petra mikuš, nataša strelec mahović meteorological and hydrological service, croatia
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Satellite-based overshooting top detection methods: comparison and validation. Petra Mikuš, Nataša Strelec Mahović Meteorological and Hydrological Service, Croatia. 1/1 5. Outline. On Overshooting tops (OT) Satellite based detection methods Weather conditions in the vicinity of the OTs - PowerPoint PPT PresentationTRANSCRIPT
Petra Mikuš, Nataša Strelec Mahović
Meteorological and Hydrological Service, Croatia
Satellite-based overshooting top detection methods: Satellite-based overshooting top detection methods:
comparison and validationcomparison and validation
On Overshooting tops (OT) Satellite based detection methods Weather conditions in the vicinity of the
OTs Conclusions
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Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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
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Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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OT appearance in satellite images:
Sandwich product:
HRV + color-enhanced IRW 10.8 μmHRV
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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OT
Storm top plume
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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COLD RING
THERMAL FEATURES: color-enhanced IR 10.8 μm
COLD U/V
All the other storm top features result from the activity of OTs: cold ring, cold U/V, storm top plumes, storm top gravity waves…!!!
Central warm area
Cold ring
Cold U shape
Close-in warm area
Distant warm area
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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Sendwich product: HRV + color-enhanced IRW
Channel differences:
• 6.2 – 10.8 µm (WV-IRW)
• 9.7 – 10.8 µm (O3-IRW)
• 13.4 – 10.8 µm (CO2 – IRW)
• COMB– combination of the WV-IRW and O3-IRW methods
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BTD Threshold
WV-IRW
IRW brightness temperature < 215 K
> 4 K
CO2-IRW > 3.5 K
O3-IRW > 13 K
COMB > 4 K & > 13 K
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
CO2 - IRW BTDWV – IRW BTD : False OT detections occur in the plume region
O3 - IRW BTD:This method is depending on the annual ozone cycle – in May BTD thresholds should be higher
COMB: WV-IRW & O3-IRW:- combination of two BTD criteria-the smallest number of false alarms
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Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
Table: Percentage of the OT pixels detected using three different BTD methods corresponding to OTs visible on HRV images.
BTD methodOT on HRV images (%)
False alarm (%)
False alarm within cold ring
or cold U/V features (%)
WV-IRW 62 38 20
CO2-IRW 72 28 14
COMB 80 20 16
• 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)
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
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• 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
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parallax correction → applied to automatic station location
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Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
0
5
10
15
20
25
30
35
12:00 13:40 15:20 17:00 18:40 20:20 22:00 23:40
time
°C;
m/s
0
20
40
60
80
100
120
%;
mm
temperature(°C) max wind speed(m/s) relative humidity(%) precipitation(mm)
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max. wind
precipitation
temperature
humidity
automatic station Weiz, Austria
Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
Wind gust
Precipitation (10-min amount)
Temperature drop
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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
0-5mm 5-10mm >10mm total
Absolute frequency 704 162 70 936
Relative frequency (%)75 17 8
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
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…)
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Croatian–USA Workshop on Mesometeorology 18 - 20 June 2012, Croatia
[email protected]@cirus.dhz.hr
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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
Type ofautomatic station
dataNumber of detected OTs
in the vicinity of the stationNumber of OTs
matching data extremes
(%)
wind gust 1352 951 70
precipitation 1165 936 80
rel. humidity 1352 776 57
temperature 1380 880 64
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.
Month Number of OT
May 6339
June 7252
July 1712
August 660
September 187
Total 16150
Table: Number of OT detection using COMB method from May to September 2009 and 2010.
Figure: Relative frequency of OTs, detected using COMB method, within given hour.