Title: Initial results from a multiyear simulation of the NW European shelf seas
1Initial results from a multi-year simulation of
the NW European shelf seas
- Roger Proctor, Jason Holt, Graham Tattersall,
Sarah WakelinProudman Oceanographic
LaboratoryLiverpool, UK
2Talk structure
- Why do it?
- Whats happened in last 50 years?
- The model study
- Initial results
- Summary
3Why do it?
- Climate change is upon us
- Need to understand its consequences
- History best clue to the future
- Need limits of predictability for future climate
change - Need baseline values against which to deduce
trend changes (for WFD as well as planning) - Modelling challenge
- EC Water Framework Directive
4Whats happened in the last 50 years
- Evidence from
- weather
- sea level (PSMSL)
- Temperature salinity (ICES database)
- Continuous Plankton Recorder
5ERA-40 period
After Hurrell www.cgd.ucar.edu/cas/jhurrell/indic
es.html
6Effects of NAO
Lerwick, NW Scotland (winter)
1982-2000
94/95
95/96
Extracts from the IACMST report UK
Marine Waters 2004 Marine Processes and Climate
http//www.oceannet.org/medag/reports/IACMST_repo
rts/MCP_report/index.htm
-
7Cypris station Irish Sea
8Sea Level changes
- Absolute rise 1mm/y
- Relative rise (mostly increasing, except N
coasts) - decrease in the rate of rise in the 20th Century
- no long-term trends in tides
Wakelin et al. (2003) have shown that winter-mean
(December to March) sea levels and the NAO Index
are significantly correlated over much of the
northwest European shelf.
9Marine Environmental Change Network (MECN)
- Establish a network to measure
- environmental change in marine
- waters
- Maintain and enhance existing
- long-term research programmes
- Restart important discontinued
- long-term research programmes
- Deliver and interpret long-term and
- broad scale contextual information to
- inform water quality monitoring
- Demonstrate the benefits of
- preserving and networking long-term
- time series programmes
- Provide information to policy makers
- and other end-users to enable them to
- produce more accurate accurate
- assessments of ecosystem state
MECN partners
http//www.mba.ac.uk/MECN/about.htm
10MECN Long time series measurements
Tiree Passage W Scotland
11Temperature SST Atlantic
ICES
FRS
12TemperatureSST - shelf
13Temperature SST North Sea
Fair Isle N Scotland
NAO accounts for 40-50 of winter SST variability
in N Sea (Loewe, 1996)
FRS
ICES
14Trends in Sea Surface Temperature
15Temperature NBT winter (IBTS)
16Temperature
- No clear trend in summer SST in the eastern
North Atlantic since the 1950s, but a warming in
winter SST since the early 1990s. - SST at the Continental Shelf Edge warmed between
0.12C and 0.29C over the past century. - Temperatures in the Rockall Trough were
relatively low in the early 1990s but then
increased. The highest temperatures reached in
the 1990s were similar to those in the 1960s. - The Faroe Shetland Channel has become warmer over
the last 40 years, with temperatures rising at a
rate of approximately 0.3C per decade from the
late 1960s minimum. - Waters around the UK have been warming since the
1980s, with the trend more pronounced in the
southern North Sea and the Irish Sea (between
0.5C and 1.0C per decade) than elsewhere
(between 0.0C and 0.5C per decade). - There is a warming trend in winter and summer
SST averaged over the northern North Sea since
the early 1980s, with a warming of about 1C and
0.5C respectively. - North Sea winter bottom temperatures increased by
about 0.3C and 0.6C per decade since a cool
period in the late 1970s. - Irish Sea annual mean SST increased by about
0.7C over the last 100 years. Winter SST from
1950 to 2002 shows a clear warming since the
1980s. An apparent cooling in summer SST since
the 1980s may be due to sparse data.
