Active and passive remote sensing aerosol observations over the south of Portugal: the case study of the Cumbre Vieja plumes event occurred from 11-13 October 2021

Aerosols of natural or anthropogenic origin play an important role in the Earth’s climate system due to their interaction with radiation and clouds. The interaction depends on aerosol optical and microphysical properties such as aerosol optical depth and particle size distributions among others. For example, volcanos are natural sources of aerosols, and they could release large amounts of gases (e.g., sulphur dioxide) and ashes into the atmosphere, which may impact the temperature at the surface and consequently, over long-term, the climate. Therefore, an appropriate aerosol characterization is fundamental and the remote sensing using active and passive methods allow for that characterization. This work aims at characterizing the Cumbre Vieja volcanic plume aerosols detected over the south of Portugal between 11-13 October 2021 by using measurements from a multi-wavelength Raman lidar and from an AERONET Sun-photometer, both installed in the atmosphere observatory at the University of Évora. Lidar observations allowed to identify a volcanic aerosol layer extending between roughly 2.5 and 5 km above sea level, characterized by low and relatively constant particle depolarization ratios and high backscatter-related Angström exponents, indicating the presence of small spherical particles. The AERONET aerosol optical depth at 500 nm also shows the predominance of fine mode particles during the whole the event

Forest Fire Smoke Layers Observed in the Free Troposphere over Portugal with a Multiwavelength Raman Lidar: Optical and Microphysical Properties

Vertically resolved optical and microphysical properties of biomass burning aerosols, measured in 2011 with a multiwavelength Raman lidar, are presented. The transportation time, within 1-2 days (or less), pointed towards the presence of relatively fresh smoke particles over the site. Some strong layers aloft were observed with particle backscatter and extinction coefficients (at 355 nm) greater than 5 Mm−1 sr−1 and close to 300 Mm−1, respectively. The particle intensive optical properties showed features different from the ones reported for aged smoke, but rather consistent with fresh smoke. The Ångström exponents were generally high, mainly above 1.4, indicating a dominating accumulation mode. Weak depolarization values, as shown by the small depolarization ratio of 5% or lower, were measured. Furthermore, the lidar ratio presented no clear wavelength dependency. The inversion of the lidar signals provided a set of microphysical properties including particle effective radius below 0.2 μm, which is less than values previously observed for aged smoke particles. Real and imaginary parts of refractive index of about 1.5-1.6 and 0.02i, respectively, were derived. The single scattering albedo was in the range between 0.85 and 0.93; these last two quantities indicate the nonnegligible absorbing characteristics of the observed particles.This work was supported by FCT (Fundação para a Ciência e a Tecnologia) through the National Re-equipment Program under REDE/1527/RNG/2007, through the project PTDC/CTEATM/65307/2006 and through the projects PTDC/AAC-CLI/104925/2008 and PTDC/GEO-MET/4222/2012. The authors also acknowledge the funding provided by the Évora Geophysics Centre, Portugal, under the contract with FCT (the Portuguese Science and Technology Foundation), PEst-OE/CTE/UI0078/2011. Sérgio Nepomuceno Pereira and Jana Preißler were funded by FCT with Grants SFRH/BPD/81132/2011 and SFRH/BD/47521/2008, respectively. CGE benefits from the membership in SPALINET, EARLINET, and ACTRIS. ACTRIS Research Infrastructure Project is supported by the European Union Seventh Framework Programme (FP7/2007–2013) under Grant agreement (no. 262254). This work was also supported by the Andalusia Regional Government through the project P10-RNM-6299

Aerosol radiative effects in photosynthetically active radiation and total irradiance at a Mediterranean site from an 11-year database

