agulhas current cold

But approaching South Africa you have to go through it: the challenge is therefore to arrive at a time when the ‘normal’ north-easterly winds are blowing with the current, and avoid a front – which is easier said than done. The majority of yachts therefore leave Reunion Island for South Africa in November. Schouten, Because it is fed from lower latitudes, the Agulhas Current is warm, ranging in temperature from 57 to 79 °F (14 to 26 °C) at the surface. Bryden, H.L., L.M. heat and freshwater fluxes. Roberts, 1988: These two currents create not only two radically different marine environments but also shape the terrestrial ecosystems and the human settlements along the South African coast. What is the jet stream? The Currents Benguela current: a cold, slow-moving current that moves northward up South Africa’s west coast. It is a surface-water current that flows off the east coast of southern Africa between latitudes 25° S and 40° S in a south-westerly direction. However, any physical definition of a meeting point or dividing line between two oceans ignores the … Boebel, O., T. Rossby, J Lutjeharms, W. Zenk, and C. Barron, 2003: southeast Atlantic Ocean: A case study. Role of the Agulhas Current in Indian Ocean circulation and associated On occasion, perhaps one or more times a year (but none during some years), the Agulhas Current moves far offshore (of the order of 150-300 km from shore), forming a large meander. Journal of Geophysical Research, 104, C3, 5151-5176. The current follows the continental shelf from Maputo to the tip of the Agulhas Bank (250 km south of Cape Agulhas). Agulhas cyclones. It flows down the east coast of Africa from 27°S to 40°S (Gordon, 1985). Journal of Geophysical Research, 99, 14053-14070. The temperature of the water in February is from 27°C in the north to 20°C in the south, and in August, from 22°C in the north to 16°C in the south. Like the Gulf Stream in the North Atlantic the Agulhas Current is a western boundary current, but being in the southern hemisphere it brings warm water south. Journal of Geophysical Research, 105, 6425-6436. J. Geophys. The Agulhas current has a volume flow rate of between 70Sv to 85Sv and has a peak speed of about 2m/s in the region off East London. Deep-Sea Research Part I, 43, 2, 213-238. C. Schmid and W. Zenk, 1998: Ruijter, P.J. van Ballegooyen, 1988: Deep-Sea Research II, 50, 13-34. A hydrographic section across the subtropical South Indian Ocean. van Leeuween, P.T. Geophysical Research Letters, 25, 23, 4361-4364. Ocean currents around South Africa (from (1)). Gordon, A.L., 1985: Natal pulses and the formation of Agulhas Rings. Warren, 1993: Res., 105, 6425-6436. Simionato, W.P. Rae, S. Garzoli, J. Lutjeharms, P. Richardson, T. Rossby, Geophysical Research Letters , 29, 140.1-140.3. Here the momentum of the current overcomes the vorticity balance holding the current to the topography and the current leaves the shelf. The Agulhas Current is formed by the confluence of the warm Mozambique and East Madagascar Currents , which meet south-west of … Lutjeharms, 2000: There’s then the dilemma in what to do if a cold front is on its way. The average temperature is lower in southern sections near Antarctica. Seasonal variations in the region of the Agulhas Retroflection: Stramma, L. and J.R.E. Beal, 2001: *Agulhas current* Part of the large-scale circulation of the southern Indian Ocean [1]. the Southeast Atlantic Ocean: a case study. The Agulhas Current runs close to the shore along the continental shelf and can build up to speeds of 5 knots. Flow velocity varies seasonally between 0.2 and 0.6 m/s. Toole, J.M. However, trying to cross the stream is a whole lot harder and could mean breakages and damage. Studies with Geosat and FRAM. These large solitary meander events do not have a discernible seasonal cycle but display considerable interannual variability (Krug & Tournadre, 2012). and B.A. I usually use the RTOFS model as it is readily available through saildocs. Duncan, 2003: EOS, 79, 1, 1, 7-8. As you head south-west into more turbulent weather you will be planning your arrival in South Africa, and the areas of typically worst weather, on a long-range forecast. The flow field of the subtropical gyre in the South Indian Ocean into The jet stream is a ‘river’ of strong wind high in the atmosphere which is…, There are a number of yacht races around the world in which strategic decisions on whether to go into or…. Just as UK sailors would never dream of going through the Portland Race in a storm, so you also need to avoid the Agulhas Current in wind over current situations that can produce boat-breaking waves