Peristera Paschou

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024–December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5×10-6-12.7×10-6 nm ⁻¹ ), followed by mixed pollen (2.3×10-6-4.8×10-6 nm ⁻¹ ), polluted continental (1.0×10-6-3.3×10-6 nm ⁻¹ ), clean continental (0.3×10-6-1.2×10-6 nm ⁻¹ ) and dust (0.4×10-6-1.3×10-6 nm ⁻¹ ). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen event showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024 – December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5 × 10⁻⁶ − 12.7 × 10⁻⁶ 𝑛𝑚⁻¹), followed by mixed pollen (2.3 × 10⁻⁶ − 4.8 × 10⁻⁶ 𝑛𝑚⁻¹), polluted continental (1.0 × 10⁻⁶ − 3.3 × 10⁻⁶ 𝑛𝑚⁻¹), clean continental (0.3 × 10⁻⁶ − 1.2 × 10⁻⁶ 𝑛𝑚⁻¹) and dust (0.6 × 10⁻⁶ − 1.3 × 10⁻⁶ 𝑛𝑚⁻¹). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen event showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024 – December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5 × 10⁻⁶ − 12.7 × 10⁻⁶ 𝑛𝑚⁻¹), followed by mixed pollen (2.3 × 10⁻⁶ − 4.8 × 10⁻⁶ 𝑛𝑚⁻¹), polluted continental (1.0 × 10⁻⁶ − 3.3 × 10⁻⁶ 𝑛𝑚⁻¹), clean continental (0.3 × 10⁻⁶ − 1.2 × 10⁻⁶ 𝑛𝑚⁻¹) and dust (0.6 × 10⁻⁶ − 1.3 × 10⁻⁶ 𝑛𝑚⁻¹). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen event showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024 – December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5 × 10⁻⁶ − 12.7 × 10⁻⁶ 𝑛𝑚⁻¹), followed by mixed pollen (2.3 × 10⁻⁶ − 4.8 × 10⁻⁶ 𝑛𝑚⁻¹), polluted continental (1.0 × 10⁻⁶ − 3.3 × 10⁻⁶ 𝑛𝑚⁻¹), clean continental (0.3 × 10⁻⁶ − 1.2 × 10⁻⁶ 𝑛𝑚⁻¹) and dust (0.6 × 10⁻⁶ − 1.3 × 10⁻⁶ 𝑛𝑚⁻¹). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen event showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024 – December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5 × 10⁻⁶ − 12.7 × 10⁻⁶ 𝑛𝑚⁻¹), followed by mixed pollen (2.3 × 10⁻⁶ − 4.8 × 10⁻⁶ 𝑛𝑚⁻¹), polluted continental (1.0 × 10⁻⁶ − 3.3 × 10⁻⁶ 𝑛𝑚⁻¹), clean continental (0.3 × 10⁻⁶ − 1.2 × 10⁻⁶ 𝑛𝑚⁻¹) and dust (0.6 × 10⁻⁶ − 1.3 × 10⁻⁶ 𝑛𝑚⁻¹). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

As part of BOWTIE (German: Beobachtung von Ozean und Wolken - Das Trans ITCZ Experiment), the German research vessel FS Meteor navigated the moist tropics of the Atlantic Ocean for 40 days in summer 2024, with an east-west trajectory. The journey started in the port of Mindelo, Cape Verde, on August 16, and finished in the port of Bridgetown, Barbados, on September 24. The objective was to measure properties of the atmosphere, upper-ocean, and air-sea interface within the Intertropical Convergence Zone (ITCZ), under a variety of wind, convection, and sea surface temperature regimes. Using a set of 29 instruments/platforms, BOWTIE sampled the near-surface conditions of the atmosphere and ocean with high temporal resolution. This included continuous measurements of: the 2-D wind field within the lowest 2 km of the atmosphere, near-surface ocean currents, cloud and precipitation properties. Profiles of the ocean state and atmospheric thermodynamics and kinematics were obtained both continuously and at discrete intervals. Furthermore, dedicated stations sampled biochemical properties of the upper-ocean. Complementing BOWTIE observations, FS Meteor hosted further dedicated field campaigns for 3D cloud and precipitation properties, as well as intensive measurements of the atmospheric boundary layer. This manuscript provides an overview of the extensive instrumentation and data collected during BOWTIE. In addition, it addresses two key aspects based on these observations. First, it examines the range and uncertainties of selected quantities measured by multiple instruments, including column-integrated water vapor, rain detection, surface ocean currents, and sea surface temperature. Second, it illustrates the diversity of sampled weather regimes through two representative cases: calm doldrum conditions and a gusty, precipitating convective state.

