Inclass
Exercise 5

**On a given day, at western Nebraska,
the 350 mb divergence is 3.99 X 10 ^{-5} s-^{1}. At the same spot, the 850 mb
divergence is -3.05 X 10-^{5} s^{-1}. Compute the one hour surface pressure tendency for this
point using the pressure tendency equation. **

** (1)**

is
the pressure tendency equation if w at top is zero and density advection is
negligible. In this case,
"top" is the tropopause (at 200 mb) and "bottom" is the surface (in this part of the
high Great Plains, 850 mb). If the
atmosphere is hydrostatic then substitution of

** (2)**

into
(1) and remembering that w = 0 at the surface, equation (1) reduces to

You
may make the following assumptions which will simplify the procedure:

(a) the
850 mb divergence is representative of the net divergence BELOW the level of

nondivergence
and the 850 mb is near the ground;

(b) the 350 mb
divergence is representative of the net divergence ABOVE the level of

nondivergence;

(c) the
tropopause is at the 200 mb level and the surface pressure at station A is 850
mb (this station is not at sealevel);