A case study is carried out for the 29 July–3 August 2000 episode of the Central California Ozone Study (CCOS), a typical summertime high-ozone event in the Central Valley of California. The focus of the study is on the low-level winds that control the transport and dispersion of pollutants in the Central Valley. An analysis of surface and wind profiler observations from the CCOS field experiment indicates a number of important low-level flows in the Central Valley: 1) the incoming low-level marine airflow through the Carquinez Strait into the Sacramento River delta, 2) the diurnal cycle of upslope–downslope flows, 3) the up- and down-valley flow in the Sacramento Valley, 4) the nocturnal low-level jet in the San Joaquin Valley, and 5) the orographically induced mesoscale eddies (the Fresno and Schultz eddies). A numerical simulation using the advanced research version of the Weather Research and Forecasting Model (WRF) reproduces the overall pattern of the observed low-level flows. The physical ...

Observed and WRF-Simulated Low-Level Winds in a High-Ozone Episode during the Central California Ozone Study

Hourly wind speed and direction data from 12 coastline stations on Sardinia, Italy, are analysed in order to characterize sea breezes in the region A set of criteria based on the diurnal reversal of wind direction, and the thermal gradient necessary to drive the circulation, is used to identify sea breeze days Statistics are presented that describe the occurrence, duration, and strength of the sea breezes On a stationwide basis, sea breezes are most frequent in the summer months (May–August), when they appear on more than one-third of the days Sea breeze occurrence and duration are the greatest for the stations on the east coast of the island The all-station average sea breeze duration reaches a maximum of about 9 h in June The strength of the sea breezes is roughly 3 m s−1 during summer months on average over all stations in the sample

An analysis of mean daily hodographs for the stations in the sample shows clearly the onshore–offshore nature of the sea breeze circulation, and the response of the sea breezes to the local coastline Sea breezes are shown to develop simultaneously on all coasts of the island under appropriate synoptic conditions Copyright © 2002 Royal Meteorological Society

The climatology of sea breezes on Sardinia

The diurnal evolution of the sea breeze hodograph over the Attic Peninsula has been studied using a three-dimensional numerical mesoscale model with fully nonlinear friction parameterization. The model results compare well with observed hodographs at three points in the modelling domain, and show that the balance of pressure gradient and terrain gradient forcing is dominant, and that this balance may result in either clockwise or anticlockwise rotation.

A study of the dynamics of hodograph rotation in the sea breezes of Attica, Greece

The diurnal evolution of the sea/land breeze hodographs over the northeastern Adriatic coast has been examined for several episodes, each lasting a few days A limited set of observations, as well as the results of a three-dimensional nonhydrostatic mesoscale model are studied by applying a rotary-component method This revealed a spatial distribution of the clockwise versus anti-clockwise rotation of the wind vectors for the sea/land breeze events An application of the rotary-component method to the results of additional numerical sensitivity tests showed that the coastal topography height considerably influences both the shape of the wind hodographs and the sense of wind rotation The method also displayed which areas are under a strong influence of the 24-h topographic forcing and which areas show a large wind consistency A further analysis of the 24-h modeled wind hodographs at several selected stations has been performed, thus revealing the hodograph shapes and the reasons for them

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Rotation of sea/land breezes along the northeastern Adriatic coast

A complete yearly record (1988) of surface measurements is used to examine the atmospheric diurnal secondary circulations over the entire area of Hong Kong in conjunction with spatial and temporal variations of surface temperature, wind speed and rainfall. Evidence of atmospheric diurnal secondary circulations is found at 10 sites. The occurrence of a summer morning rainfall maximum over the coast results from the interaction of the large-scale summer monsoon and local mesoscale secondary circulations. The afternoon onshore secondary circulation accelerates the advection of warm, humid unstable air and, coupled with the upward orographic lifting, produces enhanced rainfall along windward mountain ridges.

Makoto Kusuda

Papers

The contribution of horizontal advection to the diurnal variation of the wind direction of land-sea breezes: theory and observations