The value of aircraft data in investigating the cause of a severe storm

Abstract

The storm of the 28 of October 2013 was one of the strongest of the last 10 years, with wind gusts up to 152 km/h above the Wadden islands. In Meteorologica, a discussion started about the cause of the high winds experienced during this storm. With the help of Mode-S EHS aircraft data it is investigated to what extent the isallobaric wind has a large contribution to the total wind field. Mode-S EHS data, which is accumulated from an enhanced surveillance air traffic control radar that follows all the aircrafts in its range, contains information about the wind and the temperature. The quality of Mode-S EHS data is checked by a comparison with the Cabauw tower and the wind profiler at Cabauw. From this comparison, it is found that the quality of the Mode-S EHS data is good to use for further research. For the case study of the storm of the 28 of October 2013, the theoretical wind is determined with the finite difference method and with the piecewise linear interpolation method with the geopotential height from Harmonie 38h1.2. With these two methods the geostrophic wind, the isallobaric wind and the inertial-advective component of the ageostrophic wind are determined. From this, it follows that the isallobaric wind and the inertial-advective component of the ageostrophic wind counteract each other near the center of the extratropical cyclone. It also shows that the modelled wind from Harmonie 38 compares well with the wind speed measured by Mode-S EHS and that the high winds were manifested in the lowest 800 m of the atmosphere.