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| DC Field | Value | Language |
|---|---|---|
| dc.contributor.author | Stamatis, Michail | en |
| dc.contributor.author | Σταμάτης, Μιχαήλ | el |
| dc.date.accessioned | 2025-10-02T09:37:17Z | - |
| dc.date.available | 2025-10-02T09:37:17Z | - |
| dc.identifier.uri | https://olympias.lib.uoi.gr/jspui/handle/123456789/39463 | - |
| dc.rights | CC0 1.0 Universal | * |
| dc.rights.uri | http://creativecommons.org/publicdomain/zero/1.0/ | * |
| dc.subject | Surface solar radiation | en |
| dc.subject | Global dimming and brightening | en |
| dc.subject | Sattelite and reanalysis data | en |
| dc.subject | Global warming | en |
| dc.subject | Radiative trasnfer model | en |
| dc.subject | Ηλιακή ακτινοβολία στη γήινη επιφάνεια | el |
| dc.subject | Μοντέλο διάδοσης της ηλιακής ακτινοβολίας στην ατμόσφαιρα | el |
| dc.subject | Πλανητική σκίαση και λάμπρυνση | el |
| dc.title | Detailed assessment of the global dimming and brightening of the Earth under all-sky and clear sky conditions using modern tools and long-term climate data | en |
| dc.title | Λεπτομερής εκτίμηση του φαινομένου πλανητικής σκίασης και λάμπρυνσης της Γης υπό συνθήκες ανέφελου και νεφοσκεπούς ουρανού με χρήση σύγχρονων εργαλείων και μακροχρόνιων κλιματικών δεδομένων | el |
| dc.type | doctoralThesis | en |
| heal.type | doctoralThesis | el |
| heal.type.en | Doctoral thesis | en |
| heal.type.el | Διδακτορική διατριβή | el |
| heal.classification | Atmospheric Physics | en |
| heal.dateAvailable | 2025-10-02T09:38:17Z | - |
| heal.language | en | el |
| heal.access | free | el |
| heal.recordProvider | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών | el |
| heal.publicationDate | 2025-09-03 | - |
| heal.abstract | In the present PhD study, the Global Dimming and Brightening (GDB), its causes and possible links with global warming rates were investigated for the 35-year period 1984-2018. To this aim, detailed radiative transfer calculations were performed by the FORTH-RTM (Foundation for Research and Technology-Hellas Radiative Transfer Model) on a monthly basis and 0.5° x 0.625° spatial resolution using modern and improved satellite (CLARISC: CLARA-A2.1 and ISCCP-H synergy for a new cloud database) and reanalysis (MERRA-2) datasets for clouds and aerosols as well as surface and atmospheric properties, respectively. This analysis was also performed on decadal time periods of the entire study period, since GDB is a decadal scale phenomenon. It has been also done worldwide, hemispherically, over ocean and land, and over specific land areas, enabling a complete understanding of the spatial and temporal features of GDB on a climatological basis all over the world. First, the FORTH RTM with CLΑRISC cloud data (or FMC) ran to provide the surface solar radiation (SSR) and the corresponding SSR trends (GDB) were computed. The model indicates a global mean brightening (increasing SSR) from 1984 to 2018, equal to 0.88 Wm⁻²decade⁻¹. This brightening is observed in 63% of the global grid points. Both land and ocean regions of the world underwent brightening; yet the land SSR increase is stronger than the oceans’ one (2.57 Wm⁻²decade⁻¹ vs 0.19 Wm⁻²decade⁻¹). Also, in line with this, a stronger brightening occurred over the North Hemisphere (NH), equal to 1.4 Wm⁻²decade⁻¹, versus a weak brightening of 0.39 Wm⁻²decade⁻¹ over the South Hemisphere (SH). All the above SSR changes are statistically significant at the 95% confidence level. Yet, the spatially averaged GDB conceals diversified, in terms of sign and magnitude, patterns. Thus, strong tendencies toward brightening are noteworthy over Europe, the Americas, the Tibetan Tableau, Indonesia, Antarctica, Australia and some oceanic regions, whereas the dimming dominates over parts of China and India, the Arabian Peninsula, the Sahara, the Arctic, the Southern Ocean and the marine stratocumulus areas. These results revise the findings of our previous FORTH-RTM version using ISCCP-H cloud data (FMI) which suggested a global dimming over the same period, and this revision is due to more realistic cloud information (CLARISC instead of ISCCP-H cloud dataset). In a next step, the reliability of the estimated FORTH-RTM SSR fluxes and GDB was investigated. The model results are reliable, as proven from their successful evaluation against data from global reference station networks. The model SSR fluxes and their