E 90e 135e 180 135w 90w

Figure 9. (Continued )

anomalies. Note that the El Nino-like case discussed here does not correspond to either the ENSO growing or decaying phase, because the experiments here are all at equilibrium.

6. Conclusion

The monsoon has great differences in detail in different regions, but at its heart is the seasonal movement of land convection zones. The convection is directly affected by evaporation in the moisture equation (2). More importantly, it is also associated with a dynamical feedback via the net energy into the atmosphere Fnet in the MSE equation (3). However, the summer monsoon includes not only the convection but also the associated monsoon circulation which is related to land-ocean heating contrast. We have argued here that the differences in the net energy into the atmospheric column Fnet are the leading cause of the land-ocean contrast, not surface temperature. Land-ocean heating contrast creates pressure gradients between continents and the neighboring oceans and induces the cyclonic summer monsoon circulation over the continental regions. The pressure gradient can be represented by the tropospheric temperature gradient. This monsoon circulation, along with mean flow, the cross-continental westerly winds in the subtropics and at midlatitudes, modifies the summer monsoon rainfall pattern via the horizontal advection of temperature and moisture — (v • VT) and — (v • Vq). The advection associated with the monsoon circulation is

(c) Prec and 850hPa wind diff

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