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Humidity QC and Analysis for Stuttgart

This document discusses a revision of the quality control process for radiosonde humidity observations in Stuttgart. It includes the implementation of stability-dependent thresholds and a spatial consistency check for integrated water vapor. The results of these revisions and their impact on the assimilation and analysis process are also presented.

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Humidity QC and Analysis for Stuttgart

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  1. relative humidity profile at Stuttgart 31 July 17 UTC 24-h precipitation analysis for 1 August 2004 , 6 UTC ‘ref’ LM assimilation opr. humidity QC setting LM ass without use of profile ref LM ass obs Stuttgart > 100 mm Revision of Quality Control for Radiosonde Humidity Christoph Schraff christoph.schraff@dwd.de Motivation 05.08.2005 - 1 -

  2. sT • further revision to increase threshold in stable conditions and in particular at inversions where model errors are known to be larger ( limit RHthr(3)(to)≤ 70 % ) b b* (1 + fstable + finvers ) , where for lapse rate  > crit = – 0.0065 K/m : fstable= ¼ * (1 + sT /(1+sT)) * (1 – min{,0} / crit ) z Tok+1  crit Tok T threshold quality control for individual observations (first guess check) • relative humidity observation RHo rejected if : | RHo – RHb | > RHthr • operational (‘ref’) : RHthr(to) = 70 % , RHthr(t[h]) = RHthr(to) * (1 + 0.1* |to – t | ) • revision (analogous to revised GME scheme): RHthr(1,3)(to) = min { (o2 + b2)½, 2 b} * cflag(1,3) , where observation error o = 10 % ( 15% for To< 233K , 20% for RHo< 20% ) background error b = 10 % ( 15% south of 30 N ) constant cflag(3) = 3.1 ( cflag(1)= 1.8 for flag 1 as used in multi-level check ) for lapse rate  > 0 : finvers= 0.2 * Tinvers * (1 + min{2,  / 0.05[K/m]})  both factors increase with increasing stability  and with increasing T 05.08.2005 - 2 -

  3. multi-level check • define ‘analysis layers’: as standard layers, except p = 50 hPa below 700 hPa p = 25 hPa below 800 hPa (boundaries of standard layers: ps , 925, 775, 600, 450, • criterion: if 4 or all consecutive standard layers contain observations with flag > 0 , set these standard layers to rejected • follow-up criterion: each analysis layer within these standard layers are rejected if they contain observations with flag > 0 all observations within these rejected analysis layers are rejected 05.08.2005 - 3 -

  4. analysis increments used to correct model background value to obtain a better estimate of ‘truth’  revised first guess check • no neighbouring observations (no GPS) : first guess check on IWV many neighbouring observations : checks consistency of current obs to them many observations used for analysis increment  better estimate of truth  decrease threshold large analysis increment = disagreement of model and obs  large uncertainty  increase threshold spatial consistency check of integrated water vapour • derive observation increments of IWV from radiosonde humidity profiles and optionally from ground-based GPS ZPD data • at each observation location, an ‘analysis increment’ is computed from neighbouring observations 05.08.2005 - 4 -

  5. NOAA IR LM ass., opr. QC (ref) 01:53 larger stability-dependent thresholds (old) GME QC thresholds new QC incl. IWV, larger thresh. ok too tight → GME thresholds revised thresholds too small (no IWV-QC) why all this ? • if threshold RHthr too small too many good observations near inversions are rejected 13 Feb 2003, 0 UTC 05.08.2005 - 5 -

  6. results, low stratus period • low-stratus period 8 – 13 Feb 2003, assimilation cycle with forecasts (GPS used / not used) • multi-level check rejects 4 % of profiles (completely or partly, above ps … 700 hPa) • IWV check rejects 1 % of profiles (completely) • << 1 % of remaining individual observations rejected by first guess check • > 80 % of rejected data are close to lateral domain boundaries (within ~ 50 grid points) new QC ref QC obs Warsaw 12 Feb 0 UTC 13 Feb 2003, 12UTC new QC ref QC obs Warsaw boundary east-west vertical cross section LM-ass. using Warsaw sounding 12 Feb 2003, 0 UTC 12 UTC • boundary fields too moist (GME-OI) • background field too moist • rejection of (good) profile 05.08.2005 - 6 -

  7. observed precipitation LM ass, ref QC LM ass, new QC new QC ref QC obs > 100 mm Stuttgart 19 July 23 UTC new QC ref QC obs > 100 mm Stuttgart 30 July 23 UTC 24-h precipitation 19 – 20 July 2004, 6 UTC humidity profile above 925 hPa rejected by first guess / multi-level check 24-h precipitation 30 – 31 July 2004, 6 UTC humidity profile rejected by spatial consistency check of IWV 05.08.2005 - 7 -

  8. observed precipitation LM ass, ref QC LM ass, new QC new QC ref QC obs 50 mm 75 mm Stuttgart 23 July 17 UTC new QC ref QC obs 20 mm 30 mm Stuttgart 22 July 23 UTC 24-h precipitation 23 – 24 July 2004, 6 UTC humidity profile rejected (only) above 850 hPa by first guess / multi-level check 24-h precipitation 22 – 23 July 2004, 6 UTC humidity profile not rejected ! 05.08.2005 - 8 -

  9. summary • introduced smaller, stability-dependent thresholds for radiosonde humidity • adjusted multi-level check, rejects 2 % (summer period) to 4 % (low-stratus winter period) of humidity profiles • introduced IWV spatial consistency check (both for radiosonde and GPS data; without dense GPS data IWV first guess check), rejects 1 % of profiles • QC accepts almost all good data near inversions • rejects most erroneous profiles of radiosonde Stuttgart (in particular the ones with worst impact) • will go into next LM version and become operational 05.08.2005 - 9 -

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