Abstract. Biomass burning (BB) over Asia is a strong source of carbonaceous aerosols during spring. From ECHAM6–HAMMOZ model simulations and satellite observations, we show that there is an outflow of Asian BB carbonaceous aerosols into the upper troposphere and lower stratosphere (UTLS) (black carbon: 0.1 to 6 ng m−3 and organic carbon: 0.2 to 10 ng m−3) during the spring season. The model simulations show that the greatest transport of BB carbonaceous aerosols into the UTLS occurs from the Indochina and East Asia region by deep convection over the Malay Peninsula and Indonesia. The increase in BB carbonaceous aerosols enhances atmospheric heating by 0.001 to 0.02 K d−1 in the UTLS. The aerosol-induced heating and circulation changes increase the water vapor mixing ratios in the upper troposphere (by 20–80 ppmv) and in the lowermost stratosphere (by 0.02–0.3 ppmv) over the tropics. Once in the lower stratosphere, water vapor is further transported to the South Pole by the lowermost branch of the Brewer–Dobson circulation. These aerosols enhance the in-atmosphere radiative forcing (0.68±0.25 to 5.30±0.37 W m−2), exacerbating atmospheric warming, but produce a cooling effect on climate (top of the atmosphere – TOA: -2.38±0.12 to -7.08±0.72 W m−2). The model simulations also show that Asian carbonaceous aerosols are transported to the Arctic in the troposphere. The maximum enhancement in aerosol extinction is seen at 400 hPa (by 0.0093 km−1) and associated heating rates at 300 hPa (by 0.032 K d−1) in the Arctic.

The water vapour variation in the upper troposphere and lower stratosphere (UTLS) is of high significance due to its impact on global warming. In this article, we present an association of occurrence frequency of double tropopauses (DTs) with convective clouds and transport of water vapour in the UTLS over subtropical South Asia using multiple multi-decadal datasets (e.g., radiosonde temperature profiles (1977-2017), Atmospheric Infrared Sounder (2003-2017), ERA-Interim reanalysis (1979-2017) and Microwave Limb Sounder (2004-2016). The diagnostic analysis of temperature, water vapour and potential vorticity indicates that convective clouds occurring during DTs enhance water in the altitude layer near the DTs. DTs are frequent ($5-55%) over the subtropical South Asia (25-30 N) and associated with an enhancement of water vapour mixing ratios by $5-40% (0.2-7.5 ppmv) above the lower tropopause. The radiosonde observations show a positive trend ($0.27 ± 0.12 to 0.4 ± 0.2%/year) in the occurrence of DTs during last 45 years, enhancing the moisture during DT days (trend 0.04 ± 0.02 to 0.26 ± 0.24 ppmv/decade above the tropopause). The convective injection of anomalously high water vapour mixing ratios in DT conditions and moistening trends in the UTLS may be consequences of global warming. The increasing trend in the water vapour in the UTLS may enhance long-wave radiation coming back down to warm the troposphere and exacerbate the global warming effect. K E Y W O R D S double tropopause, ERA-interim water vapour and temperature, upper troposphere and lower stratosphere (UTLS), Wyoming radiosonde temperature

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Abstract. Biomass burning (BB) over Asia is a strong source of carbonaceous aerosols during spring. From ECHAM6-HAMMOZ model simulations and satellite observations, we show that there is an outflow of Asian BB carbonaceous aerosols into the Upper Troposphere and Lower Stratosphere (UTLS) (black carbon: 0.1 to 4 ng m−3 and organic carbon: 0.6 to 9 ng m−3) during the spring season. The model simulations show that the greatest transport of BB carbonaceous aerosols into the UTLS occurs from the Indochina and East Asia region by deep convection over the maritime continent that extends to the Bay of Bengal and the South China Sea. The increase in BB carbonaceous aerosols enhances atmospheric heating by 0.002 to 0.02 K day−1 in the UTLS. The aerosol-induced heating and circulation changes increase the water vapour mixing ratios in the upper troposphere (20–80 ppmv) and in the lowermost stratosphere (0.02–0.3 ppmv) over the tropics. Once in the lower stratosphere, water vapour is further transported to the South Pole by the lowermost branch of Brewer-Dobson circulation. These aerosols enhance the in-atmosphere radiative forcing (0.68 ± 0.25 W m−2 to 5.30 ± 0.37 W m−2), exacerbating atmospheric warming but produce cooling effect on climate (TOA: −2.38 ± 0.12 W m−2 to −7.08 ± 0.72 W m−2). The model simulations also show that Asian carbonaceous aerosols are transported to the Arctic in the troposphere. The maximum enhancement in aerosol extinction is seen at 400 hPa (by 0.0093 km−1) and associated heating rates at 300 hPa (by 0.032 K day−1) at the Arctic.