Circulation of the Atmosphere
World is made up of three regions: Atmosphere (air) Hydrosphere (water) Lithosphere (land) - Geosphere All regions interact to produce weather (day to day variations) and climate (long-term weather patterns)
Atmosphere: The Big Picture Different amounts of solar energy are absorbed at different latitudes. Interaction of the ocean and atmosphere moderates surface temperature, shapes Earth s weather and climates, and creates waves and currents. Earth s rotation causes the Coriolis effect, the apparent curvature of the path of moving air. Large storms are spinning masses of unstable air that develop between or within air masses.
Uneven Solar Heating & Latitude What factors govern the global circulation of air? Uneven solar heating spread out by wind and water The Coriolis Effect
Radiant Energy From the sun Some reaches earth converted to heat energy Some absorbed by atmosphere Some reflected by into space Solar energy is most intense at the equator.
Sunlight Sunlight 90 N North Pole 66.5 N Arctic circle Tropic of Cancer 23.5 N Most direct sunlight Sunlight Sunlight Equator Tropic of Capricorn Arctic circle 66.5 S 90 S South Pole 0 23.5 S
The tilt of the Earth on its axis (23.5º) produces seasonal variation in temperature patterns resulting from changes in the orientation of the northern and southern hemispheres. It is summer when the hemisphere is closest to the sun.
Atmospheric Properties What are some properties of the atmosphere? Water vapor occupies up to 4% of the volume of the atmosphere. The density of air is influenced by temperature and water content.
Atmospheric Composition 78.1% Nitrogen (N 2 ) 20.9% Oxygen (O 2 ) Small amounts of: water vapor, Argon (Ar), carbon dioxide (CO 2 ), Neon (Ne), Helium (He), methane (CH 4 )
Greenhouse Effect Greenhouse effect insulating capacity of gases in Earth s atmosphere Greenhouse gases (particularly carbon dioxide) have increased since the Industrial Revolution Sunlight Atmosphere Some heat escapes into space Greenhouse gases trap some heat Earth s Surface
The Water Cycle As air rises, it cools. Humidity: moisture in the air Atmospheric water vapor condenses as it cools. Water droplets form and fall as precipitation. Atmospheric and surface temperatures determine the precipitation form (rain, snow, sleet ). http://www.epa.gov/ogwdw/kids/flash/flash_watercycle.html
*Ascending air cools as it expands. Cooler air can hold less water, so water vapor condenses into clouds. *Descending air warms as it compresses and the clouds evaporate.
Convection Cell
Hypothetical Model of Atmospheric Circulation
The Coriolis Effect 1. The Earth s rotation affects linear movement it is deflected, the path is not linear, rather it is curvilinear. 2. The effect is too subtle to notice over short distances, but things which travel over long distances such as airplanes, winds, and water currents display the Coriolis Effect. http://www.youtube.com/watch?v=_36micus1ro&feature=related
The Coriolis Effect 3. In the Northern Hemisphere, the Coriolis Effect deflects things clockwise (to the right). 4. In the Southern Hemisphere, the Coriolis Effect deflects things counterclockwise (to the left).
Gaspar Gustave de Coriolis (1835) derived the mathematical relationship between the Earth s eastward rotation and the deflection of atmospheric objects. Napoleon hired de Coriolis to determine why his cannon balls missed their targets; we now understand that when launching an object (or flying a plane), the Earth s rotation has to be accounted for when launching a cannon ball or filing a flight plan.
Viewed from the side of the Earth, both disks complete a single rotation in a 24 hour period. The Quito disk must cover a greater distance since the Earth s circumference at the equator is greater than at the higher location where Buffalo is located. From the Earth s surface, the location of Buffalo, NY and Quito, Ecuador can be seen as two independent disk rotating in the same direction at different speeds. Locations at lower latitudes move faster than locations at higher latitudes.
Remember that the Earth is rotating clockwise (to the east). Objects in the northern hemisphere are deflected to the right (clockwise). Objects in the southern hemisphere are deflected to the left (counterclockwise).
Atmospheric Circulation Cells 1. Hadley Cells: Tropical atmospheric convection cells that are formed when warm air rises at the Equator and moves toward 30 N and S, where the air descends.
Atmospheric Circulation Cells 2. Ferrel Cells: Mid-latitude atmospheric convection cells that are formed when warm air rises at 60 N and S and moves toward 30 N and S latitude and then falls. 3. Polar Cells: Form at the poles when warm air rises at 60 N and S and moves toward the poles and then descends.
Atmospheric Circulation Cells The doldrums are calm equatorial areas where two Hadley cells converge. The horse latitudes are areas between Hadley and Ferrel cells. There is little surface wind in this area. The trade winds are surface winds of Hadley cells. The westerlies are surface winds of Ferrel cells.
Global Wind Patterns 1. As the winds travel long distances, they are deflected by the Coriolis Effect. 2. Equatorial winds are also referred to as Trade Winds, the trade winds are deflected away from the equator at a 45 angle.
Global Wind Patterns 3. Winds are steady over water, but vary in intensity and direction when they are modified by a land mass early navigators always relied on the trade winds as they are persistent. The trade winds blow toward the equator from the 30 latitude N and S.
