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A comprehensive characterisation of atmospheric aerosols in the subtropical eastern North Atlantic has been carried out using long-term ground-based Aerosol Robotic NETwork (AERONET) photometric observations over the period 2005–2020 from a unique network made up of four stations strategically located from sea level to 3555 m on the island of Tenerife. This site can be considered a sentinel for the passage of airmasses going to Europe from Africa, and therefore the aerosol characterisation performed here adds important information for analysing their evolution during their path toward Northern Europe. Two of these stations (Santa Cruz de Tenerife – SCO – at sea level and La Laguna – LLO – at 580 m a.s.l.) are located within the marine atmospheric boundary layer (MABL), and the other two (Izaña – IZO – at 2373 m a.s.l. and Teide Peak – TPO – at 3555 m a.s.l.) are high mountain stations within the free troposphere (FT). Monthly climatology of the aerosol optical depth (AOD), Ångström exponent (AE), aerosol concentration, size distribution and aerosol optical properties has been obtained for the MABL and FT. Measurements that are quite consistent across the four sites have been used to categorise the main atmospheric scenarios, and these measurements confirm an alternation between predominant background conditions and predominant dust-loaded Saharan air mass conditions caused by seasonal dust transport over the subtropical North Atlantic. Background conditions prevail in the MABL and FT for most of the year, while dust-laden conditions dominate in July and August. The MABL under background conditions appears as a well-mixed layer with a low aerosol concentration (the volume concentration, VolCon, ranges from 0.02 ± 0.01 to 0.04 ± 0.02 µm3 µm−2), a predominance of coarse-mode marine aerosols (the effective radius, Reff, changes from 1.60 ± 0.19 to 1.91 ± 0.34 µm), and a volume contribution of the fine-mode fraction Vf/Vt . The clean FT is characterised by remarkably low aerosol loading and a predominant impact of fine-mode aerosols throughout the year (Vf/Vt has a maximum value of 0.93 ± 0.13), with an average Reff of 0.16 ± 0.02 µm. However, under dust-laden conditions and mainly in summer, we observe a predominance of coarse-mode aerosols with maximum VolCon values of 0.26 ± 0.23 µm3 µm−2 for the MABL and 0.16 ± 0.12 (0.06 ± 0.05) µm3 µm−2 for IZO (TPO), and a similar and quite consistent fine-mode fraction of 0.12 ± 0.03 in the vertical within the MABL and FT. Similarities in micro-physical and optical intensive aerosol properties confirm that the Saharan Air Layer (SAL) is a well-mixed layer in terms of the particulate composition. An estimation of the difference in the aerosol loading in the 1 km layer between IZO and TPO (in terms of VolCon and AOD) is performed in this study, and this shows that aerosol loading at IZO is double that at TPO, but they have similar fine-mode fractions, effective radii and intensive optical properties. The long-term trend analysis at SCO shows a significant negative trend in the fine-mode AOD between 2005 and 2020 (−1.8 ± 0.5) × 10−5 yr−1, which might be linked to the large reduction in oil-refining SO2 emissions from the SCO refinery in 2012.

A comprehensive characterization of atmospheric aerosols in the Subtropical Eastern North Atlantic has been carried out using long-term ground-based Aerosol Robotic NETwork (AERONET) photometric observations from a unique network made up of four stations strategically located from the sea level to 3555 m height on the island of Tenerife over the period 2005–2020. This site is can be considered a sentinel of the passage of airmass going to Europe from Africa and therefore the aerosol characterization performed here adds important information to analyse their evolution during the path toward Northern Europe. Two of these stations (Santa Cruz de Tenerife –SCO- at sea level and La Laguna –LLO- at 580 m asl) are located within the Marine Boundary Layer 5 (MBL) and the other two (Izana –IZO- at 2373 m asl and Teide Peak –TPO- at 3555 m asl) are high mountain stations within the Free Troposphere (FT). Monthly climatology of Aerosol Optical Depth (AOD), Angstrom Exponent (AE), aerosol concentration, size distribution, and aerosol optical properties has been obtained for the MBL and FT. Quite consistent measurements at the four sites have been used to categorise the main atmospheric scenarios confirming the predominance of the alternating background to dust-loaded Saharan air mass conditions seasonally affecting the sites as a result of the seasonal dust transport over the Subtropical North Atlantic. Background conditions prevail in the MBL and FT most of the year while dust-laden conditions dominate in July and August. The MBL under background conditions appears as a well-mixed layer with low aerosol concentration (volume concentration, VolCon, ranging from 0.02±0.01 to 0.04±0.02 μm3 · μm−2) with a predominance of coarse mode marine aerosols (effective radius, Re ff, changing from 1.60±0.19 to 1.91±0.34 μm) and fine mode fraction < 0.35. The clean FT has been characterised by remarkably low aerosol loading and a predominant impact of fine mode aerosols throughout the year (V f / V t with a maximum value of 0.93±0.13) with an average Re ff of 0.16±0.02 μm. However, under dust-laden conditions, we observe the predominance of coarse mode aerosols, mainly in summer, with maximum VolCon values of 0.26±0.23 μm3 · μm−2 for MBL and 0.16±0.12 (0.06±0.05) μm3 · μm−2 for IZO (TPO) and a similar and quite consistent fine mode fraction of 0.120.03 in the vertical within MBL and FT. Similarities in micro-physical and optical intensive aerosol properties confirm the Saharan Air Layer (SAL) as a well-mixed layer in terms of the particulate composition. An estimation of the difference in the aerosol loading in the 1-km layer between IZO and TPO (in terms of VolCon and AOD) is performed in this study, showing that aerosol loading at IZO is double that of TPO but with similar fine mode fraction, effective radius and optical intensive properties. The long-term trend analysis at SCO shows a negative significant trend in the fine AOD mode between 2005 and 2020 (-1.8±0.5) ·10−5 yr−1, which might be linked to the large reduction of oil refining SO2 emissions at SCO refinery in 2012.

