Page 168 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

132 part I The energy–atmosphere System
During July in the Northern Hemisphere, isotherms shift toward the poles over land as higher temperatures dominate continental interiors. July temperatures in Verk- hoyansk, Russia, average more than 13°C, which represents a 63 C° seasonal range between January and July averages. The Verkhoyansk region of Siberia is probably Earth’s most dramatic example of continental effects on temperature.
The hottest places on Earth occur in Northern Hemi- sphere deserts during July, caused by clear skies, strong surface heating, virtually no surface water, and few plants. Prime examples are portions of the Sonoran Desert of North America, the Sahara of Africa, and the Lut Desert in Iran (desert climates are discussed in Chapter 10).
January and July Polar-Region
Temperature Maps
Figures 5.14 and 5.15 show January and July tem- peratures in the north polar and south polar regions. The north polar region is an ocean surrounded by land, whereas the south polar region is the enormous Antarctic ice sheet (covering the Antarctic continent) surrounded by ocean. The island of Greenland, hold- ing Earth’s second largest ice sheet, has a maximum elevation of 3240 m, the highest elevation north of the Arctic Circle. Two-thirds of the island is north of the Arctic Circle, and its north shore is only 800 km from the North Pole. The combination of high latitude and
interior high elevation on this ice sheet produces cold midwinter temperatures in January (Figure 5.14a).
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▲Figure 5.14 January average temperatures for polar regions. January temperatures in Celsius for (a) north polar region and (b) south polar region. note that each map is at a different scale. [adapted by author and redrawn from national Climatic Data Center, Monthly Climatic Data for the World, 47 (January 1994), and WMO and nOaa.]
In Antarctica (Figure 5.14b), “summer” is in December and January. This is Earth’s coldest and highest land- mass (in terms of average elevation). January average tem- peratures for the three scientific bases noted on the map are –3°C at McMurdo Station (on the coast); –28°C at the
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CRITICALthinking 5.2
Begin a Full Physical Geography Profile of Your area
With each temperature map (Figures 5.12, 5.13, and 5.16), begin by finding your own city or town and noting the tem- peratures indicated by the isotherms for January and July and the annual temperature range. record the informa- tion from these maps in your notebook. remember that the small scale of these maps permits only generalizations about actual temperatures at specific sites, allowing you to make only a rough approximation for your location.
as you work through the different maps throughout this text, add such data as atmospheric pressure and winds, annual precipitation, climate type, landforms, soil orders, and vegetation to your profile. By the end of the course, you will have a complete physical geography profile for your re- gional environment. •
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