Loop Current
Encyclopedia
A parent to the Florida Current
, the Loop Current is a warm ocean current in the Gulf of Mexico
that flows northward between Cuba
and the Yucatán
peninsula, moves north into the Gulf of Mexico, loops east and south before exiting to the east through the Florida Straits
and joining the Gulf Stream
.
A related feature is an area of warm water called an "Eddy
" or "Loop Current ring" that separates from the Loop Current, somewhat randomly. These rings then drift to the west at speeds of about 5 cm/s (0.18 km/h or 0.11 mph) and bump into the coast of Texas
or Mexico
.
Around 1970, it was believed that the Loop Current exhibited an annual cycle in which the Loop feature extended farther to the north during the summer. Further study over the past few decades, however, has shown that the extension to the north (and the shedding of eddies) does not have a significant annual cycle.
The Loop Current and its eddies may be detected by measuring sea surface level. Sea surface level of both the Eddies and the Loop on September 21, 2005 was up to 60 cm
(24 in) higher than surrounding water, indicating a deep area of warm water beneath them. On that day, Hurricane Rita
passed over the Loop current and intensified into a Category 5 storm with the help of the warm water.
In the Gulf of Mexico, the deepest areas of warm water are associated with the Loop Current and the rings of current that have separated from the Loop Current are commonly called Loop Current eddies. The warm waters of the Loop Current and its associated eddies provide more energy to hurricanes and allow them to intensify.
The turbulent environment of hurricanes pulls up water from beneath the surface, often upwelling cooler water. Stronger hurricanes upwell deeper water. If the water in the lower levels is significantly cooler, the water will limit the hurricane's ability to strengthen, and may even cause it to weaken. But if the water is still warm at lower depths, then water being pulled to the surface remains warm, and the hurricane can increase in intensity if other atmospheric conditions are also conducive to strengthening. Meteorologists look for areas of deep warm water of at least 26 degrees Celsius (79°F). A continuous supply of warm water is one of several critical factors in enabling hurricanes to intensify beyond the initial level of a major hurricane (Category 3).
An example of how deep warm water, including the Loop Current, can allow a hurricane to strengthen, if other conditions are also favorable, is Hurricane Camille
, which made landfall on the Mississippi Gulf Coast
in August 1969. Camille formed in the deep warm waters of the Caribbean, which enabled it to rapidly intensify into a Category 3 hurricane in one day. It rounded the western tip of Cuba, and its path took it directly over the Loop Current, all the way north towards the coast, during which time the rapid intensification continued. Camille became a Category 5 hurricane, with an intensity rarely seen, and extremely high winds that were maintained until landfall (190 mph / 305 km/h sustained winds were estimated to have occurred in a very small area to the right of the eye).
In 1980, Hurricane Allen
strengthened to a Category 5 hurricane while moving over the Loop Current, but it weakened before landfall in Texas
.
In 2005, Hurricane Katrina
and Hurricane Rita
both greatly increased in strength when they passed over the warmer waters of the Loop Current. Hurricane Wilma
of 2005 was expected to make its Florida landfall as a Category 2 hurricane, but after encountering the southeastern portion of the Loop Current, it reached the Florida coast as a Category 3 instead. http://www.weather.gov/storms/wilma/wilma_trak_lg.jpg
In 2008, Hurricane Gustav
transited the Loop Current, but due to the current's temperature (then only in the high 80's-degrees-F) and truncated size (extending only halfway from Cuba to Louisiana, with cooler water in-between its tip and the Louisiana coast) the storm remained a Category 3 hurricane instead of increasing strength as it passed over the current.
Hurricane Opal
crossed a Loop Current eddy and went from a Category 1 to a Category 4 in 14 hours. Hurricane Ivan
rode the Loop Current twice in 2004.
(ERC) occurring at that time. The ERC and other atmospheric factors are why Rita did not reintensify when subsequently passing over the Eddy Vortex.
Also of note: tropical depressions, tropical storms, and hurricanes gain strength from, but are not steered by, the temperature of the water. They are steered by the atmosphere, and the atmospheric level involved in steering a hurricane is different at different intensities (i.e., it relates to the minimum pressure of the hurricane).
Kevin E. Trenberth
of the National Center for Atmospheric Research
, with others, wrote "It should be recognized that the issue is not black or white, but rather that global warming has a pervasive influence on ocean SST [sea surface temperature] and heat content, atmospheric temperature, water vapor, and atmospheric and oceanic general circulation patterns, all of which affect tropical cyclones in complex, not yet fully understood ways." and "in our view the growing body of evidence suggests a direct and growing trend in several important aspects of tropical cyclones, such as intensity, rainfall, and sea level[a proxy for sea temperature] , all of which can be attributed to global warming."
and thus (all other factors, such as water depth, being equal) a vertical column of water will rise slightly higher when warmed. Thus sea level is often used as a proxy for deep sea temperatures.
NOAA
's National Data Buoy Center
maintains a large number of data buoys in the Gulf of Mexico, some of which measure sea temperature one meter below the surface.
