A Polar Low Flight

A small delegation of atmospheric modellers from the University of Bergen had the possibility to visit the ACCACIA field campaign. With the idea that meeting experimental meteorologists and looking out of the window instead of staring at a computer screen would broaden our views we went off to Kiruna. My PhD-project is about the dynamics of polar lows, also known as arctic hurricanes. These winter storms are well known by local fishermen and people living along the north-west coast of Norway for their sudden appearance and are usually accompanied by heavy snowfall and hurricane force winds. So far March had been a month of high polar low activity, including the period of the ACCACIA field campaign. Despite the focus of the campaign on aerosols and clouds, there’s always a chance that other meteorological features can become the target for the day.

Plan B became reality: we went off to fly into a polar low! There was a remarkable agreement between the met.no forecast and the latest satellite overpass, so we were very likely to actually find the polar low (usually the forecast and reality don’t match that well). It was my first flight on a research aircraft and this plane looks like one big instrument, everywhere on the outside there are instruments mounted and the inside has some seats, but most of the space is occupied by instrument racks and screens.

Flight Manager

Steph & Matt at the flight manager’s console

After take-off from Kiruna we headed straight to the polar low area. First two legs in the polar low zone were at high altitude, zzzzzzhp and another dropsonde is doomed to have a seaman’s grave… We dropped 11 of those, providing us with a nice glimpse of the state of the atmosphere, and than descended to finish with two low legs. Really low legs: approximately 100ft over a rough ocean state: high demand flying for the pilots (and too bumpy to take pictures), as far as I know this is one of very few direct measurements of the surface fluxes in a polar low. As the dropsonde data indicated, and now confirmed by looking out of the window: we were at the right location. Flying into wind speeds around 25 m/s and looking down at rough sea states, which changed suddenly into a calm and cosy ocean with wind speeds around 5m/s. A remarkable change, often mentioned by fishermen: it looks like a black wall is coming towards you and within a few minutes there is a transit from calm conditions to severe storm…

Annick Terpstra

A typical day (2)

For most of the science team flying days start about 5:30am, getting up to check the latest forecasts and to grab the most up to date sea ice data and satellite imagery of cloud cover. Satellite imagery and retrievals of sea surface temperature and chlorophyll concentration are provided by NEODAAS – we email a subset of these out to the team on the research ship to help guide their sampling too. The aircraft ground crew and many of the instrument operators have a much earlier start. Pre-flight preparation starts 4 hours before take-off: 5am for most of the ACCACIA flights.

146 startup

The 146 being started up ready for flight

Just over an hour before take-off we all meet in the operations room at the airport for a quick briefing to ensure everyone knows the plan for the day; then it’s all aboard ready for the flight. Almost all our flights have had a 9am take-off from Kiruna. Although we’re primarily interested in low-level process for ACCACIA, measurements start straight away.

Flight manager

Matt Gascoyne at the flight managers console

Our area of interest is mostly over sea ice around Svalbard; this is around a 2-hour transit from Kiruna. In order to maximise our science time, we stop for a refuel at Longyearbyen. Depending on the plan for the day, we may do some science on the approach to Svalbard – releasing dropsondes to measure the vertical thermodynamic structure of the atmosphere, and mapping the cloud field with a lidar.

Approach to Longyearbyen

View of the approach into Longyearbyen from the flight deck

Once in the operational area the aircraft flies a complicated pattern of ‘legs’ to measure the vertical and horizontal structure of the boundary layer, cloud, and aerosol. The science is directed by the ‘mission scientist’ who sits up front just behind the pilots.

Mission scientist

Me in the mission scientists position up front

While the mission scientist has a laptop on which to view some of the measurements as they are made, they rely heavily on the rest of the team to keep them informed of the full array of measurements in real time. Very often we end up changing our original plan in the light of the conditions we actually find – this can take a lot of quick thinking, and good information and advice from those down the back. Flight time is expensive (over £100 a minute) so we can’t afford to take our time thinking about what to do next.

Jim McQuaid at filters

Jim McQuaid at the filters instrument rack

Kelly downloading data

Kelly Baustian downloading data from the low-turbulence inlet system at the filters rack

The main cabin is packed with instrument racks, and a science team of anything up to 19 people. FAAM provide a core team of instrument operators, and university or MetOffice instruments usually have their own operators. Then there are a handful of people who don’t have specific instruments to deal with, but monitor the real-time data and keep the mission scientist informed. Everyone keeps some sort of log or notes of what’s going on – these are eventually compiled to provide a detailed set of notes on each flight to help interpret the data during later analysis.

Angela at core cloud console

Angela Dean at the core cloud microphysics console

cloud probes

Cloud microphysics probes beneath the wing

Discussing clouds

Discussing cloud measurements with Ian Crawford

After the flight, a quick debrief and chat with the team on the ground to discuss what went well, what problems occurred, and to see what’s planned for the next day. It’s usually about 8pm by the time we get back to the hotel – time to find some dinner, a well-deserved beer, and an early night ready to start all over the next day.

post-flight

A post-flight discussion between Ians Brooks and Renfrew