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

The unprecedented 2017-2018 stratospheric smoke event : Decay phase and aerosol properties observed with the EARLINET

© Author(s) 2019. This open access work is distributed under the Creative Commons Attribution 4.0 License (https://creativecommons.org/licenses/by/4.0/).Six months of stratospheric aerosol observations with the European Aerosol Research Lidar Network (EARLINET) from August 2017 to January 2018 are presented. The decay phase of an unprecedented, record-breaking stratospheric perturbation caused by wildfire smoke is reported and discussed in terms of geometrical, optical, and microphysical aerosol properties. Enormous amounts of smoke were injected into the upper troposphere and lower stratosphere over fire areas in western Canada on 12 August 2017 during strong thunderstorm-pyrocumulonimbus activity. The stratospheric fire plumes spread over the entire Northern Hemisphere in the following weeks and months. Twenty-eight European lidar stations from northern Norway to southern Portugal and the eastern Mediterranean monitored the strong stratospheric perturbation on a continental scale. The main smoke layer (over central, western, southern, and eastern Europe) was found at heights between 15 and 20 km since September 2017 (about 2 weeks after entering the stratosphere). Thin layers of smoke were detected at heights of up to 22-23 km. The stratospheric aerosol optical thickness at 532 nm decreased from values > 0.25 on 21-23 August 2017 to 0.005-0.03 until 5-10 September and was mainly 0.003-0.004 from October to December 2017 and thus was still significantly above the stratospheric background (0.001-0.002). Stratospheric particle extinction coefficients (532 nm) were as high as 50-200 Mm-1 until the beginning of September and on the order of 1 Mm-1 (0.5- 5 Mm-1) from October 2017 until the end of January 2018. The corresponding layer mean particle mass concentration was on the order of 0.05-0.5 μg m-3 over these months. Soot particles (light-absorbing carbonaceous particles) are efficient ice-nucleating particles (INPs) at upper tropospheric (cirrus) temperatures and available to influence cirrus formation when entering the tropopause from above. We estimated INP concentrations of 50-500 L-1 until the first days in September and afterwards 5-50 L-1 until the end of the year 2017 in the lower stratosphere for typical cirrus formation temperatures of -55 ?C and an ice supersaturation level of 1.15. The measured profiles of the particle linear depolarization ratio indicated a predominance of nonspherical smoke particles. The 532 nm depolarization ratio decreased slowly with time in the main smoke layer from values of 0.15-0.25 (August-September) to values of 0.05-0.10 (October-November) and < 0.05 (December-January). The decrease of the depolarization ratio is consistent with aging of the smoke particles, growing of a coating around the solid black carbon core (aggregates), and thus change of the shape towards a spherical form. We found ascending aerosol layer features over the most southern European stations, especially over the eastern Mediterranean at 32-35? N, that ascended from heights of about 18-19 to 22-23 km from the beginning of October to the beginning of December 2017 (about 2 km per month). We discuss several transport and lifting mechanisms that may have had an impact on the found aerosol layering structures.Peer reviewe

The unprecedented 2017–2018 stratospheric smoke event: decay phase and aerosol properties observed with the EARLINET

