Extra-Tropical Cyclones Automated Tracking

1- Methodology:

Tracking based on synoptic scale gradient wind vorticity as proposed by:
Sinclair, M. R., 1997: Objective identification of cyclones and their circulation intensity, and climatology. Wea. Forecasting, 12, 595–612.

To be considered, cyclones (i.e. vorticity maxima) must reach a given threshold value (+1,5x10-5 s-1) and last at least 24 h.

After computation, vorticity (and other model fields) is smoothed using a Cressman filter with a smoothing radius of 800 km to removed (real and ficticious) small scale details.

2- Trajectory maps description:



1- Day and time (UTC) of cyclone appearance
2- Location of gradient wind vorticity maximum
3- Gradient wind vorticity maximum value (x10-5 s-1)

Voricity centres are mapped every 3 or 6 hours following the availability of model data

Vorticity maximum values are mapped every 6h only.

3- 4 panel animation description:

Animation every 6h showing :



A- Mean sea level pressure (or 500 hPa heights) after filtering
B- Original (i.e. without filtering) mean sea level pressure (or 500 hPa heights)
C- Gradient wind vorticity after filtering
D- Gradient wind vorticity after filtering greater than the threshold value of +1,5x10-5 s-1

4- Model data resolution used:

Analyses (GEM-REG) - 50km (at 60N)
GEM (REG and GLB) - 60km (at 60N)
GFS, NAM and UKMET - 100km (at 60N)