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The Structure of the Marine inversion Layer off the Central California Coast: Mesoscale Conditions

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  • 1 Department of Meteorology. San Jose State University, San Jose, California
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Abstract

Data collected on board an instrumented aircraft during the Marine Atmospheric Boundary Layer Experiments, West Coast (MABLES WC) field study are examined. The data were collected at several levels in the marine and inversion layers approximately 200 km west of the central California coast during August 1978. Composite sounding and cross sections of wind and temperature variables are presented to provide an overview of the mesoscale structure of the offshore marine and inversion layers at the time of MABLES WC.

Under typical summertime synoptic conditions, which prevailed early in the study period (three flights examined), a strong inversion is found. Base heights and temperature increases across the inversion base are comparable to values observed in the San Francisco Bay area. The topography of the inversion base shows a slope downward toward the east during all three of these flights and also suggests the presence of convective activity, gravity-wave activity, or both, during two of the three flights. The inversion weakened later in the study period when atypical synoptic conditions prevailed.

During typical conditions, wind-speed minima were found near the base of the inversion, and jets with speeds as high as 17–18 m−1 were found within the inversion layer. These observations of the vertical wind profile agree with those made in the San Francisco Bay area. Further, in two of the three cases, a well-organized horizontal structure of the jet was apparent. Data gathered during a flight later in the study period (“atypical” synoptic conditions) are also presented and show a particularly good example of the jet in the offshore region.

Abstract

Data collected on board an instrumented aircraft during the Marine Atmospheric Boundary Layer Experiments, West Coast (MABLES WC) field study are examined. The data were collected at several levels in the marine and inversion layers approximately 200 km west of the central California coast during August 1978. Composite sounding and cross sections of wind and temperature variables are presented to provide an overview of the mesoscale structure of the offshore marine and inversion layers at the time of MABLES WC.

Under typical summertime synoptic conditions, which prevailed early in the study period (three flights examined), a strong inversion is found. Base heights and temperature increases across the inversion base are comparable to values observed in the San Francisco Bay area. The topography of the inversion base shows a slope downward toward the east during all three of these flights and also suggests the presence of convective activity, gravity-wave activity, or both, during two of the three flights. The inversion weakened later in the study period when atypical synoptic conditions prevailed.

During typical conditions, wind-speed minima were found near the base of the inversion, and jets with speeds as high as 17–18 m−1 were found within the inversion layer. These observations of the vertical wind profile agree with those made in the San Francisco Bay area. Further, in two of the three cases, a well-organized horizontal structure of the jet was apparent. Data gathered during a flight later in the study period (“atypical” synoptic conditions) are also presented and show a particularly good example of the jet in the offshore region.

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