DAVIS Vantage Pro2 manual Barometric Pressure, Solar Radiation

Weather Data Measured & Calculated

units (inches or millimeters) at the time it is displayed. Converting at display time reduces possible compounded rounding errors over time.

Four separate variables track rain totals: “rain storm”, “daily rain”, “monthly rain”, and “yearly rain”. Rain rate calculations are based on the interval of time between each bucket tip, which is each 0.01'' rainfall increment or 0.2 mm.

Barometric Pressure

The weight of the air that makes up our atmosphere exerts a pressure on the surface of the earth. This pressure is known as atmospheric pressure. Gener- ally, the more air above an area, the higher the atmospheric pressure, this, in turn, means that atmospheric pressure changes with altitude. For example, atmospheric pressure is greater at sea-level than on a mountaintop. To com- pensate for this difference and facilitate comparison between locations with different altitudes, atmospheric pressure is generally adjusted to the equivalent sea-level pressure. This adjusted pressure is known as barometric pressure. In reality, the Weather Envoy measures atmospheric pressure. When you enter your location’s altitude in Setup Mode, the Weather Envoy stores the neces- sary offset value to consistently translate atmospheric pressure into barometric pressure.

Barometric pressure also changes with local weather conditions, making baro- metric pressure an extremely important and useful weather forecasting tool. High pressure zones are generally associated with fair weather while low pres- sure zones are generally associated with poor weather. For forecasting pur- poses, however, the absolute barometric pressure value is generally less important than the change in barometric pressure. In general, rising pressure indicates improving weather conditions while falling pressure indicates deteri- orating weather conditions.

Solar Radiation

Note:	Requires optional solar radiation sensor (#6450, included on Vantage Pro Plus
	weather stations).

What we call “current solar radiation” is technically known as Global Solar Radiation, a measure of the intensity of the sun’s radiation reaching a horizon- tal surface. This irradiance includes both the direct component from the sun and the reflected component from the rest of the sky. The solar radiation read- ing gives a measure of the amount of solar radiation hitting the solar radiation

sensor at any given time, expressed in Watts /sq. m (W/m2).

Note:	The solar radiation sensor measures energy received in the spectral band between
	400 and 1100 nm.

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