MM5 simulations of a SCOS97-NARSTO episode

MM5 simulations of the 4–7 August SCOS97-NARSTO ozone episode in the SoCAB showed that a relatively rare easterly upper-level background flow influenced surface wind flow directions at in-land sites. An inland-moving surface convergence zone resulted where the offshore background flow met an inland moving westerly (sea breeze plus thermal upslope) onshore flow. Maximum inland penetration of the zone was to the San Gabriel Mountains, where it produced peak observed ozone concentrations. MM5 reproduced the main qualitative features of the evolution of the diurnal sea breeze cycle, as it reproduced the opposing easterly flow, inland movement of the sea breeze front, and retreat of the land breeze front. The accuracy of predicted surface winds and temperatures were improved by modifications of MM5 and/or its input parameters, e.g., by use of the PSU MBLI scheme, analysis nudging with NCAR/NCEP model output, accurate specification of deep-soil temperature, observational nudging with SCOS97-NARSTO surface and upper level winds and temperatures, and use of updated urban land-use patterns.