UV-Indien network: ground-based measurements dedicated to the monitoring of UV radiation over the western Indian Ocean

Abstract

Abstract. Within the framework of the UV-Indien network, nine ground stations have been equipped with ultraviolet broadband radiometers, five of them have also been equipped with an all-sky camera, and the main station in Saint-Denis de la Réunion is also equipped with a spectroradiometer. These stations are spatially distributed to cover a wide range of latitudes, longitudes, altitudes, and environmental conditions in five countries of the western Indian Ocean region (Comoros, France, Madagascar, Mauritius, and Seychelles), a part of the world where almost no measurements have been made so far. The distribution of the stations is based on the scientific interest of studying ultraviolet radiation not only in relation to atmospheric processes but also in order to provide data relevant to fields such as biology, health (prevention of skin cancer), and agriculture. The main scientific objectives of this network are to study the annual and inter-annual variability in the ultraviolet (UV) radiation in this area, to validate the output of numerical models and satellite estimates of ground-based UV measurements, and to monitor UV radiation in the context of climate change and projected ozone depletion in this region. A calibration procedure including three types of calibrations responding to the various constraints of sustaining the network has been put in place, and a data processing chain has been set up to control the quality and the format of the files sent to the various data centres. A method of clear-sky filtering of the data is also applied. Here, we present an intercomparison with other datasets, as well as several daily or monthly representations of the UV index (UVI) and cloud fraction data, to discuss the quality of the data and their range of values for the older stations (Antananarivo, Anse Quitor, Mahé, and Saint-Denis). Ground-based measurements of the UVI are used to validate satellite estimates – Ozone Monitoring Instrument (OMI), the TROPOspheric Monitoring Instrument (TROPOMI), and the Global Ozone Monitoring Experiment (GOME) – and model forecasts of UVI – Tropospheric Emission Monitoring Internet Service (TEMIS) and Copernicus Atmospheric Monitoring Service (CAMS). The median relative differences between satellite or model estimates and ground-based measurements of clear-sky UVI range between −34.5 % and 15.8 %. Under clear skies, the smallest UVI median difference between the satellite or model estimates and the measurements made by ground-based instruments is found to be 0.02 (TROPOMI), 0.04 (OMI), −0.1 (CAMS), and −0.4 (CAMS) at Saint-Denis, Antananarivo, Anse Quitor, and Mahé, respectively. The diurnal variability in UVI and cloud fraction, as well as the monthly variability in UVI, is evaluated to ensure the quality of the dataset. The data used in this study are available at https://doi.org/10.5281/zenodo.4811488 (Lamy and Portafaix, 2021a).

Solar Ultraviolet Radiation Temporal Variability Analysis from 2-Year of Continuous Observation in an Amazonian City of Brazil

“…A maximum happening in months of transition to the dry period the rainy (December-January) was also reported by [4,38] in their studies of UVI variability at tropical latitudes. [4] found comparable characteristics by studying the variability of UVI at Indian Ocean stations located at different latitudes between the equator and 20° S. For example, they observed that Mahé, at 4.6° S, had a higher mean UVI than the cities more at the south and explained that the difference was due to latitude. Santarém is located in a tropical region, at a low latitude, close to the equator, therefore solar zenith angle (SZA) is lower throughout the year, which induces a higher UVR, smaller amplitude between the seasons, as well as a very low photoperiod variation.…”

“…A maximum happening in months of transition to the dry period the rainy (December-January) was also reported by [4,38] in their studies of UVI variability at tropical latitudes. [4] found comparable characteristics by studying the variability of UVI at Indian Ocean stations located at different latitudes between the equator and 20 • S. For example, they observed that Mahé, at 4.6 • S, had a higher mean UVI than the cities more at the south and explained that the difference was due to latitude.…”

“…Solar Ultraviolet Radiation (UVR) comprises a set of electromagnetic waves with wavelengths between 100 and 400 nm that represents a small fraction (5%) of the solar radiation that reaches the terrestrial surface [1][2][3]. This spectrum of solar radiation has a direct effect on human health, terrestrial and aquatic ecosystems, and the degradation of materials [4,5]. The amount of UVR reaching the Earth's surface depends on solar variations (such as Schwabe solar cycle), on the variations in the Earth's position relative to the Sun, on atmospheric, geographical, and temporal parameters which include the angle 2 of 13 of incoming UVR (affected by latitude, season and time of day), altitude, albedo, clouds, aerosols, and others atmospheric constituents [6][7][8].…”

MAP-IO, an atmospheric and marine observatory program onboard Marion Dufresne over the Southern Ocean

“…The manufacturer offers a calibration accounting for the solar zenith angle and the total ozone column. Between each vessel rotation, the radiometers undergo recalibration at the Saint-Denis UV station, a part of the UV-Indien network (Lamy et al, 2021a), in Reunion Island. This process involves comparing the radiometers' readings with the calibrated values of a Bentham DTMc300 spectroradiometer (https://www.bentham.co.uk/products/components/ dtmc300-double-monochromator-39, last access: 8 November 2023).…”

Protective role of melatonin in ultraviolet radiation- induced oxidative stress in human skin photoaging

“…(17,18,59,60) Solar UVR consists of electromagnetic wavelengths between 100 and 400 nm that reach the terrestrial surface and has a direct effect on human health and terrestrial and aquatic ecosystems, as well as material degradation. (61)(62)(63)(64) It is divided into three components, depending on its transmission capability in the atmosphere and its biological effects: UVA (315-400 nm) makes up most of the UVR received on the terrestrial surface; UVB (280-315 nm) which is partially absorbed into the atmosphere, and UVC (100-280 nm) which is completely absorbed by stratospheric ozone. (34,64) Both UVA and UVB wavelengths have been shown to contribute to photoaging, by imbalanced ROS/ RNS production and/or by direct DNA damage.…”