scholarly journals Aerosol radiative effect during the summer 2019 heatwave produced partly by an inter-continental Saharan dust outbreak. 1. Shortwave dust-induced direct impact

2020 ◽  
Author(s):  
Carmen Córdoba-Jabonero ◽  
Michaël Sicard ◽  
María-Ángeles López-Cayuela ◽  
Albert Ansmann ◽  
Adolfo Comerón ◽  
...  
Keyword(s):  
Saharan Dust ◽  
Relative Mass ◽  
Radiative Effect ◽  
Centre Of Mass ◽  
Backscatter Coefficient ◽  
Radiative Impact ◽  
Total Particle ◽  
The Mean ◽  
Interaction Research ◽  
Major Data

Abstract. The shortwave (SW) direct radiative effect during the summer 2019 heatwave produced partly by a moderate, long-lasting Saharan dust outbreak over Europe is analysed in this study. Two European sites (periods) are considered: Barcelona, Spain, (23–30 June) and Leipzig, Germany (29–30 June). Major data are obtained from AERONET and MPLNET observations. Modelling is used to describe the different dust pathways. The dust coarse (Dc) and fine (Df) components (total dust, DD = Dc + Df) are separated in the profiles of the total particle backscatter coefficient using the POLIPHON method in synergy with MPLNET measurements. This information is used to calculate the relative mass loading and the centre-of-mass height, as well as the contribution of each dust mode to the DD radiative effect (DRE). The mean dust optical depth and its Df / DD ratios are, respectively, 0.153 and 24 % in Barcelona and 0.039 and 38 % in Leipzig. The dust produced a cooling effect on the surface with a daily mean DRE (Df / DD DRE ratio) of −9.1 W m−2 (37 %) in Barcelona and −2.5 W m−2 (52 %) in Leipzig. Although less intense than on surface, a cooling is also observed at the top-of-the-atmosphere (TOA), where the Df / DD DRE ratio is even though higher (45 % and 60 %, respectively, in Barcelona and Leipzig). Despite the predominance of Dc particles under dusty conditions, the SW radiative impact of Df particles can be comparable to, even higher than, that induced by the Dc ones. In particular, the Df / DD DRE ratio in Barcelona increases by +2.4 % (surface) and +2.9 % (TOA) day−1 along the dusty period. These results are especially relevant for the next ESA EarthCARE mission (planned in 2022), as devoted to aerosol-cloud-radiation interaction research.

scholarly journals Aerosol radiative impact during the summer 2019 heatwave produced partly by an inter-continental Saharan dust outbreak – Part 1: Short-wave dust direct radiative effect

2021 ◽  
Vol 21 (8) ◽  
pp. 6455-6479
Author(s):  
Carmen Córdoba-Jabonero ◽  
Michaël Sicard ◽  
María-Ángeles López-Cayuela ◽  
Albert Ansmann ◽  
Adolfo Comerón ◽  
...  
Keyword(s):  
Short Wave ◽  
Saharan Dust ◽  
Relative Mass ◽  
Radiative Effect ◽  
Backscatter Coefficient ◽  
Dust Transport ◽  
Total Dust ◽  
Radiative Impact ◽  
Total Particle ◽  
Transport Path

