Aerosol radiative properties are investigated in southeastern
Spain during a dust event on 16–17 June 2013 in the framework of the ChArMEx/ADRIMED
(Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Impact on the
regional climate in the MEDiterranean region) campaign. Particle optical and
microphysical properties from ground-based sun/sky photometer and lidar measurements, as
well as in situ measurements on board the SAFIRE ATR 42 French research aircraft, are
used to create a set of different levels of input parameterizations, which feed the 1-D
radiative transfer model (RTM) GAME (Global Atmospheric ModEl). We consider three
datasets: (1) a first parameterization based on the retrievals by an advanced aerosol
inversion code (GRASP; Generalized Retrieval of Aerosol and Surface Properties) applied
to combined photometer and lidar data, (2) a parameterization based on the photometer
columnar optical properties and vertically resolved lidar retrievals with the
two-component Klett–Fernald algorithm, and (3) a parameterization based on vertically
resolved optical and microphysical aerosol properties measured in situ by the aircraft
instrumentation. Once retrieved, the outputs of the RTM in terms of both shortwave and
longwave radiative fluxes are compared against ground and in situ airborne measurements.
In addition, the outputs of the model in terms of the aerosol direct radiative effect are
discussed with respect to the different input parameterizations. Results show that
calculated atmospheric radiative fluxes differ no more than 7 % from the measured ones.
The three parameterization datasets produce a cooling effect due to mineral dust both at
the surface and the top of the atmosphere. Aerosol radiative effects with differences of
up to 10 W m
The radiative effect by atmospheric aerosol is estimated to produce a net cooling effect
of the Earth's climate. However, an accurate quantification of this cooling is extremely
difficult. In fact, the aerosol radiative effect (ARE) is affected by large
uncertainties. Due to the direct aerosol–radiation interaction, the ARE is estimated to
be
In previous studies, the AREs in longwave (LW) spectral range were commonly neglected due to the complexity of an accurate quantification of the optical properties in this spectral range (Roger et al., 2006; Mallet et al., 2008; Sicard et al., 2012). However, the contribution of the LW component to the ARE is nonnegligible for large aerosol particles, i.e., marine aerosol or mineral dust (e.g., Markowicz et al., 2003; Vogelmann et al., 2003; Otto et al., 2007; Perrone and Bergamo, 2011; Sicard et al., 2014a, b; Meloni et al., 2018).
The contribution of mineral dust to the ARE in the infrared spectral range is especially
relevant because of its large size and abundance (Meloni et al., 2018). Mineral dust is
estimated to be the most abundant aerosol type in the atmosphere by mass (e.g., Ginoux et
al., 2012; Choobari et al., 2014), with global emission between 1000 and
3000 Mt yr
One of the areas frequently influenced by mineral dust is the Mediterranean Sea region,
affected by dust intrusions from the close by Sahara or the Middle East region (Moulin et
al., 1998; Israelevich et al., 2012; Gkikas et al., 2013) producing significant
perturbations to the shortwave (SW) and the LW radiation balance (di Sarra et al., 2011;
Papadimas et al., 2012; Perrone et al., 2012; Meloni et al., 2015) as well as the
regional climate (Nabat et al., 2015). The ARE in the Mediterranean region can be
responsible for a strong cooling effect both at the surface (or bottom of the atmosphere,
BOA) and at the top of the atmosphere (TOA). The so-called forcing efficiency (FE), which
is defined as the ratio between the ARE and the aerosol optical depth (AOD) for the SW
spectral component ranges between
The Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region
(ADRIMED) field campaign within the Chemistry-Aerosol Mediterranean Experiment (ChArMEx,
In this paper, we present an analysis of the mineral dust radiative properties during this particular episode and take advantage of the thorough database that is available. Multiple datasets are used as input in a radiative transfer model (RTM) to evaluate the influence of the different measurements and data processing in the retrieved direct ARE. The model used here is the Global Atmospheric ModEl (GAME; Dubuisson et al., 1996, 2005), which allows for calculating both the solar and thermal infrared fluxes. An evaluation against aircraft in situ measurements of radiative fluxes is also presented.
Two main goals are pursued: (i) the quantification of the direct ARE for two case studies within a dust transport episode and (ii) the evaluation of the model estimate sensitivity to the aerosol input used.
The paper is structured as follows: Sect. 2 includes a description of both the ground-based and in situ aircraft instrumentation and a short description of the retrieval algorithms used for the present study, Sect. 3 is devoted to the description of GAME and the input datasets used here, and results are presented in Sect. 4; finally, a short summary and concluding remarks are included in Sect. 5.
