Chapter 7

 Weather is an all-encompassing term used to describe all of the many and varied phenomena that can occur in the atmosphere of a planet. The term is normally taken to mean the activity of these phenomena over short periods of time, usually no more than a few days in length.  Average atmospheric conditions over significantly longer periods (30+ years) are known as climate.  Because the Earth's axis is tilted (not perpendicular to its orbital plane), sunlight is incident at different angles at different latitudes: higher latitudes have a lower angle of incidence, which results in less heating than at lower latitudes nearer the equator  A secondary cause of temperature differences on the Earth is that different surface areas (such as ocean waters, forest lands, and ice sheets) have differing reflectivity, and therefore absorb and radiate different amounts of the solar energy they receive

Weather –local areas short term temperature, precipitation, humidity, wind speed, cloud cover and other physical conditions of the lower atmosphere Climate – general atmospheric conditions measured over a long period of time

 Seasons  Solar Intensity/Latitude  Solar radiation  Convection Currents  Coriolis effect  Rain shadow effect  Jet streams  Frontal weather  Cyclonic storms  Seasonal winds  ENSO  Milankovich cycles

 The two most important aspects of climate are temperature and precipitation. ◦ These two factors determine what type of species (biome) will be found in a given location.  The climate in an area is determined by 1.Latitude 2.Direction from which winds arrive 3.Proximity to large bodies of water and mountains

Key A climograph includes both the average precipitation and the average temperature data. Your climograph should look like the one below. Be sure to include a title for your graph and a key showing the symbols that represent the average precipitation and the average temperature.

 Warm air rises; cold air falls  Warm air holds more moisture than cold air  When air rises, it cools; when air falls, it warms  SO, warm, moist air rises, cools, and loses moisture as rain; cool, dry air falls, warms, and picks up moisture from the ground. Cool, dry warm, dry Warm, moist precipitation

Air circulation in lower atmosphere is due to Uneven heating of the earth’s surface by the sun Rotation of the earth on its axis Properties of air, water, and land

 As the earth spins, it pulls on the surface air and causes it to spin in the direction of movement.  The ground spins faster at the equator than at the poles, so in any given cell, the air closer to the equator is pulled more.  This gives rise to prevailing winds that are predictable in all areas of the world. They have been used by sailors for centuries.

 This causes winds to form huge circular paths – clockwise in the N. Hem and counter-clockwise in the S. Hem.

 Wind ◦ Indirect form of solar energy, ◦ part of the earth’s circulatory system for heat, moisture, plant nutrients, soil particles and long lived air pollutants Dust blown from West Africa – soil nutrients in Amazonian rain forests, toxic air pollutants in the US

Fig. 7-3, p. 142 Cold deserts 60°N Air cools and descends at lower latitudes. Westerlies Forests Northeast trades Hot deserts 30°N Warm air rises and moves toward the poles. Equator Forests 0° Solar energy Air cools and descends at lower latitudes. The highest solar energy input is at the equator. Southeast trades Hot deserts 30°S Westerlies Forests Cold deserts 60°S Currents Prevailing winds Earth’s rotation Redistribution of heat from the sun Global Air Circulation

 Wet areas (warm, moist air rising) ◦ 0 o (equator) - TRF ◦ 60 o (Seattle) - TempRF  Dry areas (cold, dry air falling) ◦ 30 o - desert ◦ 90 o (poles) - tundra

Fig. 7-6, p. 144 Moist air rises, cools, and releases moisture as rain Polar cap Arctic tundra Evergreen coniferous forest 60° Temperate deciduous forest and grassland 30° Desert Tropical deciduous forest Equator 0° Tropical rain forest 30° Desert 60° Temperate deciduous forest and grassland Tropical deciduous forest Polar cap Global Air Circulation, Ocean Currents, and Biomes 6 giant convection cells moist air rises,cool dry air sinks

Figure 8-4

Figure 8-5

Oceans absorb heat from the earth’s circulation patterns : most of this heat is absorbed in tropical waters, which receive most of the sun’s heat Heat and differences in water density (mass/unit volume) create warm an cold ocean currents. Prevailing winds and irregularly shaped continents interrupt these currents and cause them to flow in roughly circular patterns between the continents Clockwise – northern hemisphere Anti clockwise – southern hemisphere

High density cold waters sinks and flows beneath warmer and less dense sea water Creates a connected loop of deep and shallow ocean currents which act like a giant conveyor belt Transfers warm and cold water between the tropics and the poles Ocean currents are affected by winds in the atmosphere and heat from the ocean affects atmospheric circulation

Greenhouse gases – H 2 O mostly visible light and some infra red – CO 2 radiation and some UV radiatio – CH 4 to pass through the atmosphere – N 2 O Greenhouse effect – long wave length infra red radiation (heat) rises to the lower atmosphere Human-enhanced global warming – burning fossil fuels, clearing forests Allow visible light, infrared and UV radiation from the sun to pass through the atmosphere

Heat is absorbed and released more slowly by water than by land. Creates land and sea breezes World’s oceans and large lakes moderate weather and climate Effect of earth’s surface features – Mountains-interrupt flow of prevailing winds and movement of storms Rain shadow effect – Cities -Microclimates bricks, concrete, asphalt absorb and hold heat and buildings block wind flow. Cars release large amount of pollutants. More haze and smog, higher temperatures and lower wind speeds

Fig. 7-7, p. 145 Prevailing winds pick up moisture from an ocean. On the windward side of a mountain range, air rises, cools, and releases moisture. On the leeward side of the mountain range, air descends, warms, and releases little moisture. Rain Shadow Effect

 Prevailing winds blowing over the oceans produce mass movements of water called currents. Driven by prevaining winds and the earth’s rotation, the major oceancurrents redistribute heat from the sun from place to place., thereby influencing climate and vegetation.

