Application and testing of the extended-Kalman-filtering technique for determining the planetary boundary-layer height over Athens, Greece

The final publication is available at Springer via http://dx.doi.org/10.1007/s10546-020-00514-zWe investigate the temporal evolution of the planetary boundary-layer (PBL) height over the basin of Athens, Greece, during a 6-year period (2011–2016), using data from a Raman lidar system. The range-corrected lidar signals are selected around local noon (1200 UTC) and midnight (0000 UTC), for a total of 332 cases: 165 days and 167 nights. In this dataset, the extended-Kalman filtering technique is applied and tested for the determination of the PBL height. Several well-established techniques for the PBL height estimation based on lidar data are also tested for a total of 35 cases. The lidar-derived PBL heights are compared to those derived from radiosonde data. The mean PBL height over Athens is found to be 1617¿±¿324 m at 1200 UTC and 892¿±¿130 m at 0000 UTC for the period examined, while the mean PBL-height growth rate is found to be 170¿±¿64 m h-1 and 90¿±¿17 m h-1 during daytime and night-time, respectively.The research leading to these results has received additional funding from the European Union 7th Framework Program (FP7/2011-2015) and Horizon 2020/2015-2021 Research and Innovation program (ACTRIS) under grant agreements nos 262254, 654109, and 739530, as well as from Spanish National Science Foundation and FEDER funds PGC2018-094132-B-I00. CommSensLab-UPC is a María-de-Maeztu Excellence Unit, MDM-2016-0600, funded by the Agencia Estatal de Investigación, Spain.Peer ReviewedPostprint (author's final draft

Planetary boundary layer height variability over Athens, Greece, based on the synergy of Raman lidar and radiosonde data: application of the Kalman filter and other techniques (2011-2016)

The temporal evolution of the Planetary Boundary Layer height over Athens, Greece for a 5-year period (2011-2016) is presented. Using the EOLE Raman lidar system, the range-corrected lidar signals were selected around 12:00 UTC and 00:00 UTC for a total of 332 cases (165 days and 167 nights). The Kalman filter and other techniques were used to determine PBL height. The mean PBL height was found to be around 1617±324 m (12:00 UTC) and 892±130 m (00:00 UTC).Peer ReviewedPostprint (published version

Board gender diversity and stock price crash risk: Going beyond tokenism

Abstract We empirically examine the role of board gender diversity in influencing stock price crash risk at the firm-level in twelve (12) Asia-Pacific Markets. Using a dataset comprising data from 1021 listed firms over the period 2006–2016, we employ a random effect model in a regression setting. Controlling for the firm and market-level variables, we find that board gender diversity results in lowering the stock price crash risk of the firm. Bifurcating women directors on corporate board into numerical representation (token and critical mass representation), the results support our main conjectures and suggest that the economic significance of this relationship is higher for firms that have three or more women directors on the board as compared to the firms that have less than three women directors on the corporate board. Our results are robust to alternative measures of stock price crash risk, potential endogeneity and selection biases

Aerosol absorption profiling from the synergy of lidar and sun-photometry : The ACTRIS-2 campaigns in Germany, Greece and Cyprus

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).Aerosol absorption profiling is crucial for radiative transfer calculations and climate modelling. Here, we utilize the synergy of lidar with sun-photometer measurements to derive the absorption coefficient and single scattering albedo profiles during the ACTRIS-2 campaigns held in Germany, Greece and Cyprus. The remote sensing techniques are compared with in situ measurements in order to harmonize and validate the different methodologies and reduce the absorption profiling uncertainties.Peer reviewe

Vertical profiles of aerosol mass concentration derived by unmanned airborne in situ and remote sensing instruments during dust events

In situ measurements using unmanned aerial vehicles (UAVs) and remote sensing observations can independently provide dense vertically resolved measurements of atmospheric aerosols, information which is strongly required in climate models. In both cases, inverting the recorded signals to useful information requires assumptions and constraints, and this can make the comparison of the results difficult. Here we compare, for the first time, vertical profiles of the aerosol mass concentration derived from light detection and ranging (lidar) observations and in situ measurements using an optical particle counter on board a UAV during moderate and weak Saharan dust episodes. Agreement between the two measurement methods was within experimental uncertainty for the coarse mode (i.e. particles having radii  > 0.5µm), where the properties of dust particles can be assumed with good accuracy. This result proves that the two techniques can be used interchangeably for determining the vertical profiles of aerosol concentrations, bringing them a step closer towards their systematic exploitation in climate models