This study addresses the analysis of the aerosol radiative forcing (ARF) and aerosol forcing efficiency (AFE) at surface in the Photosynthetically Active and Total radiation ranges in a Southwest Mediterranean site. A thorough analysis of a long-term database (2008–2018) has been performed, bringing very valuable results about both, the absolute values and trends in ARF and AFE for both spectral intervals. The largest monthly mean for aerosol optical depth at 500 nm (AOD500) is found in summer (0.16 at July and August) meanwhile the lowest value is in winter (0.08 at November and December), with an interannual range varying from 0.11 ± 0.03 (in 2018) to 0.17 ± 0.03 (in 2014). The AFE variation range has been estimated between −12 and − 198 Wm−2τ−1 for PAR and between −9 and − 450 Wm−2τ−1 for Total irradiance. ARF varies between −1 Wm−2 and -23 Wm−2 in the PAR range, taking values from −1 to −40 Wm−2 in the Total one. This result points out the relevance of the aerosol effects on the PAR range, which can involve up to a 50% of the Total ARF. Moreover, a notable dependence of ARF and AFE on the solar position has been detected, increasing their absolute values at solar zenith angle from 0o to 45o-60o and decreasing to zero for lower solar positions. Additionally, this analysis has revealed the existence of a significant downward trend in AFE values for PAR, with a slope of 2.7 Wm−2τ−1year−1. Although the slope is positive, taking into account that the AFE values are negative, the slope value implies that the aerosol cooling radiative effect of aerosols is decreasing. However, no trends have been detected neither in AFE nor ARF values in the Total solar range. These results evidence the long-term aerosol effects over the different spectral intervals and emphasize the need for detailed analysis of the aerosol radiative effects on fundamental spectral intervals such as the PAR range.Peer reviewe

Modelling actual evapotranspiration using a two source energy balance model with Sentinel imagery in herbaceous-free and herbaceous-cover Mediterranean olive orchards

To the European Space Agency for the imagery of the Sentinel Missions and its open access. Special thanks to Radoslaw Guzinski for share and make accessible (https://github.com/radosuav/pyDMS) the implemented software for the used sharpening process (likewise to Hector Nieto for the implemented TSEB-PT, https://github.com/hectornieto/pyTSEB).To the Group of Castillo de Canena for the use of their farm as an experimental site and their people for continuous cooperation. We also give special thanks to Andrew S. Kowalski for his advice and suggestions. We would like also to express our gratitude to the anonymous reviewers for their comments and suggestions that enhanced this work. This work was supported by the Spanish Ministry of Science and Innovation through project CGL2017-83538-C3-1-R (ELEMENTAL) and PID2020-117825GB-C21 (INTEGRATYON3) Including European Union ERDF funds [grant number PRE2018-085638]. Funding for open access charge: Universidad de Granada/CBUA.Precipitation deficit and more extreme drought and precipitation events are expected to increase in the Mediterranean region due to global warming. A great part of this region is covered by olive orchards, representing 97.5% of the world’s olive agricultural area. Thus, the adaptation of olive cultivation demands climate-smart management, such as the optimization of water use efficiency, since evapotranspiration is one of the most important components of the water balance. The novelty of this work is the combination of the remote sensing data fusion and the Two Source Energy Balance (TSEB) model (through Sentinel-2 and Sentinel-3 imagery) to estimate the actual daily evapotranspiration (ETd), at high spatial (20 m) and temporal (daily) resolution, in an olive orchard under two management regimes: herbaceous free (HF) and herbaceous-cover (HC); along a three years period, based on the hypothesis that TSEB is still able to track and estimate the evapotranspiration over more complex canopies. The study was carried out from 2016 to 2019 in an olive orchard in the South of Spain, where the flux estimates were validated and assessed by in situ eddy covariance (EC) measurements. The results show better agreement in HC for net radiation (Rn) and the soil heat flux (G), but similar for both surfaces regarding the sensible (H) and latent (λE) heat fluxes, as well as ETd. On both surfaces greater differences obtained at higher H, and the magnitude of overestimation of λE and ETd were influenced by the EC energy imbalance. By contrast, G was overestimated with HC probably influenced by herbs, and equally underestimated for HF surfaces. The obtained results are in agreement with similar studies in tree crop orchards, and show the consistency of the used methodology and its usefulness for some farming activities, even on the more heterogeneous surface.Spanish Government CGL2017-83538-C3-1-R PID2020-117825GB-C21European Commission PRE2018-085638Universidad de Granada/CBU

Tropospheric water vapour and relative humidity profiles from lidar and microwave radiometry

