swiss alpine snow variability: its links to large scale flow patterns

Swiss Alpine snow variability:Its links to large scale flow patterns

ICAM-MAP meeting, Brig (CH)

Fri 23th May 2003

Simon C. Scherrer C. Appenzeller

Federal Office of Meteorology and Climatology

(MeteoSwiss), Switzerland

scs@meteoswiss.ch

scs@meteoswiss.ch

Swiss snow variability

Engadin (GR)

Klosters 1999 (GR)

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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

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New Swiss new snow data set

A new roughly homogenous snow data set (1931(57)-1999)

89 stakes

France

Germany

Austria

ItalyA

LP S

46°N

48°N

6°E 11°E

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EOF analysis of Swiss DJF new snow sums: EOF 1

58% (sign.)r = 1

r = 0.30

No trend

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Swiss DJF new snow sums: EOF 2

15% (sign.)r = 1

r = 0.30

r = -1

r = -0.30

No trend

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Swiss DJF new snow sums: EOF 3

8% (sign.)r = 1

r = 0.30

r = -1

r = -0.30

small trend

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EOF 3 shows a distinct height dependence

New snow EOF‘s: height dependence

Alt

itu

de

[m

a.s

.l.]

2500

0

1500

r~-0.6

Correlation coefficient

1000

500

2000

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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)

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Running correlations: New snow sums - NAOI

NEW SNOW PC‘s - NAOI

PC 3

95%

99%

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Correlation maps: SLP – (new snow PC3)

SLPPattern 3:

„NAO like“

SVD 3:SCF: 5%r = 0.70

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SVD 1: European and Hemispheric view

SVD 1HN - SLP

Swiss Alpine region

4

- 4mbar

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

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Influence of “blocking”

based on standard TM Blocking Index modified central latitude

NAO-

NAO+

Atlantic ocean

Sw

iss

Alp

s

Atlantic ocean

Sw

iss

Alp

s

60°N 50°NNAO+

NAO-

DJF

“bl

ocki

ng”

freq

uenc

y

DJF

“bl

ocki

ng”

freq

uenc

y

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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

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THE END

THE END

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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

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