The formation of a cyclonic region in which nonlinear interactions generate turbulence in the form of small-scale vortices can be observed because of the different rotating air masses. Turbulence dynamics in cyclones (specifically hurricanes) has been under-researched; therefore, assessing the shear term is crucial to identify the onset of cyclonic formation within a region of the atmosphere. Earth observation techniques are able to provide relevant information on this physical process. In this article, we propose a new framework that is useful for connecting the study of the dynamics of a cyclonic system with the observations generated by geostationary satellite facilities. In particular, we applied the proper orthogonal decomposition (POD), a technique widely used in turbulent analysis to decompose a generic scalar or vector field in empirical eigenfunction, to investigate a tropical cyclone, the Faraji hurricane, from a dynamic point of view, beginning from the temporal evolution of its temperature field. The latter was obtained by elaborating on data and images collected by the SEVIRI radiometer, installed on the Meteosat Second Generation-8 (IODC) satellite. Using the POD, the energy spectra of both the spatial and temporal components of the temperature field obtained through remote sensing techniques were studied separately. Important information was then extracted and used for an in-depth characterization of the properties of the turbulence in the non-linear evolution of this phenomenon.

<p>In the general framework of the atmosphere, the in-depth study of extreme events of complex nature such as tropical cyclones remains an open problem. Nowadays, it is possible to study and predict the directionality that a cyclone can acquire in a very short term. However, the search for mechanisms and geographical areas of formation and dynamics of such events in different regions needs better constraints on the preliminary nature of the current results. This work focuses on a diagnostic analysis of a tropical cyclone, with the aim of identifying key points that characterize its evolution, from a dynamic and observational point of view. The study is applied to Hurricane Faraji, the most powerful tropical cyclone of the 2021 Indian Ocean season, classified as fifth-category on the Saffir-Simpson intensity scale. The study develops in three main sections, all related to each other. The starting point is a large set of satellite products from both polar and geostationary platforms. From the data acquired by the polar instruments, an accurate study of the evolution of the hurricane is carried out, focused on the extraction of physical information related to the system (temperature and altitude of the associated cloudy system, temperature gradient, pressure in the different regions) at moderate resolutions. From the data acquired by the geostationary instruments, it is possible to obtain very high temporal resolution pictures of the temperature field of the cyclone, from which a study of the turbulent dynamics is carried out. In particular, to investigate the maximum energy content in the different regions of the cyclone, the Proper Orthogonal Decomposition (POD) technique is used to extract the associated spectra of both the spatial and temporal components, studied separately on three different ranges of scales.</p>

In the general framework of the atmosphere, the in-depth study of extreme events of complex nature such as tropical cyclones remains an open problem. Nowadays, there are different useful studies aiming to enlarge the current knowledge of these events. Under this perspective, the search for mechanisms and geographical areas of formation and dynamics of tropical cyclones at different latitudes needs better constraints on their preliminary results.This work focuses on a diagnostic analysis of a tropical cyclone, with the aim of identifying key points that characterize its evolution, from a dynamic and observational point of view. The study is applied to Hurricane Faraji, the most powerful tropical cyclone of the 2021 Indian Ocean season, classified as fifth-category on the Saffir–Simpson intensity scale. The study develops in three main sections, all related to each other. The starting point is a large set of satellite products from both polar and geostationary platforms. From the data acquired by the polar instruments, an accurate study of the evolution of the hurricane is carried out, focused on the extraction of physical information related to the system (temperature and altitude of the associated cloudy system, temperature gradient, pressure in the different regions) at moderate resolutions. From the data acquired by the geostationary instruments, it is possible to obtain very high temporal resolution pictures of the temperature field of the cyclone, from which a study of the turbulent dynamics is carried out. In particular, to investigate the maximum energy content in the different regions of the cyclone, the Proper Orthogonal Decomposition (POD) technique is used to extract the associated spectra of both the spatial and temporal components, studied separately on three different ranges of scales.

Using the general analogies with the descriptive models of the tropical cyclones, some climate change effects identify a significant increase in the Mediterranean sea surface temperature. This phenomenon, in conjunction with its peculiar morphological predisposition, could justify the acceleration, recently observed, and the formation of cyclones at these latitudes, so-called medicanes (“MEDIterranean HurriCANES”). Their observations are based on a typical rotational motion around a low-pressure center in the atmospheric mesoscale, including the air-sea interaction effects. In this work, different kinds of analyses were carried out about the spatial and temporal evolution of the Ianos medicane (Mediterranean cyclone that developed in 2020 in the middle of the Ionian sea). In particular, we use the Proper Orthogonal Decomposition (POD) method to decompose a database of spatio-temporal data collected by SEVIRI radiometer, onboard the Meteosat Second Generation - 11 geostationary satellite. Within this approach, we study the superposition regions of the rotating air masses, starting from the temperature field, in order to extract important informations about the evolution and distribution of the energy in the different scales of the event. Through this technique, it has been possible to study the turbulent dynamics of Ianos at different scales, obtaining a basis of empirical eigenfunctions along with their relative temporal coefficients. The ability of the POD to capture the maximum energy content in the spectrum, allows to separate different ranges of scales with similar characteristics, suggesting a different origin for the various kinds of emerging structures. On the other hand, through the use of specific remote sensing techniques, the diagnostics of Ianos were studied using databases obtained from LEO satellites. The capabilities of the VIIRS and MODIS sensors, on board the Suomi NPP and EOS-Terra/Aqua platforms, which have 2D images with higher spatial resolutions, were explored. The aim of this analysis is based on the extraction of some atmospheric parameters, such as the temperature field within the Ianos cloud system, associated with altitude values, and the assessment of the ice pixel percentage using the split window. In addition, a study of atmospheric instability was carried out using the vertical temperature gradient and sea surface temperature, and the pressure field for the characterization of the minimum in the eye of the cyclone.