Halfway - Counting droplets

Simone Placidi: "I use data from Meteosat for my research." (Photo: Hans Stakelbeek/FMAX)

Name: Simone Placidi (28)
Nationality: Italian
Supervisor: Professor Herman Russchenberg (Faculty of Electrical Engineering, Mathematics and Computer Science)
Subject: The influence of cloud droplet number concentration on climate
Thesis defence: In about two and a half years

“There is no straightforward method to measure the amount of droplets in the clouds, apart from taking an airplane and flying through them. Because of the costs, I try to study the density of droplets in the clouds using remote sensing techniques from the ground and satellites. Do you know the images of clouds moving above Europe you see during the weather forecast on television? They are obtained by a European geostationary satellite, Meteosat, which flies 36,000 kilometres above the equator. I use the data from this satellite for my research; it measures the amount of Sun radiation that is reflected back to space by clouds.
Until now this kind of research was focused on calculating how big the water droplets are, how much light is blocked by the clouds (cloud optical thickness) and the total quantity of liquid water. Instead, I’m using and improving an existing algorithm to determine also how thick the cloud is and how many liquid water droplets the clouds contain. It’s important to understand this correctly, because the amount of droplets determines the cloud life span and how much Sun radiation is blocked and thus does not reach the Earth’s surface. The cloud droplet density is also influenced by pollution. Anthropogenic aerosols function as cloud condensation nuclei, leading to higher numbers of small droplets. So, by studying the cloud droplet density and how thick they are, you can also say something about the influence of air pollution on clouds and their feedbacks on climate.
I’m focusing my work on low level clouds, or liquid water clouds, that float below an altitude of 2-kilometres and contain only liquid water droplets and no ice crystals. A nice cloud example is the stratocumulus, which is a horizontally homogeneous single layer cloud that does not precipitate.
I’m confident that the algorithm is quite correct. I applied it to synthetic data generated from a simulator and got nice results. However, I still must validate it by flying through a cloud and measuring the cloud droplet number density with an optical sensor that counts the droplets in the cloud.
This validation part will bring my PhD to a close. But it will require good organization: there are only a few aircrafts or helicopters equipped with such sensors. The measuring will take place at Cabauw, where the Cesar observatory for atmospheric remote sensing is located. The satellite scans that area every 15 minutes.
The logistics for flying is complicated by the fact that we need to get clearance from the Schiphol air traffic control. Since it’s crowed in the air, we need to plan ahead and ask for permission in advance. This will also require good knowledge of the weather conditions in the period when we want to perform the aircrafts measurements.”