MJO Modulation of Lightning in Mesoscale Convective Systems Katrina S. Virts and Robert A. Houze, Jr. University of Washington AGU Fall Meeting, San Francisco, 11 December 2013

Identifying MCSs using A-Train data MODIS 10.8 m brightness temperature AMSR-E rain rate Years included: 2007-2010 MODIS = moderate resolution imaging spectroradiometer; AMSR-E = advanced microwave scanning radiometer for earth observing system Details in Yuan and Houze 2010

“Separated” active MCS 260K Heavy Rain Closed contour Rain “Separated” active MCS Separated HCS “HCS” Avg CMCS = 44000 km2; SMCS = 40000 km2 “Connected” active MCS Details in Yuan and Houze 2010

World-Wide Lightning Location Network (WWLLN) Global network of 70+ sensors Monitors very low frequency radio waves Lightning strokes located to within 5 km and a few s

World-Wide Lightning Location Network (WWLLN) Global network of 70+ sensors Monitors very low frequency radio waves Lightning strokes located to within 5 km and a few s Lightning in one-hour window Separate coordinate system for each MCS, centered on largest raining core Lightning in cloudy grid boxes

MCS climatology Indian Ocean Maritime Continent Western Pacific Ocean SPCZ

More frequent lightning, broader lightning maximum during break period Maritime Continent SMCSs Active period - phases 3-4-5 Break period - phases 7-8-1 60% increase in ltg freq during break period; 40% increase in MCS size during active period More frequent lightning, broader lightning maximum during break period

MCS environments more unstable during break period

Peak lightning at end of break period Lower lightning density in CMCSs

TRMM radar precipitation features Contiguous areas with near-surface rain rate > 0 Use features with maximum height of 30 dBZ > 6 km Size equivalent to smallest and largest 50% of MCSs Years included: 1998-2012 TRMM RPF data obtained from University of Utah TRMM database. Details in Liu et al. 2008

Peak convective rain fraction at end of break period Lower convective rain fraction in large precipitation features

Conclusions Larger, more connected, and more numerous MCSs during MJO active period Peak lightning just prior to active period (except over SPCZ) Lower lightning densities and lower convective rain fractions during active period Higher lightning densities in SMCSs

The End This research was supported by NASA grant NNX10AM28G and DOE grant DE-SC0008452.