3.3.9 Cyclone Tracking

The Cyclone Tracking Major Mode of MetCal is the most complex in terms of usage. Any two dimensional variable (in the Identifier field) can be operated on in the region of a tracked cyclone. Note that all cyclones are tracked using the height field (on pressure levels, default 1000~hPa in the Level entry) and that it must therefore be present in the primary input file, along with the field of interest. The Maximum Cyclone Phase Speed entry allows the user to track cyclones of different speeds. You will probably only run into a problem if this is set too low, but the default value of 30 m/s is already pretty high. The Radius of Interest defines the low-centre-relative region over which to operate on the field of interest. The default value for this entry is 1000 km.

The Cyclone Tracking Major Mode produces text output files of any or all of the field of interest's mean, standard deviation, minimum, or maximum near the low centre. These files are named with the Text Output Root prefix and -mean, -sd, -min, or -max suffixes. The output format is space-separated “time value” for forecast data, or “date value” for analysis data. These text files can be ingested directly into a plotting program such as xmgrace or (shudder) Excel to produce time-series of storm-following quantities.

Two execution modes are selectable by the user. The automatic start mode searches for the lowest height on the pressure level (i.e. the deepest low) in the initial field, and continues to track that feature. Manual start mode allows the user to input the x,y grid coordinates of the cyclone to be tracked. Similarly, the automatic step mode allows the algorithm to track the cyclone automatically (or at least to attempt to). If the routine senses that it has lost the track, it will prompt the user for the x,y coordinate at a specific time in MetCal's parent shell. The manual step mode always asks the user for the location of the storm at every step.

Because of the unique interactive nature of this Major Mode, MetCal must be run in the foreground of the parent shell for correct functionality. We hope to rectify this problem with an interactive TopLevel window in future versions of the interface.