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North-Atlantic SST amplified recent European land temperature extremes and trends.

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North-Atlantic SST amplified recent European land temperature extremes and trends.

Julien Cattiaux

Robert Vautard & Pascal Yiou.

LSCE – IPSL

CEA / CNRS / UVSQ

Gif sur Yvette FRANCE

(2)

Introduction: European recent warming

Dataset: E-OBS

Interpolated from ECA

stations dataset: daily mean temperature over 1950-2007.

Tobs anomalies (wrt 1961-90): 1978-2007 trend

(3)

Introduction: European recent warming

Dataset: E-OBS

Interpolated from ECA

stations dataset: daily mean temperature over 1950-2007.

1978-2007 trend:

+0.55 (+/- 0.16) °C/decade

Tobs anomalies (wrt 1961-90): 1978-2007 trend

(4)

Introduction: European recent warming

Dataset: E-OBS

Interpolated from ECA

stations dataset: daily mean temperature over 1950-2007.

1978-2007 trend:

+0.55 (+/- 0.16) °C/decade Seasonality:

MAM 0.66 (+/- 0.26) °C/dec JJA 0.67 (+/-0.24) °C/dec SON 0.30 (+/- 0.26) °C/dec p-value ~ 6%

DJF 0.59 (+/- 0.46) °C/dec p-value ~ 4%

Tobs anomalies (wrt 1961-90): 1978-2007 trend

(5)

Introduction: European recent warming

Dataset: E-OBS

Interpolated from ECA

stations dataset: daily mean temperature over 1950-2007.

1978-2007 trend:

+0.55 (+/- 0.16) °C/decade Seasonality:

MAM 0.66 (+/- 0.26) °C/dec JJA 0.67 (+/-0.24) °C/dec SON 0.30 (+/- 0.26) °C/dec p-value ~ 6%

DJF 0.59 (+/- 0.46) °C/dec p-value ~ 4%

Recent extreme seasons (MAM 2007, JJA 2003, SON 2006, DJF 2006).

Tobs anomalies (wrt 1961-90): 1978-2007 trend

(6)

Atmospheric patterns associated with European temperatures

Spatial correlation of Z500d (NCEP) with Tobs time series

(7)

Seasonal Dynamics Index (SDI): based on regional averages of Z500d anomalies.

Atmospheric patterns associated with European temperatures

Spatial correlation of Z500d (NCEP) with Tobs time series

(8)

Can European temperatures be described by this Seasonal Dynamics Index (SDI)?

Are European recent warming and extremes explained by circulation changes?

Atmospheric patterns associated with European temperatures

Spatial correlation of Z500d (NCEP) with Tobs time series

(9)

North-Atlantic dynamics and European temperatures

Fitting SDI on Tobs time series...

(10)

North-Atlantic dynamics and European temperatures

r = 0.81 r = 0.76

r = 0.71 r = 0.81

Fitting SDI on Tobs time series...

(11)

North-Atlantic dynamics and European temperatures

r = 0.81 0.79 0.25 r = 0.76 0.66 0.11

r = 0.71 0.67 0.27 r = 0.81 0.78 0.63

.. comparing to analogues [Vautard & Yiou, GRL 2009]

and NAO index [Jones, IJC 1997; Osborne, Weather 2006].

Fitting SDI on Tobs time series...

(12)

North-Atlantic dynamics and European temperatures

r = 0.81 0.79 0.25 r = 0.76 0.66 0.11

r = 0.71 0.67 0.27 r = 0.81 0.78 0.63

… dynamics explains Tobs variability ...

Fitting SDI on Tobs time series...

(13)

North-Atlantic dynamics and European temperatures

r = 0.81 0.79 0.25 r = 0.76 0.66 0.11

r = 0.71 0.67 0.27 r = 0.81 0.78 0.63

… dynamics explains Tobs variability , but not trends.

Fitting SDI on Tobs time series...

(14)

North-Atlantic recent surface warming

Dataset: NCEP re-analyses.

SST anomalies (wrt 1961-90): 1978-2007 trend

(15)

North-Atlantic recent surface warming

Dataset: NCEP re-analyses.

1978-2007 trend:

+0.29 (+/- 0.05) °C/decade.

SST anomalies (wrt 1961-90): 1978-2007 trend

(16)

North-Atlantic recent surface warming

Dataset: NCEP re-analyses.

1978-2007 trend:

+0.29 (+/- 0.05) °C/decade.

High seasonality:

MAM 0.15 (+/- 0.08) °C/dec

JJA 0.23 (+/- 0.10) °C/dec

SON 0.44 (+/- 0.09) °C/dec

DJF 0.31 (+/- 0.08) °C/dec

SST anomalies (wrt 1961-90): 1978-2007 trend

(17)

North-Atlantic recent surface warming

Dataset: NCEP re-analyses.

1978-2007 trend:

+0.29 (+/- 0.05) °C/decade.

High seasonality:

MAM 0.15 (+/- 0.08) °C/dec JJA 0.23 (+/- 0.10) °C/dec SON 0.44 (+/- 0.09) °C/dec DJF 0.31 (+/- 0.08) °C/dec

Did SSTs contribute to recent European warming trend and extremes?

SST anomalies (wrt 1961-90): 1978-2007 trend

(18)

Atlantic SST contribution to land warming

r = 0.81 r = 0.76

r = 0.71 r = 0.81

Adding SST time series to Tobs–SDI linear regressions...

