Radius of outermost closed isobar

Last updated
Size descriptions of tropical cyclones
ROCI Type
Less than 2 degrees latitude Very small/midget
2 to 3 degrees of latitude Small
3 to 6 degrees of latitude Medium/Average
6 to 8 degrees of latitude Large
Over 8 degrees of latitude Very large [1]

The radius of outermost closed isobar (ROCI) is one of the quantities used to determine the size of a tropical cyclone. It is determined by measuring the radii from the center of the storm to its outermost closed isobar in four quadrants, which is then averaged to come up with a scalar value. It generally delimits the outermost extent of a tropical cyclone's wind circulation. [2]

Tropical cyclone Is a rotating storm system

A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. A hurricane is a tropical cyclone that occurs in the Atlantic Ocean and northeastern Pacific Ocean, and a typhoon occurs in the northwestern Pacific Ocean; in the south Pacific or Indian Ocean, comparable storms are referred to simply as "tropical cyclones" or "severe cyclonic storms".

A scalar or scalar quantity in physics is a physical quantity that can be described by a single element of a number field such as a real number, often accompanied by units of measurement. A scalar is usually said to be a physical quantity that only has magnitude and no other characteristics. This is in contrast to vectors, tensors, etc. which are described by several numbers that characterize their magnitude, direction, and so on.

Contents

Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with North Atlantic tropical cyclones roughly half their size. [3] Active databases of ROCI are maintained by the National Hurricane Center for systems tracked in the eastern north Pacific and north Atlantic basins.

An active database is a database that includes an event-driven architecture which can respond to conditions both inside and outside the database. Possible uses include security monitoring, alerting, statistics gathering and authorization.

National Hurricane Center division of the United States National Weather Service

The National Hurricane Center (NHC) is the division of the United States' National Weather Service responsible for tracking and predicting tropical weather systems between the Prime Meridian and the 140th meridian west poleward to the 30th parallel north in the northeast Pacific Ocean and the 31st parallel north in the northern Atlantic Ocean. The agency, which is co-located with the Miami branch of the National Weather Service, is situated on the campus of Florida International University in University Park, Florida.

Database

Hurricane Sandy at peak intensity. Sandy Oct 25 2012 0400Z.JPG
Hurricane Sandy at peak intensity.

Active databases of ROCI are maintained by the National Hurricane Center for systems tracked in the eastern north Pacific and north Atlantic basins, within a database known as the Extended Best Track Database. The values are determined in real-time every six hours. The eastern north Pacific database runs from 2001 to present, while the north Atlantic database runs from 1988 to present. [4] Other than these official databases, a global once-daily dataset was compiled for a 1984 research paper, which covered global tropical cyclones between 1957 and 1977. [3] Previously, a database was created to determine ROCI values for the western north Pacific Ocean in 1972, using data from 1945 to 1968. [5] Another database with additional ROCI information is currently being modified at the Hydrometeorological Prediction Center for use in matching ongoing tropical cyclones to past systems for the purposes of finding rainfall analogs to an ongoing event, [6] which has fairly continuous data running back to 1959 for the north Atlantic ocean. [7]

Variation

Tropical cyclones tend to be smaller during the mid-summer, and largest in October in the Northern Hemisphere. As tropical cyclones initially develop, the size of their ROCI initially contracts. [8] Once tropical cyclones reach maturity, their isobaric patterns increase in size. During the mature stage, the broadening pressure pattern leads to some reduction in their maximum sustained wind, but the extent of their tropical storm and hurricane-force winds is the most extensive within the storm's life cycle. [9] An increase in size is also noted as a tropical cyclone gains latitude. [8] As tropical cyclones weaken, their ROCI values diminish. In general, the size of a tropical cyclone shows little relation to its intensity. Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with North Atlantic tropical cyclones roughly half their size. [3]

Northern Hemisphere half of Earth that is north of the equator

The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North Pole.

The maximum sustained wind associated with a tropical cyclone is a common indicator of the intensity of the storm. Within a mature tropical cyclone, it is found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Wind measuring has been standardized globally to reflect the winds at 10 metres (33 ft) above the Earth's surface, and the maximum sustained wind represents the highest average wind over either a one-minute (US) or ten-minute time span, anywhere within the tropical cyclone. Surface winds are highly variable due to friction between the atmosphere and the Earth's surface, as well as near hills and mountains over land.