The Canary Islands are a leading tourist destination. Their strong economic dependence on this sector makes them vulnerable to climate change. The steep orography of the islands causes impact of climate change and their potential influence on tourism to be spatially heterogenous. To account for this variability, regional climate simulations were computed using the Weather Research and Forecast (WRF) numerical weather prediction model driven by the results of three CMIP5 global climate models as boundary conditions, using two different future greenhouse gas emission scenarios (RCP4.5 and RCP8.5) for the projections. The simulations were performed at a spatial resolution of 3 km for three 30-year periods, recent past (1980–2009), mid-century (2030–2059), and end-century (2070–2099). For two widely used indices of tourist attractiveness (the Tourism Climate Index TCI and the Holiday Climate Index HCI), the coastal region of most islands currently has between 20 and 30 “excellent” and “ideal” days per month for tourism, with a decrease at higher elevations. Future leisure conditions are expected to improve at higher locations and during the autumn, winter and spring. In the RCP8.5 scenario, “excellent” days are projected to increase in winter at the end of the century. Nevertheless, in the southern areas, where most of the hotel infrastructure is located, the indices indicate significantly worsened conditions in summer, with only a few “excellent” days expected in some locations. Thermal comfort was identified as the most important factor determining the expected changes.

Global warming and ultraviolet radiation (UVR) affect marine organisms worldwide. However, we still lack knowledge about the consequences of these environmental changes to range-restricted macroalgae species, such asGelidium canariense, a habitat-forming endemic of the Canary Islands. The aim of this study is to provide useful data for analyzing the conservation status of this endemic species. To do this, (1) we compared distributional data from 1987 with the data collected in 2008 and 2019 along the northern coast of Tenerife; (2) we assessed the variation in macroalgae assemblages dominated byG. canarienseover the last decade on this same cost; and (3) we explored the correlation of these results with the actual trends of sea surface temperature (SST), air temperature at 2 m above the sea surface (T2m), UVR, and downward solar radiation (DSR). The results showed significant changes in the distribution ofG. canariensein the last 30 years at Tenerife. More than 90% of its populations have declined. The endemic macroalgae have been replaced by the globally distributed speciesPterocladiella capillaceaat nearly all the sites studied. The cover ofG. canarienseandGelidium arbusculadecreased significantly with increasing SST and T2m. Additionally,G. canarienseis negatively related to the rise in UVR. These results highlight the vulnerability of both species ofGelidiumto global warming and UVR, but especially ofG. canariense. The drastic decline of this species reveals the need to upgrade its conservation status and implement protection measures to reduce the damage that predicted global change scenario may have to their relict populations.

The marine boundary layer (MBL) is a key component of Earth’s climate system, and its main characteristics (height, entrainment efficiency, energy and mass fluxes, cloud formation processes, etc.) are closely linked to the properties of the inversion layer, which generally determines its height. Furthermore, cloud response to a warmer climate, one of the main sources of uncertainty in future climate projections, is highly dependent on changes in the MBL and in the inversion-layer properties. Long-term trends of the time series of MBL parameters at 32 stations in the Atlantic Ocean have been analyzed using conveniently homogenized radiosonde profiles from 1981 to 2010. In general, decreasing trends are found in the strength and thickness of the inversion layer and in the difference between the precipitable water vapor (PWV) in the free troposphere and the MBL. In contrast, positive trends are found in the height of the bottom of the inversion layer, the lapse rates of virtual and equivalent potential temperatures, the PWV within the boundary layer, and the sea surface temperature (SST). The weakening trend of the inversion layer and the increasing desiccation of the free troposphere relative to the MBL could have important consequences for both the evolution of low cloud cover in a greenhouse-warming climate and the fragile local ecosystems, such as “cloud forests.”

It is widely accepted by the scientific community that in the coming decades the Earth's climate will undergo significant changes, which will affect the ecosystems and the population in various ways. In this work, climate change impacts on solar photovoltaic (PV) resources were evaluated in the Canary Islands, an orographically complex archipelago located in the sub-tropical Atlantic Ocean, using high resolution dynamical downscaling techniques. To alleviate the high computational cost of high resolution simulations, the pseudo-global warming technique was used to compute the initial and boundary conditions from a reanalysis dataset and from the monthly mean changes obtained by the simulations of fourteen global climate models included in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Projections of annual-mean daily irradiation and PV potential were obtained for two future decades (2045–2054 and 2090–2099) and for two different greenhouse gas emission scenarios (RCP4.5 and RCP8.5), and the corresponding results were compared with those for a recent period (1995–2004). During winter, a generalized increase in PV potential is expected, as a consequence of a reduction in cloud cover. However, during summer, future simulations indicate a decrease in PV potential because of the rise of temperature and, therefore, a reduction in PV panel efficiency.

Tourism is an essential sector of the economy of the Canary Islands. Tourism Climate Index (TCI) and Holiday Climate Index (HCI) are good indicators of environmental conditions for leisure activities. Regional climate model (RCM) has been addressed to analyze the impact of climate change on the indices of tourist areas. The initial and boundary conditions for future scenarios are prescribed through three CMIP5 models (GFDL, IPSL and MIROC) surface and lateral boundary conditions within the Meteorological Research and Forecast (WRF), with a high resolution, 3x3 km. Two time periods (2030 – 2059, and 2070-2099) and two Representative Concentration Pathways (RCPs 4.5 and 8.5) are considered. Tourism indicators are projected to improve significantly during the winter and shoulder seasons, but will worsen in the summer months, including October, in the southeast, which is where hotels are currently located.

Large-scale atmospheric patterns and near-surface winds are expected to be modified in the future due to climate change, altering the availability of wind resources on a regional scale. These possible changes are especially important in isolated power systems, as is the case for a great percentage of the islands. High-resolution climate regionalization is therefore necessary to assess the future projections of wind resource, mainly in the case of orographically complex territories, such as The Canary Islands. In this work, WRF was used to perform a dynamic regionalization in this Archipelago, using the pseudo-global warming technique to compute the initial and boundary conditions from a reanalysis dataset and from the monthly mean changes obtained from the simulations of fourteen global climate models included in the Coupled Model Intercomparison Project Phase 5 (CMIP5). Projections of mean wind, wind energy density and extractable wind power were obtained for two future decades (2045–2054 and 2090–2099) and for two different greenhouse gas scenarios (RCP4.5 and RCP8.5) and the results were compared with those for 1995–2004. Statistically significant changes in wind resource were found in some areas, mainly during summer. Most of these areas correspond to zones where at present wind farms are located.

