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The Bomem has been operating at Halley periodically since 2002. It’s a spectrometer: an instrument that splits light into its component colours.

It is designed to look specifically at the very faint light emitted by molecules of OH (an oxygen atom combined with a hydrogen atom) which form a layer very high up in the atmosphere at about 87km altitude.

By looking at the exact colour of the light emitted by the molecules we can calculate how fast they are spinning. The faster they are spinning, the hotter the atmosphere at that altitude is. Thus the spectrometer is a very sensitive thermometer measuring the temperature of the atmosphere 87km up.

We are looking to see how long-term changes in the Sun cause changes in the temperature of the Earth’s atmosphere. This is so we can distinguish this natural variability from the changes caused by increasing amounts of greenhouse gases.

The all-sky airglow imager is a joint BAS-Utah State University project that observes the OH layer in the infrared. It’s a very sensitive digital camera with a fish-eye lens that takes long-exposure pictures of the whole sky during the hours of darkness.

It can measure small changes in the brightness of the layer caused by atmospheric waves as they pass through. These waves are known to drive the circulation of the upper atmosphere. By measuring the strength and directions of the waves, we can estimate the effect they have on the atmosphere and how this changes with time.