•
SCOTIAN SLOPE CURRENT VARIABILITY FROM
TOPEXIPOSEIDON ALTIMETRY
••
Guoqi Han
,
Biological and Physical Oceanography Section
Northwest Atlantic Fisheries Centre
Fisheries and Oceans Canada
S1. John's, NL Canada AIC 5XI 2002
Can. Tech. Rep. Hydrogr. Ocean Sci. 224
"
ILl
"'I"
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,
Rep. Hydrogr.
Scotian Slope Current Variability
. 224
TOPEXJPoseidon Altimetry
by
Guoqi Han
Biological and Physical Oceanography Section Northwest Atlantic Fisheries Centre Fisheries and Oceans Canada St. John' NL Canada 1 5Xl of Supply and
No. Fs 97-1
2000
ISSN 0711-6764
citation
Variability from TOPEXlPoseidon Altimetry. Can.
Rep.
p.
11
TABLE OF CONTENTS
PAGE
of List
................................................................................................................................ v ABSTRACT .................................................................................................................................. vii RESlTME....................................................................................................................................... Vll 1. Introduction ................................................................................................................................ 1 Methodology ..................................... .
.. .................................................................................. 1 3. Results ......................................................................................................................................... 3 ................................................................................................................................ 5 5. Summary and Discussion ............................................................................................................. 6 Acknowledgement ........................................................................................................................... 7 ....................................................................................................................................... 8 of Tables
Table 1.
................... 9 IV of
and adjacent
and deep oceans with a schematic
The labeled lines are the
TIP
tracks on
thick dashed line indicates the location of a
which the analysis is perfonned.
current; SWC: Slope Water current. Gulf
hydrographic
section.
rings are depicted as
. .................................................................................... 10 Figure 1. Map
height anomalies
Track 071 on October
Figure 2. (a) Along-track profiles TIP sea
20, 1999:
(thin line) vs. smoothed with the digital
(b)
Associated cross-track geostrophic currents ........................................................................... 11
3.
TIP sea level anomalies (thin line) and associated
cross-track geostrophic surface current
(thick
positive westward)
track 071
from August-November
................................................................................................. 12
Climatological
currents over
Scotian Slope
from Han
et a1.'s (1997) model results. Also depicted are positions
shelf/slope
(thick dashed
lines) and
Gulf
northern boundary (dash-dotted lines)
the study period
the
next subsection) ...................................................................................................................... . 5. The positions of the Gulf Stream northern boundary (dash-dotted line) and
and the warm temperature
of surface water (solid line)
satellite thennal imagery
the week August 21,
..................................................... 14
6.
of current
at nominal 1000-m (thick line)
4000-m (thin line)
water depths on the four descending tracks .............................................................................. 15
7.
variability over
Scotian Slope
from the TIP altimetry data from
depicted are positions of the
1992 to 2000 and plotted as twice the nns values.
Gulf
northern boundary (dash-dotted
shelf/slope front (thick dashed lines) and
line)
the period ................................................................................................................. 16 8. Variability of
current
from 1992 to 2000 plotted as twice
nns values (thick
thin
twice the rrns values when Han et
a1.'s
means are included.
depicted are positions of
front (thick
dashed lines) and the Gulf
northern boundary (dash-dotted line)
the period .......
over the
on the frontal
personal communication, 2001) from 1992 to 2000. A
total of
days was included in
Also depicted are positions of the shelf/slope
line) for the
front (thick dashed
the Gulf Stream northern boundary
period ..................................................................................................................................... 18
10.
(b) 050, (c) 088,
of the altimetric current anomalies nonnal to the
for
(a) 012,
(d) 126.................................................................................................... 19 v
11.
distribution of monthly sea level
(m)
data ............. . Figure 12. Seasonal-mean currents over the Scotian Slope in (a) winter, (b) spring, (c) summer
and (d) fall:
anomalies plus
e t ' (1997) model means. Also depicted are
positions of the shelf/slope front (thick dashed lines) and the Gulf Stream northern boundary
(dash-dotted line)
each season ................................................................................ .
Figure 13. Seasonal
sea
anomalies over the Scotian Slope,
for four
based on bathymetry. The seasonal means are
with a five-point moving
Figure 14. Seasonal TIP sea level anomaly distribution over the Scotian Slope in the time-latitude
domain for track 050 and 088, including both the Scotian Shelf and Slope.
seasonal
mean anomalies are smoothed with a 5-point
The dashed lines indicate water
depths ..................................................................................................................................... . Figure 15. Winter current
from altimetric anomalies and
et's (1997) model means
over the Scotian
Also
are pOSItIOns the shelf/slope front (thick dashed
lines) and the Gulf Stream northern boundary (dash-dotted lines) in individual winters ....... 28
Frontal analysis data
December 1999, showing ring
(solid line) and the
front (thick dashed lines) and
Gulf Stream northern boundary
positions of the
(dash-dotted lines)
altimetric current
................................. ..
Figure 17. (a) Gulf
rings (solid lines) on Sept.
