High Ice Concentrations Research Articles

Comparison between C band synthetic aperture radar and 3‐D laser scanner statistics for the Baltic Sea ice

A statistical analysis was performed for nearly simultaneously acquired C band synthetic aperture radar (SAR) images and ice freeboard statistics. The data analyzed were collected during a CryoSat calibration‐validation campaign in March 2005 in the Baltic Sea. The 3‐D ice freeboard topography along transects with a total length about 150 km and width of 300 m was constructed from cross‐track scanning airborne laser scanner measurements. The SAR image data set consisted of two nearly coincident Envisat Advanced Synthetic Aperture Radar alternating polarization precision and image mode precision images at HH polarization with their incidence angle ranges deviating about 20°. The data set represents primarily low‐salinity thin first year ice with high ice concentration and thin snow cover under cold weather conditions. The variance of the mean freeboard increased with increasing mean freeboard with the chosen window size (300 m) up to the mean freeboard of 15 cm. This multiplicative character of sea ice cover forms the basis by which we can expect that the C band backscattering coefficient response, which depends only on the ice surface roughness and the top part of ice medium, can provide information on the sea ice thickness. A nonlinear regression model with three control variables, the backscattering coefficient, the dominant thickness of the level ice which has deformed, and a variable accounting the effect of the SAR incidence angle, was established to predict the variation of the ice freeboard. The applied Bayesian approach also provided means to estimate the uncertainty range for the model fitting and the model predictions. The modeled predictions were mostly in good agreement with the measured values. The predictions for three different test lines accounted for 67%–85% of the measured freeboard variance in 300 m scale. In cold conditions with thin snow cover it was possible to estimate the degree of ice deformation and ice thickness quantitatively from C band SAR images.

Mystery of ice multiplication in warm‐based precipitating shallow cumulus clouds

High concentrations of ice crystals exceeding those of background ice nuclei have often been observed in warm‐based precipitating shallow cumulus clouds. Laboratory experiments reveal that such ice multiplication can occur when large ice particles collide with cloud droplets (Hallett‐Mossop mechanism). Further studies suggested that this mechanism is unable to account for the exceedingly high ice concentrations in those kinds of clouds. However, the results of our numerical simulations show that the ice multiplication phenomena can be explained by the Hallett‐Mossop mechanism with the freezing of a narrow band of supercooled raindrops which act as rimers playing a crucial role.

Observed Feedback between Winter Sea Ice and the North Atlantic Oscillation

Abstract Feedback between the North Atlantic Oscillation (NAO) and winter sea ice variability is detected and quantified using approximately 30 years of observations, a vector autoregressive model (VAR), and testable definitions of Granger causality and feedback. Sea ice variability is quantified based on the leading empirical orthogonal function of sea ice concentration over the North Atlantic [the Greenland Sea ice dipole (GSD)], which, in its positive polarity, has anomalously high sea ice concentrations in the Labrador Sea region to the southwest of Greenland and low sea ice concentrations in the Barents Sea region to the northeast of Greenland. In weekly data for December through April, the VAR indicates that NAO index (N) anomalies cause like-signed anomalies of the standardized GSD index (G), and that G anomalies in turn cause oppositely signed anomalies of N. This negative feedback process operates explicitly on lags of up to four weeks in the VAR but can generate more persistent effects because of the autocorrelation of G. Synthetic data are generated with the VAR to quantify the effects of feedback following realistic local maxima of N and G, and also for sustained high values of G. Feedback can change the expected value of evolving system variables by as much as a half a standard deviation, and the relevance of these results to intraseasonal and interannual NAO and sea ice variability is discussed.

