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@article{Añel2025b,

title = {Nineteenth- and twentieth-century semi-quantitative surface ozone along subtropical European to tropical Africa Atlantic coasts},

author = {J. A. Añel and J. -C. Antuña-Marrero and A. Cid Samamed and C. Pérez-Souto and L. Torre and M. A. Valente and Y. Brugnara and A. Saiz-Lopez and L. Gimeno},

url = {https://essd.copernicus.org/articles/17/2437/2025/},

doi = {10.5194/essd-17-2437-2025},

year  = {2025},

date = {2025-06-06},

urldate = {2025-01-01},

journal = {Earth System Science Data},

volume = {17},

number = {6},

pages = {2437–2446},

keywords = {dataset, pre-industrial era, tropospheric ozone},

pubstate = {published},

tppubtype = {article}

}

@article{BLUM2025113476,

title = {Geometric calibration of all-sky cameras using sun and moon positions: A comprehensive analysis},

author = {Niklas Blum and Paul Matteschk and Yann Fabel and Bijan Nouri and Roberto Román and Luis F. Zarzalejo and Juan Carlos Antuña-Sánchez and Stefan Wilbert},

url = {https://www.sciencedirect.com/science/article/pii/S0038092X25002397},

doi = {https://doi.org/10.1016/j.solener.2025.113476},

issn = {0038-092X},

year  = {2025},

date = {2025-03-24},

urldate = {2025-01-01},

journal = {Solar Energy},

volume = {295},

pages = {113476},

abstract = {All-sky imagers (ASIs) have been applied to enable accurate very-short-term forecasts of the production of solar power plants and to derive measurements which facilitate the efficient and reliable operation of such plants. Overall, ASIs can support the grid integration and efficient operation of solar power plants. These tasks often require to reconstruct ‘world coordinates’ of observed scene points from their position in the ASI images. This requires a practically feasible geometric calibration of each ASI regarding camera-intrinsic lens distortion parameters and the ASI’s external orientation. We present ‘SuMo’ an open-source Python tool which determines all relevant parameters only using regular ASI images of Sun and Moon. The method avoids a manual interference on-site, can be applied retrospectively and can also be used to continuously monitor an ASI’s geometric calibration. We validate the calibration method on five cameras at three sites and over various datasets representing different seasons, atmospheric conditions, exposure times and sun/ moon elevation and azimuth angles. Already a single month of images from either summer or winter yields an accurate calibration (RMSE ?0.14?). A comparable calibration accuracy (RMSE 0.14 – 0.38?) could be achieved for all tested ASIs without modifying any of the method’s parameters. Image quality moderately influenced the calibration accuracy. An additional cross-validation with the star-based ORION calibration method further confirms the high accuracy of our method over the entire sky dome (MAE 0.14?). We provide a Python package and >2 years of ASI images and irradiance measurements with the publication.},

keywords = {All-sky imager, Celestial bodies, External orientation, Geometric calibration, Intrinsic calibration, sky camera},

pubstate = {published},

tppubtype = {article}

}

@article{Antuña-Marrero2025b,

title = {Comparing Integrated Water Vapor Sun Photometer Observations Over the Arctic With ERA5 and MERRA-2 Reanalyses},

author = {J. C. Antuña-Marrero and R. Román and V. E. Cachorro and D. Mateos and C. Toledano and A. Calle and J. C. Antuña-Sánchez and R. Gonzalez and M. Antón and J. Vaquero-Martínez and Á.  M. Frutos Baraja},