1999 and altimetric cross-track current
anomalies (arrows) on Track 071 on
30, 1999; (b) Comparison of the altimetric crossof the
track current anomalies and ADCP data (thick an·ows). Also depicted are
shelf/slope front
dashed lines) and the Gulf
northern boundary (dash-dotted
lines) ....................................................................................................................................... 31
18. CTD temperature and salinity distribution across the ADCP section and Comparison
of the steric height relative to the 500db and the TIP sea level anomalies on
12.
1 for location ................................................................................................................... .
19. (a) Climatological
current
in
summer and fall
over the Scotian
from Han et 's (1997) model solutions. (b) The altimetry-rninus­
model
are for the four seasons. Also depicted are positions of the shelf/slope
(thick dashed lines)
the Gulf Stream northern boundary (dash-dotted
for
season ..................................................................................................................................... .
current variability at crossovers, shown as twice the rms values. Also
front (thick dashed lines) and the Gulf Stream
depicted are positions of the
northern boundary (dash-dotted lines)
the study
................................................ 36
VI
ABSTRACT G.
2002.
Rep. Hydrogr.
Slope Current Variability from TOPEXIPoseidon
Sci.
viii +
p.
Tech.
sea
middle
to early 2000 are analysed to investigate
data with
current variability over
Scotian Slope.
first treat I-second sea
de-spiking and smoothing
the along-track direction,
then calculate sea level
relative to local means for
period. Geostrophic
current anomalies nonnal to ground
are
derived from the sea level anomalies.
surface currents nonnal
circulation
to
ground tracks are also obtained from the solutions of a regional
model. Model means
current anomalies are superimposed to produce nominal
variability. Statistical
absolute CUlTents. Derived currents are analysed for spatial and
analyses are
out
on topographic
for longshore and cross-shore variability
Slope Current.
altimetric results reveal prominent current variability over the
The intensification seems to be associated
Slope, intensifying
the west and
and with the proximity to
Stream.
occurrence of Gulf Stream wann core
of these
often
and interannual
are
rotational
The slope circulation from the altimetric observations is
in winter/fall and
weakest
summer/spring.
analysis
indicates that the winter circulation was
strongest in 1998 and weakest in 1996. The altimetric currents are consistent with frontal
CTD observations, and numerical model
data, ADCP
RESUlVrE
G.
2002.
Rep. Hydrogr.
Slope
Sci.
Vlll
Variability from TOPEXfPoseidon Altimetry.
+ 36 p.
donnees
des courants la surface
abord
et ni velees
puis
de la mer sont calculees en fonction
pendant cette
anomalies
surface perpendiculairement aux trajectoires au
niveau
la
solutions d'un modele regional
par elements finis pennettent
surface
qui sont
au
On superpose
moyennes du modele et les
anomalies altimetriques des courants
de produire des courants absolus nominaux.
courants
ainsi
sont
la
spatiale et temporelle.
analyses
basees sur
sont
obtenir
des
du littoral et perpendiculairement au littoral sur
altimetriques
courants Ie
indiquent la principale variabilite
courants sur Ie talus
s'intensifie vers
l'ouest et Ie sud.
attribuable aux
anneaux a noyau
dans
sur Ie ni veau
talus
de la
a
Gulf Stream
qu'a la
souvent 1 m/s.
rotation
ces anneaux
saisonnieres et
D'apres
est a son maximum pendant 1
la
en
fronto!ogiques, aux
Vlll
1. Introduction
The Scotian Slope (Fig. 1) and Rise off Nova Scotia is generally considered to be a region
of strong current variability (Smith and Petrie 1982; Csanady and Hamilton 1988). The mean
circulation is believed, to be a broad cyclonic gyre in the Slope Water, between the northeastward
Gulf Stream carrying warm and saline water and the equatorward shelf-edge current mainly
composed of the colder and fresher Labrador Current water and the Gulf of St. Lawrence outflow
water. Meanders and anticyclonic warm rings pinched off from the Gulf Stream often modify the
Slope Water circulation. These rings generate significant temporal and spatial variability in currents
(Joyce, 1991) and provide an important mechanism for shelf/deep-ocean exchange processes. It has
been found that the Labrador Current transport and the Gulf Stream position experienced significant
interannual changes in the past decade.
Studies of Slope Water circulation including both observational programs and theoretical
studies have been limited, compared with those of the Gulf Stream and the shelf areas. Therefore,
our present quantitative knowledge about the currents and circulation in the Slope Water region is
limited, particularly over the Scotian Slope. Recent mooring projects initiated under DFOIPERD
programs together with drifter studies (Fratantoni, 2001) have started a new phase'of observing the
Slope Water currents variability. Satellite altimetry provides instantaneous sea surface height
measurements relative to a reference surface, and has been used to study the Gulf Stream and the
shelf edge currents (e.g. Han, 1995). Earlier exploratory studies also indicate TIP altimetry's
potential in complementing in situ measurements for quantifying current variability and
understanding dynamics in the Slope Water region (Han et al., 2000; Han, 2002).
The primary purpose of this study is to use TOPEXfPoseidon (TIP) satellite altimeter data
for estimating surface current statistics for the Scotian Slope. In conjunction with front analysis data
and other hydrographic data, this manuscript describes and discusses major current features.
Knowledge of currents and their variability will be particularly important for offshore oil and gas
acti vities in the deep waters of the Scotian Slope.
