Study Of The Transport And Spatial-temporal Variations Of The Trace Gases In The Tropical Upper Troposphere And Lower Stratosphere

Using satellite observations,reanalysis datasets,combined with the Whole Atmosphere Community Climate Model,the spatial-temporal variations of carbon monoxide(CO) in the tropical upper troposphere(UT) and lower stratosphere(LS) and the phase changes of the tropical stratospheric CO quasi-biennial oscillation(QBO) are analyzed. The effects of the horizontal transport from the extratropics to the tropics driven by the Asian summer monsoon anticyclone on the spatial-temporal variations of CO in the tropical UTLS are also analyzed. The temporal and spatial distribution of the tracers from different regions in the UTLS is also analyzed. The main conclusions are as follow:(1) Using the WACCM, the relative importance of CO emissions, chemical and dynamical processes on the spatial-temporal variations of CO in the tropical UTLS is investigated. The semi-annual cycle(SAO) in the tropical UT and the annual cycle(AO) in the tropical LS detected in the MLS CO observations can be well captured by the model. The model simulations reveal that the CO surface emissions explain most of the SAO signals in the tropical UT, with the remainder being attributed to dynamical and chemical processes. The CO AO in the LS primarily results from combined effects of dynamical and chemical processes while the dynamical and chemical processes make opposite contributions to the CO AO signals. Our analysis further reveals that CO surface emissions tends to weaken the amplitude of the CO annual cycle in the tropical lower stratosphere while the annual variations in the meridional component of the BD circulation can amplify the annual variations of CO above 30 hPa. The model simulations also indicate that the CO annual cycle in the LS has a mixed behavior with the annual variations of tropical upwelling reflected in CO between ~70 hPa and ~50 hPa and a standard tape-recorder signal above 50 hPa. Moreover, the AO signals of CO exist up to 10 h Pa when the chemical processes are switched off. The tropical deep convection and the horizontal transport associated with the Asian summer monsoon anticyclone circulation lead to an increase of the tropical CO in May.(2) The MLS satellite observations of CO from 2005 to 2014 have been analysed to study the inter-annual variations of the tropical stratospheric CO. The results show that the tropical stratospheric CO quasi-biennial oscillation(QBO) has a phase change at ~30 hPa. The model results from the chemistry-climate model show that the CO QBO primarily results from combined effects of dynamical and chemical processes associated with CO, while the dynamical process is mainly associated with the transport of CO caused by QBO-induced meridional circulation. The combined effects of dynamical and chemical processes lead to a reverse of the vertical gradient in the tropical stratospheric CO mixing ratios at ~ 30 hPa, consequently, the CO QBO exihibits a phase change around this level. The model results also show that the chemical processes associated with CO not only tend to weaken the amplitude of the CO QBO, but also can lead to a phase difference by ~ 3 months in the QBO signals between the zonal wind and CO at 10-30 hPa.(3) The WACCM model is used to investigate the impacts of CO surface emissions from Tibetan Plateau, East China, India and Mainland Southeast Asia on a persistent maximum associated with the Asian summer monsoon anticyclone and the spatial-temporal variations of the tropical CO in the UTLS. The model simulations show that the CO emissions from Tibetan Plateau and India can eventually lead to high CO values inside the Asian summer monsoon anticyclone, with the maximum in July and May, respectively. The CO emissions from East China and Mainland Southeast Asia tend to cause high CO along the Asian summer monsoon anticyclone, with the maximum appeared in August and May, respectively. The model simulations also show that the CO from the four regions can all lead to an increase in the tropical CO in May-September through the horizontal transport from the extratropics into the tropics driven by the Asian summer monsoon anticyclone, but the maximum CO in the tropical UTLS which originate from Tibetan Plateau, East China, India and Mainland Southeast Asia appear in July, Augest, June and June, respectively. In addition, the results show that the CO surface emissions from Mainland Southeast Asia make the largest contribution to CO increases in the tropical UTLS in May-September, if the surface emissions from Tibetan Plateau, East China, India and Mainland Southeast Asia are same.(4) Using WACCM the characteristics of dynamical transport of passive tracers released from different regions to the UTLS are analysed. The model simulations show that the tracers released from Southeast Asia and Southwest Asia are more likely to enter into the stratosphere than those from the other regions. The tracer released from Europe is less likely to enter into the stratosphere than the tracer realeasd from other regions. The model simulations also show that the tracers are mainly distributed in the regions where the deep convection occurs,including Indonesia,the central and western equatorial Pacific Ocean,the regions(60°W-120°E, 10°S-30°N,including India, Mainland Southeast Asia, Arabian Sea and the Bay of Bengal),Africa, the central parts of South America, the eastern Pacific Ocean in the northern hemisphere(120°W-80°W, 0°-30°N) and the western equatorial Atlatic Ocean(80°W-20°W, 10°N-10°S). At 100 hPa, the tracers released from Africa and South America are mainly distributed in Africa and the central parts of South America in the boreal winter, respectively, which can be due to the strong deep concevtion in these two regions. The tracers released from the regions except Africa and South America are mainly distributed in Indonesia and the central and western equatorial Pacific Ocean in the boreal winter, and it can be linked with the horizontal transport associated with equatorial easterlies and anticyclone in the western equatorial Pacific Ocean. The tracers released from Europe, Eastern China, Southeast Asia and Southwest Asia are mainly distributed in the regions(60°W-120°E,10°S-30°N) in the boreal summer at 100 hPa, which is combined effects of the deep convection and the horizontal transport associated with the Asian summer monsoon anticyclone circulation. The weak anticyclone in the south of North America in June can lead to the high values in the eastern Pacific Ocean in the northern hemisphere of the tracers, which are released from North America and South America. The high values of the tracers released from North America and South America in May in the western equatorial Atlatic Ocean may be linked with equatorial easterlies.