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Meteorology 535/835

Homework 2: Due at Beginning of Class, September 16, 2011). (Students Reviewing These Papers Are Released from this Homework)

Reading 1:       The Distinction between Large-scale and Mesoscale Contribution to Severe Convection:  A Case Study Example (pdf)

1.  How might forecasters might infer that the low level moisture field might be modified to remove one of the two obstacle for convection in the Topeka area.

Forecasters can assume that diurnal heating, warm advection and moisture advection (advection of higher mixing ratios as evidenced by higher dew points) would simultaneously weaken or eliminate the inversion and increase the potential sbCAPE. Diurnal heating is strong in the spring and the synoptic-scale pattern would be contributing to the factors altering the sounding in the mesoscale area around Topeka.

2.  Doswell's definition of "dynamics" and "thermodynamics" has been adopted generally in the profession (despite the misuse of these terms still in the field). What are those definitions?

"Dynamics", according to Doswell, refers to the synoptic-scale lift as diagnosed by the quasigeostrophic omega equation and quasigeostrophic horizontal motion patterns that create a mesoscale focus for DMC and also can provide destabilizing influences to existing soundings. and "thermodynamics" is the combination of moisture and lapse rate distributions that makes DMC possible.

3.  Why could the quasigeostrophic forcing for vertical motion be more significant for the subtle patterns in the middle and upper troposphere during Spring and Summer? (This question involves considerable synthesis at a qualitative level. Make sure you discuss WHY the patterns in the spring and summer might be expected to be associated with weaker quasigeostrophic effects yet the equation provides the answer to how these effects can be increased despite this).

While the two primary forcing functions in the quasigeostrophic omega equation relate to advective effects (related either to vorticity advection or temperature advection), they are both "weighted" by a factor of 1/sigma. Sigma is the static stability paramenter, and is defined for dry adiabatic ascent only....and is thus always positive and large at the synoptic scale. Its effect is to REDUCE the magnitude of each forcing function. In essence, the forcing functions are directly proportional to advection and inversely proportional to the stability. In the spring and summer, the strength of the advection fields weakens (largely a function of the decreasing wind speeds, but also due to decreasing temperature and vorticity gradients). However, static stability also decreases, and can decrease in focussed areas so greatly (around and along moisture tongues ahead of the dry line) that the actual net forcing can be greater than that associated with the stronger synoptic scale systems of the winter.