MAGAZINE . Saint Helena High
Little more than a dot in the South Atlantic Ocean, the island of Saint Helena is famous not only as the final home of Napoleon I, but also for its high-pressure system affecting the climate between Africa and South America. Saint Helena: a volcanic island that rises 823 metres out of the ocean.
Lying 15°56’ south and 5°42’ west, the island of Saint Helena is just 122 km², and was discovered by accident. 2,000 kilometres off the coast of Africa and more than 3,500 kilometres off the coast of Brazil, the British Overseas Territory is in the heart of a high-pressure system that creates calm weather and fleeting breezes. The island was not very visible on the horizon, but on the third Portuguese expedition towards the Indies, Captain João da Nova discovered Ascension Island (1501) then Saint Helena (May 21st, 1502) in the middle of nowhere!
Landing on the unsheltered shores of this uninhabited land, da Nova built a chapel and a few houses which served as places to stay on commercial voyages between Europe and Asia. The discovery of this isolated island continued to determine shipping routes, as the Portuguese introduced goats and planted lemons. Saint Helena became a stop-over used to take on fresh water and fresh supplies, particularly citrus fruit, whose high concentration in vitamin C helped reduce the risk of scurvy, a disease that struck many crews on long-distance voyages.
Isolated land, island of exile
In 1588, Sir Thomas Cavendish was the first British person to set foot on the island on his first circumnavigation, the third successful voyage of its kind after those by Fernando Magellan (1519-1522) and Sir Francis Drake (1577-1580). Aboard his ship Desire, this mercenary privateer followed in the wake of his predecessor by burning three towns built by the Spanish and capturing thirteen ships and their cargo of gold for Queen Elizabeth of England. The discovery of Saint Helena by the English enabled Her Majesty’s fleet to land and attack the Portuguese caravels on their return voyage from the Indies. In 1592, King Felipe II of Spain ordered his fleet returning from Goa not to stop at Saint Helena, which left the door wide open for the Dutch to take possession of the island in 1633. But as they had not really colonised the island, they abandoned it in favour of Cape Town in South Africa.
The British East India Company decided to fortify the island and landed cultivators in 1657 under the governance of Richard Cromwell. Soon after, the fleet of Captain John Dutton settled the fortifications, which during the restoration of the monarchy in 1660 were renamed James Fort, with the adjoining town named Jamestown. This strategic point was the site of several battles as the Dutch East India Company took possession at Christmas in 1672, forcing the then Governor Beale to escape to Brazil. Beale regained control in May 1673 and set up a garrison of 250 soldiers, whilst Charles II declared the island of Saint Helena part of England, “in the same manner as East Greenwich in the County of Kent”! As this volcanic land is not on the trade wind route, it remained more or less ignored, and even suffered terrible damage from the goats that devastated the island’s forests and vegetation.
The end of an empire
Saint Helena became famous when Napoleon was exiled there by the British after his defeat at Waterloo on June 18th, 1815. The Emperor, who had managed to escape from the island of Elba, was no longer able to contact his supporters, particularly as the British laid claim at the same time to the “neighbouring” Ascension Island to establish a naval garrison. Napoleon died on May 5th, 1821 in his residence at Longwood House, in conditions which remain a mystery to this day, with suspicions that he was poisoned. Bonaparte was buried on May 9th in Valley of the Willows under the authority of the Governor Sir Hudson Lowe. King Louis-Philippe succeeded in recovering the ashes, which were returned to France and kept at the Hôtel des Invalides in Paris. In 1858, Napoleon III purchased his ancestor’s residence, and the valley, now called Sane Valley, have been managed by the French Ministry of Foreign Affairs ever since.
The Zulu king Dinuzulu kaCetshwayo succeeded the Emperor in being exiled on the island for seven years from 1890. Then, during the Second Boer War (1899-1902), the British army transformed the island into a detention centre where more than 5,000 Boer prisoners were deported along with General Piet Cronjé. Lacking a sheltered harbour, the 4,000 inhabitants are still very isolated nowadays, with just one single British ship, RMS St Helena, in charge of the postal service and regular supplies with the port of Cape Town. An airport is currently being built and should open in 2016.
The counterpart of the Azores
In meteorological terms, Saint Helena is just as renowned in the Southern Hemisphere as the Azores are in the North Atlantic! The austral island and northern archipelago are both associated with high-pressure or anticyclonic systems, which are relatively stable throughout the year. Both systems are in the intertropical zone, but their positions do fluctuate from day to day, depending on the passage of low-pressure systems, or depressions, from Brazil, which push them, compress them, cause them to shift and sometimes even split them in two. The Azores High is more volatile than that of Saint Helena, due not only to the configuration of the land which surrounds the Azores, but also to the scale of the ice caps of the North and South Poles.
The differences in pressure lie at the origin of the thermal contrast marking the polar cold and the equatorial heat. As the Earth turns on its axis, it carries the adjacent atmosphere along with it. Under the effect of the Coriolis force (deviation of a mass in movement towards the right in the northern hemisphere and the left in the southern hemisphere), this movement mixes masses of hot and cold air, which tend to even out the temperature of the globe with the thermal exchanges between the systems of low and high pressure.
The Saint Helena High thus generates a system of trade winds that turn in an anticlockwise direction around this volcanic island, which lies roughly at the centre. The southern flow along the coast of Africa (Namibia, Angola) turns south-east in the Gulf of Guinea and below the Doldrums, then turns south-east off Brazil, before turning north-west at the latitude of Trinidad and west in the Roaring Forties. This vast circulation meant that the mariners travelling from Europe to the Indies (or on a circumnavigation) had to sail far to the west of these high-pressure systems to avoid remaining stuck in irons, becalmed in the middle of the system.
The clipper route
These general phenomena were known to seafarers in the 19th century. They used pilot charts (having charted average ocean winds from a compilation of sailing ship’s logbooks) to plot their route from Europe to the Indies or the Antipodes (Australia, New Zealand, New Caledonia). The most regular route would therefore depend on the season, autumn being the best time to leave Europe to latch onto the Portuguese trade winds then those of the Canary Islands in order to cross the doldrums between 25° and 30°W. The boats would then head down along the coast of Brazil to Cabo Frio (Rio de Janeiro) on a beam reach before being carried by an Argentinian low to the Cape of Good Hope.
So this is the route, now optimised by modern meteorological data (wind files, digital simulation, satellite images, etc.), that Spindrift 2 has been following since she left Ushant on Sunday November 22nd. But her high speeds of close to 30 knots enable her to latch on to the succession of weather systems very quickly. Dona Bertarelli, Yann Guichard and the crew are setting their sights on a low which is forming off Uruguay this weekend and which will squeeze the Saint Helena High and open the way towards the Cape of Good Hope.