The Meteorological Research Flight (MRF) was a Met Office facility, which flew a well-instrumented C-130 Hercules aircraft for atmospheric research purposes.

This dataset contains airborne atmospheric and chemistry measurements taken on board the Met Office C-130 Hercules aircraft flight A756 for the Atmospheric Chemistry and Transport of Ozone in the upper troposphere-lower stratosphere (UTLS) (ACTO) campaign. The flight was located over the North Atlantic.

"Stratospheric Studies, with a low tropopause

The tropopause was crossed in this experiment in order to study true stratospheric air with the available instrumentation. Ozone mixing ratios of up to 400ppb were measured and the corresponding CO mixing ratios were around 30 ppb. The discrimination between the two NOy channels was quite apparent: indicating a clear presence of HNO3. PAN was just detectable in this air.

On descending back below the tropopause, at around 22,000ft, it was noted that the NOy channel, with the Rosemount inlet, was suddenly found to measure more NOy than the other NOy channel. This correlated better with a change in humidity than with the change in temperature. It has been suggested that the change in conditions causes nitrogen compounds (HNO3?) to be 'flushed off' the inlet. Suggestions have been made to change the inlet to the make it identical to the other inlet (backward facing PFA). The instruments generally worked well. There were some problems with the peroxide, as the flows were very poor, at FL270 and above, and the formaldehyde was measuring high values, thought to be due to a leak in the inlet line. The carbon monoxide instrument showed good anti-correlation with the ozone, after the first run at FL250 (when there were problems due to blockages affecting the flow to the optical filter). It was observed that the HORACE reading is high by about 15 ppb relative to the PC reading.

Meteorology

The situation was dominated by a low pressure system centred over Ireland (centre pressure 1000mb). The associated low tropopause made the situation ideal for studying stratospheric chemistry with the C-130.