In section 2, we describe the TIP data and processing techniques, derivation of surface
currents, and frontal analysis data. Section 3 presents sea level and currents features and statistics at
various temporal and spatial scales. Comparisons of altimetric results with other observations and
model solutions are made in Section 4. Section 5 provides a brief summary and discussion.
2. Methodology
2.1 TIP altimeter data
We used corrected TIP sea-surface height data for the period from mid 1992 to early 2000,
obtained from NASA Pathfinder Project. Four TIP ascending tracks and three descending tracks
were selected across the Scotian Slope and Rise off Nova Scotia (Fig. 1). The satellite has a
nominal repeat cycle of 10 days, and there are 276 observations at each location. The along-track
resolution is about 6 km. The data were corrected based primarily on the principles in Benada
(1997) for various atmospheric and oceanographic effects:
1
1)
2)
ionosphere
4) electromagnetic
height;
5)
barometric
6) ocean,
solid
TIP microwave
from the
Centre for
model;
on the dual frequency altimeter measurement;
(due to ocean wave influences) using
significant wave
sea surface height to atmospheric pressure
pole tides.
The standard
Goddard Space Flight
precise orbit
Model-3 (JGM-3)
used to produce
sea surface
km and a flattening
ellipsoid with equatorial radius of 6378.
and
on the Joint Gravity
relati ve to a
of 11298.257.
spikes in
sea-surface height data were removed with an
filter. A mean sea
was constructed
the available TIP
mean sea smface. Both
geoid and mean
the sea smface
relative to
oceanic topography are removed
procedure. An
digital
with an
approximate
scale of 18
was performed to
influences on
current
height data unless indicated
will be based on the
anomalies for Track 071 are shown in
2 for October 20,
otherwise. The sea
3
August-November
1999 and in
2.2 Deri vation
surface current
From the TIP sea
2 and 3,
surface currents
to the track
of surface current
these are
about the mean only, ;)V\.-lall..\.l with the
sea surface
local wind-driven flows are not
pressure
Calculation
currents
approximate way of
absolute surface currents is
surface current anomalies with
mean circulation
study we
used climatological-mean currents from
model solutions. The
surface currents are
components
to the track were then
We can see a
shelf edge and
upper continental
a northeastward current along the lower
upper slope
slope.
likely that these model currents underestimate
mean flows offshore of
topography offshore
1000-m isobath.
model used fals.e
Frontal analysis
analysis data provide
information on the location of
fronts (shelf/slope front, Gulf Stream rings
Stream)
on satellite
2
imagery (e.g., Drinkwater et al., 1994). Frontal positions have been digitized from
"Oceanographic Features Analysis" charts published by NOAA up to the end of September 1995
(Drinkwater K. and R. Pettipas, personal communication, 2001). Starting in April 1996, the
charts have been referred to as "Jennifer Clark's Gulf Stream". After digitization, the positions of
the northern boundary of the Gulf Stream and the Shelf/Slope front were averaged at each degree
of longitude for each chart.
As an example, Figure 5 shows the shelf/slope front (the narrow boundary separating cool
shelf water from the warmer Slope Water immediately offshore), the Gulf Stream northern
boundary separating the Stream from the Slope Water, and warm temperature patches with some of
them associated with Gulf Stream warm core rings (WCR), for the week of August 21, 1995. A
Gulf Stream ring is apparent over the continental slope off Georges Bank and the western Scotian
Shelf (where Tracks 071 and 012 cross).
3. Results
3.1 General description
The sea surface height anomalies on Track 071 (Fig. 3) show large along-track variations in
the Slope Water region (39-42'N), associated with fluctuations in the Gulf Stream position and the
occurrence of WCRs. The associated current anomalies (normal component) often have magnitudes
of order 1 mis, particularly south of 42 'N (Fig.3). Anticyclonic ring circulation apparently occurred
in September-October 1999 between 40 and 42 'N, indicated by the negative (eastward) current
anomalies around 41'N between September 11 and October 20.
There are significant interannual variations in the current anomalies, as seen in time series
of the anomalies near the 1000- and 4000-m isobaths (Fig. 6) on the descending tracks that are
approximately normal to the shelf edge (Fig. 1). The seasonal and intra-seasonal changes are also
apparent. For Tracks 12 and 50 the currents variability at the 4000-m water depth is much larger
than that at 1000-m depth, while differences for Tracks 88 and 126 are not evident. This is
consistent with the increasing distance of the Gulf Stream from the continental slope as one
proceeds eastward from Georges Bank towards Grand Bank.
Figure 7 shows the root mean square (rms) values of the altimetric sea level anomalies.
There is generally increased variability as one proceeds offshore towards the Gulf Stream. Typical
values are 10 cm over the upper slope. The magnitude increases westward, particularly over the
lower slope and continental rise.
