Cold-ring shaped storms

Transcription

1 MARTIN SETVÁK CZECH HYDROMETEOROLOGICAL INSTITUTE Cold-ring shaped storms 25 June 2006 (Czech Republic and Austria) EUMeTrain Convection Training Week June 2008

2 Our storms cloud-tops team: 1, Petr Novák 2, Michaela Radová 1, Jindřich Šťástka 1 Pao Wang 3, Daniel Lindsey 4, Robert Rabin 5 1 CHMI, Satellite Dept., Czech Republic 2 CHMI, Radar Dept., Czech Republic 3 University of Wisconsin-Madison, U.S.A. 4 NOAA/NESDIS/RAMMB, CIRA/CSU, U.S.A. 5 NOAA/NSSL, and SSEC, U.S.A. Modified version of presentations given at: and The ECSS2007 (European Conference on Severe Storms), September 2007, Trieste, Italy The EUMETSAT-INMW Convective workshop at Krakow, November 2007, Poland Parts of this research were carried out under support of the Grant Agency of the Czech Republic, project #205/07/0905.

3 What are the cold-ring shaped storms? - appearance, terminology, examples and basic characteristics

4 EXAMPLE: 25 June 2006, Czech Republic and Austria HRV Meteosat-8 (MSG1) 13:45 UTC IR 10.8 BT ENH

5 Necessity to apply suitable image color enhancement!!! This specific brightness temperature range (BT K) of the color enhancement is suitable for typical European storms; however for some cases it may need certain adjustment...

6 Description and examples of cold-ring shaped type of storms Terminology: CENTRAL WARM SPOT (CWS) COLD RING No formal quantitative definition of the cold-rings and CWS in terms of their temperature differences and thresholds, shape and size, duration

7 Description and examples of cold-ring shaped type of storms Terminology: sometimes also called as doughnut-shaped storms Wrong concept!!!

8 Description and examples of cold-ring shaped type of storms Examples:

9 Description and examples of cold-ring shaped type of storms Examples:

10 Description and examples of cold-ring shaped type of storms Examples:

11 Description and examples of cold-ring shaped type of storms Examples:

12 Description and examples of cold-ring shaped type of storms Examples:

13 Description and examples of cold-ring shaped type of storms Examples:

14 Description and examples of cold-ring shaped type of storms Examples:

15 Description and examples of cold-ring shaped type of storms Examples:

16 Description and examples of cold-ring shaped type of storms Main characteristics: temperature difference between the cold ring and CWS: several Kelvins and higher... up to about K (in the MSG imagery) CWS size: typically up to several SEVIRI pixels across CWS duration: from one single scan to several 15-minute MSG repeat cycles (for one single CWS)

17 Description and examples of cold-ring shaped type of storms Other: in some cases difficult to decide whether the observed feature can be classified as a cold-ring shaped storm or not (namely due to its small size or shape), depends also on the level (strength) of the image enhancement; resemblance of the cold-ring shaped storms to the cold-u shaped storms, in some cases difficult to decide between these (no formal distinction between them, absence of formal quantitative definitions); sometimes more accurate to speak generally about a storm exhibiting a distinct enclosed warm spot (area), not mentioning the cold-ring or cold-u shape.

18 Resemblance of the cold-ring shaped storms to the cold-u (enhanced-v) shaped storms - basic characteristics of the cold-u shaped storms, their possible mechanisms, links to the cold-ring shaped storms...

19 Cold-U shaped storms Example of a cold-u shaped storm: 26 May 2007, Germany Meteosat-9 (MSG2) 15:00 UTC DISTANT WARM AREA (DWA) CLOSE-IN WARM AREA (CWA) COLD-U

20 Cold-U shaped storms Originally called as enhanced-v (since observed in enhanced IR imagery), presently stressed the nature of the feature by naming them as cold-u or cold-v shape (or cold-u/v shape). The enhanced-v features documented first in early 1980 s on the basis of GOES and NOAA/AVHRR imagery, showing a very close correlation with severe weather or supercells. However, this feature alone does not automatically classify a storm as a supercell!!! If observed, it indicates a possible severity of the storm, nothing more! Mechanism of the cold-u/v and CWA couplet formation: still not quite well (unambiguously) explained, several different approaches, mechanisms. For details of these see the original papers, addressing this topic.

