Surface Heat Budget of the Arctic Ocean

Ice reflects sunlight more readily than open water. Snow-covered sea ice reflects about 80% of the incident sunlight. Seasonal changes in the Arctic result in clear skies and radiational cooling from snow-covered sea ice in the constantly dark Arctic winter. In spring, with the return of sunlight, melt pools begin to form and increase the rate of heat absorption from the sun. In summer, during continuous daylight, clouds form that reflect solar radiation while reducing heat loss from the ocean. In order to quantify these effects over a large portion of Earth's surface, studying the Arctic Ocean required a large-scale scientific data-gathering and analysis effort over the span of a year. funded a study to better quantify these processes. ==Ice Station SHEBA==

(right) with CCGS Louis S. St-Laurent''. The scientific party traveled aboard the Canadian Coast Guard Ship Des Groseilliers to the Arctic Ocean. It arrived at a location on 2 October 1997, where the plan was to allow the ship to become frozen in the pack ice and be the base for scientific observations. The ice camp was established in the Beaufort Sea and subsequently drifted westward into the Chukchi Sea, allowing observations across different Arctic oceanic and atmospheric regimes. Those observations included measurements of the oceanic and atmospheric processes from the water beneath the ice, near the ship, to the top of the atmosphere. Measurements included: • Radiative fluxes: longwave and shortwave • Heat flux: turbulent fluxes of latent and sensible heat • Cloud height, thickness, and other properties • Processes of energy exchange in the boundary layers of the atmosphere and ocean • Snow depth and ice thickness • Ocean salinity, temperature, and currents The ship remained stationary with respect to the ice for one year, leaving on 11 October 1998. It became known as "Ice Station SHEBA." The drifting observatory approach used during SHEBA was later adopted and expanded in subsequent Arctic expeditions, most notably the MOSAiC Expedition (2019–2020), which employed a similar year-long drift to investigate the Arctic climate system. ==Results==

Observations from SHEBA and related experiments highlighted the central role of clouds in controlling the Arctic surface energy budget, particularly through their influence on longwave and shortwave radiation. During the summer period, 15% of the under-ice area was covered by under-ice meltwater layers and false bottoms. The average depth of under-ice meltwater layers was 0.31 m with a salinity of 1.5. The average thickness of false bottoms was 0.2 m. ==Modeling==

SHEBA observations provided critical validation data for atmospheric and climate models, particularly for improving the representation of cloud microphysics and radiative transfer processes in Arctic conditions. The experimental results allowed meaningful modeling of the seasonal heat budget processes occurring through the Arctic Ocean sea ice and atmosphere. The scope of the model was the column from below the ice pack through the top of the atmosphere. The scientists realized that the key to the model was correctly characterizing the changing reflectivity or albedo of the ice surface, owing to changes in snow pack and ice melting. Cloud cover was key to describing how much energy reached or escaped the ocean surface. Ocean processes The model incorporated the observation that solar radiation is the dominant heat source to the surface. It accounted for the change in the open ocean from a 5% maximum in June and the changes in albedo. Approximately 8% of incoming solar radiation was absorbed into the ocean through the ice. Atmosphere processes The scientists were able to define parameters for near-surface turbulence that characterize the degree to which air movement can cool or warm the surface of the ice, seasonally. In summer, the surface becomes rougher and slows down air flow. The lidar cloud measurements and balloonsonde temperature and turbulence data allowed scientific characterization of the role of the atmosphere above the ice in promoting or inhibiting the warming or cooling of the ocean surface. ==Participants==

The following individuals and organizations participated in SHEBA: == See also ==