Figure 8 shows the spatial distribution of rms variability of the cross-track currents on the 7
tracks. Over the Scotian Slope, the variability increases westward and offshore, especially in the
western part. This westward intensification can be attributed to proximity of the Gulf Stream to the
shelf edge and increased WCR acti vity to the west (Fig. 9). The percentage occurrence of WCRs for
a selected area is computed as the ratio of the number of days when a ring's average radius is 90 km
or larger and its average center is located inside the area, to the number of total days. We also
3
calculated the percentage occurrence with average radii of> 60 and 120 km respectively and found
that the relative occurrence among the four areas is insensitive to the choice of the radius. The RMS
values for the four bands for each track also demonstrate the decrease in anomaly strength with
distance from the Gulf Stream.
To provide further statistical information on the spatial structure of the current anomalies on
the 4 cross-slope tracks, four along-track bands were selected based on bathymetry: (i) 200-1000m
(referred to as upper slope), (ii) 1000-3000m, (iii) 3000-4000m (referred to as lower slope) and (iv)
4000-4500m (referred to as continental rise). Fig. 10 presents percentage occurrence of CUlTents for
the four bands and shows the rms values of the altimetric current anomalies. Overall, the variability
is strongest with higher occurrence of extreme currents on Tracks 012 and 071 off Northeast
Channel and Georges Bank, and weakest with lower occurrence of extreme currents on Track 126
off Sable Island Bank (also see Table 1).
The inclusion of the present model mean currents does not change the statistics significantly
(especially over the lower slope), indicating the eddy kinetic energy is overwhelmingly dominant
over the mean kinetic energy for the Scotian Slope surface circulation. Nevertheless, It is likely that
inclusion of a refined model mean with a more realistic representation of the Gulf Stream and
associated currents would result in quantitative changes in the current statistics, particularly
offshore of the 1000-m isobath.
3.2 Seasonal variability
The TIP sea level anomalies at each location are averaged monthly and over all years and
plotted in the month-latitude domain for each track (Fig. 11). There are large seasonal changes,
higher in summer and lower in winter. The magnitudes generally increase westward and offshore.
Typical ranges are 10 cm for the upper slope, and up to 20 cm for the lower slope. The seasonal
cycle seems to be associated with the thermal expansion and contraction as a result of solar heating
and advection and possibly with the south-north movement of the Gulf Stream position. The
monthly means are not only consistent with the annual sea level harmonic of Han et a1. (2002), but
also provide more information on intra-seasonal variability.
Altimetric seasonal-mean current anomalies (Jan-Mar, Apr-Jun, Jul-Sep, and Oct-Dec for
winter, spring, summer and fall respectively) averaged over all years were calculated from the TIP
current anomaly data. Long-term seasonal-mean current fields (Fig. 12) were then constructed by
adding the model mean flows (Han et aI., 1997) to the altimetric seasonal-mean anomalies. The
southwestward shelf edge current is strongest in winter/fall and weakest in spring/summer. The
seasonal range amounts to 10-20 cmls. The eastward slope current (with the mean current toward
the northeast (Fig. 4)) over the lower continental slope in the vicinity of the 4000-m isobath seems
stronger in winter/fall, except for track 050 in winter. The rms current magnitude of the long-term
seasonal means is 12.2,8.0, 8.0 and 10.8 cmls for winter, spring, summer and fall, respectively.
3.3 Interannual variability
For each cross-slope ground track, the TIP sea level anomalies at each location are first
4
and
(ii) 1000-3000m, using a the sea level
a pronounced
Over the lower
interannual cycle, with an
magnitude towards deeper waters
13). Sea level
1994 to 1996, with a
on all the four tracks nA"'"'''' a significant sea level fall
rapid rebound after 1997. The sea level range amounts to 10-20
fluctuations at shorter
among the tracks
upper continental
the 200- and 1000-m
sea
variability
less. In fact, the sea level
out of phase with
over the Scotian Shelf (Han,
illustrate details of
uU"uu,,, plot of sea level
up/down is highly coherent across the
in certain periods.
were large sea
the coast) over the
the upper continental
are associated with
shelf-edge currents (Fig.
mean shelf-edge flow is directed southwestward (Fig. 4).
we examined the
14). The sea
and slope is
(upwards
1997 and early 1998,
this period since the
Evaluation
1
analysis
data
the same location
over 1 mls. These
and are usually
Scotian Shelf. Altimetric data not
the infrared images, but
currents.
from
circulation features are
images. When
analysis data, the
show anticyclonic
17a).
geostrophic currents associated with these
drift westward and move
They can last a few
if they move onto the
confirm the occurrence
rings revealed
provide important quantitative information about associated
and CTD data
On September 27
Stream/WCR front on
can see approximate
18 shows the temperature
shows that the temperature is
calculated from the
at a section across a
Nova
et
1999). The near
Current Profiler) data are presented in Fig.
eastward current on the
of the ring.
