Unit 9—Energy in the Earth System Name______
Chapter 27 Weather and Climate
27.1 Earth’s Heating and Cooling
n Satellite data is used to map patterns of heating and cooling.
n The National Oceanic and Atmospheric Administration (or NOAA) uses infrared photography to map how much heat is reflected or emitted from different areas of Earth each day.
n Latitude lines measure distance from the equator. These lines run parallel to the equator and are labeled in degrees north or degrees south.
n Longitude lines run vertically from the north pole to the south pole.
o The line that runs through Greenwich, England, is labeled 0 degrees longitude and is called the prime meridian.
o Lines east of the prime meridian are numbered from 1 to 179 degrees east, while lines west of the prime meridian are numbered from 1 to 179 degrees west.
o The 0- and 180-degree lines are not labeled east or west.
n Earth’s temperature varies with latitude.
o At higher latitudes, solar radiation is less intense. Sunlight spread over a larger area is less intense, while sunlight hitting the earth more directly covers a smaller region and is more intense. As a result, Earth is not evenly heated.
o The same thing happens to the sun’s energy when it reaches the south pole at an angle.
n Temperature and Rotation
o As Earth rotates, the portion of the globe facing the sun warms as it absorbs more solar radiation than it emits. This is another reason that the Earth is not evenly heated.
o Earth constantly emits some of the absorbed energy as infrared radiation.
o This emission of heat cools the dark side of the planet.
n Why Does the Earth Have Seasons? Because its axis is tilted at an angle
27.2 Global Winds and Ocean Currents
n Earth’s wind is the result of uneven heating on Earth.
n Uneven heating on Earth leads to heat being transferred. This is evident by wind, and evaporation and condensation.
n Thermals are small convection currents in the atmosphere.
n While thermals form on a local level, there are also giant convection currents in the atmosphere.
n These form as a result of the temperature difference between the equator and the poles.
n Air near the equator is responsible for initiating the process of wind and ocean currents because higher temperatures cause air to expand and rise.
n The bending of wind and ocean currents due to Earth’s counterclockwise rotation is called the Coriolis effect, after the French engineer mathematician Gaspard Gustave de Coriolis (1792-1843), who first described the phenomenon in 1835.
n There are three important global surface wind patterns in each hemisphere:
o trade winds
o polar easterlies
o prevailing westerlies
n These global wind cells play a large role in shaping Earth’s weather patterns
n Global Wind Patterns
n Global wind patterns and Earth’s rotation cause surface ocean currents to move in large circular patterns called gyres.
27.3 Weather Patterns
n Three important factors that shape the weather in a given region are:
o temperature
o air pressure
o water content in the atmosphere
n Temperature
o When cold air moves in and replaces warm air at Earth’s surface, this is known as a cold front.
o Warm air rises, cold air moves in below it.
o Sometimes cold air gets trapped near the ground and warm air moves in above it, like in a valley.
o This is known as a temperature inversion. The warm ceiling of air traps pollutants close to the ground.
o Temperature inversions most commonly cause smog.
n A sling psychrometer can measure water in the air.
n Water in the atmosphere exists in all three states of matter.
n High in the troposphere, there are ice crystals.
n Tiny water droplets, much too small to see, are suspended throughout the troposphere virtually all the time.
n Other water molecules in the atmosphere are truly in the gas state, separate from all other molecules.
n An increase in temperature and a decrease in pressure will increase the rate of evaporation.
n Different conditions cause different clouds.
n Cumuliform clouds form when convection causes rising pockets of air in the atmosphere. They look like heaps of popcorn with flat bottoms.
n Stratiform clouds form when a large mass of stable air gradually rises, expands, and cools. These clouds look like smooth, flattened blankets. They can give the sky a uniformly gray appearance.
n Sometimes a cloud formation combines aspects of both cumuliform and stratiform clouds.
n We call these clouds stratocumulus clouds. They look like lumpy blankets because a formerly smooth cloud developed pockets of convection and condensation within it.
n Cirrus clouds are thin lines of ice crystals high in the sky, above 6,000 meters. They have a “mare’s tail” appearance.
n They are just a thin streak of white across a blue sky.
n When more water in the air is condensing than evaporating, the dew point temperature has been reached. The dew point being reached is one condition necessary for rain to fall.
n A raindrop begins to form when water molecules condense on a speck of dust.