From February 22 to 24, 2020, an intense dust storm affected the Spanish archipelago of the Canary Islands. Here we assess the radiological impact on the Canary Islands population of several natural and artificial radionuclides (40K, 137Cs, 210Pb, 7Be), and other radiological parameters (gross alpha and gross beta activity concentrations) measured in atmospheric aerosols before, during and after the dust storm. Total Suspended Matter highly correlated with PM10 (Pearson's correlation coefficient, ro = 0.98), showed increments ranging from 849% to 1778% against the background average levels, reaching levels of >3000 μg m−3. 40K and 137Cs radionuclides showed activity values over the minimum detection activity from January to March 2020, coupled with dust intrusion episodes during the study. This finding supports the use of these radionuclides as radiotracers for African low altitude dust intrusions occurring particularly during winter months over the Canary Islands. A high correlation between gross beta and 210Pb activities suggests that the latter is the main source for gross beta emitters in aerosol samples collected in the study region. 210Pb and 7Be showed a moderate positive correlation and did not show any significant change during the storm, suggesting a similar dynamics of alpha and beta emitters in the low atmosphere. A Principal Component Analysis of these observations showed two components representing a Saharan component (based on 40K, 137Cs, gross alpha, and PM10) and a heterogeneous component representing North Atlantic and Europe air masses (based on 7Be, 210Pb, and gross beta). In addition, a K-means cluster analysis helped to disentangle the origin of air masses arriving at the archipelago. Three different clusters were identified: a continental cluster (based on gross beta, 210Pb, and 7Be activity concentrations); an oceanic cluster (with low values of PM10 air concentrations, gross beta, gross alpha, and 210Pb, and 7Be and 40K activity concentrations), reflecting the Atlantic air contributions with lower radionuclide activity and microparticulate matter; and a dust intrusion cluster (with high PM10 values and 137Cs, 40K and gross alpha activity concentrations) representing dust intrusion episodes observed in Tenerife Island. These studies allow the detection and monitoring of radioactive elements, estimating the potential radiological risk to the population associated with mineral dust intrusions.

Airborne viruses and their relation to dust storms, as a possible route for dispersion, have not been widely investigated. There are, however, studies that have described the airborne dispersal of pathogenic viruses and their potential impact on public and agronomical health. Atmospheric samples were collected in an urban area of Tenerife during 2009, 2010, 2012 and 2013 and screened for the presence of enteric viruses using PCR and sequencing. The potential relationship of viral data with African dust storms and other climatic variables (viz., the seasonality, origin of the air mass and PM levels) was analyzed. Enteroviruses and Rotaviruses were detected in 15.4% (20/130) and 36.9% (48/130) of the samples, respectively. No significant statistical relationships were observed with African dust storms or the origin of the air masses, although higher percentages of positives were obtained for dust storm days. Enterovirus detection was significantly linked to warmer seasons, and PM2.5 levels showed an inverse correlation with a rotaviral presence. This is the first multi-year report to describe the presence of Enterovirus and Rotavirus genetic sequences in air samples collected in an outdoor urban environment. The data illustrates the need for source region sampling to determine links and the influence of the weather and climatic and regional wind patterns on long-range atmospheric dispersion of viruses in future research efforts.

The complex orography of the Canary Islands favors the creation of microclimates, which cannot be studied using global climate models or regional models with moderate resolution. In this work, WRF is used to perform a dynamic climate regionalization in the archipelago, using the pseudo–global warming technique to compute the initial and boundary conditions from a reanalysis dataset and from results of 14 global climate models. The simulations were performed for three decades, one at present (1995–2004) and two in the future (2045–54 and 2090–99), and for two different greenhouse gas scenarios (RCP4.5 and RCP8.5), defined in phase 5 of the Coupled Model Intercomparison Project. The obtained results, at a 5-km horizontal resolution, show a clear dependence of temperature increase with height and a positive change in diurnal temperature range, which is mainly due to a reduction in soil moisture and a slight decrease in cloud cover. This negative change in soil moisture is mainly a consequence of a decrease in precipitation, although the evaluation of simulated reduction in precipitation does not show statistical significance in most of the Canary Islands for the analyzed periods and scenarios.

The Weather Research and Forecasting (WRF) model has been used to simulate clouds, and their effects on precipitation and radiation, in Africa. The results have been compared with observational databases, mainly based on satellite measurements. The Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) has been used to consistently compare simulated clouds with satellite data, allowing us to evaluate not only the total cloud cover but also the cloud amount of different cloud types, classified according to their optical thickness and cloud-top pressure. Nine WRF simulations, for the 2002–2006 period, were carried out to evaluate the influence on cloud cover of different physical parametrizations and model configurations. In general, model simulations show similar results, underestimating total cloud cover in most of the studied region. In the tropical convective area, high clouds are underestimated, but the net effect on the radiation is partially compensated by the overestimation of cloud optical depth. Major differences appear over subtropical areas dominated by marine boundary-layer clouds, mainly off the coast of Namibia. In this area, simulations show too many thick clouds and too few clouds with lower optical thickness. The net result is an underestimation of low cloud cover. Also, the transition from stratocumulus to shallow cumulus away from the coast is not realistically modelled.

In this work, precipitable water vapour (PWV), its diurnal variability and water vapour vertical profiles have been obtained from Weather Research and Forecasting (WRF) model simulations. The PWV simulated values have been validated using observations from the Global Navigation Satellite Systems (GNSS) for three locations in an orographically complex region, the Canary Islands archipelago, while the vertical water vapour profiles have been compared with radiosonde data available for this region. Initial and boundary conditions for simulations are given by National Center for Environmental Prediction (NCEP) global models: FNL (Global Final Analysis) and GFS (Global Forecast System). Several parametrizations and assumptions, related to cloud microphysics, boundary-layer and land surface models, number of vertical levels, moisture transport and 3D nudging techniques, have been applied to evaluate the sensitivity of the WRF results. In general, a good agreement between WRF and GNSS data was obtained, with correlation coefficients larger than 0.95 and centred root mean square differences about 2 mm. Furthermore, for PWV and water vapour vertical distribution, no appreciable differences were observed between the different experiments carried out, since the main contribution to water vapour in a region with small land coverage comes from the large-scale processes, which are reasonably represented when analysis data are used as the forcing boundary conditions of the model. The ability of the WRF simulations to reproduce the PWV diurnal cycle was also verified. Additionally, the skills of the WRF simulations to determine PWV were evaluated for different nudging strategies when 48 h forecast simulations were performed; these showed insignificant differences.

