The small ice cap instability in seasonal energy balance models

Results from a two-dimensional energy balance model with a realistic land-ocean distribution show that the small ice cap instability exists in the Southern Hemisphere, but not in the Northern Hemisphere. A series of experiments with a one-dimensional energy balance model with idealized geography are used to study the roles of the seasonal cycle and the land-ocean distribution. The results indicate that the seasonal cycle and land-ocean distribution can influence the strength of the albedo feedback, which is responsible for the small ice cap instability, through two factors: the temperature gradient and the amplitude of the seasonal cycle. The land-ocean distribution in the Southern Hemisphere favors the small ice cap instability, while the land-ocean distribution in the Northern Hemisphere does not. Because of the longitudinal variations of land-ocean distribution in the Northern Hemisphere, the behavior of ice lines in the Northern Hemisphere cannot be simulated and explained by the model with zonally symmetric land-ocean distribution. Model results suggest that the small ice cap instability may be a possible mechanism for the formation of the Antarctic icesheet. The model results cast doubt, however, on the role of the small ice cap instability in Northern Hemisphere glaciations. Offprint requests to: J Huang     

An investigation of the small ice cap instability in the Southern Hemisphere with a coupled atmosphere-sea ice-ocean-terrestrial ice model

 A simple climate model has been developed to investigate the existence of the small ice cap instability in the Southern Hemisphere. The model consists of four coupled components: an atmospheric energy balance model, a thermodynamic snow-sea ice model, an oceanic mixed layer model and a terrestrial ice model. Results from a series of experiments involving different degrees of coupling in the model show that the instability appears only in those cases when an explicit representation of the Antarctic ice sheet is not included in the model. In order to determine which physical processes in the ice sheet model lead to a stabilization of the system we have conducted several sensitivity experiments in each of which a given ice sheet process has been removed from the control formulation of the model. Results from these experiments suggest that the feedback between the elevation of the ice sheet and the snow accumulation-ice ablation balance is responsible for the disappearance of the small ice cap instability in our simulation. In the model, the mass balance of the ice sheet depends on the air temperature at sea level corrected for altitude and it is, therefore, a function of surface elevation. This altitude-mass balance feedback effectively decouples the location of the ice edge from any specific sea level isotherm, thus decreasing the model sensitivity to the albedo-temperature feedback, which is responsible for the appearance of the instability. It is also shown that the elevation-radiative cooling feedback tends to stabilize the ice sheet, although its effect does not seem to be strong enough to remove the instability. Another interesting result is that for those simulations which include the terrestrial ice model with elevation-dependent surface mass balance, hysteresis is exhibited, where for a given level of external forcing, two stable solutions with different, non-zero ice-sheet volume and area and different air and ocean temperature fields occur. However, no unstable transition between the two solutions is ever observed. Our results suggest that the small ice cap instability mechanism could be unsuitable for explaining the inception of glaciation in Antarctica. Received: 14 April 1997 / Accepted: 22 October 1997     

Forecasting the intrawater ice formation and ice jams in the Neva River

Considered is a dangerous ice phenomenon developing in the Neva River during its freezing, the formation of the intrawater ice resulting in the corking of water intakes, and ice jams causing a sharp water runoff decrease downstream of them and floods. Described are the forecasting techniques of the intrawater ice formation intensity, peak ice jam water levels, and thickness of ice jams.     

Sensitivity of open-water ice growth and ice concentration evolution in a coupled atmosphere-ocean-sea ice model

