Wind Belts

Wind Belts The general circulation of winds arises from the global redistribution of heat from warm low latitudes to cold high latitudes, driven by the development of surface pressure gradients. Wind blows from high to low pressure regions, although airflow is deflected by the Coriolis force as a result of the Earth's rotation, and tends to follow more east-west trends rather than north-south trends. Air movement at or near the equator is light. At sea the region became known to sailors as the Doldrums. Air from the subtropical zones in the Northern and Southern Hemispheres converges here in a zone called the Inter-Tropical Convergence Zone (ITCZ). These low latitude wind belts became known as the Northeast and Southeast Trades, which merchant ships used to cross the Atlantic Ocean from Europe to the New World. In the Indian Ocean, Northeast Trade winds blow throughout the winter months. During the Northern Hemisphere summer however, the ITCZ is shifted well to the north of the equator, when the midday Sun is overhead at the Tropic of Cancer at latitude 23.5° north. The Southeast Trade winds now cross the equator, and are deflected to the right by the Coriolis force, forming the Southwest Monsoons. This summertime airflow picks up considerable moisture crossing the Indian Ocean, and brings a heavy and prolonged wet season to India and Southeast Asia through April to September, known as the Monsoon. The temperate mid-latitudes are influenced by a stream of westerly airflow. In the Northern Hemisphere the winds became known as the Southwest Antitrades, which prevail for much of the year. In the Atlantic, the Gulf Stream enhances the warmth of the southwesterly air masses, which influence the mild weather of the UK and Western Europe. This warm flow of air collides with the Polar Easterlies from the Arctic region, generating a zone of cyclonic low pressure, where frontal depressions frequently form. In the Southern Hemisphere, the westerlies are known as the Roaring Forties, which blow more or less continuously around the Earth due to the absence of significant landmasses. Philippine wind system These two types of wind are caused by different high and low pressure cells situated near the islands. Wind flows from high pressure towards low pressure. Sometimes if a high pressure is situated to the north and east of the island with low pressure to the south or west, you end up with an east or northeast wind (Amihan). The other way around for habagat. El Nino/La Nina strongly influences which wind regime you are in. During El Nino, high and low pressure set up one way, but in La Nina they set up the other way so the winds are in different direction. The direction of the wind also influences which parts of the islands get rain and which parts get little or none. When wind is blowing upslope, it tends to enhance rainfall, and on the other side of the mountain, it doesn't rain (rainshadow effect). So these winds are important in deciding where rain is going to be plentiful and where there is going to be little.

Cold front

From Wikipedia, the free encyclopedia Jump to: navigation, search For the Star Trek: Enterprise episode, see Cold Front (Enterprise).

The symbol of a cold front: a blue line with triangles pointing in the direction of travel A cold front is defined as the leading edge of a cooler and drier mass of air, replacing (at ground level) a warmer mass of air.

Contents [hide] •

1 Development of cold front

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2 Precipitation

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3 Temperature changes

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4 Association with warm fronts

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5 Formation

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6 See also

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7 References

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8 External links

[edit] Development of cold front The cooler, denser air wedges under the less dense warmer air, lifting it, which can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. This upward motion causes lowered pressure along the cold front. On weather maps, the surface position of the cold front is marked with the symbol of a blue line of triangles/spikes (pips) pointing in the direction of travel. A cold front's location is at the leading edge of the temperature drop off, which in an isotherm analysis would show up as the leading edge of the isotherm gradient, and it normally lies within a sharp surface trough. Cold fronts can move up to twice as fast and produce sharper changes in weather than warm fronts. Since cold air is denser than warm air, it rapidly replaces the warm air preceding the boundary. Cold fronts, are usually associated with an area of low pressure, and sometimes, a warm front. In the northern hemisphere, a cold front usually causes a shift of wind from southeast to northwest, and in the southern hemisphere a shift from northeast to southwest. Common characteristics associated with cold fronts include: Weather phenomenon Temperature Atmospheric pressure Winds

Prior to the Passing of While the Front After the Passing of the the Front is Passing Front Warm Cooling suddenly Steadily cooling Lowest, then Decreasing steadily Increasing steadily sudden increase Gusty; shifting • Southwest to • North to west

(usually northwest) (northern hemisphere)

southeast (northern hemisphere) •

•

Northwest to northeast (southern hemisphere)

Precipitation/conditions* Brief showers Clouds*

Increasing: Cirrus, cirrostratus, and cumulonimbus

Visibility*

Fair to poor in haze

Dew Point

High; steady

South to west (usually southwest) (southern hemisphere)

