46, 2558 (1988). In order to understand that we have carried out a mixed layer heat budget of the model solution for the alongshore section off the Somali coast. Note, however, that intensity of upwelling in the northern part of the section is weaker in the observations compared to the model simulation possibly due to the lack of enough observed profiles in the gridded observation data in this region and rigid smoothing that are imposed while gridding these datasets. volume9, Articlenumber:7598 (2019) The Somali Current (SC)/Undercurrent (SUC) is the western boundary current (WBC) system of the Arabian Sea. Seasonal Cycle and Annual Reversal of the Somali Current in an Eddy Sorbonne Universit Abstract Surface currents and some surface temperatures in the Somali Basin have been plotted for May and June of each year from 1900 to 1973 when any data were available. S2). Further, in addition to the coastal upwelling, thermocline also shoals offshore at ~57E for 8N and 10N section owing to the return flow of GW. A large part of the Somali peninsula is a tableland. By submitting a comment you agree to abide by our Terms and Community Guidelines. Bakun, A. PDF A steady state model of the Somali current - Springer During the colder months, December to February, visibility at higher elevations is often restricted by fog. It is now well known that Somali coast experiences a low level southwesterly surface jet during summer, called as Findlater Jet13, that drives the surface currents northward1,2,14,15. Model is forced by surface fluxes obtained from various sources. J. Geophys. Hovmoller diagram of sea level anomaly from altimeter (left) and model (right) along 7N exhibits westward phase propagation of downwelling Rossby waves. Varela, R., lvarez, I., Santos, F., deCastro, M. & Gmez-Gesteira, M. Has upwelling strengthened along worldwide coasts over 19822010? 10,320km2 (3,980sqmi), Area - comparative: It is called Guban. Nevertheless, influence of nonlinear eddy driven divergence for the generation of GW and its associated upwelling can not be neglected. Article On the other hand, downwelling signals forced by the interior negative windstress curl ultimately deepen the thermocline along the Somali coast and therefore, impact the upwelling along the Somali coast to negatively feedback to the land-sea thermal gradient over this region. Tech. Further, we show that the surface cooling of coastal waters are dominantly driven by subsurface entrainment and surface heat fluxes. Also, as the negative windstress curl strengthens during June-August, the thermocline along CSEC deepens to more than 100m. Note, however, that Rossby waves generated at the interior ocean takes about 12 months to reach the coast and thereby, deepening of the thermocline is seen only by late July or early August i.e. Here we present results from observations and ocean model to show that the upwelling along the Somali coast is limited to the early phase of the summer monsoon and later primarily limited to the eddy dominated flows in the northern and some extent in the southern part of the coast. Somalia Maps & Facts - World Atlas Notably, the results presented here are robust and independent of the section chosen along a slightly different isobath. 8 (1979): 28. Seasonal Cycle and Annual Reversal of the Somali Current in an - Energy The Solmali Current as we found it appears to be of theoretical interest because, although like the Gulf Stream and Kuroshio it flows toward the north as an intense boundary current along the western coast of a great ocean basin, it differs fron them in fundamental ways: (1) it is present during only part of the year, since the driving In the absence of direct observations, numerical modelling is the only possible approach in this scenario. 209, 588590 (1980). Regions of sustained upwelling exist on both eastern- and western-ocean boundaries. The Somali Current is a warm ocean boundary current that runs along the coast of Somalia and Oman in the Western Indian Ocean and is analogous to the Gulf Stream in the Atlantic Ocean. Certain higher areas in the north, however, record more than 500 millimeters (19.7in) a year, as do some coastal sites. 0000005223 00000 n There are four main seasons around which pastoral and agricultural life revolve, and these are dictated by shifts in the wind patterns. Prakash, S. & Ramesh, R. Is the Arabian Sea getting more productive? The vertical mixing is based on K-profile parametrization scheme (KPP45) and for the horizontal mixing a Smagorinsky type combination of bihermonic and Laplacaian mixing is used. 8 (1979): 28. Annihilation of the Somali upwelling system during summer monsoon. Since the fetch of the negative windstress curl is about the width of the Arabian Sea (i.e. In a recent study based on satellite derived SST Kankan et al.40 showed that Somali coast exhibits one of weakest SST front among the other persistent frontal systems of the north Indian Ocean. The Haud south of Hargeysa is covered mostly by a semiarid woodland of scattered trees, mainly acacias, underlain by grasses that include species especially favored by livestock as forage. Moreover, the strong positive net surface flux over the cold wedge of the GW (Figs10 and S6) is