1. Prospects for Wintertime European Seasonal Prediction
Warwick Norton
Walker Institute (University of Reading)
& PCE Investors

2. North Atlantic Oscillation

3. Outline
Predictability/persistence of the NAO on intraseasonal timescales (10-30 days).
Predictability of the NAO on seasonal timescales with 1-6 month lead time.
Examine reanalysis datasets and HiGEM - a new high resolution coupled atmosphere/ocean model.
Contrast winter & summer

4. HiGEM Model Based on the new Hadley Centre HadGEM1 climate model
HiGEM Atmosphere:
horizontal resolution 1 (N144)
38 z-levels
non-hydrostatic semi-Lagrangian dynamics
aerosols
HiGEM Ocean:
horizontal resolution 1/3
40 z-levels with analytic stretching for 2nd order accuracy
HiGEM Ice:
EVP scheme with 5 ice categories
50 year control integration has just been completed

5. The UK in HiGEM

7. 1st EOF of winter (DJF) monthly MSLP (NAO)
ERA40
- explains 38%
of total variance
HiGEM
- explains 34%
of total variance

8. Projection of NAO pattern onto daily MSLP gives daily NAO timeseries
ERA40
HiGEM
Lack of persistence at days in HiGEM

9. 1st EOF of summer (JJA) monthly MSLP (NAO)
ERA40
- explains 30%
of total variance
HiGEM
- explains 28%
of total variance

10. Projection of NAO pattern onto daily MSLP gives daily NAO timeseries
HiGEM
ERA40
Less persistence of NAO in summer, HiGEM ok

11. Middle Atmosphere GCM experiment where middle/upper Stratosphere is damped (Norton 2003)
North Pole Temperatures at 30 km
damped
control
No stratospheric warmings in strong drag experiment

12. Autocorrelation of daily surface AO index
Control experiment
Strong drag experiment
Reduction in memory of surface AO from less variable stratosphere
Supports the hypothesis that lack of NAO persistence in HiGEM is due to inadequate representation of the stratosphere.

13. Seasonal DJF Mean NAO
Significant low frequency variability with correlation at lag 1 year.
What is the source of this? Is it predictable?

14. Seasonal JJA Mean NAO Smaller amplitude than in winter
Very little low frequency variability

15. Correlation of May SSTs with following Dec-Jan Central England Temperatures
Non-ENSO years only (33)
All years
(see also Rodwell & Folland, 2002; Czaja & Frankignoul, 2002)

16. May Sea Surface Temperatures
Composite of: , 1962, 1966, 1969, 1980, 1995
(region inside solid contour is different from mean at 95% confidence interval)
2005

17. Dec-Jan “Composite” Forecast
Atlantic SST anomaly has persisted
Cold temperatures centred over Eastern Europe
Dry conditions in the North-West Atlantic extending into the UK

18. Dec-Jan 2005/6 Atlantic SST anomalies have persisted
Cold temperatures centred over Eastern Europe
Very warm over Canada - influence of weak La Nina?
Dry conditions in the North-West Atlantic extending into the UK

19. 2m Air Temperatures - Berlin
Years: 1962, 1966, 1969, 1978, 1980, 1981, 1995, 1996, 2005/6
(Long term trend removed)

20. Dec-Jan Atmosphere GCM Experiment (low resolution HadAM3)
Reinforcement by cold SSTs .  .
Circulation anomaly (anticyclone)
Precipitation anomaly
Rossby wave propagation into Europe

21. How does HiGEM do in getting the SST signal?
Correlation of May SSTs with following Dec-Jan Central England Temperatures
HiGEM
Observations
No signal in the subtropics

22. Correlation of November SSTs with following Dec-Jan Central England Temperatures
HiGEM
Observations
No signal in the subtropics

23. Conclusions
Representation of the stratosphere appears to be important for persistence of NAO in winter.
Atlantic SSTs can force the NAO in ENSO neutral years.
Coupled atmosphere/ocean models only partially represent the NAO/Atlantic SST relationship.
Getting the Pacific SSTs right is important but an ENSO event happens only ~50% of years. The tropical/subtropical Atlantic SSTs are also important for seasonal prediction (and hurricanes).