Arctic Summer-time Cyclones Field Campaign in Svalbard

Hannah Croad –

The rapid decline of sea ice is permitting increased human activity in the summer-time Arctic, where it will be exposed to the risks of Arctic weather. Arctic cyclones are the major weather hazard in the summer-time Arctic, producing strong winds and ocean waves that impact sea ice over large areas. My PhD project is about understanding the dynamics of Arctic summer-time cyclones. One of the biggest uncertainties in our understanding is the interaction of cyclones with the surface and sea ice. Sea ice-atmosphere coupling is greatest in summer when the ice is thinner and more mobile. Strong winds associated with cyclones can move and alter the sea ice, but the sea ice state also feeds back on the development of cyclones, determining surface drag and turbulent fluxes of heat and moisture

My PhD project is closely linked with the Arctic Summer-time Cyclones NERC project, and therefore, I had the opportunity to join the associated field campaign. The field campaign team is comprised of scientists, engineers and pilots from the University of Reading, the University of East Anglia and British Antarctic Survey (BAS). The primary aim of the field campaign was to fly through Arctic cyclones, (i) mapping cyclone structure and (ii) obtaining measurements necessary to characterise the cyclone-sea interaction. In particular, observations of near-surface fluxes of momentum, heat and moisture over sea ice and ocean are needed, as these fluxes dictate the impact of the surface on cyclones. These observations are needed to evaluate and improve the representation of turbulent exchange in numerical weather prediction (NWP) models, especially over sea ice where there are not many existing observations. To obtain accurate measurements of near-surface fluxes, we need to be quite close to the surface (no higher than 300 ft). To do this, we would be using BAS’s Twin Otter aircraft, equipped with Meteorological Airborne Science INstrumentation (MASIN). The twin-engine prop aircraft is small and light, and is therefore ideal for flying at low-levels just above the surface (as low as 50 ft!). There are many instruments fitted on the MASIN research aircraft, but the most important measurements for our purposes were temperature, wind speed, humidity (important for mapping cyclone structure), surface layer turbulent fluxes (from the 50 Hz turbulence probe), and ice surface properties (from laser altimeter).

British Antarctic Survey’s Twin Otter aircraft, fitted with the MASIN equipment. You can see the turbulence probe on the boom at the front of the aircraft, and the CAPS (cloud, aerosol, and precipitation spectrometer) probe on the left wing. The pilot is on top of the aircraft, carrying out final checks before a science flight. Photo from John Methven.

After a 1-year delay due to the Covid-19 pandemic, the field campaign took place in July and August 2022. We were based on the Norwegian archipelago of Svalbard, a 3-hour flight north of Oslo. The team was based in Longyearbyen, the main town on Svalbard. At 78°N, Svalbard is the most northern town in the world! Longyearbyen is located within a valley on the shore of Adventfjorden. The town is a strange but charming place with lots of eccentricities. Longyearbyen is populated with wooden buildings, with pipes above the ground (as the ground freezes in winter), and old mining structures on the sides of the valley. The town is small, but well provided for, with a few tourist shops, restaurants, and a supermarket. As Svalbard is in the Arctic circle, during the summer months it experiences 24-hour sunlight, which was very strange! Furthermore, Longyearbyen is one of the only places on Svalbard that is ‘polar bear safe’ – you should only leave the town limits if you have a rifle!

The field campaign team worked at Longyearbyen airport. The team would study the forecasts from different weather models for the next week, to decide on flight plans. We were primarily looking for strong winds (ideally associated with cyclones, but beggars can’t be choosers!) over the sea ice, within range of the Twin Otter aircraft (approximately 600 nautical miles). With flight planning, there were many things to consider. It was a case of waiting for good weather to come to us, and planning rest days for the pilots when the weather wasn’t looking so interesting in the forecast. Flight plans would consist of transit to and from the target region, where science would be conducted. Science flying included low-level legs to obtain turbulent flux measurements, vertical profiles of the boundary layer, and stacked cross-sections through cyclone features (e.g. fronts) in and above the boundary layer. For flights where low-level flying was planned, it was key that there should not be low cloud in the target area, as this would prevent the aircraft from flying below 1000 ft for safety reasons. It was also important that there were no bad conditions (poor visibility or strong winds) in Longyearbyen, which would prevent the aircraft from taking off or landing. Longyearbyen is an isolated airfield, and the aircraft cannot carry enough fuel to make it back to the mainland if conditions are too poor to land, so this was a very important consideration. Furthermore, the American and French THINICE project field campaign was being conducted at the same time in Svalbard, with the SAFIRE ATR42 aircraft flying at higher levels, looking downwards on Arctic cyclones. We were able to co-ordinate several flights through the same weather systems, with the Twin Otter aircraft flying below the ATR42.

