Radiative Effects of Cloud, Temperature, and Water Vapor in the TTL Above Tropical Cyclones.

Abstract:

The tropical tropopause layer (TTL) is the transition layer between the troposphere and the stratosphere. Tropical cyclones may impact the TTL radiative balance 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 cloud-assisted retrieval approach to retrieve the water vapor and temperature profiles above the thick high-level clouds using the A-Train satellite measurements overpassing the tropical cyclones.

By compositing the different fields including cloud, water vapor, temperature and radiation with respect to cyclone center location, we identify the signature of cyclone impact on the distribution patterns of these variables and their relation. For instance, we find that the cloud radiative heating/cooling effect in the TTL can be well indicated by the window band infrared radiance intensity.

The cloud-assisted retrieval disclosed a vertically oscillating pattern of the temperature and water vapor above deep convective clouds, with cooling and dehydration at and near the cloud top (between 16 and 17.5km) but warming and hydration above 18km.

Furthermore, using radiative transfer calculations, we find that the radiative heating rate within the TTL is dominated by cloud longwave cooling. Compared with the effects of temperature and the cloud, the water vapor anomaly has a weaker radiative effect in the TTL.