(19)

Atlantic SST contribution to land warming

r = 0.81 0.83 r = 0.76 0.9

r = 0.71 0.83 r = 0.81 0.84

… improves the fit, especially in fall and winter.

Adding SST time series to Tobs–SDI linear regressions...

(20)

SST sensitivity experiments: set-up

(21)

SST sensitivity experiments: set-up

Model

MM5 = Penn State University / NCAR 5

th

generation of Mesoscale Model.

Non-hydrostatic equations of motion over a predefined domain.

32 vertical levels and 4 active soil layers.

See [Duddhia 1993, Mon. W. Rev ; Grell et al., 1994, NCAR Tech. Note].

(22)

SST sensitivity experiments: set-up

Model

MM5 = Penn State University / NCAR 5

th

generation of Mesoscale Model.

Non-hydrostatic equations of motion over a predefined domain.

32 vertical levels and 4 active soil layers.

See [Duddhia 1993, Mon. W. Rev ; Grell et al., 1994, NCAR Tech. Note].

Domain

Eastern Atlantic – Western Europe [40W-30E ; 20-67N] area.

150x150 grid points, horizontal resolution of ~35km.

Simulations are driven with boundary conditions from ECMWF (4 x daily).

(23)

SST sensitivity experiments: set-up

Model

MM5 = Penn State University / NCAR 5

th

generation of Mesoscale Model.

Non-hydrostatic equations of motion over a predefined domain.

32 vertical levels and 4 active soil layers.

See [Duddhia 1993, Mon. W. Rev ; Grell et al., 1994, NCAR Tech. Note].

Domain

Eastern Atlantic – Western Europe [40W-30E ; 20-67N] area.

150x150 grid points, horizontal resolution of ~35km.

Simulations are driven with boundary conditions from ECMWF (4 x daily).

Sensitivity experiments

For each season of 2003-2007:

AS: Actual SST (as from 4xdaily NCEP re-analyses).

CS: Climatological SST (as from 1961-1990 4xdaily NCEP climatology).

Nudging on wind 3D field, not on temperature and humidity 3D fields.

(24)

SST sensitivity experiments: set-up

Model

MM5 = Penn State University / NCAR 5

th

generation of Mesoscale Model.

Non-hydrostatic equations of motion over a predefined domain.

32 vertical levels and 4 active soil layers.

See [Duddhia 1993, Mon. W. Rev ; Grell et al., 1994, NCAR Tech. Note].

Domain

Eastern Atlantic – Western Europe [40W-30E ; 20-67N] area.

150x150 grid points, horizontal resolution of ~35km.

Simulations are driven with boundary conditions from ECMWF (4 x daily).

Sensitivity experiments

For each season of 2003-2007:

AS: Actual SST (as from 4xdaily NCEP re-analyses).

CS: Climatological SST (as from 1961-1990 4xdaily NCEP climatology).

Nudging on wind 3D field, not on temperature and humidity 3D fields.

>> AS – CS: SST anomaly influence.

(25)

SST sensitivity experiments: AS – CS SST forcings

= SST anomalies averaged over 2003-2007.

(26)

SST sensitivity experiments: AS – CS T2m responses

= SST anomalies contribution to 2003-2007 land warming.

(27)

SST sensitivity experiments: AS – CS T(altitude) responses

SST anomalies seem advected from the Atlantic during seasons of strong westerlies.

Near-surface amplifying feedbacks appear in summer.

(28)

Statistical vs. Dynamical estimations of SST contribution

Agreement

Positive contributions for all seasons of 2003-2007 + strong seasonality .

(SDI+SST) Rec – SDI Rec AS – CS T2m response

(29)

Statistical vs. Dynamical estimations of SST contribution

Agreement

Positive contributions for all seasons of 2003-2007 + strong seasonality .

Limits

Statistics: SST-Tobs causal link is not identified. Over-estimation (esp. in MAM-JJA).

MM5: Unrealistic prescribing of both dynamics and SST .

(SDI+SST) Rec – SDI Rec AS – CS T2m response

(30)

Statistical vs. Dynamical estimations of SST contribution

Agreement

Positive contributions for all seasons of 2003-2007 + strong seasonality .

Extreme seasons

Autumn 2006: SST contributed to ~30%

[Cattiaux et al. GRL 2009; Shongwe et al. Clim Dyn 2009].

Summer 2003: Minor contribution (land-atmosphere feedback more important) [Fischer et al. GRL 2007; Seneviratne et al. Nature 2006].

(SDI+SST) Rec – SDI Rec AS – CS T2m response

(31)

Conclusions

European temperatures variability remains driven by North-Atlantic dynamics, with season-dependent patterns.

Recent land warming is incompatible with circulation changes only.

Annual cycle of North-Atlantic SSTs has been both warming and delaying, which recently causes high SST anomalies in fall and winter.

The warming of SSTs enhances European land temperatures, since warmer air masses are advected from North-Atlantic.

Since both westerlies and anomalous SST are higher in autumn and winter, the land temperature response is more important during these two seasons, and SST

significantly contributed to recent trends and extremes.

Land temperature responses to SST are less pronounced in spring or summer,

where local feedbacks (soil-atmosphere, clouds, aerosols) are the main amplifiers of recent extremes.

… submitted in Climate Dynamics, in revision.

Références

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