A new version of the general circulation model CNRM-CM has been developed jointly by CNRM-GAME (Centre National de Recherches Meteorologiques—Groupe d’etudes de l’Atmosphere Meteorologique) and Cerfacs (Centre Europeen de Recherche et de Formation Avancee) in order to contribute to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The purpose of the study is to describe its main features and to provide a preliminary assessment of its mean climatology. CNRM-CM5.1 includes the atmospheric model ARPEGE-Climat (v5.2), the ocean model NEMO (v3.2), the land surface scheme ISBA and the sea ice model GELATO (v5) coupled through the OASIS (v3) system. The main improvements since CMIP3 are the following. Horizontal resolution has been increased both in the atmosphere (from 2.8° to 1.4°) and in the ocean (from 2° to 1°). The dynamical core of the atmospheric component has been revised. A new radiation scheme has been introduced and the treatments of tropospheric and stratospheric aerosols have been improved. Particular care has been devoted to ensure mass/water conservation in the atmospheric component. The land surface scheme ISBA has been externalised from the atmospheric model through the SURFEX platform and includes new developments such as a parameterization of sub-grid hydrology, a new freezing scheme and a new bulk parameterisation for ocean surface fluxes. The ocean model is based on the state-of-the-art version of NEMO, which has greatly progressed since the OPA8.0 version used in the CMIP3 version of CNRM-CM. Finally, the coupling between the different components through OASIS has also received a particular attention to avoid energy loss and spurious drifts. These developments generally lead to a more realistic representation of the mean recent climate and to a reduction of drifts in a preindustrial integration. The large-scale dynamics is generally improved both in the atmosphere and in the ocean, and the bias in mean surface temperature is clearly reduced. However, some flaws remain such as significant precipitation and radiative biases in many regions, or a pronounced drift in three dimensional salinity.

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The CNRM-CM5.1 global climate model: description and basic evaluation

The Max-Planck-Institute global ocean/sea ice model with orthogonal curvilinear coordinates

[1] We present our best estimate of the thickness and volume of the Arctic Ocean ice cover from 10 Ice, Cloud, and land Elevation Satellite (ICESat) campaigns that span a 5-year period between 2003 and 2008. Derived ice drafts are consistently within 0.5 m of those from a submarine cruise in mid-November of 2005 and 4 years of ice draft profiles from moorings in the Chukchi and Beaufort seas. Along with a more than 42% decrease in multiyear (MY) ice coverage since 2005, there was a remarkable thinning of ∼0.6 m in MY ice thickness over 4 years. In contrast, the average thickness of the seasonal ice in midwinter (∼2 m), which covered more than two-thirds of the Arctic Ocean in 2007, exhibited a negligible trend. Average winter sea ice volume over the period, weighted by a loss of ∼3000 km3 between 2007 and 2008, was ∼14,000 km3. The total MY ice volume in the winter has experienced a net loss of 6300 km3 (>40%) in the 4 years since 2005, while the first-year ice cover gained volume owing to increased overall area coverage. The overall decline in volume and thickness are explained almost entirely by changes in the MY ice cover. Combined with a large decline in MY ice coverage over this short record, there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the Arctic Ocean ice cover. Seasonal ice, having surpassed that of MY ice in winter area coverage and volume, became the dominant ice type. It seems that the near-zero replenishment of the MY ice cover after the summers of 2005 and 2007, an imbalance in the cycle of replenishment and ice export, has played a significant role in the loss of Arctic sea ice volume over the ICESat record.

Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008

Heat flow anomalies on the oceanic ridges and the large free air gravity anomalies observed from the earth's surface and from satellites are often believed to be surface expressions of high temperatures and flow within the mantle. A simple model for the temperature within a spreading sea floor can, however, reproduce the shape and magnitude of the observed anomalies. Thus, it is not necessary for the upper mantle to be hotter beneath ridges than it is elsewhere. A similar model may be used to relate the free air gravity anomaly to the stress in the lithosphere. The results show that long-wavelength harmonics of the external gravity field cannot be supported by the strength of the lithosphere. Most free air anomalies observed on the surface can be maintained in this way, except possibly the largest of those over the trenches.