Relationships between polar mesospheric clouds, temperature, and water vapor from Solar Occultation for Ice Experiment (SOFIE) observations

The goal of this work is to explore relationships between polar mesospheric clouds (PMCs), temperature, and water vapor and to understand the extent that bulk thermodynamic equilibrium can explain observed PMC characteristics. We use observations from the Solar Occultation for Ice Experiment (SOFIE) and employ a simple PMC model which assumes that ice exists in thermodynamic equilibrium with the local temperature and water vapor. Model results using SOFIE temperatures and water vapor are found to reproduce the observed ice layer altitudes, ice frequency versus time and altitude, ice mass density (expressed as the gas phase equivalent contained in the ice phase, Qice) versus time and altitude, and the vertical column abundance of ice (or ice water content (IWC)). The differences (model ‐ SOFIE) for July 2008 were −0.1 km in the altitude of peak ice mass density (Zmax), 16% in Qice at Zmax, and 35% in IWC. These results suggest that on average, PMCs can exist in equilibrium with the surrounding environment, and the results also imply that ice nucleation may occur throughout the PMC altitude range. Good correlations were found between ice abundance and temperature (or saturation ratio), although knowledge of both water vapor and temperature is required for a quantitative prediction of observed ice characteristics. Our results indicate that the seasonal dependence of ice abundance is generally controlled by temperature and that in a broad sense, changes in water vapor are a result of changes in ice. We also find that lower temperatures are associated with higher ice mass density, higher ice concentration, and slightly smaller particle radii. This finding indicates that the increase in ice mass density is due to the nucleation of more particles rather than the growth of existing ice, and this finding points to nucleation as an important factor in determining PMC variability.

On the onset of the ice phase in boundary layer Arctic clouds

Airborne measurements in slightly supercooled Arctic boundary layer stratocumulus have been carried out in Spitsbergen on 29 May during the ASTAR 2004 campaign. Cloud measurements have been performed in both warm and cold sectors of a cold front passing the observation area. The results show a north–south gradient in freezing properties and thus evidence of significant differences in the cloud microstructure. Ahead of the front line, in the warm sector (cloud top temperature at −4°C), no ice particles were detected. The cloud formed in clean air conditions (aerosol concentration of 300 cm−3) with subsequent large effective diameter (20–26 μm) and low concentration (50 cm−3) of cloud droplets. Therefore, the collision‐coalescence process was effective, favoring the drizzle formation with concentration up to 300 L−1 (D > 50 μm). In the cold sector behind the front, with a lower cloud top temperature (−6°C), ice crystals were observed in the entire cloud layer, and no droplets larger than about 50 μm (drizzle) were detected. The observations confirm high ice particle concentrations (up to 50 L−1) even with rather warm cloud top (−6°C) compared to previous studies in Arctic clouds. The shattering of isolated drops during freezing and the ice splinter production during riming appear to be the most likely processes to explain the observations of high ice concentration in the cold sector. Analysis of back trajectories did not reveal significant differences in the origin of the air masses in the warm and cold sectors that might have contributed to the differentiation of aerosol composition and thus cloud properties. A cloud top temperature colder than −4°C appears to be required for the onset of the ice phase in this slightly supercooled stratiform cloud.

A new sea ice albedo scheme including melt ponds for ECHAM5 general circulation model

Today we experience an accelerated melting of sea ice in the Arctic which global circulation models are inadequate to predict. We believe one of the reasons is the shortcomings in the sea ice albedo schemes for these models. This paper investigates a physically based sea ice albedo scheme for ECHAM5 GCM, which separates between snow‐covered sea ice, bare sea ice, melt ponds, and open water (separately for the albedos and albedo fractions). The new albedo scheme includes important components such as albedo decay due to snow aging, bare sea ice albedo dependent on the ice thickness, and a melt pond albedo dependent on the melt pond depth. The explicit treatment of melt pond albedos has, to our knowledge, not been included in general circulation models before and represents a substantial improvement when simulating the annual cycle of sea ice albedo. The new albedo scheme overall reduces the sea ice albedo both in winter, because of snow aging, and in summer, because of melt ponds. The reduced sea ice albedo leads to overall reduced sea ice thickness, concentration, and volume, with large temporal and spatial variations. In the Northern Hemisphere in March, some areas experience increased albedo, resulting in thicker sea ice and higher ice concentration, but in August the pattern is spatially homogeneous, with reduced albedo, thickness, and concentrations for all areas where the new scheme has a significant effect.