The Twin Otter aircraft holds 3-4 people, including the pilot. With an instrument engineer also on board, this left space for 1 or 2 scientists on each flight (Note: to fly on the aircraft we had to do helicopter underwater escape training – see my previous blog at The cabin is very small (too small for a person to stand up), and is rather cramped, with a considerable amount of space taken up by the extra range fuel tank! The aircraft is flown between 50 and 10,000 ft, and so the cabin is not pressurized. For low-level flying, the crew must wear immersion suits and life jackets on the aircraft (in the unlikely event that the aircraft must ditch in the ocean). On the flight the crew wear noise-cancelling headphones (as the engines are rather loud), and everyone can speak to each other over the intercom. During the flight the scientists will alter the flight plan if necessary, depending on the conditions they encounter, and take notes of the environment and any notable events that occur during the flight. This includes noting what they can see out of the window (e.g. sea ice fraction, cloud), any interesting observations from the live feed of the instrument output within the aircraft (e.g. boundary layer depth), and any instruments that are not working or faulty.

I had the opportunity to fly on the aircraft on the third science flight of the field campaign (I wrote about this in another blog: We were targeting a region to the north-west of Svalbard, in the Fram Strait, where there was forecast to be strong northerly winds over the marginal ice zone. The primary objective was to measure turbulent fluxes over sea ice at low-level. However, on reaching the target region, we were unable to descend lower than 500 ft due to cloud and Arctic sea smoke (formed as cold Arctic air moves over warmer water in between the sea ice floes) at the surface – not safe conditions for flying at low-level! Through gaps in the clouds, we got a glimpse at the Arctic sea smoke over the marginal ice zone (see below). (Note: Several other flights in the field campaign encountered better conditions and were able to get to low levels – see video below!). We searched for better conditions near the target region for an hour, but didn’t find any, so made the return trip home. It was a shame that we could not fly low enough to obtain turbulent flux measurements, but the flight was still useful for obtaining profiles of wind structure in the boundary layer, and for our understanding of forecast performance in the region.

Photos taken from the Twin Otter aircraft 500 ft above the surface, with a layer of Arctic sea smoke overlaying the ice floes of the marginal ice zone. Here visibility is too low to descend any further. Photos from Hannah Croad.
Flying over the marginal ice zone at 70 ft in good visibility conditions, with the shadow of the Twin Otter aircraft visible. Video from John Methven.

During the month-long field campaign a total of 17 science flights were conducted, flying in all directions from Longyearbyen, with an accumulated 80 hours of flying time. This included 4 Arctic cyclone cases, and 7.5 hours of surface layer turbulent flux measurements (more than we could have hoped for!). The data from the aircraft is currently undergoing quality control. Analysis will now proceed in two streams:

  1. Run simulations of Arctic cyclone cases in NWP models, evaluating against field campaign observations and using various tools to relate surface friction and heating to cyclone evolution (led by the University of Reading team)
  2. Use observations of turbulent fluxes in the surface layer over the marginal ice zone and sea ice properties to improve the representation of turbulent exchange over sea ice – i.e. develop parametrizations (led by the University of East Anglia team)

Building on the outputs and findings from these two work packages, we will then run sensitivity experiments of Arctic cyclones in NWP models, using the revised turbulent exchange parametrizations, to understand the impact on cyclone development.

A summary of all the science flights conducted during the Arctic Summer-time Cyclones field campaign. Flight routes are coloured blue-yellow, indicating flight altitude. Also plotted is the campaign mean sea ice fraction (AMSR2).

I really enjoyed my time on the field campaign, and I learnt a lot! It was great to help the team with forecasting and flight planning, and to be on a science flight. I also got to do a bit of media work, talking on BBC Radio 4’s Inside Science programme ( It was a fantastic experience, and now the team and I are looking forward to getting started with the analysis and using the data!

Arctic Summer-time Cyclones field campaign team (some missing) in front of the Twin Otter aircraft. Photo from Dan Beeden.

