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The short and the long of extreme storms

Monitoring and forecast of extreme atmospheric events (e.g. tropical cyclones and volcanic eruptions) remains a major challenge mainly due to sparse in situ measurements during such destructive weather phenomena. EU-funded scientists have combined ground data with satellite observations to overcome this limitation.
The short and the long of extreme storms
Many aspects of deep convective systems and volcanic eruptive clouds are poorly represented in current global climate models. By statistically analysing satellite observations and providing long-term statistics from these data, the project CONSYDER (Convective systems detection and analysis using radio occultations) highlighted observational constraints for improving the theoretical representations.

Researchers relied on radio occultation observations from global positioning system (GPS) satellites. Although GPS satellites are mostly used for navigation, signals sent from one GPS satellite to another are refracted by the atmosphere. From measurements of the associated propagation delay, the refractive index and bending angle, it is possible to estimate key atmospheric parameters.

The CONSYDER team used data acquired in the period 2001-2012 via this technique to create a reference atmosphere from the Earth’s surface to 80 km altitude. More specifically, they developed 3D maps of refractivity, pressure, temperature and water vapour together with the frequency and standard deviation of measurements at each location and altitude.

These radio occultation observations were combined with high-resolution and high-precision measurements from other satellites and ground based sensors. This unique combination allowed researchers to detect the cloud top height of the extreme events accurately and their inner structure. The aim was to gain a better understanding of the clouds´ structure especially in the upper troposphere and the lower stratosphere.

CONSYDER results indicated that tropical cyclones should be studied in connection to the ocean basin where they develop. Basins in the northern and southern hemisphere commonly show different thermal structures with storms reaching higher altitudes in the southern hemisphere.

On the other hand, the temperature anomaly above the tropical cyclones’ cloud top becomes positive in northern hemisphere ocean basins. The reason for this puzzling warming of the storm cloud top was not clear and is a topic of further investigations beyond the end of CONSYDER.

Before the end of the project, a dataset of radio occultation measurements co-located with tropical cyclones was compiled. Since GPS observations are evenly distributed over the globe, the dataset is suitable for studying extreme events even in remote areas.

CONSYDER also demonstrated that the technique developed for detecting cloud tops of convective systems and tropical cyclones can also be used for detecting and monitoring volcanic cloud tops and inner structure. Volcanic ash clouds and SO2 clouds have a different impact on the atmospheric thermal structure. The results revealed a clear warming signature from SO2 clouds after the eruption of Nabro and a cooling signature from the ash cloud after the Puyehue eruption.

The evolution of tropical cyclones and eruptive clouds, the lifetime of deep convective systems and associated environmental parameters analysed in CONSYDER provide a framework for comparison with model simulations. Besides diagnosing the underlying mechanisms, project outcomes provide guidance for parameterising convective processes in global climate models.

Related information


Deep convective systems, global climate models, CONSYDER, GPS satellites, radio occultation, tropical cyclones, ocean basin, volcanic eruptions, volcanic clouds
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