ATMOSPHERIC SCIENCE

Air pollution kills more than 5.5 million people/year, the majority being in China & India

The Atmosphere

Troposphere: Weather occurs in this zone Mesosphere: Coldest Layers of the Atmosphere Ozone layer= Pale blue gas O 3 ABSORBS most of the Sun’s Ultraviolet-B & UV-C radiation Provides critical protection because UV radiation is a mutagen & carcinogen Protects Earth’s surface from harmful X-ray & UV radiation

Atmospheric Properties Air movement within the troposphere is caused by changes in … Pressure & Density Humidity Temperature 1. Atmospheric Pressure & Density: Gravity pulls gas molecules toward Earth’s surface and less so as altitude increases That means the atmospheric pressure (the force per unit area produced by a column of air) decreases with altitude With increasing height, you have more molecules below you than above you

Atmospheric Properties 2. Humidity The ratio of water vapor a given volume of air contains Phoenix, AZ 31% humidity vs tropical island of Guam, where it never goes below 80% People are sensitive to changes in humidity because we perspire to cool our bodies When humidity is high, the air is already holding nearly as much water vapor as it can, so sweat evaporates slowly and the body cannot cool itself efficiently

Atmospheric Properties 3. Temperature Temperature varies over Earth’s surface because the sun’s rays strike some areas more directly than others. On a local scale, temperature varies because of topography: plant cover vs asphalt (Heat Island Effect), proximity to water, etc.

Stable air mass that traps pollutants close to the ground How they are created: 1. Asphalt & concrete-covered land absorb large amounts of heat that is re-radiated at night. 2. This heat retention creates an island of heat around a city that deflects weather would otherwise disperse pollutants. 3. As a result, pollutants are held close to the city Temperatures in large cities can be up to 5 degrees higher than the surrounding areas. Stable air mass that traps pollutants close to the ground How they are created: 1. Asphalt & concrete-covered land absorb large amounts of heat that is re-radiated at night. 2. This heat retention creates an island of heat around a city that deflects weather would otherwise disperse pollutants. 3. As a result, pollutants are held close to the city Temperatures in large cities can be up to 5 degrees higher than the surrounding areas.

Atmospheric Properties: Temperature Energy from Sun heats air in atmosphere, which drives air movement, which helps create seasons and influences weather and climate (temperature & precipitation). 70% of solar energy from sun is absorbed by the atmosphere & Earth’s surface, the rest is reflected back.

Atmospheric Properties: Temperature Due to tilt of the Earth on its axis, the Northern and Southern Hemispheres each tilt toward the sun for half the year, resulting in the change in seasons. Regions near the equator are largely unaffected by this tilt (they experience 12 hours of sunlight 7 darkness everyday throughout the year) Near the poles, however, the effect is strong and seasons are more pronounced.

Atmospheric Properties: Temperature Convective circulation Warm air is less dense, thus it will rise and create vertical atmospheric currents. As the warm air rises into regions of lower atmospheric pressure, it expands and cools. Once the air cools, it sinks and becomes denser, replacing warm air that is rising The air picks up heat and moisture near ground level and prepares to rise again, continuing the process. Similar convection patterns occur in ocean waters and in magma beneath Earth’s surface, or even in a pot of boiling water Convective circulation influences both weather and climate

Convective Currents

“Climate is what we expect; weather is what we get.” –Mark Twain Weather & climate involve physical properties of troposphere, like temperature, pressure, humidity, cloudiness and wind Weather= atmospheric conditions over short periods of time (hours or days) within a geographic area Climate= patterns of atmospheric conditions over a long period of time within a geographic area

Air masses interact to produce weather Weather changes when air masses with different physical properties meet. Boundary between air masses that differ in temperature and moisture= front When a mass of warmer, moister air replaces a mass of colder, drier air= warm front Produces a light rain When a colder, drier air mass displaces a warmer, moister air mass= cold front Produces thunderstorms

Air masses interact to produce weather Air masses may also differ in atmospheric pressure. High-pressure system= contains air that moves outward away from a center of high pressure as it descends Brings fair weather Low-pressure system= contains air that moves toward the low atmospheric pressure at the center of the system and spirals upward. The air will then expand and cool. Brings clouds and precipitation

Temperature Inversions Under most conditions, air in troposphere decreases in temperature as altitude increases. Because warm air rises, vertical mixing occurs Occasionally, however, a layer of cool air occurs beneath a layer of warmer air. This is called a temperature inversion or thermal inversion The cooler air is denser then the warmer air on top, so it resists vertical mixing & remains stable. The effect: air pollutants are not dispersed but are “trapped” near the ground Inversions regularly cause smog buildup in large cities Commonly occurs in mountain valleys, where the slopes block morning sunlight, keeping ground-level air within the valley shaded and cooled

Temperature Inversions

Particulate matter from forest fires, urban pollution & volcanoes cools the Earth OTHER WEATHER PATTERNS THAT CAN OCCUR…

