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
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
PURPOSE Review past discoveries in relation to radar. ● Explore prospects for operational severe storm detection. ●
THE FIRST PICTURES TIROS-I 27 May 1960, 1719 LST from: L. Whitney JAM 1963: Severe Storm Clouds as seen from TIROS
From: L. F. Whitney, 1963, JAM, figure 3
●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 sever
Relationships between size of cirrus shields and severity R. J. Boucher 1967, JAM TIROS IV-VII 17 cases 1962 -1964 From: Fig. 2
●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
Satellite imagery and severe weather warnings James F. W. Purdom, 1971 Polar orbiting: NOAA-1 ●Squall lines: characteristic appearance, narrowing to s ●Locations of jets: polar and subtropical ●Shear with height: thermal ridge and amount of veering
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 - Mc. Cann(1979) linked collapsing tops to downdraft and tornado formation
CONVECTIVE INITIATION
Some uses of high-resolution GOES imagery in the mesoscale forecasting of convection and its behavior James F. W. Purdom, 1976 MWR
●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 ●Given and intersecting of boundaries favorable conditions: - New convection and intensification
EXPLORATION OF INFRARED IMAGERY
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
On overshooting-collapsing thunderstorm tops Donald W. Mc. Cann, 1979 ●Previously ●Collapse ●May observed by aircraft (Fujita, 73; Umenhofer, does NOT cause tornado be related to acceleration of gust front: - Occlusion of mesolow - Strong surface outflow (i. e. bow echo)
Mesoscale convective complexes Robert Maddox, 1980 BAMS
●Identified ●Defined unique class of convective system from IR imagery - Cold cloud tops (< -32 C) - Size (> 100, 000 km**2) - Shape: circular (eccentricity > 0. 7) - Duration: > 6 hours ●Produce ●Difficult wide variety of severe weather to forecast - Weak upper-level support - Low-level warm advection
GROWTH RATES
Thunderstorm intensity as determined from satellite data (SMS 2: IR 5 -minute) Robert Adler and Douglas Fenn, JAM 1979
●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 rad
Observations of damaging hailstorms from geosynchronous satellite digital data (GOES 30 -minute data: 9 storms) David W. Reynolds, 1980 MWR
●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
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
●Combine parameters into single index ●Index correlated with severe weather and max reflectiv - 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 Mc. Cann findings ●Limitations - Identification of cloud tops during certain stages - Resolution in IR (cloud tops too warm) - Ambiguity in height from cloud top temperature
THE ENHANCED-V AND RELATED STRUCTURE
Detection of tropopause penetrations by intense convection with GOES enhanced infrared imagery Peter Mills, Elford Astling, 1977, 10 th SLS First observations of warm spots on anvil ●Near tropopause penetrations - confirmed by radar ●Possible causes - higher emissivity above updraft - stratospheric cirrus - rapid sinking ●
The enhanced-V: a satellite observable severe storm signature Donald W. Mc. Cann 1983, MWR
●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
Thunderstorm cloud top dynamics as inferred satellite observations and a cloud top parcel m Robert Adler, Robert Mach, 1986 JAS
●Used ●Three GOES stereoscopic observations (May 1979) 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
per-level structure of Oklahoma tornadic storm n 2 May 1979, I: Radar and satellite observations Gerald Heymsfield, Roy Blackmer, Steven Schotz JAS, 1983
●Three ●“V” severe storms investigated (single day) 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
●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
Satellite-observed characteristics of Midwest severe thunderstorm anvils Gerald Heymsfield, Roy Blackmer, MWR 1988
●Statistics ●Thermal from several cases (9) 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
●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
Aircraft overflight measurements of Midwest severe storms: Implications on geosynchronous satellite interpretations Gerald Heymsfield, Richard Fulton, James Spinhirne, MWR 1991
●Dimensions of overshooting tops - Size of single GOES pixel - 15 degs colder than GOES ●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
Passive microwave structure of severe tornadic storms on 16 November 1987 Gerald Heymsfield, Richard Fulton, 1994 MWR
●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
PLUMES: SHORT WAVE IR REFLECTANCE
The AVHRR channel 3 cloud top reflectivity of convective storms Martin Setvak, Charles Doswell, 1991 MWR
●Areas of enhanced reflectivity at 3. 7 microns - Convective cell: widespread or localized - Plume-like: less common ●Association ●Not with hail (limited sample) often associated with “V” ●Possible cause - Very small ice crystals - Generated from vigorous updrafts
Multispectral high-resolution satellite observations of plumes on top of convective storms Vincenzo Levizzani, Martin Setvak, 1996 JAS
●Enhanced reflectivity - Small ice crystals - Limited growth time: strong updraft (BWER) - Vertical lifting/gravitational settling ●Vertical separation between plume and anvil ●Different ●Link from Fujita's (1982) stratospheric cirrus between plume source position and warm spo
Satellite observations of convective storm tops in the 1. 6, 3. 7 and 3. 9 spectral bands Martin Setvak, Robert Rabin, Charles Doswell, Vincenzo Levizzani, 2003 Atmos. Res.
