Dvorak technique

The Dvorak technique (developed between 1969 and 1984 by Vernon Dvorak) is a widely used system to estimate tropical cyclone intensity (which includes tropical depression, tropical storm, and hurricane/typhoon/intense tropical cyclone intensities) based solely on visible and infrared satellite images. Within the Dvorak satellite strength estimate for tropical cyclones, there are several visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The primary patterns used are curved band pattern (T1.0-T4.5), shear pattern (T1.5–T3.5), central dense overcast (CDO) pattern (T2.5–T5.0), central cold cover (CCC) pattern, banding eye pattern (T4.0–T4.5), and eye pattern (T4.5–T8.0).

Both the central dense overcast and embedded eye pattern use the size of the CDO. The CDO pattern intensities start at T2.5, equivalent to minimal tropical storm intensity (40 mph, 65 km/h). The shape of the central dense overcast is also considered. The eye pattern utilizes the coldness of the cloud tops within the surrounding mass of thunderstorms and contrasts it with the temperature within the eye itself. The larger the temperature difference is, the stronger the tropical cyclone. Once a pattern is identified, the storm features (such as length and curvature of banding features) are further analyzed to arrive at a particular T-number. The CCC pattern indicates little development is occurring, despite the cold cloud tops associated with the quickly evolving feature.

Several agencies issue Dvorak intensity numbers for tropical cyclones and their precursors, including the National Hurricane Center's Tropical Analysis and Forecast Branch (TAFB), the NOAA/NESDIS Satellite Analysis Branch (SAB), and the Joint Typhoon Warning Center at the Naval Meteorology and Oceanography Command in Pearl Harbor, Hawaii.

DvorakCDP1973
Common developmental patterns seen during tropical cyclone development, and their Dvorak-assigned intensities

Evolution of the method

Subtropical Storm Andrea 2007
The Dvorak technique does not correctly diagnose cyclone intensity for storms like Subtropical Storm Andrea since it applies to tropical cyclones only

The initial development of this technique occurred in 1969 by Vernon Dvorak, using satellite pictures of tropical cyclones within the northwest Pacific Ocean. The system as it was initially conceived involved pattern matching of cloud features with a development and decay model. As the technique matured through the 1970s and 1980s, measurement of cloud features became dominant in defining tropical cyclone intensity and central pressure of the tropical cyclone's low-pressure area. Use of infrared satellite imagery led to a more objective assessment of the strength of tropical cyclones with eyes, using the cloud top temperatures within the eyewall and contrasting them with the warm temperatures within the eye itself. Constraints on short term intensity change are used less frequently than they were back in the 1970s and 1980s. The central pressures assigned to tropical cyclones have required modification, as the original estimates were 5–10 hPa (0.15–0.29 inHg) too low in the Atlantic and up to 20 hPa (0.59 inHg) too high in the northwest Pacific. This led to the development of a separate wind-pressure relationship for the northwest Pacific, devised by Atkinson and Holliday in 1975, then modified in 1977.[1]

As human analysts using the technique lead to subjective biases, efforts have been made to make more objective estimates using computer programs, which have been aided by higher-resolution satellite imagery and more powerful computers. Since tropical cyclone satellite patterns can fluctuate over time, automated techniques use a six-hour averaging period to lead to more reliable intensity estimates. Development of the objective Dvorak technique began in 1998, which performed best with tropical cyclones that had eyes (of hurricane or typhoon strength). It still required a manual center placement, keeping some subjectivity within the process. By 2004, an advanced objective Dvorak technique was developed which utilized banding features for systems below hurricane intensity and to objectively determine the tropical cyclone's center. A central pressure bias was uncovered in 2004 relating to the slope of the tropopause and cloud top temperatures which change with latitude that helped improve central pressure estimates within the objective technique.[1]

