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 A753 for the Atmospheric Chemistry and Transport of Ozone in the upper troposphere-lower stratosphere (UTLS) (ACTO) campaign. The flight was located over the Irish sea.

The purpose of the flight was to investigate further the various filaments of air that were sampled in flight A752. That is polluted air, having origins in the Mediterranean region; clean marine boundary layer air; ozone-rich, dry upper tropospheric air (from upper tropospheric jet) and also polluted boundary layer air, which has been uplifted from N. America. The region should be very structured having many different characteristics. The filaments of air were expected to be aligned zonally, sloping downwards to the North.

The flight was successful in that some of the filaments were found. However, the filaments were not found in the expected area. During a level hold at FL160 (for air traffic) and at the beginning of the first run at FL170 (NOxy calibrations), a dry ozone-rich filament was sampled. Later during the same run, air with moderately high ozone (around 70 ppb), high relative humidity and elevated peroxide was observed. At the subsequent level (FL240) ozone mixing ratios were generally lower (around 45-50 ppb) and the CN count was elevated (2500). However, during the turn at ca. 12:10 on FL240 (SE corner of the flight), another dry, ozone-rich filament was found. A further filament was expected to the North but this was not found. Towards the end of the flight further investigations were made at FL170, in order to try to find the first area of high ozone air (i.e. the air that was sampled during the first NOxy cal run). This air was found but interestingly, the ozone-rich dry air also correlated with high PAN and black carbon.

The instruments generally worked well. The FWVS was adjusted in flight and then found to maintain a good correlation with the GE. Neither the CO nor the HCHO were flown due to previously existing faults. There was a problem with the peroxide pump but this was not until the end of the flight.

Meteorology

The meteorological situation was dominated by high pressure, centred to the north of Scotland. The south of the country was in a more showery regime. However, not much cloud was observed during flight: small cumulus, broken stratocumulus and some cirrus, were observed at times.