1) Moderate El Ni ñ o (a) Rossby wave propagation (b) Via stratosphere, weak polar vortex (2) Stratosphere (a) Equatorial cooling, polar warming (idealised models) (b) Easterly QBO - Holton-Tan mechanism - direct impact on troposphere? (3) Blocking as the mechanism of negative NAO Woollings et al (2008) Tim’s presentation Negative AO, NAO – potential factors
1) Moderate El Niño (a) Rossby wave propagation (b) Via stratosphere, weak polar vortex (2) Stratosphere (a) Equatorial cooling, polar warming (idealised.
Dec 21, 2015
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1) Moderate El Niño
(a) Rossby wave propagation
(b) Via stratosphere, weak polar vortex
(2) Stratosphere
(a) Equatorial cooling, polar warming (idealised models)
(b) Easterly QBO - Holton-Tan mechanism
- direct impact on troposphere?
(3) Blocking as the mechanism of negative NAO
Woollings et al (2008) Tim’s presentation
Negative AO, NAO – potential factors
(1) Moderate El Nino
(a) Rossby wave propagation
(b) Via stratosphere, weak polar vortex
Negative AO, NAO – potential factors
PMSL DJF 09/10
PMSL response to moderate El Nino, Jan-Feb 1950-2000
Toniazzo & Scaife (2006)
(2) Response to stratospheric heatingP10 Polar heating (10K)
5K0K
5K 0K
E5 Equatorial heating (5K) U5 Uniform heating (5K)
10K
Zonal wind responseE5 U5 P10
Idealised GCM
Haigh et al (2005)
See alsoLorenz & de Weaver (2007)
Control zonal wind
Equatorward jet shift for:
•Tropical cooling
•Polar heating
NAO/AO onset in December 2009
www.met.reading.ac.uk/Data/CurrentWeather/ using data from ECMWF operational analyses
Tropopause animation, 27 Nov – 4 Dec
Tropopause animation, 4-11 Dec
Tropopause animation, 11-18 Dec
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