Geology Reference
In-Depth Information
(a)
(b)
Sinha's rule
T
a
-
10°C
T
Ts/i
Air
temperature
-
10°C
(c)
T
Ts/i
-
10°C
snow
ice
0°C
0°C
0°C
Figure 3.2
Illustration of N. K. Sinha's rule (coined by CIS operators) to determine roughly the snow‐ice interface
temperature and temperature profiles in snow and ice for freshwater ice covers; bottom temperature of sea ice
should be adjusted to −1.8 °C (Courtsey of M. Johnston, NRC of Canada).
while the rest were covered by snow or remained exposed
to the air. The temperature measurements were transmit-
ted to the Argos satellite system and downloaded to a
laboratory in Environment Canada in Toronto. Argos is a
satellite data collection system dedicated to studying and
protecting the environment. It receives data from any
ground sensor (such as the temperature probe in this
case), identifies the geographic location of the sensor, and
transmits the measurements to a given specific destina-
tion so that the data can be analyzed online (
http://www.
Temperature profiles are shown in Figure 3.3 for selected
days (almost weekly interval) from December to February.
The measured profiles end at 80 cm ice depth. Ice thick-
ness can be estimated from the profiles by assuming that
the ice‐water interface is at −1.8 °C and the profile contin-
ues its linear shape to the bottom of the ice. Ice thickness
was also measured by the operators of the Mould Bay
weather station of Environment Canada. It was 70 cm on
12 December 1996 and grew rapidly to 90 cm on 19
December as the air temperature dropped by about 25 °C.
Ice thickness reached 131 cm on 26 February, 1997. Snow
depth increased slightly from 40 cm on 12 December to
about 48 cm on 19 December and remained virtually con-
stant during the entire period. Figure 3.3 shows nearly iso-
thermal ice temperature profile on 12 December within
both the snow and ice, following a period of subzero air
temperature. However, a very sharp temperature decrease
is noticeable at the snow base (bottom 8 cm).
Once the air temperature dropped below −20 °C by
mid‐December and remained below that level for the rest
of the winter, stable ice temperature profiles were estab-
lished. The profiles demonstrate a strong linear trend in
the ice and the bottom 20 cm of the snow cover and a
slightly nonlinear profile above that level. Note the slight
nonlinearity of the ice temperature near the surface on 9
January. The cause is possibly the effect of precipitation
of salt. This affects the thermal balance inside brine
pockets since it activates the latent heat of fusion. The
average temperature gradient within the ice is 0.111 °C/cm
with a standard deviation ±0.018. Air temperature
dropped from −27.52 to −44.26 °C between 25 December,
1996 and 9 January, 1997. This caused a 6 °C drop in the
ice temperature near the surface and 2 °C at 80 cm depth.
Temperature profiles in the snow feature a fairly linear
trend of decrease from the snow base temperature
upward, yet with a steeper gradient than that of ice tem-
perature. A nonlinear behavior (milder temperature
decease) is observed near the top where the snow tem-
perature becomes nearly equal to the air temperature.
Figure 3.4 shows how fast the top layer of the snow cover
is responsive to changes in atmospheric temperature. The
figure shows the temperature profiles in snow and ice
when air temperature dropped from −24.4 to −32.3 °C
within 36 h during 16 and 17 December, 1996. While the
effect of air temperature is more pronounced in the upper
20-30 cm of the snow pack, the rest of the snow and cer-
tainly the entire ice depth were not affected during that
short period. Variation of air temperature below −22 °C
(i.e., roughly the precipitation temperature of sodium
chloride) does not leave impact on ice temperature
because the ice composition remains virtually unchanged.
Petrich and Eicken
[2009] presented similar profiles of
snow and ice temperature from measurements using ther-
mistor probe frozen into land‐fast FY ice near Barrow,
Alaska, in 2008. They observed the transition from win-
ter to summer conditions in terms of change in the direc-
tion of the temperature gradient.
