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| DC Field | Value | Language |
|---|---|---|
| dc.contributor.author | Γαβρούζου, Μαρία | el |
| dc.contributor.author | Gavrouzou, Maria | en |
| dc.date.accessioned | 2024-01-17T09:04:41Z | - |
| dc.date.available | 2024-01-17T09:04:41Z | - |
| dc.identifier.uri | https://olympias.lib.uoi.gr/jspui/handle/123456789/33435 | - |
| dc.identifier.uri | http://dx.doi.org/10.26268/heal.uoi.13151 | - |
| dc.rights | CC0 1.0 Universal | * |
| dc.rights.uri | http://creativecommons.org/publicdomain/zero/1.0/ | * |
| dc.subject | Αερολύματα σκόνης | el |
| dc.subject | Επεισόδια σκόνης | el |
| dc.subject | Λεκάνη Μεσογείου | el |
| dc.subject | Ηλιακή ακτινοβολία | el |
| dc.subject | Μοντέλο διάδοσης της ηλιακής ακτινοβολίας | el |
| dc.subject | Νέφη | el |
| dc.subject | Θερμοκρασιακές αναστροφές | el |
| dc.subject | Δορυφορικά δεδομένα | el |
| dc.subject | Δεδομένα επανανάλυσης MERRA-2 | el |
| dc.title | Three dimensional solar radiative effects of Mediterranean dust aerosol episodes and implications for the regional weather and climate | en |
| dc.title | Τρισδιάστατη ανάλυση της επίδρασης των επεισοδίων αερολυμάτων σκόνης στη Μεσόγειο στην ηλιακή ακτινοβολία και επιπτώσεις στον καιρό και το κλίμα της περιοχής | el |
| dc.type | doctoralThesis | en |
| heal.type | doctoralThesis | el |
| heal.type.en | Doctoral thesis | en |
| heal.type.el | Διδακτορική διατριβή | el |
| heal.classification | Μετεωρολογία και επιστήμες της ατμόσφαιρας | el |
| heal.dateAvailable | 2024-01-17T09:05:41Z | - |
| heal.language | en | el |
| heal.access | free | el |
| heal.recordProvider | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών | el |
| heal.publicationDate | 2023-09-22 | - |
| heal.abstract | In the present PhD study, the three-dimensional solar radiative effects of Mediterranean dust episodes and their implications on the regional weather and climate were investigated for the 15-year period 2005-2019. This was achieved using different kinds of data (ground-based, satellite and reanalysis) and tools (a satellite algorithm and a deterministic radiative transfer model). In the first part of the study, a satellite algorithm, which is based on key aerosol optical properties, namely spectral aerosol optical depth (AOD), Ångstrom exponent and aerosol index (AI), was used to determine the occurrence of dust episodes over the broader Mediterranean Basin (MB). The algorithm first identifies the dominance of Dust Aerosols (DA) in the atmospheric column by applying specific thresholds on the input aerosol optical properties. Then, after the identification of DA, the algorithm determines the occurrence of strong or extreme Dust Aerosol Episode (DAE) on a specific day and pixel whenever the AOD is greater than its climatological mean value plus two or four standard deviations, respectively. Whenever at least 30 DAEs are identified on a specific day, this day is characterized as a Dust Aerosol Episode Day (DAED). Subsequently, DAEDs were grouped into DAECs, which are series of n (n ≥ 1) sequent days with extended dust episodes (DAEDs) over the Mediterranean Basin. The output of the algorithm includes information about the annual and monthly frequency of occurrence and the dust loading, in terms of AOD, for DAEDs. Running the algorithm over the entire study period, the obtained results were averaged on mean annual and seasonal basis to yield climatological like information. The interannual variability and trends of DAEDs and DAECs was also investigated. According to the algorithm results, more than 8 strong and 2 extreme DAEs take place over the desert areas of N. Africa and Middle East in every year. DAEs are also frequent over the Mediterranean Sea (3-4 strong episodes/year and 0.7-1.5 extreme episodes/year). The annual mean AOD during DAEs is maximum (1.7 and 4.0 during strong and extreme DAEs, respectively) across the coastal areas of Algeria, Libya and Egypt. A clear seasonal cycle with maxima during the warm and minima during the cold periods of the year was found. Specifically, strong DAEs are more frequent in summer (up to 5.2 episodes/season over Algeria and Morocco) while extreme ones in spring (up to 2 episodes/season across the coastal areas of Algeria and Libya). As it concerns the episodic days, in overall 166 (116 strong and 50 extreme) DAEDs occurred over the MB during the period 2005-2019. DAEDs are observed mostly in spring (47%) and summer (38%), with strong DAEDs occurring primarily in spring and summer and extreme ones in spring. Decreasing, but not statistically significant, trends of the frequency, spatial extent and intensity of DAECs from 2000 to 2019 are revealed. Moreover, a total number of 98 DAECs was found, primarily in spring (46 DAECs) and secondarily in summer (36 DAECs). The seasonal distribution of the frequency of DAECs varies geographically, being highest in early spring over the eastern Mediterranean, in late spring over the central Mediterranean and in summer over the western MB. In the second part of the present thesis, the FORTH deterministic spectral Radiation Transfer Model (RTM) was used to estimate in detail three-dimensional distributions of the Direct Radiative Effects (DREs) and their consequent modification of the thermal structure of the regional atmosphere during the 162 DAEDs (four DAEDs in 2019 were not included in this part of the study due to the unavailability of ISCCP-H cloud data which are used in the FORTH RTM) that were determined from 2005 to 2018 in the first part of the thesis. The RTM operated on a 3-hourly temporal and 0.5° × 0.625° spatial resolution, using 3-D aerosol optical properties (i.e., aerosol optical depth, single scattering albedo, and asymmetry