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In the past decades, boreal summers have been characterized by an increasing number of extreme weather events in the Northern Hemisphere extratropics, including persistent heat waves, droughts and heavy rainfall events with significant social, economic and environmental impacts. Many of these events have been associated with the presence of anomalous large-scale atmospheric circulation patterns, in particular persistent blocking situations, i.e., nearly stationary spatial patterns of air pressure. To contribute to a better understanding of the emergence and dynamical properties of such situations, we construct complex networks representing the atmospheric circulation based on Lagrangian trajectory data of passive tracers advected within the atmospheric flow. For these Lagrangian flow networks, we study the spatial patterns of selected node properties prior to, during and after different atmospheric blocking events in Northern Hemisphere summer. We highlight the specific network characteristics associated with the sequence of strong blocking episodes over Europe during summer 2010 as an illustrative example. Our results demonstrate the ability of the node degree, entropy and harmonic closeness centrality based on outgoing links to trace important spatio-temporal characteristics of atmospheric blocking events. In particular, all three measures capture the effective separation of the stationary pressure cell forming the blocking high from the normal westerly flow and the deviation of the main atmospheric currents around it. Our results suggest the utility of further exploiting the Lagrangian flow network approach to atmospheric circulation in future targeted diagnostic and prognostic studies. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No813844. RVD has been additionally supported by the Federal Ministry for Education and Research of Germany (BMBF) via the JPI Climate/JPI Oceans project ROADMAP (grant no. 01LP2002B). CL and EHG also acknowledge support from MINECO/AEI/FEDER through the María de Maeztu Program for Units of Excellence in R&D (MDM-2017-0711, Spain). ; No

Trabajo presentado en la European Geosciences Union General Assembly (EGU General Assembly 2021), celebrada online del 19 al 30 de abril de 2021. ; In the past decades, boreal summers have been characterized by a number extreme weather events such as heat waves, droughts and heavy rainfall periods with significant social, economic and environmental impacts. One of the most outstanding examples occurred in the summer of 2010 when an anomalously strong heatwave persisted over Eastern Europe for several weeks while extreme rainfalls struck Pakistan, leading to the country's worst floods in record history. Both events were related to the presence of an anomalously persistent atmospheric blocking situation - that is a large-scale, nearly stationary, atmospheric pressure pattern - over Eastern Europe. The high impact of blocking events has motivated numerous studies. However, there is not yet a comprehensive theory explaining their onset, maintenance and decay and their prediction remains a challenge. In this work, we employ a Lagrangian dynamics based, complex network description of the atmospheric transport to study the connectivity patterns associated with atmospheric blocking events. The network is constructed by associating nodes to regions of the atmosphere and establishing links based on the flux of material between these nodes during a given time interval, as described in Ser-Giacomi et al. [1]. One can then use the tools and metrics developed in the context of graph theory to explore the atmospheric flow properties. In particular, we demonstrate the ability of measures such as the network degree, entropy and harmonic closeness centrality to trace the spatio-temporal characteristics of atmospheric blocking events. ; This research was conducted as part of the CAFE Innovative Training Network (Climate Advanced Forecasting of sub-seasonal Extremes, http://www.cafes2se-itn.eu/) which has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 813844.

Assessing the inherent uncertainties in satellite data products is a challenging task. Different technical approaches have been developed in the Earth Observation (EO) communities to address the validation problem which results in a large variety of methods as well as terminology. This paper reviews state-of-the-art methods of satellite validation and documents their similarities and differences. First, the overall validation objectives and terminologies are specified, followed by a generic mathematical formulation of the validation problem. Metrics currently used as well as more advanced EO validation approaches are introduced thereafter. An outlook on the applicability and requirements of current EO validation approaches and targets is given. ; This work has received funding from the EC FP7 Quality Assurance for Essential Climate Variables (QA4ECV) (grant agreement 607405) Project for the preparation of the Copernicus Climate Service, and the EC Horizon 2020 project GAIA-CLIM (grant agreement 640276). Parts of the work were also supported through the ESA Climate Change Initiative (CMUG and GHG-CCI) and the European Commission's eartH2Observe Project (European Union's Seventh Framework Program, grant agreement 603608).