In this paper, we outline an iterative method to calibrate the water vapour mixing ratio profiles retrieved from Raman lidar measurements. Simultaneous and co-located radiosonde data are used for this purpose and the calibration results obtained during a radiosonde campaign in summer and autumn 2011 are presented. The water vapour profiles measured during night-time by the Raman lidar and radiosondes are compared and the differences between the methodologies are discussed. Then, a new approach to obtain relative humidity profiles by combination of simultaneous profiles of temperature (retrieved from a microwave radiometer) and water vapour mixing ratio (from a Raman lidar) is addressed. In the last part of this work, a statistical analysis of water vapour mixing ratio and relative humidity profiles obtained during 1 year of simultaneous measurements is presented.This work was supported by the Andalusian Regional Government through projects P12-RNM-2409 and P10-RNM-6299, by the Spanish Ministry of Science and Technology through projects CGL2010-18782, CSD2007-00067, CGL2011-13580-E/CLI and CGL2011-16124-E; and by the EU through the ACTRIS project (EU INFRA-2010-1.1.16-262254)

Dynamics of the Atmospheric Boundary Layer over two middle-latitude rural sites with Doppler lidar

The Atmospheric Boundary Layer (ABL) over two middle-latitude rural sites was characterized in terms of mean horizontal wind and turbulence sources using a standard classification methodology based on Doppler lidar. The first location was an irrigated olive orchard in Úbeda (Southern Spain), representing one of the most important crops in the Mediterranean basin and a typical site with Mediterranean climate. The second location was PolWET peatland site in Rzecin (Northwestern Poland), representing one of the largest natural terrestrial carbon storages that have a strong interaction with the climate system. The results showed typical situations for non cloud-topped ABL cases, where ABL is fully developed during daytime due to convection, with high turbulent activity and strong positive skewness indicating frequent and powerful updrafts. The cloud-topped cases showed the strong influence that clouds can have on ABL development, preventing it to reach the same maximum height and introducing top-down movements as an important contribution to mixing. The statistical analysis of turbulent sources allowed for finding a common diurnal cycle for convective mixing at both sites, but nocturnal wind shear driven turbulence with marked differences in its vertical distribution. This analysis demonstrates the Doppler lidar measurements and the classification algorithm strong potential to characterize the dynamics of ABL in its full extent and with high temporal resolution. Moreover, some recommendations for future improvement of the classification algorithm were provided on the basis of the experience gained.Fundacion Ramon ArecesEuropean Space Agency 4000119961/16/NL/FF/mgPolish National Science Centre (NCN) 2021/40/C/ST10/00023Spanish Government CGL2015-73250-JIN CGL201681092-R CGL2017-83538-C3-1-R CGL2017-90884-REDT PID2020117825GB-C21 PID2020-120015RB-100Andalusian Regional Government P18-RT-3820FEDER-UGR program ARNM-430-UGR20University of GranadaACTRIS-2 Research Infrastructure Project of the European Union's Horizon 2020 research and innovation program 654109European Cooperation in Science and Technology (COST) CA18235Universidad de Granada/CBU

Vertical characterization of fine and coarse dust particles during an intense Saharan dust outbreak over the Iberian Peninsula in springtime 2021

An intense and long-lasting Saharan dust outbreak crossed the Iberian Peninsula (IP) from the southwest (SW) to the northeast (NE) from 25 March until 7 April 2021. This work aims to assess the optical and mass contribution of both fine and coarse dust particles along their transport. Five Iberian lidar stations were monitoring the transport and evolution of the Saharan dust particles, i.e. El Arenosillo/Huelva, Granada, Torrejon/Madrid and Barcelona in Spain, and evora in Portugal. The particular meteorological conditions determined the aerosol scenario along the overall dust event, differing in the first part of the event (25-31 March), in which the strongest dust incidence occurred on 29-31 March at the south and central stations and 1 April at Barcelona, from the second one (1-7 April). The use of the two-step POLIPHON algorithm showed the relevance of using polarized lidar measurements for separating the aerosol properties of dust fine and coarse particles as an added value. Both the fine dust (Df) and coarse dust (Dc) components of the total particle backscatter coefficient (total dust, DD = Dc + Df) were separately derived. The dust plume was well-mixed with height and no significant differences were found in the vertical structure of both the Dc and Df particle backscatter coefficients. From the beginning of the dust outbreak until 1 April, the vertical Df / DD mass ratio was nearly constant in time at each station and also in altitude with values of & SIM; 10 %. Moreover, the mean dust optical depth at 532 nm was decreasing along that dust pathway, reporting values from SW to NE stations of 0.34 at El Arenosillo/Huelva, 0.28 at Granada, 0.20 at evora, 0.28 at Torrejon/Madrid, and 0.14 at Barcelona, although its Df / DD ratio remained almost constant (28 %-30 %). A similar pattern was found for the total dust mass loading and its Df / DD ratio, i.e. mostly decreasing mean mass values were reported, being constant in its Df / DD ratio (& SIM; 10 %) along the SW-NE dust pathway. In addition, the episode-mean centre-of-mass height increased with latitude overall, showing a high variability, being greater than 0.5 km at the southern sites (El Arenosillo/Huelva, Granada, evora) and & SIM; 1.0 km at Torrejon/Madrid and Barcelona. However, despite the relatively high intensity of the dust intrusion, the expected ageing of the dust particles was hardly observed, by taking into account the minor changes found in the contribution and properties of the coarse and fine dust particles. This is on the basis that the IP is relatively close to the Saharan dust sources and then, under certain dust transport conditions, any potential ageing processes in the dust particles remained unappreciated. The following must be highlighted: the different relative contribution of the fine dust particles to the total dust found for their optical properties (& SIM; 30 %) associated with the radiative effect of dust, with respect to that for the mass features (& SIM; 10 %) linked to air quality issues, along the overall dust event by crossing the IP.Ministry of Science and Innovation, Spain (MICINN) Spanish Government PID2019-104205GB-C21/AEI/10.13039/50110001103