Abstract. The short-wave (SW) direct radiative effect (DRE) during the summer 2019 heatwave produced partly by a moderate, long-lasting Saharan dust outbreak over Europe is analysed in this study. Two European sites (periods) are considered: Barcelona, Spain (23–30 June), and Leipzig, Germany (29 and 30 June), 1350 km apart from each other. Major data are obtained from AERONET and polarised Micro-Pulse Lidar (P-MPL) observations. Modelling is used to describe the different dust pathways, as observed at both sites. The coarse dust (Dc) and fine dust (Df) components (with total dust, DD = Dc + Df) are identified in the profiles of the total particle backscatter coefficient using the POLIPHON (POlarisation LIdar PHOtometer Networking) method in synergy with P-MPL measurements. This information is used to calculate the relative mass loading and the centre-of-mass height, as well as the contribution of each dust mode to the total dust DRE. Several aspects of the ageing of dust are put forward. The mean dust optical depth and its Df/DD ratios are, respectively, 0.153 and 24 % in Barcelona and 0.039 and 38 % in Leipzig; this Df increase in Leipzig is attributed to a longer dust transport path in comparison to Barcelona. The dust produced a cooling effect on the surface with a mean daily DRE of −9.1 and −2.5 W m−2, respectively, in Barcelona and Leipzig, but the Df/DD DRE ratio is larger for Leipzig (52 %) than for Barcelona (37 %). Cooling is also observed at the top of the atmosphere (TOA), although less intense than on the surface. However, the Df/DD DRE ratio at the TOA is even higher (45 % and 60 %, respectively, in Barcelona and Leipzig) than on the surface. Despite the predominance of Dc particles under dusty conditions, the SW radiative impact of Df particles can be comparable to, even higher than, that induced by the Dc ones. In particular, the Df/DD DRE ratio in Barcelona increases by +2.4 % d−1 (surface) and +2.9 % d−1 (TOA) during the dusty period. This study is completed by a second paper about the long-wave and net radiative effects. These results are especially relevant for the next ESA EarthCARE mission (planned in 2022) as it is devoted to aerosol–cloud–radiation interaction research.

scholarly journals Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their Direct Radiative Effect

2014 ◽  
Vol 14 (18) ◽  
pp. 25533-25579 ◽  
Author(s):  
F. Peers ◽  
F. Waquet ◽  
C. Cornet ◽  
P. Dubuisson ◽  
F. Ducos ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Single Scattering ◽  
Saharan Dust ◽  
Aerosol Layer ◽  
Radiative Effect ◽  
East Atlantic ◽  
Aerosol Absorption ◽  
Cloud Optical Thickness ◽  
The Mean ◽  
Aerosol Properties

Abstract. The albedo of clouds and the aerosol absorption are key parameters to evaluate the direct radiative effect of an aerosol layer above clouds. While most of the retrievals of above clouds aerosol characteristics rely on assumptions on the aerosol properties, this study offers a new method to evaluate aerosol and cloud optical properties simultaneously (i.e. aerosol and cloud optical thickness, aerosol single scattering albedo and angström exponent). It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER – Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate the scattering aerosol optical thickness and the aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and the cloud optical thickness. In addition, a procedure has been developed to process the shortwave direct radiative effect of aerosols above clouds based on exact modeling. Besides the three case studies (i.e. biomass burning aerosols from Africa and Siberia and Saharan dust), both algorithms have been applied on the South East Atlantic Ocean and results have been averaged through August 2006. The mean direct radiative effect is found to be 33.5 W m−2. Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not much the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

scholarly journals Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect

2015 ◽  
Vol 15 (8) ◽  
pp. 4179-4196 ◽  
Author(s):  
F. Peers ◽  
F. Waquet ◽  
C. Cornet ◽  
P. Dubuisson ◽  
F. Ducos ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Case Studies ◽  
Biomass Burning ◽  
Optical Thickness ◽  
Single Scattering ◽  
Original Method ◽  
Saharan Dust ◽  
Radiative Effect ◽  
Cloud Optical Thickness ◽  
The Mean

