1. Teleconnections in MINERVA experiments
Franco Molteni,
Frederic Vitart, Linus Magnusson
European Centre for Medium-Range Weather Forecasts

2. Outline
Predictive skill for NAO and PNA for seasonal (DJF) and month-2 (Dec) means
Predictive skill for Indo-Pacific rainfall and teleconnections with NH 500 hPa height
Blocking frequency (TM index) and SSW – NAO correlation (from L. Magnusson)

3. PNA and NAO: EOF vs. covariance with 2-box index
80W-40E,
25-85N
[25W-5E,
30-45N] -
[40-10W,
55-70N]

4. PNA, DJF (m2-4)
ac = 0.68
ac = 0.66

5. NAO, DJF (m2-4)
ac = 0.26
ac = 0.51

6. NAO, Dec (m2)
ac = 0.37
ac = 0.50

7. Ensemble-mean NAO fc. for DJF

8. Local correlation SST – precip, DJF 1981-2008

9. Precip. teleconnections in DJF: GPCP 2.2

10. Precip. teleconnections in DJF: System 4 (from Nov.)

11. Z 500_hPa vs. precip: ERA-Int. and System-4

12. W. Indian Oc. teleconnections, ENSO removed
Full precip
anomaly
Anomaly
orthogonal
to Nino3.4 SST

13. Predictive skill for W.Ind and E.Ind-W.Pac SST/precip

14. Western & Central Indian Ocean (wcio), DJF

15. Western & Central Indian Ocean (wcio), DJ

16. Eastern Indian – West Pacific (eiwp), DJF

17. Eastern Indian – West Pacific (eiwp), DJ

18. Nino-4, 10N-10S (nino4w), DJF
T319
T639

19. Correlations of Indo-Pac. rainfall and NAO (DJF)
WCIO
obs
EIWP
NAO
T319
T639
-0.14
0.35
-0.54
-0.48
0.21
-0.06
-0.18
NINO4W
0.19
-0.82
-0.08
0.59
0.55
-0.81
-0.80
0.24
0.20

20. composites for below-average rainfall in WCIO
DJF
T319
T639 DJ
T319
T639

21. Blocking frequency (1 day or longer)
DJF
MAM
SON
JJA

22. Blocking frequency (5 day or longer)
DJF
MAM
JJA
SON

23. Sudden stratospheric warmings -> NAO
DJF
JJA

24. Summary
On seasonal timescale, T639 has the same predictive skill as T319 for PNA, but a (notably) higher skill for NAO; the NAO skill improvement is also seen in month-2 means.
For Indo-Pacific rainfall, the MINERVA runs (as Sys-4) simulate stronger links between rainfall in Western/central Indian Ocean and over Maritime Continents and central Pacific than those found in GPCP data. As a result, extratropical teleconnections from these three tropical regions look more similar than in observation, and the NAO – Indian Ocean rainfall connection is underestimated. This problem is marginally alleviated in T639 wrt T319.
T639 shows a stronger signal than T319 in the North Atlantic associated with below-average rainfall in the W/C Indian Ocean, and a higher frequency of “Greenland blocking”.
At both resolutions, the lagged correlation between sudden stratospheric warmings and NAO is poorly represented.
So, why are the T639 NAO forecasts better?

25. ECMWF seasonal fc. System 4: main features
IFS model cycle: 36r4 (op. Nov May 2011), T255-L91
Ocean model : NEMO (v coupling interface)
ORCA-1 configuration (~1-deg. resol., ~0.3 lat. near the equator)
42 vertical levels, 20 levels with z < 300 m
Variational ocean data assimilation (NEMOVAR)
FGAT 3D-var, re-analysis (ORA-S4) and near-real-time system
Collaboration with CERFACS, UK Met Office, INRIA
Operational forecasts
51-member ensemble from 1st day of the month, released on the 8th
7-month integration
13-month extension (with 15 ens. members) from 1st Feb/May/Aug/Nov
Re-forecast set
30 years, start dates from 1 Jan 1981 to 1 Dec 2010
15-member ensembles, 7-month integrations
13-month extension from 1st Feb/May/Aug/Nov