# On global summer monsoonal drought mechanics

- Received:
- Revised:

DOI: 10.1007/BF02839266

- Cite this article as:
- Sankar-Rao, M. & Sachidananda, S.V. Proc. Indian Acad. Sci. (Earth Planet Sci.) (1987) 96: 147. doi:10.1007/BF02839266

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## Abstract

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.

### Keywords

MonsoonbreakRossby wavesmiddle latitudesteleconnections### List of Symbols

*B*=−(

*RP*_{s}/U_{0δ}f P_{δ}) (1/*a*) (*∂T*_{0δ}/∂φ)*b*=−(

*RP*_{s}/U_{0}d2T f P_{T}) (1/*a*) (*∂T*_{0}T/∂ Φ)- D
any dependent variable

- D
time mean of

*D*=*D*_{0}+*D*_{*}*D*_{0}zonal mean of

*D**D*_{*}Axially asymmetric perturbation part =

*D*exp (im λ)- D
amplitude of

*D*_{*}*d*=−(

*RP*_{s}/U_{0T}f P_{T})*f*=2 Ω sin Φ

*K*_{0}=[(

*∂T*_{0}/∂P) −(*RT*_{0}/PC_{p})]^{−1}- l
Ekman friction constant

- M =
−(

*RP*_{s}/U_{0δ}f P_{δ})*U*_{0 δ gρδ}/K_{0δ}a)- m
longitudinal wave number

*N*=−

*RP*_{s}/U_{0δ}f P_{δ}- P
pressure

*P*_{s}surface standard pressure

*S*_{1}=−

*f*^{2}PK_{0}/RP_{s}^{2}*S*_{2}=[

*-f*^{2}(∂/∂P) (*PKA12BC066*_{0})]*RP*_{S}*S*_{3}=(1/

*U*_{0}) [(1/*a*)*(∂*_{η0}/∂Φ) + (f∂/∂P) (K_{0}/a) (∂T_{0}/∂Φ)]- T
temperature

- u
eastward velocity

- v
northward velocity

- ζ
relative vorticity

*η*=*f*+ ζ, the absolute vorticity- λ
longitude

*v*=−

*(RP*_{s}/U_{0δ}f P_{δ}) (gP_{δ}l/K_{0δ}a)- ξ
*P/P*_{s}, the usual coordinate in many GCMs- ρ
density

- Φ
latitude

- Ω
angular velocity of the earth

*ω*=*dp/dt**∇*^{2}horizontal spherical Laplacian Suffixes

*T*and δ denote top and bottom of the atmosphere considered