Introduction to Geography Arthur Getis Mark D Bjelland
Introduction to Geography Arthur Getis, Mark D. Bjelland, Victoria L. Getis Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Physical Geography: Weather and Climate Chapter 4 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Overview l l l l Introduction Air Temperature Air Pressure and Winds Ocean Currents Moisture in the Atmosphere Climate Regions Climatic Change 3 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Introduction l Weather l l Climate l l State of the atmosphere at a given time and place Long-term average weather conditions in a place Geographers analyze differences in weather and climate from place to understand how they affect human occupance of the earth 4 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Introduction l Troposphere is of particular concern l l Atmospheric layer closest to the earth Contains virtually all of the air, clouds, and precipitation of the earth 5 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature l Why do temperatures vary from place to place? l l l Need to understand how heat accumulates on the earth’s surface Solar energy is transformed into heat primarily at the earth’s surface and secondarily in the atmosphere Insolation (amount of incoming solar radiation) l Solar radiation received at the earth’s surface l Determined by angle of the sun’s rays and number of daylight hours 6 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature l Angle of sun’s rays, number of daylight hours and these modifying variables determine the temperature at any given location: l l l Amount of water vapor in the air Cloud cover Nature of the surface of the earth (land or water) Elevation Degree and direction of air movement 7 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature Earth’s Movements l l Rotation Revolution 8 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature Earth Inclination l l l Axis of the earth tilts at ≈ 23. 5° Location of highest incoming solar radiation varies during the year Summer Solstice in Northern Hemisphere (about June 21) l l Northern Hemisphere tilted toward the sun Vertical rays of the sun at noon are at 23. 5° N 9 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature Earth Inclination l l Winter Solstice in the Northern Hemisphere (about December 21) l Northern Hemisphere tilted away from the sun l Vertical rays of the sun at noon are at 23. 5° S Spring and fall equinoxes in the Northern Hemisphere (about March 21 and September 21, respectively) l Vertical rays of the sun at noon are at the equator 10 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature Earth Inclination l Causes variation in length of days and nights l l l At the equator l 12 hours of light each day of the year Inside the Arctic Circle and Antarctic Circle l 24 hours of daylight/darkness on solstices Angle of the sun’s rays above the surface of the earth l The larger the angle, the more energy available 11 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature: Reflection and Radiation Emission l Clouds in the atmosphere and light colored surfaces on the earth reflect 32% of incoming solar energy back to outer space l Radiation cycle l l Shortwave solar radiation is absorbed by the surface of the earth, thereby heating the surface. Then radiation is emitted from the earth into the atmosphere in the form of longwave radiation. Earth’s atmosphere is mainly heated by terrestrial radiation. 12 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature: Reflection and Radiation Emission l Daily cycle of temperature l l Air temperature rises when incoming solar radiation exceeds energy lost through reflection and terrestrial radiation Air temperature drops when energy lost through reflection and terrestrial radiation exceeds incoming solar radiation 13 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature: Reflection and Radiation Emission l Water heats and cools more slowly than land l l Marine environment l Cooler summers, warmer winters Land heats and cools more rapidly than water l Continental environment l Hotter summers, colder winters 14 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Temperature The Lapse Rate l Temperature generally decreases as altitude increases in the troposphere l l Lapse rate l Average of 3. 5° F per 1000 feet (6. 4° C per 1000 m) Temperature inversion l Cooler air trapped below warmer air l Contributes to smog problems 15 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds l How do differences in air pressure from place to place affect weather conditions? l Air pressure = weight of the atmosphere Normal sea level pressure = 14. 7 pounds or 6. 7 kilograms Air pressure is highest closest to the earth’s surface l l 16 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds l Temperature and air pressure relationship (for equal amounts of cold and hot air): l l Cold air is denser than warm air: high pressure Warm air is lighter than cold air: low pressure l Air pressure is measured by a barometer in inches of mercury or millibars l Air pressure at a given location changes as surfaces heat or cool Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 17