Helicopter Underwater Escape Training for Arctic Field Campaign

Hannah Croad

The focus of my PhD project is investigating the physical mechanisms behind the growth and evolution of summer-time Arctic cyclones, including the interaction between cyclones and sea ice. The rapid decline of Arctic sea ice extent is allowing human activity (e.g. shipping) to expand into the summer-time Arctic, where it will be exposed to the risks of Arctic weather. Arctic cyclones produce some of the most impactful Arctic weather, associated with strong winds and atmospheric forcings that have large impacts on the sea ice. Hence, there is a demand for improved forecasts, which can be achieved through a better understanding of Arctic cyclone mechanisms. 

My PhD project is closely linked with a NERC project (Arctic Summer-time Cyclones: Dynamics and Sea-ice Interaction), with an associated field campaign. Whereas my PhD project is focused on Arctic cyclone mechanisms, the primary aims of the NERC project are to understand the influence of sea ice conditions on summer-time Arctic cyclone development, and the interaction of cyclones with the summer-time Arctic environment. The field campaign, originally planned for August 2021 based in Svalbard in the Norwegian Arctic, has now been postponed to August 2022 (due to ongoing restrictions on international travel and associated risks for research operations due to the evolving Covid pandemic). The field campaign will use the British Antarctic Survey’s low-flying Twin Otter aircraft, equipped with infrared and lidar instruments, to take measurements of near-surface fluxes of momentum, heat and moisture associated with cyclones over sea ice and the neighbouring ocean. These simultaneous observations of turbulent fluxes in the atmospheric boundary layer and sea ice characteristics, in the vicinity of Arctic cyclones, are needed to improve the representation of turbulent exchange over sea ice in numerical weather prediction models. 

Those wishing to fly onboard the Twin Otter research aircraft are required to do Helicopter Underwater Escape Training (HUET). Most of the participants on the course travel to and from offshore facilities, as the course is compulsory for all passengers on the helicopters to rigs. In the unlikely event that a helicopter must ditch on the ocean, although the aircraft has buoyancy aids, capsize is likely because the engine and rotors make the aircraft top heavy. I was apprehensive about doing the training, as having to escape from a submerged aircraft is not exactly my idea of fun. However, I realise that being able to fly on the research aircraft in the Arctic is a unique opportunity, so I was willing to take on the challenge! 

The HUET course is provided by the Petans training facility in Norwich. John Methven, Ben Harvey, and I drove to Norwich the night before, in preparation for an early start the next day. We spent the morning in the classroom, covering helicopter escape procedures and what we should expect for the practical session in the afternoon. We would have to escape from a simulator recreating a crash landing on water. The simulator replicates a helicopter fuselage, with seats and windows, attached to the end of a mechanical arm for controlled submersion and rotation. The procedure is (i) prepare for emergency landing: check seatbelt is pulled tight, headgear is on, and that all loose objects are tucked away, (ii) assume the brace position on impact, and (iii) keep one hand on the window exit and the other on your seatbelt buckle. Once submerged, undo your seatbelt and escape through the window. After a nervy lunch, it was time to put this into practice. 

The aircraft simulator being submerged in the pool (Source: Petans promotional video

The practical part of the course took place in a pool (the temperature resembled lukewarm bath water, much warmer than the North Atlantic!). We were kitted up with two sets of overalls over our swimming costumes, shoes, helmets, and jackets containing a buoyancy aid. We then began the training in the aircraft simulator. Climb into the aircraft and strap yourself into a seat. The seatbelt had to be pulled tight, and was released by rotating the central buckle. On the pilots command, prepare for emergency landing. Assume the brace position, and the aircraft drops into the water. Hold on to the window and your seatbelt buckle, and as the water reaches your chest, take a deep breath. Wait for the cabin to completely fill with water and stop moving – only then undo your seatbelt and get out! 

The practical session consisted of three parts. In the first exercise, the aircraft was submerged, and you had to escape through the window. The second exercise was similar, except that panes were fitted on the windows, which you had to push out before escaping. In the final exercise, the aircraft was submerged and rotated 180 degrees, so you ended up upside down (and with plenty of water up your nose), which was very disorientating! Each exercise required you to hold your breath for roughly 10 seconds at a time. Once we had escaped and reached the surface, we deployed our buoyancy aids, and climbed to safety onto the life raft. 

Going for a spin! The aircraft simulator being rotated with me strapped in
Ben and I happy to have survived the training!

The experience was nerve-wracking, and really forced me to push myself out of my comfort zone. I didn’t need to be too worried though, even after struggling with undoing the seatbelt a couple of times, I was assisted by the diving team and encouraged to go again. I was glad to get through the exercises, and pass the course along with the others. This was an amazing experience (definitely not something I expected to do when applying for a PhD!), and I’m now looking forward to the field campaign next year.