Federal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss Weather types and gridding of daily precipitation in the Alpine region – early finger exercises Reinhard Schiemann and Christoph Frei COST733 WG4 meeting, Brussels March 6/7, 2008

2 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei MeteoSwiss 1.Weather types and Alpine precipitation Description of the statistical relationship for the COST733 classifications Selection and more detailed investigation for a "particularly suitable" weather type classification 2.Gridding Construction of daily precipitation grids based on rain gauge data and other meteorological information

3 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Finger exercise I: Precipitation composites Example: Hess-Brezowsky Grosswetterlagen (29 types) Westlage anticyclonicWestlage cyclonic (COST733)

4 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Finger exercise I: Precipitation composites Example: Hess-Brezowsky Grosswetterlagen (29 types) Westlage anticyclonicWestlage cyclonic MEAN 90%-quantile mm/d

5 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Finger exercise II: Locally "explained" precipitation variance total variance = between-type variance + within-type variance PETISCO, D06, 37 types PETISCO, D06, 37 types SANDRA, D06, 22 types PCACA, D06, 5 types PCACA, D06, 5 types SCHUEEPP, (D06), 40 types SCHUEEPP, (D06), 40 types

6 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Aims

7 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Gridding: What is our problem?  data from only few stations in the days immediately succeeding an interesting precipitation event

8 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Gridding: What is our problem? provisional analysis ( ) final analysis ( ) Christoph Frei, MeteoSwiss

9 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Gridding: What is our problem? LD stations ~real-time HD stations not real-time weather typeSLP, Z 850, Q 850,... precipitation grids daily "high" spatial resolution realistic estimation of the (spatial) error structure available in near real time precipitation grids daily "high" spatial resolution realistic estimation of the (spatial) error structure available in near real time

10 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Analogy: Reconstruction time #Stationen Reconstruction LD stations HD grid e.g., Schmidli et al., 2001: optimal interpolation Gridding HD stations HD grid e.g., Frei and Schär, 1998 "Nowstruction" LD stations HD grid ???

11 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei But... daily precipitation is „annoyingly“ distributed Example: rain gauge at Interlaken, CH Existing reconstructions handle more pleasantly distributed data, e.g. monthly precipitation, (SS)Ts. Methods may not carry over in a straightforward way.

12 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Finger exercise III: Regression with univariate target variable Y ~ X INT + X ULR + X VIS + X GRH

13 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Finger exercise III: Regression with univariate target variable distribution of errors (QQ-plot): stand. residuals theor. quantiles  erroneous confidence intervals for model parameters and forecasting intervals

14 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Reconstruction method: Optimal interpolation time #Stationen Step 1: PCA during calibration period Step 2: Least squares estimation of PC coefficients during reconstruction period Kaplan et al., 1997; Schmidli et al., 2001

15 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei PCA of daily precipitation MEAN (mm/d)PC1 (32%) PC2 (15%)PC3 (12%)

16 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei PCA of daily precipitation Scatterplots of PC-scores Colours: Weather types according to PCACA, D06 (5 types)

17 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/ Reinhard Schiemann and Christoph Frei Summary and preliminary conclusions Daily precipitation composites with respect to different weather types clearly differ from one another. This holds true not only for the mean but also for quantiles of the precipitation distribution. In the Alpine region, the locally explained variance is in the order of 10-20%. WTCs differ considerably in subregions of low/high EV (e.g., north vs. south,west vs. east of the Alpine ridge). Days corresponding to different weather types occupy different but overlapping regions in principal-component space. The added value of WTCs for precipitation gridding remains to be quantified.