Page 268 - NS-2 Textbook

METEOROLOGY 263

that the geography of the continents and seas can also in- mountains. These lows are common just east of the Rocky
fluence the wind and weather. Mountains in Colorado.

HIGHS (ANTICYCLONES) MOUNTAIN WINDS

In the Northern Hemisphere, air flows in a clockwise We have just mentioned the lows that sometimes form on
manner around high-pressure centers of action (also the lee side of mountain ranges. These winds are so per-
called anticyclones). Air subsides (sinks) in the center and sistent and predictable in some areas that they have
diverges (blows outward) from the center of the high- earned their own names. Topography is a major factor in
pressure area. Few clouds are formed. Generally fair the formation of such winds, but temperahlre differences
\.\Teather prevails, either ,varnl or cold, depending upon and the rotation of Earth also contribute.
the season. As vvarm air rises on one side of the mountains, it
Local high-pressure areas will develop anyplace cools and loses its moisture as rain or snow. The dry,
v\There air cools, compresses, and subsides. The Horse cooler air then rushes down the opposite side, heating the
Latihldes and the polar highs are good examples of this. air and pushing it into the low. Famous mountain winds
But high-pressure areas can develop anywhere. When a are the Chinooks of the Rockies, the Santa Anas of south-
high develops, the clockwise anticyclonic spiral of air de- ern California, and the foehns of the Swiss and French
velops and air begins flowing to surrounding lower- Alps. These winds sometimes reach gale force and, in the
pressure areas. western United States, often become dust storms.
Major high-pressure areas exist near the poles. They
produce very cold air, dependent on the seasons. A high-
VALLEY WINDS
pressure 3Tea exists over Greenland all the time because of
the vast ice cap there. Subtropical highs can usually be Probably the most famous valley wind system is the Mis-
found southwest of California and near the Azores in the tral of southern France. This is a cold, dry wind that rushes
Atlantic. The high associated with the North Polar zone down the Rhone Valley toward the low-pressure system
repeatedly creates icy polar fronts, which evelY winter that often develops over the Mediterranean Sea. Some-
sweep over most of North America east of the Rockies. times reaching whole gale and storm force over 60 mph,
This area is called the North American High. A similar this wind is one the U.S. Sixth Fleet must be on the alert for
high-pressure area exists in Siberia, where the temperate \,\-Then involved in western Mediterranean operations.
zone's coldest temperatures have been recorded. The
North American and Siberian Highs are continental highs.
MONSOONS
Monsoons are seasonal winds characteristic of South and
LOWS
Southeast Asia, though they oCCUl' elsewhere with less
The only "permanent" low-pressure area on Earth is the intensity and regularity. The monsoon is a very persis-
Doldrum Belt near the equator. The Aleutian Low off tent wind that blows on predictable seasonal paths and
Alaska is a low-pressure cell associated with the Polar lilith definite seasonal characteristics.
Front and influenced by the Japanese Current. It is in- SU1llmer (Southwest) Monsooll. As continental Asia be-
tense during the winter but ill-defined in StmUller. An- gins to warm in the spring, the water area over the In-
other low-pressure area lying near Iceland is called the dian Ocean remains relatively cool. The warming effect
Icelandic Low. The Gulf Stream influences this low. gradually creates a continental low over the central
Traveling low-pressure cells are frequently fOtmd in Asian plateaus and desert. This low draws cooler air
the area of the Polar Front. These are formed by the in- from the south. As the moisture-laden Indian Ocean air
teraction of the polar air to the north and the maritime pushes northeastward over the land, it begins to cool and
tropical air to the south. These lows are called migratory condense. TI1e rains begin to fall in southern India in
lows. Migratory storms filay also move into Im·ver lati- mid-May and continue to build up in intensity as the
tudes from the Polar Front. Such storms often occur in continent ·warms. The wet air rushes into the southern
the south-central Unlted States and on the u.s. East slopes of the Hinmlaya Mountains and dumps astound-
Coast near Cape Hatteras. ing amotmts of rain on the southern Asian countries. It is
Local lows often form directly below large thunder- common for the southeast Burmese coast to have 200
head clouds. Heat lows form over deserts and other in- inches of rainfall during the period between mid-May
tensely hot areas; a low-pressure area lasts most of the and late September. At the foothills of the Himalayas, 500
sununer over the Arizona and California deserts. Lows inches of rain in the same period have been recorded al-
sometimes form on the leeward side of mountain ranges most every year. The greatest rainfall ever recorded oc-
and cause rushing "'Tinds to U pour" down from the nearby curred at Cherraptmji, India, during the monsoon: 1,041.78