Core Case StudyBlowing in the Wind: A Story of Connections • Wind connects most life on earth. • Keeps tropics from being unbearably hot. • Prevents rest of world from freezing. Figure 5-1
CLIMATE: A BRIEF INTRODUCTION • Weather is a local area’s short-term physical conditions such as temperature and precipitation. • Climate is a region’s average weather conditions over a long time. • Latitude and elevation help determine climate.
Climate • Climate is the average weather conditions that occur in a place over a period of years. • The two most important factors are temperature and precipitation.
Solar Energy and Global Air Circulation: Distributing Heat • Global air circulation is affected by the uneven heating of the earth’s surface by solar energy, seasonal changes in temperature and precipitation. Figure 5-3
Definition Air Pressure • Air pressure is pressure exerted by the weight of Earth’s atmosphere. At sea level it is equal to 14.69 pounds per square inch. • A barometer is used to measure atmospheric pressure.
Pressure Gradient Air Pressure • Changes from high to low. On a map there is an arrow to show this. A higher pressure gradient means stronger winds (the isobars on a weather map would be drawn closer together).
Cause Wind • Wind is caused by the pressure gradient force. High pressure means more air, and low pressure means less air. The air moves from high to low, causing wind.
Coriolis Effect Wind • Global air circulation is affected by the rotation of the earth on its axis. Figure 5-4
The Coriolis Effect Wind • Forces in the atmosphere, created by the rotation of the Earth on its axis, that deflect winds to the right in the N. Hemisphere and to the left in the S.Hemisphere.
Friction Wind • A combination of the pressure gradient force and the coriolis effect. Friction at the Earth’s surface causes winds to turn a little. Friction runs parallel to the isobar.
Upper Level Flow Wind • There is little friction up in the upper troposphere, driving surface features. Ex. during big thunderstorms, the wind in the upper level will tell which way the thunderstorm will move.
Cyclones Wind • (called hurricanes in the Atlantic and typhoons in the Pacific) • Violent storms that form over warm ocean waters and can pass over coastal land. • Giant, rotating storms with winds of at least 74 mph. The most powerful ones have wind velocities greater than 155 mph.
Anticyclones Wind • An extensive system of winds spiraling outward from a high-pressure center, circling clockwise in the N. Hemisphere and counter-clockwise in the S. Hemisphere.
Polar vs. Tropical Air Masses and Storms • The atmosphere has three prevailing winds. Prevailing winds that blow from the northeast near the North Pole or from the southeast near the South Pole are called polar easterlies. • Tropical winds that blow from the northeast in the N. Hemisphere or from the southeast in the S. Hemisphere are called trade winds.
Continental vs. Maritime Air Masses and Storms • Continental fronts are generally cool and dry, whereas maritime (ocean) fronts are generally warm and moist. When these two air masses converge, the result is usually rain.
Convection Currents • Global air circulation is affected by the properties of air water, and land. Figure 5-5
Convection Cells • Heat and moisture are distributed over the earth’s surface by vertical currents, which form six giant convection cells at different latitudes. Figure 5-6
Circulation Patterns Hadley Cells • Warm moist air rises at the equator. Rain • As air rises, it spreads out north & south, then cools and sinks at 30 degrees. Dry • This is why most of the world’s deserts are found at 30 degrees. • These are called the horse latitudes (3o degrees) because early settlers would get stuck here in their boats & couldn’t move. They would finally throw their horses overboard to lighten the load & get moving again. • Trade Winds blow towards equator
Circulation Patterns Ferrell Cells • Warm air rises at about 60 degrees. Rain • and sinks at around 30 degrees, dry, both north and south. • Westerlies. Predominant winds in US
Polar Cells Circulation Patterns • Air rises at about 60 degrees. Rain • floats north, and sinks at around 90 degrees, both north and south. Dry • Easterlies
Convection Cells Circulation Patterns • Ocean water transfers heat to the atmosphere, especially near the hot equator. (Trade winds) • This creates convection cells that transport heat and water from one area to another. • The resulting convection cells circulate air, heat, and moisture both vertically and from place-to-place in the troposphere, leading to different climates & patterns of vegetation.
Sea, Land, Valley, & Mountain Breezes • Sea - ocean-to-land breezes that occur during the day. • Land - land-to-ocean breezes that occur at night. • Valley - the wind blows from the plains into a valley between two mountains, the wind must divert into a smaller area. This causes high winds to form through the valleys. • Mountain - Cool air coming from the top of the mountain sinks down on the eastern slope, causing increased winds on the mountain.
Ocean Currents: Distributing Heat and Nutrients • Ocean currents influence climate by distributing heat from place to place and mixing and distributing nutrients.
Topography and Local Climate:Land Matters • Interactions between land and oceans and disruptions of airflows by mountains and cities affect local climates. Figure 5-8
Earth’s Current Climate Zones Figure 5-2
Ocean Currents: Distributing Heat and Nutrients • Global warming: • Considerable scientific evidence and climate models indicate that large inputs of greenhouse gases from anthropogenic activities into the troposphere can enhance the natural greenhouse effect and change the earth’s climate in your lifetime.
Weather • Weather is the condition in the atmosphere at a given place and time. • Weather includes temperature, atmospheric pressure, precipitation, cloudiness, humidity, and wind.