Chronic p53-independent p21 expression causes genomic instability by deregulating replication licensing

The cyclin-dependent kinase inhibitor p21WAF1/CIP1 (p21) is a cell-cycle checkpoint effector and inducer of senescence, regulated by p53. Yet, evidence suggests that p21 could also be oncogenic, through a mechanism that has so far remained obscure. We report that a subset of atypical cancerous cells strongly expressing p21 showed proliferation features. This occurred predominantly in p53-mutant human cancers, suggesting p53-independent upregulation of p21 selectively in more aggressive tumour cells. Multifaceted phenotypic and genomic analyses of p21-inducible, p53-null, cancerous and near-normal cellular models showed that after an initial senescence-like phase, a subpopulation of p21-expressing proliferating cells emerged, featuring increased genomic instability, aggressiveness and chemoresistance. Mechanistically, sustained p21 accumulation inhibited mainly the CRL4–CDT2 ubiquitin ligase, leading to deregulated origin licensing and replication stress. Collectively, our data reveal the tumour-promoting ability of p21 through deregulation of DNA replication licensing machinery—an unorthodox role to be considered in cancer treatment, since p21 responds to various stimuli including some chemotherapy drugs

Study of tropospheric aerosols using ground-based and spaceborne techniques: data processing and statistical analysis