Abstract. This study presents an original method to evaluate key parameters for the estimation of the direct radiative effect (DRE) of aerosol above clouds: the absorption of the the cloud albedo. It is based on multi-angle total and polarized radiances both provided by the A-train satellite instrument POLDER – Polarization and Directionality of Earth Reflectances. The sensitivities brought by each kind of measurements are used in a complementary way. Polarization mostly translates scattering processes and is thus used to estimate scattering aerosol optical thickness and aerosol size. On the other hand, total radiances, together with the scattering properties of aerosols, are used to evaluate the absorption optical thickness of aerosols and cloud optical thickness. The retrieval of aerosol and clouds properties (i.e., aerosol and cloud optical thickness, aerosol single scattering albedo and Ångström exponent) is restricted to homogeneous and optically thick clouds (cloud optical thickness larger than 3). In addition, a procedure has been developed to process the shortwave DRE of aerosols above clouds. Three case studies have been selected: a case of absorbing biomass burning aerosols above clouds over the southeast Atlantic Ocean, a Siberian biomass burning event and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies, both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. The mean DRE is found to be 33.5 W m−2 (warming). Finally, the effect of the heterogeneity of clouds has been investigated and reveals that it affects mostly the retrieval of the cloud optical thickness and not greatly the aerosols properties. The homogenous cloud assumption used in both the properties retrieval and the DRE processing leads to a slight underestimation of the DRE.

scholarly journals Radiative Effect and Mixing Processes of a Long-Lasting Dust Event over Athens, Greece, during the COVID-19 Period

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 318
Author(s):  
Panagiotis Kokkalis ◽  
Ourania Soupiona ◽  
Christina-Anna Papanikolaou ◽  
Romanos Foskinis ◽  
Maria Mylonaki ◽  
...  
Keyword(s):  
Atmospheric Pollutants ◽  
Saharan Dust ◽  
Radiative Effect ◽  
Atmospheric Conditions ◽  
Dust Event ◽  
Mixing Processes ◽  
Hysplit Model ◽  
European Continent ◽  
Dust Layer ◽  
Ground Based Lidar

We report on a long-lasting (10 days) Saharan dust event affecting large sections of South-Eastern Europe by using a synergy of lidar, satellite, in-situ observations and model simulations over Athens, Greece. The dust measurements (11–20 May 2020), performed during the confinement period due to the COVID-19 pandemic, revealed interesting features of the aerosol dust properties in the absence of important air pollution sources over the European continent. During the event, moderate aerosol optical depth (AOD) values (0.3–0.4) were observed inside the dust layer by the ground-based lidar measurements (at 532 nm). Vertical profiles of the lidar ratio and the particle linear depolarization ratio (at 355 nm) showed mean layer values of the order of 47 ± 9 sr and 28 ± 5%, respectively, revealing the coarse non-spherical mode of the probed plume. The values reported here are very close to pure dust measurements performed during dedicated campaigns in the African continent. By utilizing Libradtran simulations for two scenarios (one for typical midlatitude atmospheric conditions and one having reduced atmospheric pollutants due to COVID-19 restrictions, both affected by a free tropospheric dust layer), we revealed negligible differences in terms of radiative effect, of the order of +2.6% (SWBOA, cooling behavior) and +1.9% (LWBOA, heating behavior). Moreover, the net heating rate (HR) at the bottom of the atmosphere (BOA) was equal to +0.156 K/d and equal to +2.543 K/d within 1–6 km due to the presence of the dust layer at that height. On the contrary, the reduction in atmospheric pollutants could lead to a negative HR (−0.036 K/d) at the bottom of the atmosphere (BOA) if dust aerosols were absent, while typical atmospheric conditions are estimated to have an almost zero net HR value (+0.006 K/d). The NMMB-BSC forecast model provided the dust mass concentration over Athens, while the air mass advection from the African to the European continent was simulated by the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model.

scholarly journals Dynamic Asymmetries Do Not Match Spatiotemporal Step Asymmetries during Split-Belt Walking

Symmetry ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 1089
Author(s):  
Stefano Scarano ◽  
Luigi Tesio ◽  
Viviana Rota ◽  
Valeria Cerina ◽  
Luigi Catino ◽  
...  
Keyword(s):  
Lower Limb ◽  
Step Length ◽  
Centre Of Mass ◽  
Mean Velocity ◽  
Rehabilitation Research ◽  
Joint Dynamics ◽  
Stance Time ◽  
After Effect ◽  
The Mean ◽  
Step Parameters

