AP Environmental Science/Winds

Wind is a very vital part of the planet's way of life. Wind, for example, effects climate: Global wind distributes heat across the world. They also distribute nutrients, such as the dust in the Sahara Desert (rich in N+P) being blown across the Atlantic Ocean by winds. Although sadly, winds also can play a damaging role in the environment by blowing pollution everywhere. Winds can also globally distribute harmful viruses, bacteria, fungi, and particles of long-lived pesticides and toxic metals. Particles of pesticides banned in the USA are blown all the way from Africa's deserts and farmlands, making it difficult for the US to meet federal air pollution standards. Pollution from Central Asia is moved across the Pacific to the west coast [of the USA], destroying air quality.

Weather

Climate is what we expect, weather is what we get - Mark Twain

Components of weather, an area's short-term atmospheric conditions which typically occur over a couple of hours or days, consist of:

1. Temperature
2. Atmospheric Pressure
3. Wind
4. Humidity
5. Precipitation
6. Sunshine

On the other hand, the climate of a given area is the area's general pattern of atmospheric or weather conditions of a period of time. In Virginia, our climate is temperate deciduous forest, meaning that Virginia's trees lose their leaves every year. The climate of a given area is determined by latitude and elevation.

Global Air Circulation

There are four huge factors that determine global air circulation patterns:

1. Uneven heating of the Earth's surface by the sun.
2. Seasonal changes in the temperature and precipitation.
3. Rotation of the Earth on its axis.
4. Properties of air, water, and land.

Air is heated a lot more at the Earth's equator rather than the Earth's poles due to the sun's rays. The sun's rays are more concentrated on the equator while they're more dispersed on the poles. This difference in solar energy [on different parts of the Earth] provides a sufficient explanation for the climate of the tropical regions (equator) and the climate of the polar regions (poles)--and everything else in between. This also creates convection currents, which are air patterns caused by the heating of air (rising; leads to precipitation) to the cooling of air (sinking; leads to dryness).

The tilt of the Earth causes regions away from the equator to be away from the sun most of the year during the Earth's orbit across the Earth. This difference causes the northern and southern hemispheres to have different (opposite) seasons.

As the earth rotates, the equator spins faster than the polar regions. This causes the Coriolis Effect to take place: Heated air masses rising above the equator come BACK down to the equator due to the sinking of the air masses which get cooled off near the polar regions (this is due to the pull of the Earth). This direction of air circulation in their according atmospheric regions causes cells, which lead to belts of prevailing winds being formed. Prevailing winds are the winds that determine weather (westerlies); distributing air, moisture, and dust all over the Earth.

Heat from the sun evaporates ocean water and transfers heat from the oceans up into the atmosphere. This evaporation of the ocean water causes cyclical convection cells that distribute air, heat, and moisture from place-place in the troposphere.

Ocean Currents

How are warm ocean currents and cold ocean currents created?

The oceans absorb heat from the air circulation patterns and create differences in density, with warm water being less dense than cold water. These factors create warm and cold currents. Ocean currents in the northern hemisphere flow clockwise while the ocean currents in the southern hemisphere flow counterclockwise--this is caused by the irregularly shaped continents disrupting the flow of the currents. Ocean currents influence climate by distributing heat received from the sun from place-place, causing a change in climate and vegetation--especially near coastal areas. They also affect productivity by mixing ocean waters and distributing nutrients to aquatic ecosystems that are in need of them.

An example of a famous ocean current is the Gulf Stream, which maintains the climates of the eastern coast of the US and Europe. Without this stream, northwestern Europe would be extremely cold.

El Niño

El Niño happens when an altercation in the direction of tropical winds heats the coastal surface water, suppresses upwellings (upward movement of the ocean water which brings cool/nutrient-rich water from the bottom of the ocean to the surface), and temporarily changes much of the earth's climate. The east winds decrease/cease, the Pacific Coast water warms, and upwelling stops.

Microclimate

A microclimate is a variation of the climate within a given area, usually influenced by hills, hollows, structures or proximity to bodies of water.

Why is it that cities and urban areas are warmer (microclimate) than the rural areas?

1. Building materials have high thermal mass.
2. Heat Island Effect (building materials absorb all the heat they've collected through the day and release the heat in the night)
3. Motors, like cars, generate heat.

Mountains: Microclimates

Mountains have different microclimates due to the increase in altitude (gets colder; decrease sunlight). The warmest, dryest part of the mountain is the West/Southern side since the western side of the mountain is getting warmer due to the increasing temperatures + direct sun (as the sun is moving towards the west) and the southern side is towards the equator. The rainiest, coolest part of the mountain is the North while it is in between these conditions in the East.

Sea and Land Breezes

See the English Wikibooks' article about Sea and Land breezes

During the daytime, the land is warmer than the sea, this is due to water's high heat capacity--resisting itself to temperature changes compared to the land (soil/sand). This is important to understand first before reading through this section.

The land, warmer than the sea, creates a small space of warm air over itself--a low pressure. The sea, cooler than the land, creates a small space of cooler area over itself--a high pressure (since cooler air is denser, thus more pressure on the Earth).

The warm air (low pressure), due to its characteristic of being less dense than cold air, moves up into the atmosphere. The cooler air (high pressure), seeing all the space, moves into the open space created by the warm air [when the warm air moved away from the land]. So: The air moves from a high pressure to a low pressure, causing a breeze; this is known as the sea breeze, as we characterize a breeze from where it originally has come from.

The vice versa applies to the land and sea situation during the night.

Rainshadow Effect

Rain Shadow Effect

The rainshadow effect is the phenomenon where both sides of a mountain have different microclimates. The side where warm, moist air rises to the top of the mountain (increasing altitude) and eventually cools down and precipitates/causes rain (due to the expansion and cooling of the warm air) is the windward side. The leeward side is where it is dry (deserts) due to the atmosphere compressing the air mass, releasing heat. Evaporation also takes place on the leeward side due to compression ("atmosphere compressing the air mass") and warming (compression of the air releases heat).

An example of the rain shadow effect is the Rocky Mountains in the Western USA.