CTD (Conductivity-Temperature-Depth) data, which
18° and salinity is 3 unit
WCR water. The
and salinity data
to the 500db is consistent
5
with
altimetric sea level anomalies on Track
that they are translated to be equal at the
Hydrodynamic model
et
's (1997)
currents over
rms current magnitude is 11.3, 8.9, 10.1
for winter,
In general,
model results show
southwestward
Slope
current in winter/fall,
to the altimetry
there are notable discrepancies in some areas.
model-altimetry rms current difference
8.5 and 4.9
winter, spring, summer and fall, respectively.
that the altimetry
provide geostrophic current estimates
from 1
to 2000, and the
solutions represent
seasonal-mean
and Discussion
We have used
data for the period
1992 to 2000 to study sea level and
current variability over
Scotian Slope. In conjunction with frontal
data and
hydrodynamic model
TIP data reveal
current variability over the Slope at
a-;:)c;a;~VIJlal, seasonal and interannual scales.
altimetric current
variability
and
Scotian
periodic occurrence
the Gulf
warm core rings.
current
variability is associated with
occurrence of the anticyclonic rings. The inclusion
the model
mean current does not
current variability
edge.
ivU,U"J0
sea level is
current is
of sea level
TT",",v·..,r"" The shelf
in summer and lower in winter, with larger
winter and smaller
summer. There is ....".r,n,-,o",,'''''; interannual
rebound
higher in
current is strongest in
geostrophic current anomaly normal to
ground track is
to be an
of the total
current anomaly
to the neglect of the along-track current
component (dependent on sea surface anomalies
to the track). Under
assumption of
isotropy, the RMS values for
total geostrophic current anomaly can be estimated as those for the
component
by a factor of 1A.
total rms
data at crossovers
descending
tracks allow us to
current
at
We have
spatially and
at crossovers.
current anomalies normal to
and
to generate
normal-to-track
are then transformed into the eastward and northward
mean square
The total rms current variability is the
root of the sum of
the peak
Inclusion of wind-driven currents and mean flows would likely
of the total
current.
6
The altimetry
variability associated
depth could
obtained
combining
available (Han
Tang, 1999).
implemented.
quantifying
current
slope.
of geostrophic currents at
with
hydrographic
when
UHl:H",.'"
,,,,,U:,",Ul with selected cross-slope
should
Acknowledgement
assistance in
B. Petrie
insightful
for
frontal
providing
and ADCP
project was
through the
Factor Program
the Federal
Program
Energy, Research
Development (PERD), the
Change Impacts on the
Energy
PERD,
Canadian Space
the Canadian Hydrographic
Transport Canada.
data were
from NASA
Propulsion Lab and Pathfinder ~rf'\lp('t
7
References
Jet Propul.
T.L.
1994.
data for
northwest
Stream
front
northern boundary of the
Can. Data. Rep. Fish. Ocean Sci.
iv + 103 pp.
Circulation
slopewater, Continental
Res., 8,
1990's observed with
circulation during
2001. North Atlantic
Res., 106,22067-22094.
1.
and Shelf Circulation
Altimeter. In: Oceanographic Application of
Ikeda
Dobson F.W. (ed.), CRC
1997.
P.C.
and lW.
Res.,
Han
the Labrador Current
from
Res., 104, 18047-18057.
Slope current variability
altimetry: an
exploratory evaluation. DFOIPERD
6pp.
G., 2002: Interannual sea level variations in the Scotia-Maine region in the 1990s. Canadian
1.
(4),58
Han
1. Phys. Oceanogr.,
810.
contributions to warm-core
Rev. Geophys., 29, 610-616.
Low frequency circulation at the edge
Scotian Shelf, 1. Phys.
U'PrTnIHJr,
Smith,
12,
R. Boyce and L. Petrie, 1999. Report on C.S.S.
Institute of Oceanography.
8
~,~,_~~
Cruise 99-028. Bedford
Table 1. Percentage
Anomalies.
of TIP-deri ved
Track 126
1
Depth (m)
200-1000
1000-3000
3000-4000
1.7%
0.0%
0.0%
19.9%
1.5%
0.1%
0.0%
18.0%
2.6%
0.3%
34.5%
9.6%
0.7%
0.1%
35.6%
12.1%
4000-4500
0.3%
9
0.0%
0.1%
1
0.0%
18.5%
I
I
46
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45
44
zo
Q)
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-.J
\
\
\
\
41
\
\
/
/
\~Ulf
Stream\
\
\
•
Atlantic
Ocean
\
39~~--~~--------~~----~~~~~~~--------~--------~
-68
-66
-64
-62
-60
-58
-56
LongitudeOW
Figure 1. Map showing the Scotian Slope and adjacent shelf and deep oceans with a schematic
representation of the circulation. The labeled lines are the selected TIP ground tracks on which
the analysis is performed. The thick dashed line indicates the location of a hydrographic survey
section. SEC: shelf-edge current; SWC: Slope Water current. Gulf Stream rings are depicted as
ellipses.
10 1
(a) Track
1999
Level Profile on
0
0.3 .
0.2 .
0.1
0
1
38
39
(b)
071 Current Profi
on 20-0ct-1999
1
38
39
40
41 Latitude (ON) (a) Along-track
1999: un smoothed (thin
vs. smoothed
cross-track geostrophic currents.
43
44
for Track 1 on
(thick line). (b)
11 Track 071 Along-Track Profile
I>­
... . ·
0.5
~
E
0
c
<l:
<l:
I
(f)
(f)
02~Aug-19.99
~
.
0
.
.
· .
1.0
· .
1.0
.
'
.
'
·
.
0
0
. ..
-0.5
· .
0
.
.
. .
-
. . . . . . . . .
1>­
iii
.
.....
