A method of determining sea ice parameters using dual‐polarized multispectral radiance data obtained with the NIMBUS 7 Scanning Multichannel Microwave Radiometer (SMMR) is presented. Sea ice concentration is determined both at a 60‐km resolution from the polarization at the 1.7‐cm wavelength and at a 30‐km resolution using the polarization at the 0.81‐cm wavelength. Multiyear sea ice fraction is obtained from the spectral gradient ratio, which is the difference of the 0.81 cm and the 1.7 cm vertically polarized radiances divided by their sum. In addition, an ice temperature is calculated from the 4.6‐cm vertical channel radiances. The use of radiance ratios greatly reduces uncertainties in the derived parameters resulting from temporal and horizontal spatial variations of ice temperature. Observed SMMR radiances from selected areas in the Arctic region for the period February 3–7, 1979, are used in computing algorithm coefficients. Polar maps of sea ice concentration, multiyear fraction, and ice temperature are illustrated for this period. The variation of the mean and standard deviation of ice concentration and multiyear ice fraction for a region of perennial ice cover over the first 11 months of SMMR operation is also presented. The standard deviation about the mean for the computed concentration varies from 2 to 5% over the 11‐month period, while that of the multiyear fraction is about 8% for all but the summer months. Discrimination between first‐year and multiyear sea ice during the summer period is indeterminate largely because the general surface melt conditions mask the distinguishing properties of the two ice types. Based on the time variation of ice concentration and multiyear fraction for the central Arctic region and on an analysis of histograms of these parameters, the precision of the calculated ice concentration is estimated to be in the range of 5–9% and that of the multiyear fraction in the range of 13–25%. Comparisons are made between the calculated sea ice parameters and information obtained from previous studies using aircraft, submarine, and surface observations. From these comparisons it is concluded that the absolute accuracy of the SMMR parameters remains uncertain. The precision of the sea ice concentration is sufficient to provide useful data on the large‐scale polar ice cover, but further study is required to increase the confidence in the multiyear ice fraction which at present contains significant uncertainties.

Stratospheric wind data for Canton Island (3°S) and Nairobi, Kenya (2°S), reveal that during the period July 1955–February 1960 alternate bands of easterly and westerly winds progressed downward from the highest level of observation (30 km) at intervals of approximately 1 year, suggesting the presence of a 2‐year zonal wind oscillation in the equatorial stratosphere. The bands circle the entire globe, reach their greatest strength near 25 km, are about 10 km deep at intermediate levels, move downward at about 1 km per month, and weaken and become erratic near the tropopause. On the basis of ozone measurements it is argued that the downward propagation represents a wave motion, not a mass transport. The periodic appearance of westerly momentum at the equator suggests the presence of disturbances in the tropical stratosphere which transport momentum in a preferred manner.

During the summer Marginal Ice Zone Experiment in Fram Strait in 1983 and 1984, fourteen mesoscale eddies, in both deep and shallow water, were studied between 78 ø and 81øN. Sampling combined satellite and aircraft remote sensing observations, conductivity-temperature-depth observations, drift of surface and subsurface floats and current meter measurements. Typical scales of these eddies were 20-40 km. Rotation was mainly cyclonic with a maximum speed, in several cases subsurface of up to 40 cm s-• Observations further suggest that the eddy lifetime was at least 20 to 30 days. Five generation sources are suggested for these eddies. Several of the eddies were topographically trapped, while others, primarily formed by combined baroclinic and barotropic instability, moved as much as 10-15 km d -• with the mean current. The vorticity balance in the nontrapped eddies is dominated by the stretching of isopycnals accompanied by a change in the radial shear. In the most completely observed eddy south of 79øN the available potential energy exceeded the kinetic energy by a factor of 2. Quantitative estimates suggest that the abundance of these eddies enhances the ice edge melt up to 1-2 km d-• !. INTRODUCTION The marginal ice zone (MIZ) is the transition region from open ocean to pack ice. Here strong mesoscale air-ice-ocean interactive processes occur which control the advance and retreat of the ice margin. To gain better understanding of these processes, the 1984 Marginal Ice Zone Experiment (MIZEX '84) was carried out in Fram Strait between Greenland and Svalbard from May 18 to July 30, !984, following a preliminary summer experiment in 1983 I-MIZEX Group, 1986]. One of the central objectives of MIZEX is to understand the physics of mesoscale eddies and their importance in the various exchange processes of mass, heat, and momentum which affect the position of the ice edge. Major investigations of mid-ocean eddies started in 1973 with the Mid-Ocean Dynamics Experiment (MODE) 1 program [Robinson, 1983]. Although it is now well established that eddies are present in all the world oceans with important implications for physical, biological, chemical, and geological oceanography and acoustics [Robinson, 1983; Maqaard et al., 1983], eddy features have not been extensively investigated in the MIZ. To qualitatively demonstrate the effect of eddies in the MIZ, a unique aerial photograph obtained on June 30, 1984 is shown in Plate 1, where the ice traces the cyclonic orbital motion of an eddy at the ice edge. (Plate 1 is shown here in black and white. The color version can be found in the separate color section in this issue.) Such motion advects large amounts of ice, Polar Water (PW), and Atlantic Water (AW) into closer contact, causing enhanced floe breakup and ice melting. While Plate 1 shows one ice edge eddy in detail, the National Oceanic and Atmospheric Administration (NOAA) satellite image from July 1, 1984 (Plate 2) establishes that eddies and meanders are the dominant features along the ice edge under moderate wind con...