●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
Moisture plumes above thunderstorm anvils and their contributions to crosstropopause transport of water vapor in midlatitudes Pao Wang, 2003, JGR
●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
Satellite multispectral identification of severe storms and their nowcasting by the microstructure of the pre-storm clouds D. Rosenfeld, A. Lerner, 2003 EMSC
● Profiles of hydrometeor size and phase - AVHRR 3. 7 micron imagery - Capture range of vertical development ● Characteristic difference for severe storms - Smaller size near top of cloud - Glaciation at colder temperatures - Effect of strong updrafts ● Possible use for severe storm detection - Application to MSG
RADAR ADVANCES IN STORM DETECTION
Tornado detection by pulsed Doppler radar R. A. Brown, L. R. Lemon, D. W. Burgess 1978, MWR
National Weather Service warning performance based on the WSR-88 D P. D. Polger, B. S. Goldsmith, R. C. Przywarty, J. R. Bocchieri, 1994, BAMS 1. 0. 8. 6. 4 . 2 1980 1985 1990 |---- RESEARCH PERIOD ---|
CURRENT APPLICATIONS
Nowcasting storm initiation and growth using GOES-8 and WSR-88 D data Rita Roberts, Steven Rutledge, 2003 WF
●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
●Intensity related to rate of cooling ●Increased lead time - 15 minutes prior to 10 d. BZ echoes aloft - 30 minutes prior to 30 d. BZ echoes aloft ●NCAR automated nowcasting system
NCAR auto-nowcast system Cindy Mueller et al, 2003, WF
●Provides ●Identify ●Fuzzy short-term (0 -1 hr) nowcasts of storm loca boundary layer convergence lines logic to combine predictor fields - Radar, satellite, mesonet, profilers, models ●Improves over extrapolation and persistence - Tested at 3 locations (3 years) - Plans to include in NWS AWIPS
Cloud-top Cooling Estimates Using Satellite-Derived Winds GOES-12 1 km Visible and 4 km Imager: 4 May 2003 Convective Cloud Mask Multi-spectral Techniques Doppler Radar for Validation Kristopher Bedka and John Mecikalski, 2004 EUMETSAT Satellite Conference
Validation and use of GOES sounder information Tim Schmit, et al. , 2002 WF
●Thermodynamic stability parameters - CAPE, CIN, PW - Hourly updates for time trends - Horizontal resolution (10 km) - Only available in clear areas ●Subjective ●Limited use in forecast offices use in NWP
Storm tracker A Web-based tool for monitoring MCS Robert Rabin, Tom Whittaker 2004
●Identify and track MCS - Cold cloud tops - Radar reflectivity - Adjustable thresholds ●Time trends of MCS characteristics - Size - Cloud top temperature stats - Radar reflectivity stats - Lightning - Storm environment from RUC, . . . ●Real-time ●Data and archived data on-line access from NOMADS/THREDDS catalog
SUMMARY ● 40 year history of satellite research ●Hot research topic through 1980's ●Limits to Operational use of early ideas - Advent of Doppler radar network - Resolution limitations - Limited early access ●Greatest impact: qualitative use of imagery
THE FUTURE? ●MSG (now) ●AWIPS ●GOES-R (2013) ●Space-borne Radars?
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