WeatherClimate

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//THE TWO MOST IMPORTANT FACTORS DETERMINING AN AREA'S CLIMATE ARE __TEMPERATURE__ AND __PRECIPITATION__.//

=__**6 Different Climates Around The Globe**__ (pg 108-109)= Currently, the Koppen-Geiger system describes 6 major Climate Zones around the planet (they look similar to the bands made by biomes, and biomes are characterized partly because of their climate) The 6 climates can be subdivided based on rainfall and season length.
 * 1) Humid Equatorial Climate
 * 2) Dry Climate- can be hot or cold
 * 3) Humid Temperate Climate
 * 4) Humid Cold Climate
 * 5) Cold Polar Climate- tundra & ice areas
 * 6) Highland Climate- usually @ tops of mountain ranges

=__**Seasons**__= Seasons are caused because of the tilt of the Earth's axis (23.5 degrees). During March 22-September 21, the northern hemisphere is in the part of its annual orbit so that it is tilted towards the sun, allowing more sunlight to fall on the northern hemisphere than the southern hemisphere. This is why we have longer days during our "summer" and also why we have warmer temperatures. During September 22-March 21, the southern hemisphere is tilted towards the sun, giving them summer like conditions. One implication of this is the larger land areas in the northern hemisphere allow for more photosynthesis (and therefore more carbon capture) to occur during March-September each year and less during September-March. This explains why the global CO2 level oscillates annually. It is always higher during the northern hemisphere winter and lower during the northern hemisphere summer, though the 50-year trend is a continual increase of the total CO2 annually.
 * Important Dates
 * December 21- shortest day in the Northern hemi, longest day in the southern hemi
 * March & September 21- the spring & autumnal equinoxes, when both hemispheres experience ~12 hours of sunlight and ~12 hours of dark.
 * June 21- longest day in the Northern hemi, shortest day in the southern hemi

=__**Wind**__= See Page 101 in the Textbook for Diagrams There are 3 main wind currents on Earth. POLAR EASTERLIES, WESTERLIES, AND TRADE WINDS.
 * Atmospheric circulation is caused by temperature differentials between different areas of earth.
 * Atmospheric gasses have weight. At sea level the gas of the atmosphere weighs approximately 14.7 lbs/sq inch. Yes, this means that there are 14.7 lbs of air resting on every square inch of your body when you are at sea level. Raising altitude means you have less air molecules above you, therefore less molecular weight of the air, therefore the pressure should be LOWER (high altitude = low pressure). This is important because atmospheric circulation also occurs because of pressure differentials. Air molecules flow from areas of high to low pressure (this is one of the reasons it is windy at the top of a mountain and calm at the base).
 * Atmospheric circulation is also caused by the Coriolis Effect (see below)

//The Simplest Circulation- The Hadley Cell// (Trade Winds) Starting at the equator, where sunlight is most consistent and direct throughout the year, the ground temperature is likely to be constantly warm and hot. The ground warms the air molecules above it. This warmed air is less dense than cold air and will constantly tend to rise upward. As it rises, it leaves space below for other air to fill in. Some of the warm air rising will cool and sink to the same location again. Other warm air rising will split and sink towards the poles. Typically, an air cycle will travel and sink approximately 30 degrees north and south of the equator. These 30 degree locations are called "Hadley Cells", and are typically seen with the intense heat leaving a rainforest biome and the air recirculating back down at the 30 degree N & S lattitude lines.
 * Hadley Cells Cause Trade Winds
 * Trade Winds are caused by the current of the Hadley cell's warm air rising and cool air falling and pushing back towards the displaced warm air near the equator. Tradewinds are constant, reliable flows and are names for the __direction they originate from__.
 * In the Northern Hemisphere the tradewinds flow from the NORTHEAST toward the southwest. Northern hemisphere tradewinds are called the NORTHEAST TRADEWINDS.
 * In the Southern Hemisphere the tradewinds flow from the SOUTHEAST toward the northwest. Southern hemisphere tradewinds are called the SOUTHEAST TRADEWINDS.

//The Effect Of The Earth's Rotation- The Coriolis Effect// (Polar Easterlies) Earth spins from west to east and rotates once every 24 hours. In order to achieve this rotation, objects (and air) at the equator are actually moving faster than objects at the poles. When an object leaves the poles, attempting to travel in a straight line, it actually ends up in a curved trajectory due to the constant rotation and ever increasing velocity of the Earth as the object approaches the equator. This means that wind leaving the poles will actually end up traveling in a curved path, which can drive atmospheric circulation. The Coriolis Effect is also seen in aquatic currents traveling toward the equator.
 * The Coriolis Effect Deflects Air In The Direction Of The Earth's Rotation
 * As air approaches the equator from the north pole, it travels in a southwestern direction
 * As air approaches the equator from the south pole, it travels in a northwestern direction
 * Polar Easterlies
 * The main air current flowing from the poles toward the equator. The winds travel from the NORTHEAST or the SOUTHEAST and are therefore called EASTERLIES.
 * New Riddle- what is always going west but left and right at the same time? The Polar Easterlies, because of the Coriolis Effect!

//Other Multilatitude Wind Patterns// (Westerlies) Geography of an area can effect high pressure vs. low pressure areas. Generally, wind flowing between 30 degrees latitude and 60 degrees latitude (polar area) flows from the WEST. These winds are called WESTERLIES.

=__**Other Effects Of Rainforests**__= In addition to the Hadley Cell, Rainforests also create a microclimate. Due to the intense plant activity of rainforest flora (due to nutrient availability, temperature, and rainfall), transpiration occurs at a fast rate, thus creating more water vapor than the area would normally experience with other types of plant life or biomes. This excess water vapor condenses in clouds above the rainforest and causes more rainfall in the immediate area. This is an example of a __positive feedback loop__. More rain = more plant growth = more transpiration = more clouds = more rain. When rainforests are removed, the microclimate is also eliminated and less rainfall will fall on the area. This, in addition to the lack of nutrients stored within the soil of the system, causes desertification.
 * After rainforests are removed, desertification occurs due to
 * reduction of microclimate and less rainfall in the area
 * continued high velocity winds not buffered by the previous trees
 * loss of nutrients from the system (the forests contains all the nutrients, none are left in the soil)

=__**Precipitation**__= Global Precipitation is driven by the water cycle. Water molecules can be in solid, liquid, or gas form depending on __temperature__. Gaseous Water molecules are carried to new locations because of wind patterns.
 * See the Ocean Circulation Page for information on evaporation of water molecules from the ocean.

//Rain Shadows//
 * Near mountains, air moves up due to the change from a high- to low-pressure system.
 * When wind is moving over a mountain range due to the wind currents, it carries water molecules with it.
 * Clouds form near the peaks of the mountains on the side of the mountain range that the wind is coming FROM.
 * This side of the mountain has a significant amount of rainfall as compared to the other side of the mountain.
 * The other side of the mountain is still windy but the wind currents have no moisture. This causes one side of the mountain to be particularly cloudy and rainy and the other to be dry and sunny. The side of the mountain in the sun is in the __Rain Shadow__.
 * In the US, the Pacific Northwest is considered the "wet" side of the Rocky Mountains and the dry Colorado area is considered in the "rain shadow."