User:Itfc+canes=me/movement and track

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A tropical cyclone is a large cyclonic swirling system that generates enormous energy, however there movements,intensity and organisation are controlled by simple conditions. Organization is controlled by Wind shear, Intensity by Sea Surface Temperatures and movements by Steering winds.

Steering winds[edit]

Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's track and has been analogized by Dr. Neil Frank, former director of the National Hurricane Center, to "leaves carried along by a stream".[1]

Tropical systems, while generally located equatorward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the subtropical ridge—a persistent high pressure area over the world's oceans.[1] In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name for the westward-moving wind currents—steer tropical waves westward from the African coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out.[2] These waves are the precursors to many tropical cyclones within this region.[3] In the Indian Ocean and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the Intertropical Convergence Zone and the monsoon trough, rather than by easterly waves.[4] Tropical cyclones can also be steered by other systems, such as other low pressure systems, high pressure systems, warm fronts, and cold fronts.

Coriolis effect[edit]

Infrared image of a powerful southern hemisphere cyclone, Monica, near peak intensity, showing clockwise rotation due to the Coriolis effect

The Earth's rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents.[5] The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.[6]

The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds – that force is the heat of condensation.[7]

Interaction with the mid-latitude westerlies[edit]

Image depicts various types of storm tracks
Storm track of Typhoon Ioke, showing recurvature off the Japanese coast in 2006

Tropical Cyclone recurvature is the change in a tropical cyclone's track from westward and poleward to eastward and poleward. An recurving Tropical Cyclone is defined as poleward movement of a Tropical Cyclone from the deep easterlies of the tropics into the strong upper tropospheric westerlies of the mid-latitudes. This motion is often seen with Tropical Cyclones that are moved northwestward around the western portion of a subtropical ridge and then turn poleward and eastward under the influence of the mid-latitude westerlies. Also some recurving TCs can be further classified with respect to how rapidly they recurve. [8] A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low-pressure system passing over China or Siberia. Many tropical cyclones are eventually forced toward the northeast by extratropical cyclones in this manner, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was Typhoon Ioke in 2006, which took a similar trajectory.[9]

Landfall[edit]

See also: List of notable tropical cyclones and Unusual areas of tropical cyclone formation
An Image depicting Hurricane Rita's Center and where landfall would occur if an island was at the eye.

Officially, landfall is when a storm's center (the center of its circulation, not its edge) crosses the coastline.[10] Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast.[10] Due to this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.[10]

Multiple storm interaction[edit]

Main article: Fujiwhara effect

When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Sakuhei Fujiwhara.[11]

See also[edit]

References[edit]

  1. ^ a b Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. "Frequently Asked Questions: What determines the movement of tropical cyclones?". NOAA. Retrieved 2006-07-25.
  2. ^ Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division. "Frequently Asked Questions: What is an easterly wave?". NOAA. Retrieved 2006-07-25.
  3. ^ Cite error: The named reference MWR Avila 1995 was invoked but never defined (see the help page).
  4. ^ DeCaria, Alex (2005). "Lesson 5 – Tropical Cyclones: Climatology". ESCI 344 – Tropical Meteorology. Millersville University. Retrieved 2008-02-22.
  5. ^ Baum, Steven K. (20 January 1997). "The Glossary: Cn-Cz". Glossary of Oceanography and the Related Geosciences with References. Texas A&M University. Retrieved 2006-11-29.
  6. ^ Cite error: The named reference BritTCtrackcoriolis was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference NOAA Question of the Month was invoked but never defined (see the help page).
  8. ^ U. S. Navy. Section 2: Tropical Cyclone Motion Terminology. Retrieved on 2007-04-10.
  9. ^ Powell, Jeff; et al. (May 2007). "Hurricane Ioke: 20-27 August 2006". 2006 Tropical Cyclones Central North Pacific. Central Pacific Hurricane Center. Retrieved 2007-06-09. {{cite web}}: Explicit use of et al. in: |author= (help)CS1 maint: date and year (link)
  10. ^ a b c National Hurricane Center (2005). "Glossary of NHC/TPC Terms". National Oceanic and Atmospheric Administration. Retrieved 2006-11-29.
  11. ^ "Fujiwhara effect describes a stormy waltz". USA Today. Retrieved 2008-02-21.

External links[edit]

Wikimedia Commons has media related to Tropical cyclones.
Learning resources
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Past storms
[[Category:Basic meteorological concepts and phenomena]]
[[Category:Tropical cyclone meteorology| ]]
[[Category:Tropical cyclones| ]]
[[Category:Types of cyclone]]
[[Category:Vortices]]
[[Category:Weather hazards]]
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