See also

Related Research Articles

1962 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1962 Atlantic hurricane season was the least active since 1939, with only five named storms. Although the season officially began on June 15, the first storm did not form until August 26. Hurricane Alma brushed the Outer Banks before becoming extratropical southeast of New England, destroying hundreds of boats and producing beneficial rainfall. In late August, Tropical Storm Becky developed unusually far east in the Atlantic Ocean, becoming the easternmost storm on record to recurve to the northeast. Celia followed in the September, forming east of the Lesser Antilles and executing a loop near Bermuda before dissipating. Hurricane Daisy was the costliest of the season, leaving about $1.1 million in damage in New England (1962 USD). The storm dropped the highest rainfall total on record in Maine, and its precipitation caused 22 traffic fatalities. The final hurricane – Ella – was also the strongest, remaining offshore of the eastern United States but causing two deaths.

1971 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1971 Atlantic hurricane season was fairly active with several notable storms. Hurricane Edith, the strongest of the season, was a Category 5 on the Saffir-Simpson scale, the highest category on the scale. It struck Nicaragua at peak intensity, killing dozens, and later hit southern Louisiana. Until 2003, Hurricane Ginger held the record for the longest known duration of a North Atlantic tropical cyclone, lasting 27.25 days from early September to early October; it is currently the second longest-lasting Atlantic hurricane. Ginger moved ashore in North Carolina, producing heavy rains and damaging winds. An unnamed storm in August attained hurricane status further north than any other Atlantic hurricane. Between 11 and 12 September five tropical cyclones were active at the same time, the record for the Atlantic basin.

1973 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1973 Atlantic hurricane season was the first season to use the Saffir–Simpson hurricane scale, a scale developed in 1971 by Herbert Saffir and Robert Simpson to rate the intensity of tropical cyclones. The season produced 24 tropical and subtropical cyclones, of which only 8 reached storm intensity, 4 became hurricanes, and only 1 reached major hurricane status. Although more active than the 1972 season, 1973 brought few storms of note. Nearly half of the season's storms affected land, one of which resulted in severe damage.

1982 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 1982 Atlantic hurricane season officially began on June 1, 1982, and lasted until November 30, 1982, and was a well below average season. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. Only six storms formed during this hurricane season: five named storms and an unnamed subtropical storm. The season only produced two hurricanes one of which reached major hurricane status. The season started early with Hurricane Alberto forming on the first day of the season. Alberto threatened the Southwestern Florida coast as a tropical storm, causing twenty-three fatalities in Cuba. The next storm, a subtropical storm, formed in June and affected the same area as Alberto, causing $10 million in damage.

2000 Pacific hurricane season hurricane season in the Pacific Ocean

The 2000 Pacific hurricane season was an above-average Pacific hurricane season, although most of the storms were weak and short-lived. There were few notable storms this year. Tropical Storms Miriam, Norman, and Rosa all made landfall in Mexico with minimal impact. Hurricane Daniel briefly threatened the U.S. state of Hawaii while weakening. Hurricane Carlotta was the strongest storm of the year and the second-strongest June hurricane in recorded history. Carlotta killed 18 people when it sank a freighter. Overall, the season was significantly more active than the previous season, with 19 tropical storms. In addition, six hurricanes developed. Furthermore, there were total of two major hurricanes, Category 3 or greater on the Saffir–Simpson hurricane wind scale.

1998 Pacific hurricane season Summary of the relevant tropical storms

The 1998 Pacific hurricane season was a below average Pacific hurricane season. It had six major hurricanes, which was well above average. The season officially started on May 15 in the eastern Pacific and on June 1 in the central Pacific, and ended on November 30; these dates conventionally delimit the period during which most tropical cyclones form in that region. The first tropical cyclone developed on June 11, about ten days later than the normal start of the season. The final storm of the year, Hurricane Madeline, dissipated on October 20. Storm activity in the Central Pacific Hurricane Center's warning zone was low, with just one tropical depression observed in the region. Two tropical cyclones from the eastern Pacific also entered the central Pacific; the former did so as a hurricane.

Atlantic hurricane season tropical cyclone season

The Atlantic hurricane season is the period in a year when hurricanes usually form in the Atlantic Ocean. Tropical cyclones in the North Atlantic are called hurricanes, tropical storms, or tropical depressions. In addition, there have been several storms over the years that have not been fully tropical and are categorized as subtropical depressions and subtropical storms. Even though subtropical storms and subtropical depressions are not technically as strong as tropical cyclones, the damages can still be devastating.

Pacific hurricane mature tropical cyclone that develops within the eastern and central Pacific Ocean

A Pacific hurricane is a mature tropical cyclone that develops within the eastern and central Pacific Ocean to the east of 180°W, north of the equator. For tropical cyclone warning purposes, the northern Pacific is divided into three regions: the eastern, central, and western, while the southern Pacific is divided into 2 sections, the Australian region and the southern Pacific basin between 160°E and 120°W. Identical phenomena in the western north Pacific are called typhoons. This separation between the two basins has a practical convenience, however, as tropical cyclones rarely form in the central north Pacific due to high vertical wind shear, and few cross the dateline.

