Role of Diurnal Cycle in the Maritime Continent Barrier Effect on MJO Propagation in an AGCM

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  • 1 Center for Prototype Climate Modeling, New York University Abu Dhabi, United Arab Emirates.
  • 2 Department of Mathematics & Statistics, University of Victoria, BC, Canada.
  • 3 Center for Prototype Climate Modeling, New York University Abu Dhabi, United Arab Emirates.
  • 4 Department of Mathematics & Center for Atmosphere and Ocean Sciences, Courant Institute of Mathematical Sciences, New York University, NY, USA.
  • 5 Center for Prototype Climate Modeling, New York University Abu Dhabi, United Arab Emirates.
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Abstract

The barrier effect of the Maritime Continent (MC) in stalling or modifying the propagation characteristics of MJO is widely accepted. The strong diurnal cycle of convection over the MC is believed to play a dominant role in this regard. This hypothesis is studied here, with the help of a coarse-resolution Atmospheric General Circulation Model (AGCM). The dry dynamical core of the AGCM is coupled to the multicloud parameterization piggybacked with a dynamical bulk boundary layer model. A set of sensitivity experiments is carried out by systematically varying the strength of the MC diurnal flux to assess the impact of the diurnal convective variability on the MJO propagation. The effect of deterministic and stochastic diurnal forcings on MJO characteristics are compared. It is found that the precipitation and zonal wind variance, on the intraseasonal timescales, over the Western Pacific region decreases with the increase in diurnal forcing, indicating the blocking of MC precipitation. An increase in precipitation variance over the MC associated with the weakening of precipitation variance over the West Pacific is evident in all experiments. The striking difference between deterministic and stochastic diurnal forcing experiments is that the strength needed for the deterministic case to achieve the same degree of blocking is almost double that of stochastic case. The stochastic diurnal flux over the MC seems to be more detrimental in blocking the MJO propagation. This hints at the notion that the models with inadequate representation of organized convection tend to suffer from the MC-barrier effect.

Corresponding author: R. S. Ajayamohan, Ajaya.Mohan@nyu.edu

Abstract

The barrier effect of the Maritime Continent (MC) in stalling or modifying the propagation characteristics of MJO is widely accepted. The strong diurnal cycle of convection over the MC is believed to play a dominant role in this regard. This hypothesis is studied here, with the help of a coarse-resolution Atmospheric General Circulation Model (AGCM). The dry dynamical core of the AGCM is coupled to the multicloud parameterization piggybacked with a dynamical bulk boundary layer model. A set of sensitivity experiments is carried out by systematically varying the strength of the MC diurnal flux to assess the impact of the diurnal convective variability on the MJO propagation. The effect of deterministic and stochastic diurnal forcings on MJO characteristics are compared. It is found that the precipitation and zonal wind variance, on the intraseasonal timescales, over the Western Pacific region decreases with the increase in diurnal forcing, indicating the blocking of MC precipitation. An increase in precipitation variance over the MC associated with the weakening of precipitation variance over the West Pacific is evident in all experiments. The striking difference between deterministic and stochastic diurnal forcing experiments is that the strength needed for the deterministic case to achieve the same degree of blocking is almost double that of stochastic case. The stochastic diurnal flux over the MC seems to be more detrimental in blocking the MJO propagation. This hints at the notion that the models with inadequate representation of organized convection tend to suffer from the MC-barrier effect.

Corresponding author: R. S. Ajayamohan, Ajaya.Mohan@nyu.edu
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