1. 1 The WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation 27-29 November 2008, St. Petersburg, Russia INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER by Branislav Chvíla and Boris Sevruk branislav.chvila@shmu.sk

2. 2 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER  Introduction – previous works  Main objectives of this work  Methods  View of the results and summary  Conclusions

3. 3 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Introduction Chvíla et al. (2002-2005) - analysis of the systematic errors for hourly and 15-min sums based on 1 minute precipitation records – the wind induced loss D = f(i, u) – separation of the stratiform and convective precipitation events according to the intensity (2002) and the weather phenomena and type of clouds (2005), - analysis of the other errors of electronic rain gauges – the dependency on ambient temperature, the errors due to in- accurate evaluationsoftware (2005)

4. 4 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Intruduction

5. 5 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Intruduction

6. 6 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Methods

7. 7 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Methods Calculation of the number of registered precipitation particles and appropriate precipitation amounts from Parsivel’s data sets for all 15- minute measuring intervals with liquid precipitation Calculation of the corresponding precipitation totals measured by weighing rain gauges, average wind speed and wind direction, mean ambient temperature Identification of convective and non-convective precipitation Explanation of the cloud’s symbols: As – altostratus, Cb – cumulonimbus, Cu – cumulus, Ns – nimbostratus, Sc – stratocumulus, Sc cugen – stratocumulus cumulogenitus, St – stratus.

8. 8 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Methods Elimination of all intervals when the precipitation was measured but not observed – false events Separation of all considered intervals when the precipitation amount not answered to the number of precipitation particles and vice versa Calculation of the relative wind induced loss D[%]=(RP- RE)/RP*100 Assessment of the influence of the ambient weather conditions (wind direction and temperature) on the number of the registered rain drops and the precipitation amounts

9. 9 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Results  the dependence of the relative wind induced errors D N and D RA on the wind speed The wind speed’s induced increase of the percentage difference of the recorded number of raindrops and the precipitation amounts between the ground level and the elevated disdrometer, related to the elevated one. Jaslovské Bohunice, Slovakia, 2007

10. 10 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Results  comparison of the dependence of the relative wind induced errors D N and D RA on the magnitude of the wind speed for non-convective and convective precipitation The increase of percentage difference of the recorded number of raindrops and the corresponding precipitation amounts between the ground level and elevated disdrometer, related to the elevated one. Non-convective (stratiform) and convective precipitation. Jaslovské Bohunice, Slovakia, 2007.

11. 11 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Results  the effect of the wind direction on the relative difference D N and D RA between the pit and elevated disdrometers The effect of wind direction on the number of registered rain drops and corresponding rain totals and the relative differences of them. Jaslovské Bohunice, Slovakia, 2007.

12. 12 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Results  the effect of the ambient air temperature on the relative wind induced errors D N and D RA Table. The effect of the ambient air temperature on the number of rain drops and respective rain amounts registered bz pit and elevated disdrometer. Jaslovské Bohunice, Slovakia, 2007. T = ambient air temperature at 2 m height n = number of considered cases N0 = number of rain drops registered using disdrometer at ground level N1 = number of rain drops registered using disdrometer at 1 m height RA0 = rain amount of disdrometer at ground level RA1 = rain amount of disdrometer at 1 m height DN = difference between registered rain drops number of disdrometer 0 and disdrometer 1 (relative related to elevated gauge) DRA = difference between rain amount of disdrometer 0 and disdromerer 1 (relative related to elevated gauge) Wind speed average in all groups varied between 1.8 and 2.3 m.s-1.

13. 13 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Results  comparison of the relative difference of rain amounts between the disdrometer and the weighing rain gauge Table. On the wind speed dependence of the relative difference of rain amounts registered by pit and elevated disdrometers and weighing rain gauges respectively. Jaslovské Bohunice, Slovakia, 2007. WS = wind speed n = number of considered cases D RA = relative difference between rain amount of Parsivel 0 and TRwS 0 (ground level) and Parsivel 1 and TRwS 1 (related to TRwS gauge)

14. 14 WMO TECO-2008, St. Petersburg, Russia Chvíla, B: INTERCOMPARISON MEASUREMENTS BY THE GROUND LEVEL AND ELEVATED DISDROMETER Conclusions  The effect of the wind speed is evident in the increasing difference of the recorded number of rain drops and precipitation amounts between the pit and elevated disdrometer.  The analysis of the field experiments showed that the difference in the influence of the wind on D between the convective and the non-convective precipitation is not significant.  The wind direction can create the differences in, by the disdrometer, registered rain drops numbers and precipitation amounts – larger differences in precipitation amounts were occured in the cases when wind was blowing along the lengthwise axial line of the disdrometer contrary to the difference of the number of registered particles.  The disdrometers overestimate the precipitation amounts in respect of the measurements made by weighing rain gauges

15. Thanks for listening !