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Nowcasting Thunderstorm Intensity from Satellite

Robert M Rabin NOAA/National Severe Storms Laboratory Norman, OK USA Cooperative Institute for Meteorological Satellite Studies University of Wisconsin Madison, WI USA. Nowcasting Thunderstorm Intensity from Satellite. Outline. Purpose The first pictures (1960's) TIROS

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Nowcasting Thunderstorm Intensity from Satellite

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  1. Robert M Rabin NOAA/National Severe Storms Laboratory Norman, OK USA Cooperative Institute for Meteorological Satellite Studies University of Wisconsin Madison, WI USA Nowcasting Thunderstorm Intensity from Satellite

  2. Outline • Purpose • The first pictures (1960's) TIROS • Basic cloud structure, Environmental conditions • GEO arrives (1970's) ATS and GOES • Time rate of change, anvil expansion • More structure, Enhanced-V • Multispectral (1990's) AVHRR and GOES • Plumes, near storm environment • Outlook for the future

  3. Review past discoveries in relation to radar. Explore prospects for operational severe storm detection. Purpose

  4. TIROS-I 27 May 1960, 1719 LST from: L. Whitney JAM 1963: Severe Storm Clouds as seen from TIROS The First Pictures

  5. From: L. F. Whitney, 1963, JAM, figure 3

  6. Clouds are “conspicuous and distinctive” • Medium size, not linear • Highly reflective, combined anvils • Sharp edges, scalloped structure • Much larger than area of radar echoes and sferics • Contiguous clear areas, useful in determining severity?

  7. Relationships between size of cirrus shields and severity R.J. Boucher 1967, JAM TIROS IV-VII 17 cases 1962-1964 From: Fig. 2

  8. From Fig. 3, Boucher 1967, JAM

  9. Diameter of cirrus shield is an index of storm severity: rarely severe < 60 n mi usually severe > 150 n mi • Penetrative convection: not always severe weather • Contiguous clear areas not common • Results based on a limited sample of cases

  10. Satellite imagery and severe weather warnings James F.W. Purdom, 1971 Polar orbiting: NOAA-1 • Squall lines: characteristic appearance, narrowing to south • Locations of jets: polar and subtropical • Shear with height: thermal ridge and amount of veering

  11. ATS-3 Visible imagery (1971): 11-minute updates on demand • Early detection of squall lines as compared to radar • Isolation of areas under threat for severe weather: often southern portion of convective clusters • Growth of anvil: pause in expansion linked time of tornado occurrence McCann(1979) linked collapsing tops to downdraft and tornado formation

  12. Convective Initiation Some uses of high-resolution GOES imagery in the mesoscale forecasting of convection and its behavior James F.W. Purdom, 1976 MWR

  13. Detection of mesoscale processes: important for storm initiation and maintenance Effects of terrain (coast lines, rivers and lakes) • Precise location of convective (outflow) boundaries • Merging and intersecting of boundaries • Given favorable conditions: New convection and intensification

  14. Exploration of Infrared imagery

  15. Anvil outflow patterns as indicators of tornadic thunderstorms Charles E. Anderson, 1979 Observed characteristics of cirrus plumes of severe storms (limited cases) Displaced to the right of the ambient wind Anticyclonic rotation Spiral bands Similarity to hurricanes

  16. On overshooting-collapsing thunderstorm topsDonald W. McCann, 1979 • Previously observed by aircraft (Fujita, 73;Umenhofer, 75) • Collapse does NOT cause tornado • May be related to acceleration of gust front: occlusion of mesolow strong surface outflow (i.e. bow echo)

  17. Thunderstorm intensity as determined from satellite data (SMS 2: IR 5-minute)Robert Adler and Douglas Fenn, JAM 1979

  18. Tornadoes during or after rapid expansion (7 of 8) • Statistical relation to severe weather: Severe storms: colder and more rapid growth • Potential warning lead time: 30 minutes • Divergence and vertical velocity: Twice as large for severe storms • Limitations: Results from a single day Existing anvil may obscure new storm growth Storm top heights underestimated as compared to radar

  19. Mesoscale convective complexesRobert Maddox, 1980 BAMS

  20. Identified unique class of convective system • Defined from IR imagery cold cloud tops (< -32 C) size (> 100,000 km**2) shape: circular (eccentricity > 0.7) duration: > 6 hours • Produce wide variety of severe weather • Difficult to forecast weak upper-level support low-level warm advection

  21. Observations of damaging hailstorms from geosynchronous satellite digital data (GOES 30-minute data: 9 storms) David W. Reynolds, 1980 MWR

  22. Cloud tops colder than tropopause Infer vigorous updrafts • Expect better relation for hail tornadoes: depend on boundary layer conditions • Large hail storms long lasting (3-5 h) large, high cloud tops • Onset of large hail rapid vertical growth cloud top becoming colder than tropopause • Requires proper enhancement

  23. The enhanced-V: a satellite observable severe storm signature Donald W. McCann 1983, MWR

  24. Relatively large sample: 884 • Interaction of winds and overshooting tops strong upper level wind (20-60 m/s) • Many severe storms do not have enhanced-V POD is low ( .25 ) Cause of enhanced-V needs more research • FAR similar to other methods (.31) • Lead time of 30 minutes • Requires proper enhancement

