NEW METHOD:

• Use 1000hPa geostrophic wind speed as additional predictor (cube root works well)

(3)

(ugeo = 1000hPa geostrophic wind speed at station from NCEP Reanalysis)

• v1, v2, v3, v4, v5, v6 and const estimated for each month of year separately Set Tde-trended(station) = 0 in Eqn. (3)

• Compute hypothetic station temperatures with Tde-trended(station) = 0 in Eqn. (3) (denoted Tde-trended infigures below) to check quality of fit

Daily temperatures (only January shown)

2. Parameter estimation:

• v1, v2, v3, v4, v5 and const estimated for eachmonth of year separately Set Tde-trended(station) = 0 in Eqn. (1)

• Use normal monthly temperatures, monthlytemperatures (not shown) or daily temperatures

• Compute hypothetic station temperatures withTde-trended(station) = 0 in Eqn. (1) (denoted Tde-trended infigures below) to check quality of fit

a) Normal Temperatures (only January shown)

b) Daily temperatures (only January shown)

DAILY MAPS OF MINIMUM AND MAXIMUM TEMPERATURE FOR NORWAY

Norwegian Meteorological Institute

Contact:

Matthias Mohr

Norwegian Meteorological InstituteMeteorology and Climate DivisionP.O. Box 43 Blindern, N-0313 Oslo

e-mail: matthias.mohr@met.noPhone: +47 2296 3000Direct phone: +47 2296 3381

ORIGINAL METHOD:

1. Used for daily mean, min and max temperatures:

De-trending: (at each station)

(1)

(Tde-trended = de-trended station temperature, Tstation = observed station temperature, zstation = station altitude, zmean, 40 km = mean altitude within circle of 40km Ø surrounding station, zmin, 40 km = lowest altitude within same circle, lat/lonstation = latitude/longitude of station, const = constant)

Kriging: (interpolation from stations to grid points)

Two-dimensional ordinary kriging, monthly uni-directional variograms from normal temperatures (Tveito et al., 2000)

Tde-trended (station) Tde-trended(grid)

Re-trending: (at each grid point)

(Tde-trended(grid) = de-trended station temperatures interpolated to grid, zDEM,Norway = digital elevation model of Norway, zmean, 40 km = mean altitude within circle of 40km Ø surrounding grid point, zmin, 40 km = lowest altitude within same circle, lat/lonstation = latitude/longitude of grid point, const = constant)

Trend variables: (for whole of Norway)

constlonvlatvzv

zvzvTstationT

stationstationkm

kmmeanstationstationtrendedde

5440min,3

40,21)(

constlonvlatvzv

zvzvgridTT

cellgridcellgridkm

kmmeanNorwayDEMtrendeddemapfinal

5440min,3

40,2,1)(

CONCLUSIONS:

• New method performs on par, but not better thanoriginal method

• Max. temperatures predicted almost as good as daily means

• Min. temperatures predicted considerably worse

• Temperatures predicted best in spring/summer and worst in winter (temperature inversions)

• UTM coordinates seem to give better results for Norway than Lat/Lon (not shown)

More work is needed…

constuvlonvlatvzv

zvzvTstationT

geostationstationkm

kmmeanstationstationtrendedde

35440min,3

40,21

6

)(

Daily mean

temperature

Minimum temperature

Maximum temperature

Correlation 0.943 0.930 0.937

RMSE (°C) 2.202 2.780 2.083

Daily mean

temperature

Minimum temperature

Maximum temperature

Correlation 0.945 0.929 0.942

RMSE (°C) 2.161 2.808 1.994

OBJECTIVE:

• Daily maps of mean, minimum and maximumtemperature with 1km resolution for Norway

• Use all available temperature observations (140 -240 stations depending on year)

• Use multiple linear regression & residual kriging

• Use information on local terrain

• Use information on large-scale atmosphericcirculation (e.g. geostrophic wind speed)

Daily mean

Temperature

Minimum temperature

Maximum temperature

Correlation 0.945 0.929 0.942

RMSE (°C) 2.162 2.809 1.997

BACKGROUND:

• Week correlation between 1000hPa geostrophicwind speed and daily temperatures

• Correlation: R ≈ 0.5 in January and R ≈ -0.3 in July

Temperatures increase with increasinggeostrophic wind speed during winter

Temperatures decrease with increasinggeostrophic wind speed during summer

WE USE THIS FACTOR AS ADDITIONAL PREDICTOR

References:Mohr, M., 2009: Comparison of Versions 1.1 and 1.0 of Gridded Temperature and Precipitation Data for Norway, met.no note # 19/2009, see http://met.no/

Mohr, M., 2008: New Routines for Gridding of Temperature and Precipitation Observations for “seNorge.no”, met.no note # 08/2008, see http://met.no/Forskning/Publikasjoner/Publikasjoner_2009/

Tveito, O. E., E. J. Førland, R. Heino, I. Hanssen-Bauer, H. Alexandersson, B. Dahlström, A. Drebs, C. Kern-Hansen, T. Jónsson, E. Vaarby Laursen and Y. Westman, 2000 : Nordic temperature maps (Nordklim), DNMI KLIMA Report09/00, see http://www.smhi.se/hfa_coord/nordklim/old/rapport0900.pdf

EXAMPLE: The Coldest (?) Day in Norway

RESULTS:

• ”Leave-one-out” cross validation (using de-trending, kriging and re-trending (see left))

• 10 years of data (Jan 2001 – Dec 2010)

• Correlation and RMSE as quality measure (only January shown in tables below)

• ca. 140 - 240 stations per day (depending on year)

1.Original method

a) Use parameters from normal temperatures

b) Use parameters from daily temperatures

2. Use new method (including geostrophic wind speeds) for min and max temperatures