Polar-6 took off this morning after a very successful HAMAG campaign.

Today’s research flight was a repetition of RF01 cruising down the Gulf of Bothnia from its northern end down South till we reach the cloud decks that usually form over the open ocean. This year’s ice extension is quite large and it takes us more than one hour to get there. Since the models did not forecast any clouds over the ice in the bay, we planned to use this section for sea ice emissivity measurements. But in contrast to the forecast we could see low clouds covering the ice surface, giving us the chance to see how the new radar performs on these.

Very thin clouds lying on the ground could not be seen, neither by the G- nor by the W-band radar. But very interestingly, the surface return and the patterns of ghost images changed as soon as clouds were in the beam width.

Cruising along the bay we reached thicker clouds organized in several layers. Between the layers, seeder-feeder effects could be seen in the radars as well as DAR signals of up to 7 dB. All in all another very successful flight with a lot of knowledge on our new GRaWAC radar.

We flew over to the Norwegian coast off Tromso to sample beautiful open and closed cell convection (see satellite image) resulting from a cold air outbreak near Svalbard. Crisp and clear flight conditions in Kiruna made take-off and landing smooth, and after passing some textbook lenticularis clouds over the mountain range, we arrived at the very cloudy survey square over the ocean.

With our flight altitude of 10,000ft (about 3.3km), it was harder to distinguish the cells’ structure, but circular, open areas were easy to see in our instruments and with our eyes. Open cells, seen in the upper left corner of the sat image, are circular areas of clear air with clouds forming along the edges: cold air sinks down in the clear air, diverges at surface, and rises at the edges, leading to ring-shaped cloud formation. Closed cells (bottom left) work the other way around: warm, moist air rises in the cell’s center, while cold air sinks around the cell’s edge. The decks here additionally get influenced by air hitting the coast line, leading to accumulation of clouds. Both cell types produce different amount of rain which we could very well observe with both our radars!

Before some of us left the team, we took the chance to take a picture of the HAMAG crew in front of our reliable research platform Polar 6 in Arena Arctica. In the middle underneath the fuselage, you can see the belly pod carrying our two radars, GRaWAC and MiRAC.

Outlook for tomorrow. For the first time, we will try a survey on the Norwegian coast.

As we reach the midpoint of HAMAG, let’s reflect on the campaign thus far. Our initial three flights have covered the region south and southeast of Kiruna and over the Bothnian Bay. The map below with a digital elevation model and sea ice concentration from the University of Bremen provides an overview of our flight trajectories.

The sea ice concentration map illustrates the closed sea ice in the northern bay and the open ocean towards the south on 9 February 2024. The transect of flight RF01 on this date covered both areas of the Bothnian Bay. Meanwhile, the other two flights focused on low clouds and fog formations over land.

We will continue to update this map to include upcoming research flights.

Today’s flight planning and go or no-go decision have not been easy. The overall situation has been similar to yesterday’s with haze all over Northern Sweden and Finland and the area around Kiruna airport showing a sunny sky with broken low-level clouds only, but with a forecast saying low visibility and difficult landing conditions throughout the day. After long discussions, we decided to go for a short survey, staying local to test different settings for GRaWAC to sense the low-level haze.

Up in the air, we tried different settings with the radars to see which works best with the thin haze. Although the haze was very thin and the ground was visible, both got a signal from time to time. To get an idea of temperature and humidity stratification, two dropsondes have been launched.

High pressure conditions gave us wonderfully sunny and crisp winter weather this weekend, but also made all the clouds disappear! We decided to target forecasted haze conditions towards Finland around Sodankylä to test our new radar GRaWAC’s sensitivity limits.
Good news: higher sensitivity to detect thin layers of cloud and haze, even close to the surface, compared to our existing cloud radar MiRAC! With today’s tests, we are optimistic that we will be able to detect Arctic haze over sea ice conditions around Svalbard, our survey area for upcoming campaigns where low-level haze is crucial for radiation characteristics. The fog today was mysterious – it looked like thicker clouds from far away, but once we reached the decks, conditions were such as seen below in the photo: we could see through it easily down to the ground. Our radar detected a 30m thickness.

We are making use of the weekend to plan upcoming flights for next week, and to start off with some coding to analyze first data measured on Friday. A high pressure system has been hanging around for a few days around, making the sky wonderfully blue without a single cloud in the vicinity of Kiruna.