Ground-based measurements used in this work were carried out at the Andalusian Institute
for Earth System Research (IISTA-CEAMA) of the University of Granada, Spain (lat 37.16,
long
IISTA-CEAMA station is equipped with a CE-318-4 (Cimel Electronique) sun/sky
photometer, which belongs to the AERONET network (Holben et al., 1998). This instrument
performs direct solar irradiance measurements, used to derive AOD, and sky radiance
measurements both measured at least at the following nominal wavelengths (
The multiwavelength aerosol Raman lidar MULHACEN, based on a customized version of
LR331D400 (Raymetrics S.A.) is operated at Granada station as part of EARLINET/ACTRIS
(European Aerosol Research Lidar Network/Aerosols, Clouds, and Trace Gases Research
Infrastructure Network;
Additionally, surface temperature and pressure are continuously monitored at IISTA-CEAMA by a meteorological station located 2 m above the ground. At the same location, the global and diffuse downward radiative fluxes for the SW component are continuously measured with a CM11 pyranometer (Kipp & Zonen) and diffuse downward radiative fluxes for the LW component are measured with a precision infrared radiometer pyrgeometer (Eppley), both being instruments regularly calibrated at the site (Antón et al., 2012, 2014).
The SAFIRE ATR 42 aircraft performed two overpasses above Granada on 16 (flight F30) and 17 June (flight F31) in 2013 during the ChArMEx/ADRIMED campaign. During F30, the SAFIRE ATR 42 descended performing a spiral trajectory from 14:15 to 14:45 UTC; whereas during flight F31, the aircraft ascended in the early morning (from 07:15 to 07:45 UTC) at around 20 km from Granada station (see Fig. 1 from Benavent-Oltra et al., 2017). Additional flight details can be found in previous studies (Denjean et al., 2016; Mallet et al., 2016; Benavent-Oltra et al., 2017; Román et al., 2018).
The airborne instrumentation includes a scanning mobility particle sizer (SMPS) and an
ultra-high sensitivity aerosol spectrometer (UHSAS) for measuring aerosol number size
distribution in the submicron range. The forward-scattering spectrometer probe model 300
(FSSP-300) and the GRIMM optical particle counter (sky-OPC 1.129) were used to measure
the optical size distributions in the diameter nominal size range between 0.28 and
20
Airborne radiative fluxes (
Radiation measurement data from the aircraft were filtered out for large pitch and roll
angles and corrected from the rapid variations in the solar incidence angle around the
SZA due to the aircraft attitude (pitch and roll). This correction also depends on
aircraft heading angle and solar position. It should be noted that, beforehand, roll and
pitch offsets must be determined (the axis sensor is not necessarily vertical on average
during a horizontal leg). Cosine errors were taken into account. Finally, data were
corrected from variations in the SZA during the flight to ease the comparison with GAME
retrievals. After these various corrections, an estimated uncertainty of
The GRASP (Generalized Retrieval of Aerosol and Surface Properties) code (Dubovik et al.,
2011, 2014) provides aerosol optical and microphysical properties in the atmosphere by
combining the information from a variety of remote sensors (e.g., Kokhanovsky et al.,
2015; Espinosa et al., 2017; Torres et al., 2017; Román et al., 2017, 2018; Chen et
al., 2018). In our case, GRASP was used
to invert simultaneously coincident lidar data (range-corrected signal, RCS, at 355, 532,
and 1064 nm) and sun/sky photometer measurements (AOD and sky radiances both from
AERONET at 440, 675, 870, and 1020 nm) providing a detailed characterization of the
aerosol properties, both column-integrated and vertically resolved. It is worthy to note
that this GRASP scheme, based on Lopatin et al. (2013), presents the main advantage that
it allows for retrieving aerosol optical and microphysical properties for two distinct
aerosol modes, namely fine and coarse. The
The GAME code is widely described by Dubuisson et al. (2004, 2005) and Sicard et
al. (2014a). It is a modular RTM that allows for calculating upward and downward
radiative fluxes at different vertical levels from the ground up to 20 km (100 km) in
the SW (LW) spectral range. The solar and thermal infrared fluxes are calculated in two
adjustable spectral ranges, which in this study were fixed to match those of the aircraft
radiation measurements (namely 297–3100 nm for the SW and 4.5–40
Summary of main GAME properties for the SW and LW spectral ranges. The altitude range corresponding to the different vertical resolution values is indicated between parentheses.