found to be determined by the positive sensible heat flux (more than 100 W/m2) into the ocean (Fig. Ocean. The southwest receives 330 to 500 millimeters (13.0 to 19.7in). Arabian Sea | Indian Ocean, Climate & Marine Life | Britannica @Cb zV$KTWbkrq] 52, 63120 (2002). \({r}_{\circ }^{2}={c}_{n}^{2}/{f}^{2}\) represents the local Rossby radius of deformation and f represents the Coriolis parameter. Clim. Curr. As a first approximation, the barotropic response to the wind stress curl was computed . ASCLME 2012. Abstract. The Somali Current continues to flow northward during October, but near-surface velocities and EKE levels are lower compared to September; note that there is an early manifestation of a cyclonic eddy located around 3N, 53E. The SC/SUC is characterized by narrow, fast jets that exhibit considerable variability in intensity, vertical profile and width on many time scales (see Schott and McCreary, 2001, and references therein). Coastal readings are usually five to ten degrees cooler than those inland. Sci. 0| =JpEB#!4YjC2Q*+j*\kuu]qQWv7AmjZZ(=Ne*rSvVtpy:((,n_kU],;VjfT Herbert L. Bodman, Nayereh Esfahlani Tohidi (1998), Suzanne G. Frayser, Thomas J. Whitby (1995). northern flanks of SG and GW, water upwells and along CSEC, where the surface currents are weaker, downwelling signal dominates. J. Ras Caseyr (Cape Guardafui) is the easternmost point of Somalia; this point joins the Guardafui Channel to the Gulf of Aden. . 0000003792 00000 n Prog. Interestingly, in the CSEC, especially towards the northern part of it, subsurface processes shows a significant cooling despite the fact that thermocline of the CSEC deepens over the course of summer monsoon. Its continental shelf is spread over 32500 km2. The model spans over 30120E and 30S30N with uniform 0.25 horizontal resolution and 40 vertical levels with 5m resolution in top 60m42. The country has second-longest coastline in all of Africa, behind the island nation of Madagascar (4828 km). Development of the flow field during the onset of the Somali . Beyond this plain is the maritime mountain range of the Karkaar Mountains (marked on the map) hosting the highest point in the country, the 2,460 m tall Mount Shimbiris. Finally, as the summer monsoon winds start to withdraw from the north Indian Ocean during September, strength of the Somali current weakens considerably. This deepens the mixed layer and mixes the warm surface water with cold thermocline waters, resulting in the net cooling of the mixed layer. Note here that sea level anomaly from altimeter is calculated based on fixed datum, whereas model calculates sea surface height as the deviation from z=0 level. Climatological data (Figs2 and S1) indicate that east African currents, likely forced by the easterly winds in the southern hemisphere16, cross the equator in early May and flow northward along the Somali coast. 419 0 obj << /Linearized 1 /O 422 /H [ 1140 450 ] /L 539868 /E 49398 /N 12 /T 531369 >> endobj xref 419 30 0000000016 00000 n %PDF-1.3 % This contradicts the existing perception about the Somali upwelling system built over the last five decades. Alluvial plains are located further south and separated from the southern coast by a massive belt of ancient sand dunes that extend from Kismaayoto to Hobyo. How will Somali coastal upwelling evolve under future warming scenarios There are a number of islands near the coastal areas. A Numerical Investigation of the Somali Current During the Southwest Ocean. Instantaneous wind stirring, scaled as the friction velocity, causes vertical entrainment mixing through vertical shear instability of wind driven horizontal currents and surface buoyancy. 0000005996 00000 n Southward the mountains descend, often in scarped ledges, to an elevated plateau devoid of perennial rivers. 47, 10491072 (2016). Thus, the nature of subsurface processes that drive the observed cold surface temperature in the CSEC are not yet clear and therefore, will be revisited again in the next section. permanent crops: 0.04% This is INCOIS contribution number 338. As stated above, Ekman mass transport is positive and transporting water offshore with an average rate of 104kg m1s1 with maximum in the south and decreases almost linearly in the north in accordance with the strength of the alongshore wind components. Deep. CAS The radiation (shortwave and longwave), momentum (windstres) fluxes and 2m specific humidity and air temperature are obtained from TropFlux data47,48. The adjacent coastal zone, which includes the lower reaches of the rivers and extends from the Mudug Plain to the Kenyan border, averages 180 meters above sea level. Indian Ocean 0m (0ft) However, we show a very complex thermocline structure along the coast of Somali as the upwelling is limited to the northern part and in some extent in the southern part of the Somali coast and the large middle part exhibits entrainment driven by downwelling. The lowland between the rivers supports rich pasturage. Further study on this is needed to understand its dynamics and implication to the regional climate. In Mogadishu, for instance, average afternoon highs range from 28 to 32C (82 to 90F) in April. The Indian Monsoon Current refers to the seasonally varying ocean current regime found in the tropical regions of the northern Indian Ocean. 