Daniela Meloni

Large atmospheric shortwave radiative forcing by Mediterranean aerosols derived from simultaneous ground-based and spaceborne observations and dependence on the aerosol type and single scattering albedo

[1]xa0Aerosol optical properties and shortwave irradiance measurements at the island of Lampedusa (central Mediterranean) during 2004–2007 are combined with Clouds and the Earths Radiant Energy System observations of the outgoing shortwave flux at the top of the atmosphere (TOA). The measurements are used to estimate the surface (FES), the top of the atmosphere (FETOA), and the atmospheric (FEATM) shortwave aerosol forcing efficiencies for solar zenith angle (θ) between 15° and 55° for desert dust (DD), urban/industrial-biomass burning aerosols (UI-BB), and mixed aerosols (MA). The forcing efficiency at the different atmospheric levels is derived by applying the direct method, that is, as the derivative of the shortwave net flux versus the aerosol optical depth at fixed θ. The diurnal average forcing efficiency at the surface/TOA at the equinox is (−68.9 ± 4.0)/(−45.5 ± 5.4) W m−2 for DD, (−59.0 ± 4.3)/(−19.2 ± 3.3) W m−2 for UI-BB, and (−94.9 ± 5.1)/(−36.2 ± 1.7) W m−2 for MA. The diurnal average atmospheric radiative forcing at the equinox is (+7.3 ± 2.5) W m−2 for DD, (+8.4 ± 1.9) W m−2 for UI-BB, and (+8.2 ± 1.9) W m−2 for MA, suggesting that the mean atmospheric forcing is almost independent of the aerosol type. The largest values of the atmospheric forcing may reach +35 W m−2 for DD, +23 W m−2 for UI-BB, and +34 W m−2 for MA. FETOA is calculated for MA and 25° ≤ θ ≤ 35° for three classes of single scattering albedo (0.7 ≤ ω < 0.8, 0.8 ≤ ω < 0.9, and 0.9 ≤ ω ≤ 1) at 415.6 and 868.7 nm: FETOA increases, in absolute value, for increasing ω. A 0.1 increment in ω determines an increase in FETOA by 10–20 W m−2.

Measurements of Mediterranean aerosol radiative forcing and influence of the single scattering albedo

[1]xa0Ground-based measurements of aerosol optical depth and surface shortwave irradiance carried out at the Mediterranean island of Lampedusa during 2004–2007 are used to estimate the surface aerosol direct radiative forcing for desert dust (DD), urban/industrial-biomass burning (UI-BB), and mixed aerosols (MA). The aerosol single scattering albedo, ω, at 415.6 and 868.7 nm is derived at 60° solar zenith angle, θ, from measurements of global and diffuse radiation using radiative transfer model calculations. The shortwave forcing efficiency (FES) is derived, for θ between 20° and 75°, for the three identified classes of aerosol and for all the observed data (AD). The absolute value of FES decreases for increasing θ for all the aerosol types. FES varies between −185 and −81.7 W m−2 for DD, −168 and −84 W m−2 for UI-BB, −251 and −120.2 W m−2 for MA, and −208 and −106.5 W m−2 for AD. The daily average forcing efficiency (FEd) at the equinox is −67.2 W m−2 for DD, −59.0 W m−2 for UI-BB, and −93.2 W m−2 for MA. The forcing efficiency of DD, UI-BB, and MA at θ = 60° was calculated for three intervals of single scattering albedo (0.7 ≤ ω < 0.8, 0.8 ≤ ω < 0.9, 0.9 ≤ ω ≤ 1) at 415.6 and 868.7 nm. The absolute value of FES decreases with increasing ω at 868.7 nm for all aerosol types, while it decreases with increasing ω at 415.6 nm for UI-BB and MA and increases for DD. A 0.1 increment in the single scattering albedo at 868.7 nm produces a reduction in FES by 25–30 W m−2, and a reduction by 10–15 W m−2 in FEd.

Empirical correction of multifilter rotating shadowband radiometer (MFRSR) aerosol optical depths for the aerosol forward scattering and development of a long-term integrated MFRSR-Cimel dataset at Lampedusa.

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 determinations 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 Lampedusa dataset will be used for aerosol climatological studies and for verification of satellite observations and model analyses.

Accounting for the Solar Radiation Influence on Downward Longwave Irradiance Measurements by Pyrgeometers

AbstractMeasurements of broadband downward longwave (LW) irradiance are carried out at Lampedusa, Italy, in the Mediterranean, jointly with solar irradiance, since 2004 using shaded and unshaded Eppley Precision Infrared Radiometers (PIRs) and Kipp & Zonen CGR4 pyrgeometers. The calibrations of the different pyrgeometers are traceable to the Physikalisch-Meteorologisches Observatorium Davos World Radiation Center (PMOD/WRC). Nighttime measurements from intercalibrated pyrgeometers agree within ±2 W m−2. The performance of the pyrgeometers when operated unshaded has been analyzed by comparison with shaded instruments. For the PIR, the nonhomogeneous dome temperature in cloud-free conditions produces differences in LW irradiance within ±4 W m−2, depending on the time of the day and the season. The effect of the LW fraction of solar radiation reaching the sensor and a possible shortwave leakage of the dome interference filter produces differences between shaded and unshaded pyrgeometers during daytime. In cl...

