The direct shortwave radiative effect of aerosols under clear-sky conditions in the Aire Limitee Adaptation dynamique Developpement InterNational – High Resolution Limited Area Model (ALADIN-HIRLAM) numerical weather prediction system was investigated using three shortwave radiation schemes in diagnostic single-column experiments: the Integrated Forecast System (IFS), acraneb2 and the hlradia radiation schemes. The multi-band IFS scheme was formerly used operationally by the European Centre for Medium Range Weather Forecasts (ECMWF) whereas hlradia and acraneb2 are broadband schemes. The former is a new version of the HIRLAM radiation scheme while acraneb2 is the radiation scheme in the ALARO-1 physics package.
The aim was to evaluate the strengths and weaknesses of the numerical weather
prediction (NWP)
system regarding aerosols and to prepare it for use of real-time aerosol information. The
experiments were run with particular focus on the August 2010 Russian
wildfire case. Each of the three radiation schemes accurately (within
The direct radiative effect of aerosols resulting from scattering and absorption of electromagnetic radiation at shortwave (SW) and longwave (LW) wavelengths has an impact on the Earth's radiation budget (e.g. Haywood and Boucher, 2000; Bellouin et al., 2005; Jacobson, 2001; Myhre et al., 2013; Yu et al., 2006; Loeb and Manalo-Smith, 2005) and on meteorology (e.g. Cook and Highwood, 2004; Takemura et al., 2005; Wang, 2004; Mulcahy et al., 2014; Bangert et al., 2012) which needs to be accounted for in numerical weather prediction (NWP) models. Climatological distributions of aerosols are commonly used in present-day operational NWP models for calculating the direct radiative effect of aerosols.
Using unrealistic aerosol distributions can lead to considerable errors in meteorological forecasts. Milton et al. (2008) showed that excluding the direct radiative effect of mineral dust and biomass burning aerosols in forecasts using the UK Met Office Unified Model during the dry season in West Africa, resulted in an inaccurate representation of the surface energy budget and a warm bias in screen level temperature. Carmona et al. (2008) presented significant correlations between errors in the aerosol optical depth (AOD) assumed in an NWP model and temperature forecast errors. Accurate simulation of the direct radiative effect of aerosols on SW radiation is important to the growing solar energy industry because under clear-sky conditions aerosols are the main modulator of SW fluxes (Breitkreuz et al., 2009).
The monthly aerosol climatology described in Tegen et al. (1997) is used in ECMWF's (the European Centre for Medium Range Weather Forecasts) global Integrated Forecast System (IFS) and in the Aire Limitee Adaptation dynamique Developpement InterNational – High Resolution Limited Area Model (ALADIN-HIRLAM) limited area modelling system used in this study. Tompkins et al. (2005) showed that replacing the Tanré at al. (1984) fixed average aerosol distribution in ECMWF's IFS model by the Tegen climatology improved forecasts of the African Easterly Jet. This change in the aerosol climatology also improved the forecast skill and seasonal mean errors (Rodwell and Jung, 2008).
Including a more complete representation of the effects of aerosols in NWP models can improve the meteorological forecasts and is an active area of research (e.g. Mulcahy et al., 2014; Bangert et al., 2012). Using real-time aerosol distributions, rather than climatological data sets, to account for the direct radiative effect of aerosols further improves the quality of the forecasts. Toll et al. (2015b) showed that the accuracy of the forecasts of near-surface conditions by the ALADIN-HIRLAM system during severe wildfires in summer 2010 in eastern Europe were improved when the direct radiative effect of the realistic aerosol distribution was included in the model hindcasts. Palamarchuk et al. (2016) also found a noticeable sensitivity of the ALADIN-HIRLAM forecasts to the treatment of aerosols where experiments were carried out under aerosol-free conditions, using sea salt aerosols only and using the default aerosols in the model. On the other hand, Toll et al. (2016) showed that when observed aerosol distributions are close to average, improvements in the SW radiation, temperature and humidity forecasts in the lower troposphere are only slightly greater when time-varying realistic aerosol data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis (Inness et al., 2013) is used in place of the Tegen climatology. Similar conclusions were drawn by Zamora et al. (2005) who showed that, for small AODs, accounting for the climatological average direct radiative effect of aerosols gives very good estimates of SW fluxes, but large biases occur when the AOD is large.
