1. Swiss Alpine snow variability: Its links to large scale flow patterns ICAM-MAP meeting, Brig (CH) Fri 23 th May 2003 Simon C. Scherrer C. Appenzeller Federal Office of Meteorology and Climatology (MeteoSwiss), Switzerland scs@meteoswiss.ch

2. Swiss snow variability  Engadin (GR)  Klosters 1999 (GR)

3. scs@meteoswiss.ch Swiss new snow - NAO: direct influence  Argument: There is a NAO – Alpine snow relation, dependent on height and has an impact on trends  Question: Is there a pronounced NAO influence on Swiss new snow variability and trends? 1931-1999

4. scs@meteoswiss.ch New Swiss new snow data set  A new roughly homogenous snow data set (1931(57)-1999) 89 stakes France Germany Austria Italy A L P S 46°N 48°N 6°E11°E

5. scs@meteoswiss.ch EOF analysis of Swiss DJF new snow sums: EOF 1 58% (sign.) r = 1 r = 0.30 No trend

6. scs@meteoswiss.ch Swiss DJF new snow sums: EOF 2 15% (sign.) r = 1 r = 0.30 r = -1 r = -0.30 No trend

7. scs@meteoswiss.ch Swiss DJF new snow sums: EOF 3 8% (sign.) r = 1 r = 0.30 r = -1 r = -0.30 small trend

8. scs@meteoswiss.ch  EOF 3 shows a distinct height dependence New snow EOF‘s: height dependence Altitude [m a.s.l.] 2500 0 1500 r~-0.6 Correlation coefficient 1000 500 2000

9. scs@meteoswiss.ch DJF EOF– NAOI relation  r (PC1, NAOI) = -0.24  r (PC2, NAOI) = -0.29  r (PC3, NAOI) = -0.57** Trend PC 3 not significant (p=0.22)

10. scs@meteoswiss.ch Running correlations: New snow sums - NAOI NEW SNOW PC‘s - NAOI PC 3 95% 99%

11. scs@meteoswiss.ch Correlation maps: SLP – (new snow PC3) SLP Pattern 3: „NAO like“ SVD 3: SCF: 5% r = 0.70

12. scs@meteoswiss.ch SVD 1: European and Hemispheric view SVD 1 HN - SLP Swiss Alpine region 4 - 4 mbar 1 - 1 SVD 1 resembles NAO/AO like pattern on hemispheric scale NAO/AO – blocking relation?  Hemispheric scale:  „European“ scale: seems to be determined by central European high- pressure regime or low- pressure

13. scs@meteoswiss.ch Influence of “blocking” based on standard TM Blocking Index modified central latitude NAO - NAO + Atlantic ocean Swiss Alps Atlantic ocean Swiss Alps 60°N 50°N NAO + NAO - DJF “blocking” frequency

14. scs@meteoswiss.ch Conclusions  Three distinct DJF new snow patterns are identified (expl. var. 81%)  There is no simple 1:1 relation between DJF new snow and the NAOI  The direct influence of the NAO on DJF new snow sums: is expressed as low-station high-station pattern (expl. variance ~8%) shows a distinct trend since the 1960‘s  The primary DJF new snow variability: is locally driven by central European high-low pressure (blocking?) is NAO/AO like on a hemispheric scale  The “Blocking” – NAO relation is ambiguous: Atlantic “blocking” is negatively correlated with the NAOI Middle-European “blocking” is positively correlated with the NAOI

15. scs@meteoswiss.ch THE END

16. scs@meteoswiss.ch Intermediate conclusions  Three “significant” DJF new snow patterns are identified, which explain 81% of total variability  There is no simple 1:1 relation between Swiss Alpine new snow sums and the NAOI  The direct influence of the NAO on new snow sums: is expressed as a low – high station pattern (8% var.) shows a distinct trend since the 1960‘s

17. scs@meteoswiss.ch