Parameterization of surface kinetic effects for bulk microphysical models: Influences on simulated cirrus dynamics and structure

A parameterization for the influences of the deposition coefficient (αd) and, therefore, surface kinetics on ice crystal vapor growth in bulk microphysical models is derived. The parameterization is developed by considering three distinct growth regimes, each of which depends on the mean size of the ice crystals: inefficient growth in which surface kinetics dominate vapor growth, efficient growth in which diffusion dominates vapor growth, and an intermediate regime in which both surface kinetics and diffusion are important. Analytical solutions to the distribution‐integrated vapor growth equations are derived for the inefficient and efficient growth regimes, whereas a plausible approximation is suggested for the intermediate growth regime. Use in a numerical cloud model requires a method to choose between the growth regimes, and we show that the kinetic length scale can be used for this purpose. The parameterization is used in eddy‐resolving simulations of a warm and unstable cirrus case. Simulation results tend to match prior microphysical studies: cirrus microphysics are insensitive to αd if αd > 0.1, whereas lower values of αd produce relatively high ice concentrations and ice supersaturations. Our simulations suggest that large changes in cirrus structure and dynamics occur when αd becomes lower than ∼0.05. When growth is this inefficient, ice concentrations are high and precipitation rates are low, which leads to a cirrocumulus‐like structure over time. The dynamic motions in these clouds are driven primarily by infrared cloud top cooling and cloud base warming. At larger values of αd (>0.05), the more efficient vapor growth leads to lower ice concentrations and larger precipitation rates. This causes the initially layered cirrus to transition into cirrus uncinus with precipitation tails. The cloud fraction in this case is low, with lifetimes almost 6 hours less than in the cases with inefficient growth (αd < 0.05).

Deep into the ice: over-wintering and habitat selection in male Atlantic walruses

New technological developments in animal-borne satellite-tracking devices in combi- nation with increased access to satellite-based environmental data are creating new possibilities for studying movement patterns and habitat selection by animals in remote, logistically challenging environments. In the present study, we report the first year-round data on movement patterns of wal- ruses in the High Arctic, including at-sea positions. Using first-passage times (FPT) to study habitat use and quantifying habitat selection using mixed-effects Cox proportional hazards models, we dis- pelled the conventional perception that seasonal movement patterns of Atlantic walruses are simply a result of them following the retraction and expansion of annually formed sea ice. Walruses in this study (n = 17 males) actively moved into areas of high ice concentration (>90%) during winter; travelling far into the ice pack, as far as 600 km from ice-free water. Additionally, high inter-annual, seasonal site fidelity was documented. Seasonal differences in habitat use patterns were also observed. In summer, when walruses feed intensively, FPTs were affected by water depth and distance to the coast (R 2 = 0.571), but these variables had no effect on walrus habitat use in winter. Sea ice concentration was the most important environmental condition during the winter season (R 2 = 0.162), though there are clearly other factors influencing where individuals occur in winter that are currently unaccounted for in these analyses. The male walruses in this study did not do much benthic diving during winter, suggesting that they did not feed often during the time that they are known to breed. Instead, they remained in areas with high ice coverage, far from their coastal summering areas, spending much of their time hauled out or in surface waters.

Saharan dust, lightning and tropical cyclones in the eastern tropical Atlantic during NAMMA‐06

During the summer of 2006, the downstream component of African Monsoon Multidisciplinary Analyses Campaign (NASA‐AMMA (NAMMA)) examined African Easterly Waves (AEWs) emerging from the coast of Africa. Six of these disturbances went on to become named systems in the Tropical Atlantic. Two of the six systems (Tropical storm Debby and Hurricane Helene) developed in the extreme eastern Atlantic and were associated with dust outbreaks, elevated ice contents and frequent lightning. Here we show that in the early tropical cyclo‐genesis stages of these systems there were thousands of cloud‐to‐ground (CG) lightning flashes as measured by a ground‐lightning network. TRMM overpasses show high precipitation ice content above the freezing level and high latent heat release. Super‐cooled water can be inferred in the lower parts of cloud systems in concert with observed high ice concentrations at high altitudes creating charge separation based on the large numbers of CG flashes.

