Variability of the Somali current system during the onset of the Southwest Monsoon, 1979
An array of six current-meter moorings and several coastal temperature recorders was deployed on the shelf and continental slope off northern Somalia from March to July 1979; a seventh mooring was placed near 2/sup 0/S. In addition, four deep-sea moorings were deployed for a period of one month in May--June farther offshore. Already during the late northeast monsoon in March the Somali Current north of 5/sup 0/N was flowing northeastward in the top 150 m. Underneath, in the depth range 150--400 m, a narrow southward undercurrent was observed from March to June. After the first onset of the southwest monsoon, which occurred around 5 May when winds shifted from easterly to southwesterly parallel to the coast, the near-surface temperatures on the shelf decreased immediately with no detectable phase difference between 6 and 10/sup 0/N, but no change was observed in the offshore circulation pattern. The final monsoon onset around 10 June was characterized by a drastic increase in wind speeds and the establishment of a strong anticyclonic wind-stress curl over the northern Somali Basin. The current measurements showed that within a few days after this onset the northern Somali gyre spun up over the deep sea and then propagated northwestward toward the coast with a speed of 12 cm s/sup -1/. These findings are in good agreement with results of satellite infrared imagery. The observed gyre kinematics can be explained by locally generated non-equatorial Rossby waves. When the onset reaches the coast the shallow coastal undercurrent is extinguished. Superimposed on the gyre-scale variability were fluctuations in the period ranges of weeks to months and of 3--5 days. There is evidence that the energies of the latter were related to the development of the Somali Current. Significant differences were found in a comparison of the 1979 current measurements south of the equator with observations obtained there during the monsoon onset of 1976.
- Research Organization:
- Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149
- OSTI ID:
- 5577939
- Journal Information:
- J. Phys. Oceanogr.; (United States), Vol. 12:12
- Country of Publication:
- United States
- Language:
- English
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