Aerosol direct radiative effects of a transatlantic biomass burning plume over Granada, Spain

This work presents the assessment of the aerosol direct radiative effects for a special episode of transatlantic transport of a biomass burning plume, performed over Granada, south-eastern Iberian Peninsula, on 20th August 2007. The knowledge of aerosol radiative impact requires an accurate determination of their optical and microphysical properties, which are obtained here using ground-based remote sensing instrumentation by means of a combination of lidar and sun-photometer. Our data highlight the presence of a multilayered structure with a well-defined planetary boundary layer and biomass-particles in elevated layers, extending up to 9 km asl, at the south-eastern part of the Iberian Peninsula. The aerosol direct shortwave radiative effects, evaluated from simulations with SBDART code, show that the biomass burning plume increases the heating rate up to 0.5 K/day in spite of the small contribution of these particles to the total aerosol optical depth (10-20%). In addition, our results indicate that the biomass burning plume strengths the negative radiative forcing about -5 down to -8 W/m2 at the surface, between noon and evening. At the TOA, radiative forcing appeared slightly positive but very close to zero at noon, and negative in the evening with a decrease of 1.5 W/m2 caused by the presence of the biomass burning plume.Postprint (published version

Extreme Saharan dust event over the southern Iberian Peninsula in september 2007: active and passive remote sensing from surface and satellite

This study investigates aerosol optical properties during the extreme Saharan dust event detected from 3 to 7 September 2007 over Granada, southern Iberian Peninsula, with both active and passive remote sensing instrumentation from surface and satellite. The intensity of the event was visualized on the aerosol optical depth series obtained by the sun-photometer Cimel CE 318-4 operated at Granada in the framework of AERONET from August 2004 until December 2008 (level 2 data). A combination of large aerosol optical depth (0.86–1.50) at 500 nm, and reduced Angström exponent (0.1–0.25) in the range 440–870 nm, was detected on 6 September during daytime. This Saharan dust event also affected other Iberian Peninsula stations included in AERONET (El Arenosillo and Évora stations), and it was monitored by MODIS instrument on board Aqua satellite. Vertically resolved measurements were performed by a ground-based Raman Lidar and by CALIPSO satellite. During the most intense stage, on 6 September, maximum aerosol backscatter values were a factor of 8 higher than other maxima during this Saharan dust event. Values up to 1.5×10−2 km−1 sr−1 at 355 and 532 nm were detected in the layer with the greatest aerosol load between 3–4 km a.s.l., although aerosol particles were also detected up to 5.5 km a.s.l. In this stage of the event, dust particles at these altitudes showed a backscatter-related Angström exponent between –0.44 and 0.53 for the two spectral intervals considered. The results from different measurements (active/passive and ground-based/satellite) reveal the importance of performing multi-instrumental measurements to properly characterize the contribution of different aerosol types from different sources during extreme events. The atmospheric stabilization effect of the aerosol particles has been characterized by computing the solar heating rates using SBDART code.This work is supported by the Spanish Ministry of Education project CGL2007-66477-C02-01 and CSD2007-00067, by Andalusian Regional Government projects P06-RNM-01503 and P08-RNM-3568, and by the EARLINETASOS project (EU Coordination Action, contract No. 025991 (RICA))