17Salinity SSS Atlantic
ICES
18Salinity SSS North Sea
GSA
Fair Isle Almost cyclical variability since the
end of the GSA in the 1970s
ICES
19Salinity SSS shelf
20Salinity
- Atlantic waters and adjacent shelf areas had low
winter and summer sea surface salinity (SSS) in
the mid-late 1970s (associated with the passage
of the Great Salinity Anomaly (GSA)), followed by
three decades of large inter-annual variability. - Salinity records from the Faroe Shetland Channel
and the Ellett line indicate a recent trend to
high salinity. - SSS averaged over the northern North Sea from
1950 to 2002 shows decreasing salinity since the
1970s and is reflected by observations at fixed
locations in the Fair Isle Current and the North
Sea fishing grounds. - There is no discernible trend in mean SSS in the
English Channel from 1900 to the early 1980s. - SSS averaged over the Irish Sea from 1950 to
2002 shows a decrease in both winter and summer.
21The Continuous Plankton Recorder
Long-term changes at the base of the food web
- Phytoplankton abundance in North Sea and NE
Atlantic
Reid et al. (1998) Nature
22The Continuous Plankton Recorder
Biogeographic Changes in the Northeast Atlantic
Warm temperate slope species
Beaugrand et al. Science 2002
23The model study
- Using POLCOMS POL Coastal Ocean Modelling
System - Configured for ocean/shelf (AMM)
- ERA-40 surface flux (SLP, 10m wind, bulk heat
flux, E-P flux) - Daily river flux (mix of climatological and
measured) - FOAM repeating annual cycle (2000/1)
-
24POLCOMS
- 3D Shallow Water equations
- Horizontal finite difference discretization on an
Arakawa B-grid - Spherical polar co-ordinates
- Terrain following co-ordinates - horizontally
varying S levels - Forward Time-Centred Space scheme in the
horizontal - Equations split into depth-mean and
depth-fluctuating components - Horizontal Advection
- Piecewise Parabolic Method (PPM) for accurate,
conservative representation of sharp gradients,
fronts, thermoclines etc. - Horizontal pressure gradients
- calculated by interpolation onto horizontal
planes, improving numerical accuracy of S
co-ordinates over steep topography - Vertical diffusion
- Mellor-Yamada-Galperin level 2.5 turbulence
closure scheme - GOTM (k-e), Canuto stability functions
25AMM-12km
Atlantic Margin Model
N Atlantic FOAM 1/9o (T,S, ?, Q)
ECMWF ERA-40 1957-2002 1 degree 6-hourly SLP, 10m
wind, 2m AT, RH, CC, E-P
Tides (9C, ?, Q)
River discharge Daily 323 rivers
Physics (T,S, ?, U,V) No data assimilation or
relaxation to climatology Modules for spm,
(light, nutrients, biology) - ERSEM
26Lack of ocean time varying bc means features
like GSA will not be simulated
27Initial results
- Point series comparisons (Cypris, )
- ICES CTD database comparisons
- Errors
- Seasons
- Trends
28Cypris station Irish Sea
29Cypris station Irish Sea
30OB (Sevenstones) station Celtic Sea
31OB (Sevenstones) station Celtic Sea
32ICES CTD database analysis
Total 61,000 CTDs 20,000 this period (95-99)
33Temperature errors Oct-Dec 1995-99
Surface
Near-bed
34Salinity errors seasonal 1995-99
Surface
Near-bed
35SST trends
36Like-for-like trends 81-99 (min of 8 years 5
obs/season / 1o cell)
37Summary
- 40 year simulation of NW European shelf without
data assimilation successfully reproduces many of
the trends seen in the ICES and MECN observed
data - Model errors highest in spring (T) and NCC (S)
- Effect of climatic oceanic circulation not
apparent - Model agrees better with obs when like-for-like
measure used. Spatial variability allows error
estimates to be made - Just the beginning, also started ecosystem runs
38POLCOMS-ERSEM 15yr (1986-2001)
Mean chl errors mg/m3 (against ICES data)
39NBT trends
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