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Weather and Climate Dynamics An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/wcd-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-2020-10
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  23 Mar 2020

23 Mar 2020

Review status
A revised version of this preprint was accepted for the journal WCD and is expected to appear here in due course.

Abrupt transitions in an atmospheric single-column model with weak temperature gradient approximation

Benjamin A. Stephens1,2,3 and Charles S. Jackson3 Benjamin A. Stephens and Charles S. Jackson
  • 1UWM Department of Mathematical Sciences, 3200 N Cramer St., Milwaukee WI 53211
  • 2University of Texas Department of Physics, 2515 Speedway, C1600, Austin TX 78712
  • 3University of Texas Institute for Geophysics, 10601 Exploration Way, Austin TX 78758

Abstract. We document a feature of the tropical atmosphere that could be relevant to episodes of abrupt transitions in global climate that regularly occurred during the last ice age. Using a single-column model incorporating the weak temperature gradient (WTG) approximation, we find that abrupt transitions occur as the sea surface temperature is steadily increased. Because these transitions arise from the interplay of scales between local deep convection and the large-scale adjustments that are required to maintain weak temperature and pressure gradients, they are only present with the WTG approximation relevant for the tropics but may be of interest as a trigger for abrupt transitions in global climate. These transitions are marked by an abrupt change in the partitioning of rainfall between convective and large-scale (microphysics) subroutines, in addition to various other features of the column including cloudiness, vertical velocity, temperature, and humidity. We conclude that the transitions are initiated by a failure of evaporative cooling in the lower free troposphere. This leads to lower-column heating and a burst of convection that heats the upper free troposphere, increasing the large-scale rainfall rate and re-stabilizing the lower-column evaporative cooling.

Benjamin A. Stephens and Charles S. Jackson

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Benjamin A. Stephens and Charles S. Jackson

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Data for "Abrupt transitions in an atmospheric single-column model with weak temperature gradient approximation" B. A. Stephens and C. S. Jackson https://doi.org/10.5281/zenodo.3694328

Benjamin A. Stephens and Charles S. Jackson

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Latest update: 09 Aug 2020
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Short summary
We analyze abrupt transitions between tropical rainfall regimes in a single-column model (SCM) of the tropical atmosphere. Multiple equilibria have been observed before in SCMs, but here we analyze actual bifurcations. We attribute the transitions to a sudden loss of evaporative cooling in the lower column due to nonlinearities in microphysics. This study may have implications for atmospheric dynamics more broadly but also for understanding abrupt transitions in paleoclimate.
We analyze abrupt transitions between tropical rainfall regimes in a single-column model (SCM)...
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