什么是 Global circulation of the atmosphere？

Example 24.7 (Four towns, four belts)

The four towns of the climate charts of Chapter 11 all lie in the northern hemisphere, at very different latitudes. Their yearly rain and snow follow the belts of the global circulation (chart below). Hilo, at $20{}^{\circ}$ N, is on an island in the trade-wind belt, in the middle of the ocean, where the trade winds pick up water vapour: about $3000\,\mathrm{mm}$ fall there in a year. Phoenix, at $33{}^{\circ}$ N, lies close to $30{}^{\circ}$, under the sinking air: less than $200\,\mathrm{mm}$. Seattle, at $47{}^{\circ}$ N, is in the westerlies, whose storms bring about $1000\,\mathrm{mm}$ a year, most of it from autumn to spring. Utqiaġvik, at $71{}^{\circ}$ N, lies under the cold air that sinks near the pole: less than $150\,\mathrm{mm}$, a cold desert.