STORM2K

Can somebody explain to me how and why an anticyclone forms on top of hurricanes?

It's a matter of the rising air in the core of a storm having to go somewhere. And as it flows outward away from the center, the Coriolis effect causes a rightward turn *(in the northern hemisphere) resulting in anticyclonic turning. In other words, it's exactly the same thing as causes cyclonic turning at the surface as air flows inward.

Hope that was clear enough.

uhh...so the coriolis causes two different effects at two levels of the atmosphere?

One involves high pressure, the other involves low pressure. That's why it's called an anti-cyclone.

look at it this way. Air in a hurricane is generally rising...due to it being an area of low pressure. As this air rises, it eventually hits a stable layer (the tropopause) and begins to "pile up". This piling causes the pressure to rise diverge away from the center of the newly developed anticylone. I hope that helps.

wall_cloud wrote:look at it this way. Air in a hurricane is generally rising...due to it being an area of low pressure. As this air rises, it eventually hits a stable layer (the tropopause) and begins to "pile up". This piling causes the pressure to rise diverge away from the center of the newly developed anticylone. I hope that helps.

Usually, it looks as if an anticyclone has started to form before the storm even goes to town. I've noticed (and Bastardi points this out) an upper low that will shear a system, and prevent tropical development, may move far enough away (usually to the West) to induce an short wave anticyclone over an area of storms that may have been enhanced when the upper low interacted with the surface feature. (why Bastardi likes small upper lows, that shear and ignite storms, than back off a feature, as compared to a long wave trough, like the TUTT low often over the West central Atlantic that shears it to death).

So, in a way, it is almost a chicken or the egg kind of thing, from my non-met educated perspective. The hurricane builds an anticyclone, but a pre-existing anticyclone sometimes seems to help develop the hurricane.


OK, no snow in HOU (hi, Wall-Cloud) but it got as close as Montgomery County.


BTW, I wish I had a met education, my dad,w ho knew low paid mets at American Airlines talked me out of it.

But the stuff I learned in petroleum engineering, mass balances, the application of the diffusivity equation, plus ideas like integral and differential calculus, concepts like multi-phase flow through hetereogeneous media, seems to make some of the met processes easier to visualize, even if I can't quantify them the way I'd like.

you are right Ed. It can be there first. The upper level divergence associated with the upper level ridge (typically the Bermuda Ridge) will aid in the development of the low level cyclone. The Law of Conservation of Mass implies that if you have divergence aloft, you must have convergence below because the air in the column is rising. This rising air creates and intensifies the low level cyclone.

On the flip side, as the low level convergence intensifies, the rising motion in the cyclone intensifies as well. This causes more precipitation and clouds which, in turn, releases latent heat. This latent heat helps to intensify the upper level anticyclone. So its a positive feedback effect from both sides.

Thanks for pointing that out Ed. I was only thinking of the relationship noted in the second paragraph of this post.

wall_cloud wrote:look at it this way. Air in a hurricane is generally rising...due to it being an area of low pressure. As this air rises, it eventually hits a stable layer (the tropopause) and begins to "pile up". This piling causes the pressure to rise diverge away from the center of the newly developed anticylone. I hope that helps.

That makes it a heck of a lot easier to understand. Thanks!

fact789 wrote:uhh...so the coriolis causes two different effects at two levels of the atmosphere?

Sorry, guess I wasn't so clear. The coriolis effect is basically the same regardless of altitude, but whereas air is flowing in at the surface, it's flowing out at high altitude.

Bumping an old topic because it deals with what I have a question about...

Out of curiosity, is there a zone between the lower level cyclonic rotation and the upper level anticyclonic rotation that is basically calm (rotation-wise)? It would seem to me that if the high were squashed directly against the low pressure, it would induce upper level shear on the storm...and since upper level shear is bad, it could potentially disrupt the entire system.

But, if there is a zone where the air is not rotating (providing cushion between the two opposite rotating levels), then the whole system *should* work fine (provided an outside source is not messing it up, of course).

I think of it like this, if you have the two sitting directly ontop of each other, that is going to be some serious direction and speed shear in the areas where the two mix up...thus making the whole system sluggish. Insert the cushion, to allow time for the air to go from rotating counterclockwise to clockwise, and there is no disruption (hence the pocket of "calm" air between the two). Interesting theory, I personally think...but I'm not a certified, trained meteorologist...so it'll probably be shot all full of holes