While walking on split-belt treadmills (two belts running at different speeds), the slower limb shows longer anterior steps than the limb dragged by the faster belt. After returning to basal conditions, the step length asymmetry is transiently reversed (after-effect). The lower limb joint dynamics, however, were not thoroughly investigated. In this study, 12 healthy adults walked on a force-sensorised split-belt treadmill for 15 min. Belts rotated at 0.4 m s−1 on both sides, or 0.4 and 1.2 m s−1 under the non-dominant and dominant legs, respectively. Spatiotemporal step parameters, ankle power and work, and the actual mean velocity of the body’s centre of mass (CoM) were computed. On the faster side, ankle power and work increased, while step length and stance time decreased. The mean velocity of the CoM slightly decreased. As an after-effect, modest converse asymmetries developed, fading within 2–5 min. These results may help to decide which belt should be assigned to the paretic and the unaffected lower limb when split-belt walking is applied for rehabilitation research in hemiparesis.

scholarly journals The Electrical Activity of Saharan Dust as perceived from Surface Electric Field Observations in Greece

2020 ◽  
Author(s):  
Vasiliki Daskalopoulou ◽  
Sotirios A. Mallios ◽  
Zbigniew Ulanowski ◽  
George Hloupis ◽  
Anna Gialitaki ◽  
...  
Keyword(s):  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Field Enhancement ◽  
Electric Circuit ◽  
Saharan Dust ◽  
Backscatter Coefficient ◽  
Lidar System ◽  
Realistic Description ◽  
Atmospheric Conductivity

Abstract. We report on the electric field variations during Saharan dust advection over two atmospheric remote stations in Greece, using synergistic observations of the vertical atmospheric electric field strength (Ez) at ground and the lidar-derived particle backscatter coefficient profiles. Both parameters were monitored for the first time with the simultaneous deployment of a ground-based field mill electrometer and a multiwavelength lidar system. The field mill timeseries are processed to extract the diurnal variations of the Global Electric Circuit and remove fast field perturbations due to peak lightning activity. In order to identify the influence of the elevated dust layers on the ground Ez, we extract a Localized Reference Electric Field from the timeseries that reflects the local fair weather activity. Then, we compare it with the reconstructed daily average behaviour of the electric field and the Saharan dust layers' evolution, as depicted by the lidar system. Reported cases of enhanced vertical electric field for detached pure dust layers suggest the presence of in-layer electric charges. Although higher dust loads are expected to result in electric field enhancement, episodic cases that reduce the electric field are also observed. To quantitatively approach our results, we examine the dependency of Ez against theoretical assumptions for the distribution of separated charges within the electrified dust layer. Electrically neutral dust is approximated by atmospheric conductivity reduction, while charge separation areas within electrically active dust layers are approximated as finite extent cylinders. This physical approximation constitutes a more realistic description of the distribution of charges, as opposed to infinite extent geometries, and allows for analytical solutions of the electric field strength, so that observed electric field variations during the monitored dust outbreaks can be explained.

scholarly journals First observations of noctilucent clouds by lidar at Svalbard

2003 ◽  
Vol 3 (1) ◽  
pp. 521-549 ◽  
Author(s):  
J. Höffner ◽  
C. Fricke-Begemann ◽  
F.-J. Lübken
Keyword(s):  
Lower Thermosphere ◽  
Degree Of Saturation ◽  
Noctilucent Clouds ◽  
Backscatter Coefficient ◽  
Maximum Volume ◽  
Height Range ◽  
Large Variability ◽  
The North ◽  
The Mean ◽  
Bad Weather

