Precipitation Measuring Instruments Length (depth) is the standard unit for measuring precipitation Millimeters is WMO standard U.S. uses the inch

Non-Recording Gauges U.S. Standard Rain Gauge 8 inch diameter at collector Inner collection tube cross-section = 1/10 collection area Rim of collector is 30 inches above ground Funnel starts 2 inches below rim Uses measuring stick to determine water amount.

British Standard Rain Gauge 5 inch diameter collector Inner collection tube cross-section area = 1/10 collector area Rim of collector 12 inches above ground Funnel starts 4 inches below rim Uses measuring glass to determine water amount.

Canadian Standard Rain Gauge 3.57 inch diameter collector Collection area 10 square inches Inner collection tube cross-section area = 1/10 collector area Rim of collector 12 inches above ground

Recording Instruments Fergusson Type Weighing Gauge Bucket rests on platform supported by spring Pen adjusted to record zero with bucket on platform Weight of water moves platform down which moves pen arm down causing recording on moving chart

Advantages: Disadvantages Removing funnel collector allows collection of solid precipitation Good in cold climates Disadvantages Winds over 25 knots cause oscillations of the balance producing errors in the recording Does not measure or record intensity. Can make rough estimations.

Tipping Bucket Gauge Water from collector is funneled into one side of the bucket mechanism Each bucket can usually hold 0.01 inch of water When full, the bucket tips and the second bucket moves under the funnell Tipping causes momentary closure of a switch, usually mercury or reed.

Momentary current drives pen arm to record 0 Momentary current drives pen arm to record 0.01 inch of precipitation each time bucket flips. Advantages: Continuous remote recording Disadvantages: No record for less than 0.01 inch of precipitation Not good for light rain, drizzle Errors result if rainfall greater than 2 inches per hour - splashing from small bucket. Buckets cannot tip fast enough. Cannot record rainfall intensity. Can make rough estimations.

Rate-of-Rainfall Recorders Jardi Recorder Rate of flow through opening is determined by height of float in a chamber which lifts a tapered spindle which allows more water to flow out of the bottom of the chamber. Float rises until rate of flow into the chamber equals the rate of flow out. Position of pen on a graph is determined by height of the float in the chamber.

Optical Rain Gauge Infrared beam transmitted across 0.5 m space through which precipitation falls Sensors are 24 to 64 photodiodes mounted in an array approximately 200 mm apart. Falling precipitation blocks IR beam from reaching sensor array, creating a shadow on some of the sensors.

Rain Gauge with Alter Shield

Another type Alter Shield

Turf Wall Rain Gauge

Measurement of Snow Snowfall - The depth (in. or cm) of new snow (Sf) Snowfall Water Equivalent - Depth (in or cm) of water when snowfall is melted. (Sw) Conversion: Weighing a core sample Melting a core sample and measuring Melting a core sample and weighing Use of a conversion factor

Snowcover: Areal extent of snow covered ground expressed as a percent of the total area of a given region. Snow Density: The ratio of the water equivalent to the depth of snow.