Tropical waves, or easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of cloudiness and thunderstorms. West-moving waves can also form from the tail end of frontal zones in the subtropics and tropics and may be referred to as easterly waves, but these waves are not properly called tropical waves; they are a form of inverted trough sharing many characteristics with fully tropical waves. An inverted trough is an atmospheric trough which is oriented opposite to most troughs of the mid-latitudes All tropical waves form in the easterly flow along the southern side of the subtropical ridge or belt of high pressure which lies north and south of the Intertropical Convergence Zone (ITCZ). The Intertropical Convergence Zone (ITCZ, also known as the Intertropical Front, Monsoon trough, Doldrums or the Equatorial Tropical waves are generally carried westward by the prevailing easterly winds along the tropics and subtropics near the equator. The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 The subtropics are the zones of the Earth immediately north and south of the tropic zone which is bounded by the Tropic of Cancer and the Tropic of They can lead to the formation of tropical cyclones in the north Atlantic and northeast Pacific basins.

Contents 1 Characteristics 2 Atlantic 3 East Pacific 4 See also 5 References 6 External links

Characteristics

A tropical wave is normally preceded by an area of sinking, intensely dry air, oriented as a northeast wind. With the passage of the trough line, the wind veers to the southeast, the humidity abruptly rises, and the atmosphere destabilizes, producing widespread showers and thunderstorms, occasionally severe. As the wave moves off westward, the showers gradually diminish.

A notable exception to the general characteristic of widespread precipitation behind a tropical wave occurs in the Atlantic. Periodically, a surge of intensely dry air known as the Saharan Air Layer (SAL) is entrained behind a tropical wave, resulting in cloudless or nearly cloudless skies as convection is capped by the dry layer inversion. The Saharan Air Layer (SAL is an intensely dry warm and sometimes Dust -laden layer of the Atmosphere which often overlies the cooler more-humid surface air of the Additionally, any dust which may be present within the SAL reflects solar radiation, slightly cooling the atmosphere below it.

Atlantic

Tropical waves in the Atlantic basin develop from disturbances which drift off the continent of Africa onto the Atlantic ocean. These are generated or enhanced by the African Easterly Jet. The African easterly jet is a region of the lower troposphere over West Africa where the seasonal mean wind speed is maximum and easterly The clockwise circulation of the large transoceanic high-pressure cell or anticyclone centered near the Azores islands impels easterly waves away from the coastal areas of Africa towards North America. A high pressure area (also called a high or high-pressure is a region where the Atmospheric pressure is greater than surrounding areas In Meteorology, an anticyclone (that is opposite to a Cyclone) is a Weather phenomenon in which there is a descending movement of the air and The Azores ( Açores ɐˈsoɾɨʃ or) is a Portuguese Archipelago in the Atlantic Ocean, about 1500 km (950  mi) from

Approximately 60% of Atlantic tropical cyclones originate from tropical waves, while approximately 85% of intense Atlantic hurricanes (Category 3 and greater) develop from tropical waves. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding The Saffir-Simpson Hurricane Scale is a classification used for most Western Hemisphere Tropical cyclones that exceed the intensities of Tropical depressions ^[1][2]

Tropical cyclones can sometimes degenerate back into a tropical wave. This normally occurs if upper-level wind shear is too strong. Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively The storm can redevelop if the upper level shear abates.

If a tropical wave is moving quickly, it can have strong winds of over tropical storm force, but is not considered a tropical storm unless it has a closed circulation. An example of this was Hurricane Claudette in 2003, where the original wave had winds of 45 mph (72 km/h) before developing a circulation. Hurricane Claudette was the third Tropical storm and first Hurricane of the 2003 Atlantic hurricane season.

East Pacific

It has been suggested that eastern Pacific Ocean tropical cyclones are formed out of tropical waves that originate in North Africa as well. The Pacific Ocean is the largest of the Earth 's Oceanic divisions North Africa or Northern Africa is the Northernmost Region of the African Continent, separated by the Sahara from Sub-Saharan ^[1] During the summer months, tropical waves can extend northward as far as the desert southwest of the United States, producing spells of intensified shower activity embedded within the prevailing monsoon regime. A monsoon is a seasonal prevailing wind which lasts for several months

See also

• Tropical cyclone
• Tropical cyclogenesis

References

External links

• Tropical Waves Presentation
• African Easterly Wave Variability and Its Relationship to Atlantic Tropical Cyclone Activity

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