Baklanov et al. (2014), Grell and Baklanov (2011), Zhang (2008) and Vogel et al. (2009) have suggested using coupled air quality and NWP models to improve forecasts of both air quality and weather. However, for operational NWP such coupled models are still too demanding computationally, and this added cost has to be evaluated against improvements in the meteorological forecasts. Mulcahy et al. (2014), Morcrette et al. (2011) and Reale et al. (2011) describe improved forecasts of the radiation budget and near surface conditions in global NWP models when prognostic aerosols are included; however the impact of aerosols on large-scale atmospheric dynamics is generally weak.
The AOD at the wavelength of 550 nm (AOD550 hereafter) and
aerosol inherent optical properties (IOPs: spectral dependence of AOD,
single scattering albedo, SSA and asymmetry factor
The vertical profile of aerosols is also very important when estimating their direct radiative effect, and there are considerable variations in the vertical distributions of aerosols over Europe (Guibert et al., 2005; Matthias et al., 2004). For example, Huang et al. (2009) showed that vertical profiles of heating rates can vary depending on the vertical profile of dust aerosol. Therefore, inaccuracies result when constant climatological profiles per aerosol species are used (as is the case in ALADIN-HIRLAM which uses the profiles of Tanré et al., 1984). For example, Guibert et al. (2005) analysed the vertical profiles of aerosol extinction over Europe and found that aerosols over southern Europe are concentrated higher in the atmosphere due to the occurrence of dust storm episodes. Meloni et al. (2005) showed that under clear-sky conditions the direct radiative effect of aerosols on surface radiation has a low dependence on the aerosol vertical profile, but that the profile has an impact on the top of the atmosphere forcing, especially for absorbing aerosols. Toll et al. (2015b) evaluated the profile of the aerosol attenuation coefficient for land aerosols in ALADIN-HIRLAM against observations for the summer 2010 Russian wildfires. They found good agreement between the distribution assumed in the model and CALIOP measurements. However, a more general evaluation of the vertical profile of aerosols in the system has not been performed.
The main goal of the present study is to focus on the impact of AOD550, aerosol IOPs, the vertical distribution of aerosols, relative humidity and radiative transfer algorithms on SW fluxes in diagnostic single-column, clear-sky experiments using the ALADIN-HIRLAM system. Such experiments are useful for developing and testing parameterisations and for running idealised experiments that focus on atmospheric physics in a simplified framework. With these experiments we can evaluate the strengths and weaknesses of the NWP model regarding the treatment of the direct radiative effect of aerosols.
The paper is structured as follows: the model setup and radiation schemes are described in Sect. 2; the aerosol data sets and atmospheric and surface input used in the experiments are given in Sect. 3; descriptions of each of the experiments and sensitivity tests are provided in Sect. 4; the results and discussion are presented in Sect. 5, while conclusions and future work are summarised in Sect. 6.
The ALADIN-HIRLAM NWP system is used for operational weather forecasting by 26 national meteorological services in Europe and North Africa which form the HIRLAM and ALADIN consortia. Pottier (2016) summarises 42 limited area configurations of the system used by the consortia members. This system can also be used for regional climate simulations (Lindstedt et al., 2015), where the direct radiative effect of aerosols can be of greater importance than in short-range NWP applications.
The HARMONIE-AROME configuration based on Seity et al. (2011) was used in this study. HARMONIE (HIRLAM ALADIN Regional Mesoscale Operational NWP in Europe) denotes the specific configuration of the ALADIN-HIRLAM system maintained by the HIRLAM consortium; AROME is a limited area model developed at Météo-France. The default setup of HARMONIE-AROME for operational NWP uses a 2.5 km horizontal grid and 65 hybrid model levels with deep convection treated explicitly. This configuration uses ALADIN non-hydrostatic dynamics (Bénard et al., 2010), non-hydrostatic mesoscale (Meso-NH) physics (Mascart and Bougeault, 2011) and the SURFEX externalised surface scheme (Masson et al., 2013). Surface physiographies are prescribed using the 1 km resolution ECOCLIMAP II database (Faroux et al., 2013) and surface elevation is based on GTOPO30 (USGS, 1998).