Details of the method

Dvorak T-Number and Corresponding Intensity[2]
T-Number 1-min Winds Category (SSHWS) Min. Pressure (millibars)
(knots) (mph) (km/h) Atlantic NW Pacific
1.0 – 1.5 25 29 45 below TD ---- ----
2.0 30 35 55 TD 1009 1000
2.5 35 40 65 TS 1005 998
3.0 45 52 83 TS 1000 991
3.5 55 63 102 TS 994 984
4.0 65 75 120 Cat 1 987 976
4.5 77 89 143 Cat 1Cat 2 979 966
5.0 90 104 167 Cat 2 970 954
5.5 102 117 189 Cat 3 960 941
6.0 115 132 213 Cat 4 948 927
6.5 127 146 235 Cat 4 935 915
7.0 140 161 260 Cat 5 921 898
7.5 155 178 287 Cat 5 906 879
8.0 170 196 315 Cat 5 890 858
8.5dagger 185 213 343 Cat 5 873 841
Note: The pressures shown for the NW Pacific basin are lower as the pressure of the entire basin are relatively lower than that of the Atlantic basin.[3]
daggerValues of 8.1–8.5 are only assigned by the CIMSS and NOAA automated advanced Dvorak systems and not used in subjective analyses.[4]
Haiyan 2013-11-07 1430Z IR-BD lineless
Dvorak enhancement imagery of Typhoon Haiyan at T8.0

In a developing cyclone, the technique takes advantage of the fact that cyclones of similar intensity tend to have certain characteristic features, and as they strengthen, they tend to change in appearance in a predictable manner. The structure and organization of the tropical cyclone are tracked over 24 hours to determine if the storm has weakened, maintained its intensity, or strengthened. Various central cloud and banding features are compared with templates that show typical storm patterns and their associated intensity.[5] If infrared satellite imagery is available for a cyclone with a visible eye pattern, then the technique utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops to determine intensity (colder cloud tops generally indicate a more intense storm). In each case a "T-number" (an abbreviation for Tropical Number) and a Current Intensity (CI) value are assigned to the storm. These measurements range between 1 (minimum intensity) and 8 (maximum intensity).[3] The T-number and CI value are the same except for weakening storms, in which case the CI is higher.[6][7] For weakening systems, the CI is held as the tropical cyclone intensity for 12 hours, though research from the National Hurricane Center indicates that six hours is more reasonable.[8] The table at right shows the approximate surface wind speed and sea level pressure that corresponds to a given T-number.[9] The amount a tropical cyclone can change in strength per 24‑hour period is limited to 2.5 T-numbers per day.[1]

Pattern types

Within the Dvorak satellite strength estimate for tropical cyclones, there are several visual patterns that a cyclone may take on which define the upper and lower bounds on its intensity. The primary patterns used are curved band pattern (T1.0-T4.5), shear pattern (T1.5-T3.5), central dense overcast (CDO) pattern (T2.5-T5.0), banding eye pattern (T4.0-T4.5), eye pattern (T4.5 – T8.0), and central cold cover (CCC) pattern.[10] Both the central dense overcast and embedded eye pattern utilize the size of the CDO. The CDO pattern intensities start at T2.5, equivalent to minimal tropical storm intensity (40 miles per hour (64 km/h)). The shape of the central dense overcast is also considered. The farther the center is tucked into the CDO, the stronger it is deemed.[11] Tropical cyclones with maximum sustained winds between 65 miles per hour (105 km/h) and 100 miles per hour (160 km/h) can have their center of circulations obscured by cloudiness within visible and infrared satellite imagery, which makes diagnosis of their intensity a challenge.[12]

The CCC pattern, with its large and quickly developing mass of thick cirrus clouds spreading out from an area of convection near a tropical cyclone center within a short time frame, indicates little development. When it develops, rainbands and cloud lines around the tropical cyclone weaken and the thick cloud shield obscures the circulation center. While it resembles a CDO pattern, it is rarely seen.[10]

The eye pattern utilizes the coldness of the cloud tops within the surrounding mass of thunderstorms and contrasts it with the temperature within the eye itself. The larger the temperature difference is, the stronger the tropical cyclone.[11] Winds within tropical cyclones can also be estimated by tracking features within the CDO using rapid scan geostationary satellite imagery, whose pictures are taken minutes apart rather than every half-hour.[13]

