Research flights during the Precision Atmospheric Marine Boundary Layer Experiment (PreAMBLE) in Southern California during May–June 2012 focused on three main features found in the nearshore marine boundary layer (MBL): the coastal jet (10 flights), the Catalina eddy (3 flights), and the initiation of a southerly surge (1 flight). Several topics were examined with case studies, but results from individual events may not represent typical conditions. Although these flights do not constitute a long-term set of data, observations from PreAMBLE are used to find common features. Two main topics are addressed: the MBL collapse into the expansion fan, and the subsequent transition into the Santa Barbara Channel (SBC). The midmorning to late afternoon flights occur during moderate to strong northerly wind. Slope of the MBL in the expansion fan varies and wave perturbations can be embedded within the expansion fan. As the cool MBL flow turns into the SBC, it moves underneath a deeper and warmer MBL that originates from the southeast over the warmer ocean. The temperature inversion between the cool and warm MBL erodes toward the east until there is only the inversion between the warm MBL and free troposphere. The dissipation of the lower layer into the SBC observed by the aircraft differs from previous conceptual models that depict a continuous MBL that thins and then deepens again in the SBC, which was inferred from sparse observations and numerical simulations. Only one flight within the SBC detected a hydraulic jump from 100 to 200 m above the surface
