[Show abstract][Hide abstract] ABSTRACT: New calculations of the relative optical air mass function are made over the 0°–87° range of apparent solar zenith angle θ, for various vertical profiles of background aerosol, diamond dust and thin cirrus cloud particle extinction coefficient in the Arctic and Antarctic atmospheres. The calculations were carried out by following the Tomasi and Petkov (2014) procedure, in which the above-mentioned vertical profiles derived from lidar observations were used as weighting functions. Different sets of lidar measurements were examined, recorded using: (i) the Koldewey-Aerosol-Raman Lidar (KARL) system (AWI, Germany) at Ny-Ålesund (Spitsbergen, Svalbard) in January, April, July and October 2013; (ii) the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite-based sensor over Barrow (Alaska), Eureka (Nunavut, Canada) and Sodankylä (northern Finland), and Neumayer III, Mario Zucchelli and Mirny coastal stations in Antarctica in the local summer months of the last two years; (iii) the National Institute of Optics (INO), National Council of Research (CNR) Antarctic lidar at Dome C on the Antarctic Plateau for a typical “diamond dust” case; and (iv) the KARL lidar at Ny-Ålesund and the University of Rome/National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) lidar at Thule (northwestern Greenland) for some cirrus cloud layers in the middle and upper troposphere. The relative optical air mass calculations are compared with those obtained by Tomasi and Petkov (2014) to define the seasonal changes produced by aerosol particles, diamond dust and cirrus clouds. The results indicate that the corresponding air mass functions generally decrease as angle θ increases with rates that are proportional to the increase in the pure aerosol, diamond dust and cirrus cloud particle optical thickness.
[Show abstract][Hide abstract] ABSTRACT: Aerosol optical properties have been measured on the island of Lampedusa (35.5°N, 12.6°E) with seven-band multifilter rotating shadowband radiometers (MFRSRs) and a CE 318 Cimel sunphotometer (part of the AERONET network) since 1999. Four different MFRSRs have operated since 1999. The Cimel sunphotometer has been operational for a short period in 2000 and in 2003–2006 and 2010–present. Simultaneous determinations of the aerosol optical depth (AOD) from the two instruments were compared over a period of almost 4 years at several wavelengths between 415 and 870 nm. This is the first long-term comparison at a site strongly influenced by desert dust and marine aerosols and characterized by frequent cases of elevated AOD. The datasets show a good agreement, with MFRSR underestimating the Cimel AOD in cases with low Ångström exponent; the underestimate decreases for increasing wavelength and increases with AOD. This underestimate is attributed to the effect of aerosol forward scattering on the relatively wide field of view of the MFRSR. An empirical correction of the MFRSR data was implemented. After correction, the mean bias (MB) between MFRSR and Cimel simultaneous AOD de-terminations is always smaller than 0.004, and the root mean square difference is ≤0.031 at all wavelengths. The MB between MFRSR and Cimel monthly averages (for months with at least 20 days with AOD determinations) is 0.0052. Thus, by combining the MFRSR and Cimel observations, an integrated long-term series is obtained, covering the period 1999–present, with almost continuous measurements since early 2002. The long-term data show a small (nonstatistically significant) decreasing trend over the period 2002–2013, in agreement with independent observations in the Mediterranean. The integrated 1559-128X/15/102725-13$15.00/0
[Show abstract][Hide abstract] ABSTRACT: Desert dust interacts with shortwave (SW) and longwave (LW) radiation, influencing the Earth radiation budget and the atmospheric vertical structure. Uncertainties on the dust role are large in the LW spectral range, where few measurements are available and the dust optical properties are not well constrained. The first airborne measurements of LW irradiance vertical profiles over the Mediterranean were carried out during the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign, which took place in spring 2008 at the island of Lampedusa. The experiment was aimed at estimating the vertical profiles of the SW and LW aerosol direct radiative forcing (ADRF) and heating rates (AHR), taking advantage of vertically resolved measurements of irradiances, meteorological parameters and aerosol microphysical and optical properties. Two cases, characterized respectively by the presence of a homogeneous dust layer (3 May, with aerosol optical depth, AOD, at 500 nm of 0.59), and by a low aerosol burden (5 May, with AOD of 0.14), are discussed. A radiative transfer model was initialized with the measured vertical profiles and with different aerosol properties, derived from measurements, or from the literature. The simulation of the irradiance vertical profiles, in particular, provide the opportunity to constrain model-derived estimates of the AHR. The measured SW and LW irradiances were reproduced when the model was initialized with the measured aerosol size distributions and refractive indices. For the dust case, the instantaneous (solar zenith angle, SZA, of 55.1°) LW-to-SW ADRF ratio was 23% at the surface and 11% at the top of the atmosphere (TOA), with a more significant LW contribution on a daily basis (52% at the surface and 26% at TOA), indicating a relevant reduction of the SW radiative effects. The AHR profiles followed the aerosol extinction profile, with comparable peaks in the SW (0.72±0.11 Kday-1) and in the LW (-0.52±0.12 Kday-1) for the considered SZA. On a daily basis, the absolute value of the heating rate was larger in the LW than in the SW, producing a net cooling effect at specific levels. This is a quite unexpected results, emphasizing the important role of LW radiation.
