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As part of the Coastal Ocean Dynamics Experiment (CODE), meteorological instruments were deployed on buoys and at coastal stations and instrumented aircraft flights and coastal soundings were made to study the three-dimensional structure of the marine boundary layer over the continental shelf off northern California during the 1981 and 1982 upwelling seasons. These measurements show that after the atmospheric spring transition the airflow in the marine layer is dominated by the North Pacific high, and the surface wind field over the shelf is characterized by periods of strong (7-15 m/s), upwellingfavorable alongshelf winds lasting for up to 30 days, interrupted by shorter periods of much weaker winds directed either equatorward or poleward. These periods of weak or reversed winds typically last several days and are called wind relaxations, even though they are primarily associated with coastally trapped perturbations of the marine layer along the central and northern California coast and not with a large-scale weakening of the North Pacific high. The atmospheric boundary layer measurements made in CODE suggest a simple conceptual model which can explain much of the physiology or structure of the marine layer and associated surface wind field during periods of persistent upwelling-favorable winds. During these periods, which represent the quasi steady state regime during the upwelling season, the inversion base of the marine layer drops eastward toward the coast until it intersects the coastal mountain range at a height of several hundred meters, and the associated thermal wind produces an alongshelf wind jet which has a maximum speed just below the inversion base. Turbulent mixing tends to homogenize any stratification in the marine layer beneath the jet and couple the jet to the ocean surface, producing strong upwelling-favorable winds over the shelf. Day/night heating/cooling over the narrow coastal strip beneath the marine layer generates a weak cross-coast secondary circulation which causes the core of the alongshelf jet to drop in elevation and shift onshore. This diurnal change in the marine layer structure explains both the daytime acceleration of the surface winds observed over and near the coast and its offshore decay and the associated offshore increase in the subdiurnal alongshelf wind. Thus the quasi-steady component of the wind stress has a significant curl over the inner shelf during periods of active upwelling. This mean summer atmospheric boundary layer regime is occasionally interrupted by synoptic and/or mesoscale events or anomalous conditions. Analysis of the CODE observations suggests five types of events, two primarily synoptic-scale conditions which lead to stronger-than-normal upwelling-favorable winds over the shelf and three primarily mesoscale events which lead to wind relaxation.About half of the wind relaxation events observed in 1981 and 1982 are believed to be associated with either coastal-trapped gravity currents or internal Kelvin waves which propagate northward in the marine lay...

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The distribution of statistical properties of the meteorological and sea surface temperature fields along the west coast of the United States is described based on 10‐yearlong observations from buoys deployed by the National Data Buoy Center. The observations suggest that properties vary differently in each of three different regions along the coast: the Southern California Bight which remains sheltered from strong wind forcing throughout the year; the central and northern California coast up to Cape Mendocino, the site of persistent equatorward winds; and the Oregon‐Washington coast, where traveling cyclones and anticyclones produce vigorous and variable forcing. Over most of the region the variance in the wind speed is roughly equally divided between the annual cycle and the synoptic forcing, corresponding to periods between 5 and 50 cycles per year. Two seasons, summer and winter, are sufficient to describe the annual cycle. During the summer, two distinct wind speed maxima occur along the coast, one near Point Conception and the other off northern California, between Point Reyes and Point Arena. In the winter a single maximum occurs, located near Point Conception. The atmospheric pressure generally increases with latitude along the coast, but the annual cycle of atmospheric pressure has a different phase, depending on location; off the coast of California, highest pressures are found during the winter, while off Oregon and Washington, the highest pressures occur during the summer. Fluctuations in air and sea temperature are highly correlated, and the sea temperature is usually higher than the air temperature, in the winter. Examination of vertical soundings of the atmosphere at Oakland, Vandenberg Air Force Base and San Diego during the same period of time reveals that a well‐defined inversion separates the marine boundary layer (MBL) from the free atmosphere above nearly 90% of the time during the summer and half the time during the winter. Station soundings consistently overestimate the MBL thickness, but the results do suggest that the MBL is supercritical part of the time in the vicinity of the three sites. An attempt is made to examine the interannual variability and compare it to the Southern Oscillation index, although the results are limited because the record length is short compared with interannual timescales. Spatially averaged temperature anomalies increase during winter 1982–1983, coincident with the large El Niño event.

Automated meteorological observations at coastal and island stations, instrumented aircraft flights, and coastal soundings were made between July 1983 and June 1985 to define the variations of the lower atmosphere over the northern half of the Gulf of California during the two important climatic seasons, the mid‐latitude winter and the subtropical summer. A marine layer is well defined over water during both seasons but dissipates within a few kilometers inland. The winter large‐scale pressure field is dominated by the Great Basin high over the southwestern United States. Modulated by upper level synoptic activity, it causes 3 to 6 days events of northwesterly winds (8–12 m s−1) directed along the gulf's axis, which are coherent over basin scales, and bring cool, dry desert air over the gulf. The vertical scale of these winds is 700–1000 m over land on the western side of the gulf, close to the height of the Baja California mountains, but only 100–400 m over water, defined by the wintertime inversion. Cross‐gulf winds, related to topographic effects during upper level trough passages over Baja California, are particularly intense in the northwestern portion of the gulf. The winter marine layer is defined by a 1° to 4.5°C temperature inversion and a dew point temperature of 6°–11°C (a moisture content of 6–8 g kg−1); weak subsidence reduces dew point values to −4°C above the inversion. Winter winds above the marine layer are coherent (0.8) across the width of the gulf. The summer large‐scale pressure field is dominated by a thermal low over the southwestern United States, and drives weak (2–5 m s−1) southeasterly winds, also directed primarily along the gulf, which are less spatially uniform than winter winds. Air temperature and moisture content are rather constant, and topographic effects are absent. The summer marine layer is on the order of 200–300 m thick, with dew point temperatures of 26°–28°C (21–24 g kg−1), and capped by a weak temperature inversion (1°–2°C) over water. Aloft, the dew point temperature is 17°–21°C, and winds are weak and uncorrelated across the width of the Gulf. During June and early July 1984, four week‐long pulses of southeasterly winds (10 m s−1) support the existence, reported previously, of moisture surges from the gulf into the Sonoran desert. A dynamical analysis of subdiurnal motions shows that the cross‐gulf momentum balance is geostrophic, the along‐gulf balance is ageostrophic, with the along‐gulf pressure gradient opposed by friction at the surface. These results are consistent with a scale analysis of the equations of motion in the marine layer over the Gulf of California.

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