Here are some pressure gradient force examples: a) Point A: 995 mb; Point B: 100

Question

Here are some pressure gradient force examples:

a) Point A: 995 mb; Point B: 1000 mb. Distance = 200 km. Density = 1.2 kg m3

PGF = 0.002083 m s2

b) Point A: 975 mb; Point B: 1000 mb. Distance = 200 km. Density = 1.2 kg m3

Point A: 975 mb = 975 hPa 975 hPa * 100 Pa / hPa = 97500 Pa = 97500 kg m1 s2)

PGF= 0.010417 m s2

c) Point A: 500 mb; Point B: 505 mb. Distance = 200 km. Density = 0.75 kg m3

Point A: 500 mb = 500hPa 500hPa * 100 Pa / hPa = 50000 Pa = 50000 kg m1 s2

PGF = 0.003333 m s2

d) Point A: 500 mb; Point B: 525 mb. Distance = 200 km. Density = 0.75 kg m3

Point A: 500 mb = 500hPa 500hPa * 100 Pa / hPa = 50000 Pa = 50000 kg m1 s2

PGF = 0.016667 m s2

My question is this....

Based on your calculations, in which case (i.e. surface or aloft) is the PGF the highest? Please defend your reasoning.

Explanation / Answer

d) Point A: 500 mb; Point B: 525 mb. Distance = 200 km. Density = 0.75 kg m3

Point A: 500 mb = 500hPa 500hPa * 100 Pa / hPa = 50000 Pa = 50000 kg m1 s2

PGF = 0.016667 m s2

In case "d" the PGF is highest.

As we move higher, surface features affect the wind less until the wind is indeed geostrophic. This level is considered the top of the boundary (or friction) layer. So, the PGF will not be higher at surface due to various frictional losses.

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