[Show abstract][Hide abstract] ABSTRACT: The urban forcing on thermo-dynamical conditions can largely influences
local evolution of the atmospheric boundary layer. Urban heat storage
can produce noteworthy mesoscale perturbations of the lower atmosphere.
The new generations of high-resolution numerical weather prediction
models (NWP) is nowadays largely applied also to urban areas. It is
therefore critical to reproduce correctly the urban forcing which turns
in variations of wind, temperature and water vapor content of the
planetary boundary layer (PBL). WRF-ARW, a new model generation, has
been used to reproduce the circulation in the urban area of Rome. A
sensitivity study is performed using different PBL and surface schemes.
The significant role of the surface forcing in the PBL evolution has
been verified by comparing model results with observations coming from
many instruments (LiDAR, SODAR, sonic anemometer and surface stations).
The crucial role of a correct urban representation has been demonstrated
by testing the impact of different urban canopy models (UCM) on the
forecast. Only one of three meteorological events studied will be
presented, chosen as statistically relevant for the area of interest.
The WRF-ARW model shows a tendency to overestimate vertical transmission
of horizontal momentum from upper levels to low atmosphere, that is
partially corrected by local PBL scheme coupled with an advanced UCM.
Depending on background meteorological scenario, WRF-ARW shows an
opposite behavior in correctly representing canopy layer and upper
levels when local and non local PBL are compared. Moreover a tendency of
the model in largely underestimating vertical motions has been verified.
[Show abstract][Hide abstract] ABSTRACT: Results from the Ground-based and Airborne Measurements of Aerosol Radiative Forcing (GAMARF) campaign carried out at Lampedusa island in 2008 are presented. The campaign was focussed on measurements of longwave (LW) irradiance profiles up to 4 km, until now absent in the Mediterranean Sea, and to the estimation of shortwave (SW) and LW aerosol direct radiative forcings (ADRFs), using data collected by ground-based and airborne instrumentation and radiative transfer simulations. The SW and LW ADRFs have been calculated for a case of desert dust characterized by relatively large aerosol
International Radiation Symposium on Radiation Processes in the; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The Ground-based and Airborne Measurements of the Aerosol Radiative Forcing (GAMARF) campaign was carried out during spring 2008 in Lampedusa Island (Central Mediterranean). Several flights were performed by an instrumented ultralight in different atmospheric conditions. In
situ measurements of aerosol size distribution vertical profiles were used together with ground-based measurements of aerosol
optical depth and ÅAngström exponent to retrieve simultaneously profiles of the aerosol radiative properties and its effective refractive index. The retrieved backscattering and extinction profiles are in agreement with independent Lidar measurements, within the estimated uncertainties. This analysis suggests that in situ measurements of aerosol distribution can be used quantitatively for the determination of the aerosol optical and radiative properties.