A prelanding assessment of the ice table depth and ground ice characteristics in Martian permafrost at the Phoenix landing site

We review multiple estimates of the ice table depth at potential Phoenix landing sites and consider the possible state and distribution of subsurface ice. A two‐layer model of ice‐rich material overlain by ice‐free material is consistent with both the observational and theoretical lines of evidence. Results indicate ground ice to be shallow and ubiquitous, 2–6 cm below the surface. Undulations in the ice table depth are expected because of the thermodynamic effects of rocks, slopes, and soil variations on the scale of the Phoenix Lander and within the digging area, which can be advantageous for analysis of both dry surficial soils and buried ice‐rich materials. The ground ice at the ice table to be sampled by the Phoenix Lander is expected to be geologically young because of recent climate oscillations. However, estimates of the ratio of soil to ice in the ice‐rich subsurface layer suggest that that the ice content exceeds the available pore space, which is difficult to reconcile with existing ground ice stability and dynamics models. These high concentrations of ice may be the result of either the burial of surface snow during times of higher obliquity, initially high‐porosity soils, or the migration of water along thin films. Measurement of the D/H ratio within the ice at the ice table and of the soil‐to‐ice ratio, as well as imaging ice‐soil textures, will help determine if the ice is indeed young and if the models of the effects of climate change on the ground ice are reasonable.

Use of Enhanced-Resolution QuikSCAT/SeaWinds Data for Operational Ice Services and Climate Research: Sea Ice Edge, Type, Concentration, and Drift

Enhanced-resolution QuikSCAT/SeaWinds (QSer) data recently entered the daily ice chart operation of the national ice services. Algorithms have been developed to extract four important sea ice parameters from this data over the whole Arctic: sea ice edge, type, concentration, and drift. This paper will summarize the different algorithms with a more detailed presentation of the sea ice concentration (IC) algorithm that has not been previously published. The sea ice edge can be detected to IC as low as 10%. Sea ice types can be roughly separated by a single threshold of 12 dB in the horizontal polarization. The IC algorithm gives reasonable qualitative results, separating into three classes: high, medium, and low ICs. It resolves even some characteristic ice features in the marginal ice zone and dynamic areas like the Fram Strait. However, it is very empirical and quantitatively not reliable. Sea ice drift can be determined with an accuracy of about 2.6 cm/s for a 48-h drift. Operating since 1999, QS is an important global data set for climate research, and two crucial applications how these sea ice products can be used for climate research are presented: the seasonal evolution of the sea ice cover and the export of sea ice volume through Fram Strait.

High-resolution sea ice in long-term global ocean GCM integrations

The resolution of the sea-ice component of a coarse-resolution global ocean general circulation model (GCM) has been enhanced to about 22 km in the Southern Ocean. The ocean GCM is designed for long-term integrations suitable for investigations of the deep-ocean equilibrium response to changes in southern hemisphere high-latitude processes. The space and time scales of the high-resolution sea-ice component are commensurate with those of the resolution of satellite passive-microwave sea-ice data. This provides the opportunity for a rigorous evaluation of simulated sea-ice characteristics. It is found that the satellite-derived continuous high ice concentration of the interior winter ice pack can only be captured when vertical oceanic mixing is modified in a way that less local, intermittent convection occurs. Furthermore, the width and the variability of the coastal polynyas around the Antarctic continent and its ice shelves are best captured when some form of ice-shelf melting is accounted for. The width of the wintertime ice edge is reasonably reproduced, while its variability remains underestimated, closely following the coarse-grid pattern of the ocean model due to its high dependence on ocean temperature. Additional variability besides daily winds, e.g. in form of idealized tidal currents, improves the temporal and spatial ice-edge variability, while leads in the interior ice pack become more abundant, more in line with the fine-scale satellite-derived texture. The coast- or ice-shelf line is described on the fine grid based on satellite passive-microwave data. This method requires parts of a coarse coastal ocean grid cell to be covered by an inert layer of “fast ice” or “ice shelf”. Reasonable long-term global deep-ocean properties can only be achieved when these areas are not inert, i.e. are exposed to heat flux and ice growth, or when the vertical mixing parameterization allows for excessive open-ocean convection. The model area exposed to cold high-latitude atmospheric conditions thus being most decisive for a realistic representation of the long-term deep-ocean properties, suggests that high-latitude coastlines are definitely in need of being represented at high resolution, including ice sheets and their effects on the heat and freshwater flux for the ocean.