url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2024JD041120},

doi = {https://doi.org/10.1029/2024JD041120},

year  = {2025},

date = {2025-03-17},

urldate = {2025-01-01},

journal = {Journal of Geophysical Research: Atmospheres},

volume = {130},

number = {6},

pages = {e2024JD041120},

abstract = {Abstract Atmospheric water vapor, a greenhouse gas, is increasing in the Arctic. It is a scientific challenge to understand the causes for this increase and determine adaptation and mitigation actions to confront its climatic effects. During the last decades, spatial and temporal coverage of water vapor satellite observations increased notably, and reanalysis water vapor estimates have steadily improved. However, the scarce spatial and temporal coverage in the Arctic of integrated water vapor (IWV) surface-based observations limits the representativeness of satellite observations and reanalysis estimate validations. Recently, we validated sun photometer IWV (IWVsp) observations with IWV from radiosondes in the Arctic. Here, we compare the hourly means of IWVsp from 13 Arctic AERONET stations and the IWV from ERA-5 and MERRA-2 reanalyses. The comparison is conducted at hourly timescale for individual stations for two Arctic regions and for the whole Arctic. The comparison showed a moist bias of IWV from reanalyses with respect to IWVsp. The individual station wise pattern shows slightly better accuracy and precision for ERA5 than for MERRA-2 also evident at the selected subregional scale. The differences of IWV from ERA5 and MERRA-2 and IWVsp show no dependence on IWVsp nor the solar zenith angle. This study corroborates that IWVsp may be used for validations of satellite IWV observations and IWV reanalyses products.},

note = {e2024JD041120 2024JD041120},

keywords = {AERONET, Arctic, Integrated water vapor, reanalysis, sunphotometer},

pubstate = {published},

tppubtype = {article}

}

@article{Añel2025,

title = {The Need for Better Monitoring of Climate Change in the Middle and Upper Atmosphere},

author = {Juan A. Añel and Ingrid Cnossen and Juan Carlos Antuña-Marrero and Gufran Beig and Matthew K. Brown and Eelco Doornbos and Scott Osprey and Shaylah Maria Mutschler and Celia Pérez Souto and Petr Šácha and Viktoria Sofieva and Laura de la Torre and Shun-Rong Zhang and Martin G. Mlynczak},

url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2024AV001465},

doi = {https://doi.org/10.1029/2024AV001465},

year  = {2025},

date = {2025-02-28},

urldate = {2025-01-01},

journal = {AGU Advances},

volume = {6},

number = {2},

pages = {e2024AV001465},

abstract = {Abstract Anthropogenic greenhouse gas emissions significantly impact the middle and upper atmosphere. They cause cooling and thermal shrinking and affect the atmospheric structure. Atmospheric contraction results in changes in key atmospheric features, such as the stratopause height or the peak ionospheric electron density, and also results in reduced thermosphere density. These changes can impact, among others, the lifespan of objects in low Earth orbit, refraction of radio communication and GPS signals, and the peak altitudes of meteoroids entering the Earth's atmosphere. Given this, there is a critical need for observational capabilities to monitor the middle and upper atmosphere. Equally important is the commitment to maintaining and improving long-term, homogeneous data collection. However, capabilities to observe the middle and upper atmosphere are decreasing rather than improving.},

note = {e2024AV001465 2024AV001465},

keywords = {climate change, Earth observation, middle atmosphere, space debris, upper atmosphere},

pubstate = {published},

tppubtype = {article}

}

@article{Antuña-Marrero2025,

title = {A Long and Fruitful Cooperation in Atmospheric Aerosol Research between Cuba and Spain},

author = {Juan Carlos Antuña-Marrero and Ángel Frutos and Rene Estevan and Victoria Cachorro and Boris Barja and Sandra Mogo and Albeht Rodríguez-Vega and Carlos Toledano and Frank García and David Mateos and Juan Carlos Antuña-Sánchez and Ramiro González and Jorge Rosas and Roberto Román and Luis Enrique Ramos-Guadalupe and Abel Calle and Iralmy Y. Platero and Carlos Hernández and Nelson Díaz and Joel Díaz},

url = {https://journals.ametsoc.org/view/journals/bams/106/2/BAMS-D-23-0138.1.xml},

