Suppressed migrating diurnal tides in the mesosphere and lower thermosphere region during El Niño in northern winter and its possible mechanism
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Published:2022-06-17
Issue:12
Volume:22
Page:7861-7874
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Cen Yetao, Yang ChengyunORCID, Li TaoORCID, Russell III James M., Dou Xiankang
Abstract
Abstract. As observed by the Sounding of the Atmosphere using Broadband Emission
Radiometry (SABER), the migrating diurnal tide (DW1) in the upper mesosphere
and lower thermosphere (MLT) region decreased by ∼ 10 %
during El Niño in the Northern Hemisphere (NH) winter
(December–January–February) from 2002 to 2020. According to the multiple
linear regression (MLR) analysis, the linear effects of El Niño on the
tropical MLT DW1 are significantly negative in both SABER observations and
SD-WACCM (the Specified-Dynamics version of the Whole Atmosphere Community
Climate Model) simulations. The DW1 response to El Niño in NH winter is
much stronger than its annual mean response. As suggested by SD-WACCM
simulation, Hough mode (1, 1) dominates the DW1 tidal variation in the
tropical MLT region. The consistency between the (1, 1) mode in the
tropopause region and the MLT region and the downward phase progression from
15 to 100 km indicates the direct upward propagation of DW1 from the
excitation source in the troposphere. The suppressed DW1 heating rates in
the tropical troposphere (averaged over ∼ 0–16 km and
35∘ S–35∘ N) during El Niño winter contribute to the
decreased DW1 tide. To evaluate the effect of the gravity waves (GWs) on the
tide, the GW forcing is calculated as the GW drag weighted by the phase
relation between DW1 GW drag and DW1 wind. The negative GW forcing in the
tropical upper mesosphere would significantly suppress the MLT DW1 tide
during El Niño winter. This tide–GW interaction could be a dominant
mechanism for DW1 response in the MLT to El Niño. During El Niño
winter, the increased ratio of the absolute and planetary vorticity (R)
suppresses the waveguide and thus the DW1 amplitude in the subtropical
mesosphere. However, the effect of the waveguide might play a secondary role
due to its relatively weak response.
Funder
China National Space Administration National Science Foundation Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences National Natural Science Foundation of China
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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