We used the single-column version of HARMONIE-AROME (also with 65 vertical levels) based on Malardel et al. (2006) for the experiments detailed in this paper. As in Malardel et al. (2006), we will refer to this model configuration as MUSC (Modèle Unifé Simple Colonne). It includes all of the atmospheric and surface parameterisations of HARMONIE-AROME but lacks the large-scale dynamics, horizontal advection, pressure gradient force and large-scale vertical motion. Because of the simplifying assumptions, MUSC is not suitable for operational weather forecasting. However, its value lies in the fact that it provides a useful means of studying the sensitivity of the model output to realistic atmospheric conditions and different physical parameterisations. The input to MUSC is derived from the output of a 3-D HARMONIE-AROME experiment. This includes the initial conditions of the atmosphere and surface, surface properties, atmospheric temperatures, specific humidities and wind speeds. Details on the input data used in our experiments are provided in Sect. 3.4.
In this study, three shortwave radiation schemes were applied in MUSC: (1) the IFS radiation scheme based on cycle 25R1 (Morcrette, 1991; White, 2004), (2) a new version of the HIRLAM radiation scheme called hlradia (Savijärvi, 1990) containing aerosol parameterisations, and (3) the acraneb2 scheme (Mašek et al., 2016). Table 1 summarises the main characteristics of these radiation schemes.
Summary of aerosol radiation experiments including details of the radiation schemes and aerosol data sets used.
Each scheme treats the atmosphere as a 1-D column consisting of a set of plane-parallel homogeneous layers. The grid box is split into a cloudy fraction and a clear-sky fraction and does not allow lateral exchanges between them. Atmospheric composition (i.e. aerosols, clouds and atmospheric gases) and the radiative properties of the surface are required as input to the radiation schemes. MUSC was run under clear-sky conditions for the experiments and sensitivity studies presented in this paper. Thus, details on cloud particles and cloud cover are not included. Further information on the basic differences between the radiation schemes is given in the following sub-sections.
The IFS SW radiation scheme (ECMWF, 2004; IFS cycle 25R1) is used by default
in MUSC and is the most detailed of the three schemes applied in our
experiments. It contains six SW spectral bands
(0.185–0.25–0.44–0.69–1.19–2.38–4.00
Hlradia, the simplest of the three schemes, considers one SW and one LW spectral band. Clear-sky transmittance, reflectance and absorptance of SW flux are taken into account at each model level to obtain the radiative heating (vertical divergence of the net SW flux) and net SW fluxes. The radiative transfer is parameterised rather than solved explicitly, in order to make the scheme very fast for NWP use (Savijärvi, 1990). The impact of ozone, oxygen and carbon dioxide on SW irradiance is assumed to be constant over time and space. In older versions of the scheme, aerosols were accounted for using constant coefficients. However, the scheme has recently been modified to include parameterisations of the direct and semi-direct effects of aerosols, calculated using the two-stream approximation equations for anisotropic non-conservative scattering described by Thomas and Stamnes (2002).
Hlradia uses the GADS/OPAC aerosols of Koepke et al. (1997) and includes the following species: soot, minerals (nucleation, accumulation, coarse and transported modes), sulphuric acid, sea salt (accumulation and coarse modes), water soluble and water insoluble aerosols. The IFS aerosols types described in Sect. 2.2.1 are mapped to GADS/OPAC species in accordance with ECMWF (2004). The aerosol IOPs are averaged over the entire SW spectrum using spectral weightings calculated, using the libRadtran/DISORT software package (Mayer and Kylling, 2005; Stamnes et al., 1988), at a height of 2 km and a solar zenith angle of 45 degrees for a standard mid-latitude summer atmosphere (Anderson et al., 1986). These IOPs are referred to as broadband IOPs hereafter in the paper. Hlradia uses the same vertical distributions of aerosols as the IFS scheme.