Once a pattern is identified, the storm features (such as length and curvature of banding features) are further analyzed to arrive at a particular T-number.[14]

Usage

Several agencies issue Dvorak intensity numbers for tropical cyclones and their precursors. These include the National Hurricane Center's Tropical Analysis and Forecast Branch (TAFB), the National Oceanic and Atmospheric Administration's Satellite Analysis Branch (SAB), and the Joint Typhoon Warning Center at the Naval Pacific Meteorology and Oceanography Center in Pearl Harbor, Hawaii.[9]

The National Hurricane Center will often quote Dvorak T-numbers in their tropical cyclone products. The following example is from discussion number 3 of Tropical Depression 24 (eventually Hurricane Wilma) of the 2005 Atlantic hurricane season:[15]

BOTH TAFB AND SAB CAME IN WITH A DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT. HOWEVER ...OFTENTIMES THE SURFACE WIND FIELD OF LARGE DEVELOPING LOW PRESSURE SYSTEMS LIKE THIS ONE WILL LAG ABOUT 12 HOURS BEHIND THE SATELLITE SIGNATURE. THEREFORE... THE INITIAL INTENSITY HAS ONLY BEEN INCREASED TO 30 KT.

Note that in this case the Dvorak T-number (in this case T2.5) was simply used as a guide but other factors determined how the NHC decided to set the system's intensity.

The Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin–Madison has developed the Objective Dvorak Technique (ODT). This is a modified version of the Dvorak technique which uses computer algorithms rather than subjective human interpretation to arrive at a CI number. This is generally not implemented for tropical depressions or weak tropical storms.[9] The China Meteorological Agency (CMA) is expected to start using the standard 1984 version of Dvorak in the near future. The Indian Meteorological Department (IMD) prefers using visible satellite imagery over infrared imagery due to a perceived high bias in estimates derived from infrared imagery during the early morning hours of convective maximum. The Japan Meteorological Agency (JMA) uses the infrared version of Dvorak over the visible imagery version. Hong Kong Observatory and JMA continue to utilize Dvorak after tropical cyclone landfall. Various centers hold on to the maximum current intensity for 6–12 hours, though this rule is broken when rapid weakening is obvious.[8]

Citizen science site Cyclone Center uses a modified version of the Dvorak technique to categorize post-1970 tropical weather.[16]

Emily-14-1915z-T60-discussion15-0300z

Hurricane Emily at T6.0

Benefits and disadvantages

The most significant benefit of the use of the technique is that it has provided a more complete history of tropical cyclone intensity in areas where aircraft reconnaissance is neither possible nor routinely available. Intensity estimates of maximum sustained wind are currently within 5 miles per hour (8.0 km/h) of what aircraft are able to measure half of the time, though the assignment of intensity of systems with strengths between moderate tropical-storm force (60 miles per hour (97 km/h)) and weak hurricane- or typhoon-force (100 miles per hour (160 km/h)) is the least certain. Its overall precision has not always been true, as refinements in the technique led to intensity changes between 1972 and 1977 of up to 20 miles per hour (32 km/h). The method is internally consistent in that it constrains rapid increases or decreases in tropical cyclone intensity. Some tropical cyclones fluctuate in strength more than the 2.5 T numbers per day limit allowed by the rule, which can work to the technique's disadvantage and has led to occasional abandonment of the constraints since the 1980s. Systems with small eyes near the limb, or edge, of a satellite image can be biased too weakly using the technique, which can be resolved through use of polar-orbiting satellite imagery. Subtropical cyclone intensity cannot be determined using Dvorak, which led to the development of the Hebert-Poteat technique in 1975. Cyclones undergoing extratropical transition, losing their thunderstorm activity, see their intensities underestimated using the Dvorak technique. This led to the development of the Miller and Lander extratropical transition technique which can be used under these circumstances.[1]

See also

Other tools used to determine tropical cyclone intensity:

