Western Hemisphere Warm Pool
Encyclopedia
The Western Hemisphere Warm Pool (WHWP) is a region of sea surface temperature
s (SST) warmer than 28.5°C that develops west of Central America
in the spring, then expands to the tropical
waters to the east.
The WHWP includes the tropical Atlantic Ocean
(TNA) east of the Lesser Antilles
, Caribbean Sea
, Gulf of Mexico
, and eastern north Pacific Ocean
(ENP).
A WHWP heating cycle begins with warmth in the eastern North Pacific in the spring. A dipole pattern off Central America appears due to surges of cooler, drier air through the gap at the Isthmus of Tehuantepec
. During spring, the warm pools grow and merge. Their warmth and moisture feed the Mexican monsoon. By summer, the warmth spreads across the Gulf of Mexico and Caribbean areas.
drives a Hadley cell
with descending air over an anticyclone north of 20°N in the subtropical North Atlantic and associated northeast trade wind
s between Africa and the Caribbean. An El Niño weakens the Amazonian cell, the anticyclone and the easterly tradewinds, causing the tropical North Atlantic to warm more than usual in the spring. About half of El Niño events persist sufficiently into the spring months for the warm pool to become unusually large by summer.
Sea surface temperature
Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...
s (SST) warmer than 28.5°C that develops west of Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
in the spring, then expands to the tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
waters to the east.
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
(TNA) east of the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
, Caribbean Sea
Caribbean Sea
The Caribbean Sea is a sea of the Atlantic Ocean located in the tropics of the Western hemisphere. It is bounded by Mexico and Central America to the west and southwest, to the north by the Greater Antilles, and to the east by the Lesser Antilles....
, Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
, and eastern north Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
(ENP).
A WHWP heating cycle begins with warmth in the eastern North Pacific in the spring. A dipole pattern off Central America appears due to surges of cooler, drier air through the gap at the Isthmus of Tehuantepec
Isthmus of Tehuantepec
The Isthmus of Tehuantepec is an isthmus in Mexico. It represents the shortest distance between the Gulf of Mexico and the Pacific Ocean, and prior to the opening of the Panama Canal was a major shipping route known simply as the Tehuantepec Route...
. During spring, the warm pools grow and merge. Their warmth and moisture feed the Mexican monsoon. By summer, the warmth spreads across the Gulf of Mexico and Caribbean areas.
Relationship with Atlantic Hurricanes
Recent studies have shown that the Atlantic portion of the WHWP (AWP) is significantly correlated with Atlantic hurricane activity. A large (or small) AWP reduces (or increases) the tropospheric vertical wind shear in the main development region for Atlantic hurricanes and increases (or decreases) the moist static instability of the troposphere, both of which favor (or don't favor) the intensification of tropical storms into major hurricanes.Relationship with El Niño
A study of climate records has shown a relationship between El Niño and the Western Hemisphere Warm Pool (WHWP). During a normal Northern Hemisphere winter, diabatic heating over the AmazonAmazon Basin
The Amazon Basin is the part of South America drained by the Amazon River and its tributaries that drains an area of about , or roughly 40 percent of South America. The basin is located in the countries of Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela...
drives a Hadley cell
Hadley cell
The Hadley cell, named after George Hadley, is a circulation pattern that dominates the tropical atmosphere, with rising motion near the equator, poleward flow 10–15 kilometers above the surface, descending motion in the subtropics, and equatorward flow near the surface...
with descending air over an anticyclone north of 20°N in the subtropical North Atlantic and associated northeast trade wind
Trade wind
The trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator...
s between Africa and the Caribbean. An El Niño weakens the Amazonian cell, the anticyclone and the easterly tradewinds, causing the tropical North Atlantic to warm more than usual in the spring. About half of El Niño events persist sufficiently into the spring months for the warm pool to become unusually large by summer.
Climate events in area
- 1200-1100 B.P.Before PresentBefore Present years is a time scale used in archaeology, geology, and other scientific disciplines to specify when events in the past occurred. Because the "present" time changes, standard practice is to use AD 1950 as the origin of the age scale, reflecting the fact that radiocarbon...
(A.D.Anno Dominiand Before Christ are designations used to label or number years used with the Julian and Gregorian calendars....
800800Year 800 was a leap year starting on Wednesday of the Julian calendar. It was around this time that the Anno Domini calendar era became the prevalent method in Europe for naming years, so from this time on, the years began being known as 800 and onwards.- Europe :* December 25 - Pope Leo III...
-900900Year 900 was a leap year starting on Tuesday of the Julian calendar.- Asia :* April 21 – Namwaran and his children, Lady Angkatan and Bukah, are granted pardon by the Datu of Tondo, as represented Jayadewa, Lord Minister of Pila, which released them of all their debts as inscribed in the...
): Collapse of Classical Maya civilizationMaya civilizationThe Maya is a Mesoamerican civilization, noted for the only known fully developed written language of the pre-Columbian Americas, as well as for its art, architecture, and mathematical and astronomical systems. Initially established during the Pre-Classic period The Maya is a Mesoamerican...
due to drought. Yucatán PeninsulaYucatán PeninsulaThe Yucatán Peninsula, in southeastern Mexico, separates the Caribbean Sea from the Gulf of Mexico, with the northern coastline on the Yucatán Channel...
in present-day MexicoMexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
. - August 29, 2005 AD: Hurricane KatrinaHurricane KatrinaHurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...
. New Orleans, MississippiMississippiMississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...
and Gulf Coast region.