A tropical cyclone rainfall climatology is developed to determine rainfall characteristics of past tropical cyclones. A tropical cyclone rainfall climatology can be used to help forecast current or upcoming tropical cyclone impacts. The degree of a tropical cyclone rainfall impact depends upon speed of movement, storm size, and degree of vertical wind shear. One of the most significant threats from tropical cyclones is heavy rainfall. Large, slow moving, and non-sheared tropical cyclones produce the heaviest rains. The intensity of a tropical cyclone appears to have little bearing on its potential for rainfall over land, but satellite measurements over the last several years show that more intense tropical cyclones produce noticeably more rainfall over water. Flooding from tropical cyclones remains a significant cause of fatalities, particularly in low-lying areas.

United States tropical cyclone rainfall climatology

The United States tropical cyclone rainfall climatology concerns the amount of precipitation, primarily in the form of rain, which occurs during tropical cyclones and their extratropical cyclone remnants across the United States. Typically, five tropical cyclones and their remnants impact the country each year, contributing between a tenth and a quarter of the annual rainfall across the southern tier of the country. The highest rainfall amounts appear close to the coast, with lesser amounts falling farther inland. Obstructions to the precipitation pattern, such as the Appalachian mountains, focus higher amounts from northern Georgia through New England. While most impacts occur with systems moving in from the Atlantic ocean or Gulf of Mexico, some emanate from the eastern Pacific ocean, with a few crossing Mexico before impacting the Southwest. Those making landfall within the Southeast portion of the country tend to have the greatest potential for heavy rains.

Mexico tropical cyclone rainfall climatology

Mexico tropical cyclone rainfall climatology discusses precipitation characteristics of tropical cyclones that have struck Mexico over the years. One-third of the annual rainfall received along the Mexican Riviera and up to half of the rainfall received in Baja California Sur is directly attributable to tropical cyclones moving up the west coast of Mexico. The central plateau is shielded from the high rainfall amounts seen on the oceanward slopes of the Sierra Madre Oriental and Occidental mountain chains.

2009 Atlantic hurricane season hurricane season in the Atlantic Ocean

The 2009 Atlantic hurricane season was a below-average Atlantic hurricane season that produced eleven tropical cyclones, nine named storms, three hurricanes, and two major hurricanes. It officially began on June 1 and ended on November 30, dates that conventionally delimit the period of each year when most tropical cyclones develop in the Atlantic basin. The season's first tropical cyclone, Tropical Depression One, developed on May 28, while the final storm, Hurricane Ida, dissipated on November 10. The most intense hurricane, Bill, was a powerful Cape Verde-type hurricane that affected areas from the Leeward Islands to Newfoundland. The season featured the lowest number of tropical cyclones since the 1997 season, and only one system, Claudette, made landfall in the United States. Forming from the interaction of a tropical wave and an upper level low, Claudette made landfall on the Florida Panhandle with maximum sustained winds of 45 mph (75 km/h) before quickly dissipating over Alabama. The storm killed two people and caused $228,000 in damage.

Glossary of tropical cyclone terms

The following is a glossary of tropical cyclone terms.

References

  1. Joint Typhoon Warning Center. Q: What is the average size of a tropical cyclone? United States Navy. Retrieved on 2007-07-04.
  2. FRÉDÉRIC MOUTON and OLA NORDBECK. Cyclone Database Manager. Archived 2011-07-18 at the Wayback Machine . Retrieved on 2008-07-14.
  3. 1 2 3 Robert T. Merrill. A Comparison of Large and Small Tropical Cyclones. Retrieved on 2008-07-14.
  4. Mark DeMaria (2009). Atlantic Extended Best Track Database. Colorado State University. Retrieved on 2009-06-14.
  5. K. S. Liu and Johnny C. L. Chan. Size of Tropical Cyclones as Inferred from ERS-1 and ERS-2 Data. Retrieved on 2008-07-14.
  6. David M. Roth and Kyle S. Griffin (2009-06-07). Cliqr Rainfall Analog. Hydrometeorological Prediction Center. Retrieved on 2009-06-14.
  7. David M. Roth (2013). "CLIQR Database". Hydrometeorological Prediction Center . Retrieved 2013-01-04.
  8. 1 2 Edward Morgan Brooks (1945). An Analysis of an Unusual Rainfall Distribution in a Hurricane. Archived 2015-04-03 at the Wayback Machine . Massachusetts Institute of Technology. Retrieved on 2008-12-31.
  9. Gordon E. Dunn and Banner I. Miller (1960). Atlantic Hurricanes. Louisiana State University Press. p. 32. ASIN   B0006BM85S.