Six months of stratospheric aerosol observations with the European Aerosol Research Lidar Network (EARLINET) from August 2017 to January 2018 are presented. The decay phase of an unprecedented, record-breaking stratospheric perturbation caused by wildfire smoke is reported and discussed in terms of geometrical, optical, and microphysical aerosol properties. Enormous amounts of smoke were injected into the upper troposphere and lower stratosphere over fire areas in western Canada on 12 August 2017 during strong thunderstorm–pyrocumulonimbus activity. The stratospheric fire plumes spread over the entire Northern Hemisphere in the following weeks and months. Twenty-eight European lidar stations from northern Norway to southern Portugal and the eastern Mediterranean monitored the strong stratospheric perturbation on a continental scale. The main smoke layer (over central, western, southern, and eastern Europe) was found at heights between 15 and 20 km since September 2017 (about 2 weeks after entering the stratosphere). Thin layers of smoke were detected at heights of up to 22–23 km. The stratospheric aerosol optical thickness at 532 nm decreased from values > 0.25 on 21–23 August 2017 to 0.005–0.03 until 5–10 September and was mainly 0.003–0.004 from October to December 2017 and thus was still significantly above the stratospheric background (0.001–0.002). Stratospheric particle extinction coefficients (532 nm) were as high as 50–200 Mm−1 until the beginning of September and on the order of 1 Mm−1 (0.5–5 Mm−1) from October 2017 until the end of January 2018. The corresponding layer mean particle mass concentration was on the order of 0.05–0.5 µg m−3 over these months. Soot particles (light-absorbing carbonaceous particles) are efficient ice-nucleating particles (INPs) at upper tropospheric (cirrus) temperatures and available to influence cirrus formation when entering the tropopause from above. We estimated INP concentrations of 50–500 L−1 until the first days in September and afterwards 5–50 L−1 until the end of the year 2017 in the lower stratosphere for typical cirrus formation temperatures of −55 ∘C and an ice supersaturation level of 1.15. The measured profiles of the particle linear depolarization ratio indicated a predominance of nonspherical smoke particles. The 532 nm depolarization ratio decreased slowly with time in the main smoke layer from values of 0.15–0.25 (August–September) to values of 0.05–0.10 (October–November) and < 0.05 (December–January). The decrease of the depolarization ratio is consistent with aging of the smoke particles, growing of a coating around the solid black carbon core (aggregates), and thus change of the shape towards a spherical form. We found ascending aerosol layer features over the most southern European stations, especially over the eastern Mediterranean at 32–35∘ N, that ascended from heights of about 18–19 to 22–23 km from the beginning of October to the beginning of December 2017 (about 2 km per month). We discuss several transport and lifting mechanisms that may have had an impact on the found aerosol layering structures

Tropospheric and stratospheric smoke over Europe as observed within EARLINET/ACTRIS in summer 2017

For several weeks in summer 2017, strong smoke layers were observed over Europe at numerous EARLINET stations. EARLINET is the European research lidar network and part of ACTRIS and comprises more than 30 ground-based lidars. The smoke layers were observed in the troposphere as well as in the stratosphere up to 25 km from Northern Scandinavia over whole western and central Europe to the Mediterranean regions. Backward trajectory analysis among other tools revealed that these smoke layers originated from strong wild fires in western Canada in combination with pyrocumulus convection. An extraordinary fire event in the mid of August caused intense smoke layers that were observed across Europe for several weeks starting on 18 August 2017. Maximum aerosol optical depths up to 1.0 at 532 nm were observed at Leipzig, Germany, on 22 August 2017 during the peak of this event. The stratospheric smoke layers reached extinction coefficient values of more than 600 Mm−1 at 532 nm, a factor of 10 higher than observed for volcanic ash after the Pinatubo eruption in the 1990s. First analyses of the intensive optical properties revealed low particle depolarization values at 532 nm for the tropospheric smoke (spherical particles) and rather high values (up to 20%) in the stratosphere. However, a strong wavelength dependence of the depolarization ratio was measured for the stratospheric smoke. This indicates irregularly shaped stratospheric smoke particles in the size range of the accumulation mode. This unique depolarization feature makes it possible to distinguish clearly smoke aerosol from cirrus clouds or other aerosol types by polarization lidar measurements. Particle extinction-to-backscatter ratios were rather low in the order of 40 to 50 sr at 355 nm, while values between 70-90 sr were measured at higher wavelengths. In the western and central Mediterranean, stratospheric smoke layers were most prominent in the end of August at heights between 16 and 20 km. In contrast, stratospheric smoke started to occur in the eastern Mediterranean (Cyprus and Israel) in the beginning of September between 18 and 23 km. Stratospheric smoke was still visible in the beginning of October at certain locations (e.g. Evora, Portugal), while tropospheric smoke was mainly observed until the end of August within Europe. An overview of the smoke layers measured at several EARLINET sites will be given. The temporal development of these layers as well as their geometrical and optical properties will be presented

Characterization and longitudinal study of aerosol particles using a synergy of lidar techniques and passive remote sensing methods in the Mediterranean basin

