Hoping for thunderstorms

Drifting balloons, airplanes, satellites, radar…no means are left untried to investigate the heavy localized precipitation events and thunderstorms that so often occur in the northwest Mediterranean’s mountain regions in late summer and early autumn and which often lead to flash floods. The precipitations, it is believed, are the result of cold winds from the north colliding or interacting with warm humid air coming from the sea.

“These complex interactions are not really well understood, making the precipitation events difficult to forecast,” says remote sensing expert, Yann Dufournet (CEG faculty), who is participating in the European research project HyMeX (HYdrological cycle in the Mediterranean EXperiment) together with one PhD student and three MSc students.

HyMex’s main goals are to better understand these weather patterns, in order to improve weather predictions, and also to figure out how climate change will influence high-impact weather events. The project was launched by the French scientific community and will last until 2020, by which time a massive amount of data must have been collected.

The Delft team have set up camp recently in southern France (near Montpelier), where they will stay for several months. They have a blog on which they give an impression on the project and their fieldwork.

For their fieldwork, the TU researchers use DTS cables (Distributed Temperature Sensing), among other equipment. These are long fibre-optic cables through which lasers fire pulses of light. As the reflection of these light pulses in the cable depends on the temperature, the researchers can use this device to measure the temperature in rivers or throughout long transects in the ground.

But they also brought with them some heavier equipment: TARA., which is a transportable atmospheric radar system consisting of two high gain antennas installed on a 12 meter long container, with which they perform precipitation and cloud measurements. The system uses Doppler shift to determine particle velocities.

The team hasn’t experienced any thunderstorms yet. “But things might change,” the students write on their blog. “So let’s hope!”

“However we still have quite some interesting cases to look at related to other meteorological situations that we can observe with our TARA radar,” says Dufournet. “These include interesting fog measurements, lightening events, strong wind gust events and different types of interesting clouds, which are formed due to the mountains around us.”