Radiation profiles from the surface up to the upper troposphere and lower stratosphere over the Tibetan Plateau

Abstract

Variations in solar shortwave and thermal longwave radiation over the Tibetan Plateau (TP) are crucial for global climate and regional ecological environment. Previous radiation studies over the TP were widely based on ground and satellite measurements of the radiation budget at the surface and at the top of the atmosphere. A stratospheric balloon-based radiation measurement system was employed in a 2019 field campaign to study how and why radiation profiles vary over the TP during the Asian summer monsoon (ASM) period. We originally provide in situ measurements of multiwavelength radiation profiles from the surface up to the upper troposphere and lower stratosphere (UTLS) over the TP. These valuable observations, combined with simultaneous operational radiosondes, ground measurements, satellite retrievals and radiative transfer model simulations, are used to study radiation variations and the radiative forcings of clouds and aerosols over the TP during the ASM period. Cloud occurrences beneath the balloon flight altitude induce more balloon-borne shortwave upward radiation and ultraviolet upward radiation but less longwave upward radiation relative to clear sky counterparts. The radiative transfer model simulations capture the variations in balloon shortwave downward radiation (SDR) profiles well. Cloud radiative forcings at the UTLS and surface vary greatly with varying cloud cover. The diurnal evolution of the SDR discrepancy between the balloon altitudes and surface and the aerosol radiative forcing at the bottom of the atmosphere are also discussed during the balloon flight periods. The results of this study are expected to improve our understanding of radiation properties in the UTLS and help us better comprehend the thermal conditions associated with clouds and aerosols over the TP during the ASM.