13 Oct 2023
 | 13 Oct 2023

Moist bias in the Pacific upper troposphere and lower stratosphere (UTLS) in climate models affects regional circulation patterns

Felix Ploeger, Thomas Birner, Edward Charlesworth, Paul Konopka, and Rolf Müller

Abstract. Water vapour in the upper troposphere and lower stratosphere is a key radiative agent and crucial factor in the Earth's climate system. The largest observed moisture anomaly in the lower stratosphere occurs in boreal summer in the Asian monsoon region, but global climate models face problems with simulating this moisture pattern and show a common regional moist bias above the Pacific. We demonstrate from combination of climate model experiments and atmospheric observations that the enhanced moisture in the Pacific lower stratosphere critically impacts regional circulation systems by inducing local longwave cooling. Related impacts involve a strengthening of isentropic potential vorticity gradients, strengthened westerlies in the Pacific westerly duct region, and a zonally extended anticyclonic monsoon circulation. Hence, improving regional biases in climate model simulated stratospheric water vapour appears to be an important factor for improving simulation of regional circulation systems, in particular in the Asian monsoon and Pacific region.

Felix Ploeger et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2196', Anonymous Referee #1, 29 Oct 2023
  • RC2: 'Comment on egusphere-2023-2196', Anonymous Referee #2, 09 Nov 2023
  • RC3: 'Comment on egusphere-2023-2196', Anonymous Referee #3, 04 Dec 2023

Felix Ploeger et al.


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Short summary
We present a novel mechanism how regional anomalies in water vapour concentrations in the upper troposphere and lower stratosphere impact on regional atmospheric circulation systems. These impacts include a broadening upper-level Asian monsoon circulation and strengthened prevailing westerlies in the Pacific region. Current climate models have biases in simulating these regional water vapour anomalies and circulation impacts, but the biases can be avoided by improving the model transport.