The two considered SAFIRE ATR 42 flights, F30 and F31, took place on 16 and 17 June 2013,
respectively, coinciding with ground-based lidar and sun/sky photometer measurements
performed at the station. On these days, mineral dust with origin in the Sahara region
(southern Morocco near the border with Algeria) reached Granada after
A summary of the experimental data used as input for GAME calculations during these two case studies is presented in Table 2. This input includes surface parameters and atmospheric profiles of meteorological variables, main gas concentrations, and aerosol properties. The aerosol properties used in the present study are parameterized using three different datasets, based on the different instrumentation and retrievals available, i.e., Dataset 1 (DS1), Dataset 2 (DS2) and Dataset 3 (DS3). A more detailed description of the different parameters is provided next.
Summary of the data sources used to obtain the input data parameterizations for
GAME computations both in the SW and LW spectral ranges, including the surface parameters
(albedo, alb, and land-surface temperature, LST), profiles of meteorological variables,
and main gases and the aerosol parameters. For the aerosol parameters (aerosol
extinction,
The surface parameters required for GAME are the surface albedo (alb(
Surface albedo, alb(
Relative humidity (RH), temperature (
Figure 1 shows the pressure (
As for the aerosol parameterization,
For the SW simulations, we run GAME using three different aerosol input datasets, i.e., DS1, DS2, and DS3 (Table 2), in order to evaluate their influence on the ARE calculations. DS1 relies on a parameterization based on the advanced postprocessing GRASP code, which combines lidar and sun/sky photometer data to retrieve aerosol optical and microphysical property profiles; DS2 relies on Klett–Fernald lidar inversions and AERONET products and corresponds to a reference parameterization (easily reproducible at any station equipped with a single- or multiwavelength lidar and an AERONET sun/sky photometer and without the need of an advanced postprocessing algorithm); and DS3 relies on in situ airborne measurements and corresponds to an alternative parameterization to DS1 and DS2.
Profiles of
Figure 2 shows
Column-integrated number concentration (
SSA profiles obtained from GRASP/DS1 on 16 June
Figure 3 presents the SSA values retrieved by the GRASP algorithm, used as input for GAME
in DS1, on 16 (F30, Fig. 3a) and 17 June (F31, Fig. 3b). The mean SSA at 440 nm is equal
to 0.92 on 15 June, whereas on 17 June it is 0.85. On 17 June the SSA profiles present
lower values and more variation with height than on 16 June; the lower SSA values
indicate the presence of more absorbing particles on 17 June. The vertical variation on
17 June is associated with the presence of two different layers, whereas a more
homogeneous dust layer is observed on 16 June. For DS2, the SSA are taken from AERONET
columnar values and assumed to be constant with height (Fig. 4a). The SSA at 440 nm was
0.89 and 0.83 on 16 and 17 June, respectively; as already observed in Fig. 3, SSA values
are lower on 17 June due to the intrusion of more absorbing particles. For DS3, SSA
values at 530 nm are obtained from the nephelometer and the CAPS or PLASMA on board the
ATR. In order to reduce the uncertainty in the measured data, only averaged values for
the column will be considered, being 0.88 and 0.83 on 16 and 17 June, respectively
(Fig. 4). Therefore, differences of up to 0.04 and 0.02 are observed on 16 and 17 June,
respectively, among the SSA values obtained with the three datasets. Despite these
differences, the retrieved SSA values obtained here are within the range of typical
values for dust aerosols (Dubovik et al., 2002; Lopatin et al., 2013) and differences are
still within the uncertainty limits, which range between 0.02 and 0.07 depending on the
aerosol load for AERONET data (Dubovik and King, 2000) and is 0.04 for the aircraft
values. In the case of
Summing up, for the SW aerosol parametrization in GAME three datasets are tested. In DS1, GRASP-derived spectral profiles at seven wavelengths of the aerosol extinction and SSA are used. In DS2, the Klett retrieved extinction profiles at three wavelengths are used together with the AERONET SSA columnar values at four wavelengths, which are assumed to be constant with height. For DS3, one extinction profile at 550 nm and a column-averaged single-wavelength value of the SSA from the airborne measurements are considered. In the three cases, the column-integrated AERONET asymmetry parameter at four wavelengths is assumed to be constant with height and used as input.
For the LW calculations, the Mie code is used to obtain
Summary of the data used to obtain
The spectral real and imaginary parts of the RI of mineral dust in the LW are obtained
from Di Biagio et al. (2017), using the Morocco source, and assumed constant with height.