doi = {10.1175/BAMS-D-23-0138.1},

year  = {2025},

date = {2025-02-21},

urldate = {2025-01-01},

journal = {Bulletin of the American Meteorological Society},

volume = {106},

number = {2},

pages = {E364 - E377},

publisher = {American Meteorological Society},

address = {Boston MA, USA},

abstract = {Cuban and Spanish scientists have been studying the properties of atmospheric aerosols in Camagüey, Cuba, for more than 15?years, achieving notable scientific results at the local, regional, and global levels. Using instruments and expertise supplied by Spain, Cuban scientists have characterized local aerosol optical and microphysical properties and their chemical composition and optical absorbing properties. Aerosol optical depth (AOD) and Ångström exponent observations were used to validate MODIS satellite observations and broadband AOD from local pyrheliometers. Sun photometer cloud optical depth allowed us to characterize local cloudiness and its radiative forcing. Scientific work included climatologies of the solar radiation for the last four decades at Camagüey and of aerosols in the Caribbean basin in the last two decades. Another result was designing, building, and processing of a low-cost all-sky camera. Besides scientific results, the cooperation allowed the Cuban sun photometer observations to contribute to the Red Ibérica de Medida Fotométrica de Aerosoles and AERONET. A workshop celebrating 10?years of cooperation was held at Camagüey in 2016. The workshop participants evaluated the progress, difficulties, and challenges and inaugurated a Spanish angular calibration bench for solar radiation sensors at Camagüey. The workshop also included the first visit of a NASA scientist to Cuba, the only one visit. Cuban scientists became members of the International Science Team of the NASA Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite mission, just launched, participating in its prelaunch activities. Considering the joint capabilities we developed, Cuban–Spanish contribution is expected for the TEMPO postlaunch validation campaign.},

keywords = {aerosol optical properties, Aerosols, atmosphere, Central America, In situ atmospheric observations, Radiation},

pubstate = {published},

tppubtype = {article}

}

@article{Herrero-Anta2025,

title = {Impact of cloud presence on sky radiances and the retrieval of aerosol properties},

author = {Sara Herrero-Anta and Roberto Román and Daniel González-Fernández and Claudia Emde and David Mateos and Celia Herrero Barrio and Ramiro González and Oleg Dubovik and Carlos Toledano and Abel Calle and Victoria E. Cachorro and Bernhard Mayer and Ángel M. de Frutos},

url = {https://www.sciencedirect.com/science/article/pii/S0169809525000304},

doi = {https://doi.org/10.1016/j.atmosres.2025.107938},

issn = {0169-8095},

year  = {2025},

date = {2025-01-18},

urldate = {2025-01-01},

journal = {Atmospheric Research},

volume = {317},

pages = {107938},

abstract = {This paper explores the influence of the presence of clouds on sky radiances. It also analyses their impact on the retrieval of aerosol properties when using an inversion algorithm whose radiative transfer model (RTM) is designed for cloud-free atmospheres. For that, synthetic observations are simulated for 9 partially cloudy skies and for their equivalent cloud-free skies, considering 16 different aerosol scenarios. A parameter named cloud enhancement factor (CEF) has been used to determine the modifications induced in the sky radiances by each partially cloudy scenario with respect to the cloud-free sky. This parameter indicates that the sky radiances remaining after applying a cloud-screening are affected by the presence of clouds. In general, they show enhancements between 0 and 20 % with respect to the cloud-free radiances, depending on the cloudy conditions and the scattering angle. The synthetic observations used as input for the retrieval of aerosol properties are the ones required by the inversion strategy used, GRASPpac: the aerosol optical depth (AOD) and sky radiances at 4 different wavelengths together with the ceilometer range corrected signal (RCS). In partially cloudy scenarios with low CEFs, the aerosol properties do not present significant changes with respect to the cloud-free conditions. However, for partially cloudy scenarios with higher CEFs, a clear differentiation between the aerosol optical properties retrieved with and without clouds is observed. In these scenarios, the precision of the retrieval is similar for both conditions, but the accuracy is lower for the cloudy conditions. In particular, under partially cloudy conditions, it is observed an overestimation of the real refractive index (RRI) and the single scattering albedo (SSA) between 0.05 and 0.06 and between 0.03 and 0.06 respectively, and an underestimation of the asymmetry factor (g) and the imaginary refractive index (IRI) of about ?0.02 and ? 0.005, respectively. These values slightly vary with the aerosol load and wavelength for the RRI and SSA. The effects on the size distribution parameters are very small, concluding that the impact of clouds is noticeable in the optical properties but not so much in the microphysical part.},