0000004430 00000 n Am. This indicates that the cooling observed in the SSEC, as shown in the previous section, is dominated by wind driven upwelling, which acts as a combination of strong offshore Ekman transport and upwelling favorable Ekman suction. Vertical sections of temperature along 4N, 6N, 8N and 10N off the Somalia coast during MaySeptember. Whereas, the surface air pressure and rainfall is prescribed from NCEP49. McCreary, J. P., Kohler, K. E., Hood, R. R. & Olson, D. B. The western plateau slopes gently southward and merges imperceptibly into an area known as the Haud, a broad, undulating terrain that constitutes some of the best grazing lands for Somali nomads, despite the lack of appreciable rainfall more than half the year. Leetmaa, A., D. R. Quadfasel and D. Wilson. 2, 587595 (2012). This period is characterized by the southwest monsoons, which rejuvenate the pasture land, especially the central plateau, and briefly transform the desert into lush vegetation. Praveen, V., Ajayamohan, R. S., Valsala, V. & Sandeep, S. Intensification of upwelling along Oman coast in a warming scenario. J. Clim. Sci. 1999, PAGE 219, Zarins, Juris (1990), "Early Pastoral Nomadism and the Settlement of Lower Mesopotamia", (Bulletin of the American Schools of Oriental Research), NEW ISSUES IN REFUGEE RESEARCH Working Paper No. Generally, rainfall takes the form of showers or localized torrential rains and is extremely variable. 0000003089 00000 n We acknowledge the financial support proved by the ESSO-Indian National Centre for Ocean Information Services, Government of India to conduct this research. The coastal zone's relative humidity usually remains about 70 percent even during the dry seasons. No restoration is applied anywhere else in the model domain. In the far north, the rugged eastwest ranges of the Ogo Mountains lie at varying distances from the Gulf of Aden coast. TropFlux Surface wind stress over the tropical oceans: Comparisons and evaluations. Cite this article, An Author Correction to this article was published on 06 December 2019. The four eastern boundary upwelling systems in the Pacific and Atlantic are well marked by the cold surface temperature. While in the upwelling regions SST is primarily determined by the cold, upwelled subsurface water; in the downwelling region, it is entrainment aided by net negative buoyancy flux and strong wind energy input that contribute to lower SST. Princeton University Press, Princeton. 0000001076 00000 n Improved bathymetric datasets for the shallow water regions in the Indian Ocean. The Haud zone continues for more than sixty kilometers into Ethiopia, and the vast Somali Plateau, which lies between the northern Somali mountains and the highlands of southeast Ethiopia, extends south and eastward through Ethiopia into central and southwest Somalia. In the more arid highlands of the northeast, Boswellia and Commiphora trees are sources, respectively, of the frankincense and myrrh for which Somalia has been known since ancient times. The frictional velocity is defined as u*=(/o)(1/2), where is surface wind magnitude and is the density of the mixed layer. The Somali Current weakens and reverses direction during the northeast (winter) monsoon. Evolution of thermocline off Somalia coast during summer from ECCO2, ORAS4 and SODA. The hottest months are February through April. Res. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Article Technical documents in hydrology series (1996). The surface buoyancy flux (B) is defined as a sum of the flux associated with the surface heat and fresh water flux and is given by B=(/Cp)Fnet+S(EP). ", "Klimatafel von Mogadischu (Mogadiscio) / Somalia", "Long term mean monthly sunshine fraction in Somalia", "Klimatafel von Chisimaio (Kismayu) / Somalia", https://www.oneearth.org/ecoregions/hobyo-grasslands-and-shrublands/, https://en.wikipedia.org/w/index.php?title=Geography_of_Somalia&oldid=1146099772, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 4.0, Source 2: Food and Agriculture Organization: Somalia Water and Land Management (percent sunshine), Westernmost point the western section of the border with Kenya**, This page was last edited on 22 March 2023, at 19:42. A.C. designed the study, model experiments and made the plots. Somali Current - Wikipedia Climatological model simulated SST (left) and model derived net surface fluxe along the alongshore section. Lett. While the alongshore winds are strongly upwelling favorable all along the coast, the remotely generated downwelling Rossby waves forced by the offshore negative windstress curl try to deepen the thermocline in the central region of the Somali coast. In the meantime, to ensure continued support, we are displaying the site without styles Comparative oceanographic eddy variability during climate change in the The Provisional Administrative Line forms the de facto southern border between Somalia and Ethiopia. 637,657km2 (246,201sqmi) Equations (11) and (12) form a coupled system of two equations. We find that the upwelling is confined only to early phase of the summer monsoon and later within the small pockets of northern flanks of the two gyres, SG and GW.