Regional Patterns of Mixing Depth and Stability: Sodar Network Measurements for Input to Air Quality Models

Abstract

A network of 13 sodars (acoustic radars) was operated in the San Francisco Bay Area for 2.5 months of the 1976 smog season. The goal was to produce a data base on time-dependent mixing depth and stability patterns for input to air quality models. The large set (?1000 site-days) of sodar facsimile records was filmed to provide a more compact, convenient, and accessible data product. A manual digitization scheme was devised and used to convert the continuous sodar data to hourly values describing mixing depth and a near-surface stability indicator. These values can easily be input to computerized air quality models and can readily be understood by a user with no sodas experience. Numerous sodar-inferred mixing depths were compared to those inferred from 1) simultaneous measurements of temperature and humidity profiles and 2) lidar-measured haze and cloud layering. These and previous tests show good overall agreement, demonstrating that in the San Francisco Bay Area, sodar measurements compare very favorably with alternate techniques for determining mixing depth. This result derives in part from the Bay Area's special meteorology (frequent strong, low, elevated inversions) and should not be extended indiscriminately to other areas. Several time-dependent maps of mixing depth illustrate the use of the data. The maps show changing patterns of mixing layer development caused by surface heating and cooling and varying marine influence. The patterns can vary markedly from day to day.