Thunderstorms, Showers, followed by sometimes severe clearing Cumulonimbus Poor, but improving Sudden drop

Cumulus Good, except in showers Falling

definition: A boundary between 2 air masses, 1 cold and the other warm

[edit] Precipitation

Illustration of a cold front A cold front commonly brings a narrow band of precipitation that follows along the leading edge of the cold front. These bands of precipitation are often very strong in nature, and especially in the Spring and Summer months, can bring severe thunderstorms and/or tornadoes. In the spring, these cold fronts can be very strong, and can bring strong winds when the pressure gradient is tighter than normal. In the summer, cold fronts can cause severe thunderstorms and hailstorms, but in the winter, cold fronts sometimes come through an area with little or no precipitation. In the autumn months, cold fronts rarely bring severe thunderstorms, but are known for bringing heavy, and widespread rainstorms. These rainstorms sometimes bring flooding, and can move very slowly because cold fronts are more prone to slow movement in the fall. In the winter, cold fronts can bring severe cold spells, and heavy snowstorms. If moisture is not sufficient, cold fronts can pass without producing any precipitation at all, and the skies could be cloudless. Cold fronts do not produce the moisture, it will just condense against the cold air into cloud and rain droplets if there is enough water vapor in either airmass. Because the cold air wedges under the

warm air, it forces it to rise, creating instability. If moisture is sufficient, it will condense, creating storms, clouds, and/or rain.

[edit] Temperature changes Cold fronts are the leading edge of a frigid air mass, hence the name "cold front". They can bring several cold spells in the fall (autumn) and winter. Very often, cold fronts are associated with deadly cold weather. Sometimes, though, cold fronts have no significant effect on the weather. The cold fronts in the late fall become more polar in nature, and tend to bring very cold weather, and temperature drops by up to 30°F. When cold fronts come through, there is usually a quick, yet strong gust of wind, that shows that the cold front is passing. The effects from a cold front can last only a few hours to several weeks, depending on when the next weather front comes through.The air behind the front is cooler than the air it is replacing. the warm air is forced to rise so it cools. as the cooler air can not hold as much moisture as warm air, clouds form and rain occurs.

[edit] Association with warm fronts

Occluded cyclone example. The triple point is the intersection of the cold, warm, and occluded fronts. Cold fronts are very often associated with a warm front, squall line, or other weather front. Very commonly, cold fronts have an adjacent warm front that is ahead of the cold front. This is known as an occluded front. This forms an area where warm air is occurring and interacting with the cold front. In this area known as a warm sector. In the warm sector, very often severe thunderstorms, tornadoes, and hailstorms occur, because of the sharp difference between the warm air that is associated with the warm front, and the cold air that is associated with the cold front. A cold front is considered a warm front if it retreats, and called a stationary front if it stalls.

[edit] Formation Cold fronts form when a cooler air mass moves into an area of warmer air. The warmer air interacts with the cooler air mass along the boundary, and usually produces precipitation.

Occluded front From Wikipedia, the free encyclopedia Jump to: navigation, search

A cyclone in the early stages of occlusion

Occluded front symbol An occluded front is formed during the process of cyclogenesis when a cold front overtakes a warm front. When this occurs, the warm air is separated (occluded) from the cyclone center at the Earth's surface. The point where the front and the occluded front meet (and consequently the nearest location of warm air to the center of the cyclone) is called the triple point.[1] There are two types of occlusion, the warm, and the cold. In a cold occlusion, the air mass overtaking the warm front is cooler than the cool air ahead of the warm front, and plows under both air masses. In a warm occlusion, the air mass overtaking the warm front is not as cool as the cold air ahead of the warm front, and rides over the colder air mass while lifting the warm air. A wide variety of weather can be found along an occluded front, with thunderstorms possible, but usually their passage is associated with a drying of the air mass. Additionally, cold core funnel clouds are possible if shear is significant enough along the cold front. Occluded fronts are indicated on a weather map by a purple line with alternating semicircles and triangles pointing in direction of travel. Occluded fronts usually form around mature low pressure areas.

Atmospheric pressure From Wikipedia, the free encyclopedia (Redirected from Atmospheric Pressure) Jump to: navigation, search "Air pressure" redirects here. For the pressure of air in other systems, see pressure. Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. A column of air one square inch in cross-section, measured from sea level to the top of the atmosphere, would weigh approximately 65.5 newtons (14.7 lbf). The weight of a 1 m2 (11 sq ft) column of air would be about 101 kN (10.3 tf) .