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Aerosol Effects on Clear-Sky Shortwave Heating in the Asian Monsoon Tropopause Layer
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  • Jie Gao,
  • Yi Huang,
  • Yiran Peng,
  • Jonathon S. Wright
Jie Gao
Tsinghua University
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Yi Huang
McGill University
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Yiran Peng
Tsinghua University
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Jonathon S. Wright
Tsinghua University

Corresponding Author:[email protected]

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Abstract

The Asian Tropopause Aerosol Layer (ATAL) has emerged in recent decades to play a prominent role in the upper troposphere and lower stratosphere above the Asian monsoon. Although ATAL effects on surface and top-of-atmosphere radiation budgets are well established, the magnitude and variability of ATAL effects on radiative transfer within the tropopause layer remain poorly constrained. Here, we investigate the impacts of various aerosol types and layer structures on clear-sky shortwave radiative heating in the Asian monsoon tropopause layer using reanalysis products and offline radiative transfer simulations. ATAL effects on shortwave radiative heating based on the MERRA-2 aerosol reanalysis are on the order of 10% of mean clear-sky radiative heating within the tropopause layer, although discrepancies among recent reanalysis and forecast products suggest that this ratio could be as small as ~5% or as large as ~25%. Uncertainties in surface and top-of-atmosphere flux effects are also large, with values spanning one order of magnitude at the top-of-atmosphere. ATAL effects on radiative heating peak between 150 hPa and 80 hPa (360 K–400 K potential temperature) along the southern flank of the anticyclone. Clear-sky and all-sky shortwave heating are at local minima in this vertical range, which is situated between the positive influences of monsoon-enhanced water vapor and the negative influence of the ‘ozone valley’ in the monsoon lower stratosphere. ATAL effects also extend further toward the west, where diabatic vertical velocities remain upward despite descent in pressure coordinates.