48
R. I. CURRIE, A. E. FISHER and P. M. HARGREAVES:
the coast, and on its northern boundary there is a rapid seaward extension of the area
of cool water at the surface (Fig. 10) as it follows the eastward sweep of the current.
Along the coast, the cool water extended northwards beyond Ras Hafun but in
about 11
0
N appears to come up against a tongue of warmer water pressing southwards
along the coast from Cape Guardafui and originating from the Gulf of Aden. At some
distance from the coast, however, the cool water achieved a greater northward extension,
and temperatures below 17 0 C were found at least 100 Ian farther north in 52 0 E longitude. The eastward margin was again bounded by warm water reaching more than 25 0 C.
The pattern of distribution of the cold surface water is thus seen to form a belt
paralleling the northward boundary of the Somali Current and developing, at its northward extremity, into a cyclonic eddy with the warmer water penetrating southward from
Fig. 11. A comparison of the areas in which the mean sea surface temperature for August was below
20 0 C, berween the mean for the years 1905 -1963, and 1964. (From G. P. BRITION, unpublished)
the Gulf of Aden. The direct current measurements described by SWALLOW and BRUCE
substantiate this pattern.
It is interesting to compare the extent of the cold surface water observed in 1964
with the mean distribution shown by surface temperature records over the years
1905 -1963 (Fig. 11, BRI1TON, unpublished). This shows that 1964 appears to have
been a rather exceptional year in which the cold waters was considerably more extensive
than is usual. This may account for the extent of the fish mortality recorded by FOXTON
(1965) during "Discovery" survey.
SWALLOW and BRUCE have described direct current measurements made on these
surveys, but there is considerable difficulty in deriving any reliable estimate of the input
of cold water into the upwelling area. They do, however, make an estimate of vertical
velocity based on the upward displacement of the 20 0 C isotherm, in the Somali Current
and this amounts to 7X 10- 3 em sec-l.
R. I. CURRIE, A. E. FISHER and P. M. HARGREAVES:
the coast, and on its northern boundary there is a rapid seaward extension of the area
of cool water at the surface (Fig. 10) as it follows the eastward sweep of the current.
Along the coast, the cool water extended northwards beyond Ras Hafun but in
about 11
0
N appears to come up against a tongue of warmer water pressing southwards
along the coast from Cape Guardafui and originating from the Gulf of Aden. At some
distance from the coast, however, the cool water achieved a greater northward extension,
and temperatures below 17 0 C were found at least 100 Ian farther north in 52 0 E longitude. The eastward margin was again bounded by warm water reaching more than 25 0 C.
The pattern of distribution of the cold surface water is thus seen to form a belt
paralleling the northward boundary of the Somali Current and developing, at its northward extremity, into a cyclonic eddy with the warmer water penetrating southward from
Fig. 11. A comparison of the areas in which the mean sea surface temperature for August was below
20 0 C, berween the mean for the years 1905 -1963, and 1964. (From G. P. BRITION, unpublished)
the Gulf of Aden. The direct current measurements described by SWALLOW and BRUCE
substantiate this pattern.
It is interesting to compare the extent of the cold surface water observed in 1964
with the mean distribution shown by surface temperature records over the years
1905 -1963 (Fig. 11, BRI1TON, unpublished). This shows that 1964 appears to have
been a rather exceptional year in which the cold waters was considerably more extensive
than is usual. This may account for the extent of the fish mortality recorded by FOXTON
(1965) during "Discovery" survey.
SWALLOW and BRUCE have described direct current measurements made on these
surveys, but there is considerable difficulty in deriving any reliable estimate of the input
of cold water into the upwelling area. They do, however, make an estimate of vertical
velocity based on the upward displacement of the 20 0 C isotherm, in the Somali Current
and this amounts to 7X 10- 3 em sec-l.