Some remarks on heat flow and gravity anomalies

The perennial ice area was drastically reduced to 38% of its climatological average in 2007 but recovered slightly in 2008, 2009, and 2010 with the areas being 10%, 24%, and 11% higher than in 2007, respectively However, trends in extent and area remained strongly negative at -122% and -135% decade (sup -1), respectively The thick component of the perennial ice, called multiyear ice, as detected by satellite data during the winters of 1979-2011 was studied, and results reveal that the multiyear ice extent and area are declining at an even more rapid rate of -151% and -172% decade(sup -1), respectively, with a record low value in 2008 followed by higher values in 2009, 2010, and 2011 Such a high rate in the decline of the thick component of the Arctic ice cover means a reduction in the average ice thickness and an even more vulnerable perennial ice cover The decline of the multiyear ice area from 2007 to 2008 was not as strong as that of the perennial ice area from 2006 to 2007, suggesting a strong role of second-year ice melt in the latter The sea ice cover is shown to be strongly correlated with surface temperature, which is increasing at about 3 times the global average in the Arctic but appears weakly correlated with the Arctic Oscillation (AO), which controls the atmospheric circulation in the region An 8-9-yr cycle is apparent in the multiyear ice record, which could explain, in part, the slight recovery in the last 3 yr

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Large Decadal Decline of the Arctic Multiyear Ice Cover

Growth, structure, and properties of sea ice.

: Equations are developed that can be used to determine the amount of gas present in sea ice from measurements of the bulk ice density, salinity and temperature in the temperature range of -2 to -30 C. Conversely these relationships can be used to give the density of sea ice as a function of its temperature and salinity, considering both the presence of gas and of solid salts in the ice. Equations are also given that allow the calculation of the gas and brine volumes in the ice at temperatures other than that at which the bulk density was determined. (Author)

Equations for determining the gas and brine volumes in sea ice samples

On a etabli des equations utilisables pour determiner le taux de gaz inclus dans la glace de mer a partir de mesures de densite, de salinite et de temperature dans des gammes de temperatures entre -2°C et -30°C. Inversement ces relations peuvent etre utilisees pour calculer la densite de la glace de mer en fonction de la temperature et de la salinite, en prenant en compte a la fois la presence de gaz et de cristaux de sel dans la glace. On donne aussi des equations qui permettent le calcul du volume de gaz et d'eau salee dans la glace a des temperatures autres que celle pour laquelle la densite a ete determinee

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Equations for Determining the Gas and Brine Volumes in Sea-Ice Samples

On the geophysical scale sea ice is a thin, fragile, dynamic, solid layer that forms under the thermodynamic conditions that occur near the Poles. There it serves as a boundary between two much larger fluid bodies — the ocean and the atmosphere. Typical scales of interest would be 103 to 106 m. In the present paper we take a more detailed view, focusing on the ice itself at scales ranging between 100 and 10−3 m, with an occasional glimpse at a scale of 10−10 m. It is our purpose to help the reader understand the internal structure of sea ice, how this structure develops, and how it affects the bulk properties of the ice. Although this is a subject that has received little attention in comparison to similar studies of metals and ceramics, it is, in our view, very important, as many details in the behavior of sea ice are structurally controlled. The variations in structure are, in turn, determined by the environmental conditions under which the ice has formed.

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The Growth, Structure, and Properties of Sea Ice

The salinity distribution in multi-year sea ice is dependent on the ice topography and cannot be adequately represented by a single average profile The cores collected from areas beneath surface hummocks generally showed a systematic increase in salinity with depth from 0‰ at the surface to about 4‰ at the base The cores collected from areas beneath surface depressions were much more saline and displayed large salinity fluctuations Salinity observations from sea ice of varying thicknesses and ages collected at various Arctic and sub-Arctic locations revealed a strong correlation between the average salinity of the ice and the ice thickness h For salinity samples collected from cold sea ice at the end of the growth season, this relationship can be represented by two linear equations: ;  It is suggested that the pronounced break in slope at 04 m is due to a change in the dominant brine drainage mechanism from brine expulsion to gravity drainage A linear regression for the data collected during the melt season gives  An annual cyclic variation of the mean salinity exists for multi-year sea ice The mean salinity reaches a maximum at the end of the growth season and a minimum at the end of the melt season

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W. F. Weeks

Papers

Growth, structure, and properties of sea ice.

Equations for determining the gas and brine volumes in sea ice samples

Equations for Determining the Gas and Brine Volumes in Sea-Ice Samples

The Growth, Structure, and Properties of Sea Ice

Salinity variations in sea ice