© Crown copyright Met Office The Met Office high resolution seasonal prediction system Anca...
-
Upload
katelyn-gillett -
Category
Documents
-
view
214 -
download
0
Transcript of © Crown copyright Met Office The Met Office high resolution seasonal prediction system Anca...
© 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
© Crown copyright Met Office
Outline
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
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
© Crown copyright Met Office
© Crown copyright Met Office
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
© Crown copyright Met Office
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
© Crown copyright Met Office
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)
© Crown copyright Met Office
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
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
© Crown copyright Met Office
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
© Crown copyright Met Office
Niño3.4 SST: ACC, RMSE/spread
ACC higher (good)
RMSE reduced (good)
May JJA Nov DJF
GloSea5 (red)
GloSea4 (blue)
© Crown copyright Met Office
JJA
DJF
Forecast Observed
Better ENSO teleconnections: precipitation Niño - Niña
Outline
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
© 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
© Crown copyright Met Office
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
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
© Crown copyright Met Office
International collaboration to improve prediction systems
Working with Chinese Meteorological Agency on
West North Pacific Subtropical High
Jianlong Li
© Crown copyright Met Office
GPCP Composite rainfall with strong WNPSH
Importance of West North Pacific Subtropical High
Jianlong Li
© Crown copyright Met Office
Obs
Previous System
New System
The variability of the WNPSH is much improved in the latest system
Jianlong Li
© Crown copyright Met Office
GPCP Correlation between SH index and rainfall
GloSea5
Jianlong Li
© Crown copyright Met Office
Correlations with observations:Previous System =0.41 ---- New System=0.83
Skill predicting interannual variability of West North Pacific Subtropical High
Jianlong Li
© Crown copyright Met Office
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
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
© Crown copyright Met Office
dry
Emily Wallace
© Crown copyright Met Office
wet
Emily Wallace
Outline
• configuration of latest operational system
• analysis of hindcasts
• ENSO
• (N)AO
• WNPSH
• rainfall ‘extremes’
• tropical storms
© Crown copyright Met Office
© Crown copyright Met Office
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
© Crown copyright Met Office
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
© Crown copyright Met Office
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
© Crown copyright Met Office
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
© Crown copyright Met Office
Thank you.