Air Pressure and Winds l l Zones of high and low air pressure exist in earth’s atmosphere Pressure gradient force l l l Causes air to flow from high to low pressure areas Wind l Velocity is in direct proportion to pressure differences Convection system l Circulatory movement of rising warm air and descending cool air 18 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds l Convectional wind effects due to differential heating and cooling of land water: l l Land sea breezes l Day: from sea to land l Night: from land to sea Mountain and valley breezes l Day: from valley to mountains l Night: from mountains to valley 19 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds l Coriolis effect l l l Result of Earth’s rotation Earth rotates in a counterclockwise direction when viewed from the position of the North Pole Earth rotates in a clockwise direction when viewed from the position of the South Pole Apparent deflection relative to the earth’s surface l Northern Hemisphere: wind veers toward the right Southern Hemisphere: wind veers toward the left Coriolis effect and pressure gradient force produce spiral wind patterns 20 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds l Frictional effect of Earth’s surface on movement of wind l l Decreases wind speed Changes wind direction 21 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds Global Air-Circulation Pattern l Equatorial low pressure l l Subtropical high pressure l l Warm air rises and moves away from Equatorial region About 30° N and 30° S of the equator Cold air aloft sinks When sinking air reaches Earth’s surface it moves away from the region of high pressure, thereby creating the trade winds and the westerlies Trade winds l In the tropics 22 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds Global Air-Circulation Pattern l Westerlies l l In the midlatitudes Subpolar low Polar easterlies Polar high 23 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds Global Air-Circulation Pattern l Jet streams l l l Belts of strong winds in the upper atmosphere l Flow from west to east in an undulating path l Bring cold air equator ward and warm air pole ward Guide the movement of weather systems More pronounced in the winter than in the summer 24 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Air Pressure and Winds Global Air-Circulation Pattern l Monsoon l l Wind system that reverses direction seasonally l Produces wet and dry seasons Significant effect on parts of southern and eastern Asia l Farm economy is dependent upon summer monsoon rains l Negative impact if rainfall arrives late or rainfall is less or more than optimum l May cause disastrous flooding and loss of lives 25 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Ocean Currents l l Surface ocean currents correspond roughly to global wind direction patterns Movement due to winds and differences in water density l l l Direction affected by Coriolis effect Direction also influenced by landmasses and shape of ocean basins North Atlantic drift l l Warm current Winters in northern Europe are warmer than expected for its latitude Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 26
Ocean Currents l Ocean currents affect precipitation on adjacent land areas l l Cold currents l Dry conditions (coastal deserts) Warm currents l Moist conditions 27 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere l Ascending air expands and cools l l Less able to hold water vapor Supersaturated air l Water vapor condenses around condensation nuclei 28 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere l Clouds l l Consist of rain droplets or ice crystals supported by upward movements of air l Droplets may coalesce and fall as rain l Temperatures below freezing - formation of snow Form and altitude of cloud depends on: l Water vapor content, temperature, wind movement 29 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere l Clouds (continued) l Types of clouds: l Cumulus l Stratus l Cirrus l Cumulonimbus 30 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere l Relative humidity l l Percentage measure of the moisture content of the air l Amount present relative to the maximum that can exist at the current temperature Dew point l Temperature at which condensation forms 31 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere Types of Precipitation l Convectional precipitation l l l Heated, moisture-laden air rises and then cools below the dew point Summer in tropical and continental climates Orographic precipitation l Warm, moisture-laden air is forced to rise over hills or mountains and is thereby cooled l Windward side § Receives a great deal of precipitation l Leeward side § Very often dry (rain shadow) Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 32
Moisture in the Atmosphere Types of Precipitation l Cyclonic (frontal) precipitation l l l Common to the midlatitudes In the tropics – originator of hurricanes and typhoons Occurs where cool and warm air masses meet Air mass l Body of air with similar temperature, pressure, and humidity characteristics throughout l Forms over a source region Front l Zone of separation between two air masses 33 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere Storms l Midlatitude Cyclone l l Masses of air circulating about a region of low atmospheric pressure Counterclockwise rotation in Northern Hemisphere Warm air moves up and over cold air along a front Can develop into a storm 34 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Moisture in the Atmosphere Storms l Hurricane l l l Typhoon l l Severe tropical cyclone with winds exceeding 74 mph Forms in low-pressure zone over warm waters; e. g. , in the Atlantic, Caribbean, or Gulf of Mexico Name for hurricanes in the western Pacific Ocean Structure of hurricane l l Eye wall Surge Concentric belts of rising air Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 35
Moisture in the Atmosphere Storms l Blizzard l l Heavy snow and high winds Tornado l l l l Most violent of all storms Smallest storm Common in Central U. S. in spring and fall Spawned in huge cumulonimbus clouds Funnel-shaped cloud of whirling winds that spins at speeds as high as 300 mph Enhanced Fujita Scale Waterspout Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 36