References

  1. ^ a b c d Velden, Christopher; Bruce Harper; Frank Wells; John L. Beven II; Ray Zehr; Timothy Olander; Max Mayfield; Charles “Chip” Guard; Mark Lander; Roger Edson; Lixion Avila; Andrew Burton; Mike Turk; Akihiro Kikuchi; Adam Christian; Philippe Caroff & Paul McCrone (September 2006). "The Dvorak Tropical Cyclone Intensity Estimation Technique: A Satellite-Based Method That Has Endured For Over 30 Years" (PDF). Bulletin of the American Meteorological Society. 87: 1195–1214. Bibcode:2006BAMS...87.1195V. doi:10.1175/bams-87-9-1195. Retrieved 2012-09-26.
  2. ^ Satellite and Information Service Division (April 17, 2005). "Dvorak Current Intensity Chart". National Oceanic and Atmospheric Administration. Retrieved 2006-06-12.
  3. ^ a b Landsea, Chris (2006). "Subject: H1) What is the Dvorak technique and how is it used?". Hurricane Research Division. Retrieved 2012-09-09.
  4. ^ Timothy L. Olander; Christopher S. Velden (February 2015). ADT – Advanced Dvorak Technique Users' Guide (McIDAS Version 8.2.1) (PDF). Cooperative Institute for Meteorological Satellite Studies (Report). University of Wisconsin–Madison. p. 49. Retrieved October 29, 2015.
  5. ^ Naval Research Laboratory. "Tropical Cyclone Forecasters Reference Guide". United States Navy. Retrieved 2006-05-29.
  6. ^ Leffler, J.W. "T-Number Curve Comparison between JTWC and JMA". Archived from the original on 2006-07-25.
  7. ^ National Oceanic and Atmospheric Administration Satellite and Information Service (2011-08-26). "The Dvorak Technique Explained". National Oceanic and Atmospheric Administration. Retrieved 2006-05-29.
  8. ^ a b Burton, Andrew; Christopher Velden (2011-04-16). "Proceedings of the International Workshop on Satellite Analysis of Tropical Cyclones Report No. TCP-52" (PDF). World Meteorological Organization. pp. 3–4. Retrieved 2012-11-23.
  9. ^ a b c Velden, Christopher; Timothy L. Olander & Raymond M. Zehr (March 1998). "Development of an Objective Scheme to Estimate Tropical Cyclone Intensity from Digital Geostationary Satellite Infrared Imagery". Weather and Forecasting. University of Wisconsin. 13: 172–186. Bibcode:1998WtFor..13..172V. doi:10.1175/1520-0434(1998)013<0172:DOAOST>2.0.CO;2. Retrieved 2012-09-09.
  10. ^ a b Lander, Mark A. (January 1999). "Pictures of the Month: A Tropical Cyclone With an Enormous Central Cold Cover". Monthly Weather Review. American Meteorological Society. 127: 132–134. Bibcode:1999MWRv..127..132L. doi:10.1175/1520-0493(1999)127<0132:atcwae>2.0.co;2.
  11. ^ a b Dvorak, Vernon F. (February 1973). "A Technique For the Analysis and Forecasting of Tropical Cyclone Intensities From Satellite Pictures". National Oceanic and Atmospheric Administration: 5–8.
  12. ^ Wimmers, Anthony; Chistopher Velden (2012). "Advances in Objective Tropical Cyclone Center Fixing Using Multispectral Satellite Imagery". American Meteorological Society. Retrieved 2012-08-12.
  13. ^ Rogers, Edward; R. Cecil Gentry; William Shenk & Vincent Oliver (May 1979). "The Benefits of Using Short-Interval Satellite Images To Derive Winds For Tropical Cyclones". Monthly Weather Review. American Meteorological Society. 107: 575–584. Bibcode:1979MWRv..107..575R. doi:10.1175/1520-0493(1979)107<0575:tbousi>2.0.co;2.
  14. ^ De Maria, Mark (1999-04-19). "Satellite Application is Tropical Weather Forecasting". Archived from the original on 2006-08-13. Retrieved 2006-05-29.
  15. ^ Stewart, Stacy (2005-10-16). "NHC Tropical Depression 24 Discussion Number 3". National Hurricane Center. Retrieved 2006-05-29.
  16. ^ "Cyclone Center". www.cyclonecenter.org. Retrieved 2015-08-05.

