On global summer monsoonal drought mechanics

  • M. Sankar-Rao
  • S. V. Sachidananda


It is shown that within the framework of a linear five-level quasi-geostrophic steady state global model the middle latitude systems can always have significant influence on the Asian summer monsoonal system through the lower tropospheric monsoonal westerly window region around 80°E. It is hypothesized that quasistationarity of the middle latitude longwave systems results in stronger teleconnections through this window and the consequent monsoon breaks when the phase is right.


Monsoon break Rossby waves middle latitudes teleconnections 

List of Symbols

B =

−(RPs/U f Pδ) (1/a) (∂T/∂φ)

b =

−(RPs/U0d2T f PT) (1/a) (∂T0T/∂ Φ)


any dependent variable


time mean ofD =D0 +D*


zonal mean ofD


Axially asymmetric perturbation part =D exp (im λ)


amplitude ofD*

d =

−(RPs/U0Tf PT)


2 Ω sin Φ

K0 =

[(∂T0/∂P) −(RT0/PCp)]−1


Ekman friction constant

M =

−(RPs/Uf Pδ)U0 δ gρδ/Ka)


longitudinal wave number

N =

RPs/Uf Pδ




surface standard pressure

S1 =


S2 =

[-f2(∂/∂P) (PKA12BC0660)]RPS

S3 =

(1/U0) [(1/a)(∂η0/∂Φ) + (f∂/∂P) (K0/a) (∂T0/∂Φ)]




eastward velocity


northward velocity


relative vorticity

η =

f + ζ, the absolute vorticity



v =

(RPs/U f Pδ) (gPδ l/Ka)


P/Ps, the usual coordinate in many GCMs






angular velocity of the earth

ω =



horizontal spherical Laplacian SuffixesT and δ denote top and bottom of the atmosphere considered


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Copyright information

© Indian Academy of Sciences 1987

Authors and Affiliations

  • M. Sankar-Rao
    • 1
  • S. V. Sachidananda
    • 1
  1. 1.Department of Aerospace Engineering and Centre for Atmospheric SciencesIndian Institute of ScienceBangaloreIndia

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