The Loop Current I Mesoscale Eddies 

 October 1979 



The CZCS pigment image on 3 October (68-2) shows a portion of the 

 Loop Current between two cloud banks in the eastern gulf, with total 

 pigment concentrations in the Loop Current of less than 0.06 mg m -'. The 

 circulation patterns in the western gulf are characterized by the presence of 

 mesoscale eddies (68-1, Inset A). The belt of relatively clear water in this 

 region seems to be the boundary of a cyclonic eddy which was also 

 observed during the cruise of the R/ V Cit(?(80G-1 ) in April 1980 (Brooks 

 and Eble, 1982). An enlarged view of this area (69-1) shows more distinctly 

 the relatively higher pigmented (chlorophyll) water mass occupying the 

 central area of the cyclonic eddy which is caused by the convergence of the 

 surface waters in the eddy. In the western Gulf of Mexico (68-2) the width 

 of the coastal front, judging from the high pigment concentrations, is 

 narrower than that found off the Yucatan Penmsula. A major 

 contribution to the mcrease m predicted pigment off the Yucatan 

 Peninsula is caused by suspended sediment and not phytoplankton. 



In the Caribbean Sea. some interesting circulation patterns are observed 

 just south of the western tip of Cuba (68-2; and 68-1. Inset B). In the 

 enlarged viewof this area (69-2) a cyclonic eddy is observed between the tip 

 of Cuba and Islas de Pinos. This eddy is formed by a countercurrent along 

 the northern coast of Cuba. Such a countercurrent is not often observed, 

 but was inferred from the geostrophic current pattern (Ichiye el al., 1973). 

 This countercurrent entrains coastal waters southward and forms a 40-km 

 eddy. Associated with this eddy are turbulent structures which are also 

 observed south of the eddv. 



68-1. Locator Map for 68-2. 69-1. and 69-2. 



The CZCS pigment image on 8 October (70-2) in the northern Gulf of 

 Mexico shows the northward intrusion of the Loop Current to within 

 approximately 60 km of the Mississippi Delta (70-1). The intrusion of 

 clear water extends westward to about 92° W (71-1) and represents the 

 farthest westward penetration of the Loop Current recorded in the 

 literature. There is a narrowing of the Loop Current around 85° W which 

 suggests that an eddy could be spinning off at some future time. Leipper 

 (1970) and Whitaker (1971) found that the maximum intrusion of the 

 Loop Current occurred in October, whereas Robinson (1973) and Maul 

 (1977) observed this maximum several months earlier. These results 

 emphasize the temporal and spatial variabilities of the Loop Current. 



As the Loop Current passes south of the Mississippi Delta, it entrains 

 coastal waters some 100- 150 km out into the Gulf of Mexico. The western 

 edge of the Loop Current generates a cyclonic eddy of coastal waters and 

 entrains this water some 50 km southward. 



In the western gulf, coastal waters with high pigment concentrations are 

 transported offshore just east of Brownsville, Texas. This entrainment is 

 caused by two eddies: a northern cyclonic eddy located around 27° N, 

 94° W. and a southern anticyclonic eddy located at 26° N, 94° W. Brooks 

 and Legeckis (1982) observed the same features in 1980 using satellite- 

 derived surface temperatures. 



Around 26° N, 92° W there is entrainment of coastal waters into the gulf 

 (70-1. stippled area). This transport was observed by El-Sayed and Trees 

 (1980). with total pigment concentrations around 0.39 mg m'. which 

 agrees well with that predicted from the CZCS images. 



ORBIT 04751 03OCT79 173017 TO 173217 GMT GAIN 1-4=1 THRESHOLD OFF TILT ANGLE 16.0 



GRID CENTER DATA: 1T311T GMT 22-+1N 088.79H SUN EL 63 AZ 173 ROLL 0-1 PITCH -0.1 YAW 0-2 



99U - 1 + a?n 



PIGMEfJT in MILLIGPAMb METEPo.i 



.19 -27 .39 -S 



ALGORITHMS; 02 01 01 00 00 03 02 00 00 00 



970 SCAN LINES PROCESSED SCAN LINES MISSING 



.B3 1.28 2-11 3.46 5.69 9.35 11.98 25.25 



CIP VER CRT NO DPS VER SPEC- # FRAME # 



V810306 ZE51901- V820821 F732040 ZG051902 



68-2. Nimbus-7. Orbit 4761. 3 October 1979. CZCS Pigment Image. 



68 



I 