anomalies correlate very well with GEBA and BSRN ground-based stations (correlation coefficient R equal to 0.97 using SSR fluxes or 0.75 using flux anomalies and 0.94 using SSR fluxes or 0.71 using flux anomalies, respectively), having small biases (less than 3%) and satisfactory RMSE (less than 15%). The model estimated GDB nicely agrees in terms of sign with the stations, namely for 80% of GEBA and 65% of BSRN stations, while the agreement is even better for statistically significant trends agreement (for 90% of GEBA and 88% of BSRN). A similar evaluation was also conducted separately for the 4 decades of the study period and the agreement was again very good (ranging from 62% to 73%). Also, similar evaluations against ground truth and inter-comparisons were also performed for several other SSR and GDB datasets during the periods 1984-2018 and 2001-2018. The results of this inter-comparison approved that FORTH-RTM is a top-performing dataset in qualitative agreement for GDB when compared to observational measurements, further reinforcing its reliability. Additionally, FORTH-RTM ranks among the best-performing datasets for SSR, enhancing confidence in its ability to study long-term GDB trends on a global scale. Subsequently, the causes of GDB were investigated based on the trends of the SSR and the input parameters to the FORTH-RTM which influence SSR. Over the four decades, surface solar radiation (SSR) exhibited distinct trends. In the 1980s, a weak dimming (-0.69 %decade⁻¹) occurred over NH and a weak brightening over SH (0.53 %decade⁻¹), followed by a significant brightening in the 1990s (+2.43 %decade⁻¹) due to large reductions in aerosol optical depth (AOD) and cloud optical thickness (COT). The 2000s saw a weaker global brightening (+0.74 %decade⁻¹) as increases in aerosols and low/high cloud amounts were partially offset by reductions in COT and mid-level cloud amount. Finally, the 2010s experienced another period of brightening (+0.83 %decade⁻¹), driven by reductions in both clouds and aerosols, particularly over land. In the following step of the investigation of the GDB causes, the contribution of the GDB drivers to the overall GDB were computed. Over the entire time period (e.g. 1984-2018), there have been large declines in high-level COT and mid-level CA across the planet in line with the general (global) increase in SSR. On the contrary, there were large increases in the COT of middle and low clouds as well as of low-level cloud amount over the SH and the oceans. The AOD decreased except over land areas of the SH. According to our analysis, the major drivers of the overall GDB (brightening) have been changes (decreases) in mid-level CA and high-level COT, while the contribution of the AOD changes (decreases) was remarkable over specific land areas with intense anthropogenic pollution, such as Europe, India and East China. The contribution of other aerosol optical properties, i.e. SSA, AP, as well as of water vapor and ozone was insignificant. During the 1980s (1984-1989), AOD generally decreased, whereas COT3 increased above in general and high-level CA increased also everywhere except over land of the SH. The existence of positive and negative trends of the GDB drivers resulted either in a weak dimming, as in the NH and over land, or in a weak brightening, as in the SH. AOD changes had the largest contribution to GDB during this decade either globally or over 11 out of 18 land selected areas of the globe, being followed by changes in high-level CA. Throughout the 1990s, large reductions in AOD, COT, and partially in CA, explain the general observed increase in SSR during this decade. More specifically, AOD changes are found to have been the strongest contributor to GDB during this decade in general, as well as over 11/18 land areas, followed by changes in high-level CA. Notably, water vapor, in spite of its generally weak role for GDB, showed some significant contribution over Australia and Mexico in this decade. Across the 2000s, AOD, and cloud amount of low- and high-level clouds increased, while COT and mid-level CA largely decreased. The coincidence of these trends led to an overall weak brightening. Especially, the changes of high-level COT, followed by those of AOD, had the strongest contribution to GDB in the 2000s either globally or over 7/18 land areas. Besides, SSA changes had significant contribution to GDB over East China in the 2000s. In