The role of individual synoptic-scale weather systems in the life cycle of European weather regimes

Transcription

1 The role of individual synoptic-scale weather systems in the life cycle of European weather regimes Christian M. Grams Institute for Atmospheric and Climate Science, ETH Zürich, Switzerland funded by thanks to the Atmospheric Dynamics groups of Heini Wernli, ETH Zurich

2 European weather regimes NAO+ (31.7%) NAO- (19.8%) Z500hPa BL (24.8%) AR (23.7%) Shading: cluster mean Z500 anomaly 2 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

3 European weather regimes NAO- (19.8%) Blocking (Schwierz et al., 2004) during weather regimes (±0.5d mx) Maximum absolute blocking frequencies: NAO- 78.5% BL 64.0% AR 93.0% BL (24.8%) AR (23.7%) Shading: cluster mean weak blocking anomaly Ctours: NDJFM mean every 5% 3 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

4 European weather regimes Challenge for NWP: Flow-dependent predictability (Ferranti et al., 2015) NWP systems struggle with WR life cycles, in particular set, decay, transiti (Reinhold, 1987; Molteni and Tibaldi, 1990; ) NAO+ NAO- BL AR Dependence : Role of synoptic weather systems in WR life cycles (Molteni and Palmer, 1993; Altenhoff et al. 2008; Michel and Rivière, 2011) horiztal resoluti, physical parametrizatis (e.g. Daws and Palmer, 2012) from Ferranti et al. (2015) Role of warm cveyor belts? 4 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

5 Warm cveyor belts rapidly ascending airstream in extratropical cycles Δp/Δt = 600hPa/48h (Madna et al., 2014) net transport of low-pv air to upper troposphere WCB outflow 300hPa (t=48h) PV- 0.5 pvu dpv dt µ dq dz Blocking? WCB inflow 900hPa, (t=0h) 0.5 pvu Figure 1 from Wernli (2015), PEN Role of WCB outflow in blocking-type regime (NAO-, BL, AR) life cycles? 5 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

6 Approach Objective definiti of individual Atlantic-European weather regime life cycles role of different weather systems during important life cycle stages Today: focus WCB outflow NAO+ (31.7%) NAO- (19.8%) BL (24.8%) AR (23.7%) 8 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

7 Weather regime life cycle Weather regime Index I wr for each regime (Michel and Rivière, 2011) Definiti of set, maximum, decay for individual weather regime threshold I BL I wr I NAO- 0 I NAO+ I AR mx dc time 9 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

8 life cycles & stages for DJF 2015/16 #events NAO+ 68 NAO- 69 BL 85 AR 78 ne (43%) Dec 2015 Jan 2016 Feb 2016 life cyclebased attributi 10 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

9 WCB outflow at set Hypothesis: diabatic WCB outflow results in ridge building at regime set WCB outflow (t=36-60h) frequency anomalies in period 0 to 2 days around set 11 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

10 WCB outflow at NAO- set Lag 0 to 2 days around set WCB outflow (36-60h) NAO- Greenland blocking Z Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

11 WCB outflow at AR set Lag 0 to 2 days around set WCB outflow (36-60h) AR Atlantic ridge Z Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

12 WCB outflow at BL set Lag 0 to 2 days around set WCB outflow (36-60h) BL Scandinavian Blocking Z Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

13 Blocking during BL set BL Scandinavian Blocking -4d to -2d -2d to 0d Z500 0d to 2d 2d to 4d strg Blocking (Schwierz et al. 2004) 15 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

14 VAPV during BL set BL Scandinavian Blocking -4d to -2d -2d to 0d Z500 RWT emerging from tropical West Atlantic 0d to 2d (Michel and Rivière, 2d to 4d2011) VAPV ( hPa) 16 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

15 WCB outflow during BL set BL Scandinavian Blocking -4d to -2d -2d to 0d Z500 0d to 2d 2d to 4d WCB outflow (t=36-60h) 17 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

16 WCB inflow during BL set BL Scandinavian Blocking -4d to -2d -2d to 0d Z500 0d to 2d 2d to 4d WCB inflow (t=0h) 18 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

17 WCB activity during BL set WCB inflow (t=0h) WCB outflow (t=36-60h) -4d to -2d -2d to 0d -4d to -2d -2d to 0d 0d to 2d 2d to 4d 0d to 2d 2d to 4d WCB activity supports set and maintenance of Scandinavian blocking 19 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

18 Summary WCB & blocking-type WR BL Scandinavian blocking AR Atlantic ridge NAO- Greenland blocking WCB activity during set and maintenance NAO+ / Atlantic RWT precursor WCB activity important for maintenance North Pacific RWP precursor WCB activity during set and maintenance BL precursor 20 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK

19 Summary NAO+ (31.7%) NAO- (19.8%) NAO- (19.8%) 3 of 4 Atlantic-European weather regimes exhibit blocking character BL (24.8%) AR (23.7%) BL (24.8%) AR (23.7%) I wr 0 I BL I NAO- I NAO+ I AR Novel objective definiti of individual weather regime life cycles mx dc time Important role of WCB outflow for blocking-type regimes WCB outflow during BL and NAOset and maintenance WCB outflow during AR maintenance and RWP precursor 21 Workshop Atmospheric Blocking, 6-8 April 2016, Reading, UK