Abstract. In summer 2001 a potassium lidar was installed near Longyearbyen (78° N) on the north polar island of Spitsbergen which is part of the archipelago Svalbard. At the same place a series of meteorological rockets ("falling spheres", FS) were launched which gave temperatures from the lower thermosphere to the stratosphere. The potassium lidar is capable of detecting noctilucent clouds (NLCs) and of measuring temperatures in the lower thermosphere, both under daylight conditions. In this paper we give an overview on the NLC measurements (the first at this latitude) and compare the results with temperatures from meteorological rockets which have been published recently (Lübken and Müllemann, 2003).. NLCs were observed from 12 June (the first day of operation) until 12 August when a period of bad weather started. When the lidar was switched on again on 26 August, no NLC was observed. The mean occurrence frequency in the period 12 June–12 August ("lidar NLC period") is 77%. The mean of all individual NLC peak altitudes is 83.6 km (variability: 1.1 km). The mean peak NLC altitude does not show a significant variation with season. The average top and bottom altitude of the NLC layer is 85.1 and 82.5 km, respectively, with a variability of ~1.2 km. The mean of the maximum volume backscatter coefficient ßmax at our wavelength of 770 nm is 3.9×10−10/m/sr with a large variability of +/−3.8×10−10/m/sr. Comparison of NLC characteristics with measurements at ALOMAR (69° N) shows that the peak altitude and the maximum volume backscatter coefficient are similar at both locations but NLCs occur more frequently at higher latitudes. Simultaneous temperature and NLC measurements are available for 3 flights and show that the NLC layer occurs in the lower part of the height range with super-saturation. The NLC peak occurs over a large range of degree of saturation (S) whereas most models predict the peak at S=1. This demonstrates that steady-state considerations may not be applicable when relating individual NLC properties to background conditions. On the other hand, the mean variation of the NLC appearance with height and season is in agreement with the climatological variation of super-saturation derived from the FS temperature measurements.

scholarly journals Two Novel Models Evaluating the Determinants of Resting Metabolic Rate in Indian Children

2021 ◽  
Author(s):  
Sandra Aravind Areekal ◽  
Anuradha Khadilkar ◽  
Veena Ekbote ◽  
Neha Kajale ◽  
Arun S. Kinare ◽  
...  
Keyword(s):  
Body Composition ◽  
Metabolic Rate ◽  
Resting Metabolic Rate ◽  
Childhood Development ◽  
Relative Mass ◽  
Kidney Volume ◽  
Indian Children ◽  
Cross Sectional ◽  
Multi Centre Study ◽  
The Mean

Abstract Resting metabolic rate (RMR) quantifies the minimal energy required to sustain vital body functions and is a crucial component of childhood development. While inter-individual variations in RMR have been studied for over a century they are poorly understood. Wang (Am. J. Hum., 2012) has modelled mean RMR per unit body mass (RMR/BM) in children grouped into age classes one year apart; this model is able to explain the variation in RMR/BM very accurately in a reference Caucasian dataset based on the relative masses of four major organs (liver, kidney, brain, heart) and the residual mass. However, it is not clear if it applies to other ethnicities, especially when the variation in the RMR is observed to be large in a population. Here we address the extent to which such a model can be adapted to explain RMR/BM in Indian children. Here we present two novel phenomenological models that describe the mean RMR/BM stratified by age in Indian children and adolescents, using data from the Multi-Centre Study (MCS) and RMR-USG. MCS is a cross-sectional dataset on 495 (235 girls) children aged 9 to 19 years with anthropometric, body composition and RMR measurements. RMR-USG consists of anthropometric data, RMR, and liver and kidney volume measured through ultrasonography in nine girls and nine boys aged 6 to 8 years. The mean RMR/BM in Indian children is observed to be significantly lower compared to their Caucasian counterparts, except in boys in the age groups 9 to 11 years and 12 to 13 years. The first is a modified Wang model in which the relative masses of four major organs are assumed to be uniformly lowered for Indian children. Theoretical predictions of size are not uniformly borne out in a pilot validation study, however, the relative mass of the kidney is indeed found to be significantly lower. We then present another version of the Wang model to demonstrate that changes in body composition alone can also explain the Indian data. Either model can be thus used phenomenologically to estimate mean RMR/BM by age in Indian children; however, understanding the mechanistic basis of variation in RMR/BM remains an open problem.

