FAQ
Please find below answers to frequently asked questions:
The name CLOUDLAB indicates that we will utilize clouds – specifically stratus clouds (or “high fog” as they are called in Switzerland) as a natural laboratory to study cloud processes and precipitation formation. During winter, stratus clouds are very common over the Swiss Plateau and are fairly stable compared to other cloud types (e.g. cumulus). The high frequency of low-level stratus clouds allows us to repeat the experiments under similar and realistic initial conditions, thus bridging the gap between laboratory and field observations.
The CLOUDLAB project aims at advancing the understanding of cloud microphysical processes leading to precipitation by using a multi-dimensional approach of targeted cloud seeding. The gained knowledge will help to improve the cloud microphysics scheme in the Swiss weather forecast model, and ultimately improve cloud and precipitation forecasts. For this purpose, we also plan to simulate cases of high fog in high-resolution, which in turn helps to improve weather forecast models. For example, a more reliable forecast of clouds could reduce the financial losses of operators of photovoltaic power plants due to better planning.
No, the goal of CLOUDLAB is to better understand microphysical processes in clouds and use this knowledge to improve weather forecast models and ultimately cloud and precipitation forecasts. The gained knowledge will also be essential in quantifying the consequences of artificial weather modification and climate interventions.
The CLOUDLAB project started in September 2021 and will last until September 2026. Field campaigns will be performed at the Rapier Platz in Eriswil during four consecutive winters (2021/22: January to March; 2022/23, 2023/24, 2024/25: December to February). We will perform seeding experiments when conditions are suitable (i.e. presence of low-level stratus with temperatures below -5 °C for the seeding material to be active). In addition, we have a constantly running setup of remote sensing devices that will enable us to fill observational gaps in Switzerland in a partnership with MeteoSwiss.
Eriswil receives a fair amount of fog and low stratus during winter. The location of Eriswil has several advantages compared to other places in the Swiss Plateau. Firstly, our measurement site in Eriswil is located at an elevation of around 900 m a.s.l., which allows the tethered balloon system to reach the clouds and to have sufficiently low temperatures for the seeding experiments. Secondly, Eriswil is located in a remote area and outside of any control area of an airport, which is favourable for the operation of the tethered balloon system and the drones. Thirdly, the measurement site in Eriswil offers enough space for the instruments and has a pre-installed power supply.
During the field campaigns, a tethered balloon system with a holographic imager is installed at the Rapier Platz to measure the cloud properties in-situ. Additionally, several devices, namely a suite of active and passive remote sensing measurement devices (e.g. a cloud radar, a ceilometer, and a microwave radiometer), are deployed throughout the year. Furthermore, several ground-based measurement devices will collect standard meteorological parameters (e.g. temperature, relative humidity, wind speed and direction), cloud microphysical parameters (e.g. droplet size distribution), and aerosol properties (e.g. particle number and size distribution).
A seeding experiment involves two steps: In the first step, ice nucleating particles (i.e. aerosol particles that aid the freezing of water droplets) are introduced by a drone into supercooled stratus clouds (cloud droplets at temperatures below 0 ºC) to induce ice crystal formation and subsequent ice crystal growth processes. In the second step, the related microphysical changes (i.e. grown ice crystals) are measured downstream by an extensive set of instrumentation, including ground-based remote sensing instruments (e.g. cloud radar), a holographic imager on a tethered balloon system, and a particle counter on an additional drone. The repetitive introduction of local perturbations in a stable environment (by varying individual parameters such as the distance between seeding and measurement) allows us to infer the ice formation and growth rates, directly furthering our understanding of precipitation initiation.
Silver iodide particles aid the transition of cloud droplets to ice crystals by providing a surface on which ice can nucleate (without the help of an ice nucleating particle like silver iodide, cloud droplets will freeze at around -38 °C). We will use silver iodide as a seeding agent because it can initiate freezing at relatively warm temperatures (around -5 °C). Silver iodide is routinely used in Switzerland as a cloud seeding agent to reduce hail damages (external pagehttps://www.baloise.ch/de/ueber-uns/engagement/hagelflieger.htmcall_madel), because in theory this seeding should lead to a larger number of ice crystals that will not grow to large hailstones. In addition, silver iodide has successfully undergone an environmental compatibility assessment in Switzerland.
The amount of released silver iodide is far less than what is used for professional/commercial cloud seeding. The step from increasing ice crystal growth to dissipating clouds or increasing precipitation requires that many more ice nucleating particles are used on a larger scale. The efficiency of the process of increasing precipitation is still under debate – which is why CLOUDLAB scrutinizes these techniques.
We engaged an external, independent environmental consulting company to assess the environmental relevance of the silver iodide emitted during the CLOUDLAB experiments. Their report shows that the CLOUDLAB experiments will not have an environmental impact and that the released amount does not endanger humans and the environment. Moreover, commercial cloud seeding generally releases more particles than we plan to release during CLOUDLAB.
As we have done for previous field campaigns, we will close the airspace around Eriswil (radius of 5 km) during the measurement periods to ensure that no other aircraft will fly into the area we are using. We have the Federal Office of Civil Aviation (FOCA) approval to activate the restricted area for the balloon and drone flights. During the missions, we are reachable by phone all the time. When requested, we can terminate all operations within 15 minutes. This ensures that our operation will not affect critical services such as REGA rescue flights.
The tethered balloon system was successfully deployed during several field campaigns (e.g. in the Swiss Plateau, in Davos, in the Arctic). The drones (Meteodrones) are manufactured by our collaborator, Meteomatics (external pagehttps://www.meteomatics.com/en/call_made), who has extensive experience in developing drones and regularly flies drone missions in Switzerland. Furthermore, a comprehensive risk assessment was performed for the operation of the drone and of the balloon, which was examined and approved by the FOCA.