Spatial And Temporal Distributions Of Co In Troposphere And Stratosphere From Satellite Observations

As a pollutant, carbon monoxide (CO) plays an important role in atmospheric environment and has an influence on the interactions between atmospheric chemistry system and climate. It has been recognized that the chemictal reaction with CO is a dominant sink of troposphere OH and it also contributes to O3production in the troposphere and lower stratosphere. Furthermore, CO is a useful tracer applied in the study of the atmospheric transport and mass exchanging. Satellite observation plays a consistent constraint on the temporal and spatial distributions of CO in the global scale. In this thesis, we conduct a study on the temporal and spatial distribution of atmospheric CO, especially focusing on the tropical troposphere and lower stratosphere, and the sub-peaks of CO concentration in stratosphere over polar region. The main conclusions are as follows.(1)The air masses get into the stratosphere mainly in the tropics and CO is a good tracer used in the study of this processes. We use the datasets of ACCMIP, MOPITT and MLS to conduct an analysis on the distributions and transport of CO in the tropics from the surface to the lower stratosphere. The results show that there are two peaks in the CO emission rates, in Aug.-Sep. and Dec.-Jan.-Feb., separately. Changes in biomass burning emissions are the main reasons for the seasonal variations of CO emissions and there is nearly no trend in the inter-annual variations. It’s well known that air mass in the tropics is transported vertically into the free atmosphere through convections. Although the CO high emissions and the deep convective areas are not fully consistent with each other, it shows that CO can be transported into convective areas through the horizontal winds from main CO sources towards tropic convections. In the upper troposphere, CO shows cluster-like structures, corresponding to the locations of the tropic convections marked by the outgoing long-wave radiation (OLR). In more upper levels, the horizontal winds come to become the main reason controlling CO distribution. Therefore, CO is trapped by anticyclones, similar as the phenomenon in the Asian summer monsoon. In the lower stratosphere, zonal winds carry CO downwind. Although there is no clear trend in CO emissions over years, the mean concentration of CO in the tropics have significant inter-annual variation.(2)The analysis of CO from space-borne ACE-FTS and Aura-MLS satellite observations shows there is a sub-peak in the CO profiles during the late winter to the early spring in the polar regions of both the Northern and Southern Hemispheres at the middle of the stratosphere, namely lOhPa. Further analysis of Aura-MLS satellite data demonstrates that air from the mesosphere, which is rich in CO, descents into the stratosphere gradually in the early winter. While the CO concentration in the upper stratosphere decreases rapidly during the late winter, the CO concentration changes very slowly in the middle stratosphere. Therefore, a suspended spherical structure of high value of CO concentration emerges dramatically in the stratosphere and the satellite observation shows such a sub-peak in the CO profiles. The analysis of the MERRA assimilated data and OH concentration from Aura-MLS satellite observation indicates that the weakening of the vertical transportation from the mesosphere to stratosphere, the enhancement of the horizontal exchange, and the recovery of the OH concentration may play important roles in reducing CO concentration in the upper stratosphere. Benefited from both the isolation of the transport barrier and the lower OH concentration in polar region, CO in the middle stratosphere can survive for a relatively longer time, maintaining the sub-peak to last from the late winter to spring.