© Crown copyright 2007

Monthly-Seasonal forecastingAlberto ArribasMonthly to Decadal group, Met Office Hadley Centre

Geneva, December 2011

Our strategy for monthly-seasonal forecasting

- Unified monthly-seasonal system, fully integrated with model development process

- Using latest available model version (from NWP to monthly-seasonal)

- Focus on understanding physical mechanisms: Aim is to improve the model faster to increase forecast skill faster

Paper documenting the system when launched in 2009:

The GloSea4 Ensemble Prediction System for Seasonal Forecasting.

Arribas et al, 2011

Mon. Wea. Rev., 139, 1891–1910.

GloSea4 (Global Seasonal Forecasting system version 4)

Link with model development means frequent model upgrades and hindcast run in real-time

(as forecast)

Consequence: shorter hindcast

Hindcastsize Update

frequency

GloSea4 history

Summer 2009:GloSea4 starts

• GA 1.0• N96L38 Orca(1)L42• Hindcast: 1989-2002

November 2010:Model upgrade

• GA 2.0• N96L85 Orca(1)L75• Sea-ice initialisation• Hindcast: 1996-2009

March 2011:Daily forecast

• Daily initialisation• Monthly system

Arribas etal, 2011

GloSea4 plans

November 2011:Model upgrade • GA 3.0

• N96L85 Orca(1)L75

Summer 2012:Model upgrade

• GA 4.0• N216L85 Orca(0.25)L75

• ~ 50km (mid-lat)

Current operational system

Model version: HadGEM3 GA2.0

Resolution: N96L85 O(1)L75 (~120 km, ~ 1 dg)

Simulations length: 7 months

Model uncertainties represented by: • SKEB2 stochastic physics

Initial conditions uncertainties represented by:• Lagged ensemble

Initialisation

Forecast (daily):Atmosphere & land surf: NWP analysisOcean & sea-ice: Seasonal ODA (Optimal

Interpolation)

14-year Hindcast (1996-2009):Atmosphere & land surf: ERA-interim Ocean & sea-ice: Seasonal ODA reanalysisFixed start dates of 1st, 9th, 17th, 25th of each month

Ensemble: lagged approach

Seasonal Forecast:2 members run each day. Forecast updated every week: 42 members (last 3 weeks)Bias corrected using hindcast (~168 members)

Hindcast (for monthly-seasonal):14 year hindcast run in real time, 3 members per year and start date completed every week (i.e. 42 members/week)

Monthly Forecast:2 members each day. Forecast updated daily: 28 members (last 7 days)Bias corrected using hindcast (~168 members)

20/06/2011

20/06/2011

How the system runs, an example

Atmos & land surf: NWP anal

Ocean/sea-ice: Seasonal ODA

Atmos & land surf: ERA-i

Ocean: Seasonal ODA reanalysis

25/07/1996 (m1)

25/07/1997 (m1)

25/07/1998 (m1)

25/07/1999 (m1)

25/07/2000 (m1)

25/07/2001 (m1)

Monday

21/06/2011

21/06/2011

25/07/2002 (m1)

25/07/2003 (m1)

25/07/2004 (m1)

25/07/2005 (m1)

25/07/2006 (m1)

25/07/2007 (m1)

Tuesday

26/06/2011

26/06/2011

25/07/2004 (m3)

25/07/2005 (m3)

25/07/2006 (m3)

25/07/2007 (m3)

25/07/2008 (m3)

25/07/2009 (m3)

Sunday

Each week: 14x 7-month forecasts, 14x 2-month forecasts (for monthly forecast) and 42x 7-month hindcasts (1996-2009)

20/06/2011

20/06/2011

21/06/2011

21/06/2011

26/06/2011

26/06/2011

An international system ...

KMA (Rep. of Korea) • Joint seasonal forecast system• Shared workload and computing costs:

possibility to extend hindcast and increase resolution

NCMRWF (India) – implementing GloSea for research

Our approach to data sharing

Happy to make NON real-time forecasts (at least 1-month old) and hindcast freely available for research

• Africa: ~ 6 centres currently analysing data from GloSea4 hindcasts

• China Meteorological Agency (hindcast)• Japan (hindcast and non real-time fcst)• UK Universities (hcst and non real-time fcst)• etc

Real time data ...

Real time forecast and hindcast data (same set of seasonal forecasting standard products) supplied to:

• WMO Lead Centre

• EUROSIP

ENSO and ENSO

teleconnections

Nino 3.4 SST

From

May

From

Nov

ACC RMSE / SpreadNino 3.4 SST

ENSO Telecon. (precip)

Observations L85 - GloSea4

JJA

DJF

An example of a recently improved physical

mechanism:

ENSO – Europe teleconnection

Importance of vertical resolution: ENSO teleconn.

January-February anomalies, NCEP 1950-2000

Toniazzo and Scaife 2006

Obs Moderate el Nino Obs Stong el Nino

L38 model – moderate Nino L38 model – stong Nino

January-February anomalies, NCEP 1950-2000

Toniazzo and Scaife 2006

Moderate el Nino Stong el Nino

L85 model – moderate Nino L85 model – stong Nino

Importance of vertical resolution: Stratospheric model

Future improvements: higher resolution

ENSO teleconnections with Indian monsoonO

bs

L38

L85

N216

N96

Future developments: Benefits of higher spatial resolution

Obs

This error is common to many climate modelsIt affects remote regionsN216 has better ENSO pattern and teleconnections

Sarah Ineson, Dave Rowell

Benefits of higher resolution: Improved Atlantic Blocking

Gulf Stream Bias

Wly wind bias

=> Blocking Deficit

No Gulf Stream Bias

No Wly wind bias

=> Good Blocking

New Model

Scaife et al., Geophys. Res. Lett., submitted.

Blocking Frequency

1 degree ocean

0.25 degree ocean

MJO

Other recent improvements:

Arctic sea-ice

Forecasting Arctic Sea-ice

observations

Hindcast Forecast

2011 Arctic Sea-ice forecast

Products from the

GloSea4 system

• We are a WMO Global Producing Centre• Member of EUROSIP• Contributor to WMO Lead Centre

• Products: hurricanes, water management, etc

• Main customer for monthly-seasonal is UK Government

Public forecast for 2011Released 26th May 2011Near- to above-normal activity predicted

Observed to dateNovember

forecastSeason total

Tropical storms 16 2 18

ACE index 111 5 116

Main forecast product for government

ENSO prediction from April-Sep (EUROSIP)

Apr May Jun

Jul Aug Sep

Inputs into forecast

Euro-SIP Output

Ensemble mean PMSL Anomalies: November

GloSea4 ECMWF MeteoFranceFrance

Inputs into forecast

GPC output

PMSL anom

Pretoria Montreal

Toulouse

Tokyo

Seoul

MelbourneWashington

CPTEC

Exeter

Beijing

ECMWF

Moscow

Inputs into forecast

Government product: Fig. 1

Government product: Fig. 2

Government product: Fig. 3