AVERAGE MONTHLY PATTERNS OF SURFACE CURRENTS MEASURED IN THE SOUTHEASTERN MEDITERRANEAN OFF THE EGYPTIAN COAST

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1 77 AVERAGE MONTHLY PATTERNS OF SURFACE CURRENTS MEASURED N THE SOUTHEASTERN MEDTERRANEAN OFF THE EGYPTAN COAST Makram A. Gerges nstitute of Oceanography an Fisheries, Alexanria, Egypt. ABSTRACT The paper presents the monthly patterns of surface currents obtaine by averaging all current measurements carrie out in each one-egree square of the stuie area over a perio of about 50 years. The obtaine patterns inicate that the current spees are generally variable an fluctuate between 2 an 20 em/sec, but rarely reach values up to 35 em/sec. t was also shown that the surface currents in the southeastern Meiterranean are mostly eastwar an southeastwar, except in a few cases when the currents near the Egyptian coast are towars the West or South-West. Some important features of the current istribution an its seasonal variability are escribe in relation to the prevailing win conitions over the investigate area. NTRODUCTON To ate, our knowlege of the current istribution in the southeastern Meiterranean epens mainly on information obtaine through inirect methos an computations. n most of the previous investigations of this area, the general circulation characteristics have been escribe in terms of the hyrographic structure an water masses (e.g. Morcos an Moustaf~Hassan, 1976), or on the basis of ynamical computations (e.g. Sharaf El-Din an Karam, 1976). The recent approach of numerical moelling was also use to investigate the circulation in the eastern Meiterranean by Moskalenko (1974) an Gerges (1976). However, in all these stuies, ata of irect measurements of currents were generally neee to confirm or to correct the circulation patterns reveale from these speculations. Therefore, it is the concern of the present stuy to provie such neee information which coul she light on the actual surface circulation pattern in the investigate area. This coul also help in unerstaning the process of exchange of water between the coastal an off-shore regions in this part of the Meiterranean Sea, the importance of which is quite evient. MATERAL AND PROCEDURE The ata use in the present stuy was obtaine through the Oceanographic Worl Data Centres, which provie all available surface current measurements collecte throughout a perio of about 50 years, up to the early Seventies. The monthly averages were calculate by a special computer programme which provies the mean current velocity an irection in each 1-egree square of the area of our concern. The information obtaine through such proceure is consiere to be more representative of the actual current conitions than that base on a single reaing or short-term observations of currents. Rapp. Comm. int. Mer Meit., 27, 6 (1981).

2 78 RESULTS AND DSCUSSON The results obtaine are presente in Figure (1), which illustrates the avera~ conitions of the observe surface current fiel in the ifferent months: from Janua~ to June (Figure 1-a) an from July to December (Figure 1-b). Although these figures are rather self-explanatory, the following important features of the obtaine current patterns may be pointe out: 1) n the months of January an February, which are typical winter months, the surface currents are mainly irecte towars the SE with a clearly eastwar current existing very close to the coaat. During this time of the year the prevailing wins over the Egyptian coast are usually westerly in both th~ NW an SW irections, with almost equal frequencies. Hence the observe currents are mostly in the irection of the blowing win. Their velocities ranging between 3 an 20 ca/sec. 2) n the month of March, when the spring season practically starts an the NW component of the win prevails,the currents are still irecte towars the SE. The eastwar coastal currents also exist, but their velocities are ~nerally weaker (from 2 to 15 em/sec). 3) During the rest of the spring season, which lasts until M8lf, the currents continue to be southeastwar. However, in the month of April, the existence of an anticyclonic gyre to the south of Crete extening close to the Egyptian coast was clearly inicate. t is worthwhile mentioning here that this particular gyre was also obtaine from the numerical moel of circulation using the ensity fiel in the Eastern Meiterranean, referre to above (Gerges, 1976). 4) Throughout the summer months (June to August), southeastwar currents are still observe, apparently uner the action of the prevailing NW win:s. Only in a few cases, southwestwar currents were observe, especially along the western part of the Egyptian coast, where currents of greater velocities, up to 25 em/sec, coul be foun. 5) During the autumn months (September to November) the surface currents are irecte southeastwars from the off-shore regions to the coast with velocities reaching up to 25 em/sec. These off-shore currents are irecte more to the South, so that when reaching the coast they sometimes create southwestwar an sometimes northwestwar currents, as is observe, in particular, in the area of the Arab Gulf. 6) n the early winter month of December, the southeastwar currents become irecte more towars the East, an a ~neral eastwar current is observe everywhere along the coast, with velocities ranging from 3 to 20 em/sec. This is obviously ue to the fact that uring this month, ~nerally southwesterly wins prevail over the investigate area. This reflects the important role of win in riving the surface currents in this area.

3 79.) 36 j \ "' ' ' \ 34'... \.... / - - \. '... 2' \ -.:;/ Jm.JAHY APRn [ 2e' 30' 32' 34' 36 24' 2~ 28' 30' ". 31,.. "'... \ \ '... \ \ ~ \ \... \......_... \ '\. ~ 36' FEBRURY 1-'.t.Y : 't.' 26' 28' 30' 32' 34' 36' 24' 26' 28' 30' 32' 34' :15"' ~, ( \ '\ \. \ " \ '\. \ \ '... '\. i \ '\. 2..., )~- 0 :.:.- MAR01.ME J~ 24' 26' 28' 30' 32' 34' 30' 32' 34' ::s J p~ ' ;60 ::5 l:.l&' l!j.g.l: Monthly patterns of the observe surface currents off the Egyptian coast (a) -Average conitions for the months January - June

4 80 j ~~... \ '\ -- ' 34 \ \ \ \ \ n K~ JULY OCT09Ell! -') 30 24' 2~. 2S' 30' 32' 34' 36_' 24' 26' 30' 32' 34' 35'.. \. \ \ \. 32' \ '\ \ \,.. '\ \ 2' AUGUST 30 24' 26' 28' 30' 32' 34 3ri' 24' 2~ 2'1 30' 32' 34' 3ft,4... "-,. \ \ \ \ \. " " J \ \ '\. \. '-.. \ j. 3i ~~~ SEPTEMPER DECEMBER o' 2:.' 25' 28' 30' 32' 34' 36' 24' 26' 28' 30' 32' 34' 3&' 30 Fig. 2: Monthly patterns of the observe surface currents off the Egyptian coast (b) - Average conitions for the months July - December

5 81 BBLOGRAPHY GERGES, M.A. (1976) - Preliminary results of a numerical moel of circulation using the ensity fiel in the Eastern Meiterranean. Symp. on the Eastern Meiterranean, Malta, Acta Ariat. 18 (10) : MORCOS, s.a. an H. MOUSTAFA-HASSAN (1976) - The water masses an circulation in the Southern Levant basin. Symp. on the Eastern Meiterranean, Malta, Acta Ariat. 18 (12) : MOSKALENKD, L.V. (1974) - Steay-state win-riven currents in the Eastern half of the Meiterranean Sea. Okeanologiya, 14 (4) : (in Russian). SHARAF EL-DN, s.h. an A.M. KARAM (1976) - Geostrophic currents in the southeastern sector of the Meiterranean Sea. Symp. on the Eastern Meiterranean, Malta, Acta Ariat. 18 (13) :

DISTRIBUTION OF TOTAL AND DIFFUSE SOLAR RADIATION AT LAHORE, PAKISTAN

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