1 The WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation 27-29 November 2008, St. Petersburg, Russia INTERCOMPARISON

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

[email protected]

2

WMO TECO-2008, St. Petersburg, RussiaChvíla, 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



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



Intruduction

0,00

10,00

20,00

30,00

40,00

50,00

0,0 2,0 4,0 6,0 8,0 10,0 12,0ie [mm.h-1]

D60 [%] < 0.80 ms-1

1.25 ms-1

2.25 ms-1

> 2.7 ms-1

0

5

10

15

20

0 2 4 6 8 10 12ie [mm.h-1]

D60

[%]non-convective

convective

5



Intruduction

-40

-20

0

20

40

0 10 20 30 T [°C]

D[%]

-50

0

50

100

1 min 2 min 3 min 5 min 10 min

D [%] 0.5 g

1 g

4 g

6



Methods

7



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.

1st step 2nd step 3rd step

presen t weather clouds synoptic situation

convective shower, thunderstorm Cu, Cb, Sc cugen cold fron t

non-convective rain St, Sc, As, Ns warm fron t

Type of precipitation

8



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



Results the dependence of the relative wind induced errors DN and DRA

on the wind speed

0

3

6

9

12

15

0 1 2 3 4 5u [m/s]

D N [%]

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

0

3

6

9

12

15

18

21

24

0 1 2 3 4 5u [m/s]

D RA [%]

10



Results comparison of the dependence of the relative wind

induced errors DN and DRA on the magnitude of the wind speed for non-convective and convective precipitation

0

3

6

9

12

15

0 1 2 3 4 5u [m/s]

D N [%]

non-convective

convective

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.

0

3

6

9

12

15

18

21

24

0 1 2 3 4 5u [m/s]

D RA [%]

non-convective

convective

11



Results the effect of the wind direction on the relative difference DN

and DRA between the pit and elevated disdrometers

––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– WD WD avg n WS range WS avg N0 N1 RA0 RA1 DN DRA [deg] [deg] [ ] [m/s] [m/s] [ ] [ ] [mm] [mm] [%] [%] ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 360 – 090 35 62 0.3 – 5.3 1.9 90229 82579 11.02 9.15 8.47 20.44 090 – 180 129 53 0.1 – 5.2 1.6 162284 143944 28.92 25.15 11.30 14.99 180 – 270 239 81 0.1 – 3.6 1.6 145170 135516 24.42 20.66 6.65 18.20 270 – 360 303 320 0.1 – 7.2 2.7 835721 757926 131.20 111.91 9.30 17.24 Calm 93 0.0 202183 193008 31.08 27.51 4.54 12.98 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– WD = wind direction WS = wind speed avg = average n = number of considered cases N0 = number of rain drops registered by disdrometer at ground level N1 = number of rain drops registered 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 disdrometer 0 disdrometer 1 (relative related to elevated gauge) DRA = difference between rain amount of disdrometer 0 and disdrometer 1 (relative related to elevated gauge)

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



Results the effect of the ambient air temperature on the relative wind

induced errors DN and DRA

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 group T average n N0 N1 RA0 RA1 DN DRA DRA [°C] [°C] [ ] [ ] [ ] [mm] [mm] [%] [mm] [%] ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– 5 – 10 9.1 149 439858 407076 68.57 60.47 7.45 8.10 13.40 10 – 15 12.8 241 692304 630772 101.17 85.98 8.89 15.19 17.67 15 – 20 17.4 167 256387 231519 49.76 41.78 9.70 7.98 19.10 20 – 25 22.0 47 45779 42307 6.90 5.98 7.58 0.92 15.38 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– T = ambient air temperature at 2 m heightn = number of considered casesN0 = number of rain drops registered using disdrometer at ground levelN1 = number of rain drops registered using disdrometer at 1 m heightRA0 = rain amount of disdrometer at ground levelRA1 = rain amount of disdrometer at 1 m heightDN = 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



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 speedn = number of considered casesDRA = relative difference between rain amount of Parsivel 0 and TRwS 0 (ground level) and Parsivel 1 and TRwS 1 (related to TRwS gauge)

–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– WS group Calm 0 – 1 m.s-1 1 – 2 m.s-1 2 – 3 m.s-1 3 – 4 m.s-1 >4 m.s-1 All speeds –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– n [ ] 88 118 127 120 70 81 604 ground level DRA [%] 30.32 28.61 25.59 36.46 33.41 43.48 31.83 elevated DRA [%] 15.28 12.41 10.32 22.77 20.77 34.14 17.46 ––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––

14



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

Thanks for listening !

Documents

1 The WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation 27-29 November 2008, St. Petersburg, Russia INTERCOMPARISON