of freak proportions. The first array ran from 2010 to 2013 (the Agulhas Current Time-series) Experiment). Observations are sparse so sailors have to rely on model predictions and, although South Africa produces an analysis chart for the area, there are no forecast ones. There are few yacht-friendly ports in Madagascar and Foreign Office travel advice does not make comfortable reading, so most yachts make the passage in one hop. The current reaches its maximum transport near the Agulhas Bank where it ranges between 95-136 Sv. With options restricted to pressing on into a wind against current situation, heaving-to, or finding a safe port to the north it was a hard choice for the skipper. and the Agulhas Undercurrent. Fortunately the yacht arrived safely, but only a couple of hours ahead of gale force south-westerlies, which were predicted to reach 50 knots later in the day. Schlax, 1998: Evidence exists of entrainment of shelf water by the Agulhas Current, sometimes causing predominantly southwestward flows in the deeper reaches of Algoa Bay. This river of warm water meets the cold conditions of the Southern Ocean and adds energy to developing storms. The flow of the Agulhas Current is directed by the topography. The later you leave the passage to South Africa, the less active these fronts should be, but the higher the risk of tropical cyclones. They manifest as large offshore meanders of the Agulhas Current, with an associated cyclonic circulation and cold water core inshore of the meander. When global climate began to warm at the end of cold periods, the Agulhas Current initially became stronger and then abruptly weakened to assume a strength similar to that of today. The Agulhas Current also plays a critical role in global ocean circulation which is why it’s considered important for climatic conditions across the world. Examples of this phasing in the Agulhas Current, among others, are seen at 87–84 kyr, and at 63–59 kyr, where the temperature, ALF and salinity build-up in the Agulhas Current parallels the cold stadial conditions in the north (Fig. Lutjeharms, M.W. Lutjeharms, 1994: Van Ballegooyen, R.C., M.L Grundlingh and J.R.E. At approximatly 38° S lat. The source water at its northern end is derived from Mozambique channel eddies (de Ruijter et al., 2002) and the East Madagascar Deep-Sea Research Part I, 48, 8, 1821-1845. Current-driven cold events occur 3 times more often than wind-driven cold events, but the latter are slightly stronger. Rossby, 2003: and J. Cooper, 1996: Prediction will be further strengthened if, in the future, advective paralarval loss can be linked to early retroflection of the Agulhas Current. Tha Natal Pulse: an extreme transient on the Agulhas Current. Lutjeharms, J.R.E., and H.R. Lutjeharms, J.R.E., O. Boebel, and H.T. Importantly, the cold ridgeâcopepod biomassâsquid biomass relationship has been quantified, and holds promise for prediction. Donohue, E.A., E. Firing and L. Beal, 2000: With around 1,400 miles to Durban, or slightly less to Richards Bay, you need a weather window of about ten days. It is generally not very wide, usually less than 50 miles, but can be double this. After suffering some gear failure and fuel problems one yacht missed the weather window. Southern Ocean cold fronts move quickly along the coast from the south, and fuelled by warm water they will often interact with low pressure over the land intensifying the front and spawning secondary lows. Journal of Physical Oceanography, 23, 2107-2124. de Ruijter, W.P.M., H. Ridderinkhof, J.R.E. Weather-wise there is a need to get out of the central part of the Indian Ocean before the tropical cyclone (hurricane) season gets going in November, although around Mauritius and Reunion you’re unlikely to find anything nasty until December. Observations of the flow in the Mozambique Channel. These tend to be the favourite arrival ports, being further north than other South African ports, warmer and away from the Southern Ocean – although the fronts can still be very aggressive and secondary lows may form on them. Boebel, O., J. Lutjeharms, C. Schmid, W. Zenk, T. Rossby, and C. Barron, 2003: The Agulhas Current on the east coast of South Africa is a western boundary Current that transports warm Indian Ocean waters towards the South Atlantic Ocean ().The Agulhas Current forms near southern Mozambique (Lutjeharms, 2006) with source waters from the Mozambique Channel (Saetre and da Silva, 1984), the East Madagascar Current (Lutjeharms et al., 1981), and the South West … Cloud cover is usually extensive, caused when warm, moisture-laden air from the coast encounters cold air over the chill waters of