Transcript cliff_mass.ppt

Lightning Assimilation Techniques
• Non-thinned Lightning Experiment
– NLDN/LR lightning strike is detected
– Lightning strike is converted into 30 minute lightning rate from nearby
LTNG observations
– Lightning rate converted into “observation” of convective rainfall rate
using Pessi/Businger convective rain rate/lightning rate relationship
– Convective rainfall is scaled up to 6 hour cumulative total to match
model background forecasted 6 hour convective rainfall
– Convective rainfall (mm) is assimilated into WRF-EnKF
Lightning Assimilation Techniques
Pessi/Businger Lightning rate/Convective rainfall rate relationship
Lightning Assimilation Techniques
• Thinned Lightning Experiment
– NLDN/LR lightning strike is detected
– Lightning strike is converted into 30 minute lightning rate from nearby
LTNG observations
– Any lightning strikes used in the density calculation are no longer
allowed to be an assimilation point, resulting in a thinning out of the
lightning “observations” (although strikes will be used to calculate
nearby densities)
– Lightning rate converted into “observation” of convective rainfall rate
using Pessi/Businger convective rain rate/lightning rate relationship
– Convective rainfall is scaled up to 6 hour cumulative total to match
model background forecasted 6 hour convective rainfall
– Convective rainfall (mm) is assimilated into WRF-EnKF
Lightning Assimilation Techniques
• Thinned Lightning Experiment – 1 hr rain
– NLDN/LR lightning strike is detected
– Lightning strike is converted into 30 minute lightning rate from nearby
LTNG observations
– Any lightning strikes used in the density calculation are no longer
allowed to be an assimilation point, resulting in a thinning out of the
lightning “observations” (although strikes will be used to calculate
nearby densities)
– Lightning rate converted into “observation” of convective rainfall rate
using Pessi/Businger convective rain rate/lightning rate relationship
– Convective rainfall is NO LONGER scaled up as model background
forecasted convective rainfall is a 1 hour cumulative total
– Convective rainfall (mm) is assimilated into WRF-EnKF
Experiment Design
• Pacific Ocean
– Low observation density; location of
important storm tracks; errors propagate
downstream to mainland United States
• North America
– High observation area; potential of forecast
improvement;
• Similar studies with similar domain
– Pessi/Businger previously studied domain for
lightning assimilation
Experiment Design
• Observations
– Control case
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Radiosondes
Surface stations (ASOS, ship, buoy)
ACARS
Cloud drift winds (no sat. radiances)
– Experimental cases
• Control observations
• Lightning
Experiment Design
• WRF Setup
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WRF 2.1.2 (Jan 27, 2006)
100 by 86 grid
45-km horizontal resolution
33 vertical levels
270 second timestep
Shortwave: Dudhia
Longwave: Rrtm
Surface: Noah land-sfc
PBL: MYJ TKE scheme
Cumulus: Kain-Fritsch (new Eta)
Experiment Design
• EnKF Setup
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90 ensemble members
6-hr Analyses
24-hr Forecasts (starting every 12 hours)
8 assimilations of “spin-up” before
lightning assimilations
Square root filter (Whitaker and Hamill,
2002)
Horizontal localization – Gaspari and
Cohn 5th order piecewise
Fixed covariance perturbations to lateral
boundaries
Zhang covariance inflation method
Localization radius – 2000 km
Test Cases
• Test Case #1
– December 16-21, 2002
• Test Case #2
– October 4-8, 2004
• Test Case #3
– November 8-12, 2006
Experiment observations example
ACARS observations spatial distribution
Experiment observations example
Cloud track wind observations spatial distribution
Experiment observations example
Radiosonde, surface station and buoy observations
•Radiosonde Obs
•Surface Stations
•Buoys
Experiment observations example
Lightning Observations