The main objective of this thesis is the study of tropospheric aerosols with ground-based andspace-borne techniques, through statistical analysis of the retrieved aerosol optical properties.In the first chapter, we present the state of the art literature, concerning the sources and theoptical-microphysical properties of tropospheric aerosols, as well as their impact on the Earth'sclimate and human health. The second chapter deals with a general overview of the existinglidar [light detection and ranging] techniques, as well as the basic formulation governing thelidar systems implemented in this thesis [lidar backscatter, Raman lidar and lidardepolarization]. In the third chapter, we present the enhanced optical design [based onupgraded algorithms for Raman lidar system optimization and optical simulations with thededicated software Zemax©], of the optimized the Raman lidar NTUA’s system [EOLE]. Thegoal of this design, was the minimization of the distance of complete overlap, at ranges below1000 m a.s.l.. In addition, the newly acquired depolarization lidar [AIAS], is extensivelypresented. The fourth chapter focuses mainly on the depolarization lidar and is divided into 3parts. In the first part the sensitivity analysis of existing calibration techniques fordepolarization lidar systems, either with simulations and with real signals is presented. For theretrieval of the particle depolarization ratio, a dedicated algorithm was developed for theprocessing of the depolarization lidar signals [GUI-Matlab©]. Based on this algorithm, thesecond and the third part present the statistical analysis of the systems calibration constant andthe aerosol depolarization ratio, as those calculated from 2-year measurements with the AIASsystem [2011-2012], respectively.The fifth chapter presents the optical and microphysical properties of different aerosols[volcanic dust and desert dust], over Athens. For these episodes, a dedicated inversionalgorithm was applied [LIRIC], to retrieve the concentration of particles, giving more optionsto lidar systems to be used in calibration studies of numerical simulations of atmosphericmodels [FLEXPART, BSC/DREAM -8b]. Finally, the sixth chapter is focused on groundbased and space borne passive remote sensing techniques. In particular, we present 3-yearclimatology [2006-2008], of the aerosol optical depth, as retrieved by the ground based sunphotometer MFR, in Athens. Furthermore, we also present the percentage of transboundarypollution that contributes to the mean AOD value in Athens. Finally, we present a comparison,of approximately 740 time- coincident cases, of aerosol optical properties, as retrieved bysatellite sensor MODIS and a ground based sunphotometer, based on the passive remotesensing techniques.Αντικείμενο της παρούσας διδακτορικής διατριβής είναι η μελέτη των τροποσφαιρικώναερολυμάτων με επίγειες και δορυφορικές τεχνικές, μέσω ανάλυσης των μετρήσεων για τηνανάκτηση των οπτικών ιδιοτήτων και την στατιστική επεξεργασία τους. Στο πρώτο κεφάλαιοπαρουσιάζουμε την υπάρχουσα διεθνή βιβλιογραφία, σχετικά με τις πηγές-προέλευση και τιςοπτικές και μικροφυσικές ιδιότητες των τροποσφαιρικών αερολυμάτων, την επίδρασή τουςστο γήινο κλίμα και στην ανθρώπινη υγεία. Το δεύτερο κεφάλαιο αναφέρεται σε μιαγενικότερη επισκόπηση της τεχνικής lidar [light detection and ranging], καθώς επίσης και στιςβασικές εξισώσεις που διέπουν τα συστήματα lidar με τα οποία ασχοληθήκαμε στην παρούσαδιατριβή [lidar οπισθοσκέδασης, Raman lidar και lidar αποπόλωσης]. Στο τρίτο κεφάλαιο,παρουσιάζεται ο αναβαθμισμένος οπτικός σχεδιασμός [μέσω αναβαθμισμένων αλγορίθμωνελέγχου-βελτιστοποίησης συστημάτων Raman-lidar και οπτικών προσομοιώσεων με τολογισμικό οπτομηχανικού σχεδιασμού Zemax©], για τη βελτιστοποίηση του συστήματοςRaman-lidar του ΕΜΠ [EOLE]. Στόχος της σχεδίασης αυτής ήταν η ελαχιστοποίηση τηςαπόστασης πλήρους επικάλυψης του συστήματος σε αποστάσεις κάτω από τα 1000 m a.s.l.Επίσης παρουσιάζεται εκτενώς το νεοαποκτηθέν σύστημα lidar αποπόλωσης [AIAS] τουΤομέα Φυσικής. Το τέταρτο κεφάλαιο, επικεντρώνεται κυρίως στο lidar αποπόλωσης καιχωρίζεται σε 3 βασικά μέρη. Στο πρώτο, πραγματοποιείται η ανάλυση ευαισθησίας τωνυπαρχουσών τεχνικών βαθμονόμησης των συστημάτων lidar αποπόλωσης, με προσομοιώσεις,αλλά και με πειραματικά σήματα. Για την ανάκτηση του λόγου αποπόλωσης των σωματιδίων,αναπτύχθηκε ειδικός αλγόριθμος επεξεργασίας των σημάτων αποπόλωσης [γραφικόπεριβάλλον Matlab©] και με βάση αυτόν τον αλγόριθμο, στο δεύτερο και τρίτο μέροςπαρουσιάζεται η στατιστική επεξεργασία της σταθεράς βαθμονόμησης και του λόγουαποπόλωσης των σωματιδίων, όπως υπολογίσθηκαν από τα δύο χρόνια μετρήσεων τουσυστήματος AIAS [2011-2012], αντίστοιχα.Επιπλέον, στο πέμπτο κεφάλαιο, παρουσιάζονται οι οπτικές και μικροφυσικές ιδιότητες σωματιδίων ηφαιστειακής τέφρας και σωματιδίων ερημικής σκόνης στην ατμόσφαιρα πάνωαπό την Αθήνα. Για τα επεισόδια αυτά, εφαρμόσθηκε ειδικός αλγόριθμος [LIRIC]αντιστροφής σημάτων lidar για την ανάκτηση και της συγκέντρωσης των σωματιδίων,δίνοντας πλέον τη δυνατότητα στα συστήματα lidar να χρησιμοποιούνται σε μελέτεςδιακρίβωσης αριθμητικών προσομοιώσεων ατμοσφαιρικών μοντέλων [FLEXPART,BSC/DREAM8b]. Τέλος, το έκτο κεφάλαιο επικεντρώνεται σε επίγειες και δορυφορικέςτεχνικές παθητικής τηλεπισκόπησης. Πιο συγκεκριμένα παρουσιάζεται η στατιστική ανάλυσηδεδομένων τριών ετών [2006-2008], του οπτικού πάχους των αιωρούμενων σωματιδίων, όπωςυπολογίσθηκε από το ηλιακό φωτόμετρο MFR, στην περιοχή της Αθήνας. Παρουσιάζεταιεπίσης, η συνεισφορά των διαφόρων πηγών σωματιδιακής ρύπανσης [ανά γεωγραφικήπεριοχή της Ευρώπης], στη μέση τιμή του οπτικού πάχους των σωματιδίων. Επίσης,πραγματοποιείται και μια σύγκριση 740 περίπου σύγχρονων χρονικά μετρήσεων τωνπροαναφερόμενων επίγειων δεδομένων με τα αντίστοιχα δορυφορικά δεδομένα παθητικήςτηλεπισκόπησης, όπως ανακτήθηκαν από τον δορυφορικό αισθητήρα MODIS. Στο έβδομοκεφάλαιο παρουσιάζονται τα βασικά συμπεράσματα της εργασίας αυτής