keywords = {Aerosols, clouds, Enhancement effect, GRASP, sky radiance},

pubstate = {published},

tppubtype = {article}

}

@article{García2025,

title = {Aerosol retrievals derived from a low-cost Calitoo sun-photometer taken on board a research vessel},

author = {Rosa D. García and África Barreto and Celia Rey and Eugenio Fraile-Nuez and Alba González-Vega and Sergio F. León-Luis and Antonio Alcantara and A. Fernando Almansa and Carmen Guirado-Fuentes and Pablo González-Sicilia and Victoria E. Cachorro and Frederic Bouchar},

url = {https://www.sciencedirect.com/science/article/pii/S1352231024005636},

doi = {https://doi.org/10.1016/j.atmosenv.2024.120888},

issn = {1352-2310},

year  = {2025},

date = {2025-01-15},

urldate = {2025-01-15},

journal = {Atmospheric Environment},

volume = {341},

pages = {120888},

abstract = {This study presents a comprehensive 5-year period assessment of aerosol optical depth (AOD) and Å ngströn Exponent (AE) data from a hand-held Calitoo sun photometer on board the Ángeles Alvariño research vessel. Observations spanned March 2018 to September 2023, focusing on key maritime regions such as the Canary Islands, coasts of North Africa, the Mediterranean, Portugal, the Cantabrian, and the Bay of Biscay. The Calitoo device measures solar irradiance at three wavelengths (465, 540, and 619 nm). Uncertainty analysis for Calitoo AOD retrievals was performed using the Monte Carlo method, yielding an expanded uncertainty (UAOD) ranging between 0.008 and 0.050 with a mean and standard deviation of 0.032 ± 0.008 for the three wavelengths. Our results also highlight the remarkable calibration stability of the Calitoo (< 2.6%) over this 5-year period. Calitoo AOD values were assessed using reference AOD data from Santa Cruz de Tenerife (the Canary Islands), El Arenosillo (Huelva), and Palma de Mallorca (the Balearic Islands) AERONET (Aerosol Robotic Network) stations. The comparison revealed a good agreement with correlation coefficients ranging from 0.727 to 0.917 and mean bias ranging from -0.030 to -0.001. Additionally, the Calitoo AOD data were compared with MODIS (Moderate Resolution Imaging Spectroradiometer) and CAMS-ECMWF (Copernicus Atmosphere Monitoring Service-European Centre for Medium-Range Weather Forecasts) aerosol products obtaining that Calitoo AOD values were generally lower, showing negative mean bias of -0.063 and -0.024, respectively. The aerosol characterizations using AE vs. AOD plots in the three maritime study regions using 5-years of non-routine Calitoo data are similar to the corresponding aerosol characterizations performed with simultaneous AERONET-Cimel data. These findings underscore Calitoo’s reliability for aerosol studies in regions where AERONET instruments or other aerosol networks are unavailable. Likewise, given the low cost of Calitoo photometers, they could be deployed onboard a large number of merchant and passenger ships or in other remote or under-monitored areas, providing near real-time AOD/AE data to enhance our understanding of aerosols processes or for model or satellite assimilation/validation.},

keywords = {AERONET-cimel, aerosol optical depth, Calitoo sunphotometer, CAMS, MODIS},

pubstate = {published},

tppubtype = {article}

}

@article{ALongandFruitfulCooperationinAtmosphericAerosolResearchbetweenCubaandSpain,

title = {A Long and Fruitful Cooperation in Atmospheric Aerosol Research between Cuba and Spain},

author = {Juan Carlos Antuña-Marrero and Ángel Frutos and Rene Estevan and Victoria Cachorro and Boris Barja and Sandra Mogo and Albeht Rodríguez-Vega and Carlos Toledano and Frank García and David Mateos and Juan Carlos Antuña-Sánchez and Ramiro González and Jorge Rosas and Roberto Román and Luis Enrique Ramos-Guadalupe and Abel Calle and Iralmy Y. Platero and Carlos Hernández and Nelson Díaz and Joel Díaz},