Circulation patterns produce climate Convective air currents contribute to broad climatic patterns: Near the equator, solar radiation sets in motion a pair of convective cells called Hadley cells. The sun is most intense here, so the surface air warms, rises, and expands. As it does this, it releases moisture, producing the heavy rainfall attributed to tropical rainforests. After releasing most of the moisture, the air diverges and moves in currents heading northward and southward The air in these currents cools and descends back to Earth at about 30 degrees latitude north and south These currents have low humidity, so the regions around 30 degrees latitude are quite arid, and give rise to deserts

Circulation patterns produce climate There are two pairs of similar but less intense convective cells, called Ferrel cells and Polar cells They lift air and create precipitation around 60 degrees latitude north and south and air to descend at around 30 degrees latitude in the polar regions These three pairs of cells account for the distribution of moisture across Earth’s surface: Wet climates near the equator Dry/arid climates near 30 degrees latitude Moist regions around 60 degrees latitude Dry conditions near the poles These patterns, along with temperature variation, explain the distribution of earth’s biomes

Wind patterns The three pairs of cells interacting with the Earth’s rotation, produce global wind patterns: As the Earth rotates on its axis, locations on the equator spin faster than locations near the poles This causes the north-south air currents of the convective cells not to travel straight, but instead to deflect in a different direction. This is known as the Coriolis Effect Near the equator: doldrums, few winds Between equator & 30 degrees: trade winds, blow from east to west From 30 to 60 degrees: westerlies, blow west to east

Coriolis Effect

El Nino This movement of wind, along with convective currents in ocean water create ocean current patterns. Trade winds weaken periodically (thus affecting ocean currents), leading to El Nino conditions.

OCEAN CURRENTS & CIRCULATION We will tie this information in to El Nino

Ocean currents are driven by a combination of temperature, gravity, prevailing winds, the Coriolis Effect & the location of the continents Northern Hemisphere: surface currents rotate in a clockwise direction Southern Hemisphere: surface currents rotate in a counter-clockwise direction These patterns of water circulation are called gyres Gyres redistribute heat in the ocean, just as atmospheric convection currents redistribute heat in the atmosphere California has cooler temperatures than areas at similar latitudes on the east coast because cold water from the polar regions moves along the west coasts of continents. Ocean currents

The Great Pacific garbage patch is a gyre of marine debris particles. The patch has relatively high concentrations of pelagic plastics, chemical sludge and other debris that have been trapped by the currents of the North Pacific Gyre. Great Pacific Garbage Patch

Surface currents Driven by wind patterns Deep currents Caused by differences in density (salinity & temperature) Denser, saltier water sinks and less-dense water rises Colder water is more dense & sinks 90% of ocean volume circulates due to density differences in salinity & temperature. 10% is involved in wind- driven surface currents Warm water travels from lower to upper latitudes and vice versa

Thermohaline circulation drives the mixing of surface water & deep water and helps to mix the water of all the oceans These ocean currents affect the temperature of nearby landmasses Thermohaline Circulation Therm= heat Haline= salt

Ocean currents help explain why some regions of the ocean support highly productive ecosystems Along the west coasts of most continents, the surface currents separate from one another, causing deeper waters to rise & replace the water that has moved away. This upward movement of water toward the surface is called upwelling The deep waters bring w/them nutrients from the ocean bottom that supports large populations of producers The producers, in turn, support large populations of fish that have long been important to commercial fisheries Upwelling

Earth’s atmosphere & ocean interact in complex ways Every 2-8 years, these interactions cause surface currents in the tropical Pacific Ocean to reverse direction due to weak trade winds These periodic changes in wind & ocean currents are collectively called El Nino- Southern Oscillation, or ENSO El Nino-Southern Oscillation (ENSO)

Normal year: During most years, trade winds push surface water from east to west Deep water moves upward (upwelling) to replace surface water that has moved westward El Nino year: During El Nino years trade winds weaken or reverse direction; warm surface water moves from west to east The warm surface water builds up along the coast of South America & prevents upwelling of the deep cold water El Nino-Southern Oscillation (ENSO)

El Nino year Normal year

El Nino year Normal year Normal vs El Nino weather

The weakening of the trade winds allows warm equatorial water to move towards the west coast of South America (instead of east-ward) This suppresses upwelling off the coast of Peru. Because the nutrients aren’t coming upwards, it decreases productivity & reduces the fish population near the coast. It is called El Nino because it often begins around Dec. 25 th Impacts of ENSO

El Nino events alter weather patterns around the world: Creates rainstorms & floods in areas that are usually dry (like southern California) Causes drought & fire in regions that are typically moist (like Indonesia) Impacts of ENSO Globally El Nino can last from a few weeks to a few years

La Nina These events are the opposite of El Nino events. Cold surface waters extend far westward in the equatorial Pacific, and weather patterns are affected in opposite ways of El Nino