Reply on RC2

Abstract. This paper is the companion paper of Córdoba-Jabonero et al. (2021). It deals with the estimation of the long-wave (LW) and net dust direct radiative effect (DRE) during the dust episode that occurred between 23 and 30 June 2019 and was paired with a mega-heatwave. The analysis is performed at two European sites where polarized micro-pulse lidars ran continuously to retrieve the vertical distribution of the dust optical properties: Barcelona, Spain, 23–30 June, and Leipzig, Germany, 29–30 June. The radiative effect is computed with the GAME (global atmospheric model) radiative transfer model separately for the fine- and coarse-mode dust. The instantaneous and daily radiative effect and radiative efficiency (DREff) are provided for the fine-mode, coarse-mode and total dust at the surface, top of the atmosphere (TOA) and in the atmosphere. The fine-mode daily LW DRE is low (< 6 % of the short-wave (SW) component), which makes the coarse-mode LW DRE the main modulator of the total net dust DRE. The coarse-mode LW DRE starts exceeding (in absolute values) the SW component in the middle of the episode, which produces positive coarse-mode net DRE at both the surface and TOA. Such an unusual tendency is attributed to increasing coarse-mode size and surface temperature throughout the episode. This has the effect of reducing the SW cooling in Barcelona up to the point of reaching total net positive dust DRE (+0.9 W m−2) on one occasion at the surface and quasi-neutral (−0.6 W m−2) at TOA. When adding the LW component, the total dust SW radiative efficiency is reduced by a factor of 1.6 at both surface (on average over the episode the total dust net DREff is −54.1 W m−2 τ−1) and TOA (−37.3 W m−2 τ−1). A sensitivity study performed on the surface temperature and the air temperature in the dust layer, both linked to the heatwave and upon which the LW DRE strongly depends, shows that the heatwave contributed to reducing the dust net cooling effect at the surface and that it had nearly no effect at TOA. Its subsequent effect was thus to reduce the heating of the atmosphere produced by the dust particles.

<strong class="journal-contentHeaderColor">Abstract.</strong> The dust direct radiative effect (DRE) in long-wave (DRE_LW), and net effect (DRE_NET), is analysed during an intense and long-lasting Saharan dust intrusion over the Iberian Peninsula, complementing the study on the short-wave DRE (DRE_SW) (L&oacute;pez-Cayuela et al., 2025). In LW, a warming effect at both bottom-of-atmosphere (BOA) and the top-of-atmosphere (TOA) levels is induced by the fine (Df) and coarse (Dc) dust particles (Dc dominant). The DRE_LW-to-DRE_SW ratio for Df ranged 4&ndash;8 % at BOA (1&ndash;4 % at TOA), and for Dc it was rather higher (39&ndash;54 % at BOA and 20&ndash;50 % at TOA). DRE_NETwas consistently negative (net cooling) at both levels, and hence the atmospheric DRE_NET was positive (net warming). The Df contribution to DRE_NET was 12 % (LW) and 30 % (SW). The SW aerosol heating rate (AHR) peaked at higher altitudes, inducing warming within the dust layer, than LW AHR (weaker cooling). Consequently, a net warming inside the dust layer was found, with potential cooling below and above. While SW dominates the net atmospheric warming, LW cooling partially mitigates it. DRE_LW (and DRE_NET) is underestimated (overestimated) by using the dust-mode separation approach when fine radii are lesser (greater) than a particular threshold (e.g., 0.1 &mu;m), revealing the particle size impact in DRE_LW. The dust-induced net effect is primarily driven by SW and modulated by LW. The classical (no separation) approach overestimates DRE_NET, with mean relative differences of -5 %/-9 % at BOA/TOA. Moreover, under moderate-to-high dust, separating Df and Dc contributions yields a weaker (stronger) net cooling at BOA (TOA).

