ncar cgd seminar june 2015 disruption of the european climate seasonal clock in a warming world...

NCAR CGD Seminar June 2015

Disruption of the European Climate Seasonal Clock in a warming world

Christophe Cassou (Cerfacs)Julien Cattiaux (Météo-France)


“Always blame global warming!” The polar vortex syndrome


Easy … but …


Temperature anomalies [5-12 Feb 2012]

“Always blame Blocking!”

850hPa wind anomaliesPressure anomalies

H


Temperature anomalies [20-25 July 2006]


H

850hPa wind anomaliesPressure anomalies


Temperature anomalies [20-25 July 2006]


H

Pressure anomalies


Pressure anomalies [20-25 July 2006]

H

“Always blame Blocking and global warming!”


The blocking syndrome

BLOCKIN

G

WILL

CAUSE

WARMER

SUMMERS

!

BLOCKIN

G

WILL

CAUSE

WARMER

SUMMERS

!


Communication is an art…

BLOCKING

BLOCKING


The seasonality of atm. circulation & Temp. over Europe

Temperature anomaliesPressure anomalies 850hPa wind anomalies

The 2012 European cold wave

The 2006 European heat wave


Evidence for strong seasonality in the atmos circulation temperature relationship.

1. Choice of the metric2. PDF Model

Climate Change effect

Summer starting datesAttribution simulation (CMIP5)Mordicus

Mechanims: snow and not land-sea contrast Work in observation today.

Winter: no change: aerosols, snow

Global warming, everywhere!

NCAR CGD Seminar June 2015Data: NCEP-NCAR reanalysis

DJF EOF modes of variability from winter days [1950-2012]

JJA EOF modes of variability from summer days [1950-2012]

Seasonality of the North Atlantic daily atm. circulation




Seasonality of the North Atlantic daily atm. circulation

Northward migration of the centers of actionand modes of variability but for blocking




Definition of a European circulation index

Northward migration of the centers of actionand modes of variability but for blocking

Definition of a annual daily box-average pressure index


Seasonal relationship between circulation and temp. (1)

Summer Surface temperature compositesWinter Surface temperature composites

Data: NCEP-NCAR reanalysis


Seasonal relationship between circulation and temp. (2)

Winter Surface temperature composites Summer Surface temperature composites

+ ECA dataset (dots)Data: NCEP-NCAR reanalysis


Definition of a western-Europe temperature index

Winter Surface temperature composites Summer Surface temperature composites

+ ECA dataset (dots)Data: NCEP-NCAR reanalysis


The seasonal clock of the European climate

Strength of the regressionbetween PSL index &

2m-TEMP index

0.33 oC/hPa

0.66 oC/hPa

1oC/hPa

Neg. Reg/Corr. Pos. Reg/Corr.



Uncertainties for the seasonal clock (NCEP)

NCEP PSL / 2mT ECA

NCEP PSL / 2mT NCEP



x 20CR PSL / 2mT 20CRNCEP PSL / 2mT ECA

NCEP PSL / 2mT NCEP

Uncertainties for the seasonal clock (20CR)


BLOCKING, everywhere!

Bilan ici et ojectives

ModelesMettre quelque part le nombre de jours traites.


Evaluation of the CNRM-CM5 model

NCEP + ECA observational datasets (1950-2010)

CNRM-CM5 historical simulation (1950-2010)


Obs. envelopHIST. envelop

The CNRM-CM5 model reproduces very well the European seasonal clock.

Neg. Reg/Corr.

The CNRM-CM5 seasonal clock

There is a slight underestimation of the PSL/TAS relationship for summer months (July and May)


Seasonal clock in [2070-2100] in RCP85

PiControl [1000 years] PiControl [1000 years]

1. Considerable reduction of the PSL/TAS relation in late winter/early spring

2. Clear increase of of the PSL/TAS relation in summer

3. No significant change in PSL/TAS relation in fall


Winter changes

PDF for PSL Winter days (PiControl)

PD

F f

or

Tem

p.

Win

ter

days

(PiC

ontr

ol)


Winter changes

PDF for PSL Winter days (PiControl)

(RCP85)

PD

F f

or

Tem

p.

Win

ter

days

(PiC

ontr

ol)

(RC

P8

5)


(Mean c

orr

ect

ed R

CP8

5)

(Mean corrected RCP85)

Winter changesPDF for PSL Winter days (PiControl)

PD

F f

or

Tem

p.