Focusing on aerosolized matter of relevance to respiratory health, a major public health issue worldwide, we studied mineral and biological aerosol (bioaerosol) composition (TSP and PM2.5) and geographical origins during dust intrusions in the Canary Islands. Seven days’ back- ward trajectories were assessed daily during March 2004 with the ends of back trajectories being the sampling station of Iza?a (high moun- tain, 2360 m a.s.l. at the Ca?adas del Teide National Park, Tenerife island), a free troposphere site allowing characterization of dust with low influence of other pollutant sources. Scanning electron microscopy (SEM) was used to survey major types of airborne particles in the dust plumes. Control, non-intrusion conditions correspond to Atlantic oceanic middle troposphere (OMT) air masses. Of the 14 samples taken, 1 corresponded to a control (clear atmosphere conditions), and the remaining 13 to dust intrusions, with the following sources: African Dust; EAM: mixture of Europe, Africa and Oceanic; MaA: maritime aerosols. Of the air masses, 79% were directly transported to the islands from Africa, and an increase of African dust events was detected when comparing with a 52-year previous data sequence. Quartz microcristals and aggregates of quartz and platy clay were the dominant minerals identified, with marine salt and gypsum also present. Freshwater diatom tests (from two Aulacoseira species) represented the most important biogenic aerosols, although fungi and pollen were also detected. The diverse and complex mixture of respirable particles in large quantities in airborne dust, especially from nearby Sahara and from the Sahelian region, is of maximum interest for air- way pathology in the Canaries, including the highly visited highlands in Tenerife.

—A group of eight Spanish lidars was formed in order to extend the European Aerosol Research Lidar Network–Advanced Sustainable Observation System (EARLINET-ASOS)project. This study presents intercomparisons at the hardware and software levels. Results of the system intercomparisons are based on range-square-corrected signals in cases where the lidars viewed the same atmospheres. Comparisons were also made for aeros backscatter coefficients at 1064 nm (2 systems) and 532 nm (all systems), and for extinction coefficients at 532 nm (2 systems). In total, three field campaigns were carried out between 2006 and 2007. Comparisons were limited to the highest layer found before the free troposphere, i.e., either the atmospheric boundary layer or the aerosol layer just above it. Some groups did not pass the quality assurance criterion on the first attempt. Following modification and improvement to these systems, all systems met the quality criterion. The backscatter algorithm intercomparison consisted of processing lidar signal profiles simulated for two types of atmospheric conditions. Three stages with increasing knowledge of the input parameters were considered. The results showed that all algorithms work well when all inputs are known. They also showed the necessity to perform, when possible, additional measurements to attain better estimation of the lidar ratio, which is the most critical unknown in the elastic lidar inversion.

A strategy to evaluate the effective radius (r eff) as a function of aerosol retrievals is provided in this work. This methodology is based on the MODerate resolution Imaging Spectroradiometer (MODIS) aerosol products, using the 0.66 and 0.87 µm bands. These data have been studied from February 2000 to December 2005 in a grid situated at Subtropical North-east Atlantic region. To reduce the number of MODIS useful variables a Factorial Analysis by Principal Components has been applied, decreasing the aerosol parameters from 18 to five. With these parameters, backscattering ratios and asymmetry factors at 0.66 and 0.87 µm besides the Angstrom parameter, a lineal multivariate analysis technique has been applied to find the combination of variables that better evaluate the r eff. The standard error for the predicted value of r eff is ±0.09 µm. The expression obtained here has the advantage that it can be applied to other remote sensors like AVHRR/NOAA, HRV/SPOT, TM/LANDSAT, and so on, with long time series.

The influence of mineral dust on ultraviolet energy transfer is studied for two different mineralogical origins. The aerosol radiative forcing ΔF and the forcing efficiency at the surface ΔFeff in the range 290–325 nm were estimated in ground-based stations affected by the Saharan and Asian deserts during the dusty seasons. UVB solar measurements were taken from the World Ozone and Ultraviolet Data Center (WOUDC) for four Asian stations (2000–04) and from the Santa Cruz Observatory, Canary Islands (2002–03), under Gobi and Sahara Desert influences, respectively. The Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth at 550 nm was used to characterize the aerosol load τ, whereas the aerosol index provided by the Total Ozone Mapping Spectrometer (TOMS) sensor was employed to identify the mineral dust events. The ΔF is strongly affected by the aerosol load, the values found being comparable in both regions during the dusty seasons. Under those conditions, ΔF values as large as −1.29 ± 0.53 W m−2 (τ550 = 0.48 ± 0.24) and −1.43 ± 0.38 W m−2 (τ550 = 0.54 ± 0.26) were reached under Saharan and Asian dust conditions, respectively. Nevertheless, significant differences have been observed in the aerosol radiative forcing per unit of aerosol optical depth in the slant path, τS. The maximum ΔFeff values associated with dust influences were −1.55 ± 0.20 W m−2 τS550−1 for the Saharan region and −0.95 ± 0.11 W m−2 τS550−1 in the Asian area. These results may be used as a benchmark database for establishing aerosol corrections in UV satellite products or in global climate model estimations.

A seasonal distribution of the Lidar Ratio (LR, extinction-to-backscattering coefficient ratio) for pure Saharan dust particles has been achieved. Simultaneous MPLNET/Micro Pulse lidar measurements in synergy with AERONET sun-photometer data were collected in the Tenerife area, a Saharan dust-influenced region, from June 2007 to November 2009. Dusty cases were mostly observed in summertime (71.4 % of total dusty cases). No differences were found among the LR values derived for spring, summertime and autumn times (a rather consistent seasonally averaged LR value of 57 sr is found). In wintertime, however, a higher mean LR is derived (65 sr), associated likely with a potential contamination from fine biomass burning particles coming from Sahel area during wintertime deforestation fires period. Results, obtained from a free-tropospheric pristine station (AEMET/Izana Observatory) under Saharan dust intrusion occurrence, provide a more realistic perspective about LR values to be used in elastic lidar-derived AOD inversion for Saharan pure dust particles, and hence in improving CALIPSO AOD retrievals.

