Change of strategy Hindcast length Frequency of system upgrades Centre's priorities JMA ~ 30 yr? ? NCEP ~ 40 yr8 yr Link to re-analysis ECWMF ~ 25 yr5 yr Med-range UK Met Office * 14 yr1 yr Link to model development * Arribas et al., 2011: GloSea4 ensemble prediction system for seasonal forecasting. MWR. 139, 1891-1910
Improved GloSea5 Range: 7months Model: HadGEM3 Resolution: N216L85O(0.25)L75 Initialisation: daily, NWP state + NEMOVAR 0.25deg Method: Full field + hindcast bias correction Ensembles: SKEB2 stoch. physics, lagged initialisation Forecasts: Seasonal 2 day -1 : 42 members updated weekly Monthly 2 day -1 : 28 members updated daily Reference: MacLachlan et al., 2013, in prep.
Atmos & land surf: ERA-i Ocean: Seasonal ODA reanalysis Atmos & land surf: NWP anal Ocean/sea-ice : NEMOVAR A coupled system for med-range and ocean forecasting 60 days6 months 6 th Dec 2012 9 th Jan 96-09 Forecasts Hindcasts 15 days - 24 members - IC perts. from MOGREPS-G - Coupled model as in GloSea5 - Run once a day - Comparison PS32 – PS34 - Operational end13 or 14? New suite:
GloSea5: Skillful NAO predictions! Scaife et al., 2013 Source: MetOffice.gov.uk R=0.60 NAO: November forecast for Dec-Jan-Feb observations forecast
PMSL anomalies from Nov for DJF 05/06 to 09/10 winters
Reasons for skilful NAO forecasts Gulf Stream Bias Wly wind bias => Blocking Deficit No Gulf Stream Bias No Wly wind bias => Good Blocking in N. Atl New Model Scaife et al., Geophys. Res. Lett., 2012. Low-res: 1 deg ocean High-res: 0.25 deg ocean
Not December! As found by Warwick Norton, there is very little skill in December Not a simple persistence of anomalies over the timescale of a few weeks Hints at a possible mechanism in late winter: ENSO/stratosphere => strongest NAO (Ineson and Scaife 2008) From Nick Dunstone
Looking at stratosphere: Data available L38 L85 GloSea4: N96 GloSea5: N216 89-0289-09 96-09
Obs No Strat Moderate NinoStrong Nino From Anna Maidens
A quick diversion: How good are ENSO forecasts in GloSea5?
Improving ENSO forecasts Obs The westward extension of Nino is a common error in many climate models. It affects remote regions. High-res model has better ENSO pattern and teleconnections Low resolution High resolution
Conclusions - GloSea5: High skill predicting winter NAO - Why? High horizontal res.; sea-ice; stratosphere - Skill highest in late winter, role of stratosphere? - Consistent with ENSO/Europe teleconnection through stratosphere and better SSW