On the Sensitivity of a Ground-Based Tropospheric Lidar to Aitken Mode Particles in the Upper Troposphere

Airborne observations have shown high concentrations of ultrafine aerosols in the Amazon upper troposphere (UT), which are key for replenishing the planetary boundary layer (PBL) with cloud condensation nuclei that sustain the “green ocean” clouds. Given their climatic relevance, longterm observations are needed, but aircraft measurements are only available in short-term campaigns. Alternatively, continuous observations of the aerosol vertical structure could be performed by a lidar (acronym for “light detection and ranging”) system in long-term campaigns. Here we assess whether a ground-based tropospheric lidar system could detect these ultrafine UT aerosols. To this aim, we simulated the lidar signal of a real instrument and then varied the instrument’s efficiency and the UT-particle concentration to determine under which conditions the detection is possible. Optical properties were computed with a Mie code based on the size distributions and numerical concentration profiles measured by the aircraft, and on the refractive indexes inverted from AERONET measurements. The aerosol optical depth (AOD) was retrieved by inverting the elastic lidar signal, and a statistical test was applied to evaluate the detection of the UT-aerosol layer. Our results indicate that, for the instrument we simulated, a 55-fold increase in the signal-to-noise ratio (SNR) is required for a 100% detection rate. This could be achieved by simultaneously time averaging over 30 min and spatially averaging to vertical bin lengths of 375 m, or by modifying the hardware. We repeated the analysis for under- and overestimated aerosol lidar ratio (Laer), and found that possible systematic errors did not affect the detection rate. Further studies are necessary to assess whether such longtime averages are feasible in the Amazon region (given the very high cloud cover), and to design a hardware upgrade. Although simulations and analyses here were based on a particular instrument and for the presence of new organic particles in the Amazonian upper troposphere, our methodology and results are general and applicable to other instruments and sites.Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 132402/2020-3 308682/2017-

Wind and Turbulence Statistics in the Urban Boundary Layer over a Mountain–Valley System in Granada, Spain

Urban boundary layer characterization is currently a challenging and relevant issue, because of its role in weather and air quality modelling and forecast. In many cities, the effect of complex topography at local scale makes this modelling even more complicated. This is the case of mid-latitude urban areas located in typical basin topographies, which usually present low winds and high turbulence within the atmospheric boundary layer (ABL). This study focuses on the analysis of the first ever measurements of wind with high temporal and vertical resolution throughout the ABL over a medium-sized city surrounded by mountains in southern Spain. These measurements have been gathered with a scanning Doppler lidar system and analyzed using the Halo lidar toolbox processing chain developed at the Finnish Meteorological Institute. We have used the horizontal wind product and the ABL turbulence classification product to carry out a statistical study using a two-year database. The data availability in terms of maximum analyzed altitudes for statistically significant results was limited to around 1000–1500mabove ground level (a.g.l.) due to the decreasing signal intensity with height that also depends on aerosol load. We have analyzed the differences and similarities in the diurnal evolution of the horizontal wind profiles for different seasons and their modelling with Weibull and von Mises probability distributions, finding a general trend of mean daytime wind from the NW with mean speeds around 3–4 m/s at low altitudes and 6–10 m/s at higher altitudes, and weaker mean nocturnal wind from the SE with similar height dependence. The highest speeds were observed during spring, and the lowest during winter. Finally, we studied the turbulent sources at the ABL with temporal (for each hour of the day) and height resolution. The results show a clear convective activity during daytime at altitudes increasing with time, and a significant wind-shear-driven turbulence during night-time.Spanish Government FPU14/03684Ministerio de Asusntos Economicos y Transformacion Digital CGL2016-81092-R CGL2017-83538-C3-1-R CGL2017-90884-REDT PID2020-120015RB-I00 PID2020.117825GB.C21Junta de Andalucia A-RNM-430-UGR20 P18-RT-3820 P20-00136Horizon 2020 Framework Programme of the European Union 654109European Cooperation in Science and Technology (COST) ES1303 CA18235Erasmus + Programme of the European UnionFundacion Ramon ArecesPolish National Science Centre (NCN) 2021/40/C/ST10/00023Excellence Units Program of the University of Granada 'Programa 7' of 'Plan Propio' of the University of Granad

