Papers by Manuel Gil Ojeda
Applied Optics, 2004
An intercomparison of aerosol backscatter lidar algorithms was performed in 2001 within the frame... more An intercomparison of aerosol backscatter lidar algorithms was performed in 2001 within the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology ͑EARLINET͒. The objective of this research was to test the correctness of the algorithms and the influence of the lidar ratio used by the various lidar teams involved in the EARLINET for calculation of backscatter-coefficient profiles from the lidar signals. The exercise consisted of processing synthetic lidar signals of various degrees of difficulty. One of these profiles contained height-dependent lidar ratios to test the vertical influence of those profiles on the various retrieval algorithms. Furthermore, a realistic incomplete overlap of laser beam and receiver field of view was introduced to remind the teams to take great care in the nearest range to the lidar. The intercomparison was performed in three stages with increasing knowledge on the input parameters. First, only the lidar signals were distributed; this is the most realistic stage. Afterward the lidar ratio profiles and the reference values at calibration height were When this research was performed, C. Böckmann
Las medidas “in situ” de ozono en la estratosfera por métodos electroquímicos en sondas embarcada... more Las medidas “in situ” de ozono en la estratosfera por métodos electroquímicos en sondas embarcadas en globos proporcionan un grado de resolución vertical imposible de alcanzar por cualquier otro método. La amenaza de una posible destrucción masiva de la capa de ozono por mecanismos similares a los quesuceden en la Antártida han impulsado la investigación basadaen campañas de investigación coordinadas desde la Unión Europea. Desde hace unos años existe una red de estaciones de sondeo con un programa conjunto establecido para estudiar el fenómeno. Entre ellas, el I>NTA opera la estación de Keflavik (640N, 230W). Los resultados de las observaciones tanto individuales como coordinadas en un proyecto general denominado “Match”, indican que el ozono se destruye en el ártico durante el invierno a un ritmo similar al que tiene lugar en la Antártida y que los mecanismos que conducen la destrucción son idénticos a los que tienen lugar en el hemisferio sur. Sin embargo, no se observan valor...
Remote Sensing of Clouds and the Atmosphere Xv, 2010
A solution based on a Kalman filter to trace the evolution of the atmospheric boundary layer (ABL... more A solution based on a Kalman filter to trace the evolution of the atmospheric boundary layer (ABL) sensed by an elastic backscatter lidar is presented. An erf-like profile is used to model the mixing layer top and the entrainment zone thickness. The extended Kalman filter (EKF) enables to retrieve and track the ABL parameters based on simplified statistics of the ABL dynamics and of the observation noise present in the lidar signal. This adaptive feature permits to analyze atmospheric scenes with low signal-to-noise ratios without need to resort to long time averages or rangesmoothing techniques, as well as to pave the way for an automated detection method. First EKF results based on synthetic lidar profiles are presented and compared with a typical least-squares inversion for different SNR scenarios.
Surface ozone-aerosol behaviour and atmospheric boundary layer structure in Saharan dusty scenario
EGUGA, Apr 1, 2016
Journal of Geophysical Research, 2001
Mean global TOMS (Total Ozone Mapping Spectrometer) ozone data, averaged in tim, e, reveals persi... more Mean global TOMS (Total Ozone Mapping Spectrometer) ozone data, averaged in tim, e, reveals persistent year-to-year differences in total ozone between continents and oceans. This feature has been named GHOST (global hidden ozone structures from TOMS). During Northern Hemisphere summer it can be seen within the latitudinal belt between 40øS and 50øN. The most pronounced land-sea difference in total ozone with values of up to 18 Dobson units is observed between latitudes 35øN and 40øN. The gradients associated with the coastlines are stronger in summer, when transient planetary wave activity decreases, but is still observable in the winter period. The Iberian Peninsula has been selected as a case study to examine the effect of each possible contribution quantitatively. It has been found that the truncation of the lower tropospheric column due to the topography explains 26% of the landsea differences, while permanent differences in tropopause height distribution can account for a further 8%. After these "corrections" other structures remain. Additional contributions due to the TOMS total ozone retrieval algorithm artifact (absorbing aerosol distribution) are also explored. After considering the optical depths and absorbance of aerosols above the Iberian Peninsula, the remaining 66% is compatible with the presence of UV-absorbing aerosols whose effects may not be correctly accounted for in the TOMS retrieval algorithm.
