Hi Bob
Im struggling to understand when the gradient wind compared to the surface wind backs and veers as to my knowledge its Veers over land by 30 degrees and reduces by 2/3 and over water by 10 degrees and 1/3 but i got question about a low pressure system and it says it backs so Im kinda confused. If you could help that would be greatly appreciated.
Cheers Sam
I suspect that you are asking about the way the surface wind behaves throughout the day (diurnal variation). The angle of deflection of the wind in relation to the isobar varies with wind speed. When the wind is slow, the deflection across the isobar is greater than when it is fast.
So, for a given location, the deflection will be greatest in the early morning when the wind is calmer. As the day goes on, there will be less deflection and the wind direction will be closer to the isobar (closer to the gradient wind). Therefore, the wind direction later in the day will have [i]backed[/i] with respect to the wind direction in the early morning.
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