WMOD00306 ‎(2)‎

• Title: Discusison of "Weather Modification in Arizona in 1971" by Herbert A. Osborn
• Date: 6/1/1972
• State: AZ
• Weather Modification - Doc Type: Report

used for opportWlity recognition and treatllent specification, the
validity of reported experimental results, and extrapolation of the
results of the model over large areas.

In Arizona, nobody has measured the total rainfall at the ground.
Osborn estimated it and bore testimony to the inadequacy of the rain
gage network to furnish an exact measure of total rainfall. Osborn
and Renard (1972) suggest a 2S percent error in estimation of rainfall
at the ground from radar and characterize radar measurements as
"highly subjective" though giving no rationale for the latter charac-
terization. For the relatively level terrain of Illinois, lluff (1971)
showed that a 2S percent variation in rainfall intensity for quarter-
inch showers occurs with a gage density of about two per square mile,
while the average gage density in the Catalina II network which Osborn
and Renard describe as "intense" was one per 7 square miles (Battan,
1966), for which Huff's gage-to-gage variability exceeds 4S percent.
Comparative data for the Catalina II and Walnut Gulch networks would
be of interest.

In ARIDROP and the Flagstaff experiments, measurements of radar reflec-

tivity were converted to estimates of rainfall at the ground using

reflectivity-rainfall relationships and raindrop-size spectra obtained

on site, frOll on-the-groWld measurements of rain, (Jones, 1966; Jones,

et ai, 1968), adopting the more conservative choice of drop-size spectra

as between seeded and unseeded clouds. This basic technique, with

improvements steJIDDing from the rapid deve10paent of radar technology,

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