Large-Scale Variability of Tropical Tropopause Layer (TTL) Cirrus and Cold Point Temperature

Abstract:

The Tropical Tropopause Layer (TTL) is the transition layer from the tropical troposphere to the stratosphere, which acts as the gateway for air to enter the stratosphere. Previous studies have shown that an important mediator of this tropical ascent of air is the enhancement of radiative heating in this layer by TTL cirrus clouds. On the other hand, the Cold Point Temperature (CPT) in the TTL constrains the amount of water vapor entering the stratosphere via “freeze drying” while also bringing air in this region to saturation through the same process to form cirrus clouds. We examine the TTL cirrus and CPT by analyzing 14 years (2006–2020) of observations from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), and Meteorological Operational Satellite A and B (METOP-A and METOP-B) . We look at the interannual variability of both the TTL cirrus and CPT using Maximum Covariance Analysis, and compare each mode of variability to four large scale dynamical processes including El Nino Southern Oscillation(ENSO), Quasi-Biennial Oscillation (QBO), Brewer-Dobson Circulation (BDC), Madden-Julian Oscillation (MJO). Our findings show that the primary mode of variability in the covariance of the TTL cirrus and CPT is ENSO followed by the QBO, BDC, and finally the MJO.