RAINFALL Weather data – Derived Variables
Davis systems come equipped with a 0.01” or 0.2 mm option for the rain. The Vantage Pro(2) and Vantage VUE are pre-configured for the type of rain collector appropriate for your region. One of the setup-screens allows for this setting to be changed if there is a need.
0.01” rain collectors are designed to be used with an inch unit display setting. 0.2 mm rain collectors are designed to be used with a millimeter (mm) display setting. Most Vantage Pro(2) and Vantage Vue consoles come pre-set to the display setting that matches the rain collector type that the system is equipped with.
Parameters Used: Rain Total (Rain rate is a measured variable in the sense that it is measured by the ISS and transmitted to the display console, whereas all other calculated variables are determined by the console from data received from the ISS.)
Under normal conditions, rain rate data is sent with a nominal interval of 10 to 12 seconds. Every time a rain tip or click occurs, a new rain rate value is computed (from the timer values) and the rate timers are reset to zero.
Rain rate is calculated based on the time between successive tips of the rain collector. The rain rate value is the highest rate since the last transmitted rain rate data packet. (Under most conditions, however, a rain tip will not occur every 10 to 12 seconds.)
If there have been no rain tips since the last rain rate data transmission, then the rain rate based on the time since that last tip is indicated. This results in slowly decaying rate values as a rainstorm ends, instead of showing a rain rate which abruptly drops to zero. This results in a more realistic representation of the actual rain event.
If this time exceeds roughly 15 minutes, then the rain rate value is reset to zero. This period of time was chosen because 15 minutes is defined by the U.S. National Weather Service as intervening time upon which one rain “event” is considered separate from another rain “event”. This is also the shortest period of time that the Umbrella will be seen on the display console after the onset of rain.
“Surface Weather Observations and Reports “. Office of the Federal Coordinator for Meteorological Services and Supporting Research, Washington, DC, 1998
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