INTERCOMPARISON – HIRLAM vs. ARPA-SIM CARPE DIEM AREA 1 Per Kållberg Magnus Lindskog

what I want to show here the HIRLAM system and experiments comparison of arpa and hirlam analyses verification of forecasts against own analyses verification of forecasts against observations precipitation forecasts conclusions

0.1º to 0.4° rotated lat/long grid Hydrostatic, hybrid coordinates Spectral (double Fourier with extension zone) Or gridpoints on the C-grid Eulerian or semi-Lagrangean time-stepping Lateral boundary relaxation - usually ECMWF LBC ISBA soil model TKE (Turbulent Kinetic Energy) turbulence closure Kain-Fritsch convection or ’STRACO’ condensation HIRLAM (HIgh Resolution Limited Area Model)

3D-Var or 4D-Var Multivariate statistical balance: vorticity - divergence - mass - moisture Scale and latitude dependent geostrophy Boundary layer friction ’NMC’-method background error statistics Ensemble assimilations to replace ’NMC’-method Moisture effects with a revised moisture control variable Initialization: normal modes or a weak digital filter Observation operators include: Conventional (TEMP PILOT AIREP DRIBU SYNOP SHIP SATOB) Raw radiances (TOVS, ATOVS) Integrated humidity from GPS Radial winds from Doppler radars HIRVDA (HIRlam Variational Data Assimilation)

hirlam experiments – nov.3 to nov.8 cdc HIRLAM °/ 0.1° 40 levels 3D-Var data assimilation digital filter initialization (DFI) ECMWF operational analyses on the boundaries ECMWF operational conventional observations ’straco’ condensation & ’cbr’ turbulence cdd no data assimilation at all, just a +144 forecast from 3 november cde as cdc but with revised horizontal structure functions (slightly smaller scales)

comparisons between the arpa and the hirlam data assimilations

analysis differences arp – cdc 850 hPa geopotential 6 Nov. 00Z we have used different orographies this affects the post-processing to pressure levels and mean sea level

2 metre temperature analysis differences 00UTC (left) and 12UTC (right)

arpa (left) and hirlam (right) 10 metre wind analyses

mean sea level pressure analysis and SYNOP observations 5 November ÙTC arpcdc

mean sea level pressure analysis and SYNOP observations 6 November ÙTC arpcdc

comparisons between the arpa and the hirlam forecasts (verified against ’own’ analyses)

the analyses and the +24h forecast errors at the analysis time mean sea level pressure on November 7th Z 12Z cdc arp cdc

verification against observations

sea level pressure (arp & cdc) fit to SYNOP/SHIP

screen level temperature (arp & cdc) fit to SYNOP/SHIP

screen level dewpoint (top) and total clouds (bottom) (arp & cdc) fit to SYNOP/SHIP

10 metre windspeed (arp & cdc) fit to SYNOP/SHIP (top) and SHIP only (bottom)

850hPa geopotential (arp & cdc) fit to TEMP 850hPa windspeed (arp & cdc) fit to TEMP/PILOT

conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier)

more conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier) P_msl 24h forecasts have comparable qualities

more conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier) P_msl 24h forecasts have comparable qualities 10-metre windspeeds. –cdc biased high, both in anlyses and – worse – in forecasts –arp strong diurnal variations in the analysis biases – good at night, to weak at day

more conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier) P_msl 24h forecasts have comparable qualities 10-metre windspeeds. –cdc biased high, both in anlyses and – worse – in forecasts –arp strong diurnal variations in the analysis biases – good at night, to weak at day screen level temperature - analyses –cdc biased warm at daytime, cool at night –arp biased cool at daytime, warm at night

more conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier) P_msl: 24h forecasts have comparable qualities 10-metre windspeeds –cdc biased high, both in anlyses and – worse – in forecasts –arp strong diurnal variations in the analysis biases – good at night, to weak at day screen level temperature - analyses –cdc biased warm at daytime, cool at night –arp biased cool at daytime, warm at night screen level temperature – forecasts –cdc has a cooling drift (well known in SMHI operations) –arp quite biasfree forecasts

more conclusions from the comparisons with observations P_msl: cdc analysis has smaller standard deviation –(arp postprocessing is noisier) P_msl: 24h forecasts have comparable qualities 10-metre windspeeds –cdc biased high, both in anlyses and – worse – in forecasts –arp strong diurnal variations in the analysis biases – good at night, to weak at day screen level temperature - analyses –cdc biased warm at daytime, cool at night –arp biased cool at daytime, warm at night screen level temperature – forecasts –cdc has a cooling drift (well known in SMHI operations) –arp quite biasfree forecasts total clouds: arp has more clouds than cdc. cdc has a diurnal cycle

more conclusions from the comparisons with observations 850hPa geopotential: analyses and forecast essentially similar fits 850hPa windspeed: cdc somewhat smaller bias and standard deviation

accumulated precipitation cdc 6 Nov. 06Z + 24h cde 6 Nov. 06Z + 24h arp 6 Nov. 00Z + 24h arp 6 Nov. 12Z + 24h Rubel 6 Nov. 06Z - 7 Nov. 06Z cdd 6 Nov. 06Z – 7 Nov. 06Z

24-hour accumulated precipitation 6 Nov 06Z to 7 Nov 06Z exp:cdc

24-hour accumulated precipitation 6 Nov 00Z to 7 Nov 00Z exp:arp

24-hour accumulated precipitation 6 Nov 12Z to 7 Nov 12Z exp:arp

24-hour accumulated precipitation 6 Nov 06Z to 7 Nov 06Z (Rubel & Rudolf, Wien )

24-hour accumulated precipitation 6 Nov 06Z to 7 Nov 06Z exp:cdd

the somewhat tighter structure functions used in the hirlam cde experiment experiment yields somewhat more intense precipitation than the cdc control experiment

24-hour accumulated precipitation 6 Nov 06Z to 7 Nov 06Z exp:cdc

24-hour accumulated precipitation 6 Nov 06Z to 7 Nov 06Z exp:cde

general conclusions from the comparisons pressure and mean sea level differences due to different orographies and different post-processing algorithms –arp noisier, especially Pmsl and geopotential at 850 too large scale of the hirlam background errors (0.4°/ 0.4° grid) –new, smaller scale background errors yield slightly more intense precipitation analysis increments on model levels problematic in steep orography dfi initialization not ideally tuned for this resolution and such a small area long integration (cdd) without D.A. still skillful, but D.A. improves the quality cdc Pmsl forecasts have generally smaller errors against own analysis precipitation forecasts qualitatively good, –arp has some very intense spots, cdc is somewhat smoother and not bad quantitatively either

what we still want to do one more hirlam assimilation with a revised turbulent momentum flux run some forecasts from each other’s analyses

Grazie mille per la vostra attenzione!