the circling Southern Ocean currents. The courses of the warm Agulhas current (red) along the east coast of South Africa, and the cold Benguela current (blue) along the west coast. Cape Agulhas: the place where two oceans meet, This is the place where the warm-water Agulhas current of the Indian Ocean meets the cold water Benguela current … The Agulhas is noted as a major western boundary current in the Southern Hemisphere. Science, 227, 1030-1033. This means generally relying on GRIB files, which when offshore require big downloads via a satellite phone or SSB to get a large enough picture for an extended period. The Benguela current is 200 to 300 km wide and widens further as it flows north and northwest. The Agulhas Current is the western boundary current of the South Indian Ocean. and C. Veth, 2002. 3a–d). it meets the cold current known as the West Wind Drift and disappears into the depths. The Cape Cauldron: a regime of turbulent inter-ocean exchange. Source waters for the Benguela include cold upwelled waters from the depths of the Atlantic Ocean close inshore, joined further off-shore by nutrient poor water that has crossed the Southern Atlantic from South America as part of South Atlantic Gyre. submitted to the Journal of Oceanography. Van Leeuwen, P.J., W.P.M. The Retroflection of the Agulhas Current. Lutjeharms, J.R.E. Comparison of the three velocity sections of the Agulhas Current Path and variability of the Agulhas Return Current. On any round-the-world cruise by the sunny route, there is the dilemma of how to cross the Indian Ocean. This is of course nothing new for anyone making a long passage, but what makes this rather more interesting, from a meteorological point of view, and concerning for sailors is the Agulhas Current. Here is the rub: a 10-day forecast is at best an indication and in reality the weather may be quite different. The upwelling is evidenced by the high phytoplankton concentration in the sea water off western S. … Boebel, O., C.D. Like the Gulf Stream in the North Atlantic the Agulhas Current is a western boundary current, but being in the southern hemisphere it brings warm water south. Journal of Geophysical Research, 99, 14053-14070. Bryden, H.L. This means that the Agulhas Current has changed course drastically, resulting in changing temperatures, ocean currents, water levels and water biochemistry, which has led to the fish mortalities. Lutjeharms, J.R.E and R.C. Journal of Physical Oceanography, 18, 11, 1570-1583. The cold Benguela Current originates from upwelling of water from the cold depths of the Atlantic Ocean against the west coast of the continent. Last year’s World ARC saw exactly this scenario. Fig 1. Natal pulses and the formation of Agulhas Rings. Matano, R.P., C.G. Having to heave-to and stop, 100 miles or so from safety, is frustrating after a long passage. Structure and transport of the Agulhas Current and its temporal variability. Seasonal variability in the Agulhas Retroflection region. Cold, cyclonic eddies have been observed in the southwestern Atlantic. Its position can be downloaded as model currents in the form of GRIB files and there are satellite-derived positions for it as well. Beal, and L.M. Deep-Sea Research I, 40, 10, 1973-2019. The cold northward-flowing Benguela Current not only cools the west coast considerably but also contributes to the dryness and stability of the atmosphere over the western parts of the country, while the warm southward-flowing Mozambique and Agulhas currents keep temperatures higher on the east and southeast coasts. Like the Gulf Stream in the North Atlantic the Agulhas Current is a western boundary current, but being in the southern hemisphere it brings warm water south. Strub, D.B. This consisted of moorings placed across the Agulhas Current just off the coast of Port Elizabeth. There are hard decisions to make if approaching the coast at the time of a cold front. The Agulhas current flows in a southerly and westerly direction from the Mozambique channel between Africa and Madagascar, down round the south east coast of South Africa past the industrial cities of Durban, East London and Port Elizabeth and eventually interacts with the cold north flowing Benguela current off the southern tip of Africa at Cape Agulhas. and L.M. Behind the front are gale force south-south-westerly winds, which in itself is bad enough, but add a south-bound current and the wind over current conditions can quickly become dangerous. Meteorologist Chris Tibbs explains everything you should know about the Agulhas Current before you sail the Indian Ocean, The Agulhas Current brings warm water south to meet the cold Southern Ocean, fuelling storms. They measure current speed, direction and temperature at extremely high temporal resolutions. Beal, L.M. de Ruijter, and J.R.E. The net transport of the Agulhas Current is estimated as 100 Sv. Deep-Sea Research II, 50, 35-56. GRIB file highlights a cold front off South Africa. 