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The Effect of the Hadley Circulation On the Meridional Propagation of Stationary Waves
Author(s) -
Watterson Ian G.,
Schneider Edwin K.
Publication year - 1987
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711347706
Subject(s) - hadley cell , barotropic fluid , climatology , rossby wave , forcing (mathematics) , atmospheric sciences , baroclinity , geology , walker circulation , potential vorticity , atmospheric circulation , zonal and meridional , wkb approximation , vorticity , physics , vortex , meteorology , general circulation model , climate change , sea surface temperature , oceanography , quantum mechanics
The effect on the meridional propagation of stationary planetary waves of the inclusion of the zonal mean Hadley circulation in linearized models of the atmosphere is examined. In a forced barotropic vorticity equation model a meridional wind in the basic state enables wave propagation through tropical easterlies in the direction of the wind. This is shown to be consistent with the WKB solution. In a multi‐level linearized steady primitive equation model with an idealized meridional circulation tropical forcing can still produce response through easterlies although propagation from one mid‐latitude to the other is much less than in the barotropic result. This is explained through WKB and wave‐tracing methods for a simplified three‐dimensional vorticity equation. the near non‐divergence of the unforced tropical motion permits a wave to travel largely within a layer of favourable winds. In a twelve‐level model using observed January and July zonal mean conditions the Hadley circulation changes the response to earth topographic forcing mainly in the subtropics. However, tropical heat forcing can now produce a large mid‐latitude response, in the winter hemisphere especially. the resulting subtropical jets suggest a mechanism for the maintenance of those observed over Australia during the northern monsoon season and adjacent to the anomalous forcing of the 1983 El Niño.