The analysis by Di Biagio et al. (2017) only covers the spectral range 3–16
In the case of DS1,
Profiles of aerosol volume concentration for the fine (blue) and coarse (red)
mode obtained from GRASP/DS1 (dotted line), and aircraft in situ/DS3 measurements (solid
line) on 16 June
For DS3, the volume concentration (or the equivalent
As a result of the simulation, GAME provides vertical profiles of radiative fluxes in the
shortwave (
Figure 6 shows the radiative flux profiles for the SW spectral range obtained with GAME
using the three different input datasets described in Sect. 3, as well as the Net
Radiative fluxes for the SW spectral range for 16 June
The evaluation against the aircraft measurements shows larger differences for altitudes
below 2.5 km (
The values at the surface (or BOA) and at the TOA for the different radiative fluxes can
also be evaluated against different instruments: measurements for the
Time series of the
At the TOA, the
The ARE
ARE profiles in the SW spectral range simulated using DS1 (blue line), DS2 (red
line), and DS3 (green line) as aerosol input data in GAME for 16 June
Differences are also observed when comparing ARE
The ARE
ARE (and FE indicated between parenthesis) at the BOA and the TOA for the SW spectral range obtained with GAME using as inputs DS1, DS2, and DS3 for 16 and 17 June 2013. The averaged values and standard deviation are also included.
Radiative fluxes for the LW spectral range for 16 June
Figure 9 shows
In general, differences in the
ARE (and FE indicated between parenthesis) at the BOA and the TOA for the LW
spectral range obtained with GAME using as inputs DS1, DS2, and DS3 for 16 and
17 June 2013. The averaged values and standard deviation are also included. The last
three columns include variations (
A comparison of GAME results against the observations from the ground-based pyrgeometer
at the Granada station is included in Fig. 10. At the BOA, the longwave radiation
measured by the pyrgeometer is in quite good agreement with GAME calculations on 16 June,
with differences within 1 W m
Time series of the
As for the ARE
Direct ARE profiles in the LW spectral range simulated using DS1 (blue line),
DS2 (red line), and DS3 (green line) as aerosol input data in GAME for
16 June
ARE (and FE indicated between parenthesis) at the BOA and the TOA for the total
(SW
Direct ARE for the total spectrum
The total ARE, including both the SW and LW component, is included in Fig. 12 and
Table 8. As observed, mineral dust produces a net cooling effect both at the surface and
the TOA on both days. Depending on the input dataset used for the aerosol properties,
values can change by up to 15 W m
A moderate Saharan dust event affecting the western Mediterranean region during the ChArMEx/ADRIMED campaign on June 2013 was extensively monitored by ground-based and aircraft instrumentation above the Granada experimental site. Radiative fluxes and mineral dust ARE both in the solar and infrared spectral ranges are calculated for this event with the RTM GAME. Three different aerosol input datasets are used by the GAME RTM in order to evaluate the impact of different input data in GAME calculations.
For the SW, very low variability with the input aerosol data (less than 1 %) is
observed for the radiative fluxes. The evaluation of GAME-calculated radiative fluxes
against the aircraft data reveals differences between the model fluxes and the
measurements below 7 %, with better agreement at altitudes above the planetary boundary
layer. The differences between the retrievals with the three aerosol datasets are quite
insignificant, especially taking into account the different approaches followed by the
model and the pyranometers and the estimated uncertainties for both the measured data
(5 W m
For the LW component, the effect of aerosol on the radiative properties is lower compared
to the SW, but certainly nonnegligible and of opposite sign. GAME retrievals using the
three aerosol datasets reveal differences in the fluxes lower than 2 W m
The total ARE, including both the SW and LW components, confirms that mineral dust
produces a cooling effect both at the surface and the TOA, as already reported in the
literature. On average, the ARE
Additionally, it is necessary to be aware of the effects of using different measurement techniques and processing methodologies when calculating aerosol radiative properties. Even though the differences observed here when using different aerosol datasets are slight, they still exist and a homogenization of the techniques to feed global models would be beneficial for a better estimate of the ARE and a reduced uncertainty.
Part of the data used in this publication were obtained as part of the AERONET and EARLINET networks and are publicly available. For additional data or information please contact the authors.
The supplement related to this article is available online at:
MJGM and MS designed the study and wrote the manuscript with contributions from all authors. MJGM, RR, JABO, CD, GB, PF, and BT provided data and performed data analysis. RB provided the initial version of the model. All authors have given approval to the final version of the manuscript.
The authors declare that they have no conflict of interest.
This article is part of the special issue “CHemistry and AeRosols Mediterranean EXperiments (ChArMEx) (ACP/AMT inter-journal SI)”. It is not associated with a conference.
This work is part of the ChArMEx project supported by CNRS-INSU, ADEME,
Météo-France, and CEA in the framework of the multidisciplinary
program MISTRALS (Mediterranean Integrated STudies at Regional And Local
Scales;