tiree passage (1981 – 2006) and ellett line shelf stations (1975 – 2005): tides, seasonality and...
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Tiree Passage (1981 – 2006)Tiree Passage (1981 – 2006)and and
Ellett Line Shelf Stations (1975 – 2005): Ellett Line Shelf Stations (1975 – 2005):
Tides, Seasonality and ClimatologyTides, Seasonality and Climatology
Mark Inall, Mark Inall, Phil GillibrandPhil Gillibrand, Colin Griffiths, Colin GriffithsNeil MacDougal, Kimberly Blackwell, Graham WalkdenNeil MacDougal, Kimberly Blackwell, Graham Walkden
OutlineOutline
• Oceanographic context: NW UK Shelf• The “Observatory”• Tiree Passage “continuous” time series
– Variability: tidal to inter-decadal– Forcing of residual flow
• Ellett Line shelf stations: shelf-wide context
• Where do we go from here?
CirculationCirculation
Ellett and Edwards schematic circulation of the NW UK Shelf
• Based on a variety of sources, including 137Cs distributions
Surface SalinitySurface Salinity
Semi-diurnal tides (Semi-diurnal tides (POLCOMSPOLCOMS))
Moorings
Met. Stations
Tide gauges
CTD Section
SST/SSS Station (Port Erin)
The “Observatory”The “Observatory”
plus satellite imagery, model products and ‘foul weather CTD opportunities’
AVHRR 11 May 2000. Peter Miller PML
POLCOMSPOLCOMS
Ellett LineEllett Line• 75 occupations since 1975• SAMS 1975 – 1992• NOC 1992-1995• SAMS/NOC Joint 1996 - present• No occupations in 1986 and 2002• SAMS Northern Seas Programme Occupations in 2001
(partial) 2003 (full), 2005 (partial), 2006 (happening now!)
Tiree Passage: Tiree Passage: Longest temperature and flow time series Longest temperature and flow time series
on the NW European continental shelfon the NW European continental shelf
• June 1981: Hourly current and temperature (11 m a.b.)• November 1987 2nd meter added at 22 m a.b.• Ended in September 1997 at both depths. • Restarted June 1999 to February 2000 and then May 2002
until the present with RCMs at 11m and 22 m a.b.• Seabird salinity added in August 2002 at 22 m above bed.• A total of 61 deployments.
Raw Tiree time seriesRaw Tiree time series
Inevitable gaps, but tidal to inter-annual (decadal?) variability captured
Temperature
Velocity
Tiree VariabilityTiree Variability
10-2
10-1
100
10-3
10-2
10-1
100
101
102
103
104
Frequency (cpd)
Pow
er
SA
K1
M2 S2
10-2
10-1
100
10-2
10-1
100
101
102
103
104
Frequency (cpd)
Pow
er
SA K1
M2 S2
10-2
10-1
100
10-2
10-1
100
101
102
103
104
Frequency (cpd)
Pow
er
SA
K1
M2 S2
Temperature: SA dominant, weak tidal
Along channel velocity: tides dominate, SA significant
X-channel velocity: tides and broad SA dominate
Northward residual flowNorthward residual flow
Residual flow for full time series = 10.8 cms-1 northwardsEquating to 6.7 104 m3s-1
SA clear in monthly means
Moorings
Met. Stations
Tide gauges
CTD Section
SST/SSS Station (Port Erin)
The “Observatory”The “Observatory”
plus satellite imagery, model products and ‘foul weather CTD opportunities’
Tiree Passage Tiree Passage Barotropic dynamicsBarotropic dynamics
Correlation Coefficients
<AD> = 0.11
<BD> = 0.46
<CD> = 0.53
<BC> = 0.83
<E,-A-B> = 0.08
<E,C> = 0.12
<E,C-A-B-D> = 0.03
EDCBA
Dt
Dv
h
rv
hy
p
yg SyA
1
(local only)
Atmospheric forcing of residual flow: Atmospheric forcing of residual flow: NAO IndexNAO Index
r = 0.59
Tiree temperature anomalies Tiree temperature anomalies Irish Sea vs. NE AtlanticIrish Sea vs. NE Atlantic
TIME SERIES r2 SIGNIFICANT
Tiree and Port Erin 0.5047 Yes
Tiree and Rockall 0.1674 Yes
Port Erin and Rockall 0.1117 Yes
Tiree and Qnet 0.0005 No
Port Erin and Qnet 0.0423 Yes
Rockall and Qnet 0.0071 No
Port Erin vs. Tiree PassagePort Erin vs. Tiree Passage
Coastal warming trendCoastal warming trend
0.57 C per decade.
Note broad cooling in late 1980s and early 1990s, and peaked warm episodes of late 1980s and 1990s.
Seasonal shiftsSeasonal shifts
Advance of date of maximum temperature by 9 days/decade: clearly not sustainable. No significant trend in date of minimum temperature
Reliable salinity - only recently:Reliable salinity - only recently:
seasonality? Probably not (Ellett Line) – too early to tellseasonality? Probably not (Ellett Line) – too early to tell
Shelf-wide ContextShelf-wide Context
Ellett Shelf StationsEllett Shelf Stations
Ellett Shelf StationsEllett Shelf Stations
Seasonally adjusted bottom and surface (10m) temperature.
Salinity ClimatologySalinity Climatology
• Salinity trend– Surface (10m) +0.044 psu/decade– Bottom +0.036 psu/decade
Where do we go from here?Where do we go from here?
• Modeling context for– Process studies of cross shelf
exchange– 30 year Hindcasts of inter-annual
variability
• X-shelf surface elevation data• Acoustics• Time to work on the data !
Predictive Capability ?Predictive Capability ?
Peak Karenia bloom versus distance from first instance (excluding Skye from correlation)
y = 0.0813x + 196.35R2 = 0.9729
150
170
190
210
230
250
270
0 100 200 300 400 500 600 700
distance (km) from point zero (Mull)
day
of
year
of
pea
k o
f b
loo
m
Mull, Lew is, Orkney, Shetland
skye
Linear (Mull, Lew is, Orkney,Shetland)
Karemia mikimotoi bloom during summer 2005
Progression of bloom from Mull – Lewis – Orkney - Shetland
MODIS Aqua image, 31 July 2005 (RSDAS)