With an Epic Arctic Ocean Expedition Over, Researchers Wrangle with Rich ARM Data
The Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) ended in October 2020, when the R/V Polarstern eased into a dock in Bremerhaven, Germany. The expedition’s fifth and final leg was over, but with so much data to absorb (about 150 terabytes), the work of MOSAiC had just begun.
To collect this abundance of measurements, the German research icebreaker―bristling with onboard and ice-camp instruments―anchored itself in October 2019 to an ice floe, setting off on a fruitful drift across the Arctic Ocean. MOSAiC’s mission was to observe and record the state of the central Arctic, which especially in the depths of the months-long polar night was in many ways a mystery. (Mission collaborators took in pan-Arctic data too, including from satellite platforms.)
Scientists on the Polarstern (and in thematic encampments arrayed around the ship) pulled in data on arctic atmospheric processes, sea ice dynamics, snow properties, ocean ecosystems, and more. Getting comprehensive physical data was an emphasis too, prompting researchers to transport home such samples as ice, algae, fish, microbes, and seawater.
Remote, unique, daring, and comprehensive, MOSAiC can be summed up in a mosaic of facts and impressions. Imagine, for instance, one year moored to an ice floe in the central Arctic. Scientists from 20 nations. Polar bears. Miles-long cracks in sea ice. Twenty arctic cyclones. Fantastical ice ridges. Snow as fragile as dry leaves.
An Eager Audience of Modelers
Matthew Shupe, co-coordinator of the expedition, was present for Legs 1 and 4 of MOSAiC. His expedition tasks included being overall co-coordinator, atmospheric team lead, and a principal investigator on multiple projects, including the ARM-generated atmospheric, cloud, precipitation, radiation, and aerosol measurements. He has funding for his MOSAiC work from DOE’s Atmospheric System Research (ASR).
The second ARM Mobile Facility (AMF2) was aboard the ship with some instrumentation close by. MOSAiC also maintained a distributed network of instruments spanning a radius of 50 kilometers (31 miles).
Shupe, who works for the Cooperative Institute for Research in Environmental Sciences (CIRES), was also the principal investigator for a project on surface energy fluxes funded by the National Science Foundation and NOAA. He expects that in the spring of 2021, a spate of summary papers will arrive and that in three years or less, earth system models will be sharpened by expedition measurements.
In particular, the rich and rare data gathered by MOSAiC scientists have an eager and immediate audience, says Shupe. “We have a whole community of international modelers just waiting anxiously for data to be packaged for them.”
That community of modelers includes those associated with the Year of Polar Prediction, the main activity of a 10-year (2013–2022) project led by the World Meteorological Organization. It brings together operational modeling centers around the world, each with an intensive interest in the Arctic.
Measured in terabytes, one of the largest fractions of MOSAiC data comes from ARM, says Shupe, much of that from 60-plus instruments in AMF2.
MOSAiC’s on-ice activities included a research station called Met City, in which ARM meteorological instruments played a significant role.
Arctic Heating and Cooling
Papers based on MOSAiC data will soon fall in flurries, as Shupe suggests, and studies are zipping ahead like sleet.
For one, Shupe is part of an emerging investigation of arctic clouds, which have a substantial impact on the sea ice surface energy budget. Such clouds can be optically thick, when dominated by liquid water, or optically thin, as in ice clouds or clear sky.
Shupe presented some of this work at AGU2020, during which he convened several MOSAiC-related sessions.
He and co-researchers are studying the response of surface energy budget processes to cloudy skies versus clear skies. In the coupled atmosphere-ice-ocean system, clouds drive changes in surface radiation. They also modulate surface temperatures, the turbulent exchange of heat at the surface, and the way heat conducts through sea ice.
Shupe and others are also examining how these surface energy budget processes shift as winter transitions into springtime. This onset of surface melt over sea ice has been the subject of studies by Shupe research collaborator Christopher Cox of NOAA’s Physical Sciences Laboratory in Colorado.
Their combined study examines the surface energy budget in detail so that springtime warm air intrusions and their effect on ice melt are better understood. The goal is a conceptual model of cloud impacts on sea ice in the central Arctic.
“I want to do more analysis to represent that,” says Shupe of the evolving work. “We’ve only just started digging in.”
Arctic Ice-Nucleating Particles
Little is known about arctic aerosols, tiny atmospheric particles that are the seeds of cloud-particle formation.
Jessie Creamean, an atmospheric scientist at Colorado State University, was among many aerosol researchers who rushed to take part in MOSAiC. (Funding for her work comes from ASR.)
In the bow of the Polarstern, AMF2 included an Aerosol Observing System, which measures the properties of atmospheric particles and trace gases. Creamean, a MOSAiC Leg 1 veteran who also used university instrumentation, has a special interest in ice-nucleating particles (INPs). In 2020, ARM hired her and Colorado State colleague Tom Hill to be its mentors for INP sampling and analysis.
Swept into the atmosphere, INPs trigger the freezing of supercooled cloud droplets and influence cloud reflectivity and life span. Creamean and three Colorado State co-authors presented a poster during AGU2020 that outlined their attempts during MOSAiC to evaluate INPs and their sources in the central Arctic.
Creamean and the others called arctic INPs “vastly understudied” before MOSAiC. Now scientists have a year’s worth of all-season INP data.
The big goal, she says, is to get a picture of INP abundance and sources (including biological) during a full sea ice cycle. Once they do that, the answer to an old question is closer: How do INPs modulate cloud-ice formation in the central Arctic?
This work was supported by the U.S. Department of Energy’s Office of Science, through the Biological and Environmental Research program as part of the Atmospheric System Research program.