Ramiro González

Columnar and surface aerosol load over the Iberian Peninsula establishing annual cycles, trends, and relationships in five geographical sectors

The study of atmospheric aerosol load over the Iberian Peninsula (IP) under a climatological perspective is accomplished by means of PM10 and AOD440 nm measurements from EMEP and AERONET networks, respectively, in the period 2000-2013. The PM10 annual cycles in five Iberian sectors show a main maximum in summer and a secondary maximum in spring, which is only observed in the southern area for the AOD climatology. The characteristics of PM10-AOD annual cycles of each geographical sector are explained by the different climatology of the air mass origins and their apportioning. The two magnitudes are correlated with a factor ranging between 20 and 90 depending on the sector. The temporal evolution of the aerosol load has shown a notable decrease in the IP since the 1980s. Statistically significant trends are obtained in the Northeastern sector with a reduction of 26% (period 1985-2000) for the total suspended particles, which continues for the PM10 data with a value of 35% per decade (2001-2013), and also in the whole column, 61% per decade in the AOD440 nm (2004-2013).

Optical calibration facility at the Izaña Atmospheric Research Center

During the last years a new optical calibration facility has been developed and deployed at the Izana Observatory for the calibration and characterization of the radiation measuring instruments within research activities. These activities require a traceable Quality Assurance & Quality Control system. This new facility allows the absolute, spectral and cosine response calibration. At present there are six set-ups running at the laboratory for radiance calibration, angular response determination, spectral response characterization, slit function determination and absolute irradiance calibration (vertical and horizontal set-ups). Each method and procedure has required the development of the corresponding protocol. These systems, as well as some examples of instrument calibrations, are presented in this work.

The annual cycle of total precipitable water vapor derived from different remote sensing techniques: An application to several sites of the Iberian Peninsula

The annual cycle of precipitable water vapor is inferred from the MODIS thermal infrared (IR) and nearinfrared (NIR) satellite products under clear-sky conditions and for the period 2002-2008 at 18 sites of the Iberian Peninsula, with the aim to evaluate the capabilities of both algorithms. The paper presents these results in relation with ground observations using different techniques (GPS, sunphotometer, radiosounding), with a special emphasis on GPS. The differences in the monthly means mostly correspond to underestimations, ranging between a few percent to 40%, being generally larger in winter than in summer. For most sites, NIR performs better than IR, and more particularly during the winter. NIR usually presents overestimations in summer that can reach up to 30%. The time-coincident comparison shows that best MODIS/GPS agreement is found for the continental region (rms∼0.3) for both methods, whereas the largest biases and rms differences are found at the Mediterranean sites.

Assessment of Sun photometer Langley calibration at the high-elevation sites Mauna Loa and Izaña

The aim of this paper is to analyze the suitability of the high-mountain stations Mauna Loa and Izaña for Langley plot calibration of Sun photometers. Thus the aerosol optical depth (AOD) characteristics and seasonality, as well as the cloudiness, have been investigated in order to provide a robust estimation of the calibration accuracy, as well as the number of days that are suitable for Langley calibrations. The data used for the investigations belong to AERONET and GAW-PFR networks, which maintain reference Sun photometers at these stations with long measurement records: 22 years at Mauna Loa 5 and 15 years at Izaña. In terms of clear sky and stable aerosol conditions, Mauna Loa (3397m a.s.l.) exhibits on average of 377 Langleys (243 morning and 134 afternoon) per year suitable for Langley plot calibration, whereas Izaña (2373m a.s.l.) shows 343 Langleys (187 morning and 155 afternoon) per year. The background AOD(500nm) values, on days that are favorable for Langley calibrations, are in the range 0.01-0.02 throughout the year, with well defined seasonality that exhibits a spring maximum at both stations plus a slight summer increase at Izaña. The statistical analysis of the long-term determination of 10 extraterrestrial signals yields to a calibration uncertainty of ~0.2-0.5%, being this uncertainty smaller in the near infrared and larger in the ultraviolet wavelengths. This is due to atmospheric variability that cannot be reduced based only on quality criteria of individual Langely plots.

Influence of sky radiance measurement errors on inversion-retrieved aerosol properties

Remote sensing of the atmospheric aerosol is a well-established technique that is currently used for routine monitoring of this atmospheric component, both from ground-based and satellite. The AERONET program, initiated in the 90’s, is the most extended network and the data provided are currently used by a wide community of users for aerosol characterization, satellite and model validation and synergetic use with other instrumentation (lidar, in-situ, etc.). Aerosol properties are derived within the network from measurements made by ground-based Sun-sky scanning radiometers. Sky radiances are acquired in two geometries: almucantar and principal plane. Discrepancies in the products obtained following both geometries have been observed and the main aim of this work is to determine if they could be justified by measurement errors. Three systematic errors have been analyzed in order to quantify the effects on the inversion-derived aerosol properties: calibration, pointing accuracy and finite field of view. Si...

Columnar aerosol characterization over Scandinavia and Svalbard

An overview of sun photometer measurements of aerosol properties in Scandinavia and Svalbard was provided by Toledano et al. (2012) thanks to the collaborative effort of various research groups from different countries that maintain a number of observation sites in the European Arctic and sub-Arctic regions. The spatial coverage of this kind of data has remarkably improved in the last years, thanks, among other things, to projects carried out within the framework of the International Polar Year 2007-08. The data from a set of operational sun photometer sites belonging either to national or international measurement networks (AERONET, GAW-PFR) were evaluated. The direct sun observations provided spectral aerosol optical depth (AOD) and Angstrom exponent (AE), that are parameters with sufficient long-term records for a first characterization at all sites. At the AERONET sites, microphysical properties derived from inversion of sun-sky radiance data were also examined. AOD (500nm) ranged from 0.08 to 0.10 in...

Characterizing aerosol optical depth measurements and forecasts of Saharan dust events at Camagüey, Cuba, during July 2009

Se comparan las mediciones del espesor optico de aerosoles (AOD) de polvo del Sahara realizadas en Camaguey, Cuba, durante Julio del 2009 con valores pronosticados de AOD por el modelo SKIRON y con mediciones de AOD realizadas por los satelites MODIS. Las diferencias entre las medias diarias del AOD pronosticado por SKIRON y medido por MODIS (tanto Terra como Aqua) son menores que las diferencias entre los maximos diarios. Los resultados demuestran la capacidad de desarrollar un sistema de alerta y seguimiento de los eventos de polvo del Sahara a traves del Atlantico.