FISHERY HILI.ETIN; VOL. 86. NO. 4 



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Figure 4.— Sea temperatures and wind off Mendocino during the 1981 upwelling season. Plotted sea tem.pefatures are estimated 

 daily means from record of continuously recording thermograph. Plotted wind velocities and directions are averages of 2-5 

 daily readings. Southerly values represent winds from south of east-west axis, northerly values represent winds from north 

 of this axis. The highly infrequent winds from due west or due east were entered as zero. In calculating values for days of 

 both northerlies and southerlies, the former were considered positive, the latter negative. The following accounts of events 

 identified in the figure cite wind velocities that exceed plotted values, which are averages. 



Event 1— Seven days of southerly winds, 19-25 March, with sea temperatures rising to 11.1°C, represented the last down- 

 welling episode of the 1980-81 downwelling season. 



Event 2— The 1981 upwelling season began on 26 March, as 2 weeks of strong northerlies (to 4 April) resulted in an abrupt 

 drop of more than 3°C in sea temperature. 



Event 3— Water temperatures fell to the lowest point of the year, 7.3°C, on 13 May following over 2 weeks of 10-30 K northerlies. 



Event 4— The first of a series of downwelling episodes during this upwelling season developed as 8-12 K southerlies on 17 

 and 18 May resulted in a sharp rise in sea temperature to 8.5°C. 



Event 5— Temperatures dipped when the wind shifted back to the north on 19 May. Over the next month variable northerlies 

 blew at less than 10 K, and although sea temperatures did not vary more than a few tenths of a degree, they were consistently 

 about 1°C warmer than before the 17-18 May downwelling episode. 



Event 6— On 28 June, the first of 6 consecutive days of 4-10 K southerlies, sea temperatures began a steep climb to above 

 10°C that marked the upwelling season's second major downwelling episode. 



Event 7— Northerlies returned on 3 July, and sea temperatures immediately dropped below 10°C again. Despite northerlies 

 of 5-7 K over the next 2 weeks, sea temperatures remained at about 9.5°C, again about 1 °C warmer than before the 28 June-2 

 July downwelling episode. 



Event 8— With southerlies of 5-10 K on 7 of the 9 days between 12 and 20 July, sea temperatures once again rose above 

 10°C to mark the season's third major downwelling episode. 



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