Abstract
Abstract. Peace River SWIPS (Shallow Water Ice Profiling Sonar) data were analyzed to quantify the roles of frazil ice and riverbed anchor ice grown in situ during the initial buildup of a seasonal ice cover. Data were derived through quasi-continuous monitoring of frazil parameters throughout the water column, providing direct and indirect measures of anchor ice volume and mass growth rates. Analyses utilized water level and air and water temperature information in conjunction with acoustic volume backscattering coefficient data to track and interpret spatial and temporal changes in riverbed and water column ice. Interest focused on four frazil intervals characterized by anomalously low levels of frazil content (relative to simulations with an anchor-ice-free river ice model) as distinguished by two strikingly different types of time dependences. A simple physical model was proposed to quantitatively account for discrepancies between measured and simulated results in terms of the pronounced dominance of anchor ice as an initial source of river ice volume and mass. The distinctive differences in temporally variable water column frazil content are attributed, in this model, to corresponding differences in the stabilities of riverbed anchor ice layers against detachment and buoyancy-driven movement to the river surface. In accord with earlier observations, the stability of in situ grown riverbed ice layers appears to be inversely proportional to cooling rates. The strength of the coupling between the two studied ice species was shown to be strong enough to detect changes in the anchor ice constituent from variations in water column frazil content.
Highlights
SWIPS (Shallow Water Ice Profiling Sonar) results obtained in early studies of Peace River freeze-up periods (Jasek et al, 2005; Marko and Jasek, 2010a, b) were indicative of highly dynamic surface- and frazil-ice environments
This conclusion was seriously called into question when initial reports on subsequent, 2011–2012, SWIPS Peace River measurements (Jasek et al, 2013; Marko et al, 2015) showed frazil fractional volume, F, rarely rises as high as 0.01 % during supercooling periods
Given the heavy reliance of river ice models on frazil ice volume, it was essential that the SWIPS-measured quantities, sV, be linked to volume-related parameters
Summary
SWIPS (Shallow Water Ice Profiling Sonar) results obtained in early studies of Peace River freeze-up periods (Jasek et al, 2005; Marko and Jasek, 2010a, b) were indicative of highly dynamic surface- and frazil-ice environments. Simulations showed the observed timings and magnitudes of surface ice changes were largely explicable in terms of buoyancy-driven surfacing of water column frazil This conclusion was seriously called into question when initial reports on subsequent, 2011–2012, SWIPS Peace River measurements (Jasek et al, 2013; Marko et al, 2015) showed frazil fractional volume, F , rarely rises as high as 0.01 % during supercooling periods. The scope and importance of river ice growth issues suggest that it is long past time to utilize the quantitative outputs of SWIPS measurements to address persisting major gaps in understanding ice cover development Such efforts are initiated below through further analyses of results from the early winter portions of the 2011–2012 Peace River field program. Both other recent work and more productive use of field and laboratory data for ice model improvement
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