Edward Mansell National Severe Storms Laboratory Donald MacGorman and Conrad Ziegler National Severe Storms Laboratory, Norman, OK Funding sources in the Office of Naval Research, NSF, NSSL, the National Research Council, and the Oklahoma State Regents Lightning at NSSL: Numerical Modeling and Data Assimilation
Storm electrification modeling: Basic understanding of electrification processes Lightning-storm relationships Lightning data assimilation (COAMPS) On mesoscale (>10km), control convection parameterization scheme. Storm-scale EnKF radar data assimilation Modeling Activities/Capabilities
Storm Model (COMMAS) Full dynamic, microphysical, and electrical simulation model Collisional charge separation, explicit small ion processes, branched lightning. Two-moment bulk microphysics: Predict particle concentrations (and mass) for all hydrometeors (droplets, rain, ice crystals, snow, graupel, hail) and simple bulk CCN. MPI capable [Mansell et al. 2002, 2005, (2009 in review), also Fierro et al, Kuhlman et al.]
Supercell Simluation
Small Storm Simluation
Lightning and Charge Structure Inferred charge structure from lightning sources + + – Model-simulated charge structure and lightning West -30km -25km East Altitude (km)
Sensitivity to CCN concentration Volume
Simulated Lightning Rate Correlations Isolated cells: 0.7 multiple cells: 0.5
Total Flash Rate Correlation Coefficient with ParameterIsolated StormsStorm Systems Maximum Elec. Field Graupel Volume Updraft Mass Flux (-10°C) Updraft Volume (>10 m s -1 ) Cloud Ice Mass Flux (- 30°C) Cloud Ice Mass Rain Mass Maximum Updraft
Assimilating Lightning Data o Unambiguous indicator of [electrified] convection o Mixed-phase ice precipitation (graupel) is present o Can complement radar data assimilation: Fill in radar voids: Mountains, oceans, other countries, radar drop-outs Potential use of flash rate relationships (storm intensity, e.g., updraft volume/mass flux) and satellite-based (e.g., GOES) total lightning detection (total flash rate in particular) [Mansell, Ziegler, and MacGorman, 2007]
Method is similar to Rogers et al. (2000) for radar assimilation. Force/suppress Kain-Fritsch based on presence/absence of lightning. Add up to 1.0 g/kg of moisture to get deep convection (10m/s updraft, 7km cloud depth). Allow KF scheme to generate precipitation rates and latent heating and evaporative cooling. (Other methods can be used to adjust or impose latent heating rates based on rainfall relations) LMA sources KS CO NE Case study with COAMPS on July 2000
Test caseSpin-up period: Obs. Precip vs. Control
Spin-up period: Obs. Precip vs. Assimilation
Spin-up period: Control vs. Assimilation
Surface Temperature (C) Warm-start Model Conditions: ControlAssimilation
01 UTC 21 July
02 UTC 21 July
0-6 hr Precip: Obs and forecasts Control Fcst from ltg. assim.
Summary Cloud modeling investigates basic aspects of lightning production by storms. Lightning data assimilation can be an effective means to initialize the effects of prior/current convection: Cold outflows better placed by forcing KF. Good potential for rapid update cycling and providing conditions for higher-resolution nest. Assimilation-based forecast shows more skill than control forecast for first few hours. Does little to correct errors in large scale fields, so range of forecast improvement limited ( < 6 hr).
Issues Must consider lightning location accuracy in terms of model resolution. What does a “flash” represent in the observing system? (large variations in flash extent) Method tied to data source. For resolved convection or convection-permitting EnKF, need to relate lightning to model variables or derived quantities. And/Or use lightning mainly to initiate deep convection.