Comparison of Model-Produced and Observed Microwave Radiances and Estimation of Background Error Covariances for Hydrometeor Variables within Hurricanes

Abstract A radiative transfer model was updated to better simulate Special Sensor Microwave Imager (SSM/I)–observed brightness temperatures in areas of high ice concentration. The difference between the lowest observed and model-produced brightness temperatures at 85 GHz has been reduced from over 100 K to roughly 20 K. Probability distribution functions of model-produced and SSM/I-observed brightness temperatures show that the model overestimates the areas of precipitation, but overall matches the SSM/I observations quite well. Estimates of vertical background error covariance matrices and their inverses were calculated for all hydrometeor variables (both liquid and frozen). For cloud and rainwater, the largest values in the matrices are located in the lower levels of the atmosphere, while the largest values in the cloud ice, snow, and graupel matrices are in the upper levels of the atmosphere. The inverse background matrices can be used as weightings for hydrometeor variables in assimilation experiments involving rain-affected observations.

Comparison of the performance of different ice slurry types depending on the application temperature

The ice slurry medium type used in a refrigeration application could influence the performance of an ice slurry system. For this reason and depending on the refrigeration application, the user has to usually carry out a judgemental selection of the ice slurry mixture type, which should take into account the solute type and its concentration. This article compares the performance of several commonly used organic and inorganic ice slurry secondary refrigerants. This study was based on thermophysical assessments carried out at different operating temperatures. The calculation method that was used to determine the ice slurry properties is first presented. Then, in order to describe the thermophysical efficiency of mixtures at various operating temperatures (−5, −20 and −35 °C), three performance criteria were compared, namely, the volume enthalpy drop, the temperature at the inlet of the application and the relative viscosity of the ice slurry. The results showed that inorganic mixtures are good selection candidates, except for situations where low temperatures and high ice concentrations are encountered at the inlet of the application. Methyl alcohol came out as a good performance candidate for all refrigeration applications, although NH 3 was the best choice based on the current thermo-physical property assessments.

In fluence parameters for a polar mesocyclone development

Polar mesocyclones are small-scale, short-living phenomena in the Arctic and Antarctic. Their forecast is difficult due to a lack of knowledge of initial and boundary conditions. Idealised sensitivity studies are performed with the mesoscale atmosphere - sea ice model METRAS-MESIM to evaluate the relevance of the large-scale meteorological situation and sea ice cover for surface heat fluxes and a mesocyclone development. The evaluation area is 340 km x 340 km, and a sea ice distribution typical for the Fram Strait is used. The area averaged surface heat flux strongly depends on the ice distribution. The surface heat flux is about 95 W m -2 for a mesocyclone moving close to the ice edge and a high sea ice concentration of 97 % in the ice covered region. Ice thickness and ocean currents do not significantly influence the average surface heat fluxes. A large-scale situation that alters the cyclone track and forces the cyclone to mostly move over ice (cover 97 %) reduces the average surface heat flux by 30 %. An increase of the heat flux by 81 % is found for a homogeneous ice distribution with the same total sea ice mass. A decrease of sea ice concentration from 97 % to 75 % increases the average surface heat flux by 44 %. Thus, for the forecast of average surface heat fluxes during a cyclone passage the knowledge of the sea ice distribution is more relevant than the knowledge of the cyclone track. The break up of sea ice distant from the ice edge might trigger the development of enhanced baroclinicity over ice covered regions and, thus, favour conditions for a mesocyclone intensification. The mesocyclone development is mainly determined by intensification at the ice edge resulting from enhanced surface heat fluxes and horizontal temperature gradients in that region. If the cyclone moves over densely ice covered regions the central pressure is up to 6 hPa higher than when it passes close to the ice edge. A homogeneous sea ice cover leads to a maximum pressure difference of 4 hPa. A 22 % reduction of sea ice concentration in the ice covered regions results in maximum pressure deviations of 2 hPa and an increase of the area averaged wind speed by 2 m s -1 . Thus, for the forecast of minimum central pressure and wind speed of a polar mesocyclone the cyclone track with respect to the ice distribution needs to be known. The actual pressure may be influenced by the cyclone passage itself by changing the sea ice distribution.

