Storm tracking & typing for lightning observations Kristin Calhoun, Don MacGorman, Ben Herzog.
Global Lightning Observations
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Transcript of Global Lightning Observations
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Global Lightning Observations
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Streamers, sprites, leaders, lightning: from micro- to macroscales
•Remote detection of lightning - information provided
•LIS and OTD - what they are and how they work
•Results from global observations•Next generation•Change ?
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A schematic of grauple - ice crystal charge A schematic of grauple - ice crystal charge transfer in a thunderstormtransfer in a thunderstorm
Lightning production is related to microphysical and dynamic cloud processes. Lightning production is related to microphysical and dynamic cloud processes.
Ice interactions seem to play the major role in thunderstorm electrification.Ice interactions seem to play the major role in thunderstorm electrification.
Particularly rebounding collisions of graupel and ice crystals – Non-inductive Particularly rebounding collisions of graupel and ice crystals – Non-inductive charging mechanism.charging mechanism.
Necessary conditions for thunderstorm electrification: a) strNecessary conditions for thunderstorm electrification: a) strong enough enough up-draft to grow precipitation size ice. b) ice-graupel collisions in the up-draft to grow precipitation size ice. b) ice-graupel collisions in the
presence of waterpresence of water
+ + + ++ + + ++ + + ++ + + +
+ + + ++ + + ++ + + ++ + + +
- - -- - -- - -- - -
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Lightning Connection to Thunderstorm Updraft,
Storm Growth and Decay
• Total Lightning —responds to updraft velocity and concentration, phase, type of hydrometeors — integrated flux of particles
• WX Radar — responds to concentration, size, phase, and type of hydrometeors- integrated over small volumes
• Microwave Radiometer — responds to concentration, size, phase, and type of hydrometeors — integrated over depth of storm (85 GHz ice scattering)
• VIS / IR — cloud top height/temperature, texture, optical depth
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Why observe lightning?(Forecasting)
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Time
TornadotimeLightning
Radar
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pp
Flux HypothesisFlux HypothesisHypothesis:Hypothesis: Lightning Lightning
frequency frequency ((F)F) proportional to product proportional to product
of upward non of upward non precipitation ice mass precipitation ice mass
flux flux (I) (I) and precipitation and precipitation ice mass flux ice mass flux (p)(p)
FF = c* = c*pp**IISupported by simple Supported by simple
calculations (Blyth et al. calculations (Blyth et al. 2001) and lightning 2001) and lightning
model results (Baker et model results (Baker et al. 1995, 1999).al. 1995, 1999).
Positive chargePositive charge
Negative chargeNegative charge
Positive chargePositive charge
Positive chargePositive charge
Negative chargeNegative charge
TemperatureTemperature
Positive chargePositive charge
Char
ging
zon
eCh
argi
ng z
one
FF
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STEPS Results – 6 June 2000
‘Garden Variety’ Single Cell Storm
Non- Precipitation ice mass flux [g s-1 m-2] * 1011
Ligh
tnin
g p
er r
ada r
vol
u me
tim
e
Precipitation ice mass flux [g s-1 m-2] * 1012
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How good is the apparent correlation between lightning and IWP and how does it vary
between regimes?
Method• Create land, ocean, coastal data mask
• Create scatter plot of data in previous figure (0.5 x 0.5o grid) for each partitionResult• Noisy, but clear correlations above sample noise floor in flash density
• Eyeball says best fit lines would be very similar
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Clarify Signal: Ocean, Coast and Land IWP Binned by Flash Density
• When averaged, correlation is very strong, best fit lines independent of regime. • ~95% (75%) of oceanic (coast) flash density distribution in sampling noise (low flash density; <.007 fl/km2/day = 0.2 fl/km2/mo), low IWP (~.01-.02 kg/m2). Sampling + DE threshold + occurrence!• Similar functional relationships between rain (Iiquid) – lightning vary by regime.
(All rain certain pixels with detectable IWP included)
TRMM PR IMP
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Sample “Virtual radar” retrieval
Truth
Retrieval
(radar)
(µwave + lightning)
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GPROF(cloud model)
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Instrument designChristian et al, J. Geophys. Res., 1989
• Fast lens, narrowband filter at 777.4 nm
• 128 x 128 CCD array, 500 fps imaging
• Frame-to-frame subtraction isolates lightning transients against bright daytime background
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Measurement: Spatial Discrimination
8 km nominal spatial resolution optimizes the lightning-to-background S/N ratio.
8 km
8 km
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Measurement:Temporal Discrimination
CCD integration interval is set to 2 ms to minimize pulse splitting between frames and minimize
integration of background signal
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Measurement: Spectral Filtering
Narrow band interference filter passes only light from 1nm wide oxygen mutiplet
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Optical Transient Detector( launched April, 1995 )
Lightning Imaging Sensor( launched November, 1997 )
Lightning Detection from Low Earth Orbit
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LIS on TRMM
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•Lower orbit, smaller Field of View, tropical inclination
History: LIS (1997-present)
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High Resolution Full Climatology Annual Flash Rate
Global distribution of lightning from a combined nine years of observations of the NASA OTD (4/95-3/00) and LIS (1/98-12/04) instruments
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Climatology: Diurnal cycle
( Local hour )
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Climatology: Diurnal cycle
( UTC Hour )
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Global lightning is modulated on annual & diurnal time scales, as well as seasonally
and interannually
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Lightning Responsive to Interannual
Variability
Winter 1997-98 (El Niño)
Winter 1998-99 (La Niña)
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Flash Rate Density-Congo
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Flash Rate Density-India
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LIS Ocean Overpass
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LIS Land Overpass
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Major Points for Severe Weather
• Primary lightning signature is high flash rates and the “jump”
• Lightning flash rate is correlated storm intensity - higher rate implies stronger storm.
• Evolution of the lightning activity follows the updraft. Increasing activity means the storm intensifying; decreasing activity means the updraft is weakening.• A jump in lightning activity is associated with a pulse in updraft intensity
• These signatures, in conjunction with other NWS assets can be used to:
• Separate intensifying from weakening storms• Identify storms in process of going severe• Quickly determine the most intense storms in a complex system• Improved warning times • Reduced false alarms rates
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Lightning Sensing from GEO
•Climate Monitoring
•Storm Development
• Ice-phase precipitation estimates
•Severe Weather Now-casting
•Data assimilation and model inputs
•Atmospheric chemistry
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GLM : Field of View at GOES West and East
•GOES W (75ºW) GOES E (135ºW)
• OTD climatology indicates lightning density• Range rings indicate limits of 10, 15, 20, & 50 km pixel
footprint
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GEO -East
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•Questions ?