Oxygen Depletion and Associated Benthic Mortalities 

 in New York Bight, 1976 



Chapter 3. Atmospheric Conditions and 



Comparison With Past Records 



Henrv F. Dia:' 



' National Climatic Center, Environmental Data and 

 Information Service, NOAA, Federal Building, Ashe- 

 ville, NC 28801 



INTRODUCTION 



During the first half of 1976, atmospheric conditions 

 along the Middle Atlantic coast departed substantially 

 from the climatological norm. Following a cold January 

 associated with a moderately amplified trough pattern in 

 the westerlies over eastern North America (Wagner 

 1976a), the mean circulation at 700 millibars (mb) over 

 the eastern United States reverted to a generally fast zonal 

 flow in February (Dickson 1976a). This pattern prevailed 

 through March (Taubensee 1976a). The pattern of 700- 

 mb heights provides a measure of the air circulation at 

 low levels. Negative height anomalies indicate relatively 

 cold conditions prevailing whereas positive departures 

 from the mean height indicate relatively warm conditions. 

 At 40° N latitude the height anomaly of the mean 700-mb 

 surface along the U.S. east coast changed from about 

 -20 m in January to around -1-45 m in February and 

 + 50 m in March. 



These departures in February and March were reflected 

 in anomalous pressure and circulation patterns (more typ- 

 ical of spring conditions) that limited the transport of cold 

 air from Canada to the United States. As a result, warm 

 maritime air masses predominated over most of the coun- 

 try, causing extreme warm conditions over the eastern 

 two-thirds of the United States during these months. 



The April circulation pattern was close to normal, al- 

 though mean temperatures in the eastern United States 

 remained 1° to 2° C above the climatological mean (Wag- 

 ner 1976b). The monthly mean pattern, however, masks 

 the very large change that occurred between the first and 

 second halves of the month. In the New England area 

 mean 700-mb heights increased by more than 100 m and 

 record cold weather during the first half of April was 

 replaced by record warm weather in the second half. 



51 



