Only 1 major sudden stratospheric warming (SSW) observed in SH (2002) but minor warmings occurred in 2009 and 2012 NH events occur in 3 out of every 5 years SH SSW in 2002 cause not very well known but infrequent due to weak wave driving Weak (strong) vortex associated with subsequent sustained low (high) SAM/NAM. Important “window of opportunity” for useful multiweek prediction of climate Aim of subproject is to determine: i) predictability and cause of SH SSW in 2002 (and 2012) ii) predictability of tropospheric anomales following SSW (both NH and SH) does resolving/initializing the stratosphere improve predictions of tropospheric climate? iii) development of diagnostics/products to monitor ongoing predictions Monthly prediction of Southern & Northern Hemisphere Stratospheric Warmings and Surface SAM/NAM impacts Harry Hendon (BoM) and Adam Scaife (UKMO)

A project with two components: 1) What is the predictive capability for SSWs (with SNAP)? sensitivity to initialization/resolution in stratosphere sensitivity to model e.g. parameterized gravity wave drag role and predictability of pre-conditioning 2) How could SSW be used for monthly prediction SAM/NAM after the warming? How well predicted are subsequent regional climate impacts e.g. reduced rainfall across subtropical Australia and cooling over N Europe? Additional outcomes could include: Understanding of pre-conditioning for SSWs Mechanism by which stratosphere drives sustained shift of the SAM/NAM e.g. Hartley et al 1998, Haines et al 1991, Perlwitz and Harnick 2003, Charlton et al 2005, Scaife et al 2012 Improved assessment of the predictability of SAM/NAM (including its sources) Research into useful forecast products

Thompson et al 2003

Surface climate anomalies in October following anomalous SH polar cap ozone in September (looks like typical low SAM anomalies)

An apparent warming/shift to low SAM also occurred in Oct 2012

Polar cap (60-90) column ozone October Strong warming in 2012, based on high ozone in October Comparable ozone shift to 2002

vs 2002: zonal mean zonal wind at 10mb 2012 warming is interesting but much weaker than the 2002 event

Sea Level Pressure Anomalies

Cooling events also occur and are associated with shifts to high SAM

not much hint of low SAM for forecasts prior to SW but some sustained low SAM if initialized when SAM is already low… POAMA forecasts of low SAM following 2012 SSW in id Oct Time series of observed SAM POAMA ensemble from 11 Oct from 1 Nov

NH: Cold and dry impact on N Europe Marshall and Scaife 2010 N European cooling due to –ve NAO Better predicted (12d vs 8d) in deep domain model

UKMO Monthly forecasts for Jan 2013 Obs Fcast Jan 2013 – SSW appearing from 21 st Dec Operational forecasts from late Dec => increased riskACTIONABLE

Stratospheric Network for the Assessment of Predictability (SNAP) Three year ( ) program funded by UK NERC and WCRP/SPARC Scientific aims to quantify: –current skill in forecasting the extra-tropical stratosphere, –the extent to which accurate forecasts of the stratosphere contribute to improved tropospheric predictability, –the partitioning of any gains in predictability with a well-resolved stratosphere between improvements in the estimation of initial conditions and improvements in the forward forecast. The centrepiece of SNAP will be to design and perform a new intercomparison of stratospheric forecasts This will also leave a legacy of datasets to be used by a broad community of researchers

Project Partners Forecasting centres: provide staff time, computer time –Met Office (UK); Environment Canada; Met Research Institute (Japan); Naval Research Laboratory (USA); Bureau of Meteorology (Australia) Research organizations: provide staff time, analysis –Exeter University (UK); New York University (USA) More partners welcome (S2S seems pretty obvious)

Next Steps January 2013: form Steering Committee April 2013: First Workshop – review existing science and future directions; design a stratospheric predictability experiment; produce an experimental strategy (Frederic will attend?) From June 2013: start running stratospheric predictability experiments