CHAPTOR 17

According to Koppen's climatic system, what major climatic type is most abundant in each of the following areas: (a) In North America (b) In South America, and (c) throughout the world?

(a) D - Moist climate with severe winter. (b) A - Moist tropical climate. (c) B - Dry climate.

Explain how arid deserts can be found adjacent to oceans.

Arid deserts are dominated by the sinking air of a subtropical high pressure system. This factor prevents significant precipitation even if oceans are nearby.

Explain why subpolar climates are also known as boreal climates and taiga climates

Because of the low temperatures, there is a low annual rate of evaporation that ensures adequate moisture to support the boreal forests of conifers and birches known as taiga. Hence, the subpolar climate is known also as a boreal climate and as a taiga climate.

Why are marine climates (Cs) usually found on the west coast of continents?

Because winds (outside the tropics) are typically westerly, giving the west coasts a marine influence.

How do C-type climates differ from D-type climates?

C: humid with mild winters. D: Warm-to-cool summers and cold winters.

1. Why do cities directly east of the Rockies (such as Denver) receive much more precipitation than cities east of the Sierra Nevada (such as Reno & Lovelock, Nevada)?

Cities located east of the Rockies receive moisture from the Gulf of Mexico. The Rockies effectively block Gulf moisture from reaching cities located to the east of the Sierra Nevada Mountains. In addition, the Sierras shield the region east of them from Pacific moisture.

7. In which of the following climate types is virga (precipitation that evaporates before hitting the ground) likely to occur most frequently: humid continental, arid desert, or polar tundra? Explain why.

In arid desert climates. Here the temperatures are warm enough to support liquid precipitation, but relative humidities are low enough to evaporate the rain before it reaches the surface.

4. Why are many structures in polar regions built on pilings?

In polar regions, the ground is frozen except in summer when the upper part thaws. Hence, the summer landscape often turns swampy. During the winter, warmth from a heated building could melt the frozen ground beneath it. This could cause the structure to settle into the ground unevenly. To prevent this, some structures are built upon pilings.

Barrow, Alaska, receives a mere 11cm (4.3in) of precipitation annually. Explain why its climate is not classified as arid or semi-arid.

In the polar tundra (ET), the average temperature of the warmest month is below 10°C (50°F), but above freezing. The temperature, rather than the precipitation, is the defining factor of this climate type.

What is the primary factor that makes a dry climate "dry"?

Potential evapotranspiration exceeds precipitation

8. As shown in Figure 17 (pg. 507), San Francisco and Sacramento, California, have similar mean annual temperatures but different annual temperature ranges. What factors control the annual temperature ranges at these two locations?

San Francisco is closer to the Pacific Ocean and experiences a maritime climate. Sacramento is inland, and air approaching Sacramento from the west must first cross a mountain range where it may contain less moisture due to orographic lifting and precipitation.

9. Why is there a contrast in climate types on either side of the Rocky Mountains, but not on either side of the Appalachian Mountains?

The Rocky Mountains are very tall and are oriented perpendicular to the prevailing wind flow(westerly). The Appalachians are shorter and are roughly parallel to the prevailing wind directions (southerly and northerly).

What factors determine the global pattern of precipitation?

The general circulation of the atmosphere; distribution of mountain ranges and high plateaus; temperature; passage of high and low pressure systems; proximity to semi-permanent highs and lows; proximity to large open water sources.

Explain why a tropical rain forest climate will support a tropical rain forest, while a tropical wet-and-dry climate will not.

The tropical wet-and-dry climate has a distinct dry season, whereas the tropical rain forest (tropical wet) climate does not.

How did Koppen define tropical climate? How did he define a polar climate?

Tropical moist climate: All months have an average temperature above 18°C (64°F). Polar climate: Extremely cold winters and summers. The average temperature of the warmest month is below 10°C (50°F).

What is the primary distinction between a Cfa and a Dfa climate?

Winters are colder in Dfa climates.

Why are large annual temperature ranges characteristic of D-type climates?

D climates are controlled by a large continent, and continents typically experience a larger annual temperature range as compared to oceans.

Why did Koppen use the 10C (50F) average temperature for July to distinguish between D and E climates?

Köppen found that the average monthly temperature of 10°C tended to represent the minimum temperature required for tree growth

5. Why are summer afternoon temperatures in a humid subtropical climate (Cfa) often higher than in a tropical wt climate (Af)?

The ground in Cfa climate areas is often drier than the ground in areas with Af climates. Dry ground warms up faster than wet ground, allowing surface temperatures to increase.

3. Los Angeles, Seattle, and Boston are all coastal cities, yet Boston has a continental rather than a marine climate. Explain why.

The prevailing westerly winds at this latitude give Boston a continental-type climate.

What accounts for the existence of a Bwk climate in the western Great Basin of North America?

