Abstract
The movement of atmospheric air masses can be seen as a continuous flow of gases and particles hovering over our planet, and it can be locally simplified by means of three-dimensional trajectories. These trajectories can hence be seen as a way of connecting distant areas of the globe during a given period of time. In this paper we present a mathematical formalism to construct spatial and spatiotemporal networks where the nodes represent the subsets of a partition of a geographical area and the links between them are inferred from sampled trajectories of air masses passing over and across them. We propose different estimators of the intensity of the links, relying on different bio-physical hypotheses and covering adjustable time periods. This construction leads to a new definition of spatiotemporal networks characterized by adjacency matrices giving, e.g., the probability of connection between distant areas during a chosen period of time. We applied our methodology to characterize tropospheric connectivity in two real geographical contexts: the watersheds of the French region Provence-Alpes-Côte d’Azur and the coastline of the Mediterranean Sea. The analysis of the constructed networks allowed identifying a marked seasonal pattern in air mass movements in the two study areas. If our methodology is applied to samples of air-mass trajectories, with potential implications in aerobiology and plant epidemiology, it could be applied to other types of trajectories, such as animal trajectories, to characterize connectivity between different components of the landscape hosting the animals.
Highlights
Atmospheric air masses are volumes of air with a defined temperature and water vapor content that have long been known to rule fundamental atmospheric phenomena like weather and air currents
It can be observed that the strongest connections tend to link nodes that are geographically close, but moderate connections exist between rather distant nodes
The connectivity in PACA is mostly oriented from North-East to South-West, which corresponds to the direction of the prevailing wind in this region
Summary
Atmospheric air masses are volumes of air with a defined temperature and water vapor content that have long been known to rule fundamental atmospheric phenomena like weather and air currents Their composition is mostly inert gases, but both organic and inorganic particles have been found to linger in high-altitude air as a consequence of the constant interaction of air masses with the earth’s surface below them. The direction and strength of these connections will be estimated by looking at the trajectories linking every pair of points/areas and weighting them according to appropriate measures In this perspective, it seems natural to resort to graph and network theory, since the formalism of nodes and edges provides an adequate environment for describing complex connections and can further be used to deepen into the topology of the constructed networks in order to infer interesting properties of the graphs, such as the presence of hubs
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