What Causes Climate? Notes

Introduction A climate is the average, year-after- year weather conditions in an area. Two factors are important in describing a climate - temperature and precipitation. A climate region is a large area that has similar climate throughout. For example, all of the southwestern United States has a hot, dry climate. The weather of one single day, or even one single year IS NOT an indication of climate.

Introduction A small area within a climate region may have climate conditions that are different from the area around it. A small area with different climate conditions is called a microclimate.

Factors Affecting Temperature Earth is divided into three temperature zones based on latitude: 1. The tropical zone is the area near the equator from 0° to 23.5°N and S. 2. The temperate zones are from 23.5°N and S to 66.5°N and S. 3. The polar zones are from 66.5°N and S to the poles (or 90°N and S).

Factors Affecting Temperature In the Tropical Zone, there is very little seasonal temperature change. It is almost always warm here because sunlight is direct all year long. In the Polar Zones, light is the least direct throughout the year, so it is alway cold. In the Temperate Zones, sunlight is direct only in the summer, and during the winter, it strikes at a much more acute angle. This leads to temperature changes between seasons.

Factors Affecting Temperature Altitude affects temperature as well. Highland areas everywhere have cool climates. For example, Mt. Kilimanjaro, which resides in East Africa, has a peak at 6km. Temperatures drop at around 10°C for every kilometer of altitude, meaning that at the top, it’s nearly 60° cooler that at sea level.

Factors Affecting Temperature Oceans and large lakes affect climate. A marine climate is the climate of an area near an ocean or large lake. Sun an area has mostly mild winter and cool summer. This is because water heats up more slowly than land. It also cools off more slowly than land. This means that coastal areas are somewhat protected from extreme temperature shifts. Remember, this is due to the relatively high specific heat of water.

Factors Affecting Temperature Continental climates have hotter and colder seasons than do marine climates. Winters are colder, while summers are hotter. The central part of the Unites States has a continental climate.

Factors Affecting Temperature Marine climates are also influenced by ocean currents. Warm water from the tropics can warm up places that have very high latitudes. For example, the Gulf Stream is a tropical current that brings warm moist air to Ireland and southern England, both of which are above 50°N latitude.

Factors Affecting Temperature At the same time, cooler, polar waters can come down and bring cold, wet air to warm, dry regions. The California Current brings cold water/air down from Alaska, making the west coast of the United States cooler than expected for those latitudes.

Factors Affecting Precipitation Prevailing winds move air masses from one place to another. If the air started over an ocean, it’ll be moist. If the air mass started over land, it’ll be very dry. The amount of water vapor in an air mass influences the amount of precipitation. The United States exists in a prevailing wind known as the westerlies. This generally moves air from the SW to the NE.

Factors Affecting Precipitation When prevailing winds force air over a mountain range, rain or snow often falls as the air is forced upwards. This also forces the air to cool and condense into a cloud, and often rain will occur. The rain will always fall on the windward side of the mountain. This is the side of the mountain thats the wind hits firsts.

Factors Affecting Precipitation The opposite side of the mountain is known as the leeward side. This side usually remains dry and hot. Air that was forced over the mountain by the prevailing winds begins to descend down the leeward side, heating up at 10°C for every kilometer that it sinks and absorbing any moisture left in the air.

Factors Affecting Precipitation Seasonal winds are wind patterns that change with the seasons over a wide area. Monsoons are seasonal winds. Monsoons are large sea and land breezes that change directions with the seasons. Winds flow from [H]igh pressure to [L]ow pressure. In general: Cool air = [H]igh Warm air = [L]ow

LH Sea BreezeLand Breeze Massive RainsVery Little Rains

The Seasons Of course, the weather changes as the seasons change. This is most extreme in the Temperate Zones from 23.5N to 66.5N and form 23.5S to 66.5S. This directly corresponds to the tilt of Earth’s axis (23.5°) in relation to the sun. It’s summer when the tilt is towards the sun (July in the Northern Hemisphere/December in the Southern Hemisphere). It’s winter when the tilt is away from the sun.