2008 ROMS/TOMS European Workshop Saint Martin d'Heres Campus Grenoble, France (1) University of Lisbon, CGUL, IDL (2) University of Hamburg, Center for Marine and Atmospheric Research (ZMAW) 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)

Summary Characterize the upwelling field in terms of sea surface temperature, 3D currents (U,V and W) and sea surface height for the year x 30 year simulations ( ERA-40, RACMO Control, RACMO A ) 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 RACMO ROMS

Cape Carvoeiro Latitude: N Longitude: 9.4 W ROMS domain

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) ( ), 1 degree RACMO (KNMI) (24 hour) ( ) and ( ), 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 temperatureRelative humidity Surface pressure Cape Carvoeiro T (  C) Q (%)P (hPa) mean max min °C 8°C

Shortwave radiationSurface wind Year 2000 Cape Carvoeiro Uwind (m/s) Vwind (m/s) Swrad (W/m2) mean max min Forcing (ERA 40) Cape Carvoeiro Year 2000

Results: Summer 2000 at Cape Carvoeiro 1 July31 August ROMS 1 July 31 August 123

Sea surface height at cape Cape Carvoeiro July31 August ROMS

Spatial variability (full year) Cape Finisterre Cape Carvoeiro Cape São Vicente Most of the events are verified simultaneously along the coast.

Validation near Cape Carvoeiro Satellite AVHRR (1/4  AVHRR daily OI SST) vs ROMS AVHRR, NOAA ROMS Nearest points

SST during the July and August 2000

Results Summer 2000 episodes variableUpwellingEpisodes SST sea surface temperature  decrease  T < - 4 K U zonal current  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 Upwelling near Iberia is episodic Episode duration ~1-2 weeks Extension < 50 km Intensity < 4 K

40 year simulation forced by ERA-40 ECMWF Surface wind( m/s) U mean (m/s) V mean (m/s) Wind turned to more Northerly Implying more frequent (simulated) upwelling Decade Mean angle(  ) Climate change impacts on upwelling

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. Number of events

RACMO model surface winds at Cape Carvoeiro From , it is observed an increase in the wind intensity, although the mean direction has not changed. Surface wind (m/s) Mean U V Surface wind (m/s) Mean U V Mean Mean angle (  ) Mean Mean angle (  )

( ) ( ) Atmospheric forcing variables 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 TEMPERATURE SURFACE PRESSURE 50%

mean U (m/s) SST (  C) ROMS forced with RACMO

ROMS forced with RACMO data (Regional Atmospheric Climate MOdel) TOTAL 2<  T< <  T< <  T< TOTAL TOTAL 2<  T< <  T< <  T< TOTAL RACMO control has no relevant decadal tendencies (unlike ERA-40) 10% more

Sligtly increase in the westward horizontal displacement Increased interanual variability Number of days with westward currentHorizontal displacement CONTROL A2 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 CONTROL A2 Upwelling duration

Slight increase in the events intensity CAT I > 4 °C || 3 °C< CATII <4 °C|| 2 °C< CATIII < 3 °C Upwelling 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 ( ) Number of upwelling events almost constant RACMO fields do not include observed climate trends ROMS A2 scenario ( ) 10% increase in the number of upwelling events (vs Control run) due to an increase in the wind intensity A 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

Mean eastward horizontal displacement (m) e e+05 westward horizontal displacement (m) e e+05 N  of days with U> N  of days with U< ROMS forced with RACMO

Initial conditions Levitus 1 January Surface salinitySurface temperature

ROMS forced with ECMWF ERA 40 data mean eastward displacement (m) e+05 westward displacement (m) e+05 N  of days with U> N  of days with U< Climate change impacts on Iberian upwelling

ROMS forced with ERA 40 2K

ROMS forced with RACMO Control vs ERA-40

ERA 40 Vs RACMO ERA 40 reanalysis data RACMO data from a climate model

Quando o modelo ROMS foi forçado com dados do ECMWF-ERA40, no período , 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 [ ] (modelo RACMO) verificou- se 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 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

mean eastward horizontal displacement (m) e e+04 mean westward horizontal displacement (m) e e+04 mean U>0 (days) mean U<0 (days) mean U (m/s) mean SST (  C)

SST Vertical sections Cape São Vicente (lat= ???N/lon=??? W) Cape Carvoeiro (lat= N/lon=9.40 W ) Cape Vilano (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

30 Year temporal series U and SST

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

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