The role of diagnostic tools in modern weather forecasting
Meredith Kurz · Meteorological Applications · 1994
An important task in modern weather forecasting is the evaluation and interpretation of the output of the operationally used numerical models. For this task the forecaster needs diagnostic tools enabling him or her to understand ‐ at least qualitatively ‐ the processes which are going on in the atmosphere now and which are simulated in the numerical forecasts. This paper describes three different forms of the quasi‐geostrophic diagnostics used in the Deutscher Wetterdienst for this purpose. Besides the conventonal form, in which vorticity and temperature advection are considered as forcing functions for vertical motions and cyclogenetic or anticyclogenetic effects connected with them, Q‐vector diagnostics are used. They are of special advantage since they allow not only a definite estimation of the omega forcing but also a diagnosis of frontogenetic (or frontolytic) effects in the geostrophic wind field and the transverse circulations released by them. As regards the onset of cyclogenesis, the monitoring of positive anomalies of the isentropic potential vorticity near the tropopause is a very effective diagnostic tool. All these parameters can be easily derived and presented on modern workstations where they can be compared with observations and satellite and radar data. Altogether, a better understanding of atmospheric processes can be reached and, resulting from that, a better transposition of numerical output into weather forecasts.