Icebreaker expedition explores intensifying atmospheric rivers - Early melting of the Arctic Ocean in spring may contribute to extreme weather events
Scientists have known that heat transported by atmospheric rivers can cause rapid sea ice melt, but the scale, sources and the effects of "rivers in the sky" in the Arctic has not been well measured and documented in part because it is challenging to install instruments on sea ice for long-term observation. Also, navigation in the Arctic Ocean is difficult before the ice melts in spring, especially in regions where multi-year ice still forms, such as in the North East Greenland-Svalbard region.
Atmospheric rivers (ARs) are relatively narrow and powerful water vapour currents which can fuel massive storms that have caused heavy snow, rain and flooding around the world, especially this winter along the west coast of the USA as well as bringing rain to the top of the 3000 m Greenland Ice Sheet just a year or two ago. Individual atmospheric rivers can be 1000 kilometres long and 100 kilometres wide and over the past decade the number and intensity of atmospheric storms coming from the south into the Arctic appears to be increasing. These increases in AR’s are due to greater fluctuations in the jet stream that is becoming wobbly around the northern hemisphere as opposed to being very confined to the upper reaches of the Arctic.
On 9 May, an international multidisciplinary expedition of 38 scientists set off from Svalbard on the Swedish Polar Research Secretariat's ARTofMELT 2023 (Atmospheric Rivers and the Onset of Sea Ice Melt) research cruise on the icebreaker Oden. The expedition aims to increase the knowledge of the Arctic climate system by studying the onset of the ice melt, for example how atmospheric rivers affect the sea-ice-snow surface and the atmosphere. The expedition will comprehensively measure changes in the Arctic spring from sea ice conditions, seawater and water vapor isotope properties. Once the Oden is positioned between Greenland, Svalbard and the North Pole, the hunt for atmospheric river events based on weather forecasts and satellite images begins. The expedition will return on 15 June 2023.
Atmospheric rivers bring the south to the Arctic
The expedition involves researchers from the University of Oulu and the Finnish Meteorological Institute. They have received funding from the Finnish Ministry for Foreign Affairs to study the Arctic water cycle and the interactions and seasonal variations between the atmosphere, sea ice and the ocean.
It is important to verify and clarify the mechanisms of influence of atmospheric rivers on sea ice, cloud formations and the thermal energy balance of the Arctic Ocean. The early melting of ice in spring has implications for weather, extreme weather events and climate worldwide. Since the 1980s, the area and thickness of the Arctic sea ice have decreased so much that only about a quarter of its volume remains.
Jeff Welker and Valtteri Hyöky on the deck of the icebreaker Oden. Photo by Marcel Schütz / Svalbard Photography.
Professor Jeff Welker from the University of Oulu and the University of Alaska, who also holds the University of Arctic Research Chairship in Arctic Ecology and Biogeochemistry (AEB), leads a team that uses water vapor and seawater isotope forensics to track and trace water vapor and seawater masses in the Arctic. "Because the Arctic’s sea ice reflects the Sun's heat back into space, as the sea ice decreases, the Earth's air conditioner is disappearing and failing," Welker says.
His AEB research team studies the isotopic attributes of water vapor over a large area of the Arctic using various measuring stations on land, for example in Pallas, Finland, in addition to ship based measurements they will take aboard the icebreaker Oden. The ratio of lighter and heavier water isotopes are geochemical fingerprints of water vapor and seawater sources, vapor transport processes and interactions with varying degrees of sea ice coverage and the distinct patterns and distributions of individual ocean currents.
"For example, we study how the atmospheric rivers accumulate water vapor over open, evaporating seas, that in turn supercharges cloud formation, and leads to excessive snow and possibly rain, depending on local and regional conditions", Welker explains. "It seems that now and more so in coming years and decades, moisture sources and transport patterns into, out of and within the Arctic are becoming increasing critical to understand, as the dry areas are becoming drier and expanding and wet areas are becoming wetter. Atmospheric rivers will bring more of the subarctic conditions into the Arctic, and the effects seem to be occurring throughout the Arctic system exemplified by the ‘Borealisation of the Arctic seas and landscapes’.”
Timo Vihma, Research Professor at the Finnish Meteorological Institute, and Doctoral Researcher Gabin Urbancic are studying how heat transported by atmospheric rivers affects the warming of snow over sea ice in spring and the melting of snow and ice as summer approaches. To do this, they will measure the vertical profile of air temperature using drones and weather balloons. The study will also focus on trajectories related to atmospheric circulation. "The atmospheric rivers transport significant amounts of heat and moisture into the Arctic. The earlier the ice starts melting in spring, the more solar radiation is absorbed by the sea. This delays the formation of ice in the autumn, leading to situations where the surface temperature of the Arctic Ocean is still around zero, but the air is already 20 degrees below zero. This is when the release of heat and moisture into the atmosphere is greatest," explains Timo Vihma.
The lack of sea ice in the Arctic can also affect extreme weather events further south, such as in Europe. For example, a winter low pressure can collect large amounts of moisture from the northern high seas and release it as heavy snowfalls and storms further south.
Additional members of Welker’s team are Research Engineer, Valtteri Hyöky, Postdoctoral Researchers Hannah Bailey, Ben Kopec and Kaisa-Riikka Mustonen, University of Oulu and Dr. Eric Klein, University of Alaska Anchorage.