Suchergebnisse

Attenuated backscatter measurements from a Vaisala CL31 ceilometer and a modified form of the well-known slope method are used to derive the ceilometer extinction profiles during rain events, restricted to rainfall rates (RRs) below approximately 10 mm/h. RR estimates from collocated S-band radar and portable disdrometer are used to derive the RR-to-extinction correlation models for the ceilometer-radar and ceilometer-disdrometer combinations. Data were collected during an intensive observation period of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE) conducted in northern Alabama. These models are used to estimate the RR from the ceilometer observations in similar situations that do not have collocated radar or the disdrometer. Such correlation models are, however, limited by the different temporal and spatial resolutions of the measured variables, measurement capabilities of the instruments, and the inherent assumption of a homogeneous atmosphere. An empirical method based on extinction and RR uncertainty scoring and covariance fitting are proposed to solve, in part, these limitations. ; This work was supported by the National Oceanic and Atmospheric Administration (NOAA) under Grant NA1501R4590232 and Grant NA16OAR4590209 and by the Department of Earth, Atmospheric, and Planetary Sciences, Purdue University. CommSensLab-Universitat Politècnica de Catalunya (UPC) (which is a María de Maeztu Excellence Unit funded by the Agencia Estatal de Investigación, Spain; MDM-2016-0600) collaborated via Spanish Government - European Regional Development Funds under PGC2018-094132-B-I00 and TEC2015- 63832-P projects, and via European Union (funds) (EU) Funds under Grant H2020 ACTRIS-2 (GA-654109) and Grant ACTRIS-PPP (GA-739530). The work of Rubén Barragán was supported by the Spanish Ministry of Science, Innovation and Universities under Grant BES-2013-066340. ; Peer Reviewed ; Postprint (published version)

Relative humidity (RH) profiling using Raman lidars requires simultaneous range-resolved temperature and pressure data that are not always available. We propose and assess a method based on the use of a locally retrieved atmospheric model to estimate the temperature and pressure profiles. This model relies on the data from daily radiosonde launches at Barcelona during a five-year-long period (2015-2019). We have computed the range-resolved error of the model compared with the radiosonde ``true'' temperature profiles. Then, we have calculated the induced uncertainty in the recalculated RH profiles, finding that the standard deviation at 5 km is <15% for more than 80% of the radiosoundings. We have applied the method to a set of lidar measurements. We have first compared the resulting profiles with lidar retrievals using radiosonde temperatures, and we found differences that are compatible with the previous statistical analysis. We also compared them with in situ radiosonde humidity measurements, finding, in this case, bigger differences due to additional sources of error. Uncertainty analysis shows that the temperature model is the most significant error source below 4-5 km. For higher altitudes, the noise of the Raman signals may become the main contribution. We show that the resulting uncertainty (commonly <15% below 5 km) is compatible with the statistical analysis of the model and comparable with the ones obtained using other instruments for temperature profiling. We show that this method permits nocturnal lidar-based RH profiling with uncertainty estimation without the need for measured atmospheric profiles. ; This work was supported by the European Union H2020 program (grant agreement no. 654109, 778349), the Spanish Ministry of Economy and Competitivity (ref. TEC2015- 63832-P), the Spanish Ministry of Science and Innovation (ref. PID2019- 103886RB-I00, CGL2017-90884-REDT), the Department of Economy and Knowledge of the Catalan autonomous government (grant 2014 SGR583), the Unity of Excellence Maria de Maeztu (ref. MDM-2016-0600), which is financed by the Agencia Estatal de Investigación (AEI) and the Juan de la Cierva-Formación Program (grant FJCI-2015-23904). ; Peer Reviewed ; Postprint (author's final draft)

It is known that the retrieval of aerosol extinction and backscatter coefficients from lidar data acquired through so-called total-power channels – intended to measure the backscattered power irrespective of the polarization – can be adversely affected by varying depolarization effects produced by the aerosol under measurement. This effect can be particularly noticeable in advanced multiwavelength systems, where different wavelengths are separated using a system of dichroic beam splitters, because in general the reflection and transmission coefficients of the beam splitters will be different for fields with polarization parallel or perpendicular to the incidence plane. Here we propose a setup for multiwavelength aerosol lidars alleviating diattenuation effects due to changing depolarization conditions while allowing measure linear depolarization. ; This work has been supported by the following projects and grants: European Union 7th Framework Programme grant agreement No. 262254 (ACTRIS), Spanish Ministry for Economy and Competitiveness grants TEC2012-34575 and UNPC10-4E-442, and by the Catalan Agency for Support to Universities and Research (AGAUR) grant 2014 SGR 583. ; Peer Reviewed ; Postprint (published version)

