Central California Ozone Study (CCOS) Model Verification

The Central California Ozone Study (CCOS) is an ongoing program of the California Air Resources Board (CARB) whose goal is to develop better meteorological and aerometric observational data bases, as well as numerical simulation models, to more completely understand and predict urban and regional-scale ozone episodes. These observations and models will form the scientific basis for the development of appropriate emission control strategies to help California meet regulatory requirements for state and federal 1-hour as well as federal 8-hour ozone standards.

Field Season

The CCOS observational field program operated from June 1 through October 2, 2000. During the CCOS 2000 field program, extensive observations were collected in central California to document high ozone episodes and the meteorology that is associated with them. During the field phase of CCOS, ETL deployed a network of 15 wind profilers across California. This network was supplemented by an additional 10 profilers provided by other agencies, for a total of 25 wind profilers in the network. In addition, ETL deployed 9 sodars, 20 surface meteorological stations, and instrumented two towers with meteorological instruments.


ETL is presently working with CARB on both the analysis of these meteorological data, and in the development and running of a meteorological numerical simulation model (MM5). The goal of the data analysis is to identify the dominant meteorological processes affecting the central valley, and to asses the impact of these processes on ozone concentrations. The goal of the numerical simulation study is to provide accurate, high-resolution meteorological simulations (a 4 km grid with 50 vertical levels) that will then be used by CARB to drive a regional air quality model. The observational data will be used to evaluate the meteorological model, as well as to optimize model skill through four-dimensional data assimilation. As part of the modeling study, three different turbulence/boundary layer parameterization schemes (ETA, MRF, and Gayno-Seaman) are being evaluated.

Regional Meteorology

Meteorological phenomena in the central California region that are known to have a pronounced impact on ozone concentrations include

  1. the sea-breeze, which can bring cooler, moister, and lower ozone concentration air as it propagates inland;
  2. flow through the San Francisco Bay area, which is the principle inflow to the Central Valley, and the split of this flow, which determines the relative inflow into the Sacramento and San Joaquin Valleys;
  3. nocturnal low-level jets, which can rapidly transport boundary layer pollutants along the Central Valley;
  4. mesoscale eddies (the Schultz, Fresno, and Bakersfield) which can re-circulate ozone and its precursors;
  5. slope flows, which result in transport in or out of the valleys, support boundary layer venting along mountain crests, and produce subsidence or ascending motion over the valleys; and
  6. the depth of the atmospheric boundary layer, which is of critical importance to air quality, as it determines the depth through which pollutants are vertically mixed.

Intensive Operating Periods (IOP's)

During the CCOS 2000 field program several moderately high ozone episodes occurred, the most interesting of which are the June 14-15, July 29-August 3, and September 16-22 intensive operating periods (IOP's). These three IOP's are being analyzed and modeled by ETL. A model evaluation web site has been developed which displays both observations, model predictions, and the difference between these two. Presently, results from IOP2 (30 July - 2 Aug) are displayed on the web site.

ETL Team Members

Members of the ETL team that are contributing to the CCOS analysis program, and their areas of expertise, are:

Jian-Wen Bao applications/development and evaluation/verification of NWP models
Dave Costa data base management and graphics development
Clark King meteorological analysis
Jessica Koury graphics and web development
Ann Keane web development
Sara Michelson applications/development and evaluation/verification of NWP models
David White meteorological analysis
Robert Zamora applications/development and evaluation/verification of NWP models
Jim Wilczak team lead