The motion of the upper-level outflow of a typhoon

Question

I was taught that while the motion of a tropical cyclone is mostly cyclonic, there is an outflow at the top whose motion is anticyclonic. So I expected an animated satellite image of a typhoon to look like a spiral spinning clockwise. However, it appeared to spin counterclockwise(Example). Why is that? Is it because the clouds generated by the outflow are too thin that they are not visible in the satellite image, even in the infrared image?

Answer 1

It's hard to see but it's definitely there in your example. You can see some upper-level clouds in the South-Southeast quadrant of the storm moving away from the center in somewhat of an anticyclonic manner. There's also some upper-level clouds at the left most part of the animation that are also migrating away from the storm center.

But yes, sometimes the clouds are too thin that they are barely visible even in infrared imagery. I suggest you to take a look at a real-time wind map online where you can vary the altitude, such as Windy. Here, you'll be able to clearly see the outflow of a tropical cyclone at a certain height. The anticyclonic outflow of a tropical cyclone is much more noticeable at stronger intensities so you may have to wait for a big storm to show up.

Answer 2

Thing is:

• The high pressure tends to be relatively weak in comparison to the low-level cyclone, such that winds are much weaker around the high aloft than around the low nearer the ground. _{^{(by strength, I'm talking about relative to surrounding or typical pressures/heights at the same level, so how abnormal a value it is/how strong the pressure gradient is)}}
• The vigorous convection of a hurricane/typhoon is forced at lower levels... so all the cumulus you see be transitioning in the cyclonic pattern following the low-level forcing.
• So because of this, and because the upper level clouds are typically thinner cirrus, you'll have to find blowoff from storms which move away so that they are not above the cumulus... combine this in with the fact that winds tend to increase with distance away from high pressure, while decreasing with distance from the low pressure (a factor of the way the pressure gradient distributions that develop... with a relatively wide and broad high, versus and sharp and tight low)... all that together means that the anticyclone will only typically tend to be noticeable at significant distance from the storm (and will still yet tend to rotate much more slowly than the significant storms in the inner core).

And to throw in one more challenge... the cirrus you'll need to track don't show as well at visible wavelengths, so if you happen to be looking at visible imagery, especially during midday, you may further struggle to see any anticyclone aloft.

So all you have to do is look away from the more interesting part of the storm, for features much less numerous (because the cirrus isn't usually a widespread feature, not forming much on its own, but only from the main storm blowoff), things are moving much less, and be looking at the right type of satellite imagery!

But it's more than possible. A neat one to me is this multi-day animation of Hurricane Irma from 2017 _{^{(and Katia and especially Jose too!)}}.

Or, we're in luck a bit datawise right now, if we can handle a key difference, with Cyclone Ilsa nearing northwest Australia as a category 4 Tropical Cyclone ^{_{(cyclone is basically the Australian term for a typhoon [or really supertyphoon], also similar to the Western Hemisphere term hurricane)}}

So some images:
(But just remember, rotation is opposite in the southern hemisphere, so low pressure rotates clockwise and high pressure counterclockwise)

Here is the infrared satellite imagery of Ilsa from CIMSS [click here for the current animation] where the anticyclone is findable:

To help, I turned on the cyan wind barbs, which are actually from an algorithm tracking the upper level cloud elements in the imagery [determined by using an algorithm on cloud temperatures I believe, then tracking which way the features move] [the cyan is between 100 and 250 mb, the yellow is between 250 and 350 mb, and the green is between 350 mb and 500 mb]

And then, here is a current global model analysis (from WeatherNerds.net) which allows us to see the full atmospheric motion, overlaying the low level winds (the black symbols, flowing towards the side of the symbol with no additional sticks/addons)) and the upper level winds (the dark blue symbols, again flowing towards the side of the symbol with no additional sticks/addons):

The purple arrow follows the blue symbols, showing the [counter-clockwise, since Southern Hem] upper-level anticyclone (high pressure), and the grey arrow follows the black symbols, showing the [clockwise, since Southern Hem] low-level cyclone (low pressure). [If you know how to read station obs, note in either imagery how the upper winds are quite weak compared to the roughly 130 kt-equivalent-typhoon speed _{^{[VERY ROUGHLY... as converting wind speeds between cyclones/typhoons/hurricanes/ground observations is a FAR too complex subject]}}]

So they're there, you just may have to look carefully.
Typically the stronger the tropical cyclone [tropical cyclone is a generic term for typhoons/cyclones/hurricanes/etc], the stronger the high pressure, because the anticyclone grows as the heat is released aloft near the center of the storm. Though there can be a bit of a chicken-egg factor sometimes... a larger, more stacked existing anticyclone itself can help strengthen a storm in the first place due to the reduced wind shear. And I suppose you also can get a leftover strongish anticyclone over a suddenly rapidly-dying tropical cyclone (if it moves over significant land/cold water).

I've also noticed that often there's more debris clouds helping to see the nearby anticyclone (note these aren't really the same as the large regional features like the Bermuda high or Pacific High, which are a whole separate, much larger scale; the Bermuda High typically covers most of the Atlantic, far north of most storms, typically steering hurricanes from west to east) on the poleward side of a tropical cyclone. This makes sense, as that is the side where the convection will interact with the mid-latitude winds aloft, which are much faster, and also where the moisture can help fuel additional cloudiness due to the more baroclinic environment. Such outflow channels can be important in the intensification of tropical cyclones. Or other times, they foreshadow a storm becoming extratropical. Here's a great example of such elongated outflow from Hurricane Ian last year:

You may be able to almost visualize the slow clockwise rotation around the northeast side of the storm just in that still image? (If not, try the loop titled Hurricane Ian Approaches Florida loop, well down this page)

So some imagery lends itself better to finding the local anticyclone about a tropical cyclone, but they're generally there.