International Radiation Symposium on Radiation Processes in the; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The seasonal evolution of the tropospheric aerosol vertical distribution and of its optical properties is investigated using lidar and multi-filter rotating shadow-band radiometer (MFRSR) measurements collected throughout the period 2006–2009 in the urban environment of Rome. The evolution of the aerosol distribution is studied also in relation to long range transport of dust.Hybrid Single-Particle Lagrangian Integrated Trajectory model backward trajectories are used to identify possible aerosol sources in remote regions.Aerosol optical depth at 500 nm, τ, and Ångström exponent, α, are derived from MFRSR measurements. The Ångström exponent generally displays relatively high values, indicating the predominance of fine particle over the entire column. The average optical depth at 500 nm and Ångström exponent over the whole period are 0.18 ± 0.09 and 1.12 ± 0.39, respectively. Cases affected by Saharan dust (class 1) are separated from those not influenced by dust (class 0) by using backward trajectories. The average values of τ and α are 0.17 ± 0.08 and 1.17 ± 0.36 for class 0, respectively, and 0.22 ± 0.09 and 0.95 ± 0.46 for class 1.About 214 days of lidar measurements are selected for the analysis. The aerosol vertical distribution is influenced by dust events that induce a marked seasonal behaviour. Desert dust generally reaches higher altitudes than other aerosol types; the maxima altitudes are observed during Spring and Summer, when the monthly average altitude exceeds 5 km. The annual average occurrence of desert dust is 27%, with maxima in Spring and in the first part of Summer. The decrease in the dust event frequency observed in winter months is mainly linked to the seasonal behaviour of the synoptic circulation in the Mediterranean. According to the back-trajectories aerosols are primarily observed below 3 km altitude throughout the year when classified as not affected by desert dust. The extinction coefficient vertical profiles for the two classes show largest differences during Spring and Summer. The extinction for non-dust profiles decreases monotonically with altitude throughout the year, except in Summer. Conversely, the aerosol extinction coefficient shows a relative minimum at the lowest sounded altitude, always except in winter, for class 1 cases. A winter maximum of the aerosol is evidently present in winter in the lower troposphere. Using the MFRSR optical depth and the lidar profiles, the lidar ratio was derived. The overall average lidar ratio is 58 sr.
Atmospheric Research 11/2012; 118:205–214. DOI:10.1016/j.atmosres.2012.06.026 · 2.42 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Raman lidar system BASIL was operational in Achern (Black Forest) between 25 May and 30 August 2007 in the framework of the Convective and Orographically-induced Precipitation Study (COPS). The system performed continuous measurements over a period of approx. 36 h from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, capturing the signature of a severe Saharan dust outbreak episode. The data clearly reveal the presence of two almost separate aerosol layers: a lower layer located between 1.5 and 3.5 km above ground level (a.g.l.) and an upper layer extending between 3.0 and 6.0 km a.g.l. The time evolution of the dust cloud is illustrated and discussed in the paper in terms of several optical parameters (particle backscatter ratio at 532 and 1064 nm, the colour ratio and the backscatter Angstrom parameter). An inversion algorithm was used to retrieve particle size and microphysical parameters, i.e., mean and effective radius, number, surface area, volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution (PSD), from the multi-wavelength lidar data of particle backscattering, extinction and depolarization. The retrieval scheme employs Tikhonov's inversion with regularization and makes use of kernel functions for randomly oriented spheroids. Size and microphysical parameters of dust particles are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the presence of a fine mode with radii of 0.1 0.2 mu m and a coarse mode with radii of 3-5 mu m both in the lower and upper dust layers, and the dominance in the upper dust layer of a coarse mode with radii of 4-5 mu m. Effective radius varies with altitude in the range 0.1-1.5 mu m, while volume concentration is found to not exceed 92 gm(3) cm(-3). The real and imaginary part of the complex refractive index vary in the range 1.4-1.6 and 0.004-0.008, respectively.
[Show abstract][Hide abstract] ABSTRACT: The planetary boundary layer includes the portion of the atmosphere
which is directly influenced by the presence of the Earth's surface.
Aerosol particles trapped within the PBL can be used as tracers to study
boundary-layer vertical structure and time variability. Aerosols can be
dispersed out of the PBL during strong convection or temporary breaks of
the capping temperature inversion. As a result of this, elastic
backscatter signals collected by lidar systems can be used to determine
the height and the internal structure of the PBL. Our analysis considers
a method based on the first order derivative of the range-corrected
elastic signal (RCS), which is a modified version of the method defined
by Seibert et al. (2000) and Sicard et al. (2006). The analysis is
focused on selected case studies collected by the Raman lidar system
BASIL during the Convective and Orographically-induced Precipitation
Study (COPS), held in Southern Germany and Eastern France in the period
01 June - 31 August 2007. Measurements were performed by the Raman lidar
system BASIL, which was operational in Achern (Black Forest, Lat: 48.64
° N, Long: 8.06 ° E, Elev.: 140 m). During COPS, BASIL collected
more than 500 hours of measurements, distributed over 58 measurement
days and 34 intensive observation periods (IOPs), covering both
night-time and daytime and the transitions between the two. Therefore
BASIL data during COPS represent a unique source of information for the
study of the boundary layer structure and evolution. Potential
temperature profiles obtained from the radiosonde data were used to get
an additional estimate of the boundary layer height. Estimates of the
PBL height and structure for specific case studies obtained from the
lidar data and their comparison with estimates obtained from the
radiosonde data will be illustrated and discussed at the Conference.