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

The dynamics and the aerosol chemistry of the air masses reaching the free troposphere of the subtropical Northeast Atlantic region during the period 1995–98 have been studied. Seven days backward trajectories were calculated daily with HYSPLIT-4 model for Izana Global Atmospheric Watch (GAW) Observatory (28.3°N 16.5°W, 2367 m a.s.l.). These back-trajectories were classified by means of a k-means clustering strategy. The daily air masses have been coded using 16 variables to detect the aerosol load of each one of them. Four clusters were found: Cluster 1, representative of Atlantic oceanic middle troposphere air masses, (OMT), has an average frequency of occurrence of 50.6%. Cluster 2, which includes air masses originated in the African continent (AfD), has been recorded in a 19.8% of time. Cluster 3 represents a mixture at least of two of the next sources: Europe, Africa and Ocean, (EAM), with a frequency of 12.7%. Finally, Cluster 4 includes air masses with a high load of maritime aerosols, (MaA), and it has been detected in a 16.9%. An analysis of four aerosol components: NO3−, NH4+, non-sea-salt-SO42−, and mineral dust and its relation with the origin and transport of the air masses have been done. The highest quantities of mineral dust and nss-SO42− are linked with African air masses with a mean value of 86.5 and 1.9 μg/m3 respectively. Whereas the highest levels of NO3−, 1.0 μg/m3, and NH4+, 0.4 μg/m3, were obtained for AfD and EAM. The lowest levels were associated with OMT and MaA air masses types: 12.7, 0.6, 0.2, and 0.5 μg/m3 for dust, NO3−, NH4+, and nss-SO42− in average for the four studied years. However, it is remarkable that the values of the median for dust are 2.2 and 3.5 μg/m3 in clusters MaA and OMT respectively. Using non-parametric statistical tests the distributions of concentrations in each cluster by year have been compared in order to detect similarities. The results show that the aerosol loads of OMT and MaA air masses are quite similar and the same occurs for AfD and EAM air masses. However, the correlation analysis between the levels of anions and ammonium evidenced important differences among the air mass types. In AfD air masses is clear a low correlation between levels of nss-SO42− and NH4+ (r2 = 0.08) suggesting that the sulfate speciation was dominated by sulfate species others than ammonium sulfate, such as calcium sulfate. CaSO4⋅2H2O (gypsum) is mainly present in the coarse mode, where the radiative effects of sulfate are less important that in the accumulative mode. For OMT air masses is noticeable an important increasing on the correlation between the levels of anions and those of NH4+ for the two last years of the study period (1997–1998, r2 = 0.61 –0.85%) with respect to the first ones (1995–1996, r2 = 0.25–0.49%), coinciding with the second strongest ENSO (El Nino Southern Oscillation) event recorded. This behavior indicates a change in the speciation of the aerosol component.

A strong African dust outbreak episode affecting the Canary Islands from 28 to 31/07/02 has been characterised at the Izana Observatory (IZO), located in the free troposphere (FT), and at Sta. Cruz de Tenerife (SCO), in the Marine Boundary Layer (MBL). The Saharan air mass intruded above the trade wind inversion layer resulting in daily mean PM levels of up to 616, 312, 98 and 26 μg m−3 of TSP, PM10, PM2.5 and PM1, respectively, at IZO. As demonstrated by the vertical sounding profiles, the MBL is compressed during the Saharan intrusion, favouring the deposition of coarse dust particles to the MBL and giving rise to daily levels of up to 85, 52 and 30 μg m−3 of PM10, PM2.5 and PM1, respectively, at SCO. A complete chemical and mineralogical characterisation has been performed for TSP and PM2.5 collected simultaneously at both sites. Levels of mineral elements increased during the Saharan episode at both sampling sites. In addition, at the MBL, the levels of the secondary inorganic aerosols registered during the Saharan episode were considerably higher than levels recorded during non-Saharan episodes. The partial formation of secondary coarse Ca and/or Na sulphates and nitrates by the reaction of gaseous pollutants (or derived oxidised phases), of a major local origin, with the natural aerosols has been deduced. These reactions may be favoured by the high concentration of coarse mineral and marine aerosols particles measured at SCO, the high relative humidity (RH) measured, as well as the strong compression of the MBL during the Saharan episode.

One of the most useful technique to evaluate the presence of atmospheric aerosol is based on the aerosol index (AI) calculated from the Total Ozone Mapping Spectrometer (TOMS) data. For this methodology, positive values of AI are related with UV-absorbing aerosols, mainly dust, smoke and volcanic aerosols, and negative values of AI are associated with non-absorbing aerosols. Using the aerosol index (AI) provided by TOMS and isentropic backwards trajectories, we have investigated the relation between the aerosol load of the air masses and the Al values. The back trajectories have been classified in eight categories attending to the contribution of the main aerosols sources, taking into account the geographical regions, the residence time in these sectors and the altitude of the air mass during its evolution towards the Izana GAW station (IZO, 28.3 °N 16.5 °W, 2367m asl), Canary Islands. The categories are: African, Maritimes, Atlantic Free Troposphere, European, Maritimes-European, Maritimes-African, European-African, and European-African-Maritimes. Thus this station is characterized mainly by clean air masses with the origin in the middle troposphere and air masses from Africa with an annual frequency of 36% and 10% respectively of the total cases study. Each point of these back trajectories has been associated with the corresponding AI value, obtaining statistical information about the relation between AI values and expected aerosol type at the station. In this Atlantic region, the most important aerosol events are associated with Saharan dust outbreaks. For these episodes we have investigated the influence of the altitude of the air masses that reach IZO station, on the AI value. The main difference is the time that these air masses spend above 2km over the African continent. For air masses associated with Al positive values greater than 0.4 this time is around the 40%, whereas for air masses associated with AI values smaller than 0.4 is around 20%. 0 2003 COSPAR.

We report on measurements of atmospheric transmission (AT T ) and aerosol optical depth (AOD T ) made at three wavelengths (368, 500, and 778 nm) with a spectroradiometer placed on Tenerife (28.5°N, 16.3°W), Canary Islands. Using the National Oceanic and Atmospheric Administration (NOAA) advanced very high resolution radiometer (AVHRR) channel 1, we also measured the aerosol optical depth (AOD S ) and albedo over a region of the North Atlantic Ocean extending from 15°-35°N to 12°-25°W. We observe large changes in AT T and AOD T when dust outbreaks pass over this region. Using all these data, we derive the asymmetry factor (g), the single-scattering albedo (ω), and the local mean AOD T and we compute the direct radiative forcing ΔF attributable to mineral dust. The local radiative forcing obtained is over the ocean ΔF = -9.7 W/m 2 and for the land ΔF=-4.5 W/m 2 with an error of±25%. Extending these results to global-scale averages, we obtain values of ΔF of -1.22 W/m 2 over the ocean and -0.57 W/m over land. The forcings attributable to dust are comparable in magnitude to those reported in the literature for anthropogenic sulphate and for biomass burning aerosols.

We investigate the effects of various types of atmospheric aerosols on satellite- derived sea surface temperature (SST) retrievals. The association between aerosol presence identified by the Earth Probe Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) and systematic errors in Advanced Very High Resolution Radiometer (AVHRR) Pathfinder SST retrievals is explored. We find a significant increase in systematic PFSST errors in the presence of dust aerosols. Average errors range from 0.34˚C for AI values between 0.5 and 1.0 to 1.74˚C for AI≥1.5. The bias is introduced by the AVHRR channel brightness temperature difference (T4 - T5) which is intended to correct for atmospheric absorption normally due primarily to water vapor. Our study shows that (T4 - T5) is sensitive to the dust aerosols (i.e., TOMS AI values). In contrast, smoke aerosols do not seem to have a significant effect on PFSST errors.