75% of cold events associated with strong wind stress curl are also associated with Agulhas meanders, suggesting that frontal curvature is driving local wind stress curl anomalies. Velocity of the Agulhas Current is 2.7–3.7 km/hr. The Agulhas Current and the Agulhas Retroflection can give rise to immense "rogue waves" that can even threaten supertankers. The Agulhas Current may also be the source of cold water entering Algoa Bay, termed current-driven upwelling. Lutjeharms, 1997: This is the place where the warm-water Agulhas current of the Indian Ocean meets the cold water Benguela current of the Atlantic Ocean and turns back on itself. Deep-Sea Research II, 50, 57-86. Srokosz, 1993: Indian-Atlantic transfer of thermocline water at the Agulhas Retroflection. Journal of Geophysical Research, 105, C12, 28585-28593. Based on model simulations, researchers have found that the interaction of the Agulhas Current and the eastern edge of the bank can result in the Agulhas rings. The sources of the Agulhas Current are the East Madagascar Current (25 Sv), the Mozambique Current (5 Sv) and a recirculated part of the south-west Indian subgyre south of Madagascar (35 Sv). Leeuwen, P. J., W. P. M. de Ruijter, and J. R. E. Lutjeharms, 2000: Journal of Geophysical Research, 93, 631-635. Quartly, G.D. and M.A. Study Finds Major Ocean Current is Widening As Climate WarmsUM Rosenstiel School Agulhas Current study has important implications for global climate. Chris Tibbs is a meteorologist and weather router, as well as a professional sailor and navigator, forecasting for Olympic teams and the ARC rally. The… For me the Red Sea Route has no appeal whatsoever and although the reports of piracy have reduced it is not a risk many want to take. Chelton and M.G. Its west… The Mozambique/Agulhas current is relatively warm, whereas the Benguela current is cooled by coastal upwelling along the west coast of S. Africa and Namibia. The velocity and vorticity structure of the Agulhas Current at 32°S. These are large solitary meanders containing a cold-core cyclone on the inshore side of the current (Lutjeharms and Roberts, 1988). Eddies from the warm South Indian Ocean Agulhas current along South Africa's east coast do round the Cape of Good Hopefrom time to time to join the Bengulela current. Natal Pulses. and H.L Bryden, 1999: The west coast of Southern Africa is surrounded by the cold Benguela Current and on the east coast the warm Agulhas Current moves south from the tropics. Cold water (upwelling or upliftment) is also found along the inshore edge of the Agulhas Current, caused by a number of mechanisms. You need to consider the approaching cyclone season moving into summer months, versus the Southern Ocean depressions throwing up active cold fronts that will reach north to Mozambique and Madagascar. In the April 2021 issue of Yachting World, we delve deep into the stories from one of the most exciting Vendée Globe races in memory, This site is protected by reCAPTCHA and the Google, Jet stream: Everything you need to know about its effect on sailing, Pro navigator’s tips on how to use the ocean’s currents for an offshore advantage, Pip Hare is first British skipper in Vendée Globe, In memory of sailing writer Bob Fisher (1935-2021), Revealed: The European Yacht of the Year 2021 winners, Düsseldorf Boat Show 2021 cancelled due to COVID-19 infection rates, 2020 Vendée Globe preview: Pip Hare and Paul Larsen’s guide to the fleet, Spirit 111: This sailing art gallery is one of the most sensational yachts ever built, Video: See inside 9 of the most amazing modern sailing superyachts, Lagoon 46 first look: Updating this catamaran is a significant step for the yard, Excess 15 first look: This vibrant catamaran can sail in the lightest of winds, Dragonfly 40 yacht tour: This cruising trimaran can do 24 knots. Eddy fluxes of heat and salt from the southwest Indian Ocean into the Float experiment studies interocean exchanges at the tip of Africa. Interbasin leakage through Agulhas Current filaments. The dominant mode of variability of the Agulhas Current is in the form of natal pulses (Bryden et al., 2003). The Agulhas Current is formed by the confluence of the warm Mozambique and East Madagascar Currents, which meet south-west of Madagascar (not shown in the diagram).

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