Win

ter

days

(PiC

ontr

ol)

Cold extremes warm more than the meanMild extremes warm less the mean

Conditional change of 2m-Temperature reduction of variance

Zonal flows are less efficient to bring heat inland Blocking flows are less efficient to bring cold westward


Summer changes


Summer changes

Loss of PSL/Temp relationship in winter due to reduced conditional variance of Temperature

Increase of PSL/Temp relationship in summer due to increase variance of Temperature (less dependant on atm. circulation)


Change in zonal gradients

2070-2100 East-West Contrast (EWC) of January = EWC in March of 1970-2000 ---> Two month seasonal advance

Maximum change in summer for land sea contrast

---> One month seasonal advance



Bilan des mecanismes des changementsde variance.

Annonce de la summer date (humour sur la recherchede la non-significativite).

Mettre mot detectableDefinition de la metrique. Mettre aussi une balance avec radiatifet advection


The summer starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0

The winter starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0

31st of March [1980-2010]

The summer starting date

NCEP20CR PiCtl

12 April

10-member Historical


The summer starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0

The winter starting date is defined as the day where the correlation between PSL and West Temp. indices crosses 0

The summer starting date (historical period)

NCEP20CR PiCtl


Earlier onset of summer by ~10 days between the 1950’s and the 1990’s (~2.5 days/decade trend)

On the verge of detectability for this metric in presence of strong interannual variability


The summer starting date (the XXIst century under RCP85)

NCEP20CR PiCtl


Earlier onset of summer by ~10 days between the 1950’s and the 1990’s (~2.5 days/decade trend)

On the verge of detectability for this metric in presence of strong interannual variability

Additional ~15 day winter shortening by [2070-2100]

The sharpest trend is now!


Ensemble Means

Detection and attribution

PiCtl

No volcanic eruption [1920-1960]

The observed current winter shortening is attributable to GHG forcing …

… But modulated by aerosols forcings


Detection and attribution

Agreement between observed very late summer onset in the 1950-1960 and HISTANT simulations. Luck? Sampling? True?

Origin of the observed earlier summer onset at the beginning of the 20th century. Quality of the data? Atlantic Multidecadal Variability (AMV) influences?


Dedicated simulations : the MORDICUS project

Definition of the SPEEDY-attribution runs for processed-oriented approach 1850-1990 anthropogenic aerosols trends contracted in 30

years --> 12 members of 30yr starting from PiControl

Doubling CO2 in 30 years --> 12 members of 30yr starting from PiControl

Confirmation of the aerosol forcing on the summer starting date (delay by X days)

Confirmation of the GHG forcing on the summer starting date (advance by X days)

AMO influences: --> 12 members of 30yr AMO+ and 12 members of 30yr AMO- starting from PiControl

AMO+

AMO-

No significant impact of AMO phases in CNRM-CM5


Mechanisms : land-sea contrast versus East-West gradient

Change in March Land-Sea contrast is NOT responsible for the ongoing trend

Reduction in Eastern-Western Europe temp. gradient in March is responsible for the ongoing earlier summer: role of Eastern Europe Snow decline

Snow cover (Eastern Europe)

Land-Sea contrast


Comparison between observed and model trends for snow cover

Snow cover (Eastern Europe)

Reduction in Eastern-Western Europe temp. gradient in March is responsible for the ongoing earlier summer: role of Eastern Europe Snow decline


Can we find year-to-come analogs today?199

6200

6201

3

1990

2007

2014


Can we find year-to-come analog today? ---> YES!

1996

2006

2013

1990

2007

2014

Snow years

Snow-free years

upper-tercile



Mettre ici les cartes des z500 et les cartes de neigede Fev? De Mars?

Annonce de la summer date (humour sur la recherchede la non-significativite).

Mettre le nombre dejours.Mettre graphe Yohan in caseof question MORDICUS.

Vanter les merrites de la metrique: integral


The winter starting date (the XXIst century under RCP85)

NCEP20CR PiCtl


No clear signal for winter starting dates


Detection and attribution (winter)

PiCtl

No volcanic eruption [1920-1960]

GHG forcing leads to later winter onset …

… but strongly counteracted by anthropogenic aerosols forcing

Ensemble Means


PiCtl

Confirmation of weak GHG forcing for later winter onset from MORDICUS experiments…

Confirmation of strong aerosols forcing for earlier winter onset from MORDICUS project

Ensemble Means

Dedicated simulations : the MORDICUS project


Thanks for your attention

ncar cgd seminar june 2015 disruption of the european climate seasonal clock in a warming world...

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