The role played by aerosols on UV radiative transfer in the atmosphere is very uncertain. This is especially true regarding mineral dust. To determine the sensitivity of the UV levels to the presence of this atmospheric specie, we have simulated the UV irradiance with different vertical distributions of mineral dust. We have used a discrete ordinates radiative transfer model to obtain the UV levels both at sea level and at 3000 m. We have computed the aerosol single-scattering albedo, the phase function, and the asymmetry factor by Mie scattering theory. The background aerosol profiles were taken from WCRP [1986] models, whereas the radiative properties of mineral dust have been calculated from the aerosol size distribution obtained during Saharan dust invasions at Tenerife island (28.5°N, 16.3°W). The values for aerosol optical depth assumed as input for the model calculations are 0.2 (at 550 nm) for clean background aerosols and 0.3 (at 550 nm) for the mineral dust component. From the results we can conclude that the dust vertical size distribution can affect the irradiance ratio F (with Saharan dust)/F (no Saharan dust) by 2-4%. In addition, we observe that to the same total optical depth the diffuse UV levels depend not only on the vertical dust distribution but also on the background aerosol vertical distribution. We have computed differences for the diffuse radiation fluxes of about 5% between a maritime and a continental model to the same mineral dust vertical distribution.

Recent studies have shown that the mineral dust is an important radiative forcing agent although the role played by this atmospheric compound in the UV-VIS radiative transfer into the atmosphere is still uncertain. To study how these particles scatter the solar radiation it is necessary to accurately know the aerosol phase function. The goodness of different phase functions with the presence of mineral dust have been tested comparing the simulated backscattered radiances in the UV-VIS region using real phase functions and different standard phase function approximations. The real ones have been calculated by the aerosol optical depth data measured with a ground-based solar photometer at Tenerife (28.5°N, 16.3°W) during Saharan dust invasions. From the comparison of these results we conclude that when a unique phase function is used in the radiative transfer model the one term Henyey-Greenstein (OTHG) is the worst approximation whereas the two parameter Henyey-Greenstein (TTHGL) is the best one, with an error of less than ±10%.

Some authors have pointed out that the mineral dust could have an important effect in the atmosphere radiative properties in oceanic regions where this component is the principal aerosol constituent (mainly in regions close to arid zones). The radiative characterization of this component is a global scale problem, so it is necessary to use satellites techniques. One of the most useful parameter to study the dynamic and radiative properties of the mineral dust is the aerosol optical depth (AOD). To minimize the possible error sources, in order to give this parameter, it is necessary to work with a realistic aerosol phase function. We propose a Henyey-Greenstein type phase function calculated only by the ratio AVHRR/NOAA Ch1/Ch2, whose parameters have been optimized to situations of mineral dust invasions. This proposed phase function has been obtained by radiometric measurements of ground-based instruments.

A global split-window algorithm for the retrieval of sea surface temperature from AVHRR has been developed using a radiative transfer code. In order to analyze the performance of the equation obtained which is applied to the Canary Islands zone, we have simulated a set of satellite measurements. The purpose was to classify the errors determined by the global algorithm, depending on the atmospheric situation at each moment. In the final results we give an explanation of the inefficient performance of global algorithm in comparison with a regional algorithm.

In this work a study about the emissivity and atmospheric effects related to the Land Surface Temperature determination is shown. For this purpose, a particular test area situated over 2300 m altitude in a volcanic terrain at Las Canadas National Park (Canary Islands) has been selected. In this zone, the prevailing trade winds system make the highest water vapor content to be concentrated under this altitude. In order to analyze the effect of this absorbent gas on the atmospheric correction, a preliminary study using radiosounding profiles and radiances simulated with MODTRAN radiance/transmittance code is made. The results of this analysis suggest that if its contribution is negligible or can be easily parameterized, the effective emissivity could be calculated by tuning its value in the radiative transfer equation and using a sufficiently representative number of in situ measurements together with the corresponding coincident satellite measurements.

The aerosol optical depth data obtained by two methods are compared. The first method uses solar radiance measurements with the spectroradiometer Optronic OL752 installed inside the Santa Cruz de Tenerife Harbour (28.48 N, 16.24 W). The second one takes the solar radiation scattered by the atmosphere using the Advanced Very High Resolution Radiometer (AVHRR) radiometer channels on board the NOAA meteorological satellites. A 91 per cent correlation between the two procedures was obtained for channel 1 (630nm).

In this work, a comparison between cloud cover data obtained from ISCCP database and different simulation results from GCMs included in the Coupled Model Intercomparison Project Phase 5 (CMIP5) has been conducted, to evaluate the skills of these models to reproduce the climatological behaviour of cloud cover over the African continent during approximately two decades, 1984 to 2005. The behaviour of all the models is very similar, they underestimate the total cloud cover but show a good space-time correlation with satellite data. However, the separate analysis of low, mid and high cloud cover produces worse results. One of the areas that show important differences correspond to marine boundary layer clouds near the coast of Namibia.

Solar radiation is the main source of energy for the Earth-atmosphere system, and directly or indirectly, is responsible for all phenomena affecting the meteorology and climatology of this system. The variation of any component of this system affects the radiative equilibrium, resulting in, for example, changes in the temperature of the system and/or in the configuration of the atmospheric circulation. In order to quantify these effects the concept of radiative forcing was introduced in the literature to show the magnitude of radiation variation due to changes in a specific atmospheric component, for instance, clouds, gases or atmospheric aerosols.

