Seasonal Development of Coastal Upwelling 

 March- July 1979 



The seasonal development of coastal upwelling is clearly indicated by 

 the following sequence of images, which show chlorophyll pigment levels 

 derived from CZCS data. Along the Pacific Coast of Baja California, on 

 17 March (14-1). onlv modest development is observed, compared with 

 subsequent images 15-1 and 15-2. one and two months later, respectively. 

 Also observed is the persistent cyclonic rotation just off Punta Eugenia 

 which is well-known from numerous hydrographic surveys. Cyclonic 

 eddies tend to spin-up there, eventually detaching and drifting westward at 

 a rate of about 4 to 5 km day"'. The isolated patch of high pigment about 

 300 km west of Punta Eugenia (15-2). may be the indication of an eddy 

 apparently having been spun-up along the coast two months earlier. Also 

 in the image several other southwestward-directed Jets of high pigment 

 water (light tones) are observed which exhibit cyclonic turning. Such jets 

 and eddies are a recurring phenomenon all along the west coast during the 

 upwelling period. They tend to appear in the same locations, in association 

 with configurations of the coastline, offshore bathymetry, and wind which 

 combine to favor intense upwelling. 



Proceeding north to southern California, a comparison of images 16-1, 

 16-2, and 17-1 shows the steady development of upwelling (light tones, 

 high pigment levels) between early April and July of 1979. Note that by 

 July ( 17-1 ). Point Conception has become a center for strong persistent 

 upwelling. Even more dramatic is the shift from winter to summer 

 conditions along northern California (18-1 and 18-2). The CZCS image 

 for July ( 18-2) shows the development of offshore jets, and a cyclonic eddy 

 is observed between Cape Mendocino and Point Arena. Such eddies occur 

 regularly at this location during the summer, from where they translate 

 southward at a rate of 5 to 10 km day'. 



Further north along the Oregon. Washington, and Vancouver Island 

 coastlines (19-1 and 19-2). similar upwelling development is observed 

 between March and July 1979. Of interest in the March image ( 19-1 ) is the 

 small amount of upwelling-induced. high-pigment water close to the coast, 

 probably induced quite temporarily by north or northeasterly winds which 

 created the cloud-free conditions to permit a view of the surface. The 

 upwelled water acts as a tracer, allowing visualization of the northward 

 current along the coastal region. This northward tlow. known as the 

 Davidson Current, appears at the surface only during winter, but is 

 actually present at greater depths throughout the year. 



ORBIT 01998 17MART9 191235 TO 191405 GMT GAIN i-+=: THRESHOLD OFF TILT ANGLE 10 -0 

 GRID CENTER DATA: 191320 GMT 27.25N 115.3TW SUN EL 61 AZ 161 ROLL -0-1 PITCH -0-0 YAH 0-3 



.19 .;T .39 -ST 



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



T2T SCAN LINE? PROCESSED SCAN LINES MISSING 



l.;8 :-U Z.V> 5-69 9-35 U-98 25.25 32 .0 



CIP VER CRT NO DPS VER SPEC # FRAME # 

 V ZE224T91 V820401 FT32C'40 ZG224791 



14-1. Nimbus-7. Orbit 1998. 17 March 1979. CZCS Pigment Image. 



14 