Determination of ultraviolet cosine-corrected irradiances and aerosol optical thickness by combined measurements with a Brewer spectrophotometer and a multifilter rotating shadowband radiometer

Combined measurements of diffuse-to-global radiation ratio and global spectral irradiances in the UV are used to derive cosine-corrected UV irradiances and aerosol optical depth (AOD). The diffuse-to-global radiation ratio is used first in the cosine correction of the global irradiance, then to calculate absolutely calibrated direct irradiances. The Beer-Lambert law is applied to derive the UV AOD using independent measurements of the extraterrestrial solar flux. The AOD can be derived with an uncertainty of about 0.03 at 60 degrees solar zenith angle. The method was applied to measurements obtained with two UV multifilter rotating shadowband radiometers (UV-MFRSRs) and a MK III Brewer spectrophotometer on the Island of Lampedusa in the Central Mediterranean during two periods of 2002 and 2004. The derived AOD at 318 and 332 nm was compared with UV AOD measured at 318, 320, and 368 nm with different techniques. The retrieved AOD, combining MFRSR and Brewer measurements, is in good agreement with the optical depth derived with the other methods.

On the complexity of the boundary layer structure and aerosol vertical distribution in the coastal Mediterranean regions: a case study

The planetary boundary layer structure in the coastal areas, and particularly in complex orography regions such as the Mediterranean, is extremely intricate. In this study, we show the evolution of the planetary boundary layer based on in situ airborne measurements and ground-based remote sensing observations carried out during the MORE (Marine Ozone and Radiation Experiment) campaign in June 2010. The campaign was held in a rural coastal Mediterranean region in Southern Italy. The study focuses on the observations made on 17 June. Vertical profiles of meteorological parameters and aerosol size distribution were measured during two flights: in the morning and in the afternoon. Airborne observations were combined with ground-based LIDAR, SODAR, microwave and visible radiometer measurements, allowing a detailed description of the atmospheric vertical structure. The analysis was complemented with data from a regional atmospheric model run with horizontal resolutions of 12, 4 and 1 km, respectively; back-trajectories were calculated at these spatial resolutions. The observations show the simultaneous occurrence of dust transport, descent of mid-tropospheric air and sea breeze circulation on 17 June. Local pollution effects on the aerosol distribution, and a possible event of new particles formation were also observed. A large variability in the thermodynamical structure and aerosol distribution in the flight region, extending by approximately 30 km along the coast, was found. Within this complex, environment-relevant differences in the back-trajectories calculated at different spatial resolutions are found, suggesting that the description of several dynamical processes, and in particular the sea breeze circulation, requires high-resolution meteorological analyses. The study also shows that the integration of different observational techniques is needed to describe these complex conditions; in particular, the availability of flights and their timing with respect to the occurring phenomena are crucial.

Global and Mediterranean climate change: a short summary

Observed changes at the global scale. An increase of the annual mean global temperature and changes of other climate parameters have been observed in the last century. The global temperature and the atmospheric concentration of greenhouse gases are changing at a very fast pace compared to those found in palaeoclimate records. Changes in the Mediterranean. Variations of some climate change indicators can be much larger at the local than at the global scale, and the Mediterranean has been indicated among the regions most sensitive to climate change, also due to the increasing anthropogenic pressure. Model projections for the Mediterranean foresee further warming, droughts, and long-lasting modifications.nnnIMPACTSnRegional climate changes impact health and ecosystems, creating new risks, determined not only by weather events, but also by changing exposures and vulnerabilities. These issues, and in particular those regarding occupational safety, have not been sufficiently addressed to date.

Determination of global and diffuse photosynthetically active radiation from a multifilter shadowband radiometer

A method to estimate the photosynthetically active radiation from multifilter shadowband radiometer (MFRSR) measurements was developed and tested from observations carried out on the island of Lampedusa in the central Mediterranean. Calibrated irradiances in the four MFRSR bands within the PAR spectral range were combined linearly to estimate PAR. The coefficients of the linear combination were derived with the least squared method for different sky conditions. The analysis shows that global PAR irradiance may be estimated with an overall uncertainty of 4%-6%. The applicability of the method was tested by using radiative transfer simulations of the diffuse irradiance spectrum for different aerosol and cloud conditions. The diffuse PAR irradiance can be estimated with an overall accuracy of less than 9%. The application of this method allows us to obtain continuous and long-term calibrated measurements of global and diffuse PAR; in addition, information on the spectral dependency of PAR can be derived from the signals in the four bands.

Vertical resolved aerosol characterization during the GAMARF campaign: Aerosol size distribution and radiative properties

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 AAngstrom 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.

Vertical profiles of shortwave and longwave aerosol direct radiative forcing during the GAMARF campaign at Lampedusa Island

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 optical depth.