Climate Regions l l Climate of an area is a generalization based on daily and seasonal weather conditions Two most important elements that differentiate weather conditions are temperature and precipitation 37 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions l Köppen climate system l Based on temperature, precipitation, and natural vegetation criteria l Six broad categories l A: tropical l B: dry l C: mild midlatitude l D: midlatitude with severely cold winters l E: polar l H: highland 38 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Tropical Climates (A) l l Generally found between Tropics of Cancer and Capricorn Tropical rainforest (Af) l l l Found in equatorial low pressure zone; also along coasts extending away from the equator High temperatures and daily convectional rainfall year Tall, dense forests 39 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Tropical Climates (A) l Tropical savanna (Aw) l l l To the north and south of rain forests High temperatures Heavy convectional rainfall in summer, dry winters Forests to grasslands Tropical monsoon (Am) l l Significant increase in rainfall when summer monsoon winds bring water-laden air Dense forests 40 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Dryland Climates (B) l Hot deserts (BWh) l l l Found in subtropical high pressure zone Considerable sunshine, high temperatures Very little precipitation Shrubs in gravelly or sandy environments E. g. , Sahara, Arabian, Australian and Kalahari Deserts 41 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Dryland Climates (B) l Midlatitude deserts and semideserts (BWk) l l Warm/hot summers and cold winters Some convectional or frontal rainfall in summer, some snowfall in winter Extremely dry areas known as cold deserts Moderately dry lands known as steppes l Among most naturally fertile soils in the world l Vegetation: grasslands, desert shrubs l Known for hot, dry summers and biting winter winds which sometimes bring blizzards 42 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Humid Midlatitude Climates (C) l Mediterranean (Cs) l l l Located in transition zone between subtropical highs and the westerlies Aside from Mediterranean region itself, generally found on the western coasts of continents in the middle latitudes; e. g. , Southern California, tip of South Africa, western Australia and central Chile Warm/hot summers and mild/cool winters Dry summer, frontal precipitation in winter Vegetation l Shrubs l Small deciduous trees Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 43
Climate Regions Humid Midlatitude Climates (C) l Humid subtropical (Cfa) l l l Located on eastern coasts on continents Hot, moist summers and moderate, moist winters Convectional summer showers, winter cyclonic storms Deciduous and coniferous forests May be affected by hurricanes 44 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Humid Midlatitude Climates (C) l Marine west coast (Cfb) l l Prevailing winds from the sea Moderate temperatures in both summer and winter Frontal and orographic precipitation Deciduous and coniferous forests 45 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Humid Continental Climates (D) l l l Cyclonic storms are more responsible for rainfall than are convectional showers Colder winters, shorter summers Prevailing winds from land Deciduous and coniferous forests Location: l l Northern and central US Southern Canada Most of European portion of Russia Northern China Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 46
Climate Regions: Subarctic Climates (Dfc, Dfd, Dwb) l Subarctic l l Cool/cold, short summers and very cold winters Coniferous forest to mosses and lichens Tundra l Treeless area between the Arctic tree line and the permanently ice-covered zone Location l Alaska l Northern Canada l Northern Russia 47 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Arctic Climates (E) l Arctic l l l Ice cap near the poles Extremely cold with light precipitation Antarctica and Greenland are icy deserts 48 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climate Regions Highland Climates (H) l l Lower temperatures than lowlands at the same latitude Variety of conditions based on: l l l Elevation Prevailing winds Orientation of slope relative to the sun Valley, slope, or peak Ruggedness 49 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climatic Change l Long-term climatic change l l l Significant variations over geologic time l Ice ages l Medieval warm period and “little ice age” May be due to variations in: shape of Earth’s orbit, tilt of the axis, gyration of the rotation axis Short-term climatic change l l Natural processes l Volcanic eruptions, oceanic circulation, sunspot activity Human processes l Enhanced greenhouse effect 50 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climatic Change l Greenhouse effect l l Certain gases in the atmosphere function as an insulating barrier, trapping infrared radiation Global warming l Caused by human activities that have increased the amount of greenhouse gases in the atmosphere l Carbon dioxide: burning fossil fuels, deforestation l Methane: natural gas and coal mining, agriculture and livestock, swamps, landfills l Nitrous oxides: motor vehicles, industry, fertilizers l Chlorofluorocarbons: industrial chemicals Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education. 51
Climatic Change l Evidence of global warming (continued) l l l 20 th century was the warmest in 600 years l Average surface temp rose over 1° F during the century Winter temps in the Arctic have risen about 7° F since the 1950 s l Loss of Arctic ice cap Glaciers are thinning and retreating 52 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
Climatic Change l Consequences of global warming include: l l Rising sea levels Changes in temperature and precipitation patterns l Impact on soils, vegetation, agriculture 53 Copyright © 2014 Mc. Graw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of Mc. Graw-Hill Education.
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