APPLICATION IN CLIMATOLOGY 1.

1. APPLICATION IN CLIMATOLOGY 1.

2. IS GROWING PERSISTENCE OF ATMOSPHERIC CIRCULATION CONDUCIVE TO INCREASING INCIDENCE OF HEAT WAVES? Radan HUTH, Jan KYSELÝ Institute of Atmospheric Physics, Prague, Czech Republic

3. QUESTIONS TO ANSWER • Which types of atmospheric circulation support the formation of heat waves? • Does higher persistence of atmospheric circulation imply higher temperatures / more intense heat waves?

4. DATA & METHODOLOGY • summer season (JJA) • whole 20th century (1901-2000) • daily mean temperature, 22 European stations • data sources: • ECA&D • MeteoSwiss • Camuffo & Jones, 2002

5. DATA & METHODOLOGY • heat waves (HWs): • at least 3 successive days with extreme surface temperature anomalies • extreme anomaly defined as 95th percentile for interval –30 to +30 days around the given day

6. DATA & METHODOLOGY • atmospheric circulation: Hess-Brezowsky (H&B) synoptic types • 29 types (+ 1 undetermined) • lifetime at least 3 days • mean residence time 4.3 to 6.2 days

7. DATA & METHODOLOGY • link between H&B types and HWs – evaluated in terms of efficiency coefficient = relative frequency of the type in HWs / its long-term mean frequency • null hypothesis: eff.coef. <= 1.0 • significance testing using block resampling

8. DATA & METHODOLOGY • effect of persistence – difference in anomalies between days 1-5 vs.>=6 in events lasting at least 6 days • event = uninterrupted sequence of the same type • done for each H&B type conducive to HWs • significance testing (null hypothesis: difference = 0) by Wilcoxon rank-sum test

9. example: Bamberg

10. with / without signif. effect of persistence central European high: HM H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

11. with / without signif. effect of persistence central European high: BM H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

12. with / without signif. effect of persistence easterly: HFA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

13. with / without signif. effect of persistence easterly: HNFA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

14. with / without signif. effect of persistence easterly: HFZ H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

15. with / without signif. effect of persistence easterly: HNFZ H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

16. with / without signif. effect of persistence southerly: TRW H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

17. with / without signif. effect of persistence southerly: SWA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

18. with / without signif. effect of persistence southerly: SWZ H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

19. with / without signif. effect of persistence southerly: SEA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

20. with / without signif. effect of persistence southerly: TB H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

21. with / without signif. effect of persistence north-east: NEA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

22. with / without signif. effect of persistence north-east: NEZ H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

23. with / without signif. effect of persistence other: WA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

24. with / without signif. effect of persistence other: NWA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

25. with / without signif. effect of persistence other: HNA H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

26. with / without signif. effect of persistence other: TRM H&B types conducive to HWs (eff.coeff. significantly > 1); infrequent types (freq. < 0.5%) omitted

27. temperature anomaly difference DAY6+ vs. DAY1-5, average over warm types (mean anomaly over +1C) 1.0 1.1 1.0 1.5 0.6 0.7 0.8 1.0 1.0 0.8 0.8 0.5 0.6 0.9 0.9 0.9 0.4 1.2 1.0 1.3 0.6 1.0

28. CONCLUSIONS • H&B types conducive to HWs • large regional differences • typical by • warm advection from SW-E • anticyclonic influence with positive radiation balance • 17 types at one station at least • larger-scale effect • central European high (HM, BM) • easterly anticyclonic • southerly

29. CONCLUSIONS • more persistent circulation (longer duration of circulation events)  higher temperatures • end of warm circulation events tends to be warmer than their beginning • mean JJA difference DAY6+ minus DAY1-5 = 0.9 C • insensitive to the choice of threshold (4 or 6 days) • recently observed increase in circulation persistence – potential contributor to increasing frequency & severity of HWs