1. GloSea4: the Met Office Seasonal Forecasting System
A. Arribas, M. Glover, D. Peterson, A. Maidens, M. Gordon, C. MacLachlan, A. Williams, M. Vellinga, A. Scaife, R. Graham and many others
EUROBRISA Dec 2010
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2. GloSea4
GloSea4 is not a model. GloSea4 is an Ensemble Prediction System for long-range forecasting.
GloSea4 is designed to:
Facilitate model development to improve skill beyond ENSO
Be flexible to allow extension to monthly and decadal timescales
Arribas et al. 2011: The GloSea4 Ensemble Prediction System for Seasonal Forecasting. MWR, in press
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3. Model development? Flexible?
Sep 2009: Operational implementation of GloSea4 (N96L38O1L42)
May 2010: Technical update of system (model versions, etc)
Oct 2010:
Upgrade to N96L85-O1L75 (developed under GloSea4)
Assimilation of sea-ice concentration
Update hindcast period to 1996 – 2010
Feb 2011:
Monthly system (daily initialisation; 2 extra fcst members per day)
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4. GloSea4: How does it run? Forecast Hindcast
Hindcast: Run real time weekly; 14 yrs, 3 members/week, 7-months fcst
Forecast: Run real-time weekly; 14 members/week, 7-months fcst.
Forecast
6th
Dec‘10
13th
Dec‘10
22th
Dec’10
Hindcast
1st
Dec
9th
Dec
17th
Dec
25th
Dec
9th
Jan
1st
Jan
14-yrs:
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5. GloSea4: How does it run?
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6. GloSea4: How does it run?
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7. Real-time, short hindcast (14-yrs) …
Makes possible to link to model development
Makes the system flexible and easy to update
What are the issues for bias correction?
F‘ = F - H
What are the issues for skill assessment?
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8. Nino 3.4; from Nov, lead 1 The sub-sampling error:
2 sigma of means when sub-sampling N-years between
The signal:
Year to year variability (2 sigma)
Between
The diamonds are values for
the last N-years
(Figure courtesy
Of Anna Maidens)
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9. N. Europe; from Nov, lead 6 The signal:
Year to year variability (2 sigma)
Between
Climate trend
The sub-sampling error
(Figure courtesy
Of Anna Maidens)
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10. Short hindcast
TROPICS SEA: The signal we are trying to predict (year to year variability) is larger than the sampling error
EXTRA-TROPICS LAND: Larger sampling errors than in tropics (signal still larger). The main issue is low frequency variability (recent years are warmer!)
VEREDICT: A 14-yr hindcast is sufficient for bias correction (even before even considering non-stationarity of observing systems)
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11. Skill assessment
A longer hindcast set could be useful for skill assessment … but, how much can we believe the skill assessment?
Hindcast are different to Forecast:
Less (and worse) observations;
Less ensemble members (~10 vs ~40)
Periods with different low freq. variability and forcing
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12. Russian Heat-wave: Skill scores for surface temperature
ROC score for upper tercile
Area of Russian heatwave has
skill only marginally better than climatology
But skill is low, so even with a signal this strong, there is a high risk of issuing a false alarm.
However, skill is higher for outer quintiles, and it’s very hard to assess skill for extreme events, as there just aren’t enough of these in our limited hindcast run to do the stats – but (hypothesis only) our feeling is that there has to be some sort of pretty strong forcing to get into such an extreme region of phases space, and that probably the results of the dynamical model are more trustworthy when it is subjected to strong forcing.
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13. Russian Heatwave Forecasts initialised in May, 40 members
August, ensemble mean
July, ensemble mean
Moscow
Moscow
Very strong signal in both July and August ensemble means.
Pdfs clearly distinct from climatology (individual ensemble members shown as diamonds)
Pdfs for area average over 50-60N, 30-40E (green box).
Moscow shown as green star.
Pdfs ok here, as anomaly space (not percentage differences) and it’s a reasonable assumption to take temperature anomalies as Gaussian to a first approximation (not entirely correct – slight deviations in Nino regions for SST, for instance).
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14. So skill assessments should be taken with caution …
But I’ll show you some analysis of the GloSea4 hindcast (L38 version) anyway
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15. ACC Nino 3.4
GloSea4
GloSea3
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16. RMSE and Spread GloSea4 rmse GloSea3 rmse GloSea4 spread GloSea3
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17. Precip. telec. (Nino – Nina)
GloSea4 (89-02)
Obs (79-07)
JJA
DJF
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18. ROC Skill Prec. over Great Horn of Africa
Nino and Nina years only
All years
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19. MJO
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20. NAO
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21. Telec. To Europe Nino - Nina QBO (E) – QBO (W) GloSea4 Obs
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22. February 2010
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23. Unless you want to see the forecasts for this winter
That’s all …
Unless you want to see the forecasts for this winter
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30. Gracias
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