The acraneb2 scheme (Mašek et al., 2016), which is more complex than
hlradia but simpler than IFS, was developed as part of the ALARO-1 suite of
physics parameterisations. Similar to hlradia, it is a broadband scheme using
a single SW radiation interval. However, it uses the Ritter and Geleyn (1992) delta two-stream system for the clear-sky radiative transfer
calculations with coefficients computed according to Räisänen (2002)
i.e. by averaging the coefficients of all of the radiatively active species,
weighted by their optical thicknesses. Acraneb2 uses the same climatologies
of ozone and fixed composition mixture of CO
The direct SW radiative effect of aerosols in MUSC is calculated using
vertically integrated AOD550 and the following aerosol IOPs: AOD spectral
scaling coefficients, spectral SSA and
Monthly climatologies of Tegen et al. (1997) vertically integrated AOD550 for six aerosol categories (see Sect. 2.2.1) are used by default in MUSC. The aerosol IOPs for each spectral band and aerosol type are parameterised following Hess et al. (1998). The default aerosol types in MUSC are translated to GADS aerosol species before being used by hlradia as outlined in Sect. 2.2.2. Spectrally averaged IOPs are used in both hlradia and acraneb2 as outlined in Sect. 2.2.2 and 2.2.3.
Each radiation scheme uses Tanré et al. (1984) climatological vertical
profiles to distribute the AODs on model levels for each aerosol type. In
these schemes the surface-normalized vertical distribution of AOD,
It is also possible to replace the monthly Tegen climatology available in MUSC with other data sets such as the Max-Planck-Institute Aerosol Climatology version 1 (MACv1, Kinne et al., 2013) or the MACC reanalysis (Inness et al., 2013) data set, which includes assimilated AOD measurements. For comparison, the MACC and Tegen aerosol data sets for August 2010 are shown in Fig. 1 (see Sect. 5.1 for further details).
In the Russian wildfire case study (see Sect. 4.1 for details) we ran some
of the simulations using AOD and IOPs derived from CIMEL sun/sky radiometer
measurements recorded at the Aerosol Robotic Network (AERONET, Holben et
al., 1998) station in Tõravere (58.3
AOD550 and AOD scaling coefficients for the six IFS SW bands, assumed valid
for the land (soot) aerosol type, were derived from the spectral AERONET
measurements. These measurements range from 340 to 1020 nm whereas the IFS
radiation scheme includes SW wavelengths from 185 to 4000 nm in the SW.
Therefore, aerosol inputs for the first and sixth SW bands in the IFS scheme (1.19–2.38 and 2.38–4.00
Global SWD radiation measurements recorded at Tõravere were compared to simulated fluxes for the August 2010 wildfire case study (see Sect. 4.1). These measurements are independent of the AERONET network but are part of the Baseline Surface Radiation Network (BSRN, Kallis, 2010) measurements described by Ohmura et al. (1998).
Summary of aerosol radiation experiments including details of the radiation schemes and aerosol data sets used.
The input atmospheric and surface fields for the severe wildfire experiments at Tõravere were generated from hourly output snapshots from a 3-D HARMONIE-AROME simulation. The simulation was carried out on a 2.5 km grid with 65 vertical levels over Estonia for 8 August 2010 as described in Toll et al. (2015a) and the outputs were interpolated to the geographical coordinates of Tõravere for use by MUSC. As the experiments in this paper were run assuming clear-sky conditions, model-level cloud water and cloud ice values were manually removed from each of the hourly atmospheric profile files generated for MUSC. These values were small but needed to be removed to allow direct comparison with observations because cloud cover observations recorded at the Tõravere synoptic station showed that the sky was clear until 14:00 UTC.
