M.L. Van Woert
160
Using climatological meteorological data, Kurtz and Bromwich [6] estimated that
38 ni of ice forms during the period May through August. Using the heat flux data
presented in this study, the 1988 and 1990 thicknesses are 37.9 and 38.9 m respectively, which are remarkably similar to the climatological estimâtes provided by
Kurtz and Bromwich [6]. In contrast, the 1989 thickness is 42.7 m, which is 12%
higher than the other 2 years (Table 2). This différence is a conséquence of a higher net heat loss to the atmosphère during 1989 than in the other 2 years (Table 2).
It should be noted, however, that while the general agreement between the historical and présent ice thickness estimâtes is encouraging, serendipity has played a
rôle in this resuit. Kurtz and Bromwich [6] used QNef(t) and Ly values that were
both 75% lower than the values used in the présent study. These factors offset each
other in Eq. (8), resulting in the congruence between the two studies.
The total volume of ice produced for any given time period is not derivable
from the ice thickness estimâtes alone; rather, an estimate of the open water fraction participating in the ice production process is also needed. Thus, the total ice
production is given by
Zto= f AreaÇt) • ^Net ^ dt.
(9)
May
p( - Ey
Kurtz and Bromwich [6] assumed a constant polynya area of 1300 km2 to arrive at
an estimate of 49.4 km3 of ice formation during the 4-month winter period. It is
straightforward to evaluate Eq. (9) using the previously derived heat flux estimâtes
and taking Area(f) to be the product of the north-south dimension of the polynya
(65 km) and the modeled polynya extent, L(t). As is the case for the ice thickness,
the 1988 and 1990 estimâtes are close to those observed by Kurtz and Bromwich
[6] while the 1989 value is higher than the alternate 2 years (Table 2). Again,
serendipity has played a rôle in achieving the close agreement between the historical and présent estimâtes of total ice produced. As mentioned previously for
HTotal, the 4-month average ratio of QNet(t)/Lf is nearly equal for the two studies. In
addition, modeled average polynya extent (Table 3) closely matches the historical
average estimate. Together, these results produce the close agreement between the
historical and présent estimâtes of total ice production in Terra Nova Bay.
Equation (9) also illustrâtes another important point about the environmental
factors controlling total ice production in the polynya. Although a time-dependent
polynya model has been used to describe fluctuations in polynya extent, Terra
Nova Bay is often well described by the steady State polynya model given by Eq.
(2) and (3) [43]. Substitution of Eq. (2) and (3) into Eq. (9) indicates that the total
ice production is independent of both QNe,(t) and Ly-and is a fonction only of the
surface wind speed, U,, and the collection depth of the ice, H,. To the degree that
polynya extent is well described by Eq. (2) and (3), total ice production is highest
during 1989 because the average wind speed is highest during the winter of 1989
(Table 1). Moreover, because of their dependence on total ice production, these
same conclusions hold for annual différences in the total productions of sait and
High Salinity Shelf Water (HSSW), which are described below.
From laboratory experiments it has been shown that Sj=0.31Sw [44], where S, is
the salinity of sea ice and Sw is the salinity of seawater, which is taken here to be
160
Using climatological meteorological data, Kurtz and Bromwich [6] estimated that
38 ni of ice forms during the period May through August. Using the heat flux data
presented in this study, the 1988 and 1990 thicknesses are 37.9 and 38.9 m respectively, which are remarkably similar to the climatological estimâtes provided by
Kurtz and Bromwich [6]. In contrast, the 1989 thickness is 42.7 m, which is 12%
higher than the other 2 years (Table 2). This différence is a conséquence of a higher net heat loss to the atmosphère during 1989 than in the other 2 years (Table 2).
It should be noted, however, that while the general agreement between the historical and présent ice thickness estimâtes is encouraging, serendipity has played a
rôle in this resuit. Kurtz and Bromwich [6] used QNef(t) and Ly values that were
both 75% lower than the values used in the présent study. These factors offset each
other in Eq. (8), resulting in the congruence between the two studies.
The total volume of ice produced for any given time period is not derivable
from the ice thickness estimâtes alone; rather, an estimate of the open water fraction participating in the ice production process is also needed. Thus, the total ice
production is given by
Zto= f AreaÇt) • ^Net ^ dt.
(9)
May
p( - Ey
Kurtz and Bromwich [6] assumed a constant polynya area of 1300 km2 to arrive at
an estimate of 49.4 km3 of ice formation during the 4-month winter period. It is
straightforward to evaluate Eq. (9) using the previously derived heat flux estimâtes
and taking Area(f) to be the product of the north-south dimension of the polynya
(65 km) and the modeled polynya extent, L(t). As is the case for the ice thickness,
the 1988 and 1990 estimâtes are close to those observed by Kurtz and Bromwich
[6] while the 1989 value is higher than the alternate 2 years (Table 2). Again,
serendipity has played a rôle in achieving the close agreement between the historical and présent estimâtes of total ice produced. As mentioned previously for
HTotal, the 4-month average ratio of QNet(t)/Lf is nearly equal for the two studies. In
addition, modeled average polynya extent (Table 3) closely matches the historical
average estimate. Together, these results produce the close agreement between the
historical and présent estimâtes of total ice production in Terra Nova Bay.
Equation (9) also illustrâtes another important point about the environmental
factors controlling total ice production in the polynya. Although a time-dependent
polynya model has been used to describe fluctuations in polynya extent, Terra
Nova Bay is often well described by the steady State polynya model given by Eq.
(2) and (3) [43]. Substitution of Eq. (2) and (3) into Eq. (9) indicates that the total
ice production is independent of both QNe,(t) and Ly-and is a fonction only of the
surface wind speed, U,, and the collection depth of the ice, H,. To the degree that
polynya extent is well described by Eq. (2) and (3), total ice production is highest
during 1989 because the average wind speed is highest during the winter of 1989
(Table 1). Moreover, because of their dependence on total ice production, these
same conclusions hold for annual différences in the total productions of sait and
High Salinity Shelf Water (HSSW), which are described below.
From laboratory experiments it has been shown that Sj=0.31Sw [44], where S, is
the salinity of sea ice and Sw is the salinity of seawater, which is taken here to be