The aim of this Doctoral Thesis is the study of the tropospheric aerosols by means ground based remote sensing and space-borne techniques, through statistical analysis of the retrieved aerosol optical properties. At the same time, advanced mathematical algorithms are applied to retrieve the aerosol microphysical properties while predictive models are used to obtain additional information, such as the source regions of the transported aerosols and their radiative forcing effect. In the opening chapter, Chapter 1, a theoretical background on atmospheric aerosols, their role in atmospheric physics and the different types of aerosols are presented, giving an overall view of the studied field. There is a variety of aerosol sources and particle sizes and therefore, aerosols can be found at different heights in the atmosphere. All atmospheric aerosols scatter incoming solar radiation, while a few ones can also absorb it. In the atmosphere, there is a mixture of both scattering and absorbing aerosols, and their net effect on Earth's energy budget depends on surface and cloud characteristics. All these aspects are shortly presented in this Chapter. In Chapter 2, except the vertical atmospheric structure, the fundamental aspects of atmospheric physic and optics are mentioned, focusing on the mechanisms of the atmospheric substances (aerosols and molecules) and their interactions with light. Absorption, transition, scattering, extinction, depolarization and fluorescence of light are the basic phenomena discussed here as a brief outline of the fundamental laws governing the transmission of light in the atmosphere centred around the Beer-Lambert law. The aerosol remote sensing techniques are included in Chapter 3, along with the available instrumentation used to obtain our results. Firstly, the lidar technique is schematically analysed and a full description of the lidar equation is presented. The relevant detection modes of the lidar signals and the different types of lidar instruments are presented as well as the instrumentation that is available at the Laser remote sensing unit of NTUA. Additionally, the lidar pre-processing methods along with aerosol data products are mentioned. Finally, a brief description of the Aerosol Robotic Network (AERONET) of sun photometer measurements is presented. Tools and modelling that exploit lidar satellite measurements which were used to enhance our findings are introduced and shortly presented in Chapter 4. The EARLINET Single Calculus Chain (SCC) is the tool used for retrieving the aerosol optical properties and the Spheroidal Inversion eXperiments (SphInX) software tool, developed at the University of Potsdam, provided the microphysical retrievals from lidar data inputs. Useful information about the HYSPLIT model which simulates the backward trajectory analysis, the Dust Regional Atmospheric Model (BSC-DREAM8b v2.0), the Library for radiative transfer (Libradtran) tool and satellite data is also provided. Our results and a comprehensive analysis are presented in Chapter 5. Firstly, we present a comprehensive analysis of the seasonal variability of the vertical profiles of the optical and geometrical properties of Saharan dust aerosols, observed in the height region between 1000 and 6000 m, over Athens, Greece, from February 2000 to September 2017. These nighttime observations were performed by the EOLE Raman lidar system under cloud-free conditions. Moreover, 4 years of lidar measurements of Saharan dust intrusions over the Mediterranean basin (2014-2017), obtained from 4 selected EARLINET stations (Granada, Potenza, Athens, Limassol) are studied in terms of aerosol optical, geometrical, mixing state and microphysical properties. Specific case studies are further analysed. Finally, simulations of the regional radiative forcing of dust events over Mediterranean are presented. The concluding remarks are given in Chapter 6, which is the final chapter of this Thesis

Χαρακτηρισμός και διαχρονική μελέτη των αιωρούμενων σωματιδίων με συνέργεια τεχνικών Lidar και παθητικής τηλεπισκόπησης σε επιλεγμένες περιοχές της Μεσογείου