Three sets of experiments were conducted in this study (short names for each experiment have been included in brackets): (1) a case study of the summer 2010 Russian wildfires where smoke plumes affected Estonia (WFEXP) and the global SWD irradiance from MUSC was compared to observations, (2) the sensitivity of SWD fluxes to AOD (AODEXP), the aerosol vertical profile (VPEXP) and relative humidity (RHEXP) and (3) aerosol radiative transfer (transmittances) compared to the accurate DISORT scheme (RTEXP). (2) and (3) are sensitivity experiments and do not simulate the summer 2010 wildfires. A summary of these experiments in terms of the aerosols and radiation schemes used is given in Table 2.
One of the worst cases of atmospheric pollution over Estonia in recent decades (Witte et al., 2011; Huijnen et al., 2012) occurred on 8 August 2010 when forest fires in the Baltic region coincided with severe thunderstorms (Toll and Männik, 2015). To study this extreme pollution event, we focussed MUSC single-column experiments on the Tõravere location in Estonia. This location was selected for three reasons: (1) the smoke plume had a strong impact on the area, (2) measurements of aerosol IOPs were available from a local AERONET station and (3) radiation flux measurements were available from the BSRN archive. We ran a series of 12 experiments using MUSC; 4 aerosol scenarios for each of the 3 radiation schemes (see Table 2 for summary). In particular, the following aerosol treatments were considered: (1) aerosol-free, (2) climatological AOD550 and parameterised IOPs, (3) observed AOD550 and parameterised IOPs and (4) aerosol observations (AOD550 and IOPs). In the experiments using observations (either AOD550 or both AOD550 and IOPs) the aerosols were assigned to the land/continental aerosol category while the remaining five categories of IFS aerosols (see Sect. 2.2.1) were set to zero. Accordingly, the climatological vertical distribution of IFS land aerosols was assumed.
In each experiment, a single time step diagnostic MUSC simulation was run using the relevant input file (see Sect. 3.4) as the starting point and repeated for each hour between 00:00 and 24:00 UTC. Thus, a series of single time step simulations were run starting from the 00:00 UTC input file, 01:00 UTC input file and so on up to 24:00 UTC. The model was run in diagnostic mode in order to focus on the radiative properties when the state of the atmosphere and surface had not yet evolved from the initial values.
In the aerosol sensitivity experiments outlined below, the 10:00 UTC atmospheric and surface files generated for the wildfire case study were used as input. In each of the experiments the relative effect of a different aerosol characteristic (AOD550, relative humidity and the vertical distribution of aerosols) on SWD fluxes was investigated. In each case, single time step diagnostic MUSC simulations were conducted for a range of values of each aerosol characteristic (see Table 2 for the summary).
Six experiments were carried out to investigate the effect of AOD550 on SWD fluxes (AODEXP). In particular, two aerosol IOP configurations (observed and parameterised) were used with the IFS, hlradia and acraneb2 radiation schemes. In each case we varied AOD550 from 0 (no aerosols) to 5 (extremely polluted) in steps of 0.1 to investigate its influence on SW radiation fluxes at the surface.
The aerosol radiative transfer algorithms in the IFS and acraneb2 radiation schemes in the current version of the ALADIN-HIRLAM system assume a constant RH of 80 %. In this regard, the hlradia scheme is more advanced as the RH dependence has been incorporated into the calculation of the radiative effect of aerosol IOPs. Four RH experiments (RHEXP) were carried out: two using hlradia and two using IFS where the latter were used to normalise the results from hlradia. As in AODEXP, the 10:00 UTC atmospheric and surface input files were used for the RHEXP experiments. Parameterised aerosol IOPs were employed in each case. Using hlradia, a series of single time step diagnostic MUSC experiments were run for RH in the range 0–1.0 in increments of 0.1. The input atmospheric file was not edited to achieve the required RH. Instead, we hard-coded RH only for the aerosol transmission calculations. The series of RH simulations were run for AOD550 values of 0.1 and 1.0, which covers average and extreme aerosol quantities. Using IFS, it was only necessary to run one diagnostic MUSC simulation for each AOD550 because the IFS aerosol calculations were formulated using an assumed RH of 80 %.