External links

Agencies issuing Dvorak intensity estimates
Other
Cyclone Monica

Severe Tropical Cyclone Monica was the most intense tropical cyclone, in terms of maximum sustained winds, on record to impact Australia. The 17th and final storm of the 2005–06 Australian region cyclone season, Monica originated from an area of low pressure off the coast of Papua New Guinea on 16 April 2006. The storm quickly developed into a Category 1 cyclone the next day, at which time it was given the name Monica. Travelling towards the west, the storm intensified into a severe tropical cyclone before making landfall in Far North Queensland, near Lockhart River, on 19 April 2006. After moving over land, convection associated with the storm quickly became disorganised.

On 20 April 2006, Monica emerged into the Gulf of Carpentaria and began to re-intensify. Over the following few days, deep convection formed around a 37 km (23 mi) wide eye. Early on 22 April 2006, the Bureau of Meteorology (BoM) assessed Monica to have attained Category 5 status, on the Australian cyclone intensity scale. The Joint Typhoon Warning Center (JTWC) also upgraded Monica to a Category 5 equivalent cyclone, on the Saffir–Simpson Hurricane Scale. The storm attained its peak intensity the following day with winds of 250 km/h (155 mph 10-minute winds) and a barometric pressure of 916 hPa (mbar; 27.05 inHg). On 24 April 2006, Monica made landfall about 35 km (22 mi) west of Maningrida, at the same intensity. Rapid weakening took place as the storm moved over land. Less than 24 hours after landfall, the storm had weakened to a tropical low. The remnants of the former-Category 5 cyclone persisted until 28 April 2006 over northern Australia.

In contrast to the extreme intensity of the cyclone, relatively little structural damage resulted from it. No injuries were reported to have occurred during the storm's existence and losses were estimated to be A$6.6 million (US$5.1 million). However, severe environmental damage took place. In the Northern Territory, an area about 7,000 km2 (4,300 mi2) was defoliated by Monica's high wind gusts. In response to the large loss of forested area, it was stated that it would take several hundred years for the area to reflourish.

Extratropical cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.

Hurricane Fausto (2002)

Hurricane Fausto was a long-lived tropical cyclone that formed during the 2002 Pacific hurricane season. The eighth tropical cyclone and fifth named storm of the season, Fausto developed on August 21 from a tropical wave that had crossed the Atlantic, and entered the Pacific on August 17. Becoming a tropical depression, the system intensified, and quickly became Tropical Storm Fausto early on August 22. Fausto rapidly intensified, and was already a hurricane on that same day as becoming a tropical storm. Rapid intensification continued, and the tropical cyclone ultimately peaked as a strong Category 4 hurricane on the Saffir–Simpson hurricane scale. At that time, the winds 145 mph (230 km/h). Fausto began to gradually weaken after attaining peak intensity on August 24, and was eventually downgraded to a tropical storm two days later. Weakening continued, and Fausto degenerated into a remnant low on August 28 while well northeast of Hawaii.

Passing north of the Hawaiian Islands, the remnants of the hurricane later began to revive, and had re-developed into a tropical depression on August 30. Additional re-intensification was not significant, although Fausto managed to become a tropical storm again on September 1. Remaining a minimal tropical storm, no further intensification occurred, and by September 3, Fausto was absorbed by a frontal system.