url = {https://journals.ametsoc.org/view/journals/bams/106/2/BAMS-D-23-0138.1.xml},

doi = {10.1175/BAMS-D-23-0138.1},

year  = {2025},

date = {2025-01-01},

urldate = {2025-01-01},

journal = {Bulletin of the American Meteorological Society},

volume = {106},

number = {2},

pages = {E364 - E377},

publisher = {American Meteorological Society},

address = {Boston MA, USA},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{https://doi.org/10.1029/2024JD041120,

title = {Comparing Integrated Water Vapor Sun Photometer Observations Over the Arctic With ERA5 and MERRA-2 Reanalyses},

author = {J. C. Antuña-Marrero and R. Román and V. E. Cachorro and D. Mateos and C. Toledano and A. Calle and J. C. Antuña-Sánchez and R. Gonzalez and M. Antón and J. Vaquero-Martínez and Á.  M. Frutos Baraja},

url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2024JD041120},

doi = {https://doi.org/10.1029/2024JD041120},

year  = {2025},

date = {2025-01-01},

urldate = {2025-01-01},

journal = {Journal of Geophysical Research: Atmospheres},

volume = {130},

number = {6},

pages = {e2024JD041120},

abstract = {Abstract Atmospheric water vapor, a greenhouse gas, is increasing in the Arctic. It is a scientific challenge to understand the causes for this increase and determine adaptation and mitigation actions to confront its climatic effects. During the last decades, spatial and temporal coverage of water vapor satellite observations increased notably, and reanalysis water vapor estimates have steadily improved. However, the scarce spatial and temporal coverage in the Arctic of integrated water vapor (IWV) surface-based observations limits the representativeness of satellite observations and reanalysis estimate validations. Recently, we validated sun photometer IWV (IWVsp) observations with IWV from radiosondes in the Arctic. Here, we compare the hourly means of IWVsp from 13 Arctic AERONET stations and the IWV from ERA-5 and MERRA-2 reanalyses. The comparison is conducted at hourly timescale for individual stations for two Arctic regions and for the whole Arctic. The comparison showed a moist bias of IWV from reanalyses with respect to IWVsp. The individual station wise pattern shows slightly better accuracy and precision for ERA5 than for MERRA-2 also evident at the selected subregional scale. The differences of IWV from ERA5 and MERRA-2 and IWVsp show no dependence on IWVsp nor the solar zenith angle. This study corroborates that IWVsp may be used for validations of satellite IWV observations and IWV reanalyses products.},

note = {e2024JD041120 2024JD041120},

keywords = {AERONET, Arctic, Integrated water vapor, reanalysis, sunphotometer},

pubstate = {published},

tppubtype = {article}

}

@article{delBarrio2024h,

title = {CAECENET: An automatic system processing photometer and ceilometer data from different networks to provide columnar and vertically-resolved aerosol properties},

author = {Celia Herrero del Barrio and Roberto Román and Ramiro González and Alberto Cazorla and Marcos Herreras-Giralda and Juan Carlos Antuña-Sánchez and Francisco Molero and Francisco Navas-Guzmán and Antonio Serrano and María Ángeles Obregón and Yolanda Sola and Marco Pandolfi and Sara Herrero-Anta and Daniel González-Fernández and Jorge Muñiz-Rosado and David Mateos and Abel Calle and Carlos Toledano and Victoria E. Cachorro and Ángel M. de Frutos},

doi = {10.1371/journal.pone.0311990},

year  = {2024},

date = {2024-12-27},

urldate = {2024-12-27},

journal = {PloS one},

volume = {19},

number = {12},

pages = {e0311990},

publisher = {Public Library of Science San Francisco, CA USA},

keywords = {aerosol, caecenet, ceilometer, Sun photometer},

pubstate = {published},

tppubtype = {article}

}

@article{Zhang2024Aerosol,

title = {Aerosol Components Derived from Global AERONET Measurements by GRASP: A New Value-Added Aerosol Component Global Dataset and Its Application},