 Differences in average annual precipitation and temperature lead to the formation of tropical, temperate, and cold deserts, grasslands, and forests, and largely determine their locations.

Major biomes – large terrestrial regions characterized by similar climate, soil, plants and animals. Mosaic of patches each with some basic similarities but different biological communities Latitude and elevation Annual precipitation Temperature –tropical, temperate, polar

Fig. 7-9, p. 147 Elevation Mountain ice and snow Tundra (herbs, lichens, mosses) Coniferous Forest Deciduous Forest Latitude Tropical Forest Deciduous Forest Coniferous Forest Tundra (herbs, lichens, mosses) Polar ice and snow Effects of Elevation and Latitude on Climate and Biomes

Fig. 7-10, p. 147 Cold Polar Tundra Subpolar Temperate Coniferous forest Desert Deciduous forest Grassland Chaparral Tropical Hot Desert Wet Rain forest Savanna Tropical seasonal forest Dry Scrubland

Majority of the world’s forests Habitats for endemic species Help regulate the earth’s climate – snow and ice covers reflect solar radiation back. Cool earth and off set global warming Can affect sea levels by storing and releasing water in glacial ice. Warmer earth adds water by melting of glaciers Major storehouses of water – Role in hydrologic cycle

 Many parts of the world experience seasonal winds, or wind direction reversals ◦ Ex. monsoons (rain shadow effect) ◦ Sirocco ◦ Santa Anas

 Monsoons: weather pattern driven by seasonal differences in heating of land and ocean  Influences prevailing winds and weather patterns Figure 7-22

 The winds in the Pacific normally blow across the surface of the water in the Westward direction  This causes ◦ Rain in Indonesia, mild winters in CA, upwelling off the coast of S.Am., cold surface waters on Eastern Pac. La Nina is an increased flow in this direction.

 In El Nino years, the winds blow across the surface in the Eastern direction  This causes ◦ Drought in Indonesia, wet winter in CA, ◦ no upwelling (fish and mammal die-offs), ◦ warm surface water in Eastern Pac.

 A front is a boundary between two air masses of different temps (and pressures). ◦ Warm front – approaching air is warmer than local air ◦ Cold front- approaching air is colder than local air ◦ Both can cause rain; cold fronts are associated with more severe weather

 all.com/science/geoa nimations/animation s/26_NinoNina.html all.com/science/geoa nimations/animation s/26_NinoNina.html

 These are storms that are characterized by masses of rotating air caused by pressure differentials between the ground and air. ◦ Hurricanes (typhoons and cyclones) form over water, and are much larger ◦ Tornadoes form over land are more localized

 Tropical Cyclones – south pacific, Hurricanes - atlantic, and Typhoons – west pacific (oh my!)  Formation: Carnot Cycle driven by heat and moisture from the ocean surface (sst>26.5°C)  Structure ◦ D:\Media\Active_Figures\68_Hurricane_Morphology \68.html

low latitudes, 5-20 o (not at the equator): f (coriolis parameter) important none in SE Pacific or S. Atlantic: SSTs important more appear in the Pacific than in the Atlantic: SSTs important

Milankovitch Cycles What are Milankovitch Cycles? Natural global warming, and cooling, is considered to be initiated by Milankovitch cycles. These orbital and axial variations influence the initiation of climate change in long-term natural cycles of 'ice ages' and 'warm periods' known as 'glacial' and 'interglacial' periods. The cycles appear to be range bound in the paleo record for the past 5 million years. Our current climate forcing shows we are outside of that natural cycle forcing range.

Mountains Agriculture Timber extraction Hydroelectric dams and reservoirs Mineral extraction Increasing tourism Urban air pollution Increased ultraviolet radiation from ozone depletion Soil damage from off-road vehicles Forests Clearing for agriculture, livestock grazing, timber, and urban development Conversion of diverse forests to tree plantations Damage from off- road vehicles Pollution of forest streams Fig. 7-20, p. 158 Large desert cities Soil destruction by off-road vehicles Deserts Soil salinization from irrigation Depletion of groundwater Land disturbance and pollution from mineral extraction Grasslands Conversion to cropland Release of CO 2 to atmosphere from burning grassland Overgrazing by livestock Oil production and off-road vehicles in arctic tundra Stepped Art NATURAL CAPITAL DEGRADATION Major Human Impacts on Terrestrial Ecosystems