Wednesday, August 22, 2007

Bring out the Blimp!

We've had a busy and interesting couple of days running the first ozone experiments of the spring season.

Experiments at Halley monitor both the 'ozone layer', the concentration of gases about 20km above us and 'surface ozone', which is found in the first 500m. The two are completely separate, although frequently (and sometimes deliberately) confused by the media.

All ozone absorbs energy in the infrared to ultraviolet frequency range. The higher 'ozone layer' absorbs short-wave Ultra-Violet light coming from the sun towards us. UV is harmful to us, so this is a Good Thing. When the 'ozone hole' opens up, Aussie cricketers dig out their heavy sunscreen and pigs get burnt.

Surface ozone, however, absorbs longer-wavelength infra-red energy being radiated out from the earth back into space, in effect trapping this heat near the earth's surface. This is a Bad Thing, as it causes local warming over the highly temperature sensitive ice shelves. This was commonly seen as Smog in cities, and is still a problem in places such as Los Angeles.

Read more about the science behind the blimp on BAS' site, here.

So, how do we do it?

We know ozone depleting gases (in the Halogen series) are released by the formation of new sea ice in the coast some 15km from Halley, so we monitor wind speed and direction, looking for a sudden shift to an on shore direction. Once the wind has changed, we watch the CASLab's ozone instruments until we see levels drop at the base. Then we bring out the blimp!

Tamsin steadying the Blimp

The blimp is a small helium filled airship, of the sort seen advertising used cars dealers and golf sales across the UK. We blow it up, attach it to a winch, send it up until it settles into stable flight, then attach the instruments and wind it up into the packet of air we're interested in.

The Blimp over its hanger

Every 10 seconds the instruments sample temperature, humidity, wind speed, wind direction and ozone levels. We raise and lower the blimp and about 5 metres a minute, slowing down when we reach an interesting height. This height is determined by a Sodar (an upward looking sonic sounder, working on similar principals to a RADAR) which reveals temperature differences in the air above the station, revealing warmer 'layers' that have arrived from the coast.

Kirsty shows Dean the controls

The Blimp can reach about 500m! Yesterday we flew for about three hours, reaching 250m and got good results.

Phew, that was probably the biggest post so far! Tune in next week for more climate saving antics...


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