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Causes of a Lack of QBO/Solar-MJO Connection in Certain CMIP6 models
  • Natasha E. Trencham,
  • Lon L. Hood
Natasha E. Trencham
Columbia University

Corresponding Author:netrencham@gmail.com

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Lon L. Hood
University of Arizona
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A connection between the quasi-biennial oscillation (QBO), the 11-yr solar cycle (SC), and the short-term convective climate oscillation, the Madden-Julian Oscillation (MJO), in boreal winter has been found in observational data, yet is generally lacking in current global climate models (GCMs). The extent to which a proposed mechanism for producing this connection is simulated in a series of GCMs participating in the Coupled Model Intercomparison Project 6 (CMIP6) is investigated. The models are found to be often lacking complete representation of several elements of this mechanism, with particular issues being QBOs that are westerly-biased and weak in the lower stratosphere, weak solar stratospheric temperature and zonal wind signals, insufficient solar or QBO-modulation of extratropical wave activity (the Holton-Tan effect), too weak reductions in equatorial tropopause static stability in response to extratropical wave forcing, and MJOs that in some cases do not respond to these reductions. Through by-passing many of these deficiencies via data selection, it is demonstrated that effects on the MJO that resemble those found in observations (strengthening of the MJO following early-winter sudden stratospheric warmings and during easterly QBO winters) can be simulated by a subset of the models. This supports operation of the proposed mechanism, and points to needed model improvements, although additional feedbacks may be needed to reproduce the full modulation.
29 Aug 2023Submitted to ESS Open Archive
31 Aug 2023Published in ESS Open Archive