The extinction-to-backscattering coefficient ratio (Lidar Ratio, LR) is an aerosol-type dependent... more The extinction-to-backscattering coefficient ratio (Lidar Ratio, LR) is an aerosol-type dependent parameter associated to the chemical composition, particle shape and size distribution of aerosols. Hence, the LR estimation from lidar measurements is a crucial task in aerosol research. However, the elastic approach for LR data inversion must be carefully applied to realistic aerosol conditions when a multiple contribution of different types of aerosols can coexist. This is the case for aerosols present in the Boundary Layer (BL), where a mixing of different particles can be expected. In this work, we present an experimental LR discrimination elastic inversion procedure focused on the LR estimation for both pure dust particles and BL mixed dust aerosols under Saharan dust intrusion occurrence. In addition, the importance of the selected aerosol scenario (“pure dust”, PDS, vs. “mixed dust”, MDS) applied together to the elastic dust LR retrieval in a two-layer (BL and Free Troposphere, ...
Sobre la implicación de los óxidos de nitrógeno en la destrucción de ozono estratosférico durante la primavera antártida
XXI Reunión bienal de la Real Sociedad española de Física: programa, Salamanca 4 al 10 de octubre, 1987, 1987, pág. 399, 1987
Atmos. Meas. Tech. Discuss., 2013
A new approximation is proposed to estimate O 3 and NO 2 mixing ratios in the northern subtropica... more A new approximation is proposed to estimate O 3 and NO 2 mixing ratios in the northern subtropical free troposphere (FT). The proposed method uses O 4 slant column densities (SCDs) at horizontal and near-zenith geometries to estimate a station-level differential path. The modified geometrical approach (MGA) is a simple method that takes advantage of a very long horizontal path to retrieve mixing ratios in the range of a few pptv. The methodology is presented, and the possible limitations are discussed. Multi-axis differential optical absorption spectroscopy (MAX-DOAS) highmountain measurements recorded at the Izaña observatory (28 • 18 N, 16 • 29 W) are used in this study. The results show that under low aerosol loading, O 3 and NO 2 mixing ratios can be retrieved even at very low concentrations. The obtained mixing ratios are compared with those provided by in situ instrumentation at the observatory. The MGA reproduces the O 3 mixing ratio measured by the in situ instrumentation with a difference of 28 %. The different air masses scanned by each instrument are identified as a cause of the discrepancy between the O 3 observed by MAX-DOAS and the in situ measurements. The NO 2 is in the range of 20-40 ppt, which is below the detection limit of the in situ instrumentation, but it is in agreement with measurements from previous studies for similar conditions.
The Science of the total environment, 2015
New particle formation (NPF) was investigated at a coastal background site in Southwest Spain ove... more New particle formation (NPF) was investigated at a coastal background site in Southwest Spain over a four-year period using a Scanning Particle Mobility Sizer (SMPS). The goals of the study were to characterise the NPF and to investigate their relationship to meteorology, gas phase (O3, SO2, CO and NO2) and solar radiation (UVA, UVB and global). A methodology for identifying and classifying the NPF was implemented using the wind direction and modal concentrations as inputs. NPF events showed a frequency of 24% of the total days analysed. The mean duration was 9.2±4.2 h. Contrary to previous studies conducted in other locations, the NPF frequency reached its maximum during cold seasons for approximately 30% of the days. The lowest frequency took place in July with 10%, and the seasonal wind pattern was found to be the most important parameter influencing the NPF frequency. The mean formation rate was 2.2±1.7 cm(-3) s(-1), with a maximum in the spring and early autumn and a minimum du...