In this study, we present the first fluorescence lidar observations over Thessaloniki, Greece, (40.63° N, 22.96° E; 60 m a.s.l.) using a multiwavelength Raman and depolarization lidar with fluorescence capabilities. For the first time in the Eastern Mediterranean fluorescence backscattering coefficient and the spectral fluorescence capacity parameter are retrieved and combined with particle depolarization ratio, lidar ratios, and Ångström exponents to characterize the aerosol load over Thessaloniki, a region influenced by diverse aerosol sources. Representative case studies of biomass-burning smoke, Saharan dust, and mixed pollen event showing distinct fluorescence properties are discussed in detail, while an extended dataset covering the period April 2024 – December 2025 is further analysed, comprising 108 aerosol layers from 50 measurement cases. A sub-dataset is also compared with the EARLINET Mahalanobis distance–based typing algorithm, highlighting the importance and complementarity of fluorescence lidar observations on the aerosol characterization in complex environments. Based on the spectral fluorescence capacity and the particle depolarization ratio, the identified layers are classified into smoke, dust, polluted continental, clean continental and mixed pollen. THELISYS retrievals show that the spectral fluorescence capacity depends on aerosol type, with smoke showing the highest values (3.5 × 10−6 − 12.7 × 10−6 𝑛𝑚−1), followed by mixed pollen (2.3 × 10−6 − 4.8 × 10−6 𝑛𝑚−1), polluted continental (1.0 × 10−6 − 3.3 × 10−6 𝑛𝑚−1), clean continental (0.3 × 10−6 − 1.2 × 10−6 𝑛𝑚−1) and dust (0.6 × 10−6 − 1.3 × 10−6 𝑛𝑚−1). The fluorescence capacity values observed for all aerosol types are comparable with other studies across central and northern Europe, however the linear particle depolarization ratio measurements attributed to pollen differ from those reported at more northern latitudes, possibly reflecting differences in pollen type.

Ground-based lidar stations play a vital role in the validation of spaceborne lidar products. While ground-based measurements have a high temporal resolution, they have limited spatial coverage, which potentially imposes implications for the Calibration and Validation (Cal/Val) of the satellite products. Therefore, in this study, we assess the representativeness of a remote ground-based ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) station, in Mindelo, Cabo Verde by utilizing the continuous observations of a ground-based PollyNET multiwavelength polarization Raman lidar. This station was selected since Cabo Verde has been a key location for the validation of two recent Earth Explorer missions of the European Space Agency (ESA), namely Aeolus and the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE). The islands are located in the Atlantic Ocean, in the outflow region of the African continent with frequent dust outbreaks, but also smoke advection and, thus, along with the local (marine) boundary layer provide an excellent atmospheric laboratory. Continuous, vertically-resolved aerosol measurements are being conducted with the state-of-the-art multiwavelength polarization Raman lidar Polly^XT at Mindelo since June 2021. Based on these observations and in combination with the LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studie (LIVAS) products available at different radii around Mindelo, a statistical analysis of the optical properties was performed to evaluate the representativeness of the station in the context of aerosol profiling Cal/Val activities. Additionally, three case studies, focusing on different distances from the ground-based station, have been closely examined for a more complete and detailed comparison. Our study results indicate that overall the ground-based station in Mindelo can be considered conditionally representative. According to the monthly analysis, at altitudes where the lofted aerosol (dust) layers occur, lidar observations were very representative for radii up to 300 km around the island, while the boundary-layer characteristics varied. Case studies confirmed the long-term results and revealed that lidar observations of lofted aerosol layers can be representative for radii up to 100 km around Mindelo and at the same time highlighted the importance of spatiotemporal homogeneity of the target. From our findings and especially for the Cabo Verde region, we conclude that it is better to use monthly averaged aerosol profiles for the validation of spaceborne profiles over long times rather than using single overpasses, as representativeness cannot be guaranteed for the latter without additional measures. Thus, using fixed radii around a certain ground site (as e.g., the frequently used 100 km) for validation activities seems to be inappropriate for profile-to-profile comparison without any further considerations. However, we show in our case studies that if representativeness can be guaranteed, also single-profile validation is possible and has its own valuable potential. Additionally, the proposed study can serve as a calibration/validation tool for the remote sensing facilities of the European Aerosol Research Lidar Network (EARLINET).

