Showing papers by "Lucas Alados-Arboledas published in 2023"

Atmospheric boundary layer height from ground-based remote sensing: a review of capabilities and limitations

Abstract: Abstract. The atmospheric boundary layer (ABL) defines the volume of air adjacent to the Earth's surface for the dilution of heat, moisture, and trace substances. Quantitative knowledge on the temporal and spatial variations in the heights of the ABL and its sub-layers is still scarce, despite their importance for a series of applications (including, for example, air quality, numerical weather prediction, greenhouse gas assessment, and renewable energy production). Thanks to recent advances in ground-based remote-sensing measurement technology and algorithm development, continuous profiling of the entire ABL vertical extent at high temporal and vertical resolution is increasingly possible. Dense measurement networks of autonomous ground-based remote-sensing instruments, such as microwave radiometers, radar wind profilers, Doppler wind lidars or automatic lidars and ceilometers are hence emerging across Europe and other parts of the world. This review summarises the capabilities and limitations of various instrument types for ABL monitoring and provides an overview on the vast number of retrieval methods developed for the detection of ABL sub-layer heights from different atmospheric quantities (temperature, humidity, wind, turbulence, aerosol). It is outlined how the diurnal evolution of the ABL can be monitored effectively with a combination of methods, pointing out where instrumental or methodological synergy are considered particularly promising. The review highlights the fact that harmonised data acquisition across carefully designed sensor networks as well as tailored data processing are key to obtaining high-quality products that are again essential to capture the spatial and temporal complexity of the lowest part of the atmosphere in which we live and breathe.

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

Abstract: Abstract. 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, Torrejón/Madrid and Barcelona in Spain, and Évora 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 ∼ 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 Évora, 0.28 at Torrejón/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 (∼ 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, Évora) and ∼ 1.0 km at Torrejón/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 (∼ 30 %) associated with the radiative effect of dust, with respect to that for the mass features (∼ 10 %) linked to air quality issues, along the overall dust event by crossing the IP.

Investigation of rainfall precursors using in-situ and remote sensing techniques in the southeast of the Iberian Peninsula

Abstract: Rainfall prediction is one of the most challenging and uncertain tasks in weather forecasting, which has a significant impact on human society. Detection of heavy rainfall trends may be masked or amplified by natural variability, and numerical weather prediction (NWP) models have difficulty to predict them accurately. Therefore, understanding of rainfall effects with the evolution of atmospheric parameters and seeking atmospheric precursors of rainfall for nowcasting or prediction become an urgent need.To date, most related studies have analyzed only a limited number of rain events or lacked long-term observations. This is likely to have a weak robustness. A multi-instrument and multi-parameter atmospheric monitoring system to detect precipitation precursors can improve the existing nowcasting system. AGORA (Andalusian Global ObseRvatory of the Atmosphere) is an ACTRIS facility located in the southeast of the Iberian Peninsula which offers unique infrastructure for the study of aerosol, clouds and precipitation. AGORA consists of two stations, an urban station located in the city of Granada (680 m asl) and a high-mountain station located in the National Park of Sierra Nevada (2580 m asl), separated by a horizontal distance of 20 km only. This infrastructure comprises state-of-the-art instrumentation covering active and passive remote sensing and in-situ techniques, including lidars, cloud radars, microwave radiometer, and weather stations. These instruments can obtain multiple atmospheric parameters (atmospheric water, aerosol, temperature, wind, etc.), including their vertical profiles.In this study, we investigate the potential of different atmospheric parameters from ground-based microwave radiometer, ceilometer, nephelometer, absorption photometer and weather stations for the nowcasting of rainfall. We use 694 rain events identified by microwave radiometer in the southeast of Iberian Peninsula to identify conditions favorable to trigger rainfall over 10 years, and to analyze how they are related to observed changes in water vapor and aerosol load and properties. The composite analysis is carried out in a long time interval of 8 hours before and 16 hours after rain, with the onset of rain serving as the time marker for this method. The aim of our study is to show the typical behavior of rainfall, to reveal the interaction of rainfall with atmospheric parameters, and to explore the precursors of rainfall.

Inter-relations of precipitation, aerosols, and clouds over Andalusia, Southern Spain revealed by the AGORA Observatory

Abstract: . The south-central interior of Andalusia experiences intricate precipitation patterns as a result of its semi-arid Mediterranean climate and the impact of Saharan dust and human-made pollutants. The primary aim of this study is to monitor the inter-relations between various factors, such as aerosols, clouds, and meteorological variables, and precipitation systems in Granada using ground-based remote sensing and in situ instruments including microwave radiometer, ceilometer, cloud radar, nephelometer, and weather station. The objective is to identify potential properties of precipitation in the region and in that 5 way improve precipitation forecasting. Over an 11-year period, we detected rain events using a physical retrieval method that employed microwave radiometer measurements. A composite analysis was applied to them to construct a climatology of the temporal evolution of precipitation. It was found that convective rain is the dominant precipitation type in Granada, accounting for 68% of the rain events. The height of the cloud base is mainly distributed at an altitude of 2 to 7 km. Integrated water vapor (IWV) and integrated cloud liquid water (ILW) increase rapidly before the onset of rain. Aerosol scattering at surface level and 10 hence the aerosol concentration is reduced during rain, and the predominant mean size distribution of aerosol particles before, during, and after rain is almost the same. A meteorological environment favorable for virga formation is observed in Granada. The surface weather station detected rainfall later than the microwave radiometer, indicating virga according to ceilometer and cloud radar data. We used rain-day events identified by weather station data to determine precipitation intensity classes and found that light rain is the main precipitation intensity class in Granada, accounting for 72% of the rain-day events. This can

Inter-relations of precipitation, aerosols, and clouds over Andalusia, Southern Spain revealed by the AGORA Observatory

Abstract: Abstract. The south-central interior of Andalusia experiences intricate precipitation patterns as a result of its semi-arid Mediterranean climate and the impact of Saharan dust and human-made pollutants. The primary aim of this study is to monitor the inter-relations between various factors, such as aerosols, clouds, and meteorological variables, and precipitation systems in Granada using ground-based remote sensing and in situ instruments including microwave radiometer, ceilometer, cloud radar, nephelometer, and weather station. The objective is to identify potential properties of precipitation in the region and in that way improve precipitation forecasting. Over an 11-year period, we detected rain events using a physical retrieval method that employed microwave radiometer measurements. A composite analysis was applied to them to construct a climatology of the temporal evolution of precipitation. It was found that convective rain is the dominant precipitation type in Granada, accounting for 68 % of the rain events. The height of the cloud base is mainly distributed at an altitude of 2 to 7 km. Integrated water vapor (IWV) and integrated cloud liquid water (ILW) increase rapidly before the onset of rain. Aerosol scattering at surface level and hence the aerosol concentration is reduced during rain, and the predominant mean size distribution of aerosol particles before, during, and after rain is almost the same. A meteorological environment favorable for virga formation is observed in Granada. The surface weather station detected rainfall later than the microwave radiometer, indicating virga according to ceilometer and cloud radar data. We used rain-day events identified by weather station data to determine precipitation intensity classes and found that light rain is the main precipitation intensity class in Granada, accounting for 72 % of the rain-day events. This can be a result of the high tropospheric temperature induced by the Andalusian climate and the reduction of cloud droplet size by the high availability of aerosol particles in the urban atmosphere. This study provides evidence that aerosols, clouds, and meteorological variables have a combined impact on precipitation which can be considered for water resource management and improving rain forecasting accuracy.