Global Wind Patterns 4. Between 30 and 60 latitude N and S, the prevailing wind direction is from the west (the Westerlies). 5. Above 60 latitude N and S, the Polar Easterlies are the prevailing wind pattern. The polar winds are the most variable of all wind patterns on Earth, owing to the extremely cold temperatures and erratic weather.
Global Wind Patterns
Keep This In Mind Winds are named for the direction from which they blow. (Origination point) IN CONTRAST Currents are named for the direction in which they flow. (End point)
Intertropical Convergence Zone Intertropical Convergence Zone (ITCZ): The equatorial area where the trade winds converge near the equator; wind convergence produces variable wind patterns (doldrums).
Meteorological Equator AKA: Thermal Equator The imaginary line that denotes the area of thermal equilibrium of the two hemispheres It is located approximately 5 N of the geographical equator, although the location shifts northward during the northern hemisphere summer.
Geographical Equator The fixed imaginary line representing 0 latitude that circles the Earth at it widest point (largest circumference).
Seasonal ITCZ Changes
Major Wind and Pressure Systems
Monsoons, Sea Breezes and Land Breezes Monsoons are patterns of wind circulation that change with the season. Areas with monsoons generally have dry winters and wet summers. Sea breeze is cool air from over the water moving toward land. Sea breezes occur after sunrise. Land breezes occur after sunset when air warmed by the land blows toward the sea.
Monsoon patterns in Africa, Australia, India, and southeast Asia. Note that the shift in the ITCZ changes the direction of wind flow, when oceanic moisture meets a land mass, rainfall occurs.
Land and sea breezes are a function of the relative temperature of the land and water. Sea breezes occur during the day (a), and land breezes form at night (b).
Storms are regional atmospheric disturbances. Storms have high winds and most have precipitation. Tropical Cyclones occur in tropical regions. These storms can cause millions of dollars worth of damage and endanger life. Extratropical Cyclones occur in Ferrel cells, and are winter weather disturbances. These storms can also cause extensive damage. Both types of storms are cyclones, or rotating masses of low-pressure air. Storms
Satellite Hurricane Image Hurricane Allen in the western Caribbean (NOAA, 1980).
Hurricane Andrew making landfall, August 24, 1992. Maximum sustained winds of 220 km (138 miles/hour) Category 4 on the Safir- Simpson scale
South Pawley s Island, SC, September 1989 following Hurricane Hugo
Formation of Extratropical Cyclone
Tropical Cyclones Large tropical cyclones are called HURRICANES. The vertical dimension is exaggerated in this model of a hurricane.
Atmospheric Water Vapor (October 1992) Tropical cyclones develop in warm, humid parts of the world with warm sea surface temperatures. Conditions in the red zones favor tropical development. (near the equator)
Tropical Cyclone Storm Tracks Notice that the storm tracks move the tropical cyclones away from the equator toward higher latitudes.
Katrina Category 5 Hurricane
Katrina, 2005
ATLANTIC HURRICANE SEASON 2005: Totals: 28 named storms, 15 hurricanes, 7 major hurricanes, 6 struck USA. Average: 6 Atlantic Hurricanes each year, within 3 years, about 5 usually strike the U.S.
Storm Surge
Saffir/Simpson Hurricane Scale
Waterspout What is a waterspout? A waterspout is just a weak tornado that forms over water. They are most common along the Gulf Coast. Waterspouts can sometimes move inland, becoming tornadoes causing damage and injuries. Most common? Around the Florida Keys
How Water Spouts Form The FIRST sign, which can be seen from the air, but usually not from a boat, is the formation of a dark spot on the ocean. Smoke flares dropped in these areas show the air is moving in a circle and upward. Many dark spots die out without progressing any further. But some begin to take on a spiral pattern of dark and lighter water. At the SECOND stage someone on a boat at the surface would probably feel the wind shift and maybe increase. Also, if you looked upward, you might see a funnel coming from a cloud overhead or off to one side. People on boats will see the THIRD stage. Even though it might be invisible, a vortex is reaching the ocean surface from the cloud. When the wind speeds reach around 40 mph, the wind begins to kick up spray in a circular pattern the spray vortex. At this time you might see the funnel pointing down from the cloud toward the ring.
How Water Spouts Form The FOURTH, or mature, stage is when the funnel reaches all the way from the cloud to the ocean. You can usually see through the funnel - it's really a thin cloud of tiny water droplets. During this stage, small waves are being kicked up and the spout leaves a bubbly wake behind as it moves across the ocean. These tiny bubbles could be carbon dioxide and other gases that are dissolved in the water that are caused to effervesce by the low air pressure in the spout's center - like a bottle of soda that's just opened. In the FIFTH, and final stage, the spray vortex weakens and the funnel becomes shorter and maybe more tapered. It often twists around and the bottom of the waterspout may move out from under the cloud. Scientists say the waterspout's dissipation usually occurs when rain begins falling from the parent cloud. Cool air brought down by the rain cuts off the supply of warm, humid air that's feeding into the waterspout to keep it going.