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Mateos D.,University of Extremadura | Anton M.,University of Extremadura | Saenz G.,University of Extremadura | Banon M.,Agencia Estatal de Meteorologia | And 2 more authors.
Climate Dynamics

As the ozone is one of the most relevant variables in the climate system, to get further in its long-term characterization is a critical issue. In this study, measurements of total ozone column (TOC) from five well-calibrated Brewer spectrophotometers placed in the Iberian Peninsula are analyzed. The temporal trend rate for TOC is +9.3 DU per decade for the period 1993–2012 in Central Iberian Peninsula. However, the low TOC levels during 2011 and 2012 over the study region notably reduce this rate. Empirical linear relationships are established between TOC and pressure, height, and temperature of the tropopause. The linear fits showed seasonal and latitudinal dependence, with stronger relationships during winter and spring. Events with the presence of a double tropopause (DT) are proved to be characteristic of the study region. The decrease in TOC levels when these anomalous events occur is quantified around 10 % in winter and spring with respect to the usual cases with a single tropopause. The total weight of the DT events with respect to the annual values is about 20 %, with a negligible occurrence in summer and autumn and being latitudinal-dependent. The North Atlantic Oscillation (NAO) index explains 30 % of the total ozone variability in winter. The DT events are found to be more frequent during phases with positive NAO. © 2014, Springer-Verlag Berlin Heidelberg. Source

Anton M.,University of Granada | Kroon M.,Royal Netherlands Meteorological Institute | Lopez M.,Agencia Estatal de Meteorologia | Vilaplana J.M.,Teledeteccion y Atmosfera | And 5 more authors.
Journal of Geophysical Research: Atmospheres

This article focuses on the validation of the total ozone column (TOC) data set acquired by the Global Ozone Monitoring Experiment (GOME) and the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) satellite remote sensing instruments using the Total Ozone Retrieval Scheme for the GOME Instrument Based on the Ozone Monitoring Instrument (TOGOMI) and Total Ozone Retrieval Scheme for the SCIAMACHY Instrument Based on the Ozone Monitoring Instrument (TOSOMI) retrieval algorithms developed by the Royal Netherlands Meteorological Institute. In this analysis, spatially colocated, daily averaged ground-based observations performed by five well-calibrated Brewer spectrophotometers at the Iberian Peninsula are used. The period of study runs from January 2004 to December 2009. The agreement between satellite and ground-based TOC data is excellent (R2 higher than 0.94). Nevertheless, the TOC data derived from both satellite instruments underestimate the ground-based data. On average, this underestimation is 1.1% for GOME and 1.3% for SCIAMACHY. The SCIAMACHY-Brewer TOC differences show a significant solar zenith angle (SZA) dependence which causes a systematic seasonal dependence. By contrast, GOME-Brewer TOC differences show no significant SZA dependence and hence no seasonality although processed with exactly the same algorithm. The satellite-Brewer TOC differences for the two satellite instruments show a clear and similar dependence on the viewing zenith angle under cloudy conditions. In addition, both the GOME-Brewer and SCIAMACHY-Brewer TOC differences reveal a very similar behavior with respect to the satellite cloud properties, being cloud fraction and cloud top pressure, which originate from the same cloud algorithm (Fast Retrieval Scheme for Clouds from the Oxygen A-Band (FRESCO+)) in both the TOSOMI and TOGOMI retrieval algorithms. Copyright 2011 by the American Geophysical Union. Source

Piedehierro A.A.,University of Extremadura | Cancillo M.L.,University of Extremadura | Serrano A.,University of Extremadura | Anton M.,University of Extremadura | Vilaplana J.M.,Teledeteccion y Atmosfera
Journal of Geophysical Research: Atmospheres

It is well known that the amount of ultraviolet solar radiation (UV) reaching the Earth's surface is governed by stratospheric ozone, which has exhibited notable variations since the late 1970s. A thorough monitoring of UV radiation requires long-term series of accurate measurements worldwide, and to keep track of its evolution, it is essential to use high-quality instrumentation with an excellent long-term performance capable of detecting low UV signal. There are several UV monitoring networks worldwide based on multifilter UV radiometers; however, there is no general agreement about the most suitable methodology for the global irradiance calibration of these instruments. This paper aims to compare several calibration methods and to analyze their behavior for different ranges of solar zenith angle (SZA). Four methods are studied: the two currently most frequently used methods referred to in the literature and two new methods that reduce systematic errors in calibrated data at large solar zenith angles. The results evidence that proposed new methods show a clear improvement compared to the classic approaches at high SZA, especially for channels 305 and 320 nm. These two channels are of great interest for calculating the total ozone column and other products such as dose rates of biological interest in the UV range (e.g., the erythemal dose). ©2015. American Geophysical Union. All Rights Reserved. Source

Mateos D.,Avda. de Elvas s n | Anton M.,Avda. de Elvas s n | Saenz G.,Avda. de Elvas s n | Banon M.,Agencia Estatal de Meteorologia | And 2 more authors.
Atmospheric Research

The analysis of extreme events is an essential key in the research of the atmospheric ozone due to their importance in biological and radiative effects. Total ozone column (TOC) databases from five ground-based sites equipped with a Brewer spectrometer are used to evaluate extreme ozone events along the Iberian Peninsula for the period 2002-2012. The monthly standard deviation is proved as a reliable metric to identify extreme cases. A total of 465 events (days) are classified as extremes events. For the database used, 2011 presents 32 events with very low TOC values (miniholes), while 2010 is the year with the maximum number (51) of events with very high TOC values (minihighs). The weight of the miniholes (minihighs) over the ozone annual mean can achieve values over the 4% (8%). The relationship between global dynamical features and ozone extreme events is also addressed in this study. Double tropopause events have explained in 2002 and 2004 up to the half of minihole events, while the North Atlantic Oscillation (NAO) negative phase is the condition prevalent in the majority of the minihighs in the entire period. These global characteristics are verified in the analysis of a case study (February-March 2004) exhibiting two periods with double tropopause events and a change in the sign of the NAO index with the consequent change in the tropopause pressure. © 2015 Elsevier B.V. Source

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