A recent seminar by Qinbin Li of NASA held at Colorado State University highlighted an important interaction between atmospheric chemistry, atmospheric transport, and weather. The talk was titled
“Trapping of deep convective pollution by upper level anticyclones: Implications for global climate”, and the abstract was
“The GEOS-Chem global 3D chemical transport model is used to analyze observations of CO and upper tropospheric clouds from the EOS Microwave Limb Sounder (MLS). MLS observations during 25 August-6 September 2004 reveal elevated CO concentrations and dense high-altitude clouds in the upper troposphere over the Tibetan plateau and southwest China, collocating with the upper-level Tibetan anticyclone. The observed dense high-altitude clouds are accompanied with relatively little precipitation, as indicated by the CMAP precipitation rate. A large fraction of these dense high clouds have relatively small particle sizes and are thus distinguished from convective clouds which have larger particles. Model simulations indicate the transport of boundary layer pollution by Asian summer monsoon convection and orographic lifting to the upper troposphere over South Asia, where the simulated distributions of CO closely resemble the MLS observations. Model results also show elevated aerosols and ozone in the anticyclone region. Analysis of simulated CO and aerosols indicate that the upper-level Tibetan anticyclone effectively ‘traps’ anthropogenic emissions lifted from northeast India and southwest China. These aerosols may be responsible for the formation of some of the dense high-altitude clouds. In a separate study, we find that in summer the semi-permanent upper-level anticyclone over the southern United States traps the convective outflow and allows it to age in the upper troposphere over the United States for several days. Rapid ozone production takes place in this outflow driven in part by anthropogenic and lightning NOx, and in part by HOx radicals produced from convectively lifted CH2O that originates from biogenic isoprene. This mechanism could explain ozonesonde observations of elevated ozone in the upper troposphere over the southeastern United States.”
One of the papers by Li et al on this important climate study is in Geophysical Research Letters in 2005 entitled “Convective outflow of South Asian pollution: A global CTM simulation compared with EOS MLS observations”. The abstract from the paper states
“A global 3-D chemical transport model is used to analyze observations of carbon monoxide (CO) and upper tropospheric clouds from the EOS Microwave Limb Sounder (MLS). MLS observations during 25 August–6 September 2004 reveal elevated CO and dense high clouds in the upper troposphere over the Tibetan plateau and southwest China, collocating with the upper level Tibetan anticyclone. Model simulations indicate the transport of boundary layer pollution by Asian summer monsoon (ASM) convection and orographic lifting to the upper troposphere over South Asia, where simulated distributions of CO resemble MLS observations. Model results also show elevated aerosols in the anticyclone region. Analysis of model simulated CO and aerosols indicate that the Tibetan anticyclone could ‘trap’ anthropogenic emissions lifted from northeast India and southwest China. These aerosols may be responsible for the formation of some of the dense high clouds.”
The paper concludes with the statement,
“Changes in cloud properties could have profound impact on the global cloud system, hydrological cycle, and climate.”
This work provides additional information to support the findings in the 2005 National Research Council report entitled “Radiative forcing of climate change: Expanding the concept and addressing uncertainties.” Climate, as influenced by human activities and by natural processes, must be considered an integrated physical, chemical and biological system. Predictions of future climate are made much more difficult as a result of the complexity exemplified in the research by Qinbin Li and colleagues.