21 Cold-U shaped storms Wake effects (R.F. Adler, A.F. Hasler, G.M. Heymsfield, R.A. Mack, D.W. McCann, A.J. Negri, R.E. Schlesinger,... ) From: Adler, R. F., and R. A. Mack, Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model. J. Atmos. Sci., 43,

22 References: Adler, R. F., M. J. Markus, and D. D. Fenn, Detection of severe Midwest thunderstorms using geosynchronous satellite data. Mon. Wea. Rev., 113, Adler, R. F., and R. A. Mack, Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model. J. Atmos. Sci., 43, Hasler, A. F., Stereographic observations from geosynchronous satellites - an important new tool for the atmospheric science. Bull. Amer. Meteor. Soc., 62, Heymsfield, G. M., R. H. Blackmer Jr., and S. Schotz, 1983a. Upper level structure of Oklahoma tornadic storms on 2 May 1979, Pt. 1 radar and satellite observations. J.Atmos.Sci., 40, Heymsfield, G. M., G. Szejwach, S. Schotz, and R. H. Blackmer Jr., 1983b. Upper level structure of Oklahoma tornadic storms on 2 May 1979, Pt. 2 Proposed explanation of "V" pattern and internal warm region in infrared observations. J. Atmos. Sci., 40, Heymsfield, G. M., and R. H. Blackmer Jr., Satellite-observed characteristics of Midwest severe thunderstorm anvils. Mon. Wea. Rev., 116, Heymsfield, G. M., R. Fulton, and J. D. Spinhirne, Aircraft overflight measurements of Midwest severe storms: Implications on geosynchronous satelite interpretations. Mon. Wea. Rev., 119, Mack, R. A., A. F. Hasler, and R. F. Adler, Thunderstorm cloud top observations using satellite stereoscopy. Mon. Wea. Rev., 111, McCann, D. W., The enhanced-v: A satellite observable severe storm signature. Mon. Wea. Rev., 111, Negri, A. J., Cloud-top structure of tornadic storms on 10 April 1979 from rapid scan and stereo satellite observations. Bull. Amer. Meteor. Soc., 63, Schlesinger, R. E., 1984: Mature Thunderstorm Cloud-Top Structure and Dynamics: A Three Dimensional Numerical Simulation Study. J. Atmos. Sci., 41,

23 Cold-U shaped storms Jumping cirrus (T.T. Fujita) From: Fujita T. T., Principle of stereoscopic height computations and their applications to stratospheric cirrus over severe thunderstorms. J. Meteor. Soc. of Japan, 60,

24 Cold-U shaped storms Gravity wake breaking mechanism (P.K. Wang, T.P. Lane,... ) ( Fujita s jumping cirrus & the above-anvil plumes) From: Wang P. K., 2007: The thermodynamic structure atop a penetrating convective thunderstorm. Atmos. Res., 83,

25 Cold-U shaped storms Other possible explanations (discussed either in the past, or recently): Transparency effects... partial IR transparency of the cloud top at the warm area region, thus the radiance originating at the lower, warmer layers inside the cloud; Warm-dome mechanism... higher elevated storm-top dome (not the overshooting tops themselves!!!), residing in the warmer lower stratosphere for a sufficiently long period, thus their skin temperature warmed up by the environmental air; Plume-masking mechanism... warmer above-anvil plume partially masking the downwind parts of the cold anvil cloud top - in combination with the cold-ring feature... (Setvák et al.)

