Papers by Alkiviadis Bais
16th International Conference on Meteorology, Climatology and Atmospheric Physics—COMECAP 2023
16th International Conference on Meteorology, Climatology and Atmospheric Physics—COMECAP 2023
Photochemical & Photobiological Sciences
This assessment provides a comprehensive update of the effects of changes in stratospheric ozone ... more This assessment provides a comprehensive update of the effects of changes in stratospheric ozone and other factors (aerosols, surface reflectivity, solar activity, and climate) on the intensity of ultraviolet (UV) radiation at the Earth’s surface. The assessment is performed in the context of the Montreal Protocol on Substances that Deplete the Ozone Layer and its Amendments and Adjustments. Changes in UV radiation at low- and mid-latitudes (0–60°) during the last 25 years have generally been small (e.g., typically less than 4% per decade, increasing at some sites and decreasing at others) and were mostly driven by changes in cloud cover and atmospheric aerosol content, caused partly by climate change and partly by measures to control tropospheric pollution. Without the Montreal Protocol, erythemal (sunburning) UV irradiance at northern and southern latitudes of less than 50° would have increased by 10–20% between 1996 and 2020. For southern latitudes exceeding 50°, the UV Index (UV...
High quality and vertical resolution profiles of ozone that cover both troposphere, UTLS and the ... more High quality and vertical resolution profiles of ozone that cover both troposphere, UTLS and the stratosphere, can be obtained by Brewer and Dobson spectrophotometers in a special viewing mode called Umkehr. As a result, this type of observations can be used in the validation of both satellite IR instrumentation, that cover from the UTLS upwards, as well as UV instrumentation, that also cover the troposphere albeit with a coarser vertical resolution. Within the IDEAS+ framework new efforts have been made to improve the operational Umkehr analysis algorithm and provide a more robust and unique validation dataset for ozone profile observations by space-born sensors such as S5P/TROPOMI, as well as GOME2 and IASI instruments on the Metop platforms. Within this work, Dobson and Brewer Umkehr retrieval methods have been optimized and applied to Umkehr ozone profile measurements for a number of selected ground-based stations. Umkehr observations were then compared to satellite ozone profil...
Living Planet Symposium, Aug 1, 2016
Aristotle University of Thessaloniki, 2003
The present study aims to validate different approaches for the estimation of three photobiologic... more The present study aims to validate different approaches for the estimation of three photobiological effective doses: the erythemal UV, the vitamin D and that for DNA damage, using high temporal resolution surfacebased measurements of solar UV from 2005-2015. Data from a UV spectrophotometer, a multi-filter radiometer, and a UV radiation pyranometer that are located in Thessaloniki, Greece are used together with empirical relations, algorithms and models in order to calculate the desired quantities. In addition to the surface-based dose retrievals, OMI/Aura and the combined SCIAMACHY/Envisat and GOME/MetopA satellite products are also used in order to assess the accuracy of each method for deriving the photobiological doses .
Current Biology, 2021
As well as guiding pollinators to the centre of flowers, areas of the corolla that absorb UV radi... more As well as guiding pollinators to the centre of flowers, areas of the corolla that absorb UV radiation may help to protect floral reproductive parts from solar UV radiation that would otherwise be reflected onto them. In their recent article, 'Floral pigmentation has responded rapidly to global change in ozone and temperature', Koski et al.1 compared herbarium specimens collected between 1941 and 2017 to investigate whether the size of the UV-absorbing area in the centre of flowers (called 'bullseyes', UV proportion, or UVP) has changed relative to the size of the flower over this period. The article, and a subsequent feature2, describe an increase in UVP of ∼2% per year across all taxa examined. However, the study's main conclusion that this trend can be partially related to changes in ozone and temperature does not withstand close examination.
Meteorologische Zeitschrift, 2018
The Journal of Steroid Biochemistry and Molecular Biology, 2020
Nature Sustainability, 2019
Comptes Rendus Geoscience, 2018
Springer Atmospheric Sciences, 2016
In Thessaloniki, Greece, a NILU-UV multi-filter radiometer has been in regular operation since 20... more In Thessaloniki, Greece, a NILU-UV multi-filter radiometer has been in regular operation since 2005 providing photosynthetically active radiation and ultraviolet (UV) measurements at 1-min intervals. In this study, a new approach to detect cloud presence based on such measurements, is evaluated with reference to all sky camera images taken at 15 min intervals during the year 2014. Daily channel measurements sampled at 1-min intervals are analyzed using singular spectrum analysis (SSA) and provide daily trend cycle, periodic and noise components for each day of the study period. A set of statistical limitations and threshold criteria are then applied to the extracted SSA components in order to detect the presence of clouds via their attenuation effect. Cloud detections are cross-referenced against all sky images for a visual confirmation and overall assessment of the algorithm.
Springer Atmospheric Sciences, 2017
Perspectives on Atmospheric Sciences, 2016
With 33 years of continuous measurements, Thessaloniki has one of the world’s longest time series... more With 33 years of continuous measurements, Thessaloniki has one of the world’s longest time series of the total ozone column (TOC) derived from a single monochromator Brewer spectrophotometer deployed since March 1982. We use the multi-decadal time series as a unique dataset for analysis of long-term changes in TOC and its parametric dependencies. We apply multiple linear regression (MLR) to monthly mean values of TOC and five proxies in the framework of a piece-wise linear trend (PWLT) model. We also perform a nonlinear time series decomposition using singular spectrum analysis (SSA) to obtain the monthly mean trend, periodicity and residual noise at mid-latitude. Both models confirm that the negative trend in TOC from 1982 exhibits a turning point during 1997 and strongly anti-correlates (ρ = −0.69 for MLR and ρ = −0.95 for SSA) with the amount of the ozone-depleting substances as represented by the EESC. Post-1997 ozone recovery is found to be evident but not statistically-significant, for the majority of the months, in the linear model. The reconstruction of TOC from the noise-free nonlinear trend model extracted from SSA is an improvement over the standard MLR linear PWLT model (ρ = 0.89 as compared to ρ = 0.76).
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Papers by Alkiviadis Bais