Aircraft Measurements and Numerical Simulations of an Expansion Fan off the California Coast

Mountains along the California coastline play a critical role in the dynamics of marine atmospheric boundary layer (MBL) airflow in the vicinity of the shoreline. Large changes in the MBL topology have been known to occur downwind of points and capes along the western coast of the United States. Large spatial gradients in wind and temperature become established that can cause anomalous electromagnetic wave propagation. Detailed airborne measurements using the University of Wyoming King Air were conducted to study the adjustment of the MBL to the Point Arguello and Point Conception headlands. Pronounced thinning of the MBL consistent with an expansion fan occurred to the south of Point Conception on 13 June 2012. A sharp cloud edge was collocated with the near collapse of the MBL. D-value cross sections derived from differential GPS altitude measurements allow assessment of the vertical profile of the horizontal pressure gradient force and hence thermal wind forcing in response to the near collapse...