This chapter serves as an introduction and preview for the entire book. Topics will be broadly introduced, to be better and more completely explained in the sequel.

The maritime tropics

It may surprise people living in the midlatitudes that the tropics have such an overwhelming role in the climate of the Earth. Yet it has been shown time and time again that the maritime tropics are the only regions on Earth where changes in the surface-boundary condition, especially sea-surface temperature (SST), have a demonstrable and robust causal correlation with weather effects in midlatitudes. This happens through the ability of warm sea-surface temperature anomalies (deviations of sea-surface temperature from its normal value for that time of year) to organize deep cumulonimbus convection and plentiful rainfall which can then emit large-scale planetary waves which subsequently travel to higher latitudes. The changes of SST, the formation of regions of persistent precipitation, and the resulting forcing of the midlatitude motions by these regions of persistent precipitation, form a set of themes that appear and recur throughout this book.

It is a good rule of thumb (these rules of thumb will be examined in much greater detail in the body of the book), in the tropical Pacific in particular, that regions of persistent precipitation lie over the warmest water, and a good rule of thumb that in the presence of persistent precipitation, the net synoptic motion is upward and the sea-level pressure low.