1. Rain Masking (Gauge Response Times) John Goddard and thanks to Elizabeth Slack for help with data Chilbolton Facility for Atmospheric and Radio Research

2. Equipment mounted on portakabin roof. Optical Rain Gauge Ground located gauges 500 metre Range at Chilbolton Cluster of gauges

3. Chilbolton Facility for Atmospheric and Radio Research DeviceManufacturerTechniqueCollector AreaRange/ Calibration RAL RRDC[1] Gauge (on roof)[1] RCRU (MKIV)Volumetric Drop150cm²5-200mm/hr, 0.004mm/drop Optical Rain GaugeSci Tech Inc. (ORG700) Optical Extinction300cm²0.1-3000mm/hr Impact DistrometerDistromet Ltd (RD-69) Impact Momentum 50cm²0.3mm-5mm (drop diameter) Rain SensorR&D Instrumet (SN-R) Volumetric Drop50cm²0.01mm/drop Tipping Bucket GaugeRWMunro (R100)Bucket Volume324cm² (8"diam)0.2mm/bucket Self-Syphoning Capacitance Gauge RMYoung (50202)Water Level ~ Capacitance 100cm²50mm/Syphon RAL RRDC Gauge (on ground) RCRU (MKIV)Volumetric Drop150cm²5-200mm/hr, 0.004mm/drop RAL RRDC Gauge (on ground) RCRU (MKIV)Volumetric Drop324cm² (8"diam)3-100mm/hr, 0.002mm/drop [1][1] Abbreviation RAL RRDC Gauge = Rutherford Appleton Laboratory Rapid Response Drop Counting Rain Gauge. Rain Sensors deployed at Chilbolton

4. Chilbolton Facility for Atmospheric and Radio Research Drop Counting Gauge Optical Gauge Tipping Bucket Gauge Distrometer Rain Sensor Syphon Gauge

5. Chilbolton Facility for Atmospheric and Radio Research 2 July 2002 16.38Spurious (?) drop on DC8 16.41Impact distrometer 16.41Optical gauge records rain 16.49DC6 records first drop 16.57Rain Sensor 17.00Tipping bucket (1020 mins.)

6. Chilbolton Facility for Atmospheric and Radio Research 2 July 2002 08.10Optical gauge and distrometer only 08.30Start of event recorded by most instruments

7. Chilbolton Facility for Atmospheric and Radio Research 4 July 2002 22.35Small event on optical gauge and impact distrometer 22.45Optical gauge and impact distrometer record stronger rain 22.55DC8 records first drop 23.01DC6 records first drop 23.20Tipping bucket (~1400 mins.)

8. Chilbolton Facility for Atmospheric and Radio Research 8 July 2002 (1) 06.25Spurious count on Rain Sensor 06.44 Optical gauge records rain 06.48DC6 and DC8 record first drops 07.47Tipping bucket (~468 mins.)

9. Chilbolton Facility for Atmospheric and Radio Research 8 July 2002 (2) 13.15Optical gauge records rain (795 min.) 13.18DC6 and DC8 record first drops 13.19Rain Sensor records drop 13.19Tipping bucket (~799 mins.)

10. Chilbolton Facility for Atmospheric and Radio Research 15.40Optical gauge records rain (940 min.) 15.54DC8 record first drops 15.55DC 6 records first drops 15.57Rain Sensor records drop 15.58Tipping bucket (~958 mins.) 8 July 2002 (3)

11. Chilbolton Facility for Atmospheric and Radio Research Conclusions Distrometer and Optical gauge - both good indicators of precipitation onset Drop counting gauges lag these by 2-5 minutes (maybe depending on how wet the collector has remained since the last event) Tipping bucket gauge - not useful for this purpose - lags of tens of minutes in weak precipitation - 2 factors, collector wetting and bucket capacity