Preprints
https://doi.org/10.5194/acp-2021-884
https://doi.org/10.5194/acp-2021-884

  25 Nov 2021

25 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Would El Niño enhance or suppress the migrating diurnal tide in the MLT region?

Yetao Cen1,2,3, Chengyun Yang1,2,3, Tao Li1,2,3, Jia Yue5,6, James M. Russell III6, and Xiankang Dou1,2,3,4 Yetao Cen et al.
  • 1CAS Key Laboratory of Geospace Environment, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China
  • 2Mengcheng National Geophysical Observatory, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China
  • 3CAS Center for Excellence in Comparative Planetology, University of Science and Technology of China, Hefei, Anhui, China
  • 4School of Electronic Information,Wuhan University,Wuhan, Hubei, China
  • 5Catholic University of America, DC, USA
  • 6Center for Atmospheric Sciences, Hampton University, Hampton, VA, USA

Abstract. Previous observations and simulations are controversial as to whether El Niño will increase or decrease the diurnal tide (DW1) in the upper mesosphere and lower thermosphere (MLT) region. This study revisited the linear response of the MLT DW1 to El Niño during the winter (December-January-February) based on 19-year satellite observations of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). The MLT DW1 temperature amplitudes decreased by ~10 % during four El Niño winters from 2002 to 2020, consistent with the results from the simulation of the Specified-Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM). According to the multiple linear regression analysis, the linear effects of El Niño-Southern Oscillation (ENSO) on tropical MLT DW1 are negative in both SABER observations and SD-WACCM simulations. In the 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 in the MLT region, as well as the downward phase progression from 15 to 100 km, indicates the direct upward propagation of DW1 from the excitation source in the troposphere. During 7 of 8 El Niño winters from 1979 to 2014, the anomalous amplitudes of the (1, 1) mode are negative in both the tropopause region and MLT region. The suppressed DW1 heating rates in the tropical troposphere (average over ~0–16 km and 35° S–35° N) during the El Niño events contribute to the decreased DW1 tide. The mesospheric latitudinal zonal wind shear anomalies during El Niño winters would lead to a narrower waveguide and prevent the vertical propagation of the DW1 tide. The gravity wave drag excited by convection also plays a role in modulating the MLT DW1 amplitude.

Yetao Cen et al.

Status: open (until 06 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Yetao Cen et al.

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Short summary
The MLT DW1 amplitude is suppressed during El Niño winters in both satellite observation and SD-WACCM simulations. The suppressed Hough mode (1, 1) in the tropopause region propagate vertically to the MLT region, leading to decreased DW1 amplitude. The latitudinal zonal wind shear anomalies during El Niño winters would narrower the waveguide and prevent the vertical propagation of DW1. The gravity waves drag excited by ENSO-induced anomalous convection could also modulate the MLT DW1 amplitude.
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