A new coupled cloud physics–radiation parameterization of the bulk optical properties of ice clouds is presented. The parameterization is consistent with assumptions in the cloud physics scheme regarding particle size distributions (PSDs) and mass–dimensional relationships. The parameterization is based on a weighted ice crystal habit mixture model, and its bulk optical properties are parameterized as simple functions of wavelength and ice water content (IWC). This approach directly couples IWC to the bulk optical properties, negating the need for diagnosed variables, such as the ice crystal effective dimension. The parameterization is implemented into the Met Office Unified Model Global Atmosphere 5.0 (GA5) configuration. The GA5 configuration is used to simulate the annual 20-yr shortwave (SW) and longwave (LW) fluxes at the top of the atmosphere (TOA), as well as the temperature structure of the atmosphere, under various microphysical assumptions. The coupled parameterization is directly compared against the current operational radiation parameterization, while maintaining the same cloud physics assumptions. In this experiment, the impacts of the two parameterizations on the SW and LW radiative effects at TOA are also investigated and compared against observations. The 20-yr simulations are compared against the latest observations of the atmospheric temperature and radiative fluxes at TOA. The comparisons demonstrate that the choice of PSD and the assumed ice crystal shape distribution are as important as each other. Moreover, the consistent radiation parameterization removes a long-standing tropical troposphere cold temperature bias but slightly warms the southern midlatitudes by about 0.5 K.

Radiative effect differences between multi-layered and single-layer clouds derived from CERES, CALIPSO, and CloudSat data

Radiative fluxes at the top of the atmosphere (TOA) and the surface were compared at two Antarctic stations, Syowa and the South Pole, using Earth Radiation Budget Experiment (ERBE) data and surface observations. Fluxes at both sites were plotted against cloud amounts derived from surface synoptic observations. Throughout the year over the snow- and ice-covered Antarctic, cloud radiation was found to heat the surface and cool the atmosphere; cloud longwave (LW) effects were greater than cloud shortwave (SW) effects. Clouds have a negligible effect on the absorption of SW by the atmosphere in the interior, and clouds slightly increase the absorption of SW by the atmosphere along the coast. At the TOA, the LW cloud effect was heating along the coast in summer and winter, heating in the interior during summer, and slight cooling in the interior during winter. This unique TOA cloud LW cooling was due to the extremely low surface temperature in the interior during winter. At the TOA, clouds induced SW...

Degenerate and non-degenerate vector solitons and their interactions in the two-component long-wave–short-wave model of Newell type

Sensitivity experiments of direct radiative forcing (RF) caused by mineral dust (MD) for the optical and physical properties of MD, surface albedo, solar zenith angle, and cloud cover were conducted using the Streamer-based Radiative Transfer Model for ADEC Sciences (SRTMAS). The atmospheric and dust profiles were simulated with a chemical transport model at four locations: the sea off Japan, the desert in Tarim Basin, the Sahara Desert, and snow in Siberia. The optimum calculation condition to estimate RF was also tested for the effect of the number of streams used in SRTMAS on the accuracy of RF by MD and the influence of all aerosols other than MD on RF by MD or all aerosols. When several types of aerosols are contained in the atmosphere, the test results showed that the RF by MD should not be calculated from the difference in net radiation between MD-only case and an aerosol-free case, but the difference in net radiation between a case containing all aerosols and a case containing all aerosols except MD. The experiment results by this method confirmed that the sensitivity of instantaneous RF in the shortwave (SW) region at the top of the atmosphere (TOA) to the refractive index strongly depends on surface albedo. Namely, the effect of the difference in the MD model on instantaneous RF is significant over high albedo surfaces and is relatively small over the sea. This is because the multiple reflection between the atmosphere (dust) and surface enhances light absorption by dust particles over high albedo surfaces. Over desert surfaces, the instantaneous RF in SW at TOA produced both positive and negative values within the possible refractive index range of MD. The diurnally averaged RF in SW at TOA also produced both positive and negative values in the possible range of desert albedo. The effect of the spectral distribution of surface albedo on RFs in SW for the TOA, surface, and atmosphere was examined for various surfaces. It was found that for small dust particles with an effective radius of less than 0.6 μm, RFs by MD changed depending on the difference in surface type even if the broadband albedo was the same. This is due to the contrast of spectral distribution between albedo and the extinction coefficient of MD. The vertical positional relationship of cloud cover to dust layer was also very important for RF at TOA in all spectral regions over desert and sea surfaces. However, the effect of cloud cover was generally small over snow surface because cloud albedo was close to the underlying snow albedo.

