The Met Office launches over 4300 balloons every year from 6 locations across the UK and is involved in launching thousands more around the globe.  These are not party balloons; they are weather balloons that take a small weather observation device, called a radiosonde, up through the atmosphere to the very edges of space.

Radiosondes take highly accurate temperature, moisture, wind and atmospheric measurements, which provide vital observations for weather forecasters, as well as data that helps monitor climate change. This data is then transmitted to a receiver on the ground to be fed into the starting conditions of our weather forecast model, along with thousands of other pieces of information.

Not only do these instruments need to work reliably in extremely challenging and varied conditions but they also need to be extremely light and, as they can’t be reused, they need to be cheap.

The Met Office has just completed trials for a new radiosonde as the one that’s been used since 2005 is being retired this year. Testing radiosondes isn’t straightforward – the atmosphere is constantly changing and a sonde can typically reach heights of 35 km, and travel many miles, before the balloon bursts and falls back to earth.  However stable, consistent measurements are vital for the climate record and we need to ensure that there are no breaks in data and that the data itself is not adversely affected by a change in technology.

A new radiosonde has been chosen and, to maintain continuity in the climate record, we are now launching both the old and new sondes at three trial sites for the next year – Rothera (Antarctica), St Helena (Atlantic Ocean) and Camborne (Cornwall). These sites represent a good spread of climate conditions and environments and allow us to continue long-standing climate records. Camborne alone has been flying radiosondes every day since the 1950s. Staff at the Met Office will analyse the data to ensure that the new radiosonde continues to operate as we expect, and that the vital climate data collected is stable.

Radiosonde trials at Rothera, Antartica (Credit Paul Samways, British Antarctic Survey) and Cambourne, Cornwall

The new radiosonde, the Vaisala RS41, has a few advantages over the sonde we have used for the past few years. It’s lighter which means we need less gas (we use helium) to lift it. Not only does this save money, it reduces our use of a valuable resource as well. At the same time, the new instruments are much easier to use. Before a launch, radiosondes have to be calibrated to ensure that the readings they take in the atmosphere are correct. They also have to undergo checks to ensure that they operate properly – we don’t want to waste money and resources launching an instrument that won’t give us any data. The RS41 allows these ground checks to take place incredibly quickly and easy, so the whole process is more efficient. The data is extremely consistent and stable, which means we can be confident in the information that we receive back and used by our forecasters and in our models.

To find out more about the 100’s of thousands of observations we receive each day and how they are a key part in the forecasting process, visit our learning pages on our website.