WXT as a disdrometer Heikki Pohjola 1 and

WXT as a disdrometer? Heikki Pohjola 1) and Leila Konkola 2) 1) 2) Vaisala Oyj University of Helsinki

The opportunity • Disdrometers are expensive and thus rare • Global distribution of DSD is badly known • Climatological research and radar measurements could benefit of reasonably priced disdrometers For example NASA´s Global Precipitation Measurement (GPM) Program: • • Satellite will be launched 2013 ? Understanding of clouds and rainfall processes Make frequent rainfall measurements on a global basis. FMI involved in ground validation with Helsinki. Testbed and radar network

Radar applications • Set one or more WXTs to blocked sectors of radar – combine d. BZ values for each image • Gapfilling between radars • Attenuation correction – between the radar and the target, some microwave power is lost. (Barnes, S. L. , 1964: A technique for maximising details in numerical weather map analysis. Jour_. App. I_Meteor. , _3, 396 -409)

Radar´s measurement volume, ~ km 3 ~0, 5 km ~0, 5. . . 1 km

Radar´s measurement volume, ~ km 3 ~0, 5 km Raingauge e. g WXT, diameter ~ 10 cm!! ~0, 5. . . 1 km

Radar´s measurement volume, ~ km 3 ~0, 5 km Raingauge, diameter ~ 10 cm! ~0, 5. . . 1 km

Z from WXT measurement Raincap sensor of WXT works as a disdrometer, and measures N and D in time unit. Thus, we can calculate reflectivity on ground Zg = Ni. Di 6 and avoid all fuzzy Z/R conversions

Data • Drop size distribution data from WXT, disdrometer (RD 69) and POSS from Järvenpää, Sorto • WXT_Z: 21. 8. -> • RD-69: 1. 8. -> • POSS: All Testbed campaings DSD data from WXT_Z Date Time D 1. 00 D 1. 25 D 1. 60 D 2. 00 D 2. 50 D 3. 20 D 4. 00 D 5. 00 2006 -09 -03 23: 15: 00 10. 9 57. 6 23. 2 9. 4 3. 1 0 1 1. 3 2006 -09 -03 23: 20: 00 21 44 27 3. 6 2. 9 0 0 2. 3 2006 -09 -03 23: 25: 00 24. 9 44. 6 27. 6 13 1 0. 7 0 0 2006 -09 -03 23: 30: 00 16. 3 41. 5 18. 1 2. 7 1. 1 0 0 0 2006 -09 -03 23: 35: 00 4. 9 15. 9 7. 7 6. 8 1. 7 0 0 0 2006 -09 -03 23: 40: 00 15. 7 49. 1 63 20. 7 4. 6 0. 7 0 0 2006 -09 -03 23: 45: 00 25. 4 57. 7 34. 7 11. 5 1. 8 0 0 0 2006 -09 -03 23: 50: 00 3. 6 6 1 0 0 0

What next? • Comparisons between disdrometer, WXT (and POSS) DSD data. • If promising, first comparisons with radar reflectivity data. Challenges: • WXT data 5 min intervals, accuracy 5 % • RD-69 data 1 min intervals, accuracy 1, 4 %!!!! • Different drop diameter classes

back up slides

Defaults for WXT 510 Disdrometer test units • • • DSD test units transmit automatically in every minute one message (so called auto composite message) which includes wind, PTU and disdrometer parameters in one string. Disdrometer counters are automatically reset after any output including disdrometer parameters. Example: 0 R 0, Dm=270 D, Sm=0. 9 M, Ta=22. 4 C, Ua=35. 8 P, Pa=1009. 7 H, 1. 00=10. 41 n, 1. 25=11. 01 n, 1. 60=6. 45 n, 2. 00=3. 44 n, 2. 50=2. 98 n, 3. 20=2. 46 n, 4. 00=0. 51 n, 5. 00=0. 00 n