A coupled atmosphere-ocean-sea ice model is applied to investigate to what degree the area-thickness distribution of new ice formed in open water affects the ice and ocean properties. Two sensitivity experiments are performed which modify the horizontal-to-vertical aspect ratio of open-water ice growth. The resulting changes in the Arctic sea-ice concentration strongly affect the surface albedo, the ocean heat release to the atmosphere, and the sea-ice production. The changes are further amplified through a positive feedback mechanism among the Arctic sea ice, the Atlantic Meridional Overturning Circulation (AMOC), and the surface air temperature in the Arctic, as the Fram Strait sea ice import influences the freshwater budget in the North Atlantic Ocean. Anomalies in sea-ice transport lead to changes in sea surface properties of the North Atlantic and the strength of AMOC. For the Southern Ocean, the most pronounced change is a warming along the Antarctic Circumpolar Current (ACC), owing to the interhemispheric bipolar seasaw linked to AMOC weakening. Another insight of this study lies on the improvement of our climate model. The ocean component FESOM is a newly developed ocean-sea ice model with an unstructured mesh and multi-resolution. We find that the subpolar sea-ice boundary in the Northern Hemisphere can be improved by tuning the process of open-water ice growth, which strongly influences the sea ice concentration in the marginal ice zone, the North Atlantic circulation, salinity and Arctic sea ice volume. Since the distribution of new ice on open water relies on many uncertain parameters and the knowledge of the detailed processes is currently too crude, it is a challenge to implement the processes realistically into models. Based on our sensitivity experiments, we conclude a pronounced uncertainty related to open-water sea ice growth which could significantly affect the climate system sensitivity.     

A load-based CO2 cap in the power sector

Oregon's governor has proposed a load-based cap and trade programme that limits carbon dioxide (CO₂) emissions to 10% below 1990 levels by 2020. A load-based programme is different from the source-based European Union Emissions Trading Scheme (EU ETS), as it regulates emissions sources, located outside the state, that serve Oregon's electricity load. This article describes the stakeholder process that developed the legislative proposal for the load-based cap. The Oregon Clean Energy Planning Model©, a modified capacity expansion model of annual load resource balances, is used to estimate programme costs. The net present value of the climate policy to Oregon ranges from a $518 million benefit to a $414 million cost under various load growth scenarios. Programme benefits are possible under low and medium load growth because the societal returns of energy efficiency exceed its cost over the life of the programme. CO₂ allowance prices in 2017–2020 are estimated in the medium case at approximately $21 per tonne. Low energy efficiency deployment could raise allowance costs to $36, while an aggressive efficiency programme could reduce them to $13.50. Competition for Northwest renewable resources could increase allowance prices in final phase to $37, indicating the interdependence in programme design among state climate policies.     

Formation of the fast ice from the seasonal ice and its destruction

Considered is the theoretical mechanism of the formation of immovable ice cover along the coast (the fast ice) from the seasonal ice and the mechanism of its destruction. It is demonstrated that the process of formation and spread of the winter stable fast ice is determined by simultaneous impact of several factors: the morphometry of the coast and bottom, the width of the close ice, dynamic effects that shear stress forces of the flow and wind make on the ice, the duration of maintaining the condition of immobility and freezing (adhesion) of the ice, the thickness of adhered ice, and the intensity of thermal growth of ice from below. It is revealed that the permanent factor is the morphometry of coasts and the bottom while the other factors have temporal variability of various scales.     

Incorporation of internal fluctuations in a meandering plume model of concentration fluctuations

A meandering plume model that explicitly incorporates the effects of small-scale structure in the instantaneous plume has been formulated. The model requires the specification of two physically based input parameters; namely, the meander ratio,M, which is dependent on the ratio of the meandering plume dispersion to the instantaneous relative plume dispersion and, a relative in-plume fluctuation measure,k, that is related inversely to the fluctuation intensity in relative coordinates. Simple analytical expressions for crosswind profiles of the higher moments (including the important shape parameters such as fluctuation intensity, skewness, and kurtosis) and for the concentration pdf have been derived from the model. The model has been tested against some field data sets, indicating that it can reproduce many key aspects of the observed behavior of concentration fluctuations, particularly with respect to modeling the change in shape of the concentration pdf in the crosswind direction.List of Symbols C Mean concentration in absolute coordinates - C _r Mean concentration in relative coordinates - C₀ Centerline mean concentration in absolute coordinates - C _r,0 Centerline mean concentration in relative coordinates - f Probability density function of concentration in absolute coordinates - f _c Probability density function of plume centroid position - f _r Probability density function of concentration in relative coordinates - i Absolute concentration fluctuation intensity (standard deviation to mean ratio) - i _r Relative concentration fluctuation intensity (standard deviation to mean ratio) - k Relative in-plume fluctuation measure:k=1/i _r ² - K Concentration fluctuation kurtosis - M Meander ratio of meandering plume variance to relative plume variance - S Concentration fluctuation skewness - x Downwind distance from source - y Crosswind distance from mean-plume centerline - z Vertical distance above ground - Instantaneous (random) concentration - Crosswind dispersion ofnth concentration moment about zero - _ny Mean-plume crosswind (absolute) dispersion - _y Plume centroid (meandering) dispersion in crosswind direction - _y,c Instantaneous plume crosswind (relative) dispersion - Normalized mean concentration in absolute coordinates:C/C ₀ - Particular value taken on by instantaneous concentration,      

