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Assimilation of Lightning Data In WRF Using 1-D + 4-D VARH. Fuelberg, I. Navon, R. Stefanescu, and M. Marchand

Florida State University

Evaluation

Background

Nudging Results | 0000 UTC 11 February 2010: End of 6 Hour Assimilation

Fierro, A., E. Mansell, D. MacGorman, C. Ziegler, and M. Xue, 2011: A lightning data assimilation scheme for the WRF-ARW model at cloud-resolving scales: Tropical Cyclone Erin (2007) and NSSL daily forecast runs. 2011 Southern Thunder / GLM Users’ Conf. , Norman, OK.

Jacobson, A., R. Holzworth, J. Harlin, R. Dowden, and E. Lay, 2006: Performance assessment of the World Wide Lightning Location Network (WWLLN), using the Los Alamos Sferic Array (LASA) as ground truth. J. Atmos. Oceanic Technol., 23, 1082–1092.

Pessi, A., and S. Businger, 2009: The impact of lightning data assimilation on a winter storm simulation over the North Pacific Ocean. Mon. Wea. Rev., 137, 3177–195.

References

• Most previous lightning data assimilation involved non-

Newtonian nudging schemes.• Fierro et al. (2011) nudged the mixed phase region (0 to -30◦C) to supersaturation where total lightning occurred and nudged down hydrometeor contents where no lightning occurred.• Pessi and Businger (2009) nudged latent heating rates from the Kain-Fritsch cumulus param. scheme to correspond to lightning flash rates.• Our scheme uses a variational approach to assimilate lightning observations to alter temperature profiles to be consistent with observed flash rates. The variational approach is implemented using WRF 3D-Var and 4D-Var.

• Our 1-D + 4-D scheme and two nudging schemes will be tested on four cases with copious lightning:• Nor’easter (tentatively the 10-11 Feb. 2010 storm)• North Pacific mid-latitude cyclone (17-19 Dec. 2009 storm)• Tropical cyclone (Hurricane Karl, 2010)• Severe thunderstorm/tornado outbreak in the U.S.

• WRF-ARW V3.3 • 6 km parent domain• 2 km nested domain• 60 vertical levels• GFS initial data• No cumulus parameterization• WRF Single Moment 6-Class microphysics scheme• WWLLN lightning data assimilated in 10 min. windows over a 6 h period in the nested domain-Poor detection efficiency—detects strongest

flashes (Jacobsen et al. 2006)• Fierro et al. used WTLN total lightning observations• When WWLLN lightning was observed in a grid cell,

we saturated the mixed phase region• Fierro et al. supersaturated the region up to 5%, depending on the flash rate• Hydrometeor contents nudged where no lightning occurs as in Fierro et al. according to:

- IF( q ≥ b/ρair ) THEN q = MAX( 0.2*q , b/ρair )

where b = 1 g m-3

Model / Nudging Specifications

d01 - 6 km