The southern desert region of North America is dry because it is dominated by the subtropical high most of the year, and winter storm systems tend to weaken before they move into the area. The northern region is in the rain shadow of the Sierra Nevada. These regions are deficient in precipitation all year long, with many stations receiving less than 13 cm (5 in.) annually.

Why are D climates found in the Northern Hemisphere but not in the Southern Hemisphere?

There are fewer large continents in the southern hemisphere, and the largest southern hemisphere land masses are in the tropics.

In which climatic region would each of the following be observed: tropical rain forest, xerophytes, steppe, taiga, tundra, and savanna?

Tropical rain forest: Tropical Moist Climate. Xerophytes: B - Dry climate. Steppe: B - Dry climate. Taiga: D - Moist climates with severe winters. Tundra: E - Polar climates. Savanna: A - Moist tropical climate

What climatic information did Koppen use in classifying climates?

Vegetation type.

Explain why, in North 'Murica, precipitation typically is a maximum along the West Coast in winter, a maximum on the central plains in summer, and fairly evenly distributed between summer and winter along the east coast.

Winter: Pacific high moves south, giving storms access to the west coast of the U.S., Bermuda high moves south, carrying less moisture to the eastern half of the U.S. Summer: Pacific high inhibits precipitation along the West Coast, Bermuda high brings moisture to eastern two-thirds of the U.S.

What are the controlling factors (climatic controls) that produce the following climatic regions? (a) tropical wet and dry (b) Mediterranean (c) marine (d) humid subtropical (e) subpolar (f) polar ice cap

(a) tropical wet and dry: In summer, the ITCZ moves poleward, bringing with it heavy precipitation, usually in the form of showers. Rainfall is enhanced by slow moving shallow lows that move through the region. Tropical wet-and-dry climates not only receive less total rainfall than the tropical wet climates, but the rain that does occur is much less reliable, as the total rainfall often fluctuates widely from one year to the next. In the course of a single year, for example, destructive floods may be followed by serious droughts. As with tropical wet regions, the daily range of temperature usually exceeds the annual range, but the climate here is much less monotonous. There is a cool season in winter when the maximum temperature averages 30°C to 32°C (86°F to 90°F). At night, the low humidity and clear skies allow for rapid radiational cooling and, by early morning, minimum temperatures drop to 20°C (68°F) or below. (b) Mediterranean: The extreme summer aridity of the Mediterranean climate, which in California may exist for five months, is caused by the sinking air of the subtropical highs. In addition, these anticyclones divert summer storm systems poleward. During the winter, when the subtropical highs move equatorward, mid-latitude storms from the ocean frequent the region, bringing with them much needed rainfall. Consequently, Mediterranean climates are characterized by mild, wet winters, and mild-to-hot, dry summers. (c) marine: During much of the year, marine climates are characterized by low clouds, fog, and drizzle. The ocean's influence produces adequate precipitation in all months, with much of it falling as light or moderate rain associated with maritime polar air masses. Snow does fall, but frequently it turns to slush after only a day or so. In some locations, topography greatly enhances precipitation totals. (d) humid subtropical: A trademark of the humid subtropical climate is its hot, muggy summers. This sultry summer weather occurs because Cfa climates are located on the western side of subtropical highs, where maritime tropical air from lower latitudes is swept poleward into these regions. Generally, summer dew-point temperatures are high (often exceeding 23°C, or 73°F) and so is the relative humidity, even during the middle of the day. The high humidity combines with the high air temperature (usually above 32°C, or 90°F) to produce more oppressive conditions than are found in equatorial regions. Summer morning low temperatures often range between 21°C and 27°C (70°F and 81°F). Occasionally, a weak summer cool front will bring temporary relief from the sweltering conditions. (e) subpolar: The exceedingly low temperatures of winter account for these areas being the primary source regions for continental polar and arctic air masses. Extremely cold winters coupled with cool summers produce large annual temperature ranges. Precipitation is comparatively light in the subpolar climates, especially in the interior regions, with most places receiving less than 50 cm (20 in.) annually. A good percentage of the precipitation falls when weak cyclonic storms move through the region in summer. The total snowfall is usually not large but the cold air prevents melting, so snow stays on the ground for months at a time. Because of the low temperatures, there is a low annual rate of evaporation that ensures adequate moisture to support the boreal forests of conifers and birches known as taiga. (f) polar ice cap: It occupies the interior ice sheets of Greenland and Antarctica, where the depth of ice in some places measures thousands of meters. In this region, temperatures are never much above freezing, even during the middle of "summer." The coldest places in the world are located here. Precipitation is extremely meager with many places receiving less than 10 cm (4 in.) annually. Most precipitation falls as snow during the "warmer" summer. Strong downslope katabatic winds frequently whip the snow about, adding to the climate's harshness.

Why are the lowest temperature in polar regions observed in the interior of large landmasses?

Along the coastlines, the reduced albedo and larger thermal capacity of nearby water increases the temperatures.