© Crown copyright Met Office The Met Office high resolution seasonal prediction system Anca Brookshaw – Monthly to Decadal Variability and Prediction,

© Crown copyright Met Office

The Met Office high resolution seasonal prediction system

Anca Brookshaw – Monthly to Decadal Variability and Prediction, Met Office Hadley Centre, UK

FOCRAII 2013

Outline

• configuration of latest operational system

• analysis of hindcasts

• ENSO

• (N)AO

• WNPSH

• rainfall ‘extremes’

• tropical storms


Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms


A recent history of improvements at the Met Office

- Summer 2009: New generation prediction system (linked to model development) becomes operational

- Nov. 2010:

- Vertical high-res (L85 stratosphere / L75 ocean)

- Sea-ice assimilation

- May 2011:

- Extension to monthly system

- Nov. 2012:

- Horizontal high resolution (50 km atm / 0.25 ocean)

- NEMOVAR – 3d-Var ocean data assimilation



Representation of orography

~ 120 km

~ 50 km

GloSea5 operational system

Model version: HadGEM3 GA3.0

Resolution: N216L85 O(.25)L75 (~50 km atm.)

Simulations length: 7 months

Model uncertainties represented by: • SKEB2 stochastic physics (Tennant et al. 2011)

Initial conditions uncertainties represented by:• Lagged ensemble


Initialisation of the system

Forecast (initialised daily):

- Atmosphere & land surf: Met Office NWP analysis (4d-Var)

- Ocean & sea-ice: NEMOVAR (3d-Var joint system for ocean, med-range, monthly and seasonal)

14-year hindcast (1996-2009):- Atmosphere & land surf: ERA-interim - Ocean & sea-ice: seasonal ODA reanalysis- Fixed start dates of 1st, 9th, 17th, 25th of each month- 3 members per start date


Ensemble: lagged approach

Seasonal Forecast:- 2 members run each day.

- Seasonal forecast updated weekly by pulling together last 3 weeks (i.e. 42 members)

Hindcast (for monthly-seasonal):14 year hindcast run in real time ( 42 members run

each week = 14 years x 3 members)

Monthly Forecast:- 2 additional members run each day.

- Monthly Forecast updated daily by pulling together last 7 days (i.e. 28 members)


20/06/2011

20/06/2011

How the system runs – an example

Atmos & land surf: NWP

analOcean/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

Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms



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


Niño3.4 SST: ACC, RMSE/spread

ACC higher (good)

RMSE reduced (good)

May JJA Nov DJF

GloSea5 (red)

GloSea4 (blue)


JJA

DJF

Forecast Observed

Better ENSO teleconnections: precipitation Niño - Niña

Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms


© Crown copyright Met Office Scaife et al., GRL, 2011

Realistic blocking frequency

Benefits of higher ocean resolution: improved bias and Atlantic blocking

Gulf Stream bias

westerly wind bias

=> blocking deficit

Low res 1o

No Gulf Stream bias

No westerly wind bias

=> good blocking

High res 0.25o


A breakthrough in predicting the NAO

GloSea5

Hindcast Atlantic pressure

Significant (98%) NAO skill r~0.6(other models: approx 0.2; not stat. sig.)

Opens up many possibilities for long range prediction for Europe

and North America

Obs Forecast Retrospective winter forecasts

Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms



International collaboration to improve prediction systems

Working with Chinese Meteorological Agency on

West North Pacific Subtropical High

Jianlong Li


GPCP Composite rainfall with strong WNPSH

Importance of West North Pacific Subtropical High

Jianlong Li


Obs

Previous System

New System

The variability of the WNPSH is much improved in the latest system

Jianlong Li


GPCP Correlation between SH index and rainfall

GloSea5

Jianlong Li


Correlations with observations:Previous System =0.41 ---- New System=0.83

Skill predicting interannual variability of West North Pacific Subtropical High

Jianlong Li


Skill predicting interannual variability of rainfall over the Yangtse River Valley

Correlations with observations:Previous System = 0.35 ---- New System= 0.69

Jianlong Li

Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms



dry

Emily Wallace


wet

Emily Wallace

Outline



• ENSO

• (N)AO

• WNPSH


• tropical storms



Tropical storm tracks: June-November 1996-2009

GloSea5 ~53 km horizontal resolution 1 member, June–November 1996–2009

Observations from JTWCJune–November 1996–2009

Increase in horizontal resolution has improved the tracks of tropical storms in the Western Pacific.

Joanne Camp


Hindcast skill: Northwest Pacific June–November 1996–2009

Tropical Storm Frequency (winds ≥34 knots)

Accumulated Cyclone Energy (ACE) Index

GloSea5 = 0.56 Glosea4 = 0.39

Pearson’s linear correlation (ensemble mean vs observations):GloSea5: Max 30 members/yearGloSea4: 9 members/year

GloSea5 shows greater skill for predictions of tropical storm numbers and ACE index in the Western North Pacific basin, compared to GloSea4.

GloSea5 = 0.88 GloSea4 = 0.80

Joanne Camp

GloSea5 storm track density:El Niño vs. La Niña

La NiñaEl Niño

Changes in storm

genesis locations

with ENSO simulated

well by GloSea5.

La Niña - El Niño

Fewer storms

Obs(JTWC)

GloSea5(ensemble

mean)

© Crown copyright Met Office Joanne Camp


An international prediction system

KMAKMA (Rep. of Korea)

• Joint seasonal forecast system

• Shared workload and computing costs: possibility to extend hindcast and increase resolution

NCMRWFNCMRWF (India)

• Implementing GloSea for research


Seamless system across timescales

GloSea5 med-range (2013)GloSea5 med-range (2013)

• Project to merge with med-range in 2013

• Aim is to have a single operational system (using coupled model at the highest possible resolution) for short-range ocean, med-range, monthly and seasonal – at the end of 2013

GloSea5 decadal (2014)GloSea5 decadal (2014)

• System to be extended – in research mode - to decadal timescales in 2013

• Seamless system med-range to decadal from 2014


Thank you.

© Crown copyright Met Office The Met Office high resolution seasonal prediction system Anca Brookshaw – Monthly to Decadal Variability and Prediction,

Documents

met office summer

monthly system

met office nwp analysis

members monthly forecast

lagged ensemble slide

office hadley centre

start date slide

members hindcast