The shortwave radiative forcing (ΔF) and the radiative forcing efficiency (ΔFeff) of natural and anthropogenic aerosols have been analyzed using estimates of radiation both at the Top (TOA) and at the Bottom Of Atmosphere (BOA) modeled based on AERONET aerosol retrievals. Six main types of atmospheric aerosols have been compared (desert mineral dust, biomass burning, urban-industrial, continental background, oceanic and free troposphere) in similar observational conditions (i.e., for solar zenith angles between 55° and 65°) in order to compare the nearly same solar geometry. The instantaneous ΔF averages obtained vary from −122 ± 37 Wm−2 (aerosol optical depth, AOD, at 0.55 μm, 0.85 ± 0.45) at the BOA for the mixture of desert mineral dust and biomass burning aerosols in West Africa and −42 ± 22 Wm−2 (AOD = 0.9 ± 0.5) at the TOA for the pure mineral dust also in this region up to −6 ± 3 Wm−2 and −4 ± 2 Wm−2 (AOD = 0.03 ± 0.02) at the BOA and the TOA, respectively, for free troposphere conditions. This last result may be taken as reference on a global scale. Furthermore, we observe that the more absorbing aerosols are overall more efficient at the BOA in contrast to at the TOA, where they backscatter less solar energy into the space. The analysis of the radiative balance at the TOA shows that, together with the amount of aerosols and their absorptive capacity, it is essential to consider the surface albedo of the region on which they are. Thus, we document that in regions with high surface reflectivity (deserts and snow conditions) atmospheric aerosols lead to a warming of the Earth-atmosphere system.

SKYNET is an international research network of ground based sky – sunphotometers for the observation and monitoring of columnar aerosol properties. The algorithm developed by SKYNET is called SKYRAD.pack, and it is used on Prede instruments only. In this study, we have modified the SKYRAD.pack software in order to adapt it to Cimel sunphotometers. A one month database of Cimel data obtained at Burjassot (Valencia, Spain) has been processed with this program and the obtained inversion products have been compared with AERONET retrievals. In general, the differences found were consistent with the individual error assessments for both algorithms. Although the aerosol optical depth compared well for any aerosol burden situation (rmsd of 0.002–0.013 for all wavelengths), inversion products such as the single scattering albedo, refractive index and asymmetry parameter compared better for higher turbidity situations. The comparison performed for cases with an aerosol optical depth at 440 nm over 0.2 showed rms differences of 0.025–0.049 for single scattering albedo, 0.005–0.034 for the real part of refractive index, 0.004–0.007 for the imaginary part of the refractive index and 0.006–0.009 for the asymmetry parameter. With respect to the volume distributions, the comparison also showed a good agreement for high turbidity cases (mainly within the 0.01–7 μm interval) although the already known discrepancy in the extremes of the distribution was still found in 40% of the cases, in spite of eliminating data and instrumental differences present in previous studies.

[1] The mixture of mineral dust with biomass burning or urban-industrial aerosols presents significant differences in optical properties when compared to those of the individual constituents, leading to different impacts on solar radiation levels. This effect is assessed by estimating the direct radiative forcing (ΔF) of these aerosols from solar flux models using the radiative parameters derived from the Aerosol Robotic Network (AERONET). These data reveal that, in oceanic and vegetative covers (surface albedo (SA) 0.30 are not present in East Asia region. At the bottom of atmosphere (BOA) the maximum ΔF values are associated with the highest AOD levels obtained for the mixture of mineral dust and biomass burning aerosols (-130 ± 44 Wm -2 with AOD = 0.8 ± 0.4 for SA < 0.30).

[1] The Evaluation of the Effects of Elevation and Aerosols on the Ultraviolet Radiation 2002 (VELETA-2002) field campaign was designed to study the influence of aerosols and altitude on solar UV irradiance. The altitude effect (AE) was evaluated for UV irradiance under cloudless conditions by taking spectral and broadband measurements in SE Spain in the summer of 2002 at three nearby sites located at different heights (680 m, 2200 m, and 3398 m). A spectral radiative transfer model (Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART)) was also applied, mainly to evaluate the tropospheric ozone impact on AE. Results are related to the optical properties and air mass origin of the aerosols as determined by back-trajectory analysis. During the 1-week observing period of the campaign, there were two main synoptic situations with different air masses (polar maritime and tropical continental air mass associated with a Saharan dust event). The AE showed a high dependency on wavelength, solar zenith angle, and aerosols, although the growth of the mixing layer during the day also caused substantial AE variability. Saharan dust caused an increase in AE, especially in the UVB region and in the erythemal irradiance. In the UVA (320–400 nm) band the AE ranged 6–8% km−1 at noon, while for the UVB (280–320 nm) band it reached 7–11% km−1. The AE for erythemally weighted irradiance ranged from 11 to 14% km−1 between the lowest and highest stations when it was calculated from spectral measurements.

[1] The AErosol RObotic NETwork (AERONET) estimates of instantaneous solar broadband fluxes (F) at surface have been validated through comparison with ground-based measurements of broadband fluxes at Mauna Loa Observatory (MLO) and by the Baseline Surface Radiation (BSRN) and the Solar Radiation Networks (SolRad-Net) during the period 1999–2005 and 1999–2006, respectively. The uncertainties in the calculated aerosol radiative forcing (ΔF) and radiative forcing efficiency (ΔFeff) at the bottom of the atmosphere were also assessed. The stations have been selected attempting to cover different aerosols influences and hence radiative properties: urban-industrial, biomass burning, mineral dust, background continental, maritime aerosols and free troposphere. The AERONET solar downward fluxes at surface agree with ground-based measurements in all situations, with a correlation higher than 99% whereas the relation of observed to modeled fluxes ranges from 0.98 to 1.02. Globally an overestimation of 9 ± 12 Wm−2 of solar measurements was found, whereas for MLO (clear atmosphere) the differences decrease noticeably up to 2 ± 10 Wm−2. The highest dispersion between AERONET estimates and measurements was observed in locations dominated by mineral dust and mixed aerosols types. In these locations, the F and ΔF uncertainties have shown a modest increase of the differences for high aerosol load, contrary to ΔFeff which are strongly affected by low aerosol load. Overall the discrepancies clustered within 9 ± 12 Wm−2 for ΔF and 28 ± 30 Wm−2 per unit of aerosol optical depth, τ, at 0.55 μm for ΔFeff, where the latter is given for τ(0.44 μm) ≥ 0.4. The error distributions have not shown any significant tendency with other aerosol radiative properties as well as size and shape particles.