Evaporation freezing by contact nucleation inside‐out

Ice formation in atmospheric clouds is crucial to our understanding of precipitation and cloud radiative properties. In recent work it was shown that heterogeneous ice nucleation rates can be strongly enhanced by a form of surface crystallization (Shaw et al., 2005). Here we present new laboratory data and consider the implications for contact nucleation and its relevance to ice nucleation in atmospheric clouds. Our observations contradict three leading hypotheses for contact nucleation and suggest, instead, that the notion of contact nucleation should be generalized to include surface crystallization from particles contacting a supercooled drop from the inside out, as well as from the outside in. Our findings lead to the hypothesis that the freezing temperature of an evaporating drop will suddenly become higher once the drop surface contacts an immersed ice nucleus. This mechanism for evaporation freezing is therefore a plausible explanation for the abundant observations of high ice concentrations associated with cloud dilution and droplet evaporation.

Origin of martian northern hemisphere mid-latitude lobate debris aprons

Lobate debris aprons in the martian mid- to high-latitudes (northern and southern hemispheres) have been interpreted as ice-related features that indicate periglacial climate conditions as recently as late Amazonian. Using MOLA topographic profiles perpendicular to apron flow fronts, we surveyed 36 debris aprons in the northern hemisphere found in the regions of Mareotis, Protonilus, and Deuteronilus Mensae and Acheron Fossae. The profiles of these aprons were compared with idealized simple plastic and viscous power law models for ice-rock mixtures. All aprons studied exhibit convex profiles similar to a simple plastic model. This confirms previous interpretations that debris aprons are ice-rich mixtures with rheologies similar to stagnant ice sheets, thus indicating high ice concentrations (>40% by volume). About 60% of the surveyed debris apron population significantly deviates from the idealized simple plastic model profile; this may be due to locally reduced ice content, which primarily controls apron topography. Although post-emplacement modification due to near-surface ice sublimation plays a secondary role in defining the overall shape of aprons, it causes conspicuous surface textures. Degradation by ice sublimation probably results in pitted and ridge-and-furrow surface textures revealed by high resolution MOC images. Such textures may indicate decreased near-surface ice stability since the formation of the aprons, possibly due to Mars' current low obliquity after their emplacement. High ice content inferred from topography suggests some debris aprons have ice cores: potentially exploitable water resources for future robotic/human operations that could prove invaluable for missions remote from polar regions.

Microstructures and precipitation development in cumulus and small cumulonimbus clouds over the warm pool of the tropical Pacific Ocean