Florida Current
The Florida Current is a thermal ocean current that flows generally from the Gulf of Mexico to the Atlantic Ocean. The current was discovered by Spanish explorer Juan Ponce de León in 1513....
, the Loop Current is a warm ocean current in the 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...
that flows northward between Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...
and the Yucatán
Yucatán
Yucatán officially Estado Libre y Soberano de Yucatán is one of the 31 states which, with the Federal District, comprise the 32 Federal Entities of Mexico. It is divided in 106 municipalities and its capital city is Mérida....
peninsula, moves north into the Gulf of Mexico, loops east and south before exiting to the east through the Florida Straits
Straits of Florida
The Straits of Florida, Florida Straits, or Florida Strait is a strait located south-southeast of the North American mainland, generally accepted to be between the Gulf of Mexico and the Atlantic Ocean, and between the Florida Keys and Cuba. The strait carries the Florida Current, the beginning of...
and joining the Gulf Stream
Gulf Stream
The Gulf Stream, together with its northern extension towards Europe, the North Atlantic Drift, is a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean...
.
A related feature is an area of warm water called an "Eddy
Eddy (fluid dynamics)
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
" or "Loop Current ring" that separates from the Loop Current, somewhat randomly. These rings then drift to the west at speeds of about 5 cm/s (0.18 km/h or 0.11 mph) and bump into the coast of Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
or Mexico
Mexico
The 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...
.
Around 1970, it was believed that the Loop Current exhibited an annual cycle in which the Loop feature extended farther to the north during the summer. Further study over the past few decades, however, has shown that the extension to the north (and the shedding of eddies) does not have a significant annual cycle.
The Loop Current and its eddies may be detected by measuring sea surface level. Sea surface level of both the Eddies and the Loop on September 21, 2005 was up to 60 cm
Centimetre
A centimetre is a unit of length in the metric system, equal to one hundredth of a metre, which is the SI base unit of length. Centi is the SI prefix for a factor of . Hence a centimetre can be written as or — meaning or respectively...
(24 in) higher than surrounding water, indicating a deep area of warm water beneath them. On that day, Hurricane Rita
Hurricane Rita
Hurricane Rita was the fourth-most intense Atlantic hurricane ever recorded and the most intense tropical cyclone ever observed in the Gulf of Mexico. Rita caused $11.3 billion in damage on the U.S. Gulf Coast in September 2005...
passed over the Loop current and intensified into a Category 5 storm with the help of the warm water.
In the Gulf of Mexico, the deepest areas of warm water are associated with the Loop Current and the rings of current that have separated from the Loop Current are commonly called Loop Current eddies. The warm waters of the Loop Current and its associated eddies provide more energy to hurricanes and allow them to intensify.
The turbulent environment of hurricanes pulls up water from beneath the surface, often upwelling cooler water. Stronger hurricanes upwell deeper water. If the water in the lower levels is significantly cooler, the water will limit the hurricane's ability to strengthen, and may even cause it to weaken. But if the water is still warm at lower depths, then water being pulled to the surface remains warm, and the hurricane can increase in intensity if other atmospheric conditions are also conducive to strengthening. Meteorologists look for areas of deep warm water of at least 26 degrees Celsius (79°F). A continuous supply of warm water is one of several critical factors in enabling hurricanes to intensify beyond the initial level of a major hurricane (Category 3).
An example of how deep warm water, including the Loop Current, can allow a hurricane to strengthen, if other conditions are also favorable, is Hurricane Camille
Hurricane Camille
Hurricane Camille was the third and strongest tropical cyclone and second hurricane during the 1969 Atlantic hurricane season. The second of three catastrophic Category 5 hurricanes to make landfall in the United States during the 20th century , which it did near the mouth of the Mississippi River...
, which made landfall on the Mississippi Gulf Coast
Mississippi Gulf Coast
The Mississippi Gulf Coast refers to the three Mississippi counties which lie on the Gulf of Mexico: Hancock, Harrison and Jackson counties.The region was severely damaged by Hurricane Camille in 1969 and again by Hurricane Katrina in 2005....
in August 1969. Camille formed in the deep warm waters of the Caribbean, which enabled it to rapidly intensify into a Category 3 hurricane in one day. It rounded the western tip of Cuba, and its path took it directly over the Loop Current, all the way north towards the coast, during which time the rapid intensification continued. Camille became a Category 5 hurricane, with an intensity rarely seen, and extremely high winds that were maintained until landfall (190 mph / 305 km/h sustained winds were estimated to have occurred in a very small area to the right of the eye).
In 1980, Hurricane Allen
Hurricane Allen
Hurricane Allen was the first and strongest hurricane of the 1980 Atlantic hurricane season. It was one of the strongest hurricanes in recorded history, one of the few hurricanes to reach Category 5 status on the Saffir-Simpson Hurricane Scale on three separate occasions, and spent more time...
strengthened to a Category 5 hurricane while moving over the Loop Current, but it weakened before landfall in Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
.
