Spring to summer northward migration of high O3 over the western

] Many investigators have reported better agreementbetween the satellite measurements and the model results intropical regions than at mid and high latitudes partly due tothe difficulty in simulating cloud convection and lightningat mid latitudes [e.g., Chandra et al., 2004; Martin et al.,2006; Ziemke et al., 2006; Hudman et al., 2007]. RecentGEOS-CHEM studies have shown that lightning NOxproduction at higher latitudes in the standard global modelneeds to be increased by up to a factor of 4 [e.g., Li et al.,2005; Martin et al., 2006; Hudman et al., 2007]. Choi et al.[2005] demonstrated that the transient enhancements oflightning NOx and the convective transport of CO havelarge enough signals for satellites to detect.[