south again during February and March. The 

 position of the Low in April caused onshore 

 winds and resulted in a large number of iceberg 

 groundings along the Labrador Coast. During 

 May, the winds along 48 °N were from the south- 

 west causing a pool of icebergs to form above 

 48°X, impeding more southerly drift. Here un- 

 protected by the retreating sea ice and subjected 

 by warming spring temperatures, the iceberg 

 population began to thin rapidly. 



The Icelandic Low continued to move west- 

 ward and fragmented in June. Continued 

 southwesterly flow over the entire Newfoundland 

 and Labrador coastlines caused northerly and 

 easterly drifts for those few surviving icebergs. 

 These icebergs melted rapidly in the open water 

 and with warm air temperature prevailing as 

 summer approached. 



The 1977 surface pressure gradients are graph- 

 ically shown in Figure 20, with a comparison to 

 their 1946-1976 normals provided. Surface pres- 

 sure gradients are the differences in surface 

 pressures between two geographical points. The 

 steeper the gradient or the more rapid a change 

 in pressure, the higher the wind velocity will be; 

 the opposite is true for shallower gradients or 

 milder pressure changes. The Ice Patrol has 

 established six such gradients from the Davis 

 Strait off the Labrador and Newfoundland 

 coasts in an attempt to better understand the 

 wind magnitudes and primary wind directions 

 flowing along the main iceberg drift routes head- 

 ing toward the Grand Banks region. These 

 gradients are depicted in Figure 21 and 22. 



The most obvious and significant feature of the 

 gradients in Figure 21 is the low valley that oc- 

 curred in gradients 1, 2 and 3 during December 

 1976 and January 1977. These valleys indicate 



the strong northwesterly flow incurred by the 

 Icelandic Low moving toward Newfoundland 

 and explain the impeded southerly drift of the 

 early season icebergs. The large peak in Feb- 

 ruary and March shows the return of strong 

 southwesterly wind flow encouraging drift to the 

 south. Once again, flow is reversed in April and 

 continues for the remainder of the season as 

 shown by the shallow valleys. Hence the de- 

 creased influx of icebergs. The southerly winds 

 across gradient 3 during this period brought 

 warm air into the region accounting for the re- 

 treat of sea ice and melting of the trapped ice- 

 bergs above 48 °N. The very slight easterly 

 winds from late May through the end of the 

 season, as shown in gradient 4, did not encourage 

 much easterly iceberg drift and thus, most ice- 

 bergs remained close to shore. 



Air temperatures over Labrador and east 

 Newfoundland show various departures from 

 climatological averages throughout the ice season. 

 all stemming from the abnormal positioning of 

 the Icelandic Low. Generally, the winter tem- 

 peratures were at or slightly above normal in the 

 northerly regions, cooler than normal in the 

 south. For the spring and early summer months, 

 temperatures were generally cooler than average 

 to the north, and near normal in the south. The 

 graphs in Figures 23 and 24 represent the 

 cumulative frost-degree-days and melting-degree- 

 days, respectively. Locations of the seven pre- 

 selected shore stations are shown in Figure 20. 

 A frost-degree-day is defined as one day mean of 

 one degree Fahrenheit below 32 °F, and a melting- 

 degree-day is defined as one day mean of one 

 degree Fahrenheit above 32 °F. That is, a daily 

 averaged temperature of 12°F equals twenty 

 frost-degree-days, and a daily averaged tempera- 

 ture of 42°F equals ten melting-degree-days. 



29 