author = {Xindan Zhang and Lei Li and Huizheng Che and Oleg Dubovik and Yevgeny Derimian and Brent Holben and Pawan Gupta and Thomas F. Eck and Elena S. Lind and Carlos Toledano and Xiangao Xia and Yu Zheng and Ke Gui and Xiaoye Zhang},

url = {https://journals.ametsoc.org/view/journals/bams/105/10/BAMS-D-23-0260.1.xml},

doi = {10.1175/BAMS-D-23-0260.1},

year  = {2024},

date = {2024-10-14},

urldate = {2024-01-01},

journal = {Bulletin of the American Meteorological Society},

volume = {105},

number = {10},

pages = {E1822 - E1848},

publisher = {American Meteorological Society},

address = {Boston MA, USA},

keywords = {aerosol optical properties, Air pollution, algorithms, atmospheric composition, remote sensing},

pubstate = {published},

tppubtype = {article}

}

@article{rs16203821,

title = {Retrieval of Solar Shortwave Irradiance from All-Sky Camera Images},

author = {Daniel González-Fernández and Roberto Román and David Mateos and Celia Herrero del Barrio and Victoria E. Cachorro and Gustavo Copes and Ricardo Sánchez and Rosa Delia García and Lionel Doppler and Sara Herrero-Anta and Juan Carlos Antuña-Sánchez and África Barreto and Ramiro González and Javier Gatón and Abel Calle and Carlos Toledano and Ángel Frutos},

url = {https://www.mdpi.com/2072-4292/16/20/3821},

doi = {10.3390/rs16203821},

issn = {2072-4292},

year  = {2024},

date = {2024-10-14},

urldate = {2024-01-01},

journal = {Remote Sensing},

volume = {16},

number = {20},

abstract = {The present work proposes a new model based on a convolutional neural network (CNN) to retrieve solar shortwave (SW) irradiance via the estimation of the cloud modification factor (CMF) from daytime sky images captured by all-sky cameras; this model is named CNN-CMF. To this end, a total of 237,669 sky images paired with SW irradiance measurements obtained by using pyranometers were selected at the following three sites: Valladolid and Izaña, Spain, and Lindenberg, Germany. This dataset was randomly split into training and testing sets, with the latter excluded from the training model in order to validate it using the same locations. Subsequently, the test dataset was compared with the corresponding SW irradiance measurements obtained by the pyranometers in scatter density plots. The linear fit shows a high determination coefficient (R2) of 0.99. Statistical analyses based on the mean bias error (MBE) values and the standard deviation (SD) of the SW irradiance differences yield results close to ?2% and 9%, respectively. The MBE indicates a slight underestimation of the CNN-CMF model compared to the measurement values. After its validation, model performance was evaluated at the Antarctic station of Marambio (Argentina), a location not used in the training process. A similar comparison between the model-predicted SW irradiance and pyranometer measurements yielded R2=0.95, with an MBE of around 2% and an SD of approximately 26%. Although the precision provided by the SD at the Marambio station is lower, the MBE shows that the model’s accuracy is similar to previous results but with a slight overestimation of the SW irradiance. Finally, the determination coefficient improved to 0.99, and the MBE and SD are about 3% and 11%, respectively, when the CNN-CMF model is used to estimate daily SW irradiation values.},

keywords = {all-sky camera, Antarctica, cloud modification factor, convolutional neural network, shortwave global horizontal irradiance, sky images},

pubstate = {published},

tppubtype = {article}

}

@article{gonzalez2024CCNeural,

title = {A neural network to retrieve cloud cover from all-sky cameras: A case of study over Antarctica},

author = {Daniel González-Fernández and Roberto Román and Juan Carlos Antuña-Sánchez and Victoria E. Cachorro and Gustavo Copes and Sara Herrero-Anta and Celia Herrero del Barrio and África Barreto and Ramiro González and Ramón Ramos and Patricia Martín and David Mateos and Carlos Toledano and Abel Calle and Ángel Frutos},

