Los Angeles Sea-Breeze Thermal Response Field Studies

Understanding changes in sea breeze temporal and spatial dynamics including inland penetration is a relevant subject in many coastal climates. The case of the California coastal summer climate is of particular importance due to the strong influence of the sea-breeze in the regional climate. Further, recent studies by the authors found that summer average-maximum air temperatures in the populated California coastal areas of San Francisco Bay Area and the South Coast Air Basin reflected cooling trends at low elevation coastal areas open to marine air penetration and warming trends at inland and high elevation coastal areas (Lebassi et al. 2009). The authors hypothesized that this coastal cooling was the consequence of an increase of sea-breeze activity during the period, reflected by the increase in sea-land pressure gradients in the region calculated, as from ECMWF ERA-40 data from 1979-2002.

These findings merit further analysis of the summer sea-breeze spatial and temporal extent in California coasts. The present study focuses on observations of maximum sea-breeze and associated regional thermal response for the South Coast Air Basin in support of the above hypotheses. A field study was configured to observe the sea-breeze intensity and penetration via surface ground stations and wind profilers along the projected transect of the sea-breeze during the summer of 2013. These surface observations are supplemented by airborne remote sensing data collected from flights using the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the MODIS/ASTER Airborne Simulator (MASTER) sensors at spatial resolutions of 30 and 50 m, respectively. Data clearly reflects that sea-breeze peaks between the hours of 1800-2000 LST, with intensities of 6 m/s at the time of maximum occurrence, consistent with the maximum temperature sea-inland thermal gradients as shown by the ground sensors for and the remote sensing data for the skin temperatures. Horizontal and boundary layer extents were measured in 50-60 km and 1.5 km, respectively as measured by wind profilers and ground station. These results may reflect changes over similarly reported sea-breeze patterns 30-50 years in the past. The presentation will review methods used in the field study, hypothesis validation, and will outline future works for sea-breeze and coastal cooling research.