2008 ROMS/TOMS European Workshop
Saint Martin d'Heres Campus
Grenoble, France
Sensitivity of Iberian upwelling to climate
change: a numerical simulation with
ROMS forced by RACMO A2 scenario
José Alves (1) Pedro M A Miranda (1) Nuno Serra (2)
(1) University of Lisbon, CGUL, IDL
(2) University of Hamburg, Center for Marine and Atmospheric Research (ZMAW)
Summary
• Characterize the upwelling field in terms of sea surface temperature, 3D currents
(U,V and W) and sea surface height for the year 2000
• 3 x 30 year simulations (1961-1990 ERA-40, RACMO Control, RACMO A2 20712100)
• Identify tendencies in terms of number, intensity and duration of upwelling events
Detailed study during the year
2000 (U, V, W, SST, SSH)
ECMWF – ERA 40
1960-2000
ROMS
RACMO
1961-1990
2071-2100
Cape Carvoeiro
Latitude: 39.35 N Longitude: 9.4 W
50
3000
48
2000
ROMS domain
46
44
1000
0
42
Latitude N
-1000
40
-2000
38
-3000
36
-4000
34
-5000
32
-6000
-30
-25
-20
-15
Longitude W
-10
ROMS RUTGERS version 3.0
Model parameters
Resolution : horizontal 1/12  (approx =7 km) Mercator projection
vertical 30 – sigma layers (theta_s =5.0 ; theta_b=0.4)
Grid: 97 x 153 x 30
Time step DT=900 s (NDTFAST=100 s)
Mellor Yamada 2.5 closure
Mix_Geo_UV and Mix_Geo_TS (mixing on geopotential) constant z
Initial Conditons
Levitus world ocean database
Boundary conditions
Radiation and Nudging
Surface forcing
ATMOSPHERIC DATA (BULK_FLUXES)
ECMWF – ERA 40 ( 6 hour) (1960-2000), 1 degree
RACMO (KNMI) (24 hour) (1961-1990) and (2071-2100), 0.5 degree
 Downward shortwave radiation (swrad)
× Downward longwave radiation (lwrad)
 2m air temperature (Tair)
 10 m wind (Uwind, Vwind)
 pressure (Pair)
 relative humidity (Qair)
Forcing (ERA 40) at Cape Carvoeiro Year 2000
Surface temperature
Relative humidity
24°C
8°C
Surface pressure
Cape
T (C)
Carvoeiro
Q (%)
P (hPa)
mean
16.41
80.31
1018.9
max
23.21
100
1037.2
min
7.90
44.88
985.94
Forcing (ERA 40) Cape Carvoeiro Year 2000
Surface wind
Shortwave radiation
Year 2000
Cape
Carvoeiro
Uwind
(m/s)
Vwind
(m/s)
Swrad
(W/m2)
mean
1.31
-2.70
155.48
max
12.64
19.18
648.62
min
-10.13
-14.40
0
Results: Summer 2000 at Cape Carvoeiro
ROMS
1
1 July
1 July
2
3
31 August
31 August
1 July
1 July
31 August
31 August
Sea surface height at cape Cape Carvoeiro 2000
ROMS
1 July
31 August
Spatial variability (full year)
20
44
19
Latitude (N)
Cape Finisterre
43
18
42
17
16
41
40
15
Cape Carvoeiro
14
39
13
38
Cape São Vicente
37
Most of the events are verified
simultaneously along the coast.
