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May - Radar blocking topography: What Shannon cannot see

The May Map of the month shows how topography can block weather radar beams, potentially compromising the quality of monitoring. The exaggerated relief used in the map shows well how hills can impact the visibility of weather radar, especially when they are close to the emitter.

Map of the Month: May

Cartographers: Dr Jesko Zimmermann & Azucena Jiménez-Castañeda

View map here: Radar blocking topography: What Shannon cannot see (PDF)

Weather forecast is a complex task involving climate models, as well as monitoring of current conditions. Besides the networks of weather stations across Ireland, recording a multitude of parameters such as temperature, rainfall, relative humidity, wind speed, and others, Met Éireann apply weather radars. Radar is an acronym for "Radio Detection And Ranging". It is a military technology developed in the 1940s. It has been rapidly applied to meteorology, as it detects hydrometeors with a high spatiotemporal resolution. However, ground radar beams can be totally or partially blocked by orography, human-made structures and others, resulting in weakening or losing the signal. It compromises the quality of data from the radar.   

The maps shows the radar beam blockage in a 100km radius around the Shannon Airport weather radar station. The blockage is layered on top of an exaggerated topography map of Ireland. And it shows very well how hills and mountains block the radar beam. As seen on the map there are two aspects of the topography that drive the blockage. Firstly, the orientation of the obstacle. Secondly, the proximity of the obstacle to the source of the radar beam, in this case Shannon Airport. Even lower obstacles can obstruct a large proportion of the beam if they are close to the radar emitter.

Each month the Teagasc spatial analysis unit use data from a number of sources and share it as a map to assist farming

View previous Maps of the Months here