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A comparison of two identification and tracking methods for polar lows Cover

A comparison of two identification and tracking methods for polar lows

Tellus
Volume 64 (2012): Issue 1
By: ,  ,  ,   and    
Open Access
|Dec 2012
Figures & tables

Figures & Tables

Fig. 1. 

Unfiltered MSLP field on 06:00 14 October 1993 (hPa).

Fig. 2. 

NOAA 11/AVHRR channel 4 thermal infrared for 1529 UTC 14 October 1993 (from www.sat.dundee.ac.uk/).

Fig. 3. 

Bandpass filtered MSLP fields on 06:00 14 October 1993 (hPa): (a) digital filter, (b) DCT, and detected minima: red by KH and green by MZ.

Fig. 4. 

Bandpass filtered 850 hPa relative vorticity fields on 06:00 14 October 1993 (10−5 s−1): (a) digital filter and (b) DCT.

Table 1. Numbers of tracks resulting from different combinations between MZ and KH (October 1993 to September 1995)

Filter Detection Tracking Numbers of tracks 1 KH KH KH 856 2 KH KH MZ 833 3 MZ KH KH 1509 4 MZ KH MZ 1400 5 KH MZ MZ 819 6 KH MZ KH 971 7 MZ MZ MZ 1421 8 MZ MZ KH 1570
Fig. 5. 

Overlapping tracks in October 1993 for combination 5 (blue) and combination 7 (red) of Table 1.

Table 2. Number N o of overlapping tracks, probability P o for overlapping tracks and ratio P m of non-overlapping tracks for different combinations in Table 1 using combination 1 as a reference

1 2 3 4 5 6 7 8 No 856 768 385 387 608 713 372 380 Po 1.00 0.91 0.33 0.34 0.73 0.78 0.33 0.31 Pm 0.00 0.09 0.67 0.66 0.27 0.22 0.67 0.69

Table 3. Number N o of overlapping tracks, probability P o for overlapping tracks and ratio P m of non-overlapping tracks for different combinations in Table 1 using combination 7 as a reference

1 2 3 4 5 6 7 8 No 372 377 989 1025 401 416 1421 1247 Po 0.33 0.33 0.68 0.73 0.36 0.35 1.00 0.83 Pm 0.67 0.67 0.32 0.27 0.64 0.65 0.00 0.17

Table 4. Numbers of retained potential polar lows after applying the respective criteria in Section 2.4 in October 1993 to September 1995

Noland Filtered minimum Wind speed vst NS supmin sum 1 856 533 508 231 81 3 84 3 1509 818 744 352 127 8 135 5 819 442 419 186 78 1 79 7 1421 738 680 303 120 7 127

[i] ‘Noland’ means that it excludes tracks over the land as applying the criterion 4; ‘filtered minimum’ means that filtered MSLP should be below –2 hPa at least once along a track as applying the criterion 1; ‘wind speed’ means that the maximum 10 m wind speed around the storm centre has to be larger than 13.9 m s−1 at least for 20% of the positions as applying the criterion 2; ‘vst’ means that vertical instability should be fulfilled as applying the criterion 3; ‘NS’ requires the tracks to go from north to south as applying the criterion 5 and ‘supmin’ means that the filtered MSLP falls below −6 hPa at least once along the track and ‘noland’ is also fulfilled as applying the criterion 6. ‘Sum’ is the final number of retained potential polar lows

Fig. 6. 

Tracks of potential polar lows after applying criteria to combination 1 (red with points) of KH and combination 7 of MZ in October 1993 (blue).

DOI: https://doi.org/10.3402/tellusa.v64i0.17196 | Journal eISSN: 3035-9554
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Language: English
Page range: 17196 - 17196
Submitted on: Jun 29, 2011
Accepted on: Jan 2, 2012
Published on: Dec 1, 2012
Published by: Stockholm University Press
In partnership with: Paradigm Publishing Services
Keywords:
cyclone,
tracking algorithm,
polar lows,
spatial filter,
North Atlantic

© 2012 Lan Xia, Matthias Zahn, Kevin I. Hodges, Frauke Feser, Hans von Storch, published by Stockholm University Press
This work is licensed under the Creative Commons Attribution 4.0 License.

Volume 64 (2012): Issue 1
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