Jesús Abril-Gago’s research while affiliated with University of Granada and other places

Mineral dust has a key role in the Earth's radiative balance, and it has become significant over the Iberian Peninsula (IP), where Saharan dust outbreaks have seemed to increase in frequency and intensity. This study quantifies the dust direct radiative effect (DRE) in the short-wave range (SW) during an intense persistent springtime dust episode over the IP. In particular, the vertical distribution of dust optical properties was derived at five lidar stations, and the Global Atmospheric Model (GAME) was used for radiative transfer simulations. Moreover, this study innovates by simulating the SW DRE using two distinct methodologies. The novel approach separates the impacts of fine (Df) and coarse (Dc) dust components and calculates the total DRE as their combined sum. In contrast, the commonly used approach directly simulates the DRE for the total dust. Along the dust pathway crossing the IP, the SW DRE consistently registered a pattern of aerosol-induced cooling at both the surface, i.e the bottom of the atmosphere (BOA), and top of the atmosphere (TOA). Results reveal that the role of Df must be highlighted, as Df particles contributed nearly half of the total SW DRE at BOA and TOA, particularly for this event. DRE simulations based on the separation of dust modes for solar zenith angles < 70° show that nearly 75 % of DRE values are lower (in absolute value) with respect to those obtained by considering the total dust. That is, a less pronounced cooling effect is observed overall when the separation of dust modes is taken into account, although relative differences between approaches are not highly significant in general (-3 % and -6 % on average at BOA and TOA, respectively). However, this behaviour reverses under moderate-to-high-dust conditions when the contributions of the Dc and Df components are considered separately; i.e. dust induces a more pronounced cooling effect. This indicates the relevant role of the fine dust particles in DRE estimations, which is likely underestimated when total dust (no separation) is taken into account in relatively high-dust environments. In addition, the cooling effect is more evident at TOA than at BOA, probably due to the presence of dust at higher levels than those usual in the troposphere. This fact can introduce relevant implications for radiometric measurements from satellite instrumentation.

Between 14 March and 21 April 2022, an extensive investigation of an extraordinary Saharan dust intrusion over Europe was performed based on lidar measurements obtained by the European Aerosol Research Lidar Network (EARLINET). The dust episode was divided into two distinct periods, one in March and one in April, characterized by different dust transport paths. The dust aerosol layers were studied over 18 EARLINET stations, examining aerosol characteristics during March and April in four different regions (M-I, M-II, M-III, and M-IV and A-I, A-II, A-III, and A-IV, respectively), focusing on parameters such as aerosol layer thickness, center of mass (CoM), lidar ratio (LR), particle linear depolarization ratio (PLDR), and Ångström exponents (ÅE). In March, regions exhibited varying dust geometrical and optical properties, with mean CoM values ranging from approximately 3.5 to 4.8 km, and mean LR values typically between 36 and 54 sr. PLDR values indicated the presence of both pure and mixed dust aerosols, with values ranging from 0.20 to 0.32 at 355 nm and 0.24 to 0.31 at 532 nm. ÅE values suggested a range of particle sizes, with some regions showing a predominance of coarse particles. Aerosol Optical Depth (AOD) simulations from the NAAPS model indicated significant dust activity across Europe, with AOD values reaching up to 1.60. In April, dust aerosol layers were observed between 3.2 to 5.2 km. Mean LR values typically ranged from 35 to 51 sr at both 355 nm and 532 nm, while PLDR values confirmed the presence of dust aerosols, with mean values between 0.22 and 0.31 at 355 nm and 0.25 to 0.31 at 532 nm. The ÅE values suggested a mixture of particle sizes. The AOD values in April were generally lower, not exceeding 0.8, indicating a less intense dust presence compared to March. The findings highlight spatial and temporal variations in aerosol characteristics across the regions, during the distinctive periods. From 15 to 16 March 2022, Saharan dust significantly reduced UV-B radiation by approximately 14% over the ATZ station (Athens, GR). Backward air mass trajectories showed that the dust originated from the Western and Central Sahara when, during this specific case, the air mass trajectories passed over GRA (Granada, ES) and PAY (Payerne, CH) before reaching ATZ, maintaining high relative humidity and almost stable aerosol properties throughout its transport. Lidar data revealed elevated aerosol backscatter (baer) and PLDR values, combined with low LR and ÅE values, indicative of pure dust aerosols.

This work aimed to study the atmospheric boundary layer height (ABLH) from COSMIC-2 refractivity data, endeavoring to refine existing ABLH detection algorithms and scrutinize the resulting spatial and seasonal distributions. Through validation analyses involving different ground-based methodologies (involving data from lidar, ceilometer, microwave radiometers, and radiosondes), the optimal ABLH determination relied on identifying the lowest refractivity gradient negative peak with a magnitude at least τ% times the minimum refractivity gradient magnitude, where τ is a fitting parameter representing the minimum peak strength relative to the absolute minimum refractivity gradient. Different τ values were derived accounting for the moment of the day (daytime, nighttime, or sunrise/sunset) and the underlying surface (land or sea). Results show discernible relations between ABLH and various features, notably, the land cover and latitude. On average, ABLH is higher over oceans (≈1.5 km), but extreme values (maximums > 2.5 km, and minimums < 1 km) are reached over intertropical lands. Variability is generally subtle over oceans, whereas seasonality and daily evolution are pronounced over continents, with higher ABLHs during daytime and local wintertime (summertime) in intertropical (middle) latitudes.

