Comparison of LM Verification against Multi Level Aircraft Measurements (MLAs) with LM Verification against Temps Ulrich Pflüger, Deutscher Wetterdienst

Comparison of LM Verification against Multi Level Aircraft Measurements (MLAs) with LM Verification against Temps by means of Time Series (June 2001 until May 2003) of monthly average of –bias and rmse of 00h, 24h, 48h Forecasts based on all MLAs/Temps in LM area –Variables are temperature wind velocity wind direction

Multi Level Aircraft Measurements are Several (not less than 4) single Aircraft Measurements during the climb or descent flight which are piecewise combined –beginning with the lowest –next < 20 km horizontal distance of the first –vertical distance < 55 hPa –etc. and then used like a Temp Measurement

LM Area All MLAs at 12 UTC 2003/05/ /05/19

LM Area All Temps Stations 12 UTC 2003/05/ /05/19

Bias of LM-Temperature against MLA Temps 00 UTC

Analysis 24 h Forecast 48 h Forecast small bias, similar structures in both cases Forecasts have annual cycle, in upper and middle troposphere positive bias in Summer, negative in Winter, near ground predominantly negativ bias

RMSE of LM-Temperature against MLA Temps 00 UTC

similar structures in both cases 0.8 similar structures in both cases, rmse(Temps) overall about 0.2 K greater than rmse(MLA)

Bias of LM-Temperature against MLA Temps 12 UTC

Negative bias > -0.3 K positiv bias < 0.4 K below 800 hPA predominantly negativ, below 800 hPA predominantly negativ below 800 hPA Summer negativ, Winter positiv below 800 hPA Summer negativ, Winter positiv

RMSE of LM-Temperature against MLA Temps 12 UTC

Same as 00 UTC

Differences at Temperature Verification Relative few differences between Verification based on MLAs and Temps When bias is small there is predominantly a negative bias against MLAs and a positive bias against Temps Overall rmse of 24/48 h Forecast is about 0.2 K greater in Verification based on Temps

Bias of LM-Wind Velocity against MLA Temps 00 UTC

Below 800 hPa, annual cycle, in winter strong positive bias Max.: 1.4 m/s Below 800 hPa, annual cycle, in winter strong positive bias Max.: 1.8 m/s Below 900 hPa predominantly negative bias Min.: -1.1 m/s, Winter less Below 900 hPa predominantly negative bias Min.: -0.8 m/s, Winter partly positive Max 0.2 m/s Below 900 hPa predominantly negative bias Min.: -0.8 m/s, Winter partly positiv Max 0.2 m/s

RMSE of LM-Wind Velocity against MLA Temps 00 UTC

Overall rmse(MLA) is about m/s greater than rmse(Temps) Overall rmse(MLA) is equal to rmse(Temps) Above 400 hPa rmse(Temps) is greater than rmse(MLA)

Bias of LM-Wind Velocity against MLA Temps 12 UTC

Below 800 hPa, annual cycle, in winter strong positive bias, Max.: 1.9 m/s Below 800 hPa, annual cycle, in winter strong positive bias, Max.: 2.4 m/s Below 800 hPa, annual cycle, in winter strong positive bias, Max.: 2.3 m/s Below 900 hPa predominantly negative bias Min.: -1.1 m/s, Winter partly positive, Max.: 0.2 m/s Below 800 hPa Summer negative bias Min.: -0.6 m/s, Winter positive, Max 0.7 m/s Below 800 hPa Summer predominantly negative bias Min.: -0.6 m/s, Winter predominantly positive, Max 0.8 m/s

RMSE of LM-Wind Velocity against MLA Temps 12 UTC

Same as 00 UTC

Differences at Wind Velocity Verification bias with annual cycle – below 800 hPa positive against MLA negativ(Winter) to slight positive(Summer) 00 UTC negativ(Winter) to positive(Summer) 12 UTC rmse with annual cycle –at Analysis overall m/s higher against MLA (wind is nudged to Temps) –at Forecasts higher rmse against Temps above 400 hPa

Bias of LM-Wind Direction against MLA Temps 00 UTC

Below 800 hPa, strong positive bias Max.: 7.4 degree, smaller in spring and autumn Below 800 hPa, strong positive bias Max.: 10.3 degree Below 800 hPa, strong positive bias Max.: 13.5 degree Below 900 hPa negative bias Min.: -4.9 degree, Winter less Below 900 hPa predominantly negative bias Min.: -7 degrees, Winter partly positive Max.: 6 degrees Below 900 hPa predominantly negative bias Min.: -10 degrees, Winter partly positiv Max 6 degrees

RMSE of LM-Wind Direction against MLA Temps 00 UTC

Overall rmse(MLA) is about 5-10 degrees greater than rmse(Temps) Overall rmse(MLA) is equal to rmse(Temps), except Summer Above 400 hPa rmse(Temps) is partly greater than rmse(MLA)

Bias of LM-Wind Direction against MLA Temps 12 UTC

Below 800 hPa, strong positive bias Max.: 6.1 degree, smaller as 00 UTC Below 800 hPa, strong positive bias Max.: 10.1 degree Below 800 hPa, strong positive bias Max.: 10.6 degree, smaller than 00 UTC Below 900 hPa Winter negative bias Min.: -4.1 degree, Summer positive Below 900 hPa predominantly positive Max.: 8 degrees, Winter smaller or negative Below 900 hPa predominantly positive, Max.: 9 degrees, single months in winter positive

RMSE of LM-Wind Direction against MLA Temps 12 UTC

Overall rmse(MLA) is about 5-10 degrees greater than rmse(Temps) Below 400 hPa rmse(MLA) is equal to rmse(Temps) except Summer Above 400 hPa rmse(Temps) is partly greater than rmse(MLA)

Differences at Wind Direction Verification bias with annual cycle – below 800 hPa Analysis and Forecast against MLAS strong positive Analysis against Temps slight negative below 900 hPa, slight positve above against Temps Forecasts against Temps partly slight negativ(Winter) to slight positive(Summer) 12 UTC rmse with annual cycle –at Analysis overall degrees higher against MLA (wind is nudged to Temps) –at Forecasts higher rmse against Temps above 400 hPa –at Forecasts higher rmse against MLA in Summer

Summary Temperature Verification shows only few differences between the two measuring systems Wind Verification shows below 800 hPa great differences between the two measuring systems Regarding the Wind Verification results up to now (Synop, Temp) LM is more likely to underestimate wind velocity Regarding the verification against aircraft measurements it seems that aircraft measurements below 800 hPa underestimate wind velocity (up to 2 m/s in the boundary layer).