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Posted by weathergaines During La Niña, the trade winds—easterly winds that blow through the tropics and subtropics—are stronger than normal. Likewise, the cold water that normally exists along the coast of South America extends to the central equatorial Pacific. La Niña reappears every three to five years At times ocean surface temperatures in the equatorial Pacific are colder than normal. These cold episodes, sometimes referred to as La Niña episodes, are characterized by lower than normal pressure over Indonesia and northern Australia and higher than normal pressure over the eastern tropical Pacific. This pressure pattern is associated with enhanced near-surface equatorial easterly winds over the central and eastern equatorial Pacific. --Previous Message--
on September 20, 2007, 11:49 am, in reply to "About La Nina"
58.69.24.1
La Niña is a coupled ocean-atmosphere phenomenon similar to El Niño. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 0.5 °C. By definition, an episode of La Niña is a period of at least 5 months of La Niña conditions
During cold (La Niña) episodes the normal patterns of tropical precipitation and atmospheric circulation become disrupted. The abnormally cold waters in the equatorial central give rise to suppressed cloudiness and rainfall in that region, especially during the Northern Hemisphere winter and spring seasons. At the same time, rainfall is enhanced over Indonesia, Malaysia and northern Australia. Thus, the normal Walker Circulation during winter and spring, which features rising air, cloudiness and rainfall over the region of Indonesia and the western Pacific, and sinking air over the equatorial eastern Pacific, becomes stronger than normal.
By studying past cold episodes scientists have discovered precipitation and temperature anomaly patterns that are highly consistent from one episode to another. Significant departures from normal are shown in the accompanying figures for the Northern Hemisphere winter and summer seasons. During cold episodes, the colder than normal ocean temperatures in the equatorial central Pacific act to inhibit the formation of rain-producing clouds over that region. Wetter than normal conditions develop farther west over northern Australia, Indonesia and Malaysia, during the northern winter, and over the Philippines during the northern summer. Wetter than normal conditions are also observed over southeastern Africa and northern Brazil, during the northern winter season. During the northern summer season, the Indian monsoon rainfall tends to be greater than normal, especially in northwest India. Drier than normal conditions during cold episodes are observed along the west coast of tropical South America, and at subtropical latitudes of North America (Gulf Coast) and South America (southern Brazil to central Argentina) during their respective winter seasons.
Mid-latitude low pressure systems tend to be weaker than normal in the region of the Gulf of Alaska, during a cold episode winter. This favors the build-up of colder than normal air over Alaska and western Canada, which often penetrates into the northern Great Plains and the western United States. The southeastern United States, on the other hand, becomes warmer and drier than normal.
So far La nina increases the formation of convection that resulted to a more enhanced formation of tropical cyclone over Western Pacific. Generally this effect begins over October and runs til December. Possibly though it is early to tell, 2008 will be an active tropical cyclone year over Western Pacific as like what happens over 1999-2000.
: Can you enumerate what are the
: characteristics of a La Nina Phenomenon,and
: what are its possibel impacts on our
: country?
:
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