316
S.E. Ibarra-Obando et al.
21.2 Oceanography and Climate
The climate and oceanography of Alta and Baja California are largely controlled by the California Current ( CC) System, which represents the eastern
limb of the large-scale, anticyclonic North Pacific gyre, and has a pronounced influence on the structure and function of the coastal upwelling
and lagoonal ecosystems. The major alongshore currents of the CC System
are an offshore, southward flow (California Current) and a nearshore,
northward flow (California Countercurrent). The western boundary of the
CC lies about 850- 900 km off the coast. The California Current is a surface
current (0-300 m) with an average speed of typically <25 em s- 1 (peak velocity 50 em s- 1 ) which transports cool, low-salinity, oxygen- and nutrientrich, subarctic water towards the North Equatorial Current. The California
countercurrent is an important nearshore surface feature along the Baja
Californian coast throughout the year. During the summer, the Countercurrent is covered by southward flowing surface waters, owing to persistent
northwesterly winds, and remains as an undercurrent at depths of 200500 m. In fall and winter, the countercurrent is strong and reaches the surface inshore of the California coast (Davidson Current). The area influenced by the countercurrent may extend up to 500 km offshore at depths
below 200m. Owing to its broad seaward extent under the California Current, it has been described as the California Undercurrent domain (McLain
and Thomas 1983). The coastal ocean off Alta and Baja California is a classic wind-driven coastal upwelling system. The strong atmospheric pressure gradient between a thermal low-pressure cell over the heated land
mass and higher barometric pressure over the cooler ocean is largely responsible for creating vigorous alongshore winds that drive the coastal
upwelling system. During the warmer seasons, strong northerly and northwesterly winds induce offshore transport of surface waters. Upwelling of
cool, nutrient-enriched water from the depth balances the resulting loss of
surface water near the coast.
Cooling and stabilization of the onshore airflow by contact with upwelled waters leads to a cool summer climate at the adjacent coast. During
upwelling seasons, the coastal inland under direct influence of coastal stratus and fog is characterized by clear atmospheric conditions which lead to
strong daytime heating by short-wave solar radiation, particularly in interior valleys, and rapid nighttime, long-wave radiate cooling (Bakun
1990). As a whole, the Mediterranean-type climate of the region is hot and
dry with prevalence of desert conditions, though considerable local variations may occur. The northern portion of the peninsula is characterized
by a Temperate Zone temperature regime (12-18 oc), the middle part of the
S.E. Ibarra-Obando et al.
21.2 Oceanography and Climate
The climate and oceanography of Alta and Baja California are largely controlled by the California Current ( CC) System, which represents the eastern
limb of the large-scale, anticyclonic North Pacific gyre, and has a pronounced influence on the structure and function of the coastal upwelling
and lagoonal ecosystems. The major alongshore currents of the CC System
are an offshore, southward flow (California Current) and a nearshore,
northward flow (California Countercurrent). The western boundary of the
CC lies about 850- 900 km off the coast. The California Current is a surface
current (0-300 m) with an average speed of typically <25 em s- 1 (peak velocity 50 em s- 1 ) which transports cool, low-salinity, oxygen- and nutrientrich, subarctic water towards the North Equatorial Current. The California
countercurrent is an important nearshore surface feature along the Baja
Californian coast throughout the year. During the summer, the Countercurrent is covered by southward flowing surface waters, owing to persistent
northwesterly winds, and remains as an undercurrent at depths of 200500 m. In fall and winter, the countercurrent is strong and reaches the surface inshore of the California coast (Davidson Current). The area influenced by the countercurrent may extend up to 500 km offshore at depths
below 200m. Owing to its broad seaward extent under the California Current, it has been described as the California Undercurrent domain (McLain
and Thomas 1983). The coastal ocean off Alta and Baja California is a classic wind-driven coastal upwelling system. The strong atmospheric pressure gradient between a thermal low-pressure cell over the heated land
mass and higher barometric pressure over the cooler ocean is largely responsible for creating vigorous alongshore winds that drive the coastal
upwelling system. During the warmer seasons, strong northerly and northwesterly winds induce offshore transport of surface waters. Upwelling of
cool, nutrient-enriched water from the depth balances the resulting loss of
surface water near the coast.
Cooling and stabilization of the onshore airflow by contact with upwelled waters leads to a cool summer climate at the adjacent coast. During
upwelling seasons, the coastal inland under direct influence of coastal stratus and fog is characterized by clear atmospheric conditions which lead to
strong daytime heating by short-wave solar radiation, particularly in interior valleys, and rapid nighttime, long-wave radiate cooling (Bakun
1990). As a whole, the Mediterranean-type climate of the region is hot and
dry with prevalence of desert conditions, though considerable local variations may occur. The northern portion of the peninsula is characterized
by a Temperate Zone temperature regime (12-18 oc), the middle part of the