Why Bern's view of the atmosphere isn't distorted by clouds

Physicist Klemens Hocke measures the ozone values in the atmosphere from the roof of one of the university buildings. They are so accurate that they are used to calibrate the measuring apparatus on board satellites. And he also knows a great deal about hurricanes raging 50 kilometres above our heads.

The plugging of the ozone hole promises to become one of the great success stories of international environment diplomacy. The Montreal protocol of 1987, which banned ozone-depleting substances like the CFCs used as propellants in aerosols, is having an effect. In 1994 the ozone layer reached its lowest value and then stabilised, and since the turn of the millennium even a slight increase in the ozone has been observed. However, it is still too early to give the all-clear. "Researchers argue about whether we can really already talk about a recovery of the ozone layer," says Klemens Hocke. He an assistant professor at the Institute of Applied Physics (IAP) and head of the Atmospheric Processes group at the Oeschger Centre - and is himself part of this success, at least to a small extent.

He is responsible for the ozone measurements that - thanks to the University of Bern's IAP - are now an important component of the network monitoring the distribution of ozone in the atmosphere. The special measuring apparatus used for this was developed in Bern by Niklaus Kämpfer, head of the division of microwave physics, and his colleagues. Since 1994 it has produced an hourly ozone profile at a height of 20 to 65 kilometres - an unbroken series of measurements, unequalled anywhere else in the world, which indicates a trend towards the recovery of the ozone layer.

Move from Japan to Bern

Klemens Hocke has been responsible for these ozone measurements since 2005. He admits candidly that he didn't have a lot of previous knowledge when he took up his post doctoral position in Bern. "But it was precisely the chance of entering a new field that attracted me to this task." Klemens Hocke completed his first degree in astronomy in Bochum, and wrote his thesis on the ionosphere in Göttingen. After that he worked on the dynamics of the upper atmosphere, including three years spent in Japan as a post doctoral student, where he used radar and GPS apparatus to study the object of his research at a height of 100 kilometres.

This way of taking measurements is known as active remote sensing. The researchers in Bern, however, work with passive technology, using what is known as microwave radiometers. The great advantage of this kind of remote sensing is that it works day and night, and it is possible to take measurements even when it is raining or when there is dense cloud cover. The device measures the radiation emitted by molecules not only of ozone but also of water vapour, and can thus deliver information about their concentration and temperature.

The apparatus, which was conceived in Bern and is constantly being refined, is known for short as GROMOS (GROund-based Millimeter wave Ozone Spectrometer), and consists of an antenna and a lot of electronics to amplify the extremely weak signals from the atmosphere. The system is installed on top of the university's Exact Sciences building, and the signals are processed straight away in an annex built on the roof. An extremely complex business, which ends with the production of a multi-coloured curve on a monitor - the calibrated line radiation of ozone at a frequency of 142 GHz.

Promoting creative research

Klemens Hocke, who came to Bern to learn the secrets of this measuring apparatus, has in parallel also continued his own academic career. He has successfully defended his habilitation thesis and gained the position of associate professor. He now lectures on atmospheric dynamics and conducts research with his own team of PhD students. This also concerns ozone, but in areas that appear rather exotic to outsiders. For example, they are investigating the impact that the entry of a meteorite into the atmosphere has on the gas, and the properties of the ozone layer of other planets. "That gives us the freedom to run through completely different ideas, which in the end can be applied to the Earth's atmosphere," he says to explain the importance of such projects. "That is extremely important for creativity." But he stresses that these aspects are not the main focus; his research centres on gaining new knowledge about the ozone in the Earth's atmosphere.

The ozone spectrometer is actually only one of a whole range of measuring devices which researchers in Bern have used in achieving a towering reputation among experts in the field. They also measure the concentration of water vapour - the most important natural greenhouse gas - and the temperature and wind conditions in the atmosphere. At a height of 50 kilometres wind speeds of 360 kph are quite normal and not just peak values. "In winter the wind can blow this strongly for a whole week."

All these measurements have one thing in common: they are made from the Earth's surface and with the help of the above-mentioned microwave radiometers. This is a technology that is used by only a handful of other monitoring stations in the world. Something that is actually exclusive to Bern is the mobile apparatus used in field campaigns in many remote places of the world. The Atmospheric Radiometry group is currently developing a mobile ozone spectrometer as well.

Ground stations help satellites

The measurements obtained by Klemens Hocke and his colleagues are of central importance for the observation of the ozone layer, because they are incorporated into an international network that monitors the atmosphere - and because they are so reliable that they can validate the ozone values measured by satellites. Ground stations are also important because satellites have a life of only five to ten years. Although gaps therefore constantly appear in the long-term series of measurements taken from space, they can be bridged by data from Bern, among others.

And the Bern technology has one more decisive advantage: it is relatively inexpensive. "Our method of taking measurements is such good value, and the data we obtain with it are of such great importance that I wonder why there are not more apparatus of the same type in other places in the world," says Klemens Hocke.