Alteraciones en el equilibrio energético de la atmósfera como consecuencia de la reducción del ozono estratosférico
XXI Reunión bienal de la Real Sociedad española de Física: programa, Salamanca 4 al 10 de octubre, 1987, 1987, págs. 353-354, 1987
Universidad Internacional de Andalucía, Jul 1, 2010
La radiación solar. El sol y el espectro electromagnético. Estructura y composición de la atmósfe... more La radiación solar. El sol y el espectro electromagnético. Estructura y composición de la atmósfera. 20 2.1.1. Definición de Radiación Solar. Características del espectro electromagnético. Definición de Cuerpo Negro. 20 2.1.2. Magnitudes de medida de la radiación solar. 22 2.1.3. Composición de la atmósfera. Elementos mayoritarios y sustancias traza. 23 2.1.4. Regiones de la atmósfera terrestre. Clasificación atendiendo al perfil térmico de temperatura: troposfera, estratosfera, mesosfera y termosfera. 24 2.2. Teoría de la transferencia radiativa terrestre: influencia de la atmósfera sobre la radiación solar. 26 2.2.1. La irradiancia extraterrestre. Procesos de absorción, dispersión y reflexión y su influencia sobre el espectro solar. 26 2.2.2. Definiciones de radiación atmosférica y terrestre. Sistema Tierra-Atmósfera y su balance energético. 27 2.2.3. Teorías de Dispersión de Rayleigh y de Mie. 29 2.2.4. Ley de Bouguer-Lamber-Beer. Espesor óptico Total. Parámetros de Ángstrom. 29 2.2.5. Instrumentación para estudios de Transferencia Radiativa. 32 2.3. Diversos procesos meteorológicos: influencia de la radiación solar sobre la atmósfera. 33 2.3.1. Circulación a escala planetaria. 33 2.3.2. Masas de aire, frentes, ciclones y anticiclones. 34 2.3.3. Sistemas de mesoescala. 37 2.3.4. Capa límite atmosférica. 39 2.4. Bibliografía. 40 TEMA III: MECANISMOS FOTOQUÍMICOS: OZONO TROPOSFÉRICO Y PARTÍCULAS ULTRAFINAS. Dr. José Antonio Adame y Dra. Mar Sorribas. Instituto Nacional de Técnica Aeroespacial. 41 3.1. Mecanismos fotoquímicos: formación de ozono troposférico. 42 3.1.1. El smog fotoquímico. 42 3.1.2. Principales ciclos fotoquímicos de los gases en la baja troposfera. 43 3.1.3. Procesos de formación y destrucción de ozono. 44 3.1.4. Variaciones diarias y estacionales del ozono. 45 3.1.5. Eventos de alta concentración. 47 3.1.6. Efectos de la contaminación fotoquímica por ozono. 48 3.2. Mecanismos fotoquímicos: partículas ultrafinas. 50 3.2.1. Distribución de tamaños del aerosol atmosférico. 50 3.2.2. ¡El tamaño sí importa! Influencia del modo ultrafino en la salud humana y el cambio climático global. 52 3.2.3. Mecanismos fotoquímicos de producción de nuevas partículas ultrafinas. 53 3.2.4. Velocidades de formación y de crecimiento de partículas en un evento de nucleación. 55 3.2.5. Gases precursores. Evidencias en diferentes ambientes atmosféricos. 56 3.2.6. Introducción sobre la instrumentación para su monitorización. 56 3.3. Bibliografía.
Atmospheric Research, 2015
The volcanic ash transport to Spain has been investigated as a part of a broader scale forecast s... more The volcanic ash transport to Spain has been investigated as a part of a broader scale forecast system. Based on a double criterion, distance and eruptive history, four volcanic areas potentially affecting Spain have been investigated: Azores Islands (Portugal), Canary Islands (Spain), Iceland, and southern Italy. The paths of simulated plumes have been computed from daily forward trajectories for the period 2005-2012 using the volcanoes' locations as departure points. The frequency of impact of the hypothetical plumes has been calculated for eight regions in Spain. The probability in all cases is low. Portuguese and Spanish volcanoes present the highest probability in the warm season (~3.5%); the volcanic ash from Iceland would be expected to arrive mainly in the cold season (b1.5%). Italian volcanoes show the lowest probability (b0.5%). The weather patterns associated to the arrival of volcanic plumes from the four volcanic areas have been identified. The mean times required for the ash plumes to reach Spain from the Canary Islands, Azores Islands, Iceland, and Italy are 40, 42, 57, and 61 h, respectively. The HYSPLIT model has been used to study the volcanic plumes' dispersion and concentration fields in three aviation reference atmospheric layers. Values with high hazard for aviation have been obtained over Spain following the hypothetical eruption of a Canary Islands volcano. Fields of medium hazard would be found over Spain after a Portuguese volcano eruption. The volcanic ash from Icelandic volcanoes shows low hazard, while Italian volcanoes indicate a null hazard in most cases.
