Preprints
https://doi.org/10.5194/wcd-2022-19
https://doi.org/10.5194/wcd-2022-19
 
31 Mar 2022
31 Mar 2022
Status: this preprint is currently under review for the journal WCD.

Trends in the tropospheric general circulation from 1979 to 2022

Adrian John Simmons Adrian John Simmons
  • European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading RG2 9AX, UK

Abstract. Atmospheric general circulation changes since 1979 are examined using the ERA5 reanalysis. Maps based on linear trends and time series for specific areas are presented. Attention is concentrated on monthly, seasonal and annual means, but shorter-timescale variability is also considered, including extremes. Changes in near-tropopause winds are the main focus, but related changes in temperature, wind and other variables throughout the troposphere are discussed.

Middle- and upper-tropospheric warming is larger in the subtropics and outer tropics than in the deep tropics, except over the Pacific. This is linked with a strengthening and meridional expansion of the tropical easterlies that has received little previous attention. Warming over several mid-latitude and subtropical land areas comes close to matching the large warming of the Arctic. Westerly upper-level winds in general weaken over the Arctic in winter, but strengthen in northern middle latitudes, contrary to arguments based on circulation changes due solely to amplified Arctic warming. The jet-stream region over the eastern North Atlantic and western Europe shifts southward. Westerlies strengthen in a band stretching south-eastwards from the tropical western Pacific to southern Australia, and in the polar-jet-stream region that surrounds Antarctica.

Extreme jet-stream winds increase over the North Atlantic. Net kinetic energy also increases, mostly associated with sub-monthly variability along the mid-latitude storm tracks and over the tropical Pacific. Available potential energy changes less. Geopotential height shows a distinct pattern of change in the stationary northern-hemispheric long-wave structure. There are increases in surface pressure over the North Pacific and southern mid-latitudes, and decreases over the Arctic Ocean and offshore of Antarctica.

Several comparisons are made between ERA5 and the JRA-55 reanalysis, and between ERA5 and the observations it assimilated. They show reassuring agreement, but some regional differences require further investigation.

Adrian John Simmons

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • AC1: 'Comment on wcd-2022-19', Adrian Simmons, 08 Apr 2022
  • RC1: 'Comment on wcd-2022-19', Theodore Shepherd, 02 May 2022
    • AC2: 'Reply on RC1', Adrian Simmons, 08 May 2022
      • RC3: 'Reply on AC2', Theodore Shepherd, 16 May 2022
        • AC3: 'Reply on RC3', Adrian Simmons, 16 May 2022
  • CC1: 'Comment on wcd-2022-19 by Gloria Manney & Michaela Hegglin', Gloria Manney, 13 May 2022
    • AC5: 'Reply on CC1', Adrian Simmons, 21 May 2022
  • RC2: 'Comment on wcd-2022-19', Anonymous Referee #2, 14 May 2022
    • AC4: 'Reply on RC2', Adrian Simmons, 20 May 2022

Adrian John Simmons

Adrian John Simmons

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Short summary
This study of changes in temperature and wind since 1979 met its twin aims of (i) increasing confidence in some findings of the latest IPCC assessment and (ii) identifying changes that had received little or no previous attention. It reports a small overall intensification and shift in position of the North Atlantic jet stream and associated storms, and a strengthening of tropical upper-level easterlies. Increases in low-level winds over tropical and southern hemispheric oceans are confirmed.