Investigations into the improvement of automated precipitation type observations at KNMI Marijn de Haij Wiel Wauben KNMI R&D Information and Observation Technology TECO-2010, Helsinki | 31 August 2010

Contents The main issues Investigation of new sensors Conclusions and outlook TECO-2010, Helsinki | 31 August 2010

Precipitation type observation Visual observations in SYNOP/METAR issued by KNMI fully automated using Vaisala FD12P scatterometers, with exception of 2 airports Combines optical (~size) and DRD12 detector (~water content) signals Differences with human observer analyzed and reported to users (e.g. Wauben, 2002) Most important issues: Discrimination of mixed/solid precipitation Classification of light precipitation events Detection of hail Precipitation detection in fog (MOR<400m) FD12P De Bilt Test TECO-2010, Helsinki | 31 August 2010

Comparison with human observer Overlapping hourly observations at 6 KNMI stations in 2000-2002 Correction rules and averaging applied on 1-min sensor data Poor skill scores found for freezing and solid precipitation Additional rules based on RH, TA, MOR evaluated with reference set Further improvement not likely -> test with ‘new’ instruments TECO-2010, Helsinki | 31 August 2010

Investigation of new sensors (2008-2010) KNMI selected four commercially available sensors: - with the potential to improve the observation (combined w/ FD12P) - which are suitable for use at AWS at an affordable price tag Ott Parsivel, Thies LPM, Lufft R2S, Vaisala WXT520 Setup: Field test in De Bilt September 2008-March 2010 Additional data: FD12P (2x), rain gauge, wind, PTU, … Assessment of possibilities for indoor check Reference: Evaluation by data validation specialists (10-min) and meteorologists (hourly) in a web tool Only precipitation type is used – wawa without intensity indication TECO-2010, Helsinki | 31 August 2010

Sensors under test Ott Parsivel Optical disdrometer 51cm2 sheet, 650nm Extinction-> D,v 8 types: L,LR,R,LRS,S,SG,SP,A Thies LPM Optical disdrometer 46cm2 sheet, 785nm Extinction-> D,v 9 types: P,L,LR,R,LRS,S,IP,SG,A Lufft R2S 24 GHz Doppler radar Frequency shift-> v 4 types: R,LRS,S,A Vaisala WXT520 RAINCAP Ø94mm Drop impact-> volume Distinction rain/hail: R,A TECO-2010, Helsinki | 31 August 2010

Example 16 January 2010: wintry precipitation Transition from liquid to solid precipitation around 19UT Captured well by disdrometers, 2 FD12P sensors show difference R2S: mixture reported due to temperature threshold 4˚C Meteorologist confirms light drizzle detections of LPM TECO-2010, Helsinki | 31 August 2010

Example 16 January 2010: wintry precipitation (2) First report LRS/S R2S 1615 PAR 1842 LPM 1845 FD12 1853 TECO-2010, Helsinki | 31 August 2010

Example 15 December 2008: dense fog Dense fog event identified in the evening (MOR<200 m), just above 0˚C Both FD12Ps report snow and snow grains at max. 0.03 mm/h Other sensors do not report precipitation, as confirmed by meteorologist TECO-2010, Helsinki | 31 August 2010

Results: evaluation Hourly evaluation performed by meteorologist beside normal duties Selection of events where disagreement with FD12P was indicated Results (≠ skill scores): Hourly observations # obs. # OK / N / NOK LPM 141 56 / 0 / 85 Parsivel 31 / 0 / 110 FD12oper 22 / 0 / 119 10-min observations # obs. # OK / N / NOK LPM 269 232 / 7 / 30 Parsivel 184 / 0 / 85 FD12oper 107 / 21 / 141 TECO-2010, Helsinki | 31 August 2010

Results: general impression Technically OK for 18 months without maintenance Frequency distribution (10-min) LPM: UP due to spiders, some added value for hail and classification of light events, no detection in fog Parsivel: high FAR for hail types, insensitive to L/SG, solid “spider” reports (no T included) WXT520: no hail events reported, although 3 confirmed cases R2S: high FAR for LRS, insect detections, threshold D≥0.3mm TECO-2010, Helsinki | 31 August 2010

Conclusions and outlook None of the automated systems has perfect performance Thies LPM is able to partially solve the issues encountered with the precipitation type observation by the FD12P Analysis of the improvement limited due to availability of reference Winter 2010-2011: Second test of LPM disdrometer at airports Schiphol and Rotterdam Entry of PW changes on a 1-minute basis by human observer Optimization of combination FD12P/LPM for precipitation type LPM issues that still need to be addressed: Contribution of false reports by spider(web)s Sensitivity/threshold Wind effect on the determination of the precipitation type TECO-2010, Helsinki | 31 August 2010

Thanks for your attention! See paper 3(2) for further details TECO-2010, Helsinki | 31 August 2010

TECO-2010, Helsinki | 31 August 2010

TECO-2010, Helsinki | 31 August 2010

Indoor check Setup of test for homogeneity and reproduceability of disdrometers Prior to field test and after 1 year Problem: accurate positioning of drops in the light sheet! Peristaltic pump Droplet plate Sensor Scale Good agreement with Thies factory calibration TECO-2010, Helsinki | 31 August 2010

Contingency table 2000-2002 TECO-2010, Helsinki | 31 August 2010

Amplitude  Diameter Duration  Velocity TECO-2010, Helsinki | 31 August 2010

Classification FD12P vs disdrometer Vaisala FD12P Disdrometer (bv. Ott/Thies) Optisch/DRD12 = “grootte”/”waterinhoud” + temperatuur + max. deeltjesgrootte + evt. temperatuur TECO-2010, Helsinki | 31 August 2010

Intermezzo scores event other method yes no reference hit miss false none Probability of detection POD = hit / (hit+miss) False alarm rate FAR = false / (hit+false) Critical succes index CSI = hit / (hit+miss+false) TECO-2010, Helsinki | 31 August 2010

Example 26 May 2009: hail event Parsivel and LPM report hail between 0215 and 0225UT Temperature drops 5˚C, radar summer hail chance >90% But unfortunately no evaluation Other sensors report heavy rain, including both FD12Ps TECO-2010, Helsinki | 31 August 2010

Overview Precipitation type PW code NWS METAR No precipitation 00 C - Unknown precipitation 40 P UP Drizzle 50 L DZ Freezing drizzle 55 ZL FZDZ Drizzle and rain 57 LR DZRA Rain 60 R RA Freezing rain 65 ZR FZRA Drizzle/rain and snow 67 LRS RASN Snow 70 S SN Ice pellets 75 IP PL Snow grains 77 SG Ice crystals 78 IC Snow pellets 87 SP GS Hail 89 A GR TECO-2010, Helsinki | 31 August 2010