12
11
36
-14 -13
-12 -11 -10
Longitude (W)
-9
-8
10
Validation near Cape Carvoeiro
Satellite AVHRR
(1/4 AVHRR daily OI SST) vs
AVHRR, NOAA
ROMS
ROMS
Nearest points
SST during the July and August 2000
Results Summer 2000 episodes
Upwelling near Iberia is episodic
Episode duration ~1-2 weeks
Extension < 50 km
Intensity < 4 K
variable
Upwelling
Episodes
SST
sea surface temperature
 decrease
T < - 4 K
 westward
U < 0.3 m/s
V
meridional current
 southward
V < 0.4 m/s
W
vertical component
 upward
W < 0.15 mm/s
SSH
sea surface height
 lower values
H < 0.06 m
U
zonal current
Climate change impacts on upwelling
40 year simulation forced by ERA-40
ECMWF
1960-1969
1970-1979
1980-1989
1990-1999
U mean (m/s)
1.05
0.97
0.63
0.56
V mean (m/s)
-1.14
-1.34
-1.15
-1.22
Decade
1960-1969
1970-1979
1980-1989
1990-1999
Mean angle()
317.35
324.10
331.28
335.34
Surface wind( m/s)
Wind turned to more Northerly
Implying more frequent (simulated) upwelling
Number
of
events
The upwelling episodes were identified through the analyses of sea
surface temperature time series. The threshold considered to identify an
upwelling event was a decrease in SST of at least 2C in less than 1 week,
followed by an increase of the same magnitude in a similar time period.
RACMO model surface winds at Cape Carvoeiro
Surface wind
(m/s)
1961-1970
1971-1980
1981-1990
Mean
1961-1990
U
2.35
1.79
2.04
2.06
V
-1.30
-1.07
-1.09
-1.15
1961-1970
1971-1980
1981-1990
Mean
Mean angle ()
298.95
300.87
298.12
299.17
Surface wind
(m/s)
2071-2080
2081-2090
2091-2100
Mean
2071-2100
U
2.87
2.79
2.48
2.71
V
-1.34
-1.59
-1.44
-1.46
2071-2080
2081-2090
2091-2100
Mean
295.03
299.68
300.14
298.31
Mean angle ()
From 2001-2100, it is observed an increase in the wind intensity,
although the mean direction has not changed.
Atmospheric forcing variables
(1961-1990)
TEMPERATURE
(2071-2100)
24
24
22
22
20
Temperatura (ºC)
Temperature (ºC)
20
18
50%
16
16
14
14
12
12
10
18
10
1
1
1025
1025
1020
1020
1015
1015
Pressão (mbar)
Pressão (mbar)
SURFACE PRESSURE
1010
1010
1005
1005
1000
1000
1
1
Increase in the mean temperature of 2.2 C / slight increase in the variability
Slight decrease in the pressure mean value / increase in the variabilty
ROMS forced with RACMO
mean
1961-1990
2070-2100
U (m/s)
-0.0096
-0.0137
SST (C)
16.224
17.9394
ROMS forced with RACMO data
(Regional Atmospheric Climate MOdel)
1961-1970
1971-1980
1981-1990
TOTAL
2<T<3
23
30
31
84
3<T<4
7
5
5
17
4<T<5
4
1
1
6
TOTAL
34
36
37
107
RACMO control has no relevant decadal tendencies (unlike ERA-40)
2071-2080
2081-2090
2091-2100
TOTAL
2<T<3
25
24
32
81
3<T<4
17
3
10
30
4<T<5
1
3
4
8
TOTAL
43
30
46
119
10% more
Horizontal displacement
Number of days with westward current
tf
x   min(U ,0)dt
ti
CONTROL
A2
Sligtly increase in the westward horizontal
displacement
CONTROL
Increased interanual variability
A2
Upwelling duration
CONTROL
A2
Increase in the number of events of short duration (1 week)
and long duration (4 weeks), decrease in the number of events
of medium duration (3 and 4 weeks) , more interdecadal variability
Upwelling intensity
CAT I > 4 °C || 3 °C< CATII <4 °C|| 2 °C< CATIII < 3 °
Slight increase in the events intensity
Conclusions
ROMS forced by ERA-40
Increase in the decadal number of upwelling events from 1960 to 2000
due to change in the mean wind direction.