Ground-based lidar stations play a vital role in the validation of spaceborne lidar products. While ground-based measurements have a high temporal resolution, they have limited spatial coverage, which potentially imposes implications for the Calibration and Validation (Cal/Val) of the satellite products. Therefore, in this study, we assess the representativeness of a remote ground-based ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) station, in Mindelo, Cabo Verde by utilizing the continuous observations of a ground-based PollyNET multiwavelength polarization Raman lidar. This station was selected since Cabo Verde has been a key location for the validation of two recent Earth Explorer missions of the European Space Agency (ESA), namely Aeolus and the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE). The islands are located in the Atlantic Ocean, in the outflow region of the African continent with frequent dust outbreaks, but also smoke advection and, thus, along with the local (marine) boundary layer provide an excellent atmospheric laboratory. Continuous, vertically-resolved aerosol measurements are being conducted with the state-of-the-art multiwavelength polarization Raman lidar PollyXT at Mindelo since June 2021. Based on these observations and in combination with the LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies) products available at different radii around Mindelo, a statistical analysis of the optical properties was performed to evaluate the representativeness of the station in the context of aerosol profiling Cal/Val activities. Additionally, three case studies, focusing on different distances from the ground-based station, have been closely examined for a more complete and detailed comparison. Our study results indicate that overall the ground-based station in Mindelo can be considered conditionally representative. According to the monthly analysis, at altitudes where the lofted aerosol (dust) layers occur, lidar observations were very representative for radii up to 300 km around the island, while the boundary-layer characteristics varied. Case studies confirmed the long-term results and revealed that lidar observations of lofted aerosol layers can be representative for radii up to 100 km around Mindelo and at the same time highlighted the importance of spatiotemporal homogeneity of the target. From our findings and especially for the Cabo Verde region, we conclude that it is better to use monthly averaged aerosol profiles for the validation of spaceborne profiles over long times rather than using single overpasses, as representativeness cannot be guaranteed for the latter without additional measures. Thus, using fixed radii around a certain ground site (as e.g., the frequently used 100 km) for validation activities seems to be inappropriate for profile-to-profile comparison without any further considerations. However, we show in our case studies that if representativeness can be guaranteed, also single-profile validation is possible and has its own valuable potential. Additionally, the proposed study can serve as a calibration/validation tool for the remote sensing facilities of the European Aerosol Research Lidar Network (EARLINET).

Ground-based lidar stations play a vital role in the validation of spaceborne lidar products. While ground-based measurements have a high temporal resolution, they have limited spatial coverage, which potentially imposes implications for the Calibration and Validation (Cal/Val) of the satellite products. Therefore, in this study, we assess the representativeness of a remote ground-based ACTRIS (Aerosol, Clouds, and Trace Gases Research Infrastructure) station, in Mindelo, Cabo Verde by utilizing the continuous observations of a ground-based PollyNET multiwavelength polarization Raman lidar. This station was selected since Cabo Verde has been a key location for the validation of two recent Earth Explorer missions of the European Space Agency (ESA), namely Aeolus and the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE). The islands are located in the Atlantic Ocean, in the outflow region of the African continent with frequent dust outbreaks, but also smoke advection and, thus, along with the local (marine) boundary layer provide an excellent atmospheric laboratory. Continuous, vertically-resolved aerosol measurements are being conducted with the state-of-the-art multiwavelength polarization Raman lidar PollyXT at Mindelo since June 2021. Based on these observations and in combination with the LIVAS (LIdar climatology of Vertical Aerosol Structure for space-based lidar simulation studies) products available at different radii around Mindelo, a statistical analysis of the optical properties was performed to evaluate the representativeness of the station in the context of aerosol profiling Cal/Val activities. Additionally, three case studies, focusing on different distances from the ground-based station, have been closely examined for a more complete and detailed comparison. Our study results indicate that overall the ground-based station in Mindelo can be considered conditionally representative. According to the monthly analysis, at altitudes where the lofted aerosol (dust) layers occur, lidar observations were very representative for radii up to 300 km around the island, while the boundary-layer characteristics varied. Case studies confirmed the long-term results and revealed that lidar observations of lofted aerosol layers can be representative for radii up to 100 km around Mindelo and at the same time highlighted the importance of spatiotemporal homogeneity of the target. From our findings and especially for the Cabo Verde region, we conclude that it is better to use monthly averaged aerosol profiles for the validation of spaceborne profiles over long times rather than using single overpasses, as representativeness cannot be guaranteed for the latter without additional measures. Thus, using fixed radii around a certain ground site (as e.g., the frequently used 100 km) for validation activities seems to be inappropriate for profile-to-profile comparison without any further considerations. However, we show in our case studies that if representativeness can be guaranteed, also single-profile validation is possible and has its own valuable potential. Additionally, the proposed study can serve as a calibration/validation tool for the remote sensing facilities of the European Aerosol Research Lidar Network (EARLINET).