The gas-aerosol composition of the atmosphere determines specific features of the radiative net irradiance in the atmosphere and the associated climatic changes. The study discusses the anthropogenic variations in the content of the most important greenhouse gases, such as carbon dioxide (CO2) and ozone (O3), as well as the atmospheric aerosol. The estimates of their radiative effects (forcing, RF) in various geophysical conditions are given. Based on the modern ECRAD radiation model, the RF values of considered anthropogenic trace gases and aerosols over the past 20 years were estimated for different seasons of the year relative to their preindustrial level for the Moscow region. We determined specific features of the vertical profiles of RF in the shortwave and longwave spectral ranges and their values at the bottom (BOA) and the top of the atmosphere (TOA) depending on solar elevation and surface albedo, both taking seasonal variations into account and without them. The total RF Total for the warm period with a low surface albedo is negative (–8,33 W/m2 at BOA and –1,35 W/m2 at TOA) if seasonal variations of all considering trace gases and aerosols are taken into account. A weakly absorbing aerosol typical of mid-latitudes plays a significant role in the negative RF. The RF Total for the cold season is –0,08 W/m2 at BOA and +0,38 W/m2 at TOA. The positive value of the total RF at the TOA is due to the positive RF of the aerosol with its absorbing properties and the influence of the high albedo of snow surface, as well as due to the positive RF of carbon dioxide. A nonlinear RF dependence of the trace gases and aerosol on the solar elevation and surface albedo was found. The radiative heating rate due to greenhouse gases at TOA is negative in all seasons of the year. At the same time, it is positive at BOA (about 0,45 K/day in the warm season and 0,25 K/day in the cold season), mainly due to the absorption by aerosol in the lower layers of the troposphere. The radiative heating rate due to CO2 is slightly positive.

The impact of moderately absorbing aerosol on surface sensible, latent, and net radiative fluxes during the summer of 2015 in Central Europe

Abstract. The direct radiative effect (DRE) during 20 intense and widespread dust outbreaks, which affected the broader Mediterranean basin over the period March 2000–February 2013, has been calculated with the NMMB-MONARCH model at regional (Sahara and European continent) and short-term temporal (84 h) scales. According to model simulations, the maximum dust aerosol optical depths (AODs) range from ∼ 2.5 to ∼ 5.5 among the identified cases. At midday, dust outbreaks locally induce a NET (shortwave plus longwave) strong atmospheric warming (DREATM values up to 285 W m−2; Niger–Chad; dust AODs up to ∼ 5.5) and a strong surface cooling (DRENETSURF values down to −337 W m−2), whereas they strongly reduce the downward radiation at the ground level (DRESURF values down to −589 W m−2 over the Eastern Mediterranean, for extremely high dust AODs, 4.5–5). During night-time, reverse effects of smaller magnitude are found. At the top of the atmosphere (TOA), positive (planetary warming) DREs up to 85 W m−2 are found over highly reflective surfaces (Niger–Chad; dust AODs up to ∼ 5.5) while negative (planetary cooling) DREs down to −184 W m−2 (Eastern Mediterranean; dust AODs 4.5–5) are computed over dark surfaces at noon. Dust outbreaks significantly affect the mean regional radiation budget, with NET DREs ranging from −8.5 to 0.5 W m−2, from −31.6 to 2.1 W m−2, from −22.2 to 2.2 W m−2 and from −1.7 to 20.4 W m−2 for TOA, SURF, NETSURF and ATM, respectively. Although the shortwave DREs are larger than the longwave ones, the latter are comparable or even larger at TOA, particularly over the Sahara at midday. As a response to the strong surface day-time cooling, dust outbreaks cause a reduction in the regional sensible and latent heat fluxes by up to 45 and 4 W m−2, respectively, averaged over land areas of the simulation domain. Dust outbreaks reduce the temperature at 2 m by up to 4 K during day-time, whereas a reverse tendency of similar magnitude is found during night-time. Depending on the vertical distribution of dust loads and time, mineral particles heat (cool) the atmosphere by up to 0.9 K (0.8 K) during day-time (night-time) within atmospheric dust layers. Beneath and above the dust clouds, mineral particles cool (warm) the atmosphere by up to 1.3 K (1.2 K) at noon (night-time). On a regional mean basis, negative feedbacks on the total emitted dust (reduced by 19.5 %) and dust AOD (reduced by 6.9 %) are found when dust interacts with the radiation. Through the consideration of dust radiative effects in numerical simulations, the model positive and negative biases for the downward surface SW or LW radiation, respectively, with respect to Baseline Surface Radiation Network (BSRN) measurements, are reduced. In addition, they also reduce the model near-surface (at 2 m) nocturnal cold biases by up to 0.5 K (regional averages), as well as the model warm biases at 950 and 700 hPa, where the dust concentration is maximized, by up to 0.4 K. However, improvements are relatively small and do not happen in all episodes because other model first-order errors may dominate over the expected improvements, and the misrepresentation of the dust plumes' spatiotemporal features and optical properties may even produce a double penalty effect. The enhancement of dust forecasts via data assimilation techniques may significantly improve the results.

