Ask a Scientist: hurricane power
Whether it is a hurricane, tropical cyclone or typhoon, they all have the potential to cause a whole heap of damage. But do these violent weather systems have more in common than some people think?
This question has been puzzling one of our readers and for this week's 'Ask a Scientist", Glenda asks: "What is the difference between typhoons and hurricanes? Is one stronger than the other? And how do they form?"
MetService meteorologist Daniel Corbett says they are in fact one and the same.
"Hurricane is synonymous with typhoon; it just depends whereabouts you are around the globe," he said.
"Typhoon is a term used mostly in the northwest Pacific region whereas hurricane is the term of choice in the northeast Pacific and the Atlantic basin when maximum sustained winds (either sustained or averaged over one minute or 10 minutes) exceed 63 knots."
We also know them as tropical cyclones, and they are usually ranked using one of several tropical cyclone scales which measure their maximum sustained winds.
"In the Southern Hemisphere, especially in the Australia-South Pacific area, the tendency is to use tropical cyclone as a generic term whether the maximum winds are gale, storm or hurricane in strength. Hurricane as a term tends to be used more informally in this part of the world."
Corbett said tropical cyclones, (hurricanes/typhoons), acquired energy through a process called latent heat release.
"When water evaporated from the ocean rises to a level where the moist air becomes saturated and condensation takes place, this releases latent heat."
He said tropical cyclones were fueled by a different heat mechanism than other cyclonic windstorms such as nor'easters, European windstorms, and polar lows.
"The characteristic that separates tropical cyclones from other cyclonic systems is that at any height in the atmosphere, the centre of a tropical cyclone will be warmer than its surroundings; a phenomenon called 'warm core' storm systems.
"In addition, the winds in a cold core system will be stronger with increasing height but not so in warm core (tropical cyclone) systems.
"MetService operates a Tropical Cyclone Warning Centre (TCWC). This is one of six TCWC’s around the globe along with 6 RSMC’s (Regional Specialised Meteorological Centres) that all monitor tropical activity in their respective areas.
"Whenever a tropical cyclone forms in the area south of 25 south from 160 east to 120 west or moves from the Nadi area of responsibility into the same area."
Corbett said tropical cyclones that formed in the Brisbane area of responsibility did move towards the Wellington area but nearly every time passed through the Nadi area first of all.
The coordinate 25 south 160 east represented the triple point where all three tropical cyclone warning areas of responsibility coincided.
Wellington monitors all tropical cyclones in its area until they are re-classified to be a "depression, formerly cyclone <insert name here>".
"This normally happens by the time the cyclone has reached 30 south," Corbett said.
"Even after the cyclone has been reclassified, Wellington may still continue to issue warnings on the system if required."
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- © Fairfax NZ News
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