In 2005, Hurricane Katrina
Hurricane Katrina
Hurricane 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...
and Hurricane Rita
Hurricane Rita
Hurricane Rita was the fourth-most intense Atlantic hurricane ever recorded and the most intense tropical cyclone ever observed in the Gulf of Mexico. Rita caused $11.3 billion in damage on the U.S. Gulf Coast in September 2005...
both greatly increased in strength when they passed over the warmer waters of the Loop Current. Hurricane Wilma
Hurricane Wilma
Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second storm , thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane of the record-breaking 2005 season...
of 2005 was expected to make its Florida landfall as a Category 2 hurricane, but after encountering the southeastern portion of the Loop Current, it reached the Florida coast as a Category 3 instead. http://www.weather.gov/storms/wilma/wilma_trak_lg.jpg
In 2008, Hurricane Gustav
Hurricane Gustav
The name Gustav has been used for five tropical cyclones in the Atlantic Ocean:* 1984's Tropical Storm Gustav - Spent most of its existence as a tropical depression hovering over Bermuda, no major damage was reported....
transited the Loop Current, but due to the current's temperature (then only in the high 80's-degrees-F) and truncated size (extending only halfway from Cuba to Louisiana, with cooler water in-between its tip and the Louisiana coast) the storm remained a Category 3 hurricane instead of increasing strength as it passed over the current.
Hurricane Opal
Hurricane Opal
Hurricane Opal was a Category 4 hurricane that formed in the Gulf of Mexico in September 1995.Opal was the ninth hurricane and the strongest of the abnormally active 1995 Atlantic hurricane season...
crossed a Loop Current eddy and went from a Category 1 to a Category 4 in 14 hours. Hurricane Ivan
Hurricane Ivan
Hurricane Ivan was a large, long-lived, Cape Verde-type hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlantic hurricane season...
rode the Loop Current twice in 2004.
Process
The process by which a hurricane increases in intensity is complex and not completely understood and consequently, difficult to predict. Passage over the Loop Current or the Eddy Vortex does not guarantee strengthening. Once Hurricane Rita left the Loop Current and passed over cooler water, it declined in strength, but the main factor in this weakening was an eyewall replacement cycleEyewall replacement cycle
Eyewall replacement cycles, also called concentric eyewall cycles, naturally occur in intense tropical cyclones, generally with winds greater than 185 km/h , or major hurricanes...
(ERC) occurring at that time. The ERC and other atmospheric factors are why Rita did not reintensify when subsequently passing over the Eddy Vortex.
Also of note: tropical depressions, tropical storms, and hurricanes gain strength from, but are not steered by, the temperature of the water. They are steered by the atmosphere, and the atmospheric level involved in steering a hurricane is different at different intensities (i.e., it relates to the minimum pressure of the hurricane).
Hurricanes and global warming
Although hurricanes do increase in strength over warmer water, it has not been shown that the Loop Current specifically has been significantly warmer than in the past.Kevin E. Trenberth
Kevin E. Trenberth
Kevin E. Trenberth is head of the Climate Analysis Section at the USA National Center for Atmospheric Research. He was a lead author of the 2001 and 2007 IPCC Scientific Assessment of Climate Change and serves on the Scientific Steering Group for the Climate Variability and Predictability program...
of the National Center for Atmospheric Research
National Center for Atmospheric Research
The National Center for Atmospheric Research has multiple facilities, including the I. M. Pei-designed Mesa Laboratory headquarters in Boulder, Colorado. NCAR is managed by the nonprofit University Corporation for Atmospheric Research and sponsored by the National Science Foundation...
, with others, wrote "It should be recognized that the issue is not black or white, but rather that global warming has a pervasive influence on ocean SST [sea surface temperature] and heat content, atmospheric temperature, water vapor, and atmospheric and oceanic general circulation patterns, all of which affect tropical cyclones in complex, not yet fully understood ways." and "in our view the growing body of evidence suggests a direct and growing trend in several important aspects of tropical cyclones, such as intensity, rainfall, and sea level
Sea level and sea temperature
Sea level is relatively easy to measure accurately using radars from satellites. Sea temperature below the surface is not as easy to measure widely, but can be inferred from the sea level since warmer water expandsThermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
and thus (all other factors, such as water depth, being equal) a vertical column of water will rise slightly higher when warmed. Thus sea level is often used as a proxy for deep sea temperatures.
NOAA
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
's National Data Buoy Center
National Data Buoy Center
The National Data Buoy Center is a part of the National Oceanic and Atmospheric Administration's National Weather Service...
maintains a large number of data buoys in the Gulf of Mexico, some of which measure sea temperature one meter below the surface.
External links
- Near Real-Time Gulf of Mexico Satellite Altimetry Data
- Ocean Surface Currents explains The Loop Current
- LSU's Earth Scan Laboratory
- National Data Buoy Center (see data buoy #42003)
- Hurricane Rita Roars through a Warm Gulf
- CU-Boulder Researchers Chart Katrina's Growth In Gulf Of Mexico
- "Global Warming: The Culprit?" (Time Magazine, October 3, 2005, pages 42–46) - Loop Current mentioned
- ScienceDaily on Loop Current and hurricanes
- Chart of the mechanisms inside the Loop Current
- Atlantic Oceanographic and Meteorological Laboratory
