Anomalous monsoonal activity in central Arizona, USA

[1] Published research has suggested that urban and agricultural activities in central Arizona may be enhancing monsoonal precipitation in the region; therefore, this study employed cloud-to-ground lightning data and topographic data to reveal spatially anomalous zones of lightning activity in central Arizona. A multiple linear regression model with topographic variables as predictors explained 85% of the variance in gridded lightning-flash counts. Clustering of large positive residuals of lightning flashes existed between 40 km and 100 km north/northeast of urbanized Phoenix. Observed lightning flashes in this zone were 40% more frequent than lightning flashes predicted by the model. Two plausible causes of the enhanced lightning activity are intensified convective storms due to Phoenix-derived water vapor and altered microphysical processes in storm clouds due to Phoenix-derived atmospheric pollution. It is possible that the positiveanomaly zone also had enhanced rainfall. Citation: Diem, J. E. (2006), Anomalous monsoonal activity in central Arizona, USA, Geophys. Res. Lett., 33, L16706, doi:10.1029/ 2006GL027259.