-0.5
., Track 071 Along-Track Profile
...
-1.0
-1.0
E
0
c
«
E
...
<II
:;
u
., I>­
. . . ..
0.5
~
E
0
c
<l:
<l:
I
(f)
(f)
· 12~Aug~1999 · .
~
·
·
....
0
-
fO~Oct~·19.99 ·
. 1.0
..
.
.
.
.
.
.
·.
0
0
. ..
-0.5
. ...
.
.
.
· .
-1.0
1>­
iii
.
.
·
·
·
-0.5
....
1.0
0
E
0
c
«
E
-1.0 t<II
::J
U
E
>­
0.5
~
E
0
c
<l:
<l:
I
(f)
(f)
\:J.
. .
.. . : . ....... . 22~Aug-1999
·
0
· . 1.0
.. 20~Oct~19:99
0.5
·.
1.0
_.
0
.
.... . . ~~
·
·
.
.
...
.
.
.....
-0.5
0
-1.0
.
0
i
>­
iii
E
0
c
«
E
-1.0 l!!
-0.5
:;
u
I>­
. · 0 1~Sep~19.99 .. 1.0
0.5
. . . -.... 30~Oct~19.99
0.5
·.
1.0
i
0
c
~
E
0
c
<l:
<l:
I
(f)
(f)
. Missing ..
0
-0.5
. . . . . .
0
...
-1.0
0
...
-0.5
. .. .
>­
iii
E
0
«
E
-1.0 ~
::J
., U
:[
. . 09-Nov~1999 . 1.0
· 1.J~Sep-1999
. 1.0
.
>-
Cij
E
0
0
c
<l:
<l:
I
...
0
-1.0
-1.0
(f)
(f)
0
l
>­
iii
E
0
c
«
E
~
:;
u
., I>­
...
0.5
· 20~Sep-1999
. 1.0
1.0
0
c
<l:
<l:
I
(f)
(f)
>­
~
~
E
E
0
...
0
-0.5
0
E
0
c
«
E
l!!
...
-1.0
::J
38
40
42
Latitude (ON)
44
38 40
42
44
u
Latitude (ON)
Figure 3. Along-track profiles of the smoothed TIP sea level anomalies (thin line) and associated
cross-track geostrophic surface current anomalies (thick line, positive westward) for track 071 from
August-November 1999.
12
/
/
46
\
/
\
/
\
/
\
\ /
j\
/
\
\
\
I
/
\
\
/
/
\
/
\
\
/
\
\
-60
LongitudeOW
currents over the
are positions of the
,-u.J"...,.... lines) for the
13 ..
47,---------.-----,-~~--------,_----_,,_~--------_r~.--~~~
46
21-Aug-1995
45
44····
41
.,
.
,
-.,;;
~
,--,,-,,-­
0
-66
"
\ I
'"
40
39
-68
,
,
-64
­
-62
-60
-58
-56
LongitudeOW
Figure 5. The positions of the Gulf Stream northern boundary (dash-dotted line) and shelf/slope
front (dashed line) and the wann temperature patches of surface water (solid line) derived from
satellite thennal imagery for the week of August 21, 1995.
14 Track 012 Time Series
_ 1 .50
~
I--'---'-~I'---'---;=:C:=====:C:=====:C:=====:C:====-=;-l
';: 0.75
co
E
g 0.00
-
(-65.67,41.79)
(-63.37,38.62)
«
C
(J)
L..,
L..,
-0.75
:::J
o _1 .50 '-----:-::--'----=-'::---L--:::-:--"--'-----:-::c---'L------=-_=__-----'---------'=-=--'--------=~---'-----~_=__-----'-____::_::_------'
92
93
94
95
96
97
98
99
00
99
00
Track 050 Time Series
_
--
1.50
(J')
E
';: 0.75
co
E
0
c 0.00
-
(-63.49,42.63)
(-60.78,38.98)
«
C
(J) -0.75
t:
:::J
0
-1.50
92
93
94
95
96
97
98
Track 088 Time Series
_
1.50
(J')
Depth: 954(m)
Depth :3973(m)
---E
';: 0.75
co
E
0
c 0.00
«
C
(J) -0.75
'­
'­
:::J
0
-1.50
92
93
94
95
96
97
98
99
00
98
99
00
Track 126 Time Series
_
--
1.50
(J')
E
';: 0.75
co
E
0
c 0.00
«
C
(J) -0.75
t:
:::J
0
-1.50
92
93
94
96
Year
95
97
Figure 6. Time series of current anomalies at nominal lOOO-m (thick line) and 4000-m (thin line)
water depths on the four descending tracks.
15
47,--------,-----,~~---------.~----~~---------.~--~~~
I
I
/
I ~/
I
20 em
I
I
46
45
I
'/.
44
"
/~
(
\
"
,.'
c:' J
\
()
\ .
'
I '
I
. ,',
\
'j
\ i. , /
, l·
\
:'1 " [('
.-
X
\
\
I
\
I
\
\
I
\ I
\
/\
41
\
\
..... ..... "..'-1-
I
I
40
I
\
I
\
\
\
39~~~~~~-------=~~--~--~~~~~~--------~--------~
-68
-66
-64
-62
-60
-58
-56
LongitudeOW
Figure 7. Sea level variability over the Scotian Slope calcul ated from the TIP altimetry data from
1992 to 2000 and plotted as twice the rms values. Also depicted are positions of the shelf/slope
front (thick dashed lines) and the Gulf Stream northern boundary (dash-dotted line) for the
period.
