Meteorological conditions and anomalies during the Intercontinental Chemical Transport Experiment-North America

Meteorological conditions are described during the Intercontinental Chemical Transport Experiment–North America (INTEX‐NA) that was conducted over the United States during July and August 2004. Relatively zonal flow dominated the contiguous United States during the first 2 weeks of the mission, while a series of large amplitude troughs traversed the eastern half of the country during the final 4 weeks. These troughs were accompanied by cold fronts reaching the Gulf of Mexico, an uncommon occurrence during August. Frontal passages over the northeast were somewhat above average, but the short time interval between passages precluded the formation of stagnant high‐pressure centers containing abundant pollution. Atmospheric chemistry during INTEX‐NA was heavily influenced by record‐breaking fires over Alaska and western Canada. Persistent high pressure over Alaska provided ideal conditions for the wildfires and for transporting their burning by‐products southeastward toward the INTEX domain where they were sampled frequently by INTEX aircraft. Forward trajectories and satellite imagery showed that the plumes later were carried to parts of Europe, Africa, and even the Arctic. Deep convection and lightning were important factors during INTEX‐NA. Cloud‐to‐ground (CG) lightning data show that horizontal patterns and numbers of lightning flashes during INTEX‐NA are similar to those of 2003 and 2005. Statistics derived from 10 day backward trajectories indicate that the DC‐8 often sampled lightning influenced air.