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A history of the idea of transporting large icebergs to arid regions to provide a fresh-water source is presented and the problem is considered in four main parts: (1) Location of a supply of icebergs. Only in the Antarctic are supplies of large tabular icebergs available. Data on the size distribution of these icebergs are reviewed and it is concluded that icebergs of almost any desired size can readily be located. (2) Towing. Steady-state towing velocities of different sized icebergs are calculated based on estimates of the drag of the icebergs and the bollard pull of tugs. Because drag increases with velocity squared, large icebergs can only be towed at very slow velocities (<c. 0.5 m/s). However, tugs that can be built within the capabilities of current technology are capable of towing extremely large icebergs. (3) Melting in transit. Calculations of melting indicate that, although melting losses are significant and may be excessive for small icebergs, when large icebergs are towed, large amounts of ice are left when the iceberg arrives at its destination. Towing trajectories, travel times, and ice delivery rates are calculated for optimum routes between the Amery Ice Shelf and Western Australia (A–A) and the Ross Ice Shelf and the Atacama Desert (R–A). Forces included in these calculations are towing, air, water, gradient current and Coriolis. Transit times exceed 107 d (A–A) and 145 d (R–A) with over 50% of the initial ice delivered. (4) Economic feasibility. After total towing charges are paid, it is possible to deliver ice to Western Australia for 1.3 mills/m3 of water and to the Atacama Desert region for 1.9 mills/m3. These costs are appreciably less than the expected price of water delivered at these locations (8 mills/m3). The water delivered by the operation of one super-tug alone would irrigate 16 000 km2. Problems related to both iceberg transport and processing are reviewed and although substantial problems do exist, they appear to be within the capabilities of current technology. It is suggested that the overall idea is indeed feasible and should be explored further by specific groups of experts.

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We have recently completed an analysis that examines in detail the spatial and temporal variations in global sea-ice coverage from 26 October 1978, through 20 August 1987. The sea-icemeasurements we analyzed are derived from data collected by a multispectral, dual-polarized, constant incidence-angle microwave imager, the Scanning Multichannel Microwave Radiometer (SMMR) on board the NASA Nimbus 7 satellite. The characteristics of the SMMR have permitted a more accurate calculation of total sea-ice concentrations (fraction of ocean area covered by sea ice) than earlier single-channel instruments and, for the first time, a determination of both multiyear sea-ice concentrations and physical temperatures of the sea-ice pack. An estimate of the SMMR wintertime total ice concentration accuracy of ± 7% in both hemispheres has been obtained. As this is an improvement over the estimated accuracies of previous microwave sensors, we are able to present improved calculations of the sea-ice extents (areas enclosed by the 15% ice concentration boundaries), sea-ice concentrations, and open-water areas within the ice margins. This analysis will be published in a book, Arctic and Antarctic sea ice, 1978–1987: satellite passive microwave observations and analysis, due for publication in1992. Some highlights from the analysis are presented in this paper.

An algorithm has been developed for estimating total and multiyear sea ice concentration from passive microwave and surface air temperature measurements. The algorithm was made for use with Nimbus 7 scanning multichannel microwave radiometer (SMMR) data. It is based on radiation physics and may thus easily be modified to suit other passive microwave instruments. A comparison between Nimbus 7 SMMR and aircraft microwave measurements indicates that estimates of total ice concentration are accurate to ±3% and those of multiyear ice concentration to ±10%. These accuracies are not valid during the melt season when the snow on the ice is wet. For the first time such a comparison of independent estimates has been performed to validate the capability of measuring sea ice coverage from space. The ability of the SMMR to follow moving patches of multiyear ice and of rain/wet snow areas has been demonstrated. From the concentration estimates the sharpness of the ice edge can be estimated. The need for accurate concentration estimates for reliable heat budget estimates in the Arctic is also discussed.