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We present data and analysis of a set of balloon‐borne sounding profiles, which includes co‐located O3, CO, CH4, and particles, over the northern Tibetan Plateau during an Asian summer monsoon (ASM) season. These novel measurements shed light on the ASM transport behavior near the northern edge of the anticyclone. Joint analyses of these species with the temperature and wind profiles and supported by back trajectory modeling identify three distinct transport processes that dominate the vertical chemical structure in the middle troposphere, upper troposphere (UT), and the tropopause region. The correlated changes in profile structures in the middle troposphere highlight the influence of the strong westerly jet. Elevated constituent concentrations in the UT identify the main level of convective transport at the upstream source regions. Observed higher altitude maxima for CH4 characterize the airmasses' continued ascent following convection. These data complement constituent observations from other parts of the ASM anticyclone. Plain Language Summary: Asian summer monsoon deep convection transports surface pollutants to the stratosphere. Although satellite data have provided clear evidence of this transport, in situ measurements are critical for characterizing how monsoon is vertically re‐distributing the regional emissions. We report new balloon‐borne measurements over the Tibetan Plateau that provide a unique data set on the northern edge of the anticyclone, complementing other observations. Key Points: A novel set of in‐situ profile measurements of O3, CO, CH4 and particles from Tibetan Plateau during Asian summer monsoon are presentedJoint analyses of the profiles provide insights into transport processes controlling the northern edge of the Asian monsoon anticycloneObserved CO profile maxima at 13–14 km (∼360–370 K) identify the level of convective transport at the upstream source regions [ABSTRACT FROM AUTHOR]

Every year during the Asian summer monsoon season from about mid-June to early September, a stable anticyclonic circulation system forms over the Himalayans. This Asian summer monsoon (ASM) anticyclone has been shown to promote transport of air into the stratosphere from the Asian troposphere, which contains large amounts of anthropogenic pollutants. Essential details of Asian monsoon transport, such as the exact time scales of vertical transport, the role of convection in cross-tropopause exchange, and the main location and level of export from the confined anticyclone to the strato sphere are still not fully resolved. Recent airborne observations from campaigns near the ASM anticyclone edge and centre in 2016 and 2017 respectively show a steady decrease in carbon monoxide (CO) and increase in ozone (O3) with height starting from tropospheric values of 80-100 ppb CO and 30-50 ppb O3 at about 365 K potential temperature. CO mixing ratios reach stratospheric background values of ~20 ppb at about 420 K and do not show a significant vertical gradient at higher levels, while ozone continues to increase throughout the altitude range of the aircraft measurements. Nitrous oxide (N2O) remains at or only marginally below its 2017 tropospheric mixing ratio of 326 ppb up to about 400 K, which is above the local tropopause. A decline in N2O mixing ratios that indicates a significant contribution of stratospheric air is only visible above this level. Based on our observations, we draw the following picture of vertical transport and confinement in the ASM anticyclone: rapid convective uplift transports air to near 16 km in altitude, corresponding to potential temperatures up to about 370 K. Although this main convective outflow layer extends above the level of zero radiative heating (LZRH), our observations of CO concentration show little to no evidence of convection actually penetrating the tropopause. Rather, further ascent occurs more slowly, consistent with isentropic vertical velocities of 0.3 - 0.8 K day-1. For gases not subject to microphysical processes, neither the lapse rate tropopause (LRT) around 380 K nor the cold point tropopause (CPT) around 390 K marks the strong discontinuity of the key tracers (CO, O3, and N2O). Up to about 10 to 20 K above the CPT, isolation of air inside the ASM anticyclone prevents significant in-mixing of stratospheric air. The observed changes in CO and O3 likely result from in-situ chemical processing. Above about 420 K, mixing processes become more significant and the air inside the anticyclone is exported vertically and horizontally into the surrounding stratosphere. [ABSTRACT FROM AUTHOR]

The Asian Summer Monsoon (ASM) creates a hemispheric scale signature in trace gas distributions in the upper troposphere and lower stratosphere (UTLS). Data from satellite retrievals are the best source of information for characterizing these large-scale signatures. Measurements from the Microwave Limb Sounder (MLS), a limb viewing satellite sensor, have been the most widely used retrieval products for these type of studies. This work explores the information content for the ASM upper troposphere from two nadir-viewing sensors, IASI and OMI. Day-to-day behaviour of carbon monoxide (CO) and ozone (O3) in the UTLS from these two nadir-viewing sensors are analysed in comparison to MLS to examine the information content for the ASM UTLS trace gas analyses. Day-to-day changes in tracer distributions in response to dynamical variability is explored, to assess whether these nadir viewing sensors provide useful information for investigating sub-seasonal variability. Our result shows that both nadir-viewing instruments capture the impact of ASM dynamics on spatial distribution of tracers in the UTLS. Despite the limited vertical resolution, tropospheric profiles from IASI are able to represent the upper tropospheric enhancement of CO in the region of ASM anticyclone. Similarly, the OMI O3 profile product is capable of distinguishing the tropospheric dominated air mass in the anticyclone from the stratospheric dominated background on a daily time scale. The high horizontal sampling density of IASI data show finer structures in the horizontal distribution of CO compared to the limb viewing MLS, including CO enhancement in the upper troposphere over the western Pacific resulting from the eastward eddy shedding of the ASM anticyclone. Sub-seasonal variability of tracers is correlated with the dynamical structure of the anticyclone as represented by the geopotential height (GPH) field, and systematic differences between the nadir and limb sounder results are discussed. [ABSTRACT FROM AUTHOR]