Clouds and Aerosols

An annual cycle of cloud and radiation measurements made as part of the Surface Heat Budget of the Arctic (SHEBA) program are utilized to determine which properties of Arctic clouds control the surface radiation balance. Surface cloud radiative forcing (CF), defined as the difference between the all-sky and clear-sky net surface radiative fluxes, was calculated from ground-based measurements of broadband fluxes and results from a clear-sky model. Longwave cloud forcing (CFLW) is shown to be a function of cloud temperature, height, and emissivity (i.e., microphysics). Shortwave cloud forcing (CFSW) is a function of cloud transmittance, surface albedo, and the solar zenith angle. The annual cycle of Arctic CF reveals cloud-induced surface warming through most of the year and a short period of surface cooling in the middle of summer, when cloud shading effects overwhelm cloud greenhouse effects. The sensitivity of CFLW to cloud fraction is about 0.65 W m−2 per percent cloudiness. The sensitivity of ...

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442(2004)017%3C0616%3ACRFOTA%3E2.0.CO%3B2

Cloud Radiative Forcing of the Arctic Surface: The Influence of Cloud Properties, Surface Albedo, and Solar Zenith Angle

Forty years (1958–97) of reanalysis products and corresponding sea ice concentration data are used to document Arctic sea ice variability and its association with surface air temperature (SAT) and sea level pressure (SLP) throughout the Northern Hemisphere extratropics. The dominant mode of winter (January–March) sea ice variability exhibits out-of-phase fluctuations between the western and eastern North Atlantic, together with a weaker dipole in the North Pacific. The time series of this mode has a high winter-to-winter autocorrelation (0.69) and is dominated by decadal-scale variations and a longer-term trend of diminishing ice cover east of Greenland and increasing ice cover west of Greenland. Associated with the dominant pattern of winter sea ice variability are large-scale changes in SAT and SLP that closely resemble the North Atlantic oscillation. The associated SAT and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the tr...

Arctic Sea Ice Variability in the Context of Recent Atmospheric Circulation Trends

Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. Interactions between numerous local feedbacks sustain these complex cloud systems, leading to the development of a resilient mixed-phase cloud system. The Arctic region is particularly sensitive to climate change. Mixed-phase clouds, comprising both ice and supercooled liquid water, have a large impact on radiative fluxes in the Arctic. These clouds occur frequently during all seasons in the region, where they often persist for many days at a time. This persistence is remarkable given the inherent instability of ice–liquid mixtures. In recent years it has emerged that feedbacks between numerous local processes, including the formation and growth of ice and cloud droplets, radiative cooling, turbulence, entrainment and surface fluxes of heat and moisture, interact to create a resilient mixed-phase cloud system. As well as the persistent mixed-phase cloud state there is another distinct Arctic state, characterized by radiatively clear conditions. The occurrence of either state seems to be related, in part, to large-scale environmental conditions. We suggest that shifts in the large-scale environment could alter the prevalence of mixed-phase clouds, potentially affecting surface radiative fluxes and the Arctic energy budget.

https://opensky.ucar.edu:/islandora/object/articles%3A18192/datastream/PDF/view

Resilience of persistent Arctic mixed-phase clouds

The Arctic has warmed more than twice as fast as the global average since the late twentieth century, a phenomenon known as Arctic amplification (AA). Recently, there have been considerable advances in understanding the physical contributions to AA, and progress has been made in understanding the mechanisms that link it to midlatitude weather variability. Observational studies overwhelmingly support that AA is contributing to winter continental cooling. Although some model experiments support the observational evidence, most modelling results show little connection between AA and severe midlatitude weather or suggest the export of excess heating from the Arctic to lower latitudes. Divergent conclusions between model and observational studies, and even intramodel studies, continue to obfuscate a clear understanding of how AA is influencing midlatitude weather.

/pdf/divergent-consensuses-on-arctic-amplification-influence-on-5g4bkm06qg.pdf

Divergent consensuses on Arctic amplification influence on midlatitude severe winter weather

A summary is presented of the Surface Heat Budget of the Arctic Ocean (SHEBA) project, with a focus on the field experiment that was conducted from October 1997 to October 1998. The primary objective of the field work was to collect ocean, ice, and atmospheric datasets over a full annual cycle that could be used to understand the processes controlling surface heat exchanges—in particular, the ice–albedo feedback and cloud–radiation feedback. This information is being used to improve formulations of arctic ice–ocean–atmosphere processes in climate models and thereby improve simulations of present and future arctic climate. The experiment was deployed from an ice breaker that was frozen into the ice pack and allowed to drift for the duration of the experiment. This research platform allowed the use of an extensive suite of instruments that directly measured ocean, atmosphere, and ice properties from both the ship and the ice pack in the immediate vicinity of the ship. This summary describes the project goal...

/pdf/surface-heat-budget-of-the-arctic-ocean-4xozsmugim.pdf

Surface Heat Budget of the Arctic Ocean

The Ocean Turbulence Laboratory in the Oceanography Department at the Naval Postgraduate School has an active research program addressing a range of ocean turbulent boundary layer problems. The group has developed observational systems for studying sub-ice boundary layers in polar regions, coastal internal waves, solitons and turbulence over the continental shelf, and the wave forced boundary bottom boundary layer over the inner shelf and surf zone.

https://calhoun.nps.edu/bitstream/10945/41607/1/Stanton_Iron_Enrichment_Experiment_%28IRONEX%29_1993.pdf

Timothy P. Stanton

Papers

Surface Heat Budget of the Arctic Ocean

Iron Enrichment Experiment (IRONEX) 1993