FESSTVaL

In numerical simulations of the atmosphere, cold pools are a key ingredient of the lifecycle of convection. But operational observational networks are mainly blind to cold pools as the typical distance between stations (O(25 km)) is coarser than the typical size of cold pools (O(1 km)) at the beginning of the lifecycle of convection. By deploying a dense network of instruments over a small region, FESSTVaL allowed for the first time to peek into the internal structure of cold pools.

FESSTVaL took place in Lindenberg (Brandenburg, near Berlin), which hosts the supersite of the German Meteorological Service, from May 16 to August 27 2021. It combined two networks (Fig. 2). The first network was a network of surface instruments comprising 80 autonomous cold pool loggers, 19 weather stations, 83 soil sensors, all deployed in a radius of 15km around Lindenberg, as well as 70 weather stations handed out to citizens.  The autonomous cold pool loggers are instruments built by the group of Prof. Felix Ament at Universität Hamburg (UHH) to specifically capture cold pools by measuring their associated temperature and pressure perturbations. The second network consisted of vertically profiling instruments, including 9 Doppler lidars and 4 microwave radiometers, distributed at 3 supersites (Falkenberg, Lindenberg, Birkholz). Additional measurements were carried out by an uncrewed aircraft, multicopters and a small radiometer network during a four-week Intensive Observing Period.

FESSTVaL not only targeted cold pools, but also the associated wind gusts and the overall development of the boundary layer during summer days. As key features, FESSTVaL:

1. explored novel techniques to measure the targeted atmospheric variability in the horizontal by deploying dense networks of self-designed, self-built and low-cost instruments;
2. applied novel retrieval algorithms for ground-based remote sensing in the vertical (e.g. to capture wind gusts);
3. emphasized capturing the 4D structure of cold pools and wind gusts, which cannot be directly derived from operational measurements.
4. involved citizens in the process of assembling and deploying instruments, e.g. with tutorial videos designed for school pupils.