the 2010s, there were large reductions in both clouds and aerosols, being stronger over land areas. On the contrary, there was an increase in COT of low clouds, and cloud amount of mid- and high-level clouds over the oceans. The general reduction in GDB drivers led to a general brightening, except over the oceans of SH where dimming prevailed. Changes in both AOD and clouds contributed strongly to GDB, with AOD being the most common contributor (over 8/18 land areas) followed by high-level CA. Moreover, in this decade water vapor significantly contributed over Mexico. The noticeable contribution of water vapor in the 1990s and 2010s against its insignificant role during the entire 35-year study period shows that one must be careful assessing the strength of the contribution of a physical parameter to climatic phenomena, like GDB, in terms of the chosen time period, since counterbalancing effects may exist during shorter periods. In final part of this PhD, the role of solar dimming and brightening in relation to the recent global warming was examined. According to our findings, the estimated GDB phases are in line with the decadal variations of Tmean as well as Tmax, Tmin, and DTR over certain land areas of the globe with significant anthropogenic pollution, such as Europe and East Asia, as well as over global land. The interdecadal phases of GDB seem to complementarily modify and differentiate the rates of warming primarily caused by the monotonically increasing concentration of greenhouse gases. More specifically, since the mid-1980s, when solar brightening took place, the global land mean temperature response, originally driven by the evolving anthropogenic greenhouse effect, was a rapid warming, which was decelerated or even stopped in the 2000s when solar dimming occurred over areas with intense anthropogenic pollution such as Europe, India and East Asia and partly masked the anthropogenic greenhouse global warming. Then, during the transition from dimming to a renewed brightening in the 2010s, the greenhouse warming was no longer masked and the warming rates increased again. This relationship between GDB, namely the rates of change of SSR, and the Earth’s surface temperature during the 35-year period 1984-2018 is in line with the conclusions drawn by other researchers for the decades from 1950-2000. Moreover, it is found that the inter-annual SSR variation also plays a role in the year-to-year changes of the Earth’s surface temperature, although of course these are also driven by other factors, e.g. anthropogenic greenhouse gases warming, volcanic eruptions or ENSO. The GDB was found to largely drive and to be more strongly related to Tmax and secondarily to the mean surface-air temperature and the daily temperature range. The derived conclusions are more valid over the global land than ocean areas and apply to a considerable degree on the global scale. Also, in many regions where strong brightening occurred, Tmax increased more than Tmin (which increased primarily due to greenhouse warming), leading to an increase of DTR, confirming that GDB plays an important role in the Tmax and DTR changes. However, the rates of brightening before and after the 2000s’ dimming are not associated with proportional surface warming rates, confirming the complexity of the links between SSR and surface temperature changes as well as the importance of the anthropogenic greenhouse effect as main factor of the ongoing global warming. | en |
| heal.advisorName | Χατζηαναστασίου, Νικόλαος | el |
| heal.committeeMemberName | Χατζηαναστασίου, Νικόλαος | en |
| heal.committeeMemberName | Wild, Martin | en |
| heal.committeeMemberName | Ματσούκας, Χρήστος | el |
| heal.committeeMemberName | Καζαντζίδης, Ανδρέας | el |
| heal.committeeMemberName | Λώλης, Χρήστος | el |
| heal.committeeMemberName | Μπάκας, Νικόλαος | el |
| heal.committeeMemberName | Φωτιάδη, Αγγελική | el |
| heal.academicPublisher | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Φυσικής | el |
| heal.academicPublisherID | uoi | el |
| heal.numberOfPages | 279 | el |
| heal.fullTextAvailability | true | - |
| heal.fullTextAvailability | true | - |
| heal.fullTextAvailability | true | - |
| Appears in Collections: | Διδακτορικές Διατριβές - ΦΥΣ | |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| ΣΤΑΜΑΤΗΣ_ΜΙΧΑΗΛ_2025.pdf | 38.3 MB | Adobe PDF | View/Open |
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