Satellitebased overshooting top detection methods comparison and validation

Satellite-based overshooting top detection methods: comparison and validation Petra Mikuš, Nataša Strelec Mahović Meteorological and Hydrological Service, Croatia

1/15 Outline � � On Overshooting tops (OT) Satellite based detection methods Weather conditions in the vicinity of the OTs Conclusions Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

2/15 On Overshooting Tops � � � domelike protrusions above thunderstorm’s anvil often penetrating into lower stratosphere manifestation of very strong updraft existing for less than 30 min diameter ~ 15 km vertical extant: up to about 2 -3 km Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

3/15 Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

4/15 OT appearance in satellite images: Sandwich product: HRV + color-enhanced IRW 10. 8 μm Storm top plume OT Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

5/15 THERMAL FEATURES: color-enhanced IR 10. 8 μm COLD RING COLD U/V Cold U shape Cold ring Central warm area Close-in warm area Distant warm area All the other storm top features result from the activity of OTs: cold ring, cold U/V, storm top plumes, storm top gravity waves…!!! Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

6/15 Sendwich product: HRV + color-enhanced IRW Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

7/15 Satellite-based detection methods Channel differences: • • 6. 2 – 10. 8 µm (WV-IRW) 9. 7 – 10. 8 µm (O 3 -IRW) 13. 4 – 10. 8 µm (CO 2 – IRW) COMB– combination of the WV-IRW and O 3 -IRW methods BTD Threshold WV-IRW CO 2 -IRW O 3 -IRW COMB > 4 K IRW brightness temperature < 215 K > 3. 5 K > 13 K > 4 K & > 13 K Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

8/15 COMB: WV-IRW WV O CO IRW -IRW BTD: & O 3 -IRW: 3 -2– -This combination two occur BTD on criteria False method OT detections isofdepending in the annual -ozone the plume smallest falsethresholds alarms the cycle region –number in Mayof. BTD should be higher Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

9/15 • Locations of the OTs defined by mentiond BTD methods were compared with visually observed OTs on HRV images • July 2009, between 15 and 16 UTC (five SEVIRI scans) Table: Percentage of the OT pixels detected using three different BTD methods corresponding to OTs visible on HRV images. BTD method OT on HRV images (%) False alarm (%) False alarm within cold ring or cold U/V features (%) WV-IRW 62 38 20 CO 2 -IRW 72 28 14 COMB 80 20 16 Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

10/15 • OTs were detected using COMB BTD method • number of OTs was calculated over 0. 2° x 0. 2° grid boxes • warm seasons 2009 and 2010 (May-September) Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

Comparison with automatic station data � 11/15 parallax correction → applied to automatic station location Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

12/15 automatic station Weiz, Austria temperature humidity max. wind precipitation Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

13/15 � � Wind gust Precipitation (10 -min amount) Wind gusts matching OT detections 5 to 10. 8 m/s 10. 8 to 17. 2 m/s >17. 2 m/s total Absolute frequency 281 428 252 951 Relative frequency (%) 30 45 25 Precipitation matching OT detections 0 -5 mm 5 -10 mm >10 mm total Absolute frequency 704 162 70 936 75 17 8 Relative frequency (%) � Temperature drop Temperature change matching OT detections 2 to 4 °C 4 to 6 °C 6 to 8 °C > 8°C total Absolute frequency 263 276 212 129 880 Relative frequency (%) 30 31 24 15 Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

14/15 Conclusions � COMB BTD method has been found to be the most appropriate BTD method for detecting the OTs, showing the smallest number of false alarms � gale wind gusts and significant 10 -min precipitation amount are observed in the vicinity of the OTs � OT is only one of many possible indicators for severe weather conditions that can be seen in the satellite images (cold ring or cold U/V, right-moving storm, above anvil plume…) Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

15/15 Thank you for your attention! petra. mikus@cirus. dhz. hr natasa. strelec. mahovic@cirus. dhz. hr Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia

Figure: Map of the study domain with locations of the automatic stations used for this study (black square).

Numerically simulated Cb cloud with OT and jumping cirrus

Table: Total number of the OTs detected using COMB BTD method within 0, 1° radius from the automatic stations measuring mentioned parameters, compared to the number of OTs matching the measured extremes. Correlation between the OTs and each measured parameter is given in the last column. Type of automatic station data Number of detected OTs in the vicinity of the station Number of OTs matching data extremes (% wind gust 1352 951 70 precipitation 1165 936 80 rel. humidity 1352 776 57 temperature 1380 880 64 )

Table: Number of OT detection using COMB method from May to September 2009 and 2010. Month Number of OT May 6339 June 7252 July 1712 August 660 September 187 Total 16150 Figure: Relative frequency of OTs, detected using COMB method, within given hour.