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A low pressure area is associated with rising air while a high pressure area is associated with subsiding air. The best explanation I could come up with is either the cyclone is an exception or the above associations are not an absolute rule in the first place. However, none of the articles I read provide an explanation on this phenomenon, indicating that I am missing something trivial. Could anyone shed some light on this? I would appreciate a layman explanation.

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I will just talk about an already formed tropical cyclone. Converging winds spiral in (counterclockwise in northern hemisphere) over the warm ocean waters towards the central low pressure area of the eye.

At the eye they spiral upwards, taking the warm, moist ocean air high into the atmosphere. As it reaches cooler elevation, the air releases its latent heat, adding more energy to the storm.

So you have a tremendous volume of air converging from 360 degrees around the hundreds of miles of the storm, all converging on the eye and spiraling up with an intense updraft, creating a very low pressure near the surface in the eye/core.

High above the eye wall this upflow begins to spread out. This permits cool dry air above the eye to sink down into the central core of the eye (that is why the eye is often clear and cloud free).

So why is the hurricane core/eye low pressure when there is cool dry air subsiding down into the core/eye?

Soundings taken within the eye show a low-level layer (at surface) that is relatively moist with an inversion above, i.e., it appears that the sinking cool dry air (which warms somewhat as it is compressed in descent) never reaches the ocean surface, but only reaches within 1 - 3 km (1 - 2 mi) of the surface. See, among other sources, http://www.aoml.noaa.gov/hrd/tcfaq/A11.html.

Sept. 9, 2023 edit: I happened across a superb meteorology textbook available under CC license (you may share it freely for non-commercial use):

Stull, R., 2017: "Practical Meteorology: An Algebra-based Survey of Atmospheric Science" -version 1.02b. Univ. of British Columbia. 940 pages. isbn 978-0-88865-283-6

Stull provides comprehensive, understandable (if you can read college-level material) coverage of tropical cyclones (as one subject of meteorology), and definition and discussion of related concepts throughout this textbook. To try to cover the contingency, that the link becomes inactive, I uploaded a copy of the text in pdf to Practical Meteorology at archive.org. Use the pdf button to obtain the copy.

For a quick hint at the Stull treatment, I include a figure from his text showing the intake system of the tropical cyclone in schematic cross section. This nicely illustrates that the majority of the updraft air coming up the walls of the eye diverges at the top of the core, rather than subsiding down the core (see text):

Fig 16.26 Intake System Tropical Cyclone

Also, a figure from Stull showing the difference in temperature within the hurricane core relative to surroundings:

Fig 16.28 Core temperatures hurricane relative to surroundings

That perhaps makes it more sensible that the warmer core air cannot continue subsiding down to the near-sea surface low at base of the core, where the air is very moist, but at lower temperature (might consider this to be a high stopping on encounter with a low).

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  • $\begingroup$ In retrospect, your answer gave me the clearest explanation. Thank you. $\endgroup$
    – jysh
    Aug 31, 2018 at 4:55
  • $\begingroup$ @JayeshBhoot Glad you decided answer ok. I was on the US New England coast when Gloria hit in 1985 Sept. 27 about 1700 UC (I refused to evacuate, but left when the sea began to come up to my apartment). It was difficult to stand in the gusts 85-90 mph. The eye was amazing. It did feel slightly moist, eerily calm and sunny with blue sky after minutes before gray hurricane rage. We drove into town over treelimbs and power lines and had free beer and seafood, the restaurants having no power and giving it away. So, the explanation of an inversion in the eye at ground level felt believable. $\endgroup$ Oct 1, 2018 at 19:12

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