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The Asian summer monsoon is a dominant feature of the global circulation. The upper-level anticyclone (ULAC) associated with the Asian summer monsoon circulation stands out vividly in satellite observations of trace gases. The ULAC also has been diagnosed as a region that is important to troposphere-to-stratosphere transport. Therefore, understanding the role of convection in transporting boundary layer air into this upper-level circulation is important to understanding the atmospheric chemistry of the upper troposphere/lower stratosphere. We ran the Weather Research and Forecasting (WRF) model at convective-permitting scales (4 km grid spacing) to simulate the atmosphere between 10-20 August 2012. Such high-resolution modeling of the Asian ULAC previously has not been documented in the literature. Comparison of our WRF simulation with reanalysis and satellite observations showed that WRF simulated the atmosphere sufficiently well to be used to study convective transport into the ULAC. A back-trajectory analysis showed that >90% of convectively influenced parcels reaching the ULAC came from the Tibetan Plateau (TP) and the southern slope (SS) of the Himalayas. A clear diurnal cycle is seen in the convective parcels, with their greatest impact occurring between 1600-2300 local solar time. This finding highlights the role of "everyday" diurnal convection in transporting boundary layer air into the ULAC. WRF output at 15 min intervals was produced for 16 August to examine convection in greater detail. This high-temporal output indicated that the weakest convection occurred over the TP. However, because the TP is at 3000-5000 m MSL, its convection does not have to be as strong to reach the ULAC as in lower altitude regions. Additionally, because the TP's elevated heat source is a major cause of the ULAC, we propose that convection over the TP and the neighboring SS is geographically situated to impact the ULAC most frequently. The vertical mass flux of water vapor into the ULAC also was calculated. Results show that the TP and SS regions dominated other Asian regions in vertically transporting moisture into the ULAC. Because convection reaching the ULAC is more widespread over the TP than nearby, we propose that the abundant convection partially explains the TP's dominant water vapor fluxes. In addition, greater outgoing longwave radiation reaches the upper levels of the TP due to its elevated terrain. This creates a warmer ambient upper level environment, allowing parcels with greater saturation mixing ratios to enter the ULAC.
Asian summer monsoon, convective transport, upper level anticyclone, WRF
Date of Defense
June 6, 2013.
A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science.
Includes bibliographical references.
Henry E. Fuelberg, Professor Directing Thesis; Vasubandhu Misra, Committee Member; Robert Hart, Committee Member.
Florida State University
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