Ocean buoy a weather aid


ON March 15th last year, a ship on its way from Denmark to the port of Julianehab in Greenland hove to just a little south of Cape Farewell. A large red object, surmounted by an antenna and an array of scientific instruments was carefully lowered overboard and allowed to float on the surface of the water.

Shortly afterwards, automatic marine station No 66595 was left to the not so tender mercies of the North Atlantic, and Ireland's latest weather buoy was on the air.

Ocean buoys, drifting with the prevailing winds and seas, are used to supplement the information provided by weather ships and satellites. By European agreement, each country contributes a number over a given period appropriate to its means, many being deployed by "ships of opportunity" ordinary merchant ships that agree to take the buoy on board at the beginning of a voyage and drop it overboard at some designated spot.

In the North Atlantic, the monthly supply ship from Denmark to the western coast of Greenland frequently obliges.

The craft are fitted out with instruments to measure air and sea temperature and atmospheric pressure, and the data is related to the satellite based ARGOS navigation system. ARGOS, operated from the American NOAA series of polarorbiting satellites, not only relays the weather information back to land based stations for onward transmission to the forecasters, but also continually monitors the geographical position of the buoys, so that recipients will know from which particular spot on the surface of the globe each weather report has come.

Being a small country, Ireland is called upon to provide a drifting weather buoy only relatively rarely, but for this very reason, when the time comes, we tend to watch its progress very closely. From its launch point just southeast of Greenland, 66595 followed a rather unusual track. It staggered a little northwards for a week or so, then reversed direction, heading south, and then went west to reach its most distant location in the early days of June. Then it headed steadily northeastwards, doing a little pirouette from time to time, to be half way between Greenland and Iceland by October, and finally to ground on an Icelandic beach in early April last.

The typical lifespan of a North Atlantic weather buoy is 250 to 300 days. During its relatively long life of 379 days, 66595 transmitted back an average of 50 reports a day to civilisation, and subsequent analysis showed the pressure values to be accurate to within a half a hectopascal, and the temperature to within a degree Celsius. Well done, 66595!