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Preprints
https://doi.org/10.5194/acp-2020-325
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-325
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  05 May 2020

05 May 2020

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

Influence of gravity wave temperature anomaly and its vertical gradient on cirrus clouds in the tropical tropopause layer – a satellite-based view

Kai-Wei Chang1 and Tristan L'Ecuyer2 Kai-Wei Chang and Tristan L'Ecuyer
  • 1Department of Atmospheric Sciences, Texas A&M University, College Station, Texas, USA
  • 2Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA

Abstract. Negative temperature perturbations (T′) from gravity waves are known to favor tropical tropopause layer (TTL) clouds, and recent studies have further suggested a possible role of dT′/dz on facilitating TTL cloud formation and maintenance. With a focus on exploring the influence of dT′/dz on TTL clouds, this study utilizes radio occultation temperature retrievals and cloud detection from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) to understand how gravity wave perturbations modulate cloud occurrence.

Cloud populations were evaluated in four phases corresponding to positive or negative T′ and dT′/dz. We find that 57 % of TTL clouds are found where T′ and dT′/dz are both negative. Regions of frequent convection are associated with higher cloud populations in the warm phase T′>0. The partitioning of cloud population among wave phases shows some dependence on the background relative humidity estimated using Aura Microwave Limb Sounder water vapor retrievals. Using effective radius (re) retrievals from the CloudSat/CALIPSO 2C-ICE product, we find that re is distributed similarly among all wave phases but a smaller mode is found in the re distribution from the phase T′<0 and dT′/dz<0.

It is shown that the strongest mean negative T′ anomaly is centered on the cloud top, resulting in positive dT′/dz above the cloud top and negative dT′/dz below. This negative T′ anomaly propagates downward with time consistent with upward propagating gravity waves. Negative (positive) T′ anomalies are associated with increased (decreased) probability of being occupied by clouds. The magnitude of T′ correlates with the increase or decrease in cloud occurrence, giving evidence that the wave amplitude influences the probability of cloud occurrence. While the decrease of cloud occurrence in the warm phase is centered on the altitude of T′ maxima, we show that the increase of cloud occurrence around T′ minima occurs below the minima in height, indicating that cloud formation or maintenance is facilitated mainly inside negative dT′/dz. Together with existing studies, our results suggest that the cold phase of gravity waves favor TTL clouds mainly through the region of wave anomalies where dT′/dz is negative.

Kai-Wei Chang and Tristan L'Ecuyer

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Status: closed
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Kai-Wei Chang and Tristan L'Ecuyer

Kai-Wei Chang and Tristan L'Ecuyer

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