stratospheric,dynamics,and, climate,predictability, · presentazione1.pptx author: chiara cagnazzo...
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Stratospheric Dynamics and Climate Predictability
Chiara Cagnazzo ISAC, CNR
Predic=ons, projec=ons and predictability
Like numerical weather predic=on, evolu=on of the system depends (or is assumed to depend) on the ini=al state. Unlike numerical weather predic=on, the =me scale of interest is beyond the range of determinis=c predictability. Like climate projec=ons, we are mainly interested in changes of sta=s=cal proper=es over a period of interest: means, extremes, etc. Unlike climate projec=on, the period of interest is less than the annual cycle (seasonal), or is a small mul=ple of it (interannual to decadal).
The stratosphere
Stratospheric meridional circula=on
Iner=o-‐Gravity waves
Planetary scale waves
Synop=c scale waves
Stratosphere-‐troposphere coupling Baldwin and Dunkerton 2001
Thompson and Wallace 2000
Stratosphere-‐troposphere coupling mechanisms Wave–zonal flow interac=on Remote response of the troposphere to stratospheric poten=al vor=city anomalies (e.g. Hartley et al., 1998; Black, 2002) Local tropospheric response maintained by feedbacks with transient eddies (Song and Robinson, 2004) ver=cal reflec=on of planetary waves (e.g. Perlwitz and Harnik, 2003) and refrac=on of synop=c waves (e.g. Simpson et al., 2009) linear interference between the climatological waves in the stratosphere and the wave response to a tropospheric forcing (Fletcher and Kushner, 2011) Impact of stratospheric changes on baroclinic instability (e.g. Riviere, 2011) and wave breaking into the troposphere (e.g. Kunz et al., 2009)
SSWs & seasonal forecast
Sigmons et al., Nature Geoscience 2013
Seasonal -‐ Interannual =mescale Scaife et al., 2014
Inter-‐annual =mescale
T at 80N and U at 60N, HT and LT
Real predic=ons with stratosphere Scaife et al., 2014
QBO predictability in two models: Blue versus observa=ons Green versus a regular 28 months period Red, theore=cal predictability
QBO teleconnec=ons
Longer =mescales: anthropogenic climate change in the SH
Zonal mean zonal wind, NDJF and linear trends, from Gerber et al.,2012
Thompson et al, Nature Geoscience, 2013
1960-‐1999 Trends in ERA40 Same trends in models with and without stratospheric O3 trends
1960-‐1999 Trends in a model with a well resolved stratosphere (top), in Nov and Dec And without a well resolved stratosphere (bodom) From Cagnazzo et al., 2013
Interface: wind-‐stress, carbon fluxes, NDJ
From Lenton et al., 2009
Rea et al., in prepara=on
Mul=-‐decadal =mescale
Connec=on bewteen SSWs varia=ons and Atlan=c Ocean circula=on, Shimanke et al., 2011: + heat flux anomalies from NA, + snow cover over Eurasia and blocking + 100 hPa heat flux weak vortex , SSWs downward propaga=on ac=ng as a stochas=c forcing , triggering an oscilla=on at the oceanic frequency
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Strong and weak vortex sequence
Downward propaga=on in the ocean
Stratosphere leading
Mul=-‐decadal =mescale
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Solar cycle signal in the stratosphere and at surface, Ineson and Scaife, Nature Geoscience 2011
Sea-‐level pressure difference for model (a) and ERA-‐40/ERA-‐Interim reanalysis (b). c,d, Near-‐surface temperature difference for model (c) and reanalysis (d).
Perspec=ves To which extent the representa=on of the above men=oned processes are key to improved predic=ons? Which effects need to be included to maximize predic=on skills at the decadal =mescale? It is necessary to : -‐ beder understand the mechanisms of the stratospheric impact on climate at different =mescales.
-‐ Longer =mescales: It may be the representa=on of the stratosphere itself and therefore of the stratosphere-‐troposphere-‐ocean-‐sea ice coupling that could lead to improved predic=on skill at the decadal =mescale:
-‐ Stratospheric chemistry and microphysics
-‐ Radia=on schemes sensi=ve to changes in solar irradiance