Aircraft Observations of the Marine Boundary Layer Adjustment near Point Arguello, California

Abstract

Northerly winds set up by synoptic conditions are persistent in the marine boundary layer (MBL) off the California coast from late spring through summer. Wind, pressure, and MBL height are modulated as the low-level flow impinges on the points and capes along the California coast. The Precision Atmospheric Marine Boundary Layer Experiment was conducted in May and June of 2012 with the primary goal to directly measure the dynamics responsible for the wind field near Point Arguello and Point Conception. Detailed measurements of the horizontal pressure field within the MBL were made using the University of Wyoming King Air research aircraft. Airborne measurements made during cases of strong northerly wind show an abrupt adjustment of the MBL near Point Arguello, including a modulation of the horizontal pressure gradient force and a near collapse of the MBL. Airborne lidar measurements complement measurements of the horizontal pressure field and help to elucidate the large changes in the MBL height in the vicinity of Point Arguello. The Weather Research and Forecasting Model was used to simulate the 20 May 2012 case at a high resolution. Model results showed large-amplitude height perturbations near Point Arguello, similar to those observed from the airborne platform. In this case, the offshore flow played an important role in the local forcing.