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

Modelling an exceptional desert dust transport toward Portugal on February 2017

The terrain surrounding the Sahara desert is formed by some mountains ranges, as the Atlas mountain system in the northern edge of the desert and the Hoggar Mountains in Southern Algeria. Such orography, jointly with atmospheric circulation, plays an important role in the mobilization and transport of desert dust over medium and large distances. This study explores the interaction between complex terrain and atmospheric circulation in order to better understand an exceptional desert dust outbreak affecting Portugal in February 2017. The Meso-NH model is able to represent the atmospheric motions in different scales, and has been implemented with a rather complete parametrization package of physical processes in the atmosphere. The capability of the model to simulate dust emission is also explored. The on-line dust emission parametrization type is taken from the distribution of emitted dust of SURFEX with no need to use chemistry to activate dusts. A set of two simulations was performed for the period between 16 February at 0000 UTC to 24 February 1200 UTC, with the Meso-NH model configured in a single domain at 10 km horizontal resolution and 300x360 grid points. The experiments were defined as a) control experiment (CTRL), and b) dust experiment (DUST). From the large domain simulations, it was possible to assess the source of dust and its mobilization over Western Sahara desert, namely over the Northern part of Mauritania and Mali and Eastern part of Algeria. The formation of a cyclonic circulation at the surface favoured the dust uplifting. Such a surface low merged with a cut-off low that moved southward over the Iberian Peninsula and remained centred in the north of Morocco. Such pattern intensified the northward flow found at 700 hPa toward the Atlas Mountains range, inducing the dust transport above 3 km altitude. As expected, the simulations showed the ability to assess important details about the atmospheric circulation not resolved by low density of observations over the domain considered. Furthermore, the simulations were able to show the way that the atmospheric ingredients were brought together to produce the exceptional transport of desert dust toward Portugal. The orographic effects playing an important role in dust mobilization (convergence and cyclogenesis at the surface) and atmospheric circulation to the maintenance of the dust transport have been highlighted. Such event were responsible for the transport of high amount of dust toward the Iberian Peninsula

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

Estimating the urban atmospheric boundary layer height from remote sensing applying machine learning techniques

This work was supported by the Spanish Ministry of Economy and Competitiveness through projects CGL2015- 73250-JIN, CGL2016-81092-R, CGL2017-83538-C3-1-R ,CGL2017-90884-REDT and PID2020-120015RB-I00 and by the University of Granada through “Plan Propio. Programa 9 Convocatoria 2013. The financial support for EARLINET in the ACTRIS Research Infrastructure Project by the European Union’s Horizon 2020 research and innovation program through project ACTRIS-2 (grant agreement No 654109). The authors thankfully acknowledge the FEDER program for the instrumentation used in this work and the University of Granada that supported this study through the Excellence Units Program. COST Action TOPROF (ES1303), supported by497 COST (European Cooperation in Science and Technology), is also acknowledged.This study proposes a new methodology to estimate the Atmospheric Boundary Layer Height (ABLH), discriminating between Convective Boundary Layer and Stable Boundary Layer heights, based on the machine learning algorithm known as Gradient Boosting Regression Tree. The algorithm proposed here uses a first estimation of the ABLH derived applying the gradient method to a ceilometer signal and several meteorological variables to obtain ABLH values comparable to those derived from a microwave radiometer. A deep analysis of the model configuration and its inputs has been performed in order to avoid the model overfitting and ensure its applicability. The hourly and seasonal values and variability of the ABLH values obtained with the new algorithm have been analyzed and compared with the initial estimations obtained using only the ceilometer signal. Mean Relative Errors (MRE) between the ABLH estimated with the new algorithm and microwave radiometer show a daily pattern with their highest values during the night-time (stable situations) and their lowest values along the day-time (convective situations). This pattern has been observed for all the seasons with MRE ranging between −5% and 35%. This result notably improves those ABLH values derived by applying the gradient method to ceilometer data during convective situations and enables the Stable Boundary Layer height detection at night and early morning, instead of only Residual Layer top height. Finally, the model performance has been directly validated in three particular cases: clear-sky day, presence of low-clouds and dust outbreak event. In these three particular situations, ABLH values obtained with the new algorithm follow the pattern obtained with the microwave radiometer presenting very similar values, thus confirming the good model performance. In this way it is feasible by the combination of the proposed method with gradient method, to estimate Convective, Stable and Residual Boundary Layer height from ceilometer data and surface meteorological data in extended network that include ceilometer profiling.Spanish Ministry of Economy and Competitiveness through projects CGL2015-73250-JIN, CGL2016-81092-R, CGL2017-83538-C3-1-R, CGL2017-90884-REDT and PID2020-120015RB-I00COST Action TOPROF (ES1303), supported by COST (European Cooperation in Science and Technology

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

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

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)