Ice drift in the Weddell Sea has been studied by using a satellite buoy deployed on an ice floe. The buoy survived for a 20‐month period, indicating a drift trajectory of 10,000 km and yielding 13 months of marine meteorological data. The drift of the ice floe was studied with respect to the winds measured by the buoy. In the central Weddell Sea, the mean drift speed of the ice floe was 0.15 m/s, which was about 3% of the wind speed. More specifically, the drift ratio was 3.4% in the marginal ice zone and 2.4% in the inner pack ice field. On average, the drift was directed 36° left of the wind direction, but the turning angle was larger during the austral summer and smaller during the winter. On time scales of days the drift was primarily wind‐dependent, except for cases during winter periods of high ice concentration and internal ice resistance. For time scales of several months, purely wind‐based simulations of the drift resulted in a discrepancy between the observed and simulated trajectories, but the inclusion of a slow (0.02 m/s) residual current made the simulations significantly better. The geostrophic wind based on European Centre for Medium‐Range Weather Forecasts pressure analyses was estimated for a 1‐month period, and the ice floe was found to drift almost parallel to the geostrophic wind with a speed of 2% of the geostrophic wind speed. Inertial‐type motion superimposed on the wind‐induced drift was found to be a characteristic feature in the marginal ice zone during the austral summer, but it could not be found from the drift in winter when kinetic energy was transferred to larger scales of motion and dissipated into the ice field.
This chapter contains sections titled: Introduction Observations Computation Method for the Fluxes Sources of Inaccuracy in Flux Estimates Results Bowen Ratio and Summary of the Surface Heat Balance Air-Mass Modification Near the Ice Shelf Conclusions Appendix: Empirical Formulae for Computation of Turbulent Surface Fluxes
Three land‐fast ice stations (one of them was the Finnish research ice breaker Aranda ) and the German research aircraft Falcon were applied to measure the turbulent and radiation fluxes over the ice edge zone in the northern Baltic Sea during the Baltic Air‐Sea‐Ice Study (BASIS) field experiment from 16 February to 6 March 1998. The temporal and spatial variability of the surface fluxes is discussed. Synoptic weather systems passed the experimental area in a rapid sequence and dominated the conditions (wind speed, air‐surface temperature difference, cloud field) for the variability of the turbulent and radiation fluxes. At the ice stations, the largest upward sensible heat fluxes of about 100 Wm −2 were measured during the passage of a cold front when the air cooled faster (−5 K per hour) than the surface. The largest downward flux of about −200 Wm −2 occurred during warm air advection when the air temperature reached +10°C but the surface temperature remained at 0°C. Spatial variability of fluxes was observed from the small scale (scale of ice floes and open water spots) to the mesoscale (width of the ice edge zone). The degree of spatial variability depends on the synoptic situation: during melting conditions downward heat fluxes were the same over ice and open water, whereas during strong cold‐air advection upward heat fluxes differed by more than 100 Wm −2 . A remarkable amount of grey ice with intermediate surface temperature was observed. The ice in the Baltic Sea cannot be described by one ice type only.
Abstract In this paper, we present the results of a one-dimensional, thermodynamic sea-ice model applied to the Baltic Air-Sea-Ice Study (BASIS) field data. In general, the model results are in good agreement with the measurements, which were made during mild weather conditions with distinct areal and temporal variations in the snow and ice thickness. The total amount of refrozen ice calculated from the surface melting water gives a first-order estimate of snow-ice formation during the BASIS experiment, and this agreed well with the total observed variation in ice thickness. The model slightly overestimated ice growth at the bottom. This may be due to the variation in sea-ice thermal properties, affected by a slush layer between the snow and ice, or to the lack of ice-ocean interaction in the model.
Marine meteorological conditions and air-sea exchange processes over the northern Baltic Sea were studied using data from three open-sea lighthouse meteorological stations and the R/V Aranda automatic weather station from the period 1991-1999. The ship data were analysed for the period from April to August from the region of 59 to 62°N, in the basic analyses only considering cases with the fetch from the coast exceeding 30 km. Compared to a previously published climatology of the Baltic Sea basin for the period 1961-1990, considerable differences in the air temperature and wind speed were found. They are partly related to the warm and windy conditions in 1990s and partly to the fact that the lighthouse station data from the open-sea regions were not available for the previous study. The turbulent surface fluxes, calculated using the bulk method from the R/V Aranda data, showed that the monthly median sensible heat flux was a few W m -2 upwards in April, July, and August. In May and June, a stable stratification and a downward sensible heat flux prevailed. The monthly median latent heat fluxes were from sea to air from April to August, but downward latent heat fluxes occurred occasionally. In AprilAugust, the relative humidity, sensible heat flux, and the Bowen ratio had their diurnal maximum values in the morning, while the latent heat flux had it in the afternoon. The fetch effect on the marine meteorological quantities was studied in stationary conditions. Depending on the meteorological conditions, the air temperature, specific and relative humidity and sensible heat flux either increased or decreased with fetch. The decrease of wind speed could be explained by probable mesoscale circulation systems, and the decrease of relative humidity with fetch was due to a dominating increase of air temperature compared to an increase of specific humidity. The changes in the sensible heat flux were related to an air-mass modification towards a neutral stratification. The latent heat flux had its largest values within 30 km off the coast.