url = {https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.4834},

doi = {https://doi.org/10.1002/qj.4834},

year  = {2024},

date = {2024-08-28},

journal = {Quarterly Journal of the Royal Meteorological Society},

volume = {n/a},

number = {n/a},

abstract = {Abstract We present a new model based on a convolutional neural network (CNN) to predict daytime cloud cover (CC) from sky images captured by all-sky cameras, which is called CNN-CC. A total of 49,016 daytime sky images, recorded at different Spanish locations (Valladolid, La Palma, and Izaña) from two different all-sky camera types, are manually classified into different CC (oktas) values by trained researchers. Subsequently, the images are randomly split into a training set and a test set to validate the model. The CC values predicted by the CNN-CC model are compared with the observations made by trained people on the test set, which serve as reference. The predicted CC values closely match the reference values within ±$$ ± $$1?oktas in 99% of the cloud-free and overcast cases. Moreover, this percentage is above 93% for the rest of partially cloudy cases. The mean bias error (MBE) and standard deviation (SD) of the differences between the predicted and reference CC values are calculated, resulting in MBE=0.007$$ mathrmMBE=0.007 $$?oktas and SD=0.674$$ mathrmSD=0.674 $$?oktas. The MBE and SD are also represented for different intervals of measured aerosol optical depth and Ångström exponent values, revealing that the performance of the CNN-CC model does not depend on aerosol load or size. Once the model is validated, the CC obtained from a set of images captured every 5?min, from January 2018 to March 2022, at the Antarctic station of Marambio (Argentina) is compared against direct field observations of CC (not from images) taken at this location, which is not used in the training process. As a result, the model slightly underestimates the observations with an MBE of ?$$ - $$0.3?oktas. The retrieved data are analyzed in detail. The monthly and annual CC values are calculated. Overcast conditions are the most frequent, accounting for 46.5% of all observations throughout the year, rising to 64.5% in January. The annual mean CC value at this location is 5.5?oktas, with a standard deviation of approximately 3.1?oktas. A similar analysis is conducted, separating data by hours, but no significant diurnal cycles are observed except for some isolated months.},

keywords = {AI, all-sky camera, Antarctic, cloud cover, convolutional neural network, image identification},

pubstate = {published},

tppubtype = {article}

}

@article{Graßl2024,

title = {From Polar Day to Polar Night: A Comprehensive Sun and Star Photometer Study of Trends in Arctic Aerosol Properties in Ny-Ålesund, Svalbard},

author = {Sandra Graßl and Christoph Ritter and Jonas Wilsch and Richard Herrmann and Lionel Doppler and Roberto Román},

url = {https://www.mdpi.com/2072-4292/16/19/3725},

doi = {10.3390/rs16193725},

issn = {2072-4292},

year  = {2024},

date = {2024-07-22},

urldate = {2024-01-01},

journal = {Remote Sensing},

volume = {16},

number = {19},

abstract = {The climate impact of Arctic aerosols, like the Arctic Haze, and their origin are not fully understood. Therefore, long-term aerosol observations in the Arctic are performed. In this study, we present a homogenised data set from a sun and star photometer operated in the European Arctic, in Ny-Ålesund, Svalbard, of the 20 years from 2004–2023. Due to polar day and polar night, it is crucial to use observations of both instruments. Their data is evaluated in the same way and follows the cloud-screening procedure of AERONET. Additionally, an improved method for the calibration of the star photometer is presented. We found out, that autumn and winter are generally more polluted and have larger particles than summer. While the monthly median Aerosol Optical Depth (AOD) decreases in spring, the AOD increases significantly in autumn. A clear signal of large particles during the Arctic Haze can not be distinguished from large aerosols in winter. With autocorrelation analysis, we found that AOD events usually occur with a duration of several hours. We also compared AOD events with large-scale processes, like large-scale oscillation patterns, sea ice, weather conditions, or wildfires in the Northern Hemisphere but did not find one single cause that clearly determines the Arctic AOD. Therefore the observed optical depth is a superposition of different aerosol sources.},

keywords = {aerosol optical depth, Angstrom Exponent, Arctic Haze, long-range transport, long-term AOD observations, polar aerosol, seasonal trends},

pubstate = {published},

tppubtype = {article}

}