An unprecedented extreme Saharan dust event was registered in winter time from 20 to 23 February 2017 over the Iberian Peninsula (IP). We report on aerosol optical properties observed under this extreme dust intrusion through passive and active remote sensing techniques. For that, AERONET (AErosol RObotic NETwork) and EARLINET (European Aerosol Research LIdar NETwork) databases are used. The sites considered are: Barcelona (41.38°N, 2.17°E), Burjassot (39.51°N, 0.42°W), Cabo da Roca (38.78°N, 9.50°W), Évora (38.57°N, 7.91°W), Granada (37.16°N, 3.61°W) and Madrid (40.45°N, 3.72°W). Large aerosol optical depths (AOD) and low Ångström exponents (AE) are observed. An AOD of 2.0 at 675 nm is reached in several stations. A maximum peak of 2.5 is registered in Évora. During and around the peak of AOD, AEs close to 0 and even slightly negative are measured. With regard to vertically-resolved aerosol optical properties, particle backscatter coefficients as high as 15 Mm−1 sr−1 at 355 nm are recorded at the lidar stations. Layer-mean lidar ratios are found in the range 40–55 sr at 355 nm and 34–61 sr at 532 nm during the event. The particle depolarization ratios are found to be constant inside the dust layer, and consistent from one site to another. Layer-mean values vary in the range 0.19–0.31. Another remarkable aspect of the event is the limited vertical distribution of the dust plume which never exceeds 5 km. The extreme aspect of the event also presented a nice case for testing the ability of two dust forecast models, BSC-DREAM8b and NMMB/BSC-Dust, to reproduce the arrival, the vertical distribution and the intensity of the dust plume over a long-range transport region. In the particular case of the February 2017 dust event, we found a large underestimation in the forecast of the extinction coefficient provided by BSC-DREAM8b at all heights independently of the site. In contrast NMMB/BSC-Dust forecasts presented a better agreement with the observations, especially in southwestern part of the IP. With regard to the forecast skill as a function of lead time, no clear degradation of the prognostic is appreciated at 24, 48 and 72 h for Évora and Granada stations (South). However the prognostic does degrade (bias increases and/or correlation decreases) for Barcelona (North), which is attributed to the fact that Barcelona is at a greater distance from the source region and to the singularity of the event. ; The research leading to these results has received funding from the H2020 program from the European Union (grant agreement no. 654109, 778349) and also from the Spanish Ministry of Industry, Economy and Competitiviness (MINECO, ref. CGL2013-45410-R, CGL2016-81092-R, CGL2017-85344-R, TEC2015-63832-P), the Spanish Ministry of Science, Innovation and Universities (ref. CGL2017-90884-REDT); the CommSensLab "Maria de Maeztu" Unity of Excellence (ref. MDM-2016-0600) financed by the Spanish Agencia Estatal de Investigación. Co-funding was also provided by the European Union through the European Regional Development Fund (ref. POCI-01-0145-FEDER-007690, ALT20-03-0145-FEDER-000004, ALT20-03-0145-FEDER-000011); by the Andalusia Regional Government (ref. P12-RNM-2409); by the Madrid Regional Government (projects TIGAS-CM, ref. Y2018/EMT-5177 and AIRTEC-CM, ref. P2018/EMT4329); by the University of Granada through "Plan Propio. Programa 9 Convocatoria 2013" and by the Portuguese Foundation for Science and Technology and national funding (ref. SFRH/BSAB/143164/2019). The BSC-DREAM8b and NNMB/BSC-Dust (now NMMB-MONARCH) model simulations were performed by the Mare Nostrum supercomputer hosted by the Barcelona Supercomputer Center (BSC). S. Basart acknowledges the AXA Research Fund for supporting aerosol research at the BSC through the AXA Chair on Sand and Dust Storms Fund, as well as the InDust project (COST Action CA16202). The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.ready.noaa.gov) used in this publication. ; Peer Reviewed ; Postprint (published version)