PV blocking index field

Here two novel indicators of blocking are introduced that are formulated in a potential vorticity (PV) framework. In this framework the phenomenon is to be viewed in terms of the evolution and pattern of its PV distribution.
Therefore a vertically averaged measure of the potential vortcity (PV within the 500 - 150 hPa layer, VAPV) is calculated, underlining the quasi-barotropic nature of blocked atmospheric state. The indicators:

APV-index field

Undulations of the two dimensional VAPV field to lower values can be regarded as a high tropopause. Low VAPV (potential blocking events) are tracked over a timeperiod that last at least a couple of days (e.g. 5 days). The obtained blocking field can subsequently be used for dynamical blocking studies.

APV*-index field

Here the tracking algrithm was applied on the VAPV-anomaly field. This anomaly field was calculated by subtracting the 30-day climatological (40 years) running mean for every timestep (6 hours). Negative VAPV-anomalies indicate possible blocking events.