Chapter 5. Weather and Climate
Weather is the state of the atmosphere at a given time and place; climate is its long-term pattern, usually averaged over 30 years or more [6].
Controls of climate: latitude, altitude, distance from the ocean, ocean currents, prevailing winds, mountain barriers and pressure systems [4].
Global circulation. Air rises at the equator (the Intertropical Convergence Zone), sinks near 30° latitude, and forms three circulation cells in each hemisphere. This pattern produces the trade winds, the westerlies and the polar easterlies, and explains why many deserts lie near 30° N and S [4][6]. The Coriolis effect deflects moving air to the right in the Northern Hemisphere and to the left in the Southern.
Köppen climate classification. The most widely used system divides climates into five main groups [7][8].
| Group | Description |
| A | Tropical: warm all year, with rainforest, monsoon and savanna types |
| B | Dry: arid desert and semi-arid steppe |
| C | Temperate: mild winters, including Mediterranean and oceanic types |
| D | Continental: cold winters, large seasonal range |
| E | Polar: very cold, including tundra and ice cap |
Monsoons are seasonal wind reversals that bring heavy summer rain to much of South and Southeast Asia. El Niño and La Niña are opposite phases of a Pacific Ocean–atmosphere cycle that can shift rainfall and temperature patterns worldwide [6].
Review: Why is the interior of a continent usually hotter in summer and colder in winter than a coastal location at the same latitude?