Mineral dust has a key role in the Earth’s radiative balance, and it has become significant over the Iberian Peninsula (IP), where Saharan dust outbreaks seem to increase in frequency and intensity. This study quantifies the dust direct radiative effect (DRE) in the short-wave range (SW), during an intense persistent springtime dust episode over the IP. A long-term analysis (14 days) was performed over five lidar stations. The vertical distribution of dust optical properties was derived, finding a wide dynamic range of aerosol concentration that allowed a suitable statistical study. The Global Atmospheric Model (GAME) was used for radiative transfer simulations. This study innovates by simulating the SW DRE using two distinct methodologies, finding differences between both approaches. The novel approach separates the impact of both fine (Df) and coarse (Dc) dust components and calculates the total DRE as their combined sum. In contrast, the approach commonly used directly simulates the DRE for the total dust as a whole. Across the dust pathway along the IP, the SW DRE consistently registered a pattern of aerosol-induced cooling at both surface (BOA) and top-of-the-atmosphere (TOA). Results agree with the fact that the Df role cannot be disregarded, that is primarily responsible for SW radiative modulation. In particular, Df contributed nearly half of the total DRE at BOA and TOA in this event. In addition, the Df-to-total ratio influences the differences in DRE obtained by comparing both methodologies, being higher when the differences of the asymmetry factor at 440 nm between the fine and total dust component are greater than a value of 0.1.

In 2018, the European Space Agency launched the first Doppler wind lidar system into space, providing wind observation profiles from the lower stratosphere down to the surface in two different channels based on the scene classification: cloudy or clear. A statistical validation campaign of Aeolus wind products has been performed with a ground-based Doppler lidar system and radiosondes at the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS)–Andalusian Global ObseRvatory of the Atmosphere (AGORA) facility in Granada (Spain). The validation activities with the automatic ground-based lidar system lasted from July 2019 to the orbit shift of June 2021. Aeolus data from two different processing baselines (10 and 11) were validated with 30 min averages of coincident ground-based lidar measurements, using a 100 km horizontal spatial collocation criterion. This resulted in 109 collocations and a mean observation distance from the ground-based lidar system of ∼50 km. The comparison did not raise any significant over- or underestimation of Aeolus horizontal line-of-sight wind speed during that period for the Rayleigh-clear and Mie-cloudy configurations. However, the ground-based lidar measurements were limited to the lower 3.5 km of the atmosphere and, consequently, the obtained results. Multiple analyses were performed varying the criteria of maximum distance and the average period for the ground-based lidar measurements in order to confirm the reliability of the criteria considered. A separate study was performed with Aeolus products after the orbit shift (baseline 12) with different collocation criteria (mean observation distance of ∼75 km, to the station), from July 2021 to May 2022. A set of seven radiosondes were launched with the aim of increasing their coincidence in space and time with the satellite overpass (∼30 min before). The radiosondes could provide full vertical coverage of Aeolus profiles (from the surface up to ∼20 km above sea level), and the comparison did not yield any significant over- or underestimation of the Rayleigh-clear wind speed, while the Mie-cloudy wind speed was significantly overestimated. Multiple analyses were performed in order to test how the spatiotemporal collocation of the radiosonde affected the results. Radiosondes not ideally collocated were proven to still be useful for comparison with the Rayleigh-clear observations but not with the Mie-cloudy observations.

Three volcanic plumes were detected during the Tajogaite volcano eruptive activity (Canary Islands, Spain, September–December 2021) over the Iberian Peninsula. The spatiotemporal evolution of these events is characterised by combining passive satellite remote sensing and ground-based lidar and sun-photometer systems. The inversion algorithm GRASP is used with a suite of ground-based remote sensing instruments such as lidar/ceilometer and sun-photometer from eight sites at different locations throughout the Iberian Peninsula. Satellite observations showed that the volcanic ash plumes remained nearby the Canary Islands covering a mean area of 120 ± 202 km2 during the whole period of eruptive activity and that sulphur dioxide plumes reached the Iberian Peninsula. Remote sensing observations showed that the three events were mainly composed of sulphates, which were transported from the volcano into the free troposphere. The high backscatter-related Ångström exponents for wavelengths 532–1064 nm (1.17 ± 0.20 to 1.40 ± 0.24) and low particle depolarization ratios (0.08 ± 0.02 to 0.09 ± 0.02), measured by the multi-wavelength Raman lidar, hinted at the presence of spherical small particles. The layer aerosol optical depth at 532 nm (AODL532) obtained from lidar measurements contributed between 49% and 82% to the AERONET total column AOD at 532 nm in event II (11–13 October). According to the GRASP retrievals, the layer aerosol optical depth at 440 nm (AODL440) was higher in all sites during event II with values between 0.097 (Badajoz) and 0.233 (Guadiana-UGR) and lower in event III (19–21 October) varying between 0.003 (Granada) and 0.026 (Évora). Compared with the GRASP retrievals of total column AOD at 440nm, the AODL440 had contributions between 21% and 52% during event II. In the event I (25–28 September), the mean volume concentrations (VC) varied between 5 ± 4 μm3cm-3 (El-Arenosillo/Huelva) and 17 ± 10 μm3cm-3 (Guadiana-UGR), while in event II this variation was from 11 ± 7 μm3cm-3 (Badajoz) to 27 ± 10 μm3cm-3 (Guadiana-UGR). Due to the impact of volcanic events on atmospheric and economic fields, such as radiative forcing and airspace security, a proper characterization is required. This work undertakes it using advanced instrumentation and methods.