Influence of Hamoun Lakes' dry conditions on dust emission and radiative forcing over Sistan plain, Iran

An aerosol model has been developed using mass size distributions of various chemical components measured at Kanpur (an urban location in the Ganga basin, GB, in northern India) and applied to estimate the radiative effects of the aerosols over the entire GB during the winter season. The number size distribution of various species was derived from the measured mass concentration, and the optical properties were calculated using Mie theory. The maximum anthropogenic contribution to the total extinction was estimated to be ∼83%. The relative contributions of various species to the aerosol optical depth (AOD) at 0.5 μm are in the following order: (NH4)2SO4 (nss‐SO4, 30%), nitrate (NO3−, 24%), salt (mainly NaCl and KCl, 18%), dust (17%) and black carbon (BC, 11%). Relative contribution of nss‐SO4, NO3− and salt to the calculated AOD decreases with wavelength, and that of dust increases with wavelength, whereas BC contribution is spectrally insensitive. The extinction coefficient strongly depends on the RH, as the scattering by fine mode fraction, which contributes 88% to the total extinction, is enhanced at high ambient RH. The spectral variation of absorption coefficient indicates that the most likely source of BC in this region is fossil fuel. The spectral variation of single scattering albedo (SSA) in the coarse mode fraction suggests mixing of BC and dust particles. During the observational period, the mean shortwave (SW) clear sky top of the atmosphere (TOA) and surface forcing over Kanpur are estimated to be −13 ± 3 and −43 ± 8 W m−2, respectively. The corresponding longwave forcings are 3.6 ± 0.7 and 2.9 ± 0.6 W m−2, respectively. Mean AOD at 0.55 μm over the GB as derived from MODIS data is 0.36 ± 0.14. Extending our model over the entire GB, the net mean TOA and surface forcing become −6.4 and −30.2 W m−2 (with overall ∼15% uncertainty). This results in high atmospheric absorption (+23.8 W m−2), translating into a heating rate of 0.67 K day−1. The SW surface to TOA forcing ratio (∼3.7) over the GB is 23% higher than the corresponding value for Indian Ocean. The aerosols reduce the incoming solar radiation reaching the surface by ∼19%, which has significant effect on the regional climate.

Daytime variation of aerosol optical depth in North China and its impact on aerosol direct radiative effects

To understand the radiative impact of tropical thin cirrus clouds, the frequency of occurrence and optical depths of these clouds have been derived. “Thin” cirrus clouds are defined here as being those that are not detected by the operational Moderate Resolution Imaging Spectroradiometer (MODIS) cloud mask, corresponding to an optical depth value of approximately 0.3 or smaller, but that are detectable in terms of the cirrus reflectance product based on the MODIS 1.375-μm channel. With such a definition, thin cirrus clouds were present in more than 40% of the pixels flagged as “clear sky” by the operational MODIS cloud mask algorithm. It is shown that these thin cirrus clouds are frequently observed in deep convective regions in the western Pacific. Thin cirrus optical depths were derived from the cirrus reflectance product. Regions of significant cloud fraction and large optical depths were observed in the Northern Hemisphere during the boreal spring and summer and moved southward during the boreal autumn and winter. The radiative effects of tropical thin cirrus clouds were studied on the basis of the retrieved cirrus optical depths, the atmospheric profiles derived from the Atmospheric Infrared Sounder (AIRS) observations, and a radiative transfer model in conjunction with a parameterization of ice cloud spectral optical properties. To understand how these clouds regulate the radiation field in the atmosphere, the instantaneous net fluxes at the top of the atmosphere (TOA) and at the surface were calculated. The present study shows positive and negative net forcings at the TOA and at the surface, respectively