16 47,---------~-------r~----------.-~--~~~----------,,~/,-/-/-~,>--,-,
, ....,
50 em/s
1i:iiiiiiiiiillil
46
45
zo
Ul
-g 43
-m
:;:::;
.....J
\
\
\
/
\
\
/
\
I
1\
41
I
I
\
40
I
\
I
\
\
\
39
-68
-66
-64
-62
-60
-58
-56 LongitudeOW
Figure 8. Variability of the altimetric cun-ent anomalies (sub-sampled spatially) from 1992 to
2000 plotted as twice the rms values (thick gray lines). The thin lines represent twice the rms
values when Han et a!.'s model means are included. Also depicted are positions of the shelf/slope
front (thick dashed lines) and the Gulf Stream northern boundary (dash-dotted line) for the
period.
17 47,---------.-----,-~7r--------_.~--~,,~r_--------~~/--.~~~
"
/
..... ,
/ -/
'
//
46
/
,
\'
\
.'.
' \. -
'<,
\
'.
45
f
~
<"",,\"
'\\
\
.) "-- ~ -=-=:-"-:-".: ',."
42 .
\
/
\
/
\
\
41
/
\
\
I
\
I
\
/
\
;'
;
.... ...
\
'-'- ,
\
40
\
\
\
39L-~---L~~--------~;~~----L---L-~~~~~-----------L--------~
-68
-64
-62
-60
-58
-56
LongitudeOW
Figure 9. Percentage occurrence of WCRs over the Scotian Slope based on the frontal analysis
data (K. Drinkwater and R. Pettipas, personal communication, 2001) from 1992 to 2000. A total
of 989 days was included in the analysis. Also depicted are positions of the shelf/slope front
(thick dashed lines) and the Gulf Stream northern boundary (dash-dotted line) for the period.
18 Track 012 Depth of 200 - 1000 (m)
31.8%(>0.25m/s)
0.1 %(>1.00m/s)
700
1600
600
1400
1200
C
1000
::I
C
:::l
o
o
U
U
800
300
600
200
400
100
f
a
-1
1
a
2
Current Anomaly (m/s)
1
2
Current Anomaly (mls)
Track 012
1000 r---;::~====='====::::::.~==:::::;-]
900
1000
800
700
800
600
c
C
:::I 8
5 500
600
u
400
400
300
200
200
-
100
I
-1
a
a
2
Current Anomaly (m/s)
Figure 10.
of the
(b) 050, (c) 088, and (d) 126.
2
Current Anomaly (mls)
current anomalies
19 to the track,
(a)
Track 050 Depth of 1000
3000
= 0.21)
20.4%(>O.25m/s) 2.6%(>0.50m/s)
0.0%(> 1.00m/s) O.0%(>1.50m/s)
I
I
2500
600
-
500
1::
::J
a
3000 (m)
200 0
400
1::
:::l
8 1500
o
300 1000
r-­
200 100 o~----~--~~~~--~------~
-2
I
50 0
o
-1
0
2
j
-1
i
o
2
Current Anomaly
Current Anomaly
Track 050 Depth of 4000
4500 (m)
(RMS = 0.31)
1200
1600
1000
1400
1200
1::
:::l
800 1000
1:: :::l
8 600 o
o
800
400 600
400
200 200
o
O~----~~-LJ-L-~~~----~
2
-2
-1
o
Current Anomaly (mls)
Current Anomaly
10 (continued).
20 2
Track 088 Depth of 1000
3000 (m)
(RMS == 0.21)
1800 1600 600 1400 500 1200 C
400 ::J
C
::J
o
o
1000 ()
()
800 300 600 200 400 100 200 -1
0
Current
Anf,m",IV
1
0
-1
2
(m/s)
1
Current
(m/s)
Current
(m/s)
2
1600
1000
1400
800
1200
§ 1000
C
::J
8
o
()
600
800
400
600
400
200
200
-1
0
1
2
Current Anomaly (m/s)
10 (continued).
21 2
Track 126 Depth of 200 - 1000 (m)
2500r-~~~~~~~~~==~
1000 800 1500 c:l
C
:l
0
0
0
0
600 1000 400 500 200 o
-1
2
Current Anomaly (m/s) Track 126 Depth of 3000
4000 (m)
Current Anomaly (mls)
(RMS '" 0.20) 2500r-~~~~~~~~~==~
(RMS '" 0.22)
1200
1000 2000 800 1500 C
C
::::l
:l
0
0
0
0
600
1000 400 500 200 O~i______~~~~~~__~_____
-2
-1
0
1
Current "'''1''''''''1\1 (m/s)
10 (continued).