Atmospheric aerosol effects on spectral global UV irradiance were evaluated during the VELETA2002 field campaign between 8 and 19 July 2002 in southeast Spain. In the first stage, seven UV spectroradiometer and six CIMEL Sun photometer measurements were carried out simultaneously, allowing them to be calibrated and intercompared. The mean ratio obtained for the global irradiance between the spectroradiometers, with regards to a reference instrument, ranges from 0.98 up to 1.04 with standard deviations that oscillate between ±0.01 and ±0.17. In particular, the two spectroradiometers used to obtain the aerosol forcing efficiencies have a ratio of 1.000 ± 0.001. The aerosol optical depth (AOD) obtained with the CIMEL Sun photometers has a standard deviation of lower than ±0.01 for all the channels. Under clear sky conditions, the diurnal aerosol forcing efficiency (ΔDF e ) and fractional diurnal forcing efficiency (ΔFDF e ,) was calculated for two Mediterranean stations: Armilla (691 m.a.s.l.) within the boundary layer and Sabinas (2200 m.a.s.l) on the lower limit of the free troposphere and 25 km away from the first station. The ΔDF e , values obtained at Armilla range between -2.72 ± 0.45 W m-2 /τ 380 and -2.88 ± 0.45 W m-2/τ 440 and between -3.22 ± 0.61 W m-2/ τ 380 and -3.40 ± 0.62 W m-2/τ 440 at Sabinas station; the ΔFDF e values range from -8.0 ± 1.4%/τ 380 to -8.6 ± 1.3%/τ 440 and -12.0 ± 2.3%/τ 380 to -12.6 ± 2.3%/τ 440 at the two stations, respectively. Also, an experimental aerosol transmittance factor, C T , used to obtain UV satellite derived products was found as a result of the dependence of the global irradiance with the AOD, under cloudless conditions. The average aerosol attenuation factor, η, obtained from the C T , is 6 ± 2% under weakly absorbing aerosols, with a negligible spectral dependence. Copyright 2007 by the American Geophysical Union.

[i] Aerosol Robotic Network (AERONET) and World Ozone and Ultraviolet Data Center (WOUDC) combined information have been used to calculate the aerosol forcing efficiency under cloud-free conditions, ΔF e , in the ultraviolet region (290-325 nm) at surface. The stations of these global networks have been collocated spatial and temporarily, resulting three common stations: two in Canada, representative of background conditions (Bratt's Lake and Saturna Island) and one in Italy, characterized by rural and industrial aerosols (Ispra). The monthly ΔF e was calculated during spring and summer time in the common period, 1999 to 2004, and for the Cimel wavelengths 500, 440, 380 and 340 nm. The ΔF e values range from -0.65 ± 0.07 Wm -2 /T 500 to -0.36 ± 0.03 Wm -2 /τ 340 for Ispra, whereas for the Canadian observatories the interval varies from -2.07 ± 0.62 Wm -2 /τ 500 to -0.16 ± 0.23 Wm -2 /τ 340 . No significant annual or seasonal trends for the ΔF e were found in any station.

This paper presents the results of the analysis of the spectral, global, and direct solar irradiance measurements in the visible range (400–700 nm) that were made in the framework of the first Iberian UV–visible (VIS) instruments intercomparison. The instruments used in this spectral range were four spectroradiometers: three Licor 1800s equipped with different receiver optics and one Optronic 754. For the direct solar irradiance measurements the spectroradiometers were equipped with collimators with different fields of view. Parallel studies have been carried out with the data given by the spectroradiometers with their original calibration file and with the same data that is corrected, following in situ calibration of the instruments using a laboratory reference lamp. To compare the series of spectral data the relative values of mean absolute deviation (MAD) and root-mean-square deviation (rmsd) have been used. The results obtained from the measurements of global irradiance show that the Licor 1800s presented very significant differences at the beginning and at the end of the day due to the deviation from ideal cosine response of the collection optics (i.e., cosine errors). This forced the analysis to be limited to the measurements corresponding to solar elevations higher than 30°. For this solar elevation range, the results of the intercomparison between the Licor instruments, before their in situ calibration, showed differences of about 5% in the visible range. The results from the measurements of direct irradiance show that, if correction factors are considered, these deviations are reduced to 3%, and when the Licors are compared with the Optronic, the deviations are less than 2%. This work was financed by the Spanish CICYT through the CLI97-0345-C05-04 project.

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

In this work we study the complete evolution of an episode of Saharan dust invasion over Canary Island. To describe adequately this phenomena two magnitudes are calculated from NOAA-AVHRR satellite data: aerosols optical depth (AOD) in the channel 1 and the ratio channel 1-channel 2 (R12) which gives us rough information about the aerosols size distribution. The aerosols optical depth, calculated to 500 nm with a ground based sunphotometer, situated above the inversion layer is used too.

The water vapor is an atmospheric component which is not evenly distributed. If we consider the total water vapor content in a vertical column, i.e. the precipitable water, W it may change from 0.5 g/cm2 for high latitudes to about 6 g/cm2 for equatorial zones. All that makes it impossible to know its distribution with only radiosondes data, because their validity is restricted to a few km2. In order to correctly characterize the water vapor content over the sea around the Canary Islands, we have used brightness temperatures of TOVS sensors onboard NOAA satellites. We have compared the total water vapor content obtained with radiosondes data, launched by Instituto Nacional de Meteorologia at Santa Cruz de Tenerife, with the nearest free-clouds data from satellite for a set of fifty days of 1994. The statistics generated with the comparison are shown and the validity of the humidity fields determined with only TOVS data are discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The determination of sea surface temperature from satellite is performed by means of multi-channel algorithms with channels 4 and 5 of AVHRRNOAA or using radiative transfer models and radiosounding profiles of air temperature and humidity. In this work, an alternative to the current algorithms has been established. A new method combining the information supplied by sensors of TOVS and AVHRR systems onboard NOAA satellites is proposed. It is based on the split-window technique, the coefficients A and B being determined as a function of the water vapour content, which is calculated using the TOVS sensors. The T4 and T5 temperatures are supplied by the AVHRR system. Then, combining both sensors the necessity of available radiosoundings is avoided.

In the modeling of aerosols effects in the energy budget, radiative forcing, two parameters are mainly used: the asymmetry parameter, g and the back scattering parameter, R. These parameters have been evaluated with the aerosols distributions obtained by King's inversion method. The aerosol optical thickness obtained from the direct radiance measurements, made by a solar photometer at the wavelengths of 368, 500 and 778 nm, have been used as input variables to this method. The temporal behavior showed during 1994 by the asymmetric and the back scattering parameters can be explained as a function of the evolution in the particles concentration. Thus, it is observed that the evolution toward an atmosphere with Mie behavior for the wavelengths of the solar spectrum is related to the relative increase of particles concentration with a ratio bigger than 0.8 /spl mu/m. The relation between the distribution function and the temporal behavior of the parameters g and R shows for small values of Angstrom parameter, /spl alpha/, scattered values of both parameters. On the other hand, when the Angstrom parameter increases both parameters g and R also increase tending to an average value of 0.8 and 0.6 respectively.