AbstractIn situ airborne measurements obtained in convective clouds in the vicinity of the Marshall Islands on 15 days in July and August 1999 are used to determine the microphysical structures and precipitation‐producing mechanisms in these clouds. The liquid water contents of the clouds were generally well below adiabatic values, even in newly risen turrets. This is attributed to the entrainment of ambient air and to the very efficient removal of cloud water by the collision and coalescence of drops. The formation of raindrops began when the concentration of droplets with radii <15 µm exceeded ∼3 cm−3 or, equivalently, when the effective cloud drop radius reached ∼ 13 µm. Clouds rained when their depth exceeded ∼1.5 km. Due to rainout, the effective radius of cloud droplets began decreasing ∼2–4 km above cloud base.Extremely high concentrations of ice particles (often >500 litre−1) formed very rapidly at temperatures between −4 and −10 °C. High‐resolution imagery of these particles, which were primarily sheaths, needles, frozen drops and irregular ice fragments, indicates that the high concentrations of ice were initiated by the freezing of individual drops, some of which fragmented upon freezing, accompanied by ice splinter production during riming. However, for ice particles < 100 µm in maximum dimension, frozen drops and ice fragments were much more numerous than columnar ice crystals, the latter being indicative of ice splinter production. Narrow (10–50 m wide) streamers of precipitation containing large (<3 mm diameter) solid and liquid particles were often encountered in growing clouds. It is proposed that the particles in these streamers grew rapidly by riming in water‐rich zones and, under appropriate conditions, the ice particles produced by both drop fragmentation and riming resulted in exceptionally high localized concentrations of ice. Convective clouds consisting entirely of liquid water produced rain rates that were similar to those from deep convective clouds containing ice.Since the concentration of drizzle and raindrops within a few kilometres of cloud base was highly correlated with cloud depth, and therefore cloud top temperature, the concentration of raindrops in cumulus and cumulo‐nimbus clouds over the warm pool of the tropical Pacific Ocean can be inferred from satellite measurements of cloud top temperatures. Copyright © 2005 Royal Meteorological Society.

Effects of climate variability on the temporal population dynamics of southern fulmars.

Ecological and population processes are affected by large-scale climatic fluctuations, and top predators such as seabirds can provide an integrative view on the consequences of environmental variability on ecosystems. Here, we examine the dynamics of a southern fulmar population in Antarctica over a 39-year period and evaluate the impact of environmental variability on the life history traits of this top predator species. Between 1963 and 2002, the number of breeding pairs fluctuated between seven and 53 in relation to variations in sea ice concentration, and increased overall (annual growth rate: 1·0035). Breeding performance tended to be lower in years with low sea ice concentration. The proportion of birds attempting to breed varied strongly from one year to the next despite the birds were alive, indicating strong environmental forcing on the decision to breed. The number of new local recruits and immigrants was correlated highly with the number of local breeders, and capture probabilities were positively related to the breeding population size. Local recruitment, number of local breeders and proportion of birds attempting to breed were lower when sea ice concentration during summer was low. Adult survival between 1964 and 2002 was on average 0·923±0·006, and decreased during years with high sea surface temperature and low sea ice concentration. Modelled population growth rate, estimated using matrix models, of the population was 0·9728, a difference of 3·6% compared to the observed rate of increase. This discrepancy is due probably to the immigration rate (3±3%). Demographic parameters were affected by sea ice concentration and sea surface temperature anomalies, probably through an impact on krill availability, the main prey of southern fulmars. During warm anomalies, birds skip breeding probably because the food availability was low and limiting for the highly energy demanding reproductive activities. We also emphasize that demographic parameters were very low during the period 1975-80 and showed a higher variability after 1980, which could be interpreted in the context of a regime shift. Our study indicates that the southern fulmar population dynamics may be very susceptible to environmental variability. Further long-lasting warm anomalies are likely to affect negatively their populations.

Atmospheric drag coefficients over sea ice–validation of a parameterisation concept

The concept of drag partitioning to parameterise the surface roughness of sea ice is validatedusing topography data of regions with high sea ice concentrations. The parameterised drag iscompared to measurements obtained by aircraft and ship. The form drag can well be expressedas a function of mean ridge heights and spacings averaged over flight legs of 12 km, if animproved approximation for the coefficient of resistance of a single ridge is used. We find agood agreement between the parameterised and observed drag coefficients. The highest sea iceroughness was encountered close to coastal regions and the lowest in the central Arctic.