Effects of the autumn-winter meteorology upon the surface heat loss in the Northern Gulf of California



Coastal meteorological data of five autumn-winter periods (1982/83 to 1986/87), are used to describe the meteorology (and its variability) affecting the Northern Gulf of California, focusing on the strong wind events which have been proposed to cause most of the autumn-winter heat loss. The 1982/83 and 1986/87 autumn-winter periods were found to have anomalous relative humidity (an ENSO event was in progress in both periods): the first one had the highest (~63%) and the second the lowest (~43%) humidity. Also, the highest mean wind speeds were recorded in 1982/83. The differences between these two periods could be due to the pathway followed by the air masses: in 1982/83, the wind direction suggests a more oceanic influence from the Pacific than in 1986/87. The heat fluxes were calculated with a 30 m-deep well-mixed model representing the shallow region at the head of the gulf, where water-mass formation takes place in autumn-winter. The model is driven by the meteorological data and a lateral heat flux obtained by heat balance. Most of the net heat loss (67%) takes place during periods of strong winds (~7 ms-1, mostly NW) and low relative humidity (~56%), lasting from 1 to 15 days. Latent heat flux is the main surface heat loss, accounting for about 67% of the total. The two most important variables for the heat fluxes, wind speed and humidity, have a bimonthly variability, which in turn modulate the latent heat flux: wind speed has maxima in November and January, while humidity has maxima in December and February. In the average the highest net heat loss occurs in November, although the strongest heat-loss events occur in October and March. The interannual meteorological variability has a noticeable effect upon the heat flux: the lowest heat loss (-2 Wm-2) occurred in the autumn-winter of 1982/83, while the highest occurred in that of 1986/87 (-30 Wm-2).

Full Text: