- #1
x_engineer
- 55
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- TL;DR Summary
- Two angular momentum impossibilities implied by the usual hurricane anatomy diagrams
Here is a NASA article on "Hurricane Anatomy"
https://earthobservatory.nasa.gov/features/Hurricanes/hurricanes_2.php
The first issue I have is the apparent reversal of the angular momentum when going from surface winds to the winds in the covering cloud cap.
In the northern hemisphere, surface winds are shown to be anti-clockwise when viewed from above, and increasing in intensity as one approaches the eyewall, and flowing towards the eyewall from outside. The wind then turns up, but remains anti-clockwise around the eye until it reaches the covering cap cloud layer, then starts flowing outward and decreasing in intensity. So far so good, everything is physical.
But then, every diagram I have seen shows the rotation flipping to clockwise before it gets to the edge of the cloud cap. Some even claim in the accompanying text that the cloud cap rotates clockwise. Does actual data show a clockwise rotation of the outer cloud cap? If so, what is the source of the clockwise torque to make this happen? Or is it just that people draw the right ward arrow denoting the decreasing angular velocity (not momentum!) too far to the right? If the point of the arrow still pointed a little bit in the anticlockwise direction things could be physical without a source of clockwise torque.
Assuming the above depiction is a mistake and the eyewall radius rotates anti-clockwise all the way to the "top" of the atmosphere, the second issue I have is the depiction of a downward flow in the center of the eye of the hurricane. This is inconsistent with calm conditions at the center of the eye. Since the source of this downward flow has anti-clockwise momentum, flows inward at the top, and there is nothing above to deliver a clockwise torque, the only possibility is increasing angular velocity as one approaches the center of the eye. However, an upward flow is consistent with calm conditions - this implies the surface flow is inward, but the angular momentum at the eyewall is bled away by friction with the surface.
So what is the true air motion? We are talking about the totally clear air in the eye of the storm and above the cloud cap,
and the direction of the cloud cap winds in the outer regions of the storm.
Does hurricane formation require pre-existing clockwise angular momentum about a latent eye in the upper atmosphere?
Niket Patwardhan
https://earthobservatory.nasa.gov/features/Hurricanes/hurricanes_2.php
The first issue I have is the apparent reversal of the angular momentum when going from surface winds to the winds in the covering cloud cap.
In the northern hemisphere, surface winds are shown to be anti-clockwise when viewed from above, and increasing in intensity as one approaches the eyewall, and flowing towards the eyewall from outside. The wind then turns up, but remains anti-clockwise around the eye until it reaches the covering cap cloud layer, then starts flowing outward and decreasing in intensity. So far so good, everything is physical.
But then, every diagram I have seen shows the rotation flipping to clockwise before it gets to the edge of the cloud cap. Some even claim in the accompanying text that the cloud cap rotates clockwise. Does actual data show a clockwise rotation of the outer cloud cap? If so, what is the source of the clockwise torque to make this happen? Or is it just that people draw the right ward arrow denoting the decreasing angular velocity (not momentum!) too far to the right? If the point of the arrow still pointed a little bit in the anticlockwise direction things could be physical without a source of clockwise torque.
Assuming the above depiction is a mistake and the eyewall radius rotates anti-clockwise all the way to the "top" of the atmosphere, the second issue I have is the depiction of a downward flow in the center of the eye of the hurricane. This is inconsistent with calm conditions at the center of the eye. Since the source of this downward flow has anti-clockwise momentum, flows inward at the top, and there is nothing above to deliver a clockwise torque, the only possibility is increasing angular velocity as one approaches the center of the eye. However, an upward flow is consistent with calm conditions - this implies the surface flow is inward, but the angular momentum at the eyewall is bled away by friction with the surface.
So what is the true air motion? We are talking about the totally clear air in the eye of the storm and above the cloud cap,
and the direction of the cloud cap winds in the outer regions of the storm.
Does hurricane formation require pre-existing clockwise angular momentum about a latent eye in the upper atmosphere?
Niket Patwardhan