Weather and Climate Dynamics
Weather and Climate Dynamics
Weather and Climate Dynamics
Preprints
https://doi.org/10.5194/wcd-2020-64
https://doi.org/10.5194/wcd-2020-64

  04 Jan 2021

04 Jan 2021

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

Zonal scale and temporal variability of the Asian monsoon anticyclone in an idealised numerical model

Philip Rupp1,a and Peter Haynes1 Philip Rupp and Peter Haynes
  • 1Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
  • acurrently at: Meteorological Institute Munich, Ludwig-Maximilians-University, Munich, Germany

Abstract. The upper-level monsoon anticyclone is studied in a 3-D dry dynamical model as the response of a background circulation without any imposed zonal structure to a steady imposed zonally confined heat source. The characteristics of the background circulation are determined by thermal relaxation towards a simple meridionally varying state, which gives rise to baroclinic instability if meridional gradients are sufficiently large. This model configuration allows study of the dependence of the monsoon anticyclone response on characteristics of both the imposed heating and the background state, in particular including interactions between the anticyclone and the active dynamics on its poleward side in the form of the jet and baroclinic eddies.

As characteristics of forcing and background state are varied a range of different behaviours emerges, many of which strongly resemble phenomena and features associated with the monsoon anticyclone as observed in re-analysis data. For a resting background state the time-mean anticyclone is highly extended in longitude to the west of the forcing region. When the active mid-latitude dynamics is included the zonal extent of the time-mean anticyclone is limited, without any need for the explicit upper-level momentum dissipation which is often included in simple theoretical models, but difficult to justify physically.

We further describe in detail the spontaneous emergence of temporal variability in the form of westward eddy shedding from the monsoon anticyclone for varying strength of the imposed heating. By varying the strength of the background mid-latitude dynamics we observe a transition of the system from a state with periodic westward eddy shedding to a state dominated by eastward shedding. The details of the time-mean structure and temporal evolution depend on the structure of the background flow and for certain flows the monsoon anticyclone shows signs of both westward and eastward shedding.

Philip Rupp and Peter Haynes

Status: open (until 15 Feb 2021)

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Philip Rupp and Peter Haynes

Philip Rupp and Peter Haynes

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Short summary
We study a range of dynamical aspects of the Asian monsoon anticyclone as the response of a simple numerical model to a steady imposed heating distribution with different background flow configurations. Particular focus is given on interactions between the monsoon anticyclone and active mid-latitude dynamics, which we find to have a zonally localising effect on the time mean circulation and to be able to qualitatively alter the temporal variability of the bulk anticyclone.