Hurricane Norbert (2008)

Hurricane Norbert is tied with Hurricane Jimena as the strongest tropical cyclone to strike the west coast of Baja California Sur in recorded history. The fifteenth named storm, seventh hurricane, and second major hurricane of the 2008 hurricane season, Norbert originated as a tropical depression from a tropical wave south of Acapulco on October 3. Strong wind shear initially prevented much development, but the cyclone encountered a more favorable environment as it moved westward. On October 5, the National Hurricane Center (NHC) upgraded the depression to Tropical Storm Norbert, and the system intensified further to attain hurricane intensity by October 6. After undergoing a period of rapid deepening, Norbert reached its peak intensity as a Category 4 on the Saffir–Simpson hurricane wind scale, with maximum sustained winds of 135 mph (215 km/h) and a minimum barometric pressure of 945 mbar (hPa; 27.91 inHg). As the cyclone rounded the western periphery of a subtropical ridge over Mexico, it began an eyewall replacement cycle which led to steady weakening. Completing this cycle and briefly reintensifying into a major hurricane, a Category 3 or higher on the Saffir–Simpson hurricane wind scale, Norbert moved ashore Baja California Sur as a Category 2 hurricane late on October 11. After a second landfall at a weaker intensity the following day, the system quickly weakened over land and dissipated that afternoon.

In preparation for the cyclone, the NHC issued hurricane warnings for coastal regions of the Baja California Peninsula. Residents living in low-lying areas and flood-prone regions were advised to evacuate, and beach-goers were warned to stay out of the water. Upon landfall, the hurricane produced waves in excess of 13 ft (4.0 m). Though the strongest winds observed were less than hurricane intensity, heavy rainfall as a result of Norbert lead to substantial damage. In Baja California Sur, roughly 5,000 homes sustained major damage; the heaviest-impacted municipality, Comondú, reported 16,000 homes affected. Thousands of people were forced into shelters, and many trees were blown down by strong winds. A total of 25 fatalities occurred in Sonora, 5 of which occurred in Álamos, where excessive rainfall caused a majority of the town to become flooded; homes were submerged to their roofs and many trees were downed. The hurricane severely impacted the fishing industry in Sinaloa, while thousands of residents were left homeless. In the United States, Norbert produced minimal rainfall. In the aftermath of the storm, many towns and municipalities were declared disaster areas. Overall, Norbert inflicted $98.5 million (2008 USD) in damage.

Maximum sustained wind

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 (see the definition, below), 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.

Over the ocean, satellite imagery determines the value of the maximum sustained winds within a tropical cyclone. Land, ship, aircraft reconnaissance observations, and radar imagery can also estimate this quantity, when available. This value helps determine damage expected from a tropical cyclone, through use of such scales as the Saffir–Simpson scale.

ODT

The term ODT can refer to several things, among them:

Computer-related

.ODT, the word processing file format of OpenDocument, an open standard for electronic documents

On-line Debugging Tool, a debugger used by certain software from Digital Equipment Corporation

Oracle Corporation's Oracle Developer ToolsMedia/Entertainment

Otago Daily Times, New Zealand's second oldest daily newspaper

O.D.T., Or Die Trying, is a video game created by Psygnosis for the PlayStation and PCOther

Outdoor Training, Outdoor Training

Order-disorder transition

Orally disintegrating tablet (or orally dissolving tablet), a pill that "melts" on contact with saliva

Omnidirectional treadmill, a treadmill which can convey objects in two dimensions

Oven dry tonne, a unit to express the dried weight of an agricultural commodity such as biomass that contained significant water weight when harvested

Omnidirectional transmission, an active sonar transmission mode

On Die Termination, a technique to reduce bounce back of electrical signals on high speed electrical connections

Dvorak technique, also known as Objective Dvorak Technique, a technique used to estimate the strength of a tropical cyclone

Olympic Discovery Trail, a multi-use trail spanning the north end of the Olympic Peninsula in Washington

Rainband

A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands can be stratiform or convective, and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as banded structure. Rainbands within tropical cyclones are curved in orientation. Tropical cyclone rainbands contain showers and thunderstorms that, together with the eyewall and the eye, constitute a hurricane or tropical storm. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.

