40 meters Discussion on Time Interval for Calculating Rain rates For WMO Intercomparison Experiment Vigna Di Valle Precipitation testbed at Sterling, VA.

40 meters

Discussion on Time Interval for Calculating Rain ratesFor WMO Intercomparison Experiment Vigna Di Valle

Precipitation testbed at Sterling, VA USAThe two systems are 40 meters apart and are identical.System consists of Geonor raingauge, single alter shieldand a small double fence intercomparison shield. Inner ring is 12 feet in diameter, outer ring is 28 feet in diameter.

5 precipitation events were chosen to examine the variability in calculatingrain intensity from two identical rain gauge configurations. In addition, a brief examination of lag times between two identical shield configurationsbut different rain gauges for the same 5 precipitation events.

Rain Rate Calculated from 1 min values

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193 201 209 217

Ratio

Geo

1 &

Geo

2

Rain Rate Calculated from 5 min values

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43

Rat

io o

f G

eo1

& g

eo 2

Rain rate Calculated from 10 min Values

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Rat

io G

eo1

& G

eo 2

Rain rate Calculated from 15 min values

0.5

0.6

0.7

0.8

0.9

1

1.1

1.2

1.3

1.4

1.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Rat

io G

eo1

& G

eo 2

The total rainfall amounts measured by both systems for the 5 events agreed with each otherwithin 1%.

Time LagsGeonor#1 vs. Geonor#2:

The time lag is defined as the time when the precipitation amounts from one gauge match those best from another, when time-shifted by the lag amount. The

time of the minimum of the squares of differences is this time. For Geonor#1 vs. Geonor#2 the time lag for the 5 days is always 0 minutes

Geonor#1 vs. Ott706The time lags for Geonor#1 vs. Ott706 are as follows:

June 1 4 minutesJuly 4 6 ½ minutesAugust 7 3 ½ minutesSeptember 8 6 minutes

October 20 4 ½ minutes

This short study is meant to stimulate discussion on how to compareThe measured rainfall intensity from dissimilar systems andthe spatial variability within the test plot.