26 References: Levizzani, V., and M. Setvák, 1996: Multispectral, high-resolution satellite observations of plumes on top of convective storms. J. Atmos. Sci., 53, Luderer, G., J. Trentmann, K. Hungershöfer, M. Herzog, M. Fromm, and M. O. Andreae, 2007: Small-scale mixing processes enhancing troposphere-to-stratosphere transport by pyro cumulonimbus storms. Atmos. Chem. Phys., 7, Setvák M., Doswell III C.A., 1991: The AVHRR Channel 3 Cloud Top Reflectivity of Convective Storms. Mon. Wea. Rev. 119, Setvák M., Rabin R.M., Doswell C.A., Levizzani V., 2003: Satellite observations of convective storm top features in the 1.6 and 3.7/3.9 m spectral bands. Atmos. Research, 67-68C, Setvák M., Rabin R.M., 2003: MODIS observations of deep convective cloud tops. Proc. The 2003 EUMETSAT Meteorological Satellite Conference, Weimar, Germany. EUM P39, ISBN , ISSN , Setvák M., Rabin R.M., Wang P.K., 2007: Contribution of the MODIS instrument to observations of deep convective storms and stratospheric moisture detection in GOES and MSG imagery. Atmos. Research, 83, Wang, P. K., 2007: The thermodynamic structure atop a penetrating convective thunderstorm. Atmos. Res., 83,

27 Link between storms exhibiting the cold-ring or cold-u features Transition of a cold-ring into a cold-u shaped storm: 26 May 2007, Germany 13:30 UTC 15:00 UTC

28 Link between storms exhibiting the cold-ring or cold-u features If a cold-ring shaped storm can transform itself into a cold-u shaped storm, could it be that the mechanisms forming the CWS and CWA are the same? Are the cold-ring and cold-u shaped storms a result of the same or similar processes? What may force the storm to transform itself from one form into another????

29 Link between storms exhibiting the cold-ring or cold-u features Model studies (Pao Wang et al.) indicate that decreasing or removing the wind shear results into a storm resembling a cold-ring, while higher shear forms a cold-u/v shape This might explain the fact that the cold-u shaped storms seem to be more common in the United States, while the cold-ring shaped storms are more common in Europe... possible impact of the wind-shear climatology?

30 Link between storms exhibiting the cold-ring or cold-u features However, possible problem (???) storms above Bulgaria and Romania, 22 April 2008 B A The cold-ring shaped storm B has developed in the track of cold-u shaped storm A, shortly after the storm A has dissipated. Several possible explanations of this: (1) different height of the cloud top of the two storms (thus different cloud-top relative winds); (2) different environment behind the storm A, (3) some mechanism related to the storm A forming its plume, in combination with consequent plume-masking effect...

31 Link between storms exhibiting the cold-ring or cold-u features If the future proves that the CWA of cold-u shaped storms and CWS of cold-ring shaped storms result from the same mechanism, then their naming should (and most likely will) be unified...

32 Cold-ring shaped storms of the 25 June 2006: - comparison of the MSG and radar data

33 25 June cold ring shaped storms, Czech Republic and Austria 14 km 10 km 5 km CZRAD radar composite 14:10 UTC

34 25 June cold ring shaped storms, Czech Republic and Austria Radar (Skalky) cross-section along the line A-B from the previous slide: 20 km Tropopause, km 15 km 10 km A 5 km B Experimental cross-section, extended up to 20 km, based on CAPPI products (step 0.5 km) derived from the radar reflectivity volume data (radar Skalky only!) Active parts of both storms penetrating high above the tropopause, up to about km!!!

35 25 June cold ring shaped storms, Czech Republic and Austria Sounding Praha Libuš (11520), 12:00 UTC

36 25 June cold ring shaped storms, Czech Republic and Austria Sounding Praha Libuš (11520), 18:00 UTC

37 25 June cold ring shaped storms, Czech Republic and Austria IR :00 UTC Evolution of the cold-ring feature

38 25 June cold ring shaped storms, Czech Republic and Austria IR :15 UTC Evolution of the cold-ring feature

39 25 June cold ring shaped storms, Czech Republic and Austria IR :30 UTC Evolution of the cold-ring feature

