Water vapor distribution and transport characteristics in boundary of upper troposphere and lower stratosphere

Based on water vapor, ice water content (IWC), and temperature data from Microwave Limb Sounder (MLS) of Aura satellite, distribution characteristics of water vapor, IWC and total water matter (sum of water vapor and IWC by reconciling the unit of ice water content to the unit of water vapor) contents in the boundary of upper troposphere and lower stratosphere (UTLS) in the Asian Summer Monsoon (ASM) region, North American Monsoon (NAM) region, Warm Pool and Iran Plateau region were analyzed. Water vapor transport and main dehydration mechanisms over the boundary of UTLS were discussed. The results show that the total water matter contents in the ASM region have large value centers between 215 hPa to 83 hPa levels and are larger than that in the NAM region. At 215 hPa level, water vapor contributes more to the total water matter contents, while IWC and water vapor have the same contribution to the total water matter contents between 147 hPa to 83 hPa levels. The confinement effect of ASM anticyclone can restrict water vapor transported by deep convections in the upper troposphere. Probability distributions of water vapor and ice water content at 147 hPa and 100 hPa levels can demonstrate different dehydration mechanisms. Due to the extreme low temperature around warm pool at 100 hPa in winter of the northern hemisphere, the peak probability of water vapor mixing ratio over that region is only 2 ppmv. The “long-tail” distribution of water vapor probability in the ASM region at 147 hPa displays a strong convective influence. IWC mainly concentrates on small values at 147 hPa and 100 hPa, which is probably caused by ice particles sedimentation with ice growth by depleting water vapor.