  25. Detection of severe Midwest thunderstorms using geosynchronous satellite data SMS-2 and GOES-1: ~5 minute data Robert Adler, Michael Markus, Douglas Fenn MWR 1985

  26. Combine parameters into single index • Index correlated with severe weather and max reflectivity parameters related to updraft intensity cloud top ascent rates expansion rates of isotherms based on 4 dependent, 1 independent case • V-shape with embedded warm spot similar to McCann findings • Limitations identification of cloud tops during certain stages resolution in IR (cloud tops too warm) ambiguity in height from cloud top temperature

  27. Thunderstorm cloud top dynamics as inferred from satellite observations and a cloud top parcel model Robert Adler, Robert Mach, 1986 JAS

  28. Used GOES stereoscopic observations (May 1979) • Three classes of storms identified and simulated 1. concentric: monotonic temperature-height Cold-warm couplet with coldest and highest point 2. collocated: isothermal 3. offset: inversion with mixing • “Close in” warm point: subsidence undershooting

  29. Upper-level structure of Oklahoma tornadic storms on 2 May 1979, I: Radar and satellite observations Gerald Heymsfield, Roy Blackmer, Steven Schotz JAS, 1983

  30. Three severe storms investigated (single day) • “V” pattern of low cloud top temperature strong divergence • Close-in warm area: 10-20 km downwind moves with storm motion forms at time of tropopause penetration subsidence mechanism proposed • Distant warm area (not in all cases) 50-75 km downwind moves with upper-level winds No visible stratospheric cirrus

  31. Rapid growth stage cold areas collocated with radar echo • After rapid growth cold areas sometimes displaced from echo core • IR temperature change not always consistant with stereographic height change

  32. Satellite-observed characteristicsof Midwest severe thunderstorm anvilsGerald Heymsfield, Roy Blackmer, MWR 1988

  33. Statistics from several cases (9) • Thermal couplets second distant warm point often observed width of V: spacing of cold and distant warm T-diff (warm-cold): related to amount of overshoot • Ingredients for “V” Strong shear near troposphere Intense updrafts and overshooting tops

  34. Various hypotheses internal cloud dynamics radiative transfer effects flow over and around storm top: waves combination of above • Limitations IR pixel resolution unknown temperature and ice crystal structure complexity of multistorm structure 3-D models too simplified

  35. Aircraft overflight measurements of Midwestsevere storms: Implications on geosynchronous satellite interpretationsGerald Heymsfield, Richard Fulton, James Spinhirne, MWR 1991

  36. Dimensions of overshooting tops size of single GOES pixel 15 degs colder • Thermal couplets: much more pronounced • Warm areas: not due to variation in optical depth • Above cloud wind and temperature perturbations cold dome in temperature field

  37. The AVHRR channel 3 cloud topreflectivity of convective stormsMartin Setvak, Charles Doswell, 1991 MWR

  38. Areas of enhanced reflectivity at 3.7 microns convective cell: widespread or localized plume-like: less common • Association with hail (limited sample) • Not often associated with “V” • Possible cause very small ice crystals generated from vigorous updrafts

  39. Passive microwave structure of severe tornadic storms on 16 November 1987Gerald Heymsfield, Richard Fulton, 1994 MWR

  40. Maximum polarization difference at 86 Ghz correlates with internal warm region convective core: symmetrical or tumbling ice particles small polarization difference warm region: oriented ice crystals large polarization difference • Microphysical variations partially explain IR structure

  41. Multispectral high-resolution satellite observations of plumes on top of convective stormsVincenzo Levizzani, Martin Setvak, 1996 JAS

  42. Enhanced reflectivity Small ice crystals limited growth time: strong updraft (BWER) vertical lifting/gravitational settling • Vertical separation between plume and anvil • Different from Fujita's (1982) stratospheric cirrus • Link between plume source position and warm spot

  43. Satellite observations of convective storm tops in the 1.6, 3.7 and 3.9 spectral bandsMartin Setvak, Robert Rabin, Charles Doswell, Vincenzo Levizzani, 2003 Atmos. Res.

  44. Study used GOES and Doppler radar • Areas of high cloud top reflectivity time scales: minutes to hours size: pixels to entire anvils linked to mesocyclone formation move downwind once formed not always associated with mesocyclones • Mechanisms remain unknown

  45. Moisture plumes above thunderstorm anvils and their contributions to cross-tropopause transport of water vapor in midlatitudesPao Wang, 2003, JGR

  46. Storm simulated using 3-D, non-hydrostatic model • Water vapor source: shell of overshooting dome • Gravity waves • Waves break when instability becomes large • Water vapor injected into stratosphere • Carried downwind in shape of a chimney plume • Transport of water vapor to stratosphere: 3 tons/sec

  47. Nowcasting storm initiation and growthusing GOES-8 and WSR-88D dataRita Roberts, Steven Rutledge, 2003 WF

  48. Based on observed cloud growth rates eastern CO (4 days), Washington DC and New Mexico (2 days) • Onset of storm development surface convergence features gust fronts, rolls, terrain, intersecting features cloud tops reaching sub-freezing altitudes rapid cooling of cloud tops

  49. Intensity related to rate of cooling • Increased lead time 15 minutes prior to 10 dBZ echoes aloft 30 minutes prior to 30 dBZ echoes aloft NCAR automated nowcasting system

  50. NCAR auto-nowcast systemCindy Mueller et al, 2003, WF

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