Parameterizing turbulent exchange over sea ice: the ice station weddell results

A 4-month deployment on Ice Station Weddell (ISW) in the western Weddell Sea yielded over 2000 h of nearly continuous surface-level meteorological data, including eddy-covariance measurements of the turbulent surface fluxes of momentum, and sensible and latent heat. Those data lead to a new parameterization for the roughness length for wind speed, z₀, for snow-covered sea ice that combines three regimes: an aerodynamically smooth regime, a high-wind saltation regime, and an intermediate regime between these two extremes where the macroscale or `permanent' roughness of the snow and ice determines z₀. Roughness lengths for temperature, z_T, computed from this data set corroborate the theoretical model that Andreas published in 1987. Roughness lengths for humidity,z_Q, do not support this model as conclusively but are all, on average, within an order of magnitude of its predictions. Only rarely arez_Tand z_Q equal to z₀. These parameterizations have implications for models that treat the atmosphere-ice-ocean system.     

A postulate of electric multipoles in growing ice crystals: Their role in the formation of ice crystal aggregates

This paper describes the basis of the postulate of electric multipoles in growing ice crystals. The postulate was initially developed to describe the orientation of aggregated ice crystals, for the purpose of learning about rate-determining forces involved in the initiation of ice crystal aggregation.A series of laboratory experiments were undertaken to test the postulate. A 6.7-m³ controlled-temperature chamber was used to investigate the aggregation of growing ice crystals. The results show that small changes in dissolved salts are important in the orientation of initial ice crystal aggregates. We interpret these results to strongly support our hypothesis of electric multipoles in growing ice crystals.     

Microscale temperature fluctuations in the atmospheric surface layer

Microscale temperature fluctuations were measured at 2 m above a grassy surface. The temperature-derivative spectrum was in general agreement with earlier results but the bump at nondimensional wavenumbers higher than 0.02 was not as pronounced as has been observed. The Obukhov-Corrsin constant for the one-dimensional temperature spectrum was evaluated to be 0.92 ± 0.05, consistent with recent results. The effects of instability and the vertical variation of temperature variance and kinetic energy dissipation are postulated to explain some of the difference with other spectra.     

Modeling of fast ice evolution in the Arctic seas

A one-dimensional model of fast ice wind-induced break-up developed before was adapted for two-dimensional case that enabled to explain many regularities of this phenomenon. A numerical scheme is proposed of the integration of the acting stresses and potential resistivity by the fast ice area as well as the method for taking into account the correlation between the wind direction and prevailing coastline orientation that enables to simulate practically any combination of tensile and shearing stresses in the basins of arbitrary shape. The seasonal variability of strengthening ice properties is taken into account. All numerical tests carried out within the frameworks of this investigation demonstrated the qualitative and, partly, quantitative similarity of computation results and regularities observed in nature. The model sensitivity to the variation of some parameters is studied. The limits of model applicability are discussed and the directions of further research are proposed.     

Dynamic-statistical model of ice redistribution in the White Sea

A numerical model of the drift ice concentration and thickness redistribution in the White Sea is described for the fall, winter, and spring periods. The results of the author’s testing are given. The method accuracy and efficiency are calculated by means of comparison with the multiyear mean data and the data of aircraft ice observations.     

