Jet Latitude in Seasonal Forecasts:variability and predictability in DJF

(UKMO, CFSv2, CMCC)

Panos Athanasiadis (CMCC, Bologna, Italy)

S. Tibaldi, A. A. Scaife, S. Gualdi, A. Hannachi, L. Hermanson, S. Materia, A. Borrelli, A. Sanna, C. MacLachlan, A. Arribas.

© P. Athanasiadis, CMCC, Bologna, 2016.

Athanasiadis et al., J. Atm. Sci., (2010) Woollings et al., J. Atm. Sci., (2008)

The jet variability, blocking / WB variability and the NAO, are different facets of the

same cube: the tropospheric LF variability over the mid-latitude N. Atlantic.

Woollings et al., Q. J. R. Met. Soc., (2010)

© P. Athanasiadis, CMCC, Bologna, 2016.

Frame et al., GRL (2013)

Different analysis methods used to examine the same phenomenon give strongly corresponding, if not equivalent, results.

© P. Athanasiadis, CMCC, Bologna, 2016.

P. Athanasiadis, M. Wallace and J. Wettstein, J. Atm. Sci., (2010)

NAO (+)

EAP (+)EAP (-)

NAO (-)

© P. Athanasiadis, CMCC, Bologna, 2016.

Teleconnectivity of daily zonal wind in DJF

U850 U250

© P. Athanasiadis, CMCC, Bologna, 2016.

C.I. = 0.025, Max = 0.60 C.I. = 0.05, Max = 0.60

CMCC-SPS-v1.5

Atmosphere: (Echam5-SILVA) T63 L19 (no stratosphere).

Ocean: (OPA8.2) ~2°, L31(sea-ice initialized from climatology)

Hindcasts: 1992–2011 (DJF)

9 members.

Basic characteristics of the examined seasonal forecasting systems.

CFSv2

Atmosphere: (GFS) T126 ~1° L64 (→0.2 hPa).

Ocean: (MOM3) ~1°, L40 (sea-ice initialized from climatology).

Hindcasts: 1992–2011 (DJF)

20 members.

UKMO - GloSea5

Atmosphere: (HadGEM3) 0.83°x0.55° L85 (→85 km).

Ocean: (NEMO) 0.25°x0.25°, L75 (with assimilated sea-ice).

Hindcasts: 1992–2011 (DJF)

24 members.

© P. Athanasiadis, CMCC, Bologna, 2016.

Athanasiadis et al., J. Clim., (2014)

© P. Athanasiadis, CMCC, Bologna, 2016.Athanasiadis et al., J. Clim., (2014)

UKMO I.B. on NAO UKMO Z500 on I.B. UKMO skill for I.B.

Athanasiadis et al., J. Clim., [in review]

ACC = 0.85

Predictive skill (ACC) for winter mean MSLP (1992—2011)

CFSv2, n=20

UKMO, n=24

CMCC, n=9

© P. Athanasiadis, CMCC, Bologna, 2016.

CFSv2 UKMO CMCC

ERA-Int NCEP

Jet Latitude distributions for DJF (1992—2011)

© P. Athanasiadis, CMCC, Bologna, 2016.

© P. Athanasiadis, CMCC, Bologna, 2016.

NAOEAP

EAPNAO

CFSv2

UKMO

SOUTH JET CENTRAL JET NORTH JET

CFSv

2

UKMO

© P. Athanasiadis, CMCC, Bologna, 2016.

Barnes et al., GRL, (2010)

© P. Athanasiadis, CMCC, Bologna, 2016.

© P. Athanasiadis, CMCC, Bologna, 2016.

Overview

The variability of the N. Atlantic eddy-driven jet can be diagnosed with a variety of methods (e.g. using EOFs of U250) that all give strongly corresponding results.

Due to the poleward tilt of the jet, zonal averaging may mask the nature of its variability (meridional shifts around the climatological jet position, as indicated by zonal wind teleconnectivity).

The traditional extratropical teleconnections, such as the NAO and the EAP, are reflections of the same two-sided phenomenon: eddy-driven jet variability and blocking / WB variability (storm track dynamics are highly relevant here).

The winter mean NAO relates very strongly to the Center and South jet counts, as well as to the variations of the blocking frequency at certain areas. All these aspects exhibit similarly significant predictive skill in seasonal forecasts.

In the contrary, the winter mean EAP and the North jet counts do not seem to be predictable at the seasonal time scale. This may relate to the fact that they

are related to variability further downstream, which is less dependent on boundary forcings upstream (just a guess).

Thank you for your attention

Predictive skill (ACC) for winter-mean U850 (1992—2011)

CFSv2, N=20

UKMO, N=24

CMCC, N=9