[Show abstract][Hide abstract] ABSTRACT: During the Convective and Orographically-induced Precipitation Study
(COPS), lidar dark and bright bands were observed by the University of
BASILicata Raman lidar system (BASIL) during several intensive (IOPs)
and special (SOPs) observation periods (among others, 23 July, 15
August, and 17 August 2007). Lidar data were supported by measurements
from the University of Hamburg cloud radar MIRA 36 (36 GHz), the
University of Hamburg dual-polarization micro rain radars (24.1 GHz) and
the University of Manchester UHF wind profiler (1.29 GHz). Results from
BASIL and the radars for 23 July 2007 are illustrated and discussed to
support the comprehension of the microphysical and scattering processes
responsible for the appearance of the lidar and radar dark and bright
bands. Simulations of the lidar dark and bright band based on the
application of concentric/eccentric sphere Lorentz-Mie codes and a
melting layer model are also provided. Lidar and radar measurements and
model results are also compared with measurements from a disdrometer on
ground and a two-dimensional cloud (2DC) probe on-board the ATR42
[Show abstract][Hide abstract] ABSTRACT: A desert dust episode in June 2007 and its radiative effects on the energy budget have been studied at three Italian stations (Rome, Lecce and Lampedusa) with the aim of investigating the interactions with different conditions and aerosol types over the Mediterranean. The three sites are representative for urban (Rome), sub-urban/rural (Lecce), and marine (Lampedusa) environment, respectively in the central Mediterranean region. Measured ground-based column-averaged aerosol optical properties and aerosol extinction profiles were used to initialize the MODTRAN4 radiative transfer model. The radiative transfer model was used to estimate the shortwave aerosol radiative forcing (ARF) and its forcing efficiency (FE) at two different solar zenith angles (20° and 60°) in the 280–2800 nm spectral range.The goal was to investigate the role of different aerosol types in the atmospheric boundary layer on the radiative budget during a dust event. During the event the aerosol optical depth was moderately high and similar at the three stations, with a maximum value of about 0.6. The Ångström exponent was found to increase with the distance from the source (0.21, 0.36, and 0.43 at Lampedusa, Rome, and Lecce, respectively). Differences in the aerosol optical properties were observed, also depending on the aerosol type assumed in the boundary layer. The estimated direct aerosol forcing appears to depend on the changes in aerosol properties and to the surface albedo. The results show that the desert dust produces a cooling effect at both surface (largest ARF of −224 W m−2 at 20° solar zenith angle at Rome) and top of the atmosphere (largest ARF of −19 W m−2 at 20° solar zenith angle at Lecce). The cooling is largest in the rural and smallest in the marine environment. The surface forcing efficiency appears to be strongly affected by the aerosol absorption in the BL. Large differences exist between our results and the FE determinations by AERONET, derived considering a single layer with homogeneous optical properties and prescribed vertical distribution. The FE deviations are around 20, 60, and 40% at the surface, TOA, and in the atmosphere, respectively. These results suggest that the detailed description of the vertical distribution of the aerosol properties is needed for an accurate determination of its radiative effects.Highlights► We describe an intense Saharan Dust event in the Central Mediterranean. ► We combine ground-based aerosol measurements and radiative transfer modelling. ► We study the desert dust optical properties and its radiative forcing. ► We investigate the dust interactions with different boundary layer aerosol and surface conditions over the Mediterranean. ► We introduce the vertical distribution of the aerosol optical properties in the radiative transfer simulations.
[Show abstract][Hide abstract] ABSTRACT: The Radiation Explorer in the Far InfraRed-Prototype for Applications
and Development (REFIR-PAD) spectroradiometer was operated from the
Testa Grigia Italian-Alps station in March 2007 during the Earth Cooling
by Water Vapour Radiation (ECOWAR) measurement campaign, obtaining
downwelling radiance spectra in the 100-1100 cm-1 range,
under clear-sky conditions and in the presence of cirrus clouds. The
analysis of these measurements has proven that the instrument is capable
of determining precipitable water vapor with a total uncertainty of 5-7%
by using the far-infrared rotational band of water. The measurement is
unaffected by the presence of cirri, whose optical depth can be instead
retrieved as an additional parameter. Information on the vertical
profiles of water vapor volume mixing ratio and temperature can also be
retrieved for three altitude levels. The ability to measure the water
vapor column with a simple, uncooled instrument, capable of operating
continuously and with a time resolution of about 10 min, makes REFIR-PAD
a very valuable instrument for meteorological and climatological studies
for the characterization of the water vapor distribution.