On the deterioration of icebergs in the marginal ice zone

Abstract

During the Labrador Ice Margin Experiment (LIMEX) of March‐April 1989, the International Ice Patrol (IIP) of the United States Coast Guard deployed two satellite‐tracked TIROS Arctic Drifter (TAD) platforms on two medium‐sized tabular icebergs. The icebergs were drifting in sea ice of about 9/10 concentration east of Newfoundland. These deployments were part of an experiment to examine differential sea‐ice/iceberg motion during spring conditions near the ice margin. Sea‐ice concentration and movement data were collected concurrently by other LIMEX investigators.

The TADs, deployed on 11 March 1989, were tracked using the ARGOS data collection and location system carried on two NOAA polar‐orbiting satellites of the TIROS family. For two months following the deployment, IIP periodically attempted to relocate the icebergs during routine aerial iceberg patrols. One of the TADs stopped transmitting on 23 April 1989 probably because of a major calving event that resulted in the TAD being crushed. As of 24 April the drift rate of the other TAD nearly doubled compared with its drift rate prior to that date, indicating that it had fallen off the iceberg and was floating on water. By 24 April there was no sea ice near either of the two icebergs.

The TAD data provide a unique datasetfor modelling the deterioration of icebergs while they emerge out of the marginal ice zone and travel in open water. It is shown that a good knowledge of the environmental conditions, pariicularly water temperature and sea state, are critical to model successfully the deterioration and calving of the two icebergs.     

Global dynamics of the Antarctic ice sheet

The total mass budget of the Antarctic ice sheet is studied with a simple axi-symmetrical model. The ice-sheet has a parabolic profile resting on a bed that slopes linearly downwards from the centre of the ice sheet into the ocean. The mean ice velocity at the grounding line is assumed to be proportional to the water depth. The accumulation rate is a linear function of the distance to the centre. Setting the total mass budget to zero yields a quadratic equation for the steady-state ice-sheet radius R. Analysis of the equilibrium states sheds light on the sensitivity of the ice-sheet radius to changes in sea level (S) and precipitation with respect to the present state (P_rel). For model parameters obtained by matching the analytical model to the present state of the Antarctic ice sheet, the sensitivity values are dR/dS = -2400 and dR/dP_rel = 4000 m/%. The model can also be used to study transient behaviour of the ice sheet. The characteristic relaxation time (e-folding time scale) is about 3500 years. Forcing the model with a sea-level and accumulation history over the past few hundred thousands of years yields Antarctic ice-volume curves that are similar to those obtained by comprehensive numerical modelling. The current imbalance predicted by the model corresponds to a sea-level rise of 0.25 mm yr^-1.     

Wind fluctuations in stable air at the boulder tower

Spectra and variances of velocity components and pressure in stable air were analyzed at the 300 m tower of the BAO.Spectra in very stable air in light winds usually contain low-frequency fluctuations of large magnitude, and high-frequency fluctuations with considerably less energy, separated by a gap. The wave-length of the gap follows Monin-Obukhov scaling.The high-frequency portion of the spectra has characteristics of turbulence.The low-frequency energy is almost certainly due to gravity waves, since there is coherence between vertical velocities and temperatures, and since surface pressure time series resemble time series of velocity components at the higher levels on the tower.Variances of surface pressure changes appear to be positively correlated with variances of vertical velocity above 100 m, and also to some extent, with horizontal velocity components at all levels. Those results have applications to diffusion estimates from continuous elevated sources, but need confirmation on the basis of measurements elsewhere and additional analyses at BAO.Returned to Inst. of Atmospheric Physics, Academia Sinica, Beijing, China.Retired September 1, 1982.     

Numerical modeling of ice drift in the Sea of Azov

Considered is the dependence of the evolution of the ice drift velocity field in the Sea of Azov on the direction and duration of the impact of wind of constant intensity based on the constructed two-dimensional mathematical model.