Observed Increase of TTL Temperature and Water Vapor in Polluted Clouds over Asia

Abstract

Satellite observations are analyzed to examine the correlations between aerosols and the tropical tropopause layer (TTL) temperature and water vapor. This study focuses on two regions, both of which are important pathways for the mass transport from the troposphere to the stratosphere and over which Asian pollution prevails: South and East Asia during boreal summer and the Maritime Continent during boreal winter. Using the upper-tropospheric carbon monoxide measurements from the Aura Microwave Limb Sounder as a proxy of aerosols to classify ice clouds as polluted or clean, the authors find that polluted clouds have a smaller ice effective radius and a higher temperature and specific humidity near the tropopause than clean clouds. The increase in water vapor appears to be related to the increase in temperature, as a result of increased aerosols. Meteorological differences between the clouds cannot explain the differences in temperature and water vapor for the polluted and clean clouds. The authors hypothesize that aerosol semidirect radiative heating and/or changes in cirrus radiative heating, resulting from aerosol microphysical effects on clouds, may contribute to the increased TTL temperature and thus increased water vapor in the polluted clouds. ** Retired.

Transport of aerosols into the UTLS and their impact on the Asian monsoon region as seen in a global model simulation

“…Temperature increases by ∼ 1-5 K near the tropical tropopause. A similar increase in temperature is reported by , , Liu et al (2009), andSu et al (2011). The interior of the anticyclone over the Tibetan Plateau experiences a significant warming as well.…”

“…Observations and modelling studies suggest that the occurrence of aerosol layers near the tropopause could strongly affect the formation of cirrus clouds and precipitation (Li et al, 2005;Yin et al, 2005;Su et al, 2011). Liu et al (2009) reported that the homogeneous freezing of SO 2− 4 particles dominates cirrus cloud formation in the upper troposphere.…”

“…When both homogeneous and heterogeneous ice nucleation are taken into account, anthropogenic soot may increase global cirrus cloud cover by ∼ 2 % and UTLS water vapour by 40 % with a change in LWCF of 1.5 W m −2 . Su et al (2011) hypothesized that aerosol semi-direct radiative heating and changes in cirrus radiative heating may contribute to the observed increase in tropical tropopause layer temperatures and to elevated water vapour concentrations in polluted clouds. Several other studies (e.g.…”

The Variations in Middle and Upper Stratospheric Water Vapour over the Past Two Decades

“…A simulation study showed that variations in transport explain 30% of the lower SWV changes over the past several decades (Tian and Chipperfield 2006). In particular, the upward transport in the Asian summer monsoon is thought to be capable of transporting a large amount of water vapour into the stratosphere (Gettelman et al 2004;Fu et al 2006;Su et al 2011;Bian et al 2011Bian et al , 2012. As volcanic eruptions can change the tropopause temperature and bring tropospheric water vapour into the stratosphere, SWV can increase significantly after such eruptions (Considine et al 2001;Joshi and Jones 2009).…”

A Quantitative Estimation of the Transport of Surface Emissions from Different Regions into the Stratosphere

“…However, the transport of surface emissions into the tropospheric atmosphere is strong influenced by many factors, e.g., topography (Fu et al 2006;Su et al 2011), convective overshooting (Sun and Huang 2015), and "Tape-recorder" (Liu et al 2007;Jiang et al 2015). Because topography and thermal characteristics vary between different regions, the transport of chemical compounds and aerosols horizontally in the troposphere and vertically from the troposphere into the stratosphere is also variable Wang et al 2014).…”