Impact of initial conditions on PDO and AMO

Impact of initial conditions on PDO and AMO PDO De. Pre. Sys – No. Assim AMO De. Pre. Sys – No. Assim 110 m ocean T, 2007 -12 AMO PDO © Crown copyright Met Office

Impact of initial conditions on the coming decade (2007 -2017) 360 m upper ocean T Surface T Precip (% of 1979 -2001 mean) • Mar 2007 to Feb 2017 • De. Pre. Sys - No. Assim © Crown copyright Met Office

Contents • The Met Office Decadal Prediction System ØInitial assessment • Impact of initial conditions on forecasts from 2007 • Reanalysis of historical ocean observations ØNeeded for hindcasts starting from 1960 etc. • New hindcasts: preliminary results © Crown copyright Met Office

Analysis of historical ocean data 1960 obs • Need hindcasts to assess likely skill of forecasts • Problem with very sparse subsurface ocean observations • Can we use optimal interpolation to reanalyse historical ocean data? Correlation of SST anomalies with SST at 1200 W on the Equator (Had. ISST, January) © Crown copyright Met Office 1980 obs

Reconstructed model temperature at 300 m from Jan 1953 obs locations Parameterised covariances R=0. 23 Actual covariances Truth R=0. 68 Observations: Jan 1953 If covariances are known, very accurate re -analysis of historical sub-surface temperature and salinity appears to be possible © Crown copyright Met Office

SST anomaly correlations: Had. CM 3 105 o. E, 5 o. N 60 o. W, 20 o. N 130 o. W, 0 o. N Obs (Had. ISST) © Crown copyright Met Office Model (Had. CM 3) R=0. 77 R=0. 48 R=0. 20

SST anomaly correlations: model ensemble 105 o. E, 5 o. N 60 o. W, 20 o. N 130 o. W, 0 o. N Obs (Had. ISST) © Crown copyright Met Office Model (Had. CM 3) Model ensemble R=0. 77 R=0. 84 R=0. 48 R=0. 77 R=0. 20 R=0. 72

Temperature at 300 m : June 2007 from 1960 obs June 2007 Had. CM 3 covariances © Crown copyright Met Office June 1960 Iter 01 All obs Iter 03