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Identifier 000460556
Title The impact of triboelectrification on desert dust flow dynamics
Alternative Title Η επίδραση του τριβοηλεκτρισμού στη δυναμική ροής σκόνης της ερήμου
Author Δασκαλοπούλου, Βασιλική Δ.
Thesis advisor Αμοιρίδης, Βασίλειος
Reviewer Τάσσης, Κωνσταντίνος
Χαρμανδάρης, Βασίλειος
Παπαδάκης, Ιωσήφ
Κυλάφης, Νικόλαος
Καζαντζής, Στυλιανός
Ulanowski, Joseph
Abstract The Global Electric Circuit (GEC) represents the electric current pathway in the Earth’s atmosphere. The electric current that flows upwards from thunderstorms and electrified clouds into the Ionosphere, spreads out over the globe along magnetic field lines to the opposite hemisphere, and returns to the surface of the Earth. Atmospheric electric parameters, such as the vertical Electric Field (Ez) and induced air-to-Earth current (Ic) through the GEC, greatly depend on ambient weather conditions and convective meteorological systems due to the re-distribution of charged or uncharged aerosols and terrestrial radioactive particles in the atmospheric circulation. Under fair weather conditions, the electrical circulation is dominated by the potential difference between the global capacitor, which in turn generates the fair weather electric field, and consequently the fair weather electric current. Amongst aerosols affecting the atmospheric electrical content, Mineral Dust represents one of the most significant contributors, due to its abundant mass, various shapes and sizes which result in varying electrical properties of the dust particles. During dust storms, dust devils and subsequent advection of elevated dust layers, the electrical parameters can vary greatly from the values under fair weather conditions. The exact mechanisms that would explain and sufficiently describe the long-range electrification of dust are not clear yet, and are a subject of investigation. Major processes that are considered responsible for the electrification of dust particles include ion attachment and contact electrification, i.e. triboelectrification. Such processes are claimed to have large impact on desert dust transport and its influence in climate and ecosystems through the retention of larger dust particles in the atmosphere, as well as to particle vertical orientation with impact on radiative transfer. Ground-based electric field measurements can be indicative of the electrical behaviour of elevated dust layers and act as a proxy for the detection of charged particles within the layers. To gain a more comprehensive understanding of the electrical characteristics of airborne dust, synergistic model implementations and vertical profiling measurements within the layers are of outmost importance. Initially, we introduce the development of a novel 1D numerical model that parametrizes both of the above charging processes in the presence of a large scale electric field, under stagnant atmospheric conditions where wind contribution is neglected. The model is able to self-consistently calculate the modification of atmospheric ion densities and the subsequent alteration of the large scale electric field, when dust particles are present and atmospheric ions attach to them, and is further updated to account for the particle charging due to the efficient collisions between particles of various sizes. Furthermore, we demonstrate the feasibility of particle orientation under the influence of electric and gravitational fields through analytical calculations of the mean orientation angle of both charged/uncharged dust particles and comment on the pre-requisites on electric field strengths for the orientation to occur on particles of various sizes. Then, in order to test the charging model hypothesis and, simultaneously, provide observational evidence of dust electrification, novel measurement techniques and instrumentation are developed, targeting signs of dust electrification from the ground and accurate profiles of the vertical electric field strength and the charge density within the layer. We demonstrate a novel methodology through ground-based observations, only, that indicates that electric field variations during Saharan dust advection can be a sign of charged dust occurrences. Synergistic observations of the vertical atmospheric electric field and lidar-derived quantities for the optical characterization of the layer, are employed. Both parameters were monitored for the first time in tandem, and in order to identify the influence of the elevated dust layers on the ground electric field, we extract a Localized Reference Electric Field from the timeseries that reflects the local fair weather activity. Then, we compare it with the reconstructed daily average behaviour of the electric field and the Saharan dust layers’ evolution. To quantitatively approach our results, we examine the dependency of E_Z against theoretical assumptions for the distribution of separated charges within the electrified dust layer through a physical approximation that constitutes a more realistic description of the in-layer distribution of charges, as to what was previously assumed. Being aware of the inherent challenges and instrumental ambiguities of atmospheric electricity measurements, we introduce the implementation of two low-cost and disposable atmospheric electricity sensors that measure the electric field strength and the space charge density, respectively, while they have launching capabilities on balloon-borne meteorological platforms. The sensors were designed, assembled and characterized in-house, their performance was assessed on-field over preparatory campaigns and eventually utilized in a major ESA Cal/Val experiment, where consistent dust observations were performed. Data by both sensors are assessed with respect to the prevailing meteorological conditions and processed for different altitude domains, while showing a good overall agreement. Finally, we target the elusive dust particle preferential orientation, which could be detected from the resulting dichroic extinction of the forward-scattered light as it transmits through dust layers in the atmosphere. We revisit an existing methodology by targeting dichroic extinction of transmitted sunlight by utilize an experimental direct-Sun polarimeter, SolPol, which is capable of continuous monitoring of the elevated layers. SolPol records the state of polarization of the direct sunlight, represented by the complete Stokes vector, at a default wavelength of 550 nm with a detection limit of 10-7. We, firstly, fully characterize the instrument and delineate its measurement technique, produce a comprehensible and user-friendly instrument manual, and then provide unique observations of increasing trends of linear polarization for sunlight propagation through these dust layers, under various loads and solar zenith angles. Concluding, we attempt to interpret the measurements as a first indication of either vertical or horizontal dust particle orientation. The observed electric fields, nonetheless, are not adequate to orient larger particles totally vertically and retain them aloft, which presumably hints to other mechanisms leading to such a behavior. As a closure to this effort, we comment that when all these scientific disciplines (models - implementations - observations) are combined, the presence of electrified dust in lofted layers away from the source is undisputable, meaning that the electrical properties of the particles impact their transport dynamics and future work will represent the modulation of particle electrification in a more realistic way.
Language English
Subject Atmospheric aerosols
Atmospheric electricity sensors
Dust electrification
Dust orientation
Dust polarization
Polarimeters
Polarimetry
Ανάπτυξη μετρητικών οργάνων
Ατμοσφαιρικά αερολύματα
Ατμοσφαιρικός ηλεκτρισμός
Γραμμική πόλωση
Ηλέκτριση σωματιδίων
Πολωσιμετρία
Προσανατολισμός σωματιδίων
Σωματίδια ερημικής σκόνης
Τριβοηλεκτρισμός
Issue date 2023-11-13
Collection   School/Department--School of Sciences and Engineering--Department of Physics--Doctoral theses
  Type of Work--Doctoral theses
Permanent Link https://elocus.lib.uoc.gr//dlib/5/c/1/metadata-dlib-1700755234-770197-6318.tkl Bookmark and Share
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