East Asia and Western Pacific METEOROLOGY AND CLIMATE

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control valve which permits ample amount of water to flow over the
tower. The spilling water is directed to a sink. At the bottom of
the tower, there is a pipe with a micro-adjustment valve which permits
a constant stream of water to flow into the collecting funnel of the
gauge. During each experiment at a fix flow rate, the total amount of
water tipped from the buckets is collected by a pan for the subsequent
computation of the mean flow rate. Depending upon the set flow rate,
each experiment runs from several minutes to several hours to make up
50 tips for observation.
A total of 80 experiments were conducted to simulate the rainfall
rate from as low as 1.5 mm per hour to an extreme of 685.8 mm per
hour. Among these experiments, 61 of them were observed to be within
the measurable limit of the instrument. The remaining 19 cases were
regarded as out of the limit, with a water stream so intense that the
draining bucket was unable to spill out the water completely before
the opposite bucket started to tip. It was observed that it required
at least 1.5 seconds to drain out the bucket water, and therefore an
upper measurable limit for this instrument is 400 counts per 10
minutes, which is equivalent to a rainfall intensity of 492 mm per
hour.
Figure 2 shows the rainfall rate and the rate-error for all 80
experiments. The data indicate a regressable change from low rainfall
up to about 492 mm per hour. Beyond this extreme, the relationship
breaks down. A regression equation within the measurable extreme (61
observations) is obtained as follow;
E = 1.266430 + 0.112730.R - 6.78523 x 10~ 5 .R 2
where E is the rate-error in percentage of underestimation, and R is
the rainfall rate represented by total number of tip counts per 10
minute.
Very seldomly will the world record of rainfall intensity exceed
the limit of 492 mm per hour. In 1956, 31.2 mm of rainfall recorded
in one minute at Unionvill, Maryland is considered to be far beyond
the measurable limit of this instrument. A rainfall of 205.7 mm
recorded in 20 minutes at Curtea de Arges, Romania is also beyond the
limit. While in 1907, a rainfall of 304.8 mm recorded in 42 minutes