parameter) and other surface and atmospheric properties from the MERRA-2 reanalysis as well as cloud properties (i.e., cloud amount, cloud optical depth, and cloud top height) from the ISCCP-H dataset. The model ran with and without dust aerosols, yielding the upwelling and downwelling solar fluxes at the top of the atmosphere, in the atmosphere, and at the Earth’s surface as well as at 50 levels in the atmosphere. The corresponding dust direct radiative effects (DDREs) were estimated by the difference between the two (one taking into account all aerosol types and another considering all except for dust aerosols) flux outputs. The atmospheric heating rates, and the subsequent buoyancy induced by the dust radiative absorption/heating, were calculated at 50 levels, from the upper troposphere down to surface, to determine how the DDREs affect the thermal structure and the dynamics of the regional atmosphere. Running the RTM for all DAEDs, the results were averaged to yield a climatology of DDREs and their effects on the Mediterranean atmosphere. The climatological annual mean DREs are positive and as high as +75 W/m2 in the atmosphere, and negative and as low as -72 W/m² at the regions’ surface. At TOA, DA cause a (planetary) heating (up to +26 W/m²) over deserts and a cooling (down to -20 W/m²) over all other sea and land areas. On a seasonal basis, the maximum atmospheric (up to 102 W/m² at 12:00UTC) and surface (down to -95 W/m² at 12:00UTC) DDREs are noted in autumn. At TOA, the maximum positive DDREs occur in summer (+32 W/m² at 12:00UTC) over Tunisia and the maximum negative (-26 W/m² at 12:00UTC) DDREs in spring over Tunisian coasts. Considerable vertically resolved DDREs, up to 4 W/m² and 8 W/m² for layers up to 4400m, were found on annual and seasonal basis. Such DDREs induce intense heating rates, up to 0.32 K/3-hour and 0.36 K/3-hour on annual and seasonal basis, respectively, modifying the regional atmospheric temperature, while inducing buoyancy up to 0.01 m/s², pointing to possible modifications of clouds due to dust episodes. Yet, it is found that DDREs can either strengthen or counteract the prevailing atmospheric convection. In the third part of the present thesis, four case study DAECs, that took place on (i) 16-18 June 2016, (ii) 12-13 May 2017, (iii) 05-07 September 2015 and (iv) 23-25 February 2006, were selected to investigate in detail their radiative and the consequent dynamic effects on the Mediterranean atmosphere. The obtained results show that DA systematically occur in two levels/layers in the atmosphere, one near the surface (up 3 Km) and an elevated one between 3-5km ASL, inducing mainly positive, but also small negative, DDREs. The maximum atmospheric DDREs and heating rates (27.1 W/m² or 0.56 K/3-hour) were found during the winter DAEC close to the surface of N. Africa, where σext,dust≈1.8 1/km, but also at higher layers over the same area, where σext,dust<0.6 1/km. This heating effect significantly affects the atmospheric buoyancy, inducing a vertical acceleration, which mainly varies between 0.01 m/s² and 0.02 m/s² in the dust layers and can be as high as 0.06 m/s² (winter DAEC) into them. In the fourth and final part of the PhD, first, the DAEs were determined based on the dust contribution to total aerosol loading (DC=DOD/AOD) provided by MERRA-2 to investigate the possible effect of DAEs on cloud occurrence. The relative frequency of occurrence of mixed and ice phase clouds was calculated with respect to the total number of days for which DC exceeds 10%, 50% and 80%. According to the results, when increasing the threshold of DC from 10% to 50%, i.e. when the presence of dust strengthens, the frequency of ice phase clouds formation significantly increases, by up to 20% between 33˚ N and 47˚ N. For even stronger presence of dust, i.e. when DA>80%, the relative frequency of mixed and ice phase clouds increases further, being greater than 0.8/0.6 respectively over Mediterranean Sea/land areas. Also, the atmospheric circulation before and during the four DAECs, and the formation of clouds, were observationally investigated using MERRA-2 and MODIS data respectively. The main characteristic of the atmospheric circulation before and during the DAECs is the presence (from the day before the episode) of a low-pressure system over northwestern Africa, causing the uplift of dust. This gradually dissipates giving place to the coexistence of a cyclonic circulation over the western MB and an anticyclonic circulation over the eastern MB, which move eastwards and cause the southwestern airflow that transports the DA into the Mediterranean. Under such conditions, mixed and phase clouds systematically form over the dust affected areas, while in the coming days, when DA persist over an area, these clouds either dissipate or remain with lower cloud top heights. | en |
| heal.advisorName | Χατζηαναστασίου, Νικόλαος | el |
| heal.committeeMemberName | Χατζηαναστασίου, Νικόλαος | el |
| heal.committeeMemberName | Μιχαλόπουλος, Νικόλαος | el |
| heal.committeeMemberName | Λώλης, Χρήστος | el |
| heal.committeeMemberName | Μπαρτζώκας, Αριστείδης | el |
| heal.committeeMemberName | Καζαντζίδης, Ανδρέας | el |
| heal.committeeMemberName | Ματσούκας, Χρήστος | el |
| heal.committeeMemberName | Μπάκας, Νικόλαος | el |
| heal.academicPublisher | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Φυσικής | el |
| heal.academicPublisherID | uoi | el |
| heal.numberOfPages | 281 σ. | el |
| heal.fullTextAvailability | true | - |
| Appears in Collections: | Διδακτορικές Διατριβές - ΦΥΣ | |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| Δ.Δ. Gavrouzou Maria 2023.pdf | 40.5 MB | Adobe PDF | View/Open |
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