surface (0.5-1. Om) temperature 

 The match is remarkably good in 

 the western portion of the study 

 area, but diminishes somewhat 

 toward the east as the time 

 separation between the imagery 

 and hydrography approaches 4 to 

 5 days. Some of the mismatch is 

 due to the coarse hydrographic 

 grid, but most is due to the fact 

 that the fronts were moving over 

 the period of the hydrographic 

 survey. A comparison of the 12°C 

 surface temperature and the 2 

 May SLAR imagery (Figure C-lOb) 

 shows an excellent match in the 

 eastern part of the study area. 

 The easternnx)st hydrographic 

 survey line was completed on 3 

 May. 



47 W 



Figure C-8 Infrared image from the Advanced Very High Resolution 

 Radiometer aboard NOAA 9 on 17 May. 



The water-mass characteristics 

 across the SLAR-detected front 

 are best illustrated by Figure C-1 1 , 

 a temperature and salinity profile 

 along section AC shown in Figure 

 C-IOa. It shows two sharp 

 thermal fronts that coincide with 

 those shown on the 26 April SLAR 

 imagery. In the north, a surface 

 temperature difference of 1 1°C 

 exists between hydrographic 

 stations on either side of the front, 

 while in the south (C), the differ- 

 ence was 8°C. Between the two 

 fronts is water of NAC origin. The 

 isotherms dome sharply down- 

 ward, with the 8°C isotherm 

 reaching 320db. In the northern 

 portion of the section (along AB) 

 cold, low salinity water indicates 

 the presence of Labrador Current 

 water flowing eastward immedi- 

 ately to the north of the northern 

 front. In this transect the core of 



the cold water was at 50 dbar, with 

 a minimum temperature of -0.9°C; 

 at this depth the salinity was 33.1 

 ppt. The cold-water core was 

 seen at all 10 of the north-south 

 sections of the first-phase hydrog- 

 raphy. Typically, the lowest 

 temperatures were found at 40m 

 to 50m. 



Figure C-1 2 shows the horizontal 

 distribution of temperature at 58m, 

 in which the 0°C contour is used 

 to define the location of the core of 

 the Labrador Current water. The 

 58m depth is chosen because it is 

 the depth of the drogue center of 

 the drifting buoys. Also plotted is 

 the trajectory of a drifting buoy (ID 

 4542) deployed from an aircraft in 

 Flemish Pass on 19 April. It 

 arrived in the study area on 25 

 April, the day before the first SLAR 

 survey and the beginning of the 

 first hydrographic survey. The 



buoy track follows the 0°C contour 

 remarkably well, recognizing that 

 over the six-day period the front 

 changed shape somewhat. The 

 average buoy speed from A to B 

 was 67 cm/s. Referring back to 

 Figure C-1 1 , the buoy passed 

 almost exactly through station 20 

 and, with the center of the drogue 

 at 58m, it was moving with the 0°C 

 water. When the buoy reached its 

 easternmost extent, it made a 

 sharp cyclonic bend (radius = 

 20km) and then moved northwest- 

 ward and eventually northward at 

 about 50 cm/s before it was 

 recovered on 3 May. 



The easternmost hydrographic 

 transect (line CD on Figure C-1 2) 

 shows a water-property distribu- 

 tion (Figure C-1 3) that is consis- 

 tent with the cyclonic bend in the 

 trajectory of buoy 4542. Sub-zero 

 water was found at both stations 



62 



