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AOMIP
For the Arctic Ocean, modeling is essential for understanding past conditions and for explaining recently observed changes. The international Arctic Ocean Model Intercomparison Project (AOMIP) is focused on the investigation of different aspects of the ocean and sea ice changes for the time period 1948-present. Among the major AOMIP themes are investigations of the origin and variability of Atlantic Water (AW) circulation, mechanisms of accumulation and release of fresh water (FW), causes of sea level rise, the role of tides in the shaping of climate, and sea ice variability. In this site, we focus on sea ice representation in different AOMIP regional and global models.
Sea ice concentration is a characteristic of the Arctic ice-ocean-atmosphere system reflecting both dynamics and thermodynamics. Concentration integrates across space and time and is useful to characterize both observed and numerically simulated systems. Concentration is a parameter reasonably well measured by remote sensing, and beginning with the satellite era, several high-quality sea ice concentration data sets are available.
We compare a suite of nine ice-ocean numerical model simulations including the spatial patterns of means and differences among models, and models and observations, for the full record and for the September sea ice minimum. Interannual variations are assessed on data with monthly climatology removed. Most of the models have similar characteristics for the winter months where 100% cover is produced. An observed minimum in sea ice concentration for 1990 is reproduced by most models. Three observational data sets are from the GSFC (the original and adjusted data sets), and the Hadley Centre, both using satellite imagery (SMMR, SSM/I).
Background
Profound changes are occurring in the arctic. Many recent changes suggest rapid and dramatic shifts in Arctic sea ice, a key indicator of climate change. The sea ice trend over the past decade shows decline with record and near-record lows in sea ice extent and concentration in the past five years. Passive microwave satellite data for 24 years (Fowler et al., 2004) suggests the loss of the oldest and thickest sea ice from the Artic. These changes warrant our attention.
Global climate modeling studies show the Arctic to be one of the most sensitive regions to climate change (Manabe and Stouffer, 1994; Rind et al., 1997; Dickson, 1999; Serreze et al., 2000). Climate models indicate that the poles are more sensitive to climate change than lower latitudes because of feedback processes driven by sea ice (Moritz et al., 2002).
Recent sea ice studies indicate a 3-4% decline per decade in sea ice extent (Parkinson et al., 1999), while under ice measurements from submarines indicate a 40% decline in thickness in the central Arctic Ocean prior to 1999 (Rothrock et al., 1999; Rothrock and Zhang, 2005). The consistency in the sign of these observations suggests real, unambiguous decline before 2000.
Identifying the scales of variability is particularly difficult because of the spatial heterogeneity of the Arctic system. Sea ice anomalies show variability at the 4 to 6 year time scale in the Western Arctic, but decadal scale variability in the Eastern Arctic (Mysak and Manak, 1989), making detection of long-term trends difficult but necessary. Ultimately, long-term observations over all seasons are needed to assess model performance that account for thermodynamic processes that dominate the annual cycle and dynamic processes that dominate interannual cycle (Walsh et al., 1985).
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AOMIP Project
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