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);