Lateral boundary conditions and forecast errors in the mid-latitudes – first results Luka Honzak, Nedjeljka Žagar, Gregor Skok CE Space-SI and University of Ljubljana 1

Errors Error sources in RCM: domain size nesting approach resolution difference between GCM and RCM temporal density of LBCs update LBCs errors We limit our study to the domain size: LBC update and nesting the same in all simulations resolution of GCM and RCM the same LBCs are assumed “truth” (analyses) 2

HchHch WRF setup Ch: Mid-latitude channel, 1439139 points (35 o N and 70 o N) Hch: Euro-Atlantic sector (100 o W and 60 o E), 639139 points Eu: Europe (45 o W and 45 o E), 319139 points Horizontal resolutions: 0.250.25 degrees IC/LBC: operational analyses of ECMWF on the same grid available with time frequency of 6 hours. Pre-processing: 91 ECMWF model levels interpolated to 31 WRF levels. Top level at 10 hPa, six levels below 850 hPa, 20 levels between 850 and 100 hPa and five levels are in the stratosphere. =0 at the top. ChChEu 3

HchHch WRF simulations ChChEu Three simulations carried out on each domain Starting dates 6 days apart ( , , ) Simulation length 3 months ( ) Verification against ECMWF on the same grid Fields: wind, geopotential, temperature on 30, 100, 250, 300, 500, 700, 850 and 925 hPa 4

Total precipitation accumulated between and Ch, exp 1 TRMM ECMWF 5

Ch Ch eridional wind at 250 hPa M eridional wind at 250 hPa Geop. height at 500 hPa Geop. height at 500 hPa Zonal wind at 250 hPa Zonal wind at 250 hPa Time averaged rmse: Ch 6

Ch M eridional wind at 250 hPa M eridional wind at 250 hPa Geop. height at 500 hPa Geop. height at 500 hPa Zonal wind at 250 hPa Zonal wind at 250 hPa Time averaged rmse: Hch HchHchHchHch 7

Ch M eridional wind at 250 hPa M eridional wind at 250 hPa Geop. height at 500 hPa Geop. height at 500 hPa Zonal wind at 250 hPa Zonal wind at 250 hPa Time averaged rmse: Eu HchHchHchHch Eu 8

Average meridional profiles of rmse Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa 10 Jan 10 Jan 10 Jan 10 Jan 20 Jan 20 Jan 20 Jan 20 Jan 30 Jan 30 Jan 30 Jan 30 Jan rmse (m/s) rmse (m/s) latitude latitude NH-ChNH-HCh NH-Ch on HCh NH-Ch NH-HCh Hch Ch Eu U wind at 250 hPa V wind at 250 hPa Geop. height at 500 hPa Geop. height at 500 hPa 9

Internal variability: total precipitation Ch, experiment 3 Ch, experiment 1 Ch, experiment 2 10

Ch Internal variability: zonal wind at 250 hPa HchHchHchHch 1. experiment ( ) 2. experiment ( ) 3. experiment ( ) 11

Internal variability: zonal wind at 250 hPa Ch HchHchHchHch Ch on Hch Ch on Eu Hch on Eu Eu 12

Internal variability: zonal wind at 250 hPa Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa Meridionalwindrmseat250hPa 10 Jan 10 Jan 10 Jan 10 Jan 20 Jan 20 Jan 20 Jan 20 Jan 30 Jan 30 Jan 30 Jan 30 Jan rmse (m/s) rmse (m/s) latitude latitude NH-ChNH-HCh NH-Ch on HCh NH-Ch NH-HCh Hch Ch Eu 1. experiment 2. experiment 3. experiment 13

Future work Coupling WRF Ch, Hch, Eu into meridionally larger WRF channel (Lch: 30 o N and 80 o N ) 14