Abrupt marine boundary layer changes revealed by airborne in situ and lidar measurements

At Point Conception strong northerly winds within the marine boundary layer (MBL) - typical during springtime along the southern California coastline – encounter the extreme eastward break of the coastline at the northern edge of the California Bight. South of this point, the MBL may thin considerably over a short distance impacting the forcing of the low-level wind. As seen in satellite imagery, the collapse of the MBL may be accompanied by a sharp transition from cloudy to clear, sometimes accompanied by stationary wave clouds. Since numerical simulations have difficultly representing these small-scale features, the Precision Atmospheric MBL Experiment (PreAMBLE) utilized the Wyoming King Air to obtain in situ aircraft measurements. The height of the MBL was measured by upward and downward pointing lidars on the King Air. Several cases were documented and reveal a range of fine scale aspects ranging from wave features several kilometers in length to an extremely abrupt discontinuity manifesting as a nearly vertical drop in the stratocumulus cloud deck at the top of the MBL. Flight strategies were designed to map the low-level wind and isobaric height to infer the forcing in the vicinity of Point Conception. In situ data combined with the continuous measurement of the MBL height provide an unprecedented view into the dynamics near this extreme bend in the coastline.