Page 323 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

Chapter 10 Global Climate Systems 287
in India and Bangladesh that affects millions of people. In the U.S. Southeast, dramatic thunderstorms are common, often spawning tornadoes, and rainfall associated with hurricanes can cause seasonal flooding events.
marine West Coast Climates
Marine west coast climates, featuring mild winters and cool summers, are characteristic of Europe and other middle- to high-latitude west coasts (see Figure 10.2). In the United States, these climates, with their cooler summers, are in contrast to the humid subtropical hot- summer climate of the Southeast.
Maritime polar air masses—cool, moist, unstable— dominate marine west coast climates. Weather systems forming along the polar front and maritime polar air masses move into these regions throughout the year, making weather quite unpredictable. Coastal fog, annu- ally totaling 30 to 60 days, is a part of the moderating ma- rine influence. Frosts are possible and tend to shorten the growing season.
Marine west coast climates are unusually mild for their latitude. They extend along the margins of the North Pacific from northern California to the Aleutian Islands, including the western parts of British Columbia, cover the southern third of Iceland in the North Atlantic and coastal Scandinavia, and dominate the British Isles. Many of us might find it hard to imagine that such high- latitude locations can have average monthly tempera- tures above freezing throughout the year. Unlike Europe, where the marine west coast regions extend quite far in- land, mountains in Canada, Alaska, Chile, and Australia restrict this climate to relatively narrow coastal envi- rons. In the Southern Hemisphere country of New Zea- land, the marine west coast climate extends across the country. The climographs for Prince Rupert, British Co- lumbia (Figure 10.9), and Dunedin, New Zealand (Figure 10.10), demonstrate the moderate temperature patterns and annual temperature range for this climate type.
An interesting anomaly occurs in the eastern United States. In portions of the Appalachian highlands, which are in the humid subtropical hot-summer climate region of the continent, increased elevation affects tempera- tures, producing a cooler summer and an isolated area of marine west coast climate, despite its continental loca- tion in the East.
mediterranean Dry-summer Climates
The Mediterranean dry-summer climate designation specifies that at least 70% of annual precipitation occurs during the winter months. This is in contrast to climates in most of the rest of the world, which exhibit summer- maximum precipitation. Across narrow bands of the planet during summer months, shifting cells of subtropi- cal high pressure block moisture-bearing winds from ad- jacent regions. This shifting of stable, warm to hot, dry air over an area in summer and away from that area in winter creates a pronounced dry-summer and wet-winter pattern. For example, in summer the continental tropical
Asian monsoon effects
35.0 38 32.5 32 30.0 27 27.5 21 25.0 16 22.5 10
20.0
4
17.5 0 –1
15.0 –7 12.5 –12 10.0 –18
7.5 –23 5.0 –29 2.5 –34
0 –40 JFMAMJJASOND
Month
(a) Climograph for Chengdu, China. (summer-wet monsoonal precipitation).
Station: Chengdu, China Lat/long: 30° 40′ N 104° 04′ E Avg. Ann. Temp.: 17°C
Total Ann. Precip.: 114.6 cm Elevation: 498 m Population: 2 500 000
Ann. Temp. Range:20 C° Ann. Hr of Sunshine: 1058
0 600 KILOMETRES
CHINA
Chengdu
PACIFIC OCEAN
(b) Agricultural fields near Chengdu, Sichuaun, China.
▲Figure 10.8 Humid subtropical winter-dry climate. [(b) TaO Images limited/alamy.]
Precipitation (cm)
Temperature (°C)
20° 90° 110° 130°
50°
30°