Responses of the Mediterranean climate
to tropical forcing
Laurent Li ([email protected])Laboratoire de Météorologie Dynamique (LMD)
Institut Pierre-Simon Laplace (IPSL) CNRS/UPMC, Paris, France
•Mediterranean Z500 ACC predictability
•Mediterranean T2m and precip time evolution predictability
•A holographic effect of atmospheric nudging (also from SST forcing)
Simulations performed with LMDZ
• 8 series + control
• 38 years 1971 to 2008
• May to September
• Ensemble of 10 members
Forcing zone in green: Africa, Asia and Tropics
Target zone in red: Mediterranean Sea
AfNFIVCl: ERA(Af) SST(clim): Atmospheric forcing from ERA in Africa, SST climatologyAfNFIVIV: ERA(Af) SST(Obs): Atmospheric forcing from ERA in Africa, SST as observedAfNFIVCl: ERA(As) SST(clim): Atmospheric forcing from ERA in Asia, SST climatologyAfNFIVIV: ERA(As) SST(Obs): Atmospheric forcing from ERA in Asia, SST as observedTrNFIVCl: ERA(Tr) SST(clim): Atmospheric forcing from ERA in Tropics, SST climatologyTrNFIVIV: ERA(Tr) SST(Obs): Atmospheric forcing from ERA in Tropics, SST as observedNonudgIV: No atmospheric forcing from ERA, SST as observedNonudgTr: No atmospheric forcing from ERA, SST as observed in Tropics, but climatology elsewhereNonudgCl: No atmospheric forcing from ERA, SST climatology
LMDZ-global: 2° in latitude and 3° in longitude
Period: 1971/2008
May, June, July, August
Ensemble: 10 members
Can we predict the Mediterranean climate ?
in terms of ACC (Anomalous Correlation Coefficient) for 500-hPa geopotential height
-1,00
-0,80
-0,60
-0,40
-0,20
0,00
0,20
0,40
0,60
0,80
1,00
1971 1975 1979 1983 1987 1991 1995 1999 2003 2007
NonudgTR
NonudgIV
-1,00
-0,80
-0,60
-0,40
-0,20
0,00
0,20
0,40
0,60
0,80
1,00
1971 1975 1979 1983 1987 1991 1995 1999 2003 2007
TrNFIVCl
TrNFIVIV
-1,00
-0,80
-0,60
-0,40
-0,20
0,00
0,20
0,40
0,60
0,80
1,00
1971 1975 1979 1983 1987 1991 1995 1999 2003 2007
AfNFIVCl
AfNFIVIV
-1,00
-0,80
-0,60
-0,40
-0,20
0,00
0,20
0,40
0,60
0,80
1,00
1971 1975 1979 1983 1987 1991 1995 1999 2003 2007
AsNFIVCl
AsNFIVIV
No
Tr
No
IV
Tr
Cl
Tr
IV
As
Cl
As
IV
Af
Cl
Af
IV
ERA
SST
0.04 -0.03 0.4 0.47 0.32 0.29 0.47 0.45 ACC
Anomalious Correlation Coefficient of 500-hPa geopotential height over the Med Region
Can we predict the Mediterranean climate ?
in terms of temporal evolution for surface air temperature and precipitation
SST clim SST observée
No nudging 0.0 0.78 (0.74)
Nudging Af 0.55 (0.53) 0.73 (0.72)
Nudging As 0.57 (0.54) 0.86 (0.85)
Nudging Tr 0.59 (0.63) 0.76 (0.74)
Temporal correlation coefficient between LMDZ and CRU (ERA)
2-m air temperature for the Mediterranean basin
SST clim SST observée
No nudging 0.0 0.24 (0.02)
Nudging Af 0.81 (0.57) 0.74 (0.54)
Nudging As 0.71 (0.50) 0.56 (0.34)
Nudging Tr 0.82 (0.61) 0.74 (0.52)
Temporal correlation coefficient between LMDZ and CRU (ERA)
Rainfall rate for the Mediterranean dasin
0
0,2
0,4
0,6
0,8
1
1,2
1965 1970 1975 1980 1985 1990 1995 2000 2005
CRU
Ano-Str
Ano-Sgl
0
0,2
0,4
0,6
0,8
1
1,2
1965 1970 1975 1980 1985 1990 1995 2000 2005
CRU
Atr-Scl
Atr-Sgl
Mediterranean area summer rainfall rate (mm/day) over land, with only SST forcing:- global: 0.24 correlation CRU- tropical: 0.37 correlation CRU
Mediterranean area summer rainfall rate (mm/day) over land, with tropical atmospheric forcing:- global SST: 0.74 correlation CRU- no SST: 0.82 correlation CRU
Extra-tropical SST (including the Med Sea) can have negative contribution to the rainfall prediction in the Med area ! ?
Is there a holographic effect of atmospheric nudging ?
Surface air temperature °C (over land)
Precipitation rate mm/d (over land)
Surface air temperature °C Surface air temperature °C
Precipitation rate mm/dPrecipitation rate mm/d
Iberia South-France
Surface air temperature °CSurface air temperature °C
Precipitation rate mm/d
Precipitation rate mm/d
Italy Greece-Turkey
Surface air temperature °CSurface air temperature °C
Precipitation rate mm/d
Precipitation rate mm/d
North-Africa-West North-Africa-East
Surface air temperature °C
Precipitation rate mm/d
Middle-East
Conclusions
• Atmospheric nudging is an interesting technique, complementary to the traditional approach of SST forcing.
• Mediterranean climate predictability of Z500 ACC: poor from SST, significant from tropical atmospheric forcing.
• Mediterranean climate predictability of temporal evolution: a certain holographic effect is observed for both surface air temperature and precipitation; SST from extra-tropics seems have negative contribution for precipitation.
