Evaluation of upper-tropospheric lower-stratospheric properties over the Asian monsoon region in a storm-resolving model

Abstract

The structure of the tropical upper troposphere-lower stratosphere (UTLS) affects radiative balance, stability, and regional dynamics in important ways. Lack of reliable observational baselines poses a challenge to evaluating model representation of UTLS properties. Here, we use in-situ data, primarily from the StratoClim field campaign over the Asian Monsoon area, to assess the UTLS temperature, moisture, and ice clouds in the Icosahedral Nonhydrostatic (ICON) model at storm-resolving grid spacing. We also employ superpressure balloon data and updrafts of the POSIDON and ATTREX campaigns to evaluate the UTLS convective updrafts and gravity wave activity in ICON. Our simulations show the upper troposphere is too cold, while the lower stratosphere is too warm and excessively dry relative to observations. These thermodynamic biases coincide with overestimated cloud ice in the upper troposphere and underestimated cloud ice in the lower stratosphere. The mean convective updraft is underestimated by 80 % in the model, and the power spectral density for temperature fluctuations of frequencies greater than 10-3 s-1 is underestimated by orders of magnitude. Too weak dynamics exacerbate a lack of ice cloud above 100 hPa. Too weak and too infrequent convective overshoots or too rapid dissipation of upper-tropospheric ice clouds in the model are two possible explanatory mechanisms for these biases.