Tropical cyclone observation
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Tropical cyclone obervation 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, 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.
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[edit] Markers in coral
Rocks contain certain isotopes of elements, known as natural tracers, which describe the conditions under which they formed. By studying the calcium carbonate in coral rock, past sea surface temperature and hurricane information can be revealed. Lighter oxygen isotopes (O-18) are left behind in coral during periods of very heavy rainfall.[1] Since hurricanes are the main source of extreme rainfall in the tropical oceans, past hurricane events can be dated to the days of their impact on the coral by looking at the increased O-18 concentration within the coral.[2]
[edit] Sediment deposition in coastal lakes
Kam Biu-Liu, a professor at Louisiana State University, has been studying sediment lying at the bottom of coastal lakes and marshes in order to study the frequency and intensity of hurricanes over the past 5,000 years. Since storm surges sweep coastal sands with them as they progress inland, a layer of sand is left behind in coastal lakes and marshes. Radiocarbon dating is then used to date the layers.[3]
[edit] Newspapers
Before the invention of the telegraph in the early to mid 19th century, news was as fast as the quickest horse, stage, or ship. Normally, there was no advance warning of a tropical cyclone impact. However, the situation changed in the 19th century as sea-faring people and land-based researchers, such as Father Viñes in Cuba, came up with systematic methods of reading the sky's appearance or the sea state, which could foretell a tropical cyclone's approach up to a couple days in advance.
[edit] Ship reports
For centuries, people have sailed the world's oceans and seas, and for just as long, they have encountered storms. The worst of the cyclones over the open seas likely took those that observed them into the depths of the oceans. However, some did survive to report harrowing tales. Before the invention of the wireless telegraph in 1905, reports about storms at sea either coincided with their arrival at the coast as ships scrambled into port, or came weeks and months afterwards from remote ports of call. Ship and buoy reports, available since the 1970s, are used in real-time not only for their temperature, pressure, and wind measurements, but also for their sea surface temperature and wave height measurements.
Wind reports from ships at sea have become increasingly based on anemometers, and less so on the Beaufort Scale. This is important to note as the Beaufort Scale underestimates winds at higher wind speeds, indicating ship wind observations taken for older storms are likely to underrepresent their true value.[4]
[edit] Surface observations
In the early 20th century, forecasting the track of cyclones was still confined to areas of the greatest surface pressure falls and climatology. These methods proved to be the cutting edge of tropical cyclone forecasting through the mid 20th century. Land-based surface observations remain invaluable as a source of real-time information at locations near the coastline and inland. Combined with ship observations and newspapers, they formed the total information network for hurricane detection until radiosondes were introduced in 1941 and reconnaisance aircraft began in 1944.[4] Land-based observations of pressure and wind can show how quickly a tropical cyclone is decaying as it moves inland. Their rainfall reports show where significant rainfall is occurring, and can be an alert for possible flooding. With the establishment of the ASOS network in the United States during the 1990s, more locations are reporting around the clock than ever before.[5]
[edit] Reconnaissance aircraft
Since 1944, aircraft have been flying out to sea to find tropical cyclones. Before regular satellite coverage, this was a hit-or-miss affair. Thereafter, aircraft flights into tropical systems became more targeted and precise. Nowadays, a C-130 is used as a hurricane hunter by the Air Force, while the P-3 Orion is used by the National Oceanic and Atmospheric Administration for research projects used to better understand tropical cyclones and improve hurricane forecasts.[5]
[edit] Unmanned aerial vehicles
In 2005, Hurricane Ophelia became the first storm where an unmanned aerial vehicle, known as an aerosonde, mission was used for real-time observation of a tropical cyclone. Unlike normal reconnaissance flights, the aerosonde stayed near the surface after a 10 hour flight within the tropical cyclone.[6]
[edit] Radar
During World War II, radar technology was developed to detect aircraft. It soon became apparent that large areas became obscured when significant weather was in the area. In 1957, the National Weather Service established the United States' first radar network to cover the coastline and act as first warning of an impending tropical cyclone. Upgraded in the 1990s to use doppler technology, radar can provide rainfall estimates, wind estimates, possible locations of tornadoes within a system's spiral bands, as well as the center location of a tropical cyclone.[5]
[edit] Satellite
Beginning with the launching of Tiros I in April 1960, satellites have been used to look for tropical cyclones. The Dvorak technique was developed from early satellite images of tropical cyclones and real-time data on the cyclone's strength. Since the 1970s, this technique has been used to estimate both the location and the intensity of tropical cyclones worldwide.[7] Since the mid 1990s, microwave imagery has been able to determine the center of rotation when that center is obscured by mid to high level cloudiness. Cloud top temperatures are used in real-time to estimate rainfall rates within the cyclone.[5]
[edit] See also
- Atlantic hurricane reanalysis
- Paleotempestology
- Radiocarbon dating
- Satellite
- Surface weather analysis
- Tropical cyclone
[edit] References
- ^ Nobu Shimizu. If Rocks Could Talk... Retrieved on 2006-12-09.
- ^ Anne L. Cohen and Graham D. Layne. Seeking a hurricane signature in coral skeleton. Retrieved on 2006-12-09.
- ^ Louisiana State University. LSU Professor looks for link between hurricanes and coastal fires: Evidence suggests risk for fire may be higher after catastrophic storms. Retrieved on 2006-12-09.
- ^ a b Brian R. Jarvinen, Charles J. Neumann, and Mary A. S. Davis. A Tropical Cyclone Data Tape For the North Atlantic Basin, 1886-1983: Contents, Limitations, and Uses. Retrieved on 2006-12-09.
- ^ a b c d Central Pacific Hurricane Center. Observations. Retrieved on 2006-12-09.
- ^ Aerosonde. Aerosonde first UAV to Recce a Tropical Cyclone. Retrieved on 2006-12-09.
- ^ Atlantic Oceanographic and Meteorological Laboratory. Subject: H1) What is the Dvorak technique and how is it used? Retrieved on 2006-12-08.
