Valentia Observatory has a long history of upper-air measurements. Its location on the Atlantic seaboard makes it one of the most strategically positioned stations in north-western Europe. Its radiosonde measurement records date back as far as 1943.
A radio transmitter sends the data back to the monitoring station. The
sonde transmits data for each parameter in rotation. This is achieved
by means of
an electrical switch, which connects each element to the transmitter in turn.
As the balloon ascends, the pressure decreases with height. Temperature also decreases with height, with some significant variations, e.g. there is likely to be an inversion off the ground on a clear night or at a higher level with the approach of a warm front etc. This decrease in temperature continues up to a level known as the tropopause from where it more or less levels off. The height of the tropopause changes with the prevailing conditions and is very significant in weather forecasting. Humidity varies with atmospheric conditions and is monitored only to the 200 hPa level.
After burst, the data for each ascent are quality controlled and are transmitted from the station personal computer, via a modem, to the Computer Section in Met Éireann, Headquarters, from where they are distributed nationally to the forecasting offices and internationally through the Global Telecommunications System (GTS) of the World Meteorological Organisation. The data are transmitted using a special meteorological numerical code that is universally understood.
The data file for each ascent contains the following information: height (m), pressure (hPa), Temperature (oC), Humidity (%), time since launch (s), wind speed (m/s) and wind direction (ddd). The computer software allows profiles of temperature, humidity, wind speed and direction to be generated as a function of altitude, atmospheric pressure and time.
The sondes are carried aloft by a balloon made of natural rubber filled with helium. Due to the decrease in atmospheric pressure as the balloon ascends the gas in the balloon expands. Eventually the elasticity of the rubber in the balloon is reached and it bursts. The ascents normally last for about 90 minutes and the balloons can attain heights of over 30,000 metres.
An Automatic Shipboard Aerological Programme (ASAP) type semi-automatic launcher, made by Vaisala, is used to launch radiosonde ascents. This type of launcher is very suitable for a location like that of the Observatory because it is capable of launching in wind speeds above 15 m/s. It can also be rotated so that the balloon will always be launched down wind. As the system is based on simple pneumatics it is extremely reliable and requires very little "downtime" for servicing. Its system of gas measurement, distribution and balloon filling is both simple and safe.
Ozone sonde ascents are launched manually from a custom built filling house.