Journal of Geophysical Research: Atmospheres, 2000
Observations of the NO2 and 03 columns using zenith-viewing differential absorption spectroscopy ... more Observations of the NO2 and 03 columns using zenith-viewing differential absorption spectroscopy in the visible range (450-540 nm) were carried out at Izafia Observatory (Tenerife, 28øN, 16øW, 2370 m above sea level.) during the eclipse of February 26, 1998 (95% occultation over the station). Ozone has been retrieved using two different spectral ranges to minimize the effect of the continuous change of the solar spectrum shape as the Sun is being occulted. Small variations before the maximum phase in agreement with previous observations are found, but because of the change in the shape of the solar spectrum, it cannot conclusively be determined whether the ozone changes are real or due to interferences with changing Fraunhofer lines. The difficulties in observing small changes of absorbing gases during solar eclipse when using remote sensing technique that uses the solar UV and visible radiation as the source are discussed. NO2 displays an increase in phase with the degree of solar occultation, as compared to a non eclipse day of 1.55 + 0.09. A simple model assuming that changes over short times scales are only due to changes in photodissociation, using 03 and temperatures obtained from an ozone sounding station close to the observatory, reproduces the observed variation when the NO2 bulk is assumed to be at an altitude of 28 km. Correction for differences between local solar zenith angle (SZA) and the SZA where the absorption takes place is taken into account. response of a noon eclipse at midlatitudes for a number of stratospheric species at three altitudes (20, 30, and 40 km) using a one-dimensional photochemical model. They calculated increases in NO2 varying from 1.4 at 20 km to 6.0 at 40 km but concluded in their paper that measurement campaigns were necessary to test the models.
Journal of Atmospheric and Oceanic Technology, 2014
Several procedures are widely applied to estimate the atmospheric boundary layer (ABL) top height... more Several procedures are widely applied to estimate the atmospheric boundary layer (ABL) top height by using aerosols as tracers from lidar measurements. These methods represent different mathematical approaches, relying on either the abrupt step of the aerosol concentration between the ABL and the free troposphere (FT) or the statistical analysis of vertical variations of the aerosol concentration. An alternative method—the cluster analysis (CA)—has been applied to lidar measurements for the first time, emerging as a useful and robust approach for calculating the ABL height, taking the advantage of both previous variables: the vertical aerosol distribution as obtained from the lidar range-corrected signal (RCS) and the statistical analysis of the RCS profiles in terms of its variance to determine a region of high aerosol loading variability. CA limitations under real situations are also tested, and the effects in ABL height determination of both noise and cloud contamination in RCS a...
Atmospheric Chemistry and Physics, 2012
Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new mu... more Iodine monoxide (IO) differential slant column densities (DSCD) have been retrieved from a new multi-axis differential optical absorption spectroscopy (MAX-DOAS) instrument deployed at the Izaña subtropical observatory as part of the Network for the Detection of Atmospheric Composition Change (NDACC) programme. The station is located at 2370 m a.s.l., well above the trade wind inversion that limits the top of the marine boundary layer, and hence is representative of the free troposphere. We report daily observations from May to August 2010 at different viewing angles. During this period, the spectral signature of IO was unequivocally detected on every day of measurement. A mean IO DSCD of 1.52×10 13 molecules cm −2 was observed at the 5 • instrument elevation angle (IEA) on clear days using a single zenith reference for the reported period, with a day-today variability of 33 % at one standard deviation. Based on the simulation of the DSCDs using radiative transfer calculations with five different hypothesized IO profiles, the IO mixing ratio is estimated to range between 0.2 and 0.4 pptv in the free troposphere. Episodes of Saharan dust outbreaks were also observed, with large increases in the DSCDs at higher IEA, suggesting an enhancement of IO inside the dust cloud.