40 25 June cold ring shaped storms, Czech Republic and Austria IR :45 UTC Evolution of the cold-ring feature

41 25 June cold ring shaped storms, Czech Republic and Austria IR :00 UTC Evolution of the cold-ring feature

42 25 June cold ring shaped storms, Czech Republic and Austria IR :15 UTC Evolution of the cold-ring feature

43 25 June cold ring shaped storms, Czech Republic and Austria IR :30 UTC Evolution of the cold-ring feature

44 25 June cold ring shaped storms, Czech Republic and Austria IR :45 UTC Evolution of the cold-ring feature

45 25 June cold ring shaped storms, Czech Republic and Austria IR :00 UTC Evolution of the cold-ring feature

46 Discussion of the central warm spot (CWS) Meteosat-8 (MSG1) 14:00 UTC IR 10.8 Highest temperatures within the warm spot: 218 K Lowest temperatures within the cold ring: K

47 Discussion of the central warm spot (CWS) Meteosat-8 (MSG1) 14:00 UTC HRV Outline of the warm spot (from the IR 10.8 image) Area of the overshooting tops The warm spot is located at the downwind side of the overshooting tops and in their lee!!!

48 Discussion of the central warm spot (CWS) In principle, three possible explanations of the warm area: Partial IR transparency of the area, thus the radiance originating at the lower warmer layers; Wake effects, or gravity wave breaking effects, similar to those assumed to be the explanation of the cold-u/v shapes and CWA couplets; Higher elevated tops, residing in the warmer lower stratosphere for a sufficiently long period of time, warmed by the environmental air warm dome mechanism (or any combination of these)

49 Discussion of the central warm spot (CWS) To decide among these, it is necessary to know (as accurately as possible) the cloud top height and its microphysical composition Necessitates the use of radar (and lidar) cloud-top observations

50 Radar study of the 25 June 2006 storm top (radar echo tops) 14:10 radar Skalky Tropopause, km 20 km 15 km 10 km A 5 km B Praha-Libus Observations at 12Z 25 Jun PRES HGHT TEMP DWPT hpa m C C tropopause

51 Radar study of the 25 June 2006 storm top (radar echo tops) The fact that these tops are indeed well above the tropopause, in the warmer lower stratosphere, is important; however the crucial question is what is the location of these elevated tops relative to the features observed in the satellite images, with respect to the location of CWA and the cold ring When comparing the satellite and radar data, it is necessary to take into account the parallax shift (for the given location and height of the cloud top).

52 Parallax effect Parallax shift Nadir view, or surface observations (e.g. radar) Geostationary view Projection of various cloud-top features to surface ("georeferencing these) strongly depends on their height above ground and on scanning geometry

53 Radar study of the 25 June 2006 storm top (radar echo tops) Parallax shift (for the area of the storm) (LAT = N, LON = 14.3 E) h height of the top (above sea level) P... parallax total Pe parallax, eastward component Pn parallax, northward component

54 Radar study of the 25 June 2006 storm top (radar echo tops) Parallax shift (correction) usually applied to satellite imagery, according to the cloud top height, derived typically from IR BT. In the following case, the parallax shift was applied to the radar CAPPI images, as if these were viewed from the geostationary orbit. Reason for this approach is in the fact that the real cloud top height is difficult to retrieve from satellite data when overshooting tops and possible wake effects (CWS, CWA) are involved.

55 Radar study of the 25 June 2006 storm top (radar echo tops) Position of the cross-section A-B in standard radar projection.

56 Radar study of the 25 June 2006 storm top (radar echo tops) Position of the cross-section A-B in the radar projection (bottom left line) and after parallax shift for a level at 15.5 km (upper right line), shown in the IR10.8 BT image.

57 Radar study of the 25 June 2006 storm top (radar echo tops) A B Position of the cross-section A-B in the radar projection, shown in the IR10.8 BT image.

58 Radar study of the 25 June 2006 storm top (radar echo tops) A Overshooting tops at CAPPI 15.5 km B Position of the cross-section A-B and CAPPI 15.5 km, shown in the IR10.8 BT image.