Local Weather • Weather is a local area’s short-term physical conditions such as temperature and precipitation. • A weather front marks the boundary between two air-masses at different densities. • A front is about 100-200 km wide and slopes where warm and cool air masses collide. Cold front Warm front
Warm & Cold Fronts Weather • Warm Front - The boundary between an advancing warm air mass and the cooler one it is replacing. Because warm air is less dense than cool air, an advancing warm front will rise up over a mass of cool air. • The leading edge of an advancing air mass of cold air. Because cool air is more dense than warm air, an advancing cold front stays close to the ground and wedges underneath less dense, warmer air. A cold front produces rapidly moving, towering clouds called thunderheads.
Stationary & Occluded Front Weather • A stationary front is a transitional zone between two nearly stationary air masses of different density. • An occluded front is the air front established when a cold front occludes (prevents the passage of) a warm front.
Seasons • The Earth’s 23.5 degree incline on its axis remains the same as it travels around the sun. As the earth spins around the sun the seasons change.
Earth-Sun-Moon Earth’s axis has a 23.5° tilt. This tilt always faces the same way, resulting in seasonal changes in sunlight and weather. Earth day: the Earth spins on its axis with respect to the stars once every 23h 56 min 4.09s (one sidereal day). The solar day, where the sun returns to its zenith, is exactly 24 hours. Solar year: the journey around the sun takes 365.2425 days. Lunar month: the time between successive full moons is 29.5 days, but the moons orbit around the Earth takes 27.3 days. Because the moon spins on its own axis once every 27.3 days, the same side of the moon always faces the Earth. All images: NASA
Orbital Cycles • Three long term cycles that the Earth goes through as it orbits the Sun are: • Axial tilt: the axis of the Earth varies from 21.5° to 24.5°. • Orbital eccentricity: Earth’s orbit varies from almost circular to elliptical. • Precession: the movement of the axes in space causes them to describe a cone. All images: NASA
Axial Tilt • The tilt of the Earth’s axis ranges between 21.5° and 24.5°. • This can have severe effects on the climate. An axis tilt of 21.5o allows more heating near the poles leading to a less extreme temperature gradient from pole to equator. When tilted at 24.5o the variation between winter and summer temperatures is much more pronounced.
Eccentricity • When Earth’s orbit is more elliptical, summers (as shown here) in the northern hemisphere can be relatively cold while winters are relatively warm. • The opposite occurs in the southern hemisphere • When the Earth’s orbit is almost circular (as it is now), both summers and winters are relatively mild. • This can trigger ice sheet build up as summer is not warm enough to melt winter snow. All images: NASA
Precession • Precession alters the orbital position of the summer and winter solstices. • Around 13,000 years ago the southern hemisphere’s summer occurred in June.
Orbital Cycles • The changes in the tilting of the Earth’s axis, combined with precession and eccentricity can cause variations in the amount of solar radiation reaching the Earth’s surface. • This can trigger the onset and recession of ice ages.
Formationof the Atmosphere • Most of the Earth’s early atmosphere was lost due to the vigorous solar wind from the early Sun. • Continuous volcanic eruptions built a new atmosphere of: • water vapor • carbon dioxide • nitrogen • methane
The auroras occur in the thermosphere and are caused by interactions between the Earth’s atmosphere and charged particles streaming from the Sun. The Atmosphere • The mixture of gases known as air, protects life on Earth by absorbing ultraviolet radiation and reducing temperature extremes between day and night. • The atmosphere is not static. Interactions involving the amount of sunlight, the spin of the planet and tilt of the Earth’s axis cause ever changing atmospheric conditions. Weather occurs in the troposphere. Gaseous water molecules held together by intermolecular forces cause the formation of clouds.
STRUCTURE AND SCIENCE The Earth’s Atmosphere • The atmosphere consists of several layers with different temperatures, pressures, and compositions.
STRUCTURE AND SCIENCE • The atmosphere’s innermost layer (troposphere) is made up mostly of nitrogen and oxygen, with smaller amounts of water vapor and CO2. • Ozone in the atmosphere’s second layer (stratosphere) filters out most of the sun’s UV radiation that is harmful to us and most other species.
The Earth’s atmosphere (where pressure becomes negligible) is over 140 km thick. Compared to the bulk of the planet, this is an extremely thin barrier between the hospitable and the inhospitable. The Atmosphere • Earth's atmosphere contains roughly: All images: NASA
Troposphere • 75% of mass of atmosphere • 0 to 11 miles in altitude • 78% nitrogen, 21% oxygen • Location of Earth’s weather • Temperature decreases with altitude until the next layer is reached, where there is a sudden rise in temperature
Stratosphere • 11 miles to 30 miles in altitude, calm • Temperature increases with altitude • Contains 1000x the ozone of the rest of the atmosphere; ozone forms in an equilibrium reaction when oxygen is converted to O3 by lightning and/or sunlight • 99% of ultraviolet radiation (especially UV-B) is absorbed by the stratosphere
Mesosphere & Thermosphere • Mesosphere • 30 to 50 miles in altitude • Temperature decreases with increasing altitude • Thermosphere • 50 to 75 miles in altitude • Temperature increases with increasing altitude • Very high temperatures
Composition of the Atmosphere • Components –Nitrogen 78%, Oxygen 21%, .93% argon, & .038% carbon • Layers – troposphere, stratosphere, mesosphere, thermosphere, exosphere (extends from 310 miles to interplanetary space)
Heat Transfer • Conduction • Warm air holds more moisture than cold air. During conduction, heat & moisture from the ocean or land moves into the atmosphere. • Ex. cold air moving over warm water (like a lake), forming steam fog. • Radiation • Radiation drives weather. Heat from the sun warms the earth, which radiates the heat back into the atmosphere.