Rainbands spawned near and ahead of cold fronts can be squall lines which are able to produce tornadoes. Rainbands associated with cold fronts can be warped by mountain barriers perpendicular to the front's orientation due to the formation of a low-level barrier jet. Bands of thunderstorms can form with sea breeze and land breeze boundaries, if enough moisture is present. If sea breeze rainbands become active enough just ahead of a cold front, they can mask the location of the cold front itself. Banding within the comma head precipitation pattern of an extratropical cyclone can yield significant amounts of rain or snow. Behind extratropical cyclones, rainbands can form downwind of relative warm bodies of water such as the Great Lakes. If the atmosphere is cold enough, these rainbands can yield heavy snow.

Satellite Analysis Branch

The United States Satellite Analysis Branch, part of National Oceanic and Atmospheric Administration (NOAA)'s National Environmental Satellite, Data, and Information Service's Satellite Services Division, is the operational focal point for real-time imagery products within NESDIS. It is also responsible for doing Dvorak technique intensity fixes on tropical cyclones. Its roots lie in the establishment of the Meteorological Satellite Section by January 1959.Its primary mission is to "operate new proof of concept satellite analysis techniques needed to support disaster mitigation and warning services" for the U.S. government and its agencies. It also distributes real-time satellite imagery from geostationary satellites. The SAB also produces graphics for Tropical Rainfall Potential forecasts for all tropical systems in the Western Hemisphere and many in the Eastern Hemisphere.Away from tropical cyclones, the SAB functions as the Washington Volcanic Ash Advisory Center, having been designated as such by the International Civil Aviation Organization in 1997. It also does snow and ice analysis, and has done so, along with its parent organizations NESDIS and SSD, since 1966.

Satellite temperature measurements

Satellite temperature measurements are inferences of the temperature of the atmosphere at various altitudes as well as sea and land surface temperatures obtained from radiometric measurements by satellites. These measurements can be used to locate weather fronts, monitor the El Niño-Southern Oscillation, determine the strength of tropical cyclones, study urban heat islands and monitor the global climate. Wildfires, volcanos, and industrial hot spots can also be found via thermal imaging from weather satellites.

Weather satellites do not measure temperature directly. They measure radiances in various wavelength bands. Since 1978 microwave sounding units (MSUs) on National Oceanic and Atmospheric Administration polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen, which is related to the temperature of broad vertical layers of the atmosphere. Measurements of infrared radiation pertaining to sea surface temperature have been collected since 1967.

Satellite datasets show that over the past four decades the troposphere has warmed and the stratosphere has cooled. Both of these trends are consistent with the influence of increasing atmospheric concentrations of greenhouse gases.

South-West Indian Ocean tropical cyclone

In the south-west Indian Ocean, tropical cyclones form south of the equator and west of 90° E to the coast of Africa.

T-number

T-number or T number may refer to:

A numerical system for the glyphs within the Pre-Columbian Mayan script, see J. Eric S. Thompson.

Dvorak technique, a system to subjectively estimate tropical cyclone intensity

Viral capsid T-number, a system to describe the icosahedral surface quasi-symmetry pattern

In music, the transposition of a tone row

In number theory, a transcendental number having finite, but unbounded, transcendence measure.

T-number (photography), an transmission aperture value in photography

Tropical Storm Andres (1997)

Tropical Storm Andres is one out of two tropical cyclones on record to strike El Salvador. The first named storm of the active 1997 Pacific hurricane season, Andres formed on June 1 off the coast of Mexico. It initially moved toward the coast, although a change in steering winds turned the storm toward Mexico and Guatemala. After passing just offshore, Andres again changed direction toward the southeast, gradually weakening in the process. On June 7, it turned toward and hit El Salvador before dissipating. The storm brought rainfall to coastlines along much of its path, destroying some houses and inflicted damage. Two fishermen were reported missing in Nicaragua due to high seas, and there were four deaths in El Salvador.