The aim of this Doctoral Thesis is the study of the tropospheric aerosols by means ground based remote sensing and space-borne techniques, through statistical analysis of the retrieved aerosol optical properties. At the same time, advanced mathematical algorithms are applied to retrieve the aerosol microphysical properties while predictive models are used to obtain additional information, such as the source regions of the transported aerosols and their radiative forcing effect. In the opening chapter, Chapter 1, a theoretical background on atmospheric aerosols, their role in atmospheric physics and the different types of aerosols are presented, giving an overall view of the studied field. There is a variety of aerosol sources and particle sizes and therefore, aerosols can be found at different heights in the atmosphere. All atmospheric aerosols scatter incoming solar radiation, while a few ones can also absorb it. In the atmosphere, there is a mixture of both scattering and absorbing aerosols, and their net effect on Earth's energy budget depends on surface and cloud characteristics. All these aspects are shortly presented in this Chapter. In Chapter 2, except the vertical atmospheric structure, the fundamental aspects of atmospheric physic and optics are mentioned, focusing on the mechanisms of the atmospheric substances (aerosols and molecules) and their interactions with light. Absorption, transition, scattering, extinction, depolarization and fluorescence of light are the basic phenomena discussed here as a brief outline of the fundamental laws governing the transmission of light in the atmosphere centred around the Beer-Lambert law. The aerosol remote sensing techniques are included in Chapter 3, along with the available instrumentation used to obtain our results. Firstly, the lidar technique is schematically analysed and a full description of the lidar equation is presented. The relevant detection modes of the lidar signals and the different types of lidar instruments are presented as well as the instrumentation that is available at the Laser remote sensing unit of NTUA. Additionally, the lidar pre-processing methods along with aerosol data products are mentioned. Finally, a brief description of the Aerosol Robotic Network (AERONET) of sun photometer measurements is presented. Tools and modelling that exploit lidar satellite measurements which were used to enhance our findings are introduced and shortly presented in Chapter 4. The EARLINET Single Calculus Chain (SCC) is the tool used for retrieving the aerosol optical properties and the Spheroidal Inversion eXperiments (SphInX) software tool, developed at the University of Potsdam, provided the microphysical retrievals from lidar data inputs. Useful information about the HYSPLIT model which simulates the backward trajectory analysis, the Dust Regional Atmospheric Model (BSC-DREAM8b v2.0), the Library for radiative transfer (Libradtran) tool and satellite data is also provided. Our results and a comprehensive analysis are presented in Chapter 5. Firstly, we present a comprehensive analysis of the seasonal variability of the vertical profiles of the optical and geometrical properties of Saharan dust aerosols, observed in the height region between 1000 and 6000 m, over Athens, Greece, from February 2000 to September 2017. These nighttime observations were performed by the EOLE Raman lidar system under cloud-free conditions. Moreover, 4 years of lidar measurements of Saharan dust intrusions over the Mediterranean basin (2014-2017), obtained from 4 selected EARLINET stations (Granada, Potenza, Athens, Limassol) are studied in terms of aerosol optical, geometrical, mixing state and microphysical properties. Specific case studies are further analysed. Finally, simulations of the regional radiative forcing of dust events over Mediterranean are presented. The concluding remarks are given in Chapter 6, which is the final chapter of this Thesis.H παρούσα Διδακτορική Διατριβή έχει ως αντικείμενο τη μελέτη των τροποσφαιρικών αερολυμάτων με τη χρήση επίγειων και δορυφορικών τεχνικών, για την ανάκτηση των οπτικών ιδιοτήτων των αιωρούμενων σωματιδίων και την στατιστική ανάλυσή τους. Παράλληλα, εφαρμόζονται μαθηματικοί αλγόριθμοι για την ανάκτηση των μικροφυσικών τους ιδιοτήτων, καθώς και γίνεται χρήση προγνωστικών μοντέλων για ανάκτηση επιπλέον πληροφοριών, όπως ο προσδιορισμός της πηγής προέλευσης των αιωρούμενων σωματιδίων, αλλά και η επίδρασή τους στο ατμοσφαιρικό ενεργειακό ισοζύγιο. Στο πρώτο κεφάλαιο (Κεφάλαιο 1) περιλαμβάνεται το θεωρητικό υπόβαθρο των ατμοσφαιρικών αερολυμάτων, ο ρόλος τους στην ατμοσφαιρική Φυσική, καθώς και οι διάφοροι τύποι αερολυμάτων, δίνοντας τη συνολική εικόνα του πεδίου μελέτης. Στο Κεφάλαιο 2 αναφέρονται οι θεμελιώδεις πτυχές της ατμοσφαιρικής Φυσικής και της Οπτικής, με έμφαση στους μηχανισμούς αλληλεπίδρασης του φωτός με τα ατμοσφαιρικά στοιχεία (αερολύματα και μόρια). Οι τεχνικές τηλεπισκόπησης αερολυμάτων που έχουν χρησιμοποιηθεί ευρέως σε αυτή τη διατριβή παρουσιάζονται στο Κεφάλαιο 3, μαζί με λοιπά διαθέσιμα όργανα που χρησιμοποιήθηκαν για τη λήψη δεδομένων των προς εξαγωγή αποτελεσμάτων. Συγκεκριμένα παρουσιάζεται η τεχνική light detection and ranging (lidar), καθώς και τα διάφορα στάδια επεξεργασίας των σημάτων lidar. Τα ατμοσφαιρικά προγνωστικά μοντέλα αλλά και εργαλεία που αξιοποιούν δορυφορικές μετρήσεις και χρησιμοποιήθηκαν για την ενίσχυση των αποτελεσμάτων μας παρουσιάζονται εν συντομία στο Κεφάλαιο 4. Η περιεκτική ανάλυση των αποτελεσμάτων παρουσιάζεται στο Κεφάλαιο 5, ενώ τα συμπεράσματα παρατίθενται στο Κεφάλαιο 6, που αποτελεί το τελευταίο κεφάλαιο αυτής της Διατριβής