2
-1
0
Current Anomaly (m/s)
2
Track 012
0.2
0.2
41
41
o
J F M A M J J A S
a
N 0
J F M A M J J A S
a
N 0
-0.2
Month Month
126
Track 088
0.2
43.2
43
42.8
42.6
0
42.4
42.2
42
J F M A M J J A SON 0
J F M A M J J A SON 0
Month
Month
Figure 11
distribution
monthly sea level
(m) from
data.
-0.2
Track 071
Track 109
0.2
42.5
42
41.5
41
0
40.5
40
39.5
39
J F M A M J J A S 0 N 0
J F M A M J J A SON 0 Month Month Track 020 J F M A M J J A SON 0 Month 11 (continued).
-0.2
Spring
Winter
LongitudeOW
Fall
Summer
39~~~~~~~~~--~--~
-68
currents over
Scotian
in (a) winter, (b) spring, (c) summer
and (d)
anomalies plus Han et a1.' (1997) model means. Also depicted are
(thick dashed
and the
northern boundary
positions of the shelf/slope
(dash-dotted
for
season.
25 Depth: 200-1000 (m)
Depth: 1000-3000 (m)
0.2
0.15
0.1
0.05
0.05 o
0
-0.05
-0.05 -0.1 -0.1
-0.15
-0.2 -0.15 92 93 94 95 96 97 98 99 00 Year
-0.2 92 i9CC:3-"-=9:-:4--'-=9-=-5--'----=-96-=-'-=97=-'"""9::-:8::-'-:9=-=9:-'-:0:-':0--'
Year Depth: 3000-4000 (m)
Depth: 4000-4500 (m)
0.2
0.15
0.15
0.1
0.1
- - -
0.05
:./
0
.
:/
-0.05
-0.05
-o.i
-0.1 -
l
-0.15
-0.2
Year
Seasonal TIP sea level
Figure
on bathymetry.
Year
for four
over the Scotian
means are smoothed with a fi ve-point moving filter.
012
050
088
126
Track 088
Year
Figure
Seasonal TIP sea
anomaly (m)
over
latitude domain for track 050 and 088, including both the Scotian
mean anomalies are
with a 5-point moving filter.
depths.
Year
Slope in
Slope. The
lines indicate water
1993 Winter
LongitudeOW
1995 Winter
45
zo
44
Q)
-
543
~ 42
41
40
-60
-58
-56
LongitudeOW
LongitudeOW from altimetric anomalies and Han et al.'s (1997)
means
depicted are positions of the shelf/slope front (thick dashed lines)
boundary (dash-dotted lines) in individual winters.
28 1998 Winter
LongitudeOW
2000 Winter
1999 Winter
47~--~-'~~--~~~----~~~
46
\
\
-60
LongitudeOW
Figure 15 (continued).
29 -58
-56
LongitudeOW
-64
-60
LongitudeOW
features (solid line)
Stream
40 cm/s
---3>­
(a)
~
\
I
~
\
I
"'" ""', ,
\
I
\
I
\
I
~~
41
I
I
~
\
\
I
\
\
'-.,
I
~
I
-1 ... ,_,_1",
"
\
\
I
\
\
\
39~·~
__
~~~
__
~~
\
__
-U~_ _~_ _~~~~~~_ _ _ _ _ _ _ _~_ _ _ _ _ _ _ _~
-68
LongitudeOW
17. (a) Gulf
27,1999 and
current
(arrows) on
30, 1999; (b) Comparison
altimetric
current anomalies and ADCP data (thick arrows). Also depicted are positions the shelf/slope
front (thick dashed lines) and the Gulf Stream northern boundary (dash-dotted lines).
31 ,..
40 cm/s
41
(b)
I
\ I
;'
41
I
\
\
\
40.5
I
I
I
/
40
\
I
\
\
\
I
\
/
\
I
\
I
\/
I
-64
LongitudeOW
Figure 17 (continued).
q­
-62
Salinity (psu)
36 ..-.. 100 ..0
u
-200
35 300 34 400 33 500 41.2
41.4
32 41 Temperature fC)
25 1
<D
20 200 15 '­
:J
~ 300 <D
10 '­
a.. 400 5
0.25
.....;,;:.::-:,..,l1lI'".................;......::::,......
0.00
---~
<:(
I
Cf)
Cf)
41
41.6
41
temperature and salinity distribution across the
section and
TIP sea level anomalies on Track 12. See
height relative to the 500db and
location.
33 Winter (RMS :::: 11.5 cm/s)
Spring (RMS :::: 8.7 cm/s)
41
40
47
46
45
z44
0
())
-g
43
...­
:;::::;
.::142
41
...
\
'~
40
-60
-58
-56
LongitudeOW
(a)
over
19. (a) Climatological
Slope
are for the four seasons.
lines) and the Gulf Stream
summer and fall
altimetry-min us-model
front (thick
are
season.
boundary (dash-dotted lines)
current anomalies
model solutions. (b)
UvIJA"CvU
34 Winter (RMS
8.3 cm/s)
\
-60
LongitudeOW
Summer (RMS = 8.6 cm/s)
Fall (RMS
(b)
Figure
(continued).
35 -58
=4.8 cm/s)
LongitudeOW
20. Altirnetric current variability at crossovers, shown as twice
rrns values.
are
of the
front
dashed
the
northern
boundary (dash-dotted lines) for
study period.
36