Victor José García GarridoVictor José García Garrido, Assistant Professor in the Department of Physics and Mathematics, is the person at Universidad de Alcalá who has participated in this research. In uah.esnoticia we asked Victor Jose about what the study of this project has meant and what conclusions have been drawn from this study.

- Can you explain the objectives of the study in which the UAH has collaborated with the CSIC?

This international interdisciplinary study, published in the journal Scientific Reports of Nature last july, has been the result of a collaboration between mathematicians of the Institute of Mathematical Sciences of the CSIC, Universidad de Alcalá and the Polytechnic University of Catalonia, and physicist of the atmosphere of the Université Cheikh Anta Diop in Dakar (Senegal) and Universidad Complutense de Madrid.

In this work mathematical tools have been applied that allow us to better understand the mechanisms of transport and mixing of dust and moisture that take place in the monsoon systems of the atmosphere, and that are crucial for the formation of clouds, and therefore for the existence of rain.

In particular, we have analyzed the Sahel region in West Africa, where the economy is mainly based on agriculture and livestock and therefore critically depends on the development of these atmospheric phenomena, in this case the West African monsoon system (WAM). In the year's season from June to September, the monsoon introduces humid Atlantic air into the African continent and it interacts with the inland winds that carry dust. In this interaction, dust particles act as moisture condensation core and contribute decisively to cloud formation.

- Explain briefly that it involves the use of this innovative mathematical tool to study the monsoons in 3D models.

For the preparation of this study, we have used three-dimensional models based on the horizontal and vertical wind speed weather data provided by the European Centre for Medium-Term Weather Forecasting (ECMWF). Based on daily data averaged over a 40-year period, we have obtained an average weather description of the wind speed fields during August, a key month for the development of the african monsoon.

Once we have done this data processing task, we have analyzed the dynamics of air particles using a mathematical tool from the theory of dynamic systems, known as lagrangian descriptors, which allow us to identify air transport routes and draw the geometric structures that underlie atmospheric currents. In this way, we can more easily and systematically determine the areas of the atmosphere that correspond to air particles that carry moisture, as they come from the ocean, and separate then from those that bring dust. Therefore, we can draw a map of where its mixture occurs. 

This tool allows us to study the dynamic behavior of a physical system that evolves over time. Applied to the description of fluids, such as the atmosphere and the ocean, it is able to identify the underlying geometric structures that characterize the currents, providing a skeleton that determines an intricate network of transport and mixing routes that governs the fate of the particles of the fluid. These structures, which can be visualized, for example, in the laboratory by injecting ink into a moving fluid, are revealed by Lagrangian descriptors in a similar way to how iron filings draw the magnetic field lines generated by a magnet.

I would also like to emphasize that this mathematical technique has proved very fruitful and versatile in other disciplines, such as Oceanography, where it has been successfully used for the planning of transoceanic missions of unmanned self-employed vehicles, and also in the real-time management of oil spills at sea. On the other hand, it has also recently found its application in the Theory of Transition in Chemistry, to describe relevant aspects of reactivity in chemical processes.

The truth is that it´s a great satisfaction to see how some ideas that come from an abstract world such as mathematics naturally find their application in solving real problems, contributing decisively to scientific advancement. Mathematics provides us with the language that Science needs to describe the world around us.

- Why has the Sahel region been chosen for the study?

West Africa´s climate plays a key role in the terrestrial climate system. In particular, the atmospheric phenomenon that determines the rainfall and droughts of this area of the African continent is the monsoon of West Africa, a complex system involving the interaction of wet winds from the ocean, as well as air currents that bring dust from within continent. 

In the Sahel, which is a semi-arid band-shaped region that extends from east to west of the African continent and separates the Sahara desert from the Sudanese savannah, the economy critically depends on the periods of droughts and rains produced by the monsoon, as it´s based on agriculture and livestock. Rainfall in this area is extremely irregular and varies significantly from station to station. Most of the rain of the year is caused by the monsoon, it takes place during the months of June to September, while the rest of the year the climate remains very dry.

- What does the study of monsoons entail with this new technique? What can identify this new tool?

Applying this mathematical technique to the monsoon study provides a new perspective for atmospheric science researchers to analyze and identfy in a more detailed way the sources of moisture and dust that give rise to these complex phenomena. This tool will help build a three-dimensional geometric representation of monsoon systems and how dust and moisture move. It therefore provides us with the opportunity to obtain an X-ray of the skeleton formed by the air currents with which we can analyze in detail the transport and mixing processes that characterize these meteorological systems. 

Victor José García Garrido

It should be noted that the technique we have used in this work has also been used in recent years by members of our research group in the field of atmospheric sciences to study the structure of the stratospheric polar jet of the southern hemisphere and the phenomena of sudden stratospheric warming. 

- What conclusions has this study opened? Do you anticipate the study of other monsoons within the research group?

The work opens a new path to explore the cloud-forming mechanisms in the monsoons that take place in Earth´s climate system. One of the most relevant conclusions of this study has been the discovery of air transport routes connecting two of the most important tropospheric air streams of the monsoon, the East African jet and the East Tropical jet. This interaction between the two currents has been a surprise as, in literature, some experts in atmospheric sciences have considered these two systems to be essentially independent, and their interactions to be minimal. The natural air exchange mechanism that this work has revealed can help to improve our understanding of the structure of monsoons. 

Currently, in the research group we are working on improving the capabilities that the mathematical tool of lagranguan descriptors can provide for the analysis of the dynamics of such atmospheric phenomena.

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