In the VPEXP experiments we tested the sensitivity of SWD fluxes and the SW
heating rate to the vertical scale height
Accurate aerosol radiative transfer is of equal importance to accurate
aerosol IOPs. To examine the performance of the aerosol radiative transfer
algorithms in MUSC, we extracted the relevant subroutines from the IFS,
hlradia and acraneb2 radiation scheme codes and ran these as stand-alone
formulations. These calculations require optical thickness, SSA,
We ran experiments using the IFS Fouquart and Bonnel (1980) clear-sky
formulation, the two-stream approximation (Thomas and Stamnes, 2002) used
in hlradia and the acraneb2 Ritter and Geleyn (1992) two-stream
approximation to calculate SW transmission through a homogeneous atmospheric
layer with optical properties resembling those of aerosols. In particular,
we used SSA
The results presented in this section include a comparison of AOD550 for the
Tegen and MACC reanalysis climatologies, time series of spectral AOD, SSA
and
AERONET measurements of AOD at Tõravere on 8 August 2010 for seven SW wavelengths (nm). The AOD550 derived from these measurements (black dashed line) and the default climatological AOD550 at Tõravere (red dashed line) are also shown in the figure. Data are not available after 14:00 UTC due to the presence of clouds.
Figure 2 shows a time series of AOD at Tõravere on 8 August 2010 for seven wavelengths (measurements from the AERONET archive). The strong spectral dependence of AOD is clear from the figure; AOD is higher for shorter wavelengths. This notable wavelength dependence is characteristic of biomass burning aerosols (Slutsker and Kinne, 1999). The AOD550, also shown in Fig. 2 (black dashed line), used in the experiments involving observations rather than the Tegen climatology, was calculated using the AERONET AOD at 500 nm (cyan line) and the Ångström exponent in the 440–675 nm spectral interval. For comparison, the significantly lower AOD550 from the Tegen climatology (red dashed line) is also included in the figure.
The remaining aerosol IOPs, SSA and
Single scattering albedo (SSA, red continuous) and asymmetry
factor (
The aerosol scattering per extinction ratio, represented by SSA, is high
(close to 0.96 with a spectral average of 0.955) at each wavelength with
little SW spectral dependence (Fig. 3, red continuous curve). This is
similar to results by Dubovik et al. (2002) who showed that the typical SSA
of smoke from biomass burning in Boreal forests is high. However, the
scattering of smoke particles from this Russian wildfire event was higher
than that of plumes from typical biomass burning in Boreal forests (Chubarova
et al., 2012). As in the case of
Figure 4a shows the global SWD radiative flux at the Earth's surface simulated using MUSC with the IFS radiation scheme for 8 August 2010 at Tõravere. We ran an experiment for each of the following four aerosol scenarios (also summarised in Table 2): (1) aerosol-free (red curve), (2) climatological AOD550 and parameterised IOPs (black curve), (3) observed AOD550 and parameterised IOPs (green curve) and (4) observed AOD550 and IOPs (cyan curve) and compared the global SWD fluxes to BSRN observations (blue curve). The discrepancy between simulated and observed SWD irradiance after 14:00 UTC is due to the development of convective clouds (Toll et al., 2015a) which are not accounted for in the MUSC clear-sky simulations.
The biases in global SWD flux (relative to observations) for the experiments
using each radiation scheme (and not just IFS) and the four different aerosol
scenarios are depicted in Fig. 4b (IFS dotted continuous lines, hlradia continuous lines, acraneb2 dashed lines; the aerosol scenario colour
scheme is the same as in Fig. 4a). Overall, the results for the three
schemes are similar (mostly to within 10–20 W m
The use of AOD550 and IOPs derived from AERONET observations gives very good
agreement between the modelled and observed global SWD fluxes for each of
the three radiation schemes (cyan curves, bias < 20 W m
Firstly, using the climatological AOD scaling factors for Tõravere in
August leads to AOD values which are 60 % higher than those estimated
from the AERONET spectral measurements. Secondly, using a delta-Eddington
optical depth scaling factor (
The sensitivity of global SWD fluxes to AOD550 is shown in Fig. 5a for
MUSC experiments run using the IFS, hlradia and acraneb2 radiation schemes.