scholarly journals Assessment of aerosol's mass concentrations from measured linear particle depolarization ratio (vertically resolved) and simulations

2013 ◽  
Vol 6 (11) ◽  
pp. 3243-3255 ◽  
Author(s):  
A. Nemuc ◽  
J. Vasilescu ◽  
C. Talianu ◽  
L. Belegante ◽  
D. Nicolae
Keyword(s):  
Atmospheric Model ◽  
Saharan Dust ◽  
Depolarization Ratio ◽  
Backscatter Coefficient ◽  
Regional Atmospheric Model ◽  
Lidar Measurements ◽  
Multi Wavelength ◽  
Different Origins ◽  
Good Agreement ◽  
Mass Concentrations

Abstract. Multi-wavelength depolarization Raman lidar measurements from Magurele, Romania are used in this study along with simulated mass-extinction efficiencies to calculate the mass concentration profiles of different atmospheric components, due to their different depolarization contribution to the 532 nm backscatter coefficient. Linear particle depolarization ratio (δpart) was computed using the relative amplification factor and the system-dependent molecular depolarization. The low depolarizing component was considered as urban/smoke, with a mean δpart of 3%, while for the high depolarizing component (mineral dust) a mean δpart of 35% was assumed. For this study 11 months of lidar measurements were analysed. Two study cases are presented in details: one for a typical Saharan dust aerosol intrusion, 10 June 2012 and one for 12 July 2012 when a lofted layer consisting of biomass burning smoke extended from 3 to 4.5 km height. Optical Properties of Aerosols and Clouds software package (OPAC) classification and conversion factors were used to calculate mass concentrations. We found that calibrated depolarization measurements are critical in distinguishing between smoke-reach aerosol during the winter and dust-reach aerosol during the summer, as well as between elevated aerosol layers having different origins. Good agreement was found between lidar retrievals and DREAM- Dust REgional Atmospheric Model forecasts in cases of Saharan dust. Our method was also compared against LIRIC (The Lidar/Radiometer Inversion Code) and very small differences were observed.

scholarly journals Inter-comparison of lidar and ceilometer retrievals for aerosol and Planetary Boundary Layer profiling over Athens, Greece

2011 ◽  
Vol 4 (1) ◽  
pp. 73-99 ◽  
Author(s):  
G. Tsaknakis ◽  
A. Papayannis ◽  
P. Kokkalis ◽  
V. Amiridis ◽  
H. D. Kambezidis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Layer Structure ◽  
Saharan Dust ◽  
Radiosonde Data ◽  
Backscatter Coefficient ◽  
Lidar System ◽  
Height Range ◽  
Tropospheric Aerosol ◽  
Filter Radiometer

Abstract. This study presents an inter-comparison of two active remote sensors (lidar and ceilometer) in determining the structure of the Planetary Boundary Layer (PBL) and in retrieving tropospheric aerosol vertical profiles over Athens, Greece. This inter-comparison was performed under various strongly different aerosol concentrations (urban air pollution, biomass burning and Saharan dust event), implementing two different lidar systems (one portable Raymetrics S.A. lidar system running at 355 nm and one multi-wavelength Raman lidar system running at 355 nm, 532 nm and 1064 nm) and one CL31 Vaisala S.A. ceilometer (running at 910 nm). To convert the ceilometer data to data having the same wavelengths as those from the lidar, the backscatter-related Ångström exponent was estimated using ultraviolet multi-filter radiometer (UV-MFR) data. The inter-comparison was based on two parameters: the mixing layer structure and height determined by the presence of the suspended aerosols and the aerosol backscatter coefficient. Additionally, radiosonde data were used to derive the PBL height. In general a good agreement is found between the ceilometer and the lidar techniques in both inter-compared parameters in the height range from 500 m to 5000 m, while the limitations of each instrument are also examined.

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