Airborne Measurements of Coastal Jet Transition around Point Conception, California

• Published in: Monthly weather review Vol. 141; no. 11; pp. 3827 - 3839
• Main Authors: RAHN, David A, PARISH, Thomas R, LEON, David
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.11.2013
• Subjects: Aerosols; Atmospherics; Boundary layers; Channels; Coastal; Collapse; Compressing; Earth, ocean, space; Exact sciences and technology; External geophysics; Global positioning systems; GPS; Hydraulics; In situ measurement; Lidar; Meteorology; Offshore; Research aircraft; Shallow water; Studies; Temperature inversions; Troposphere; Turbulent flow; Wind; Santa Barbara Channel; California; Point Conception; Santa Barbara County California; United States; Wyoming; United States > US; INE, USA, California Bight; USA, Wyoming; INE, USA, California, Point Conception; INE, USA, California, Santa Barbara Channel; Supercritical flow; Marine atmosphere; aerosols; Summer; Pressure gradient; troposphere; turbulence; North America; Shallow water; horizontal gradient; Temperature reversal; Inversion layer; Measurement in situ; Mixed layer; coastal zone; winds; Atmospheric boundary layer; Spring(season); Radar observation; Lidar; Isobaric surface; collapse
• ISSN: 0027-0644; 1520-0493
• DOI: 10.1175/MWR-D-13-00030.1

Low-level winds along the Californian coast during spring and early summer are typically strong and contained within the cool, well-mixed marine boundary layer (MBL). A temperature inversion separates the MBL from the warmer free troposphere. This setup is often represented by a two-layer shallow-water system with a lateral boundary. Near a prominent point such as Point Conception, California, the fast-moving MBL flow is supercritical and can exhibit distinct features including a compression bulge and an expansion fan. Measurements from the University of Wyoming King Air research aircraft on 19 May 2012 during the Precision Atmospheric MBL Experiment (PreAMBLE) captured wind in excess of 14 m s super(-1) off of Point Conception under clear skies and wind similar to 2 m s super(-1) east of San Miguel in the California Bight. A compression bulge was identified upwind of Point Conception. When the flow rounds the point, the MBL undergoes a near collapse and there is a spike in MBL height embedded in the general decrease of MBL height with greater turbulence just downwind that is associated with greater mixing through the inversion layer. Lidar and in situ measurements reveal that transport of continental aerosol is present near the pronounced MBL height change and that there is a complex vertical structure within the Santa Barbara Channel. Horizontal pressure gradients are obtained by measuring the slope of an isobaric surface. Observations of wind and pressure perturbations are able to be linked through a simple Bernoulli relationship. Variation of MBL depth explains most, but not all of the variation of the isobaric surface.