Atmospheric Measurement Techniques, 2013
This paper presents the preliminary results of nocturnal Aerosol Optical Depth (τ a) and Angström... more This paper presents the preliminary results of nocturnal Aerosol Optical Depth (τ a) and Angström Exponent (α) obtained from a new lunar photometer prototype, trade name Cimel CE-318U. Due to the variation of the moon's illumination inherent to the lunar cycle, the typical Langleyplot Method used in solar photometry to calibrate these instruments cannot be applied. In this paper, we propose three different methods to carry out the lunar-photometer calibration. In order to validate the results, we have selected three events which encompass seven nights and ten days under different atmospheric conditions, including several saharan dust intrusions episodes. Method#1 is introduced in this work as a modification of the usual Langley Method. This technique, called Lunar-Langley Method, requires the extraterrestrial irradiances from a lunar irradiance model, providing similar accuracies on τ a to those of AERONET (± 0.01-0.02). It makes comparable daytime and nighttime measurements. Method#2 consists of transferring the current calibration from a master used by sunphotometers. Its results are again within the limit of accuracy expected for the instrument. Method#3 uses an integrating sphere and the methodology proposed by Li et al. (2008) to determine sky calibration coefficients (C j) and the instrument's solid angle fieldof-view (), respectively. We observe significant τ a differences between Method#1 and #3 (up to 0.07), which might be attributed to the errors propagation in Method#3. The good results obtained from the comparison against a second CE-318U prototype, and against daytime data from a Precision Filter Radiometer (PFR), constitute a valuable assessment of CE-318U performance. Results of α and its spectral variation (δα) show good agreement between daytime and nighttime, being able to identify the aerosol properties associated with each event.
AccessScience
Stratospheric ozone acquired a huge importance two decades ago because of the discovery of strong... more Stratospheric ozone acquired a huge importance two decades ago because of the discovery of strong anomalies above the Antarctica due to gases of anthropogenic origin. From that date, stratosphere has become one of the research lines receiving more funding. A result, an important progress in the development of observational techniques, the understanding of the dynamics of the polar regions and, above all, in understanding of the chemical interactions among the species that influence the chemical-radiative balance of ozone. In this article a general revision is made of the distribution of the ozone in the stratosphere, the mechanisms that determine its equilibrium, the gases that contribute to its destruction, the present situation and the forecast of the health state of the layer.
Foreword 2019 was an important year for the World Meteorological Organization (WMO). The Eighteen... more Foreword 2019 was an important year for the World Meteorological Organization (WMO). The Eighteenth World Meteorological Congress adopted a historical reform of the WMO constituent bodies to embrace a more comprehensive Earth system approach, with a stronger focus on water resources and the ocean, more coordinated climate activities and a more concerted effort to translate science into services for society. In the new arrangement, the Research Board was tasked with bringing the large international scientific community together to foster an integrated and multidisciplinary research approach to weather, climate, water and the environment and to facilitate the develop ment of all elements of the value chain, from discovery science to serving society, all within the context of the Earth system approach. Current research programmes, namely the Global Atmosphere Watch (GAW) Programme, the World Weather Research Programme (WWRP) and the co-sponsored World Climate Research Programme (WCRP), constitute the building blocks of this multidisciplinary research approach at WMO. The GAW Programme marked its 30 th anniversary this year. GAW provides international leadership in research and capacity development in atmospheric composition observations and analysis from the global to the local scale. The programme promotes high-quality science, enabling the development of a new generation of products and services. An extensive research infrastructure supports the objectives of the programme. It is a pleasure for me to present this report summarizing the many activities of the Izaña Atmospheric Research Center. The Center's leadership in research and development regarding state-of-the-art measurement techniques, calibration and validation, as well as international cooperation have given it an outstanding reputation in weather, climate, hydrology and related environmental issues. I hope that it will inspire Members to consider becoming involved in the GAW Programme and in other WMO research programmes.
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Papers by Manuel Gil Ojeda