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Some Aspects of the Characteristics of Monsoon Disturbances Using a Combined Barotropic-Baroclinic Model


doi: 10.1007/BF02657007

  • A standing Rossby wave of wavelength 30o longitude with a finite amplitude along the meridional direction is superimposed on the zonal mean component of the monsoon flow and the stability of such a flow is examined by a quasi-geostrophic barotropic, as well as by a quasi-geostrophic combined barotropic and baroclinic model on a beta plane centered at 18oN latitude. It is found that the growth of synoptic scale disturbance increases with the amplitude of the meridional wind. The barotropic stability analysis at 700 hPa pressure level shows that there is a critical value (Umax=11m/s) of the maximum mean zonal wind below which the computed disturbance moves to the west due to the wave-wave superposition. For maximum mean zonal wind greater that 11 m / s, the westerly wind dominates and the disturbance moves to the east. In another analysis the stability of the zonally asymmetric basic flow is studied with a combined barotropic-baroclinic model where cumulus heating is included. The growth rate, intensity, horizontal scale and the westward velocity of computed disturbances reasonably agree with those of observed monsoon disturb?ances. The fastest growing mode has a horizontal wavelength of 2000 kms and the e-folding time is about 3 days, when the meridional amplitude of the Rossby wave is 4 m / s at 700 hPa pressure level. When cumulus heating is in?cluded in the analysis the intensity of geopotential perturbation at 700 hPa disturbance is -304 m2 / s2. Energy calcu?lations show that the kinetic energy of the mean zonal flow is the main source of energy for the perturbation to grow. It is also found that the contribution of the kinetic energy of the basic Rossby wave to the growth of perturbation is more in comparison to the available potential energy.
  • [1] LI Rui, ZHANG Zuowei, WU Lixin, 2014: High-Resolution Modeling Study of the Kuroshio Path Variations South of Japan, ADVANCES IN ATMOSPHERIC SCIENCES, 31, 1233-1244.  doi: 10.1007/s00376-014-3230-4
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Manuscript History

Manuscript received: 10 October 1995
Manuscript revised: 10 October 1995
通讯作者: 陈斌, bchen63@163.com
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Some Aspects of the Characteristics of Monsoon Disturbances Using a Combined Barotropic-Baroclinic Model

  • 1. Centre for Atmospheric Sciences, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India,Centre for Atmospheric Sciences, Indian Institute of Technology, Hauz Khas, New Delhi-110016, India

Abstract: A standing Rossby wave of wavelength 30o longitude with a finite amplitude along the meridional direction is superimposed on the zonal mean component of the monsoon flow and the stability of such a flow is examined by a quasi-geostrophic barotropic, as well as by a quasi-geostrophic combined barotropic and baroclinic model on a beta plane centered at 18oN latitude. It is found that the growth of synoptic scale disturbance increases with the amplitude of the meridional wind. The barotropic stability analysis at 700 hPa pressure level shows that there is a critical value (Umax=11m/s) of the maximum mean zonal wind below which the computed disturbance moves to the west due to the wave-wave superposition. For maximum mean zonal wind greater that 11 m / s, the westerly wind dominates and the disturbance moves to the east. In another analysis the stability of the zonally asymmetric basic flow is studied with a combined barotropic-baroclinic model where cumulus heating is included. The growth rate, intensity, horizontal scale and the westward velocity of computed disturbances reasonably agree with those of observed monsoon disturb?ances. The fastest growing mode has a horizontal wavelength of 2000 kms and the e-folding time is about 3 days, when the meridional amplitude of the Rossby wave is 4 m / s at 700 hPa pressure level. When cumulus heating is in?cluded in the analysis the intensity of geopotential perturbation at 700 hPa disturbance is -304 m2 / s2. Energy calcu?lations show that the kinetic energy of the mean zonal flow is the main source of energy for the perturbation to grow. It is also found that the contribution of the kinetic energy of the basic Rossby wave to the growth of perturbation is more in comparison to the available potential energy.

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