MM5 simulations of a SCOS97-NARSTO episode

Abstract

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. r

Modeled large-scale warming impacts on summer California coastal-cooling trends

“…Up-slope winds (up to 2 m s −1 ) have developed over the mountains, while sea breezes (up to 2.5 m s −1 ) are confined to a narrow coastal strip. A near-calm region is located between the sea breeze and upslope winds, consistent with other SoCAB modeling studies for such hours [Boucouvala et al, 2003].…”

“…These upslope flows converge at inland mountain tops, producing strong vertical motions, which create upper‐level return offshore‐directed flows. Polluted air is prevented from exiting the SoCAB (in the pass between the San Gabriel and San Bernardino Mountains) by opposing upper level easterly flows associated with mesoscale highs north of that gap [ Boucouvala et al , 2003].…”

The sea breeze/land breeze circulation in Los Angeles and its influence on nitryl chloride production in this region

“…Nighttime chemical transformations can be important in determining the overall impact of the land breeze on air quality within the basin, especially since the products of these nighttime reactions are swept inland on the sea breeze during the following day and are known to be widely distributed throughout the basin [ Cass and Shair , 1984]. The influence of this phase of the sea breeze/land breeze circulation has been less well studied, in part due to the smaller number of nighttime measurements over water, which have been limited to studies that have taken place either at the coast or at island sites [ Boucouvala et al , 2003].…”

California Coastal - Cooling a Reverse Reaction from Global Warming General Circulation and Mesoscale Effects

“…Downscaled regional climate modeling by Kueppers et al (2007) showed western-US irrigation lowering average temperature (T ave ) and T max values at rates comparable to the increases from GHG warming. Similar modeling by Miller et al (2003) showed California T ave warming rates of 2.1-4.5°C, while ensemble downscaling by Maurer (2007) of 1950-99 JJA median temperatures showed warming rates that decreases from 0.13°C decade -1 in inland California to 0.08°C decade -1 at coastal areas north of the SoCAB. While this showed coastal influences, its coarse spatial resolution could not sufficiently resolve local topographic features that affect mesoscale circulations and thus local temperature trends.…”