23 Apr 2021

23 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

Impacts of tropical cyclones on the thermodynamic conditions in the tropical tropopause layer observed by A-train satellites

Jing Feng and Yi Huang Jing Feng and Yi Huang
  • Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada

Abstract. The tropical tropopause layer (TTL) is the transition layer between the troposphere and the stratosphere. Tropical cyclones may impact the TTL by perturbing the vertical distributions of cloud, temperature, and water vapor, although this impact is poorly quantified due to the lack of collocated data. To address this problem, we implement a synergistic retrieval approach to obtain the thermodynamic profiles and ice water content above thick high-level clouds using the A-Train satellite measurements that pass over the tropical cyclones.

This study detects the signature of cyclone impact on the distribution patterns of cloud, water vapor, temperature, and radiation by compositing these thermodynamic fields with respect to cyclone center locations. It is found that tropical cyclone events considerably increase the occurrence of TTL clouds, in the form of cirrus clouds above a clear troposphere. The amount of TTL cloud ice, however, is found to be mostly contributed by overshooting deep convections that penetrate the bottom of TTL.

Using the synergistic retrieval method, we find a vertically oscillating pattern of temperature anomalies above tropical cyclones, with warming beneath the cloud top (around 16 km) and cooling above. The atmospheric column above 16 km is generally hydrated by overshooting convections, although dehydration is detected above non-overshooting TTL clouds. Above overshooting deep convections, the column-integrated water vapor is found to be on average 40 % higher than the climatology.

Moreover, the TTL above tropical cyclones is cooled due to longwave radiative cooling. The radiative heating rates above cyclones are well differentiated by the brightness temperature of a satellite infrared channel in the window band. Using radiative calculations, it is found that TTL hydration is usually associated with radiative cooling of the TTL, which inhibits the diabatic ascent of moist air. The radiative balance of the TTL under the impact of the cyclone, therefore, is not in favor of maintaining the moist anomalies in the TTL or transporting water vertically to the stratosphere.

Jing Feng and Yi Huang

Status: open (until 18 Jun 2021)

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Jing Feng and Yi Huang

Jing Feng and Yi Huang


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Short summary
This study conducts a comprehensive analysis of thermodynamic fields above tropical cyclones. Using a synergistic retrieval method, we develop the first infrared hyperspectra-based dataset of collocated temperature and water vapor profiles above deep convective clouds. It discloses the unique impacts of convective overshoots on the tropical tropopause layer (TTL). Challenging conventional views, our study suggests that convective hydration may be limited by the radiative balance above cyclones.