The demarcation between fast ice and drift ice or between different zones of drift ice. When used as a climatologic term, for describing the position of the boundary of spreading of ice of any concent
ration or age in any given month or a period based on the observation data for a number of years, the tem should be preceded by a word mean, median, minimum or maximum with indication of the ice cover characteristic after it. For example: Median boundary of multiyear close ice.
Sea ice terminology that describes the differentiation at any given time between fast ice and floating ice, or between areas of ice of different concentrations, types and/or floe sizes.
Same as the wet-bulb temperature when the latter is below 0C and the water on the thermometer is frozen. Note that in dry conditions the wet bulb of a psychrometer may freeze when the air temperature
is appreciably above the freezing point.