Weekly, seasonal, and decadal predictions of Arctic sea ice conditions
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Weekly, seasonal, and decadal predictions of Arctic sea ice conditions
Sea ice is an important component of the climate system. It mediates different climate feedbacks and regulates the fluxes between ocean and atmosphere. It is one of the export media for fresh water from the Arctic Ocean. Recent changes have underlined the early warning function of Arctic sea ice for climate change. Remote sensing is essential for the assessment of the changes in Arctic sea ice.
The low heat conductivity of sea ice and its isolating properties regarding gas exchange make sea ice an important regulator of fluxes between the atmosphere and the ocean. Its impact on the radiation budget through its high albedo provide additional impact on the climate system. Furthermore, sea ice transport carries huge amounts of fresh water from the Arctic to the subpolar Atlantic. Changes in this fresh water transport pathway have consequences for regional sea level and for the large scale ocean circulation. Thus, climate predictions need good initial conditions for the sea ice component of a climate model. Observations of sea ice drift and concentration (and in the future also sea ice thickness) are used to improve ocean-sea ice models that provide hindcasts and forecasts.
Combination of observations and models
Furthermore, these data enter data assimilation schemes that optimize model initial and boundary conditions to yield a model trajectory close to the actual state of the system. This has been employed for initializing saisonal probabilistic sea ice forecasts („sea ice outlook“) and will be used for optimization of ship routing through the Arctic Ocean by providing forecasts of sea ice parameters for up to ten days on an operational basis. Furthermore, the data will be utilized to initialize multi-year predictions with regional climate models in the framework of the REKLIM program of the Helmholtz Society.
Validation of satellite observations using airborne observations
Ice thickness is a key variable regarding the future development of the Arctic ice cover. Snow cover makes estimates of ice thickness from satellite altimeters uncertain. More direct measurements of ice thickness from the AWI research aircraft Polar 5 are used to calibrate and validate radar altimeter data from Cryosat.
© AWI
Sea ice concentration for June 2009 as simulated by NAOSIM
(click on the picture to enlarge)
© AWI
Polar 5 measuring ice thickness in the Arctic Ocean using the EM-bird
(Photo: C.Haas, source: Alfred-Wegener-Institut)
(Click on the picture to enlarge it)
Optimizations of ship routing
Similar to the seasonal forecast, the NAOSIM model is run until the current date with known atmospheric forcing. Forecast of sea ice concentration, sea ice drift, sea ice thickness, and snow cover are then calculated using weather predictions. Proper initialization of the forecast using Arctic-wide sea ice obserbations is essential to generate forecasts that are useful for navigational purposes on bord ships operating in the Arctic Ocean.
Initialization of decadal climate predictions
On a decadal time scale, largest uncertainty in sea ice development stems from long-term natural variability. Between the short term prediction and century long scenario calculations, decadal prediction is thus especially demanding. Initializing the ocean and sea ice components of coupled climate models to be close to observed states and at the same time satisfy the governing equations without artificial terms is the only chance of achieving skillful decadal predictions.
Seasonal prediction of sea ice extent
We use the NAOSIM (North Atlantic/Arctic Ocean Sea Ice Model) under realistic atmospheric conditions to calculate the state of ocean and sea ice at the end of winter. Available satellite data of sea ice concentration and sea ice drift as well as observations of oceanic temperature and salinity are used to keep the model close to observations. The simulation is then continued with atmospheric forcing from different past years to generate an ensemble of sea ice concentration fields for late summer. The ensemble properties allow probability estimates for the upcoming minimum sea ice cover.
Profile:
Science on climate, ice and oceans
The Bremerhaven-based Alfred Wegener Institute is a leading center of excellence for climate research in polar regions and the oceans. Antarctica and the Arctic are key areas for understanding of global climate change. With its innovative science, excellent research infrastructure and long-lasting experience the Alfred Wegener Institute is among the few institutes worldwide conducting research in the icy worlds at both poles.
Contact
Prof. Dr. Rüdiger Gerdes
Tel.: +49 (0)471 4831-1827
Fax: +49 (0)471 4831-1797
ruediger [dot] gerdes [at] awi [dot] de
www.awi.de
Alfred-Wegener-Institut
Bussestr. 24
27570 Bremerhaven, Germany
Dr. Daniel Steinhage
Tel.: +49 (0)471 4831-1198
Fax: +49 (0)471 4831-1926
daniel [dot] steinhage [at] awi [dot] de
www.awi.de
Alfred-Wegener-Institut
Am Alten Hafen 26
27568 Bremerhaven, Germany
