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Figure 14: CCN concentration upwind and downwind of Houston along the aircraft’s flight track on 1 October 3004. <br />st <br />4.3 Cloud microphysical study: September 24, 2004 <br />The remnants of tropical storm Ivan moved onshore on the 23rd of September 2004 and farther into <br />southeast Texas on the 24th. Very moist flow off the Gulf and significant moisture convergence over <br />southeast Texas near the center of Ivan resulted in numerous showers and storms over that region. This <br />is shown by the satellite imagery in Figure 16. The research aircraft launched from south central Texas to <br />sample convective development over those regions after which it progressed eastward to sample a <br />feeder band coming onshore in the Lake Charles, Louisiana area. Upper level features were rather weak <br />with weak to moderate westerly flow across much of central Texas in advance of a deepening trough over <br />the desert southwest. Deep moisture and strong surface heating resulted in surface based CAPE values <br />of around 1000 J/kg across south central Texas. Scattered convection developed in this region despite <br />the lack of surface focusing mechanisms. By 2200 UTC most of this activity was weakening across south <br />central Texas while feeder bands continued to move onshore in the Beaumont, Texas region. Surface <br />based CAPE based upon the RUC initialization data around Beaumont was near 2000 J/kg at 1900 UTC. <br />38 <br />