n At first it is round, but when it is large enough that it begins to fall, air resistance causes the underside of the drop to flatten, so that it looks more like a hamburger bun.
n As it grows larger, it looks more like an upside down bowl with a thick rim.
n If it hasn’t hit the ground by this point, it will break up into smaller droplets and the process repeats itself.
n For snow to form, water droplets and ice crystals are present in the sky. The ice crystals then grow large enough to fall to the ground. As the ice crystals fall, the temperature near the ground has to be near or below 32°F so that the crystals stay frozen.
n An air mass is a large body of air with consistent temperature and moisture characteristics throughout.
n Changing atmospheric conditions and global wind currents eventually cause these air masses to move.
n Movement of these large air masses is affected by high-altitude fast moving winds called the jet streams.
o There are two big jet streams in each hemisphere formed where there are sharp boundaries between cold and warm temperatures.
o These winds move around the globe from west to east near the top of the troposphere and have a speed of at least 54 miles per hour.
o Pilots flying west to east often try to ride the jet streams, while pilots flying east to west try to avoid them.
n Pressure differences between warm and cold air masses cause air to flow from regions of high to low pressure.
n A cold front is when a cold air mass moves in and replaces warm air at Earth’s surface. A warm front is when a warm air mass overtakes cooler air in a region.
n When a cold front moves into a region and warm air is forced upward, an area of low pressure is created near Earth’s surface at the boundary between the two air masses.
n So if the air pressure decreases throughout the day, that means more cold air moves in. This cold air mixes with the warm air, winds pick up and precipitation often occurs
n A center of high pressure tends to be found where a stable cold air mass has settled in a region.
n Isobars show areas with the same atmospheric pressure on map.
27.4 Storms
A storm cell
n Both tornadoes and hurricanes are systems of rotating wind around a low pressure system.
n Since the Coriolis effect is minimal along the equator, there is a lack of rotating wind so hurricanes and tornadoes don’t often form in these areas.
n Thunderstorms arise when air near the ground is strongly warmed and rises high into the troposphere.
n As the air rises, it cools and condenses, forming a towering cumulonimbus cloud.
n Eventually some of the cloud droplets become large enough to fall as rain.
n After a rainstorm, the temperature may increase slightly because latent heat is being released.
n Several conditions must be present for a rotating system to become a hurricane:
o wind speeds of at least 74 miles an hour.
o warm ocean water must be at least 46 meters deep.
o the air must be warm and moist to a point at least 5,500 meters above sea level.
A tropical cyclone (a hurricane)
n A tornado, like a hurricane, is a system of rotating winds around a low pressure center.
n An average tornado is tiny, compared with the average diameter of a hurricane.
n However, the wind speeds of a tornado are much greater than those of a hurricane.
n A tornado’s wind speed can reach 400 kilometers per hour.
A tornado
n Scientists have discovered cyclic patterns in storm activity.
n One such cyclic storm pattern is El Niño. There have been nine of these between 1954 and 1994
o During an El Niño event, residents in Indonesia experience dryer than normal conditions (see illustration)
o Trade winds weaken
o Warm water flows from the western Pacific toward South America
o Eastern Pacific countries (near Peru) get more precipitation and thunderstorm activity
27.5 Weather and Climate
n Climate is defined as the long-term average of a region’s weather.
n Climate depends on many factors:
o latitude
o precipitation
o elevation (like Denver, air is thinner)
o topography
o distance from large bodies of water
n Scientists divide the planet into climate regions called biomes.
n Examples of biomes include desert, tropical rain forest, grassland, temperate forest, taiga, and tundra.
o Deserts experience the greatest daily temperature change due to lack of cloud cover
o Tropical rain forests are found near the equator (23.5°N-23.5°S). Converging air from the northern and southern trade winds rises, cools, and condenses. This causes afternoon thundershowers almost every day.
o The taiga covers the largest amount of Earth’s land surface.
o The tundra has the coldest climate on Earth due to its latitude.
o Here the ground is permanently frozen from 25 cm to 100 cm below the surface.
o This is referred to as permafrost.
o The permafrost acts as a carbon sink, an area that stores more carbon than what is released into the atmosphere.
o Scientists fear that another effect of global warming will be the melting of the permafrost and the release of this stored carbon, hence serving as another source of greenhouse gases, worsening global warming