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WXT as a disdrometer?

WXT as a disdrometer?. Heikki Pohjola 1) and Leila Konkola 2) Vaisala Oyj University of Helsinki. The opportunity. Disdrometers are expensive and thus rare Global distribution of DSD is badly known

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WXT as a disdrometer?

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  1. WXT as a disdrometer? Heikki Pohjola1) and Leila Konkola2) Vaisala Oyj University of Helsinki

  2. 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 HelsinkiTestbed and radar network

  3. Radar applications • Set one or more WXTs toblocked sectors of radar • combine dBZ valuesfor 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_. AppI_Meteor., _3,396-409)

  4. Radar´s measurement volume, ~ km3 ~0,5 km ~0,5...1 km

  5. Radar´s measurement volume, ~ km3 ~0,5 km Raingauge e.g WXT, diameter ~ 10 cm!! ~0,5...1 km

  6. Radar´s measurement volume, ~ km3 ~0,5 km Raingauge, diameter ~ 10 cm! ~0,5...1 km

  7. 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 groundZg = NiDi6 and avoid all fuzzy Z/R conversions

  8. 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

  9. 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

  10. back up slides

  11. Defaults for WXT510 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: • 0R0,Dm=270D,Sm=0.9M,Ta=22.4C,Ua=35.8P,Pa=1009.7H,1.00=10.41n,1.25=11.01n,1.60=6.45n,2.00=3.44n,2.50=2.98n,3.20=2.46n,4.00=0.51n,5.00=0.00n

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