88
Fig. 14. Wind velocity around
the SIMI camp site between
February and March, 1994. u-vel
is the eastward velocity and
v-vel
20
15
co
!. 10
'"
,~
g 5
a;
> 0
"0
c:
!: ·5
~
'I: ·10
:>
(/l
-15
-20
30
S. LI, Z. CHENG, AND W.F. WEEKS
l.
J'
I
•
•
'Il
, .
i\I\ J\
/I
~
M
\
f1l ~ I~ II.J
\ k
AJ ~ '\ '/ 1 \rr~ ~
~ 1\1 I!
VI
40
50
60
70
80
90
Julian Dates in 1994
Dalll derived from unidat3 for 75° IlSS· W
to be at this transitional location and recorded the divergence and shear by buoy measurements.
Another significant event occurred between March 9 and 12, 1994. Before that time
period, there was an interval of about 10 days during which persistent west winds prevailed with an average speed around 8-10 m/s. According to Overland (1994, pers. discussion), fractures had already developed under stress but did not show simply
because they did not present themselves as conspicuous features such as leads. However, a change of wind direction by 90 0 from the original west to north gave the fractures an opportunity to open, possibly with significant shear. This is exactly what happened during the time period between March 9 and 12 (marked on the x-axis as day
68). Because the same mechanism applies to all pack ice, the entire pack experiences
significant divergence and shear with the northern part undergoing less significant
deformation simply because of the greater strength of the thicker and larger multiyear ice there.
4.7
Summary
An understanding of ice deformation, especially of sea ice divergence, which produces
leads resulting in thin ice and open water, and sea ice convergence which produces pressure ridges, is critical to many aspects of sea ice research. This chapter describes one
way in which ASF ice motion products can be used to extract quantitative descriptors
of such ice deformation processes. A special, fully automatic computer program has
been designed, tested, and applied for this purpose. The program consists of five components: a tie point locator, an edge point trimmer, a gap filler, a deformation generator, and an extension tracer. The accuracy of the program is ±10/0 for a single grid cell
and ±0.10/0 for a motion field with a size greater than 50 x 50 km.
Fig. 14. Wind velocity around
the SIMI camp site between
February and March, 1994. u-vel
is the eastward velocity and
v-vel
20
15
co
!. 10
'"
,~
g 5
a;
> 0
"0
c:
!: ·5
~
'I: ·10
:>
(/l
-15
-20
30
S. LI, Z. CHENG, AND W.F. WEEKS
l.
J'
I
•
•
'Il
, .
i\I\ J\
/I
~
M
\
f1l ~ I~ II.J
\ k
AJ ~ '\ '/ 1 \rr~ ~
~ 1\1 I!
VI
40
50
60
70
80
90
Julian Dates in 1994
Dalll derived from unidat3 for 75° IlSS· W
to be at this transitional location and recorded the divergence and shear by buoy measurements.
Another significant event occurred between March 9 and 12, 1994. Before that time
period, there was an interval of about 10 days during which persistent west winds prevailed with an average speed around 8-10 m/s. According to Overland (1994, pers. discussion), fractures had already developed under stress but did not show simply
because they did not present themselves as conspicuous features such as leads. However, a change of wind direction by 90 0 from the original west to north gave the fractures an opportunity to open, possibly with significant shear. This is exactly what happened during the time period between March 9 and 12 (marked on the x-axis as day
68). Because the same mechanism applies to all pack ice, the entire pack experiences
significant divergence and shear with the northern part undergoing less significant
deformation simply because of the greater strength of the thicker and larger multiyear ice there.
4.7
Summary
An understanding of ice deformation, especially of sea ice divergence, which produces
leads resulting in thin ice and open water, and sea ice convergence which produces pressure ridges, is critical to many aspects of sea ice research. This chapter describes one
way in which ASF ice motion products can be used to extract quantitative descriptors
of such ice deformation processes. A special, fully automatic computer program has
been designed, tested, and applied for this purpose. The program consists of five components: a tie point locator, an edge point trimmer, a gap filler, a deformation generator, and an extension tracer. The accuracy of the program is ±10/0 for a single grid cell
and ±0.10/0 for a motion field with a size greater than 50 x 50 km.