The Cloud Detectives

Researchers at the University of Leicester have developed a cloud detection system which will lead to them gaining a better understanding of greenhouse gases.

The team in the Earth Observation Science Group have identified a method that eliminates inaccuracies in monitoring how dynamics, radiation and chemical processes interact and control greenhouse gas distributions, and how industrial and human activities affect them.

The UK has invested £300 million in instruments onboard the European Space Agency’s largest satellite, ENVISAT, which is dedicated to observing land, ocean, ice and the atmosphere.

The Leicester Earth Observation Science group is using an atmospheric instrument on ENVISAT called MIPAS, to study the vertical ‘profiles’ of greenhouse gases in the atmosphere.

As ENVISAT orbits the Earth every 100 minutes, the MIPAS collects atmospheric emission spectra from which the unique “signature” of various gases can be retrieved.

However, as the tropical Upper Troposphere has a high cloud occurrence frequency (between 40 and 60%) it can result in inaccurate concentration retrievals due to cloud contamination of measured spectra.

The cloud detection scheme developed at the University of Leicester identifies cloud-free MIPAS data, so that ‘decontaminated’ water vapour and ozone information can be used to study key regions of the tropical atmosphere.

The Leicester team has already found:

Ozone enhancement over Equatorial Africa, which may be caused by biomass burning or transport. This moves through the Upper Troposphere (UT) and Lower Stratosphere (LS) (collectively called the UTLS).

The strong presence of high altitude sub-visible cloud (which cannot be seen with the naked eye) over South America, Africa, Indonesia and Darwin and the Pacific Ocean.

Large variability in UTLS water vapour, particularly an intensely dry atmosphere over Indonesia compared to the rest of the tropical UTLS. The mechanisms of how this feature occurs are still unknown.

This Leicester research will make a contribution to a major international aircraft field campaign called SCOUT- O3 that will take place in Darwin, Australia, in November 2005.

The Earth Observation Science group at the University of Leicester will be part of the satellite support team, aid pre-flight analysis and be responsible for providing greenhouse gas and cloud information to complement aircraft and balloon measurements of the tropical UTLS.

Postgraduate research student Harjinder Sembhi explained the significance of the research:

“The tropical lower atmosphere from 10 to 21 km altitude is a significant and fascinating region of the Earth’s atmosphere, which is unfortunately very poorly monitored by ground and air-based atmospheric instruments.

“Ozone above 20 km acts as a protective shield from harmful ultraviolet radiation. However in the troposphere it is a greenhouse gas and has the ability to affect the concentrations of other important greenhouse gases in this region. It is therefore essential to study the distribution of these gases in the tropical UTLS to help understand their impact on the global atmosphere and climate.”