59 Radar study of the 25 June 2006 storm top (radar echo tops) A B Position of the cross-section A-B and CAPPI 15.5 km in the radar projection (bottom left line) and after parallax shift for a level at 15.5 km (upper right line), shown in the IR10.8 BT image.

60 Radar study of the 25 June 2006 storm top (radar echo tops) A B Position of the cross-section A-B and CAPPI 15.5 km, both after parallax shift, shown in the IR10.8 BT image.

61 Radar study of the 25 June 2006 storm top (radar echo tops) These elevated tops appear to be a part of the cold ring area, not of the CWS!!! In the IR10.8 image continuous cloud shield, not a gap like here, in the radar data >>> the radar sees less of the cloud then the IR10.8 satellite band 20 km Tropopause, km 15 km 10 km A 5 km B

62 Radar study of the 25 June 2006 storm top (radar echo tops) Radar cross-section C-D and CAPPI 15.5 km after parallax shift shown in the IR10.8 BT image. The C-D plane was chosen to intersect the CWS; also it is oriented in the direction of parallax shift.

63 Radar study of the 25 June 2006 storm top (radar echo tops) Radar cross-section C-D and CAPPI 13.0 km (just above the tropopause) after parallax shift shown in the IR10.8 BT image.

64 Radar cross-sections (along line C-D) of the 25 June 2006 storm top

65 Radar cross-sections (along line C-D) of the 25 June 2006 storm top (CWS according to IR10.8)

66 Radar cross-sections (along line C-D) of the 25 June 2006 storm top

67 Radar cross-sections (along line C-D) of the 25 June 2006 storm top Since the CWS was located for most of its existence also above the cloud (echo) tops close to the tropopause, the warm dome mechanism can be most likely excluded.

68 Possible problems and errors: radar echo top and real cloud top (as seen by satellite in the IR10.8 band) are not the same, radar fails to detect smaller particles => possible underestimation of the cloud top height by the radar; radar beam width ambiguity of the echo top height of about ± 1.5 km (at 200 km distance and 15 km height); additional possible errors as a result of the CAPPI computation method (PPI => volume data => CAPPI => cross sections)

69 Possible problems and errors: Echo-top height uncertainty related to the beam width and distance from a radar

70 Summary In this case, the wave effect or gravity wave breaking mechanism seem to be more likely than the warm dome mechanism; Exceptional cloud-top heights for Central Europe of the storms from 25 June however, how many similar storms do occur here? Necessity to apply the parallax shift correction for similar studies; Storms exhibiting cold-ring or cold-u features appear in average much warmer than ordinary storms; however their tops may actually be significantly higher than those of the regular storms, thus these storms are likely to be more severe than the regular ones; Derived satellite products (namely CTH), and also storm tracking algorithms or rain estimates based on satellite IR data are likely to fail when treating storms with cold-ring or cold-u shapes (strongly underestimate these).

71 What next? Studies of other similar storm cases (satellites, ground radar, ) on national basis, depending on radar data availability; also utilizing the MSG rapid-scan data (might significantly help thanks to its 5-minute repeat cycle; Modeling of similar cases... cold-ring versus cold-u shaped storms (the role of storm environment, wind shear); RTM studies; Special attention to shape transitions and to the effect of plumemasking mechanism Use of CloudSat and CALIPSO observations: might significantly help, but a timing problem overpass of these satellites is too close to local noon, before the onset of any significant convection; Perhaps use of polarimetric research radars (where available);

72 21/22 June cold ring shaped storms, Austria Another example of CWS developing in the wake of overshooting tops: MSG IR10.8 warm spot (CWS) Parallax-shifted overshooting tops at radar CAPPI levels ~ km Due to storm s location and reach of it by radars in Austria, Czech Republic, Slovakia and Hungary, a good case for a possible joint study of the storm, for tests of merging the satellite and radar data (and parallax correction)...???

73 At least one mystery solved THE END

74