PBL Velocity Profile: Sinusoidal Variation w/ Height

In summary: I guessed that wrong ... will do some reading :smile:Thank you all for your replies. I am not sure if the author is talking about the Ekman spiral or not.
  • #1
MOHAMMAD UMAIR
4
1
Why does the planetary boundary layer velocity profile shows a sinusoidal variation with height?
Reference: Fig:14.10 Page 576 Fluid Mechanics - Kundu and Cohen 2nd edition
 
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  • #2
I don't see any mention of sinusoidal variation with height in the text ? Perhaps you have misinterpreted what is shown in fig 4.10 (b) ?

I think that the general topic is explained quite well by the author .

Please post new questions if you have any specific problems .
 
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  • #3
Nidum said:
I don't see any mention of sinusoidal variation with height in the text ? Perhaps you have misinterpreted what is shown in fig 4.10 (b) ?

I think that the general topic is explained quite well by the author .

Please post new questions if you have any specific problems .
Thanks Nidum for your reply. I know that the general topic is explained quite well in the text but the author has presented the boundary layer velocity profile in the figure without explaining why there is an undulation of the velocity profile with height. You won't find such undulations in the general boundary layer velocity profiles on a flat plate.
 
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  • #5
jim mcnamara said:
My apologies if I am making a mess of this question. But. Is Figure 1 in the linked pdf file what you are talking about?

people.atmos.ucla.edu/jcm/turbulence_course_notes/planetary_boundary_layers.pdf

interesting article, thanks :smile:
MOHAMMAD UMAIR said:
Why does the planetary boundary layer velocity profile shows a sinusoidal variation with height?
Reference: Fig:14.10 Page 576 Fluid Mechanics - Kundu and Cohen 2nd edition
I don't have access to that article/book ... it would be good for you to copy and paste the section or if you cannot, scan it or at bare minimum type out the paragraph or two that you are referring to, so that we are all on the same page

As a result, I have no idea which boundary you are referring to ??
Moho ?, upper/lower mantle ?, mantle/outer core ?
MOHAMMAD UMAIR said:
I know that the general topic is explained quite well in the text but the author has presented the boundary layer velocity profile in the figure without explaining why there is an undulation of the velocity profile with height. You won't find such undulations in the general boundary layer velocity profiles on a flat plate.

assuming you are referring to one of my listed ones, and probably the Moho boundary,

Why would you expect to ? the Earth isn't flat and nor are the layers and their boundariesDave
 
  • #7
Thank you all for showing your keen interest in answering the question I've posed. Davenn I am reffering to the Ekman boundary layer profile that you have in your lecture notes on page number 24 figure15 a.
 
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  • #8
jim mcnamara said:
I believe he is talking about this, which is why I am cautious, cannot see the book he referenced. (meteorology, laminar flow (fluid dynamics) and more intricacies):
https://en.wikipedia.org/wiki/Planetary_boundary_layer

There is a really great graphic there.

ohhh, we are going up, not down, I guessed that wrong ... will do some reading :smile:
 
  • #9
MOHAMMAD UMAIR said:
Thank you all for showing your keen interest in answering the question I've posed. Davenn I am reffering to the Ekman boundary layer profile that you have in your lecture notes on page number 24 figure15 a.
Are you asking why the "Ekman spiral" spirals?
 

What is PBL Velocity Profile?

The PBL Velocity Profile refers to the variation of wind speed with height within the planetary boundary layer (PBL). The PBL is the layer of the atmosphere closest to the Earth's surface, where turbulence and mixing are most active. The PBL Velocity Profile is typically represented by a graph showing the change in wind speed as a function of height.

What is Sinusoidal Variation?

Sinusoidal variation refers to a pattern or function that follows a sinusoidal curve, also known as a sine wave. It is characterized by a repetitive oscillation between maximum and minimum values, with a consistent period and amplitude. In the context of PBL Velocity Profile, sinusoidal variation refers to the sinusoidal shape of the wind speed curve as it changes with height within the PBL.

Why is Height Important in PBL Velocity Profile?

Height plays a crucial role in PBL Velocity Profile because wind speed is highly influenced by the surface roughness and topography of the Earth's surface. As wind moves from the surface to higher altitudes, it encounters different surface features and experiences changes in turbulence and mixing, resulting in a change in wind speed. Therefore, understanding the variation of wind speed with height is essential for studying and predicting atmospheric processes.

What Factors Affect the PBL Velocity Profile?

Several factors can affect the PBL Velocity Profile, including surface roughness, topography, atmospheric stability, and surface heating. The roughness of the Earth's surface can create drag on the wind, causing it to slow down and change direction. Topography, such as mountains or valleys, can also impact wind speed and direction. Atmospheric stability, which is influenced by temperature and humidity, can affect the intensity of turbulence within the PBL. Finally, surface heating can cause temperature differences that lead to changes in wind speed and direction.

How is PBL Velocity Profile Measured?

PBL Velocity Profile is typically measured using instruments such as anemometers, sonic anemometers, and lidars. These instruments can accurately measure wind speed and direction at various heights within the PBL. Data collected from these instruments can be used to create a graph of the PBL Velocity Profile, providing valuable insights into the variability of wind speed with height in the PBL.

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