The results depicted by the cyan curves are for the case where observed IOPs
(i.e. 10:00 UTC observation at Tõravere from the AERONET archive) were used
in the simulations. Parameterised IOPs were used where the experiment results
are shown in green. For an AOD550 of 1, global SWD irradiance is
Global SWD flux as a function of AOD550 for MUSC experiments run
using the IFS (dotted continuous curve), hlradia (continuous curve) and
acraneb2 (dashed curve) radiation schemes. The results depicted by the
cyan curves are for the cases where observed IOPs (SSA,
The effect of AOD550 on direct SWD flux is shown in Fig. 5b for the three
radiation schemes and observed (cyan curves) and parameterised (green curves) IOPs. For example,
when parameterised IOPs were used, an increase in AOD550 from 0 to 1 (i.e. no
aerosols to heavy pollution) reduced the global SWD irradiance by
The impact of relative humidity (RH), accounted for in the aerosol radiative
transfer calculations in the hlradia scheme, on global and direct SWD fluxes
is shown in Fig. 6a. RH was varied from 0 to 1 in steps of 0.1; the AOD550
was set to 0.1 in the grey curves and to 1.0 (significant pollution) in the
black curves. IFS land aerosol parameterised IOPs at Tõravere were used.
Increasing RH from 0 to 1 increases global SWD flux by 1.5 % when AOD550
The inherent uncertainties associated with assuming fixed vertical profiles
were investigated by modifying the assumptions about the shape of the IFS
climatological vertical aerosol profile. Figure 7a shows normalised net SW
fluxes on pressure levels for MUSC experiments run with the IFS radiation
scheme and vertical scale heights (
Figure 7b shows the SW heating rates for the same experimental setup as in
Fig. 7a, where the heating rate is normalised relative to the
corresponding aerosol-free simulations. The heating rates in the boundary
layer changed by up to a factor of 2 in response to the aerosol vertical
distribution (e.g. when
Figure 8a shows transmission as a function of optical depth through a
homogeneous atmospheric layer containing aerosol (SSA
We carried out single-column diagnostic experiments using the MUSC model and three radiation schemes (IFS, hlradia and acraneb2) to examine the influence of the direct radiative effects of aerosols on SW radiative flux. In particular, we focused on the effect of AOD550, aerosol IOPs, the relative humidity, vertical profile of AOD and the radiative transfer formulations on SW fluxes.
In the wildfire case study, we showed that the bias in modelled global SWD
flux relative to observations was lowest when observed AOD550 and IOPs were
included in the simulations (within
The dependency of the direct radiative effect of aerosols on relative
humidity was up to
The influence of improvements in the representation of the direct radiative effect of aerosols on meteorological forecasts needs further study using 3-D simulations. We plan to upgrade the aerosol climatology in the HARMONIE-AROME configuration of the ALADIN-HIRLAM system to the more realistic MACC reanalysis data set. We will also investigate the option of acquiring real-time aerosol input, including the vertical profile of the aerosol properties, from 3-D aerosol IOP estimates from the C-IFS model or chemical transport model simulations, possibly coupled to the NWP model. We also plan to carry out a similar study to the one presented here for all-sky fluxes.
The experiments were designed and run by Emily Gleeson, Velle Toll, Laura Rontu and Kristian Pagh Nielsen. Emily Gleeson prepared the manuscript with contributions from all co-authors.
We acknowledge the support of the International HIRLAM-B and ALADIN programmes. This work was also supported by research grant No. 9140 from the Estonian Science Foundation and by institutional research funding IUT20-11 from the Estonian Ministry of Education and Research. We would like to thank Erko Jakobson for his effort in maintaining the Tõravere AERONET site, which archives the aerosol data used in this study and Ain Kallis for his effort in maintaining the Tõravere BSRN station, whose archived radiation data were used in this study. Finally, we would like to thank the two anonymous reviewers and the editor for their very useful feedback and comments which have helped to improve the paper significantly. Edited by: B. Vogel