Content:

1. The Atmosphere

2. Atmospheric Circulation

3. Atmospheric Pressure

4. Wind Pattern

1. The Atmosphere

• Atmospheric Layers

• The earth is surrounded by four atmospheric layers (near to far)

• Troposphere

• The boundary level that separates the troposphere from the next atmospheric layer is called Tropospause

• The tropopause acts as a lid to contain water vapor and the associated weather within the troposhere

• The troposphere extends from the surface of the earth to an average altitude of 36,000 ft. MSL

• As the altitude in this layer increases, the teperature decreases 2 degrees Celsius every 1,000 ft to about -51 degrees Celsius; beyond this point, atmospheric temperature becomes unpredictably erratic

• The troposphere is elliptical and its altitude varies with latitude and the season

• Characteristically, it is lower near the poles and higher near the equator

• During the winter months, the altitude of the troposphere over the poles is lower and during the summer months, the altitude increases over the equator

• Stratosphere

• The stratosphere extends to an average altitude of about 160,000 ft. MSL

• The temperature rises with altitude to about -15 degree Celsius because the ultraviolet rays of the sun meet no resistance

• Mesosphere

• The temperature decreases rapidly with an increase in altitude and can reach temperatures of -120 degrees Celsius

• The thick gas concentration in this layer slow debris, such as meteors from the space

• Most of the debris burns up before it reaches the layers closer to the earth's surface

• Thermosphere

• Begins at an altitude exceeding 250,000 ft. This layer has no protection from the rays of the sun

• Thermosphere temperatures increase with altitude because the small amount of residual oxygen absorbs solar radiation

• The few particles of gas in this area can reach 2,500 degrees Celsius during the day

• Temperatures are highly dependent on solar activity, and can rise to 15,000 degrees Celsius

• Cubic Foot of Atmosphere:

• 78% Nitrogen

• 21% Oxygen

• 1% Other Gases

• Water Vapor - Responsible for major changes in the weather

2. Atmospheric Circulation

• Cause of Temperature Differences

• The earth's rotation combines with the energy coming from the sun to cause atmospheric circulation

• Most weather occurs in the troposphere, which experiences the greatest differences in temeprature

• Near the equator, the sun's energy falls perpendicular to the surface, so any given area receives the maximum possible solar heating

• The same amount of solar energy falls on the polar regions, but that emergy is spread over a much greater surface area, so the surface is heated less

• The difference in temperature between the tropics and the poles drives our largest atmospheric circulation patterns

• Convection Circulation Process

• Convection is the process of transporting heat from warmer area to cooler areas

• The convection process:

• Results from differences in temperature

• Creates atmospheric circulation

• The convection process begins when the warm air from the equatorial regions rises and moves toward the cooler air in the polar regions

• As air cools in the polar regions it moves toward the warmer equatorial regions

• This circulation process continues as the surface of the earth heats and cools

• Three-cell Circulation Patterns

• If the earth didn't rotate, a huge convective circulation pattern would develop as air flowed from the poles to the equator and back again. The earth's rotation breaks this hemispheric pattern into three cells

• Air in the Hadley cell

• Rises at equator and flows toward the poles

• Reaches only 30 degrees latitude before it begins to sink

• Air in the Polar cell

• Rises at about 60 degrees latitude

• Flows towards the pole where it cools and sinks

• Air in the Ferrel cell

• Moves opposite the air in the Hadley and Polar cells

• Is located between 30 degrees and 60 degrees latitude

• Is believed to be the result of air movement in Hadley and Polar cells

3. Atmospheric Pressure

• Effects of Unequal Heating

• Modifies air density

• Creates circulation patterns

• Creates areas of high pressure

• Is the primary cause of variations in altimeter settings between weather-reporting points

• Purpose of Isobars

• Connect points of equal pressure on a weather map

• Measure atmospheric pressure in millibars

• Identify the position of high- and low-pressure

• Illustrate the pressure gradient pattern

• Closely spaced indicate a strong pressure gradient

• Widely spaced indicate a weak pressure gradient

• Identify pressure systems

• Five Types of Pressure Systems

• High

• Low

• Ridge - elongated area of relatively high?pressure

• Trough - elongated area of relatively low pressure

• Col - neutral area between two highs or two lows or the intersection of a ridge and a trough

• Effects of Pressure Gradients on Air Flow

• Air flows from high-pressure areas to low-pressure areas

• Strong pressure gradient produce strong winds

• Weak pressure gradient produce light winds

• The force that moves air from area sof high pressure to areas of lower pressure is the pressure gradient force

• Effects of the Coriolis Force (Results from the rotation of the earth)

• Influences the paths of all objects that move freely across the face of the earth

• Deflects moving objects to the right in the northern hemisphere

• Differs in amount of deflection depending on latitude

• Differs with the speed of the moving object

• Breaks up atmospheric circulation into the three-cell circulation model

• Deflects wind until the Coriolis force and the pressure gradient are in balance

• Frictional Force

• Reduces the Coriolis force

• Allow the wind to flow toward low pressure areas

• Causes wind to shift directions when near the earth's surface

4. Wind Pattern

• Three Global Wind Patterns

• Polar Easterlies

• Prevailing Westerlies

• Trade Winds

• Sea Breeze

• Costal winds that flow from cooler water toward warmer land are called sea breezes

• Sea breezes occur during the day when the air above the water is cooler than the air above the land

• Sea breezes are caused by convective circulation

• The cool dense air over the water creates an area of high pressure

• The warm air over the land mass creates an area of low pressure

• The cool air over the water moves inland from the area of high pressure toward the area of low pressure

• The rising air cools and sinks as it flows back out over the water on its return flow

• The air becomes denser, it again moves toward the area of low pressure

• Land Breeze

• Coastal winds that flow from cooler land toward warmer water?

• Convective circulation:

• The cool dense air over the land creates an area of high pressure

• The temperature of the air over the water creates an area of low pressure

• The cool dense air flows from the high-pressure area on shore to the low-pressure area off shore

• Valley Breeze

• Inland winds that flow from valleys upslope toward warm regions

• Valley breezes blow during the day when the sun warms the air above the mountain slope

• Convective circulation:

• The air warms and rises, creating an rea of low pressure

• The cooler air in the valley creates an area of high pressure

• The air flows unslope from the high-pressure area to the low-pressure area

• The rising air cools and sinks, but return flow from the mountain tops is very weak

• Mountain Breeze

• Occur at night when the air at the top of the mountains is cooler than the air in the valley below

• Convective circulation:

• The higher terrain cools, the air also cools and creates and area of high pressure

• The air over the valley remains warm, creating an area of low pressure

• The air in the high-pressure area flows toward the low pressure and the winds are directed down slope along the mountain slopes and valley floor

• The warm air from the valley floor rises, creating a return flow above the maountaintops

• Katabatic Winds

• Any wind that blows downslope is a katabatic wind

• These winds are similar to mountain breezes, but they are much stronger

• Two types of katabatic winds:

• Cold downslope winds

• Occurs when ice and snow in mountainous terrain cools the overlying air to very low temperatures

• The overlying air creates a shallow dome of high-pressure

• Pressure gradient forces pushes the cold air through gaps in the mountains

• Can become intense as it rushes downhil from snow-covered plateaus or steep mountain slopes

• Warm downslope winds

• Occurs when a warm airmass moves at a high altitude across a mountain range

• The movement creates a trough of low pressure on the downwind side of the slope

• The air flows downslope toward the low pressure below

• The air temperature increases due to compression