Storm hunter for Attica

The National Observatory of Athens (NOA) has acquired a new weapon – a storm hunter – to use in the battle against bad weather. The ultra-modern mobile Doppler X-band Polarimetric Radar (XPOL) can detect rain and storms at a range of dozens of kilometers and give warning of dangerous weather conditions. The XPOL was built in the US by Blinet Inc in collaboration with the National Center of Atmosphere Research (NCAR). It has been described as a hunter because the devices, which can be attached to vehicles, are used in the United States to pursue storms and hurricanes, recording their progress minute by minute. Varied topography In Greece, more basic problems need solving and the XPOL has already gone into operation next to the National Observatory in Pendeli. Being mobile, the radar unit can easily be moved to different locations. It can scan both horizontally and vertically and has a range of 150 kilometers, although currently it is only scanning in a range of 60 kilometers. «This is the limit of our visibility because of the topography of the area,» Yiannis Kalogyros, a researcher at the observatory’s environmental institute, told Kathimerini. The highly varied topography of Attica means great variations in rainfall distribution. «We use the radar’s observations to calculate with great accuracy the extent and duration of rainfall, both hail and rain, as well as wind.» The observatory’s researchers will not just observe weather phenomena approaching Attica. That can already be done to a large extent by the fixed radar that the National Meteorological Service set up a year ago on the island of Aegina. «It is not simply a matter of seeing a bad weather front approaching. We need much more specific and accurate forecasts. For example, we need to know precisely where and with what intensity rain is falling. Will it fall near streams or on places that flood? All that information is crucial for flood management,» explained Kalogyros. «Our aim is to draw up a rain map of the whole Attica basin by means of specific algorithms and computational models.» When the models are complete, the data can be collected and fed into the models that record the volume and intensity of the rain and issue early warnings to the state and public. No matter how accurate the radar is, the observatory’s researchers always cross-check its data with statistics gathered from standard rain meters and another instrument called a distrometer, of which the observatory possesses one of the few in existence. The distrometer uses two rays of light at right angles and fast linear scanning cameras to record the shape of the rain drops (or snowflakes or hail). Distrometer «The distrometer’s discernment is extraordinary (0.2 millimeters) and it accurately calculates the speed of rainfall, horizontal speed, average diameter, shape and the angle of incline of each raindrop, as well as the distribution of the the drops by size and the intensity of the rain.» said Kalogyros. The combined data from the radar and the other instruments can lead to effective algorithms for predicting rainfall. But, naturally, the formation of prediction models is much more complex. «Meteorologists, hydrologists and other experts need to work on it together,» he said, because it is not only the rain that falls that matters but also what happens on the ground.