitation these weather systems produced during 2000–2008. We find distinct seasonal and regional differences, such as fronts precipitating a lot in fall and winter over the North Atlantic, but high-pressure systems mostly in summer over the continent by way of thunderstorms.

We investigate the stratospheric influence on marine cold air outbreaks (MCAOs) using ERA-Interim reanalysis data. MCAOs are associated with severe Arctic weather, such as polar lows and strong surface winds. We find that the key ingredients of MCAO formation in the Barents Sea are linked to the surface impact of Sudden Stratospheric Warming (SSW) events. As SSWs have a long-term surface influence, this study sheds light on the predictability of MCAOs in the Arctic for winters with SSW events.

In this paper we investigate the role of the tropospheric forcing in the occurrence of the Sudden Stratospheric Warming (SSW) that took place in February 2018, its predictability and teleconnection with the Madden-Julian oscillation (MJO) by analysing the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble forecast. The purpose of the paper is to present the results of the analysis of the atmospheric circulation before and during the SSW and clarify the driving mechanisms.

We find, by tracing backward in time, that air masses causing extensive melt of the Greenland Ice Sheet originate from further south and lower altitudes than usual. Their exceptional warmth further arises due to ascent and cloud formation, which is special compared to near-surface heatwaves in the midlatitudes or the Central Arctic. The atmospheric systems and transport pathways identified here are crucial in understanding and simulating the atmospheric control of the ice sheet in the future.

We study the interactions between the tropical convective activity and the mid-latitude circulation in the Northern Hemisphere during boreal summer. We identify two circumglobal wave patterns with phase shifted corresponding to the South Asian and the western North Pacific monsoon systems at intraseasonal time scale. These patterns show a two-way interactions in a causal framework at weekly time scale and assess how El Niño affects these interactions.