Tropical cyclone observation

Tropical cyclone observation has been carried out over the past couple of centuries in various ways. The passage of typhoons, hurricanes, as well as other tropical cyclones have been detected by word of mouth from sailors recently coming to port or by radio transmissions from ships at sea, from sediment deposits in near shore estuaries, to the wiping out of cities near the coastline. Since World War II, advances in technology have included using planes to survey the ocean basins, satellites to monitor the world's oceans from outer space using a variety of methods, radars to monitor their progress near the coastline, and recently the introduction of unmanned aerial vehicles to penetrate storms. Recent studies have concentrated on studying hurricane impacts lying within rocks or near shore lake sediments, which are branches of a new field known as paleotempestology. This article details the various methods employed in the creation of the hurricane database, as well as reconstructions necessary for reanalysis of past storms used in projects such as the Atlantic hurricane reanalysis.

Typhoon Angela

Typhoon Angela, known in the Philippines as Typhoon Rosing, was a catastrophic Category 5 typhoon with 180 mph (290 km/h) sustained winds. Typhoon Angela was the third storm in a row that struck the Philippines, following Yvette and Zack. Typhoon Angela was the twenty-ninth tropical cyclone, and the fifth super typhoon of the moderately active 1995 Pacific typhoon season.

Angela caused 9.33 billion Philippine pesos in catastrophic damage across the Philippines, resulting in 882 fatalities. It was the strongest typhoon to hit the Philippines in 25 years.

Typhoon Lan

Typhoon Lan, known in the Philippines as Typhoon Paolo, was the third-most intense tropical cyclone worldwide in 2017. A very large storm, Lan was the twenty-first tropical storm and ninth typhoon of the annual typhoon season. It originated from a tropical disturbance that the United States Naval Research Laboratory had begun tracking near Chuuk on October 11. Slowly consolidating, it developed into a tropical storm on October 15, and intensified into a typhoon on October 17. It expanded in size and turned northward on October 18, although the typhoon struggled to intensify for two days. On October 20, Lan grew into a very large typhoon and rapidly intensified, due to favorable conditions, with a large well-defined eye, reaching peak intensity as a "super typhoon" with 1-minute sustained winds of 250 km/h (155 mph) – a high-end Category 4-equivalent storm – late on the same day. Afterwards, encroaching dry air and shear caused the cyclone to begin weakening and turn extratropical, before it struck Japan on October 23 as a weaker typhoon. Later that day, it became fully extratropical before it was absorbed by a larger storm shortly afterwards.

Lan caused significant impacts in Japan, with over 380,000 evacuations occurring in Japan, and the cancellations of several domestic flights. In total, approximately 17 deaths were attributed to the typhoon, mainly due to flooding from its rainbands. Damage totals were estimated to have been at least US$2 billion (2017 USD), making it one of the costliest typhoons to have struck Japan.

Vernon Dvorak

Vernon F. Dvorak is a retired American meteorologist. He studied meteorology at the University of California, Los Angeles and wrote his Master thesis An investigation of the inversion-cloud regime over the subtropical waters west of California. in 1966. In 1973 he developed the Dvorak technique to analyze tropical cyclones from satellite imagery. He worked with the National Environmental Satellite, Data, and Information Service. Dvorak was a recipient of a United States Department of Commerce Meritorious Service award in 1972 and in 2002 he received a Special Lifetime Achievement Award from the National Weather Association. He now lives in Ojai, California.

Weather satellite

The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be polar orbiting, covering the entire Earth asynchronously, or geostationary, hovering over the same spot on the equator.Meteorological satellites see more than clouds and cloud systems: city lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc. Other types of environmental information are collected using weather satellites. Weather satellite images helped in monitoring the volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna. Smoke from fires in the western United States such as Colorado and Utah have also been monitored.

Other environmental satellites can detect changes in the Earth's vegetation, sea state, ocean color, and ice fields. For example, the 2002 Prestige oil spill off the northwest coast of Spain was watched carefully by the European ENVISAT, which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface.

El Niño and its effects on weather are monitored daily from satellite images. The Antarctic ozone hole is mapped from weather satellite data. Collectively, weather satellites flown by the U.S., Europe, India, China, Russia, and Japan provide nearly continuous observations for a global weather watch.

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