ARTofMELT2023 expedition studies the arrival of summer in the Arctic

“The ultimate goal is to increase our knowledge of the Arctic climate system, and we do that by going there during a time of year with very few direct observations,” says Michael Tjernström.

While summer comes gradually on land, the transition between the seasons in the Arctic Ocean may be more abrupt. The researchers’ hypothesis is that this transition may be triggered by strong inflows of warm and moist air coming from further south that feed into feedbacks between the frozen sea-ice-snow surface and the atmosphere. These so-called atmospheric rivers occur at all times of the year but are most common in the winter.

“We know almost nothing about what these atmospheric rivers look like, especially their vertical shape, and in this expedition we want to study them and their effects on the surface. For example, how the sea ice and snow change, but also how the frozen surface affects the warm air coming from south – how the air becomes ‘Arctic air.’ Primarily, the air is cooled from below, and therefore clouds or fog often form. But the clouds, in combination with the warm air, also contribute to the surface warming,” explains Michael Tjernström.

Some studies suggest that atmospheric rivers have become more frequent, stronger and longer lasting in a warmer climate. To more reliably predict future climate – in the Arctic and globally – current computer models must factor in both the atmospheric rivers and their effects on the surface.

"By measuring the physical and chemical properties of aerosols, we can obtain information about their sources. Are they natural – or manmade pollutants, and how much of each type is there?” says Paul Zieger.

Atmospheric rivers can also bring large amounts of tiny particles in the air to the high Arctic. These particles, known as aerosols, can be of natural origin, such as sea salt, pollen or bacterial spores, or they can be manmade, such as soot, formed from the incomplete combustion of biomass and fossil fuels.

Aerosols can act as nuclei for ice crystals in the atmosphere, “seeding” the formation of Arctic clouds, which, in turn, affects the amounts of sunlight and thermal radiation that reach the sea ice. They can also be deposited on the snow and ice, which darkens the surface and accelerates melting by absorbing more sunlight. During ARTofMELT2023, the researchers hope to learn more about the properties, size and distribution of different aerosol particles transported by atmospheric rivers, as well as the clouds these particles help form during these events.

“In the high Arctic, aerosol concentrations can be extremely low. Since aerosols are essential for cloud formation, if we were to change their concentrations there, we could potentially be changing cloud properties which, in turn, would affect how much energy can be transported to and from the ice. The latter could impact the onset of the sea ice melt,” says Paul Zieger.

According to the latest climate report by the IPCC, clouds and aerosols contribute the largest uncertainty to estimates and interpretations of the Earth's changing energy budget. Zieger hopes that the data from the expedition could provide some of the answers.

”Our observations will hopefully help reduce the uncertainty by providing much needed field data to better understand how aerosols and clouds influence Arctic climate. This information would help us improve our climate models, which are essential for future climate predictions both in the Arctic and globally,” says Paul Zieger.

“We will use helicopters and drones to see how the atmosphere behaves over a larger area. At the same time, a mini-submarine will be used to study how the atmosphere affects the ice,” says Michael Tjernström.

When Oden is in an area of an atmospheric river, many different scheduled measurements will be carried out simultaneously in a so-called column ‒ from the upper part of the ocean, up through the ice and through the atmosphere.

The lowest atmosphere will be studied with the help of a tethered balloon, drones and instruments suspended below a helicopter, but also with different types of so-called remote sensing techniques, such as radar, lidar and microwaves.

The researchers will complement the scheduled measurements with continuous ones, which will provide high-resolution information about the composition of the atmosphere near the surface.

“We will continuously and in high detail study the properties of atmospheric gases, particles and clouds as well as the energy exchange at the surface. It will be a challenge not to contaminate our observations with emissions coming from Oden though, so we will turn the ship into the wind as much as possible,” says Paul Zieger.

The scientists will also carry out additional activities, such as weather balloons released every six hours and similar instruments lowered into the sea. The results from the former will be sent to weather services worldwide to improve the weather forecasts we all depend on so much.

Finally, taking measurements on the ice surface will also be on the list.

“It will be possible to work on the ice, but only with equipment that can be taken onboard in one day,” says Michael Tjernström.