Everyone wants to know what weather is in store for them, but when you are actually up among the clouds it becomes even more important. That’s why modern aircraft are equipped with weather radar as one of their on-board radar systems, usually located in the nose of the aircraft.
The weather radar system uses the reflective effect of microwave pulses on substances such as rain to obtain a picture of conditions ahead of the airplane. Basically, the raindrops which are often found in stormy areas reflect the radar beams, and the more rain that is in the air, the stronger the reflected signal will be. Weather radar is strong enough to “see” up to 320 miles ahead of the aircraft, giving the pilot ample time to plan an alternative route avoiding storms and turbulence in many cases.
The system incorporates something called a Doppler Turbulence Detection circuit which can measure variations in the horizontal speed of raindrops – a reliable indicator of strong winds. Another feature is a Forward Looking Windshear detector which gives between 10 and 60 seconds of approaching “windshear,” when wind speed and direction can change dramatically over a very short distance. That’s why when the pilot warns of approaching turbulence over the aircraft intercom and asks passengers to fasten their seatbelts, the turbulence can sometimes seem to arrive as soon as he has finished speaking!
Modern aircraft are equipped with Weather Radar
Interestingly, thunderstorm reflectivity can be divided into three parts. The bottom third of the storm is composed entirely of water and is the part of the storm that most efficiently reflects radar energy. The middle third of the storm is composed of a combination of super-cooled water and ice crystals. Reflectivity in this part of the storm begins to reduce as ice crystals are very poor radar reflectors. The top third of the storm is composed entirely of ice crystals and is almost invisible to radar. To combat this potentially misleading picture, MultiScan Radar takes information from different radar scans and merges the information into a more accurate total weather picture.
The weather radar system presents the pilots with a topographic map type display of weather formations and features such as rivers, coastlines and cities, allowing him to see a huge amount of information at a glance.
All in all, an impressive collection of technology – particularly when you remember that the whole thing works in an aircraft that is constantly changing its speed, direction and altitude.