Numerical models—Numerical models solve systems of equations describing the fundamental physics, fluid motion, and thermodynamics of an Earth system component. These models can include single Earth system components (i.e., sea ice, ocean, land, or atmosphere) or can include multiple components that are coupled through the exchange of heat, water, and momentum (i.e., ice-ocean models, global climate models). Biogeochemistry, chemistry, and other aspects can also be incorporated through the inclusion of additional coupled equations or parameterizations.

Marginal ice zone—A band of pack ice 100 to 200 km (62 to 124 mi.) wide that forms a buffer between open seas and dense interior pack ice; here, waves, swells, and eddies have strong impacts that affect the ice, creating highly variable ice conditions.

Multiyear Ice—Ice that has survived at least one melt season; the thickness of multiyear ice floes can range from 2 to 20 m (6.6 to 66 ft) thick.

Predictability—The extent to which future states of a system may be predicted based on knowledge of current and past states of the system. Predictability is inherently limited because knowledge of the system’s past and current states is imperfect and future variations of the external forcings are not exactly known.

Seasonal scale (21 days to 1 year)—The terms “prediction” and “outlook” are commonly used when referring to this timescale.

Statistical models—A model based on statistical relationships between different variables in past behavior of the system to be modeled.

Weather scale (1 hour to 10 days)—The term “forecasting” is commonly used when referring to this timescale.

sustained and coordinated conversation among the user, modeling, and observation communities. It was noted that this approach needs to go beyond ad hoc workshops and demands long-term, continuous, two-way interaction. This theme, which is discussed in more detail in Chapter 3, drove many of the key challenges and strategies laid out in the report.

The report addresses Arctic sea ice prediction over the seasonal to decadal timescales as a driver of the need for improved understanding of sea ice variability (Box 1.1). The committee's focus was on ice conditions during all seasons within the whole Arctic marine environment (i.e., Arctic Ocean and the subpolar seas, including the seasonal sea ice zone).

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