Potential vorticity inversion diagnosis of the development of polar lows

The objectives of this dissertation are to: 1) identify the bulk microphysics schemes (BMS) that is likely to be most suitable for model-based investigations of the role of moist processes in the dynamics of polar low development, 2) examine the relative influences of upper-tropospheric, lower-tropospheric, and diabatic potential vorticity (PV) anomalies in the development of polar lows.;Five mixed-phase BMSs were evaluated in numerical simulations of polar lows. The model simulations were validated against the satellite observed cloud top temperatures and precipitation rates and against gauge-calibrated surface radar precipitation estimates around Japan. Results from the WRF Single-Moment 6-class (WSM6) scheme appear to reproduce the cloud and precipitation processes most realistically. The model produced precipitation intensities comparable to validation products over the Sea of Japan. However, in the Nordic Sea cases, all five schemes produced significantly more precipitation than the satellite microwave estimates.;The piecewise PV inversion method was used to diagnose the development processes of two polar lows, one over the Sea of Japan and the other over the Nordic Sea. The main synoptic development of polar lows was successfully captured using the inversion method. Both of the polar lows were initiated when the positive upper-tropospheric PV anomaly approached the surface positive temperature anomaly. Further intensification was contributed by the latent heat release associated with cloud and precipitation processes. For the case over the Sea of Japan, the rapid height falls at lower troposphere were primarily contributed to the upper-tropospheric PV anomaly. However, the development of the polar low over the Nordic Sea was mainly a result of the boundary temperature anomaly contributed by the strong air-sea interaction.;Comparing between the two polar lows, it was suggested that the upper-tropospheric PV anomaly is a necessary condition to support the further development of polar lows. The shorter lifecycle of the Nordic Sea case may be an artifact of the upper-tropospheric PV anomalies inability to support its further development. Furthermore, the intense air-sea interaction which led to the boundary temperature anomaly was more important for the Nordic Sea case while its effect was smaller in the case over the Sea of Japan.