Journal of Geophysical Research Atmospheres 01/2011; 116(D2):2310-. DOI:10.1029/2010JD014530 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: During the Convective and Orographically-induced Precipitation Study (COPS), lidar dark bands were observed by the Univ. of BASILicata Raman lidar system (BASIL) on several IOPs and SOPs (among others, 23 July, 15 August, 17 August). Dark band signatures appear in the lidar measurements of particle backscattering at 355, 532 and 1064 nm and particle extinction at 355 and 532 nm, as well as in particle depolarization measurements. Lidar data are supported by measurements from the University of Hamburg cloud radar MIRA 36 (36 GHz), the University of Hamburg dual-polarization micro rain radars (24.1 GHz) and the University of Manchester Radio UHF clear air wind profiler (1.29 GHz). Results from BASIL and the radars are illustrated and discussed to support in the comprehension of the microphysical and scattering processes responsible for the appearance of the lidar dark band and radar bright band.
[Show abstract][Hide abstract] ABSTRACT: The Raman lidar system BASIL was operational in Achern (Supersite R, Lat: 48.64° N, Long: 8.06° E, Elev.: 140 m) in the frame of the Convective and Orographically-induced Precipitation Study. BASIL operated continuously over a period of approx. 36 hours from 06:22 UTC on 1 August to 18:28 UTC on 2 August 2007, to cover IOPs 13 a-b. In this timeframe the signature of a severe Saharan dust outbreak episode was captured. An inversion algorithm was used to retrieve particle size distribution parameters, i.e., mean and effective radius, number, surface area, and volume concentration, and complex refractive index, as well as the parameters of a bimodal particle size distribution, from the multi-wavelength lidar data of particle backscattering and extinction. The inversion method employs Tikhonov's inversion with regularization. Size distribution parameters are estimated as a function of altitude at different times during the dust outbreak event. Retrieval results reveal the dominance in the upper dust layer of a coarse mode with radii 3-4 mum. Number density and volume concentration are in the range 100-800 cm-3 and 5-40 mum3/cm3, respectively, while real and imaginary part of the complex refractive index are in the range 1.41-1.53 and 0.003-0.014, respectively.
[Show abstract][Hide abstract] ABSTRACT: The Raman lidar system BASIL was deployed in Achern (Supersite R, Lat: 48.64° N, Long: 8.06° E, Elev.: 140 m) in the frame of the Convective and Orographically-induced Precipitation Study. On 20 July 2007 a frontal zone passed over the COPS region, with a Mesoscale Convective System (MCS) imbedded in it. BASIL was operated continuously during this day, providing measurements of temperature, water vapour, particle backscattering coefficient at 355, 532 and 1064 nm, particle extinction coefficient at 355 and 532 nm and particle depolarization at 355 and 532 nm. The thunderstorm approaching determined the lowering of the anvil clouds, which is clearly visible in the lidar data. A cloud deck is present at 2 km, which represents a mid-level outflow from the thunderstorm/MCS. The mid-level outflow spits out hydrometeor-debris (mostly virga) and it is recycled back into it. The MCS modified the environment at 1.6-2.5 km levels directly (outflow) and the lower levels through the virga/precipitation. Wave structures were observed in the particle backscatter data. The wave activity seems to be a reflection of the shear that is produced by the MCS and the inflow environmental wind. Measurements in terms of particle backscatter and water vapour mixing ratio are discussed to illustrate the above phenomena.
[Show abstract][Hide abstract] ABSTRACT: In this study we present an intercomparison of measurements of very low
water vapor column content obtained with a Ground-Based Millimeter-wave
Spectrometer (GBMS), Vaisala RS92k radiosondes, a Raman Lidar, and an IR
Fourier Transform Spectrometer. These sets of measurements were carried
out during the primary field campaign of the ECOWAR (Earth COoling by
WAter vapor Radiation) project which took place on the Western Italian
Alps from 3 to 16 March, 2007.