Rainfall

Primary rain gage

Most of the precipitation in the wider area of Athens is in the form of rainfall. Since the main objective of the METEONET project is the investigation of the occurring rain events, the increase of the network's reliability in this issue was promoted, by installing two rain gages per station in order to ensure the non-stop recording of the rain height, intensity and temporal distribution, in case of a malfunction in one of the two rain gages.

 

Research has shown that a conventionally shaped rain gage interferes with the airflow and that the flow accelerates and turbulence increases over the top of the funnel than otherwise would have fallen on the ground. To overcome this problem, aerodynamic rain gages were installed with a profile which has been designed to reduce drag and turbulence and therefore be sited conventionally on exposed sites with confidence. Furthermore, no object is near the gage in a distance of two times it's height. Emphasis was given to ensure an obstacle free angle of 30 - 45 degrees, from the top of the gauge to the surrounding objects. The gages are placed 1.5 m above ground level.

 

In both rain gages rainfall is measured by the well-proven tipping bucket method. Precipitation is collected by the funnel and is passed to one of the two buckets situated at either end of a short balance arm. The balance arm tips when the first bucket is full, emptying this bucket and positioning the second bucket under the funnel. The tipping process repeats indefinitely as long as the rain continues to fall, with each tip corresponding to a fixed quantity of rainfall; at each tip the moving arm forces a magnet past a reed switch, causing contact to be made for a few milliseconds.

 

The pulses returned during rainfall may be counted over any time interval desired allowing accurate determination of the rainfall rate (this variable is called intensity, is frequently used in soil erosion studies and is relevant to some aspects of crop pathology).

The measuring error is less than 5%

 

Secondary rain gage

Primary rain gage technical characteristics:

 

Secondary rain gage technical characteristics:

Variables: rainfalltemperaturerelative humiditysolar radiationsunshine durationwind direction and velocity