Seventeen-year systematic measurements of dust aerosol optical properties using the eole ntua lidar system (2000-2016)

A comprehensive analysis of the seasonal variability of the optical properties of Saharan dust aerosols over Athens, Greece, is presented for a 17-year time period (2000-2016), as derived from multi-wavelength Raman lidar measurements (57 dust events with more than 80 hours of measurements). The profiles of the derived aerosol optical properties (aerosol backscatter and extinction coefficients, lidar ratio and aerosol Ångström exponent) at 355 nm are presented. For these dust events we found a mean value of the lidar ratio of ~52±13 sr at 355 nm and of ~58±8 sr (not shown) at 532 nm (2-4 km a.s.l. height). For our statistical analysis, presented here, we used monthly-mean values and time periods under cloud-free conditions. The number of dust events was greatest in late spring, summer, and early autumn periods. In this paper we also present a selected case study (04 April 2016) of desert dust long-range transport from the Saharan desert

Seventeen-year systematic measurements of dust aerosol optical properties using the eole ntua lidar system (2000-2016)

A comprehensive analysis of the seasonal variability of the optical properties of Saharan dust aerosols over Athens, Greece, is presented for a 17-year time period (2000-2016), as derived from multi-wavelength Raman lidar measurements (57 dust events with more than 80 hours of measurements). The profiles of the derived aerosol optical properties (aerosol backscatter and extinction coefficients, lidar ratio and aerosol Ångström exponent) at 355 nm are presented. For these dust events we found a mean value of the lidar ratio of ~52±13 sr at 355 nm and of ~58±8 sr (not shown) at 532 nm (2-4 km a.s.l. height). For our statistical analysis, presented here, we used monthly-mean values and time periods under cloud-free conditions. The number of dust events was greatest in late spring, summer, and early autumn periods. In this paper we also present a selected case study (04 April 2016) of desert dust long-range transport from the Saharan desert

Aerosol optical properties variability during biomass burning events observed by the eole-aias depolarization lidars over Athens, Greece (2007-2016)

The EOLE multi-wavelength aerosol Ramandepolarization lidar, and the AIAS depolarization lidar, in synergy with a sun photometer (CIMEL), were used, in the period 2007-2016, to provide the vertical profiles of the aerosol optical properties over Athens, Greece. More than 30 biomass burning events (fresh and aged smoke particles) were observed, with smoke layers between 1.5 up to 4-5 km height, while their duration ranged from 1-3 days. Lidar ratio (LR) values ranged from 40-105 sr (at 355 nm) and from 40-100 sr (at 532 nm), while the linear particle depolarization ratio (LPDR) at both 355 and 532 nm, remained <7%. The extinction-related Ångström exponent (AEa) at 355 nm/532 nm) ranged from 0.3 to 2.1. Additionally, a case of a near-range transport of biomass burning aerosols arriving over Athens up to 4 km height, between 27 and 28 June 2016, was studied. For this case, we found LRs of the order of 70±5 sr (355 nm) and 65±15 sr (532 nm) and AEa(355 nm/532 nm) around 1