ROMS forced by RACMO control run (1961-1990)
Number of upwelling events almost constant
RACMO fields do not include observed climate trends
ROMS A2 scenario (2071-2100)
10% increase in the number of upwelling events (vs Control run)
due to an increase in the wind intensity
A2 2071-2100 simulated upwelling
Increased event duration variability (More long and short events)
Slight increase in mean event intensity
Increased interdecadal variability
Future work
Add Tagus estuary to the computational domain in order to study
the circulation within the Tagus estuary – grid nesting
Use atmospheric data with a higher spatial resolution
Apply boundary conditions from a global ocean model
Look at other upwelling diagnostics
ROMS forced with RACMO
Mean
1961-1990
2070-2100
eastward horizontal
displacement (m)
4.2793e+05
3.9527e+05
westward horizontal
displacement (m)
-7.2722e+05
-8.2122e+05
N of days with U>0
167.56
155.40
N of days with U<0
192.69
204.85
Initial conditions
Levitus 1 January
Surface salinity
Surface temperature
20
44
36.8
44
19
43
36.6
43
18
42
36.4
42
17
36.2
41
36
40
35.8
39
Latitude (N)
Latitude (N)
37
16
41
15
40
14
39
35.6
38
13
38
35.4
37
35.2
36
-14
-13
-12 -11 -10
Longitude (W)
-9
-8
35
12
37
11
36
-14
-13
-12 -11 -10
Longitude (W)
-9
-8
10
Climate change impacts on Iberian upwelling
ROMS forced with ECMWF ERA 40 data
mean
1961-1990
eastward
displacement (m)
6.9122e+05
westward
displacement (m)
-9.5504e+05
N of days with U>0
140.30
N of days with U<0
220.70
ROMS forced with ERA 40
2K
ROMS forced with RACMO Control vs ERA-40
ERA 40 Vs RACMO
ERA 40
RACMO
reanalysis data
data from a climate model
•
Quando o modelo ROMS foi forçado com dados do ECMWF-ERA40, no período
1960-2000, verificou-se um aumento do número de episódios de upwelling,
enquanto que quando se utilizou o forçamento do modelo RACMO, para o mesmo
período, se verificou que o número de episódios de upwelling se manteve
praticamente constante.
•
Nas projecções para o final do século XXI [2071-2100] (modelo RACMO) verificouse um aumento do vento junto ao Cabo Carvoeiro e um consequente aumento do
número de episódios de upwelling, cerca de 10 % em relação ao verificado no
período 1961-1990.
•
No Cabo Carvoeiro a maioria dos episódios de upwelling eram e vão continuar a
ser de longa duração (4 semanas ou mais) e de baixa intensidade (2<T<3),
embora se tenha verificado um ligeiro aumento na intensidade dos episódios.
•
O número de dias de upwelling por ano praticamente não sofre alteração.
Sea surface temperature
SST at layers 30-20-10
1961-1990
2070-2100
mean eastward horizontal
displacement (m)
1.7830e+04
1.6470e+04
mean westward horizontal
displacement (m)
-3.0321e+04
-3.4218e+04
mean U>0 (days)
167.56
155.40
mean U<0 (days)
192.69
204.85
1961-1990
2070-2100
mean U (m/s)
-0.0096
-0.0137
mean SST (C)
16.224
17.9394
Cape Vilano (lat= ???N/ lon=???W )
SST Vertical sections
Cape Carvoeiro (lat= 39.35 N/lon=9.40 W )
Cape São Vicente (lat= ???N/lon=??? W)
July and August 2000
SST; SSH; currents U and V
30 year temporal series
Horizontal displacement (m)
Number of days with U>0 and U<0
U and SST
30 Year temporal series
Currents (U, V and W)
Sea surface height
SSH
Lower values close to the coast during upwelling
episodes due to …
STATIONS
Map with stations locations
FLOATS
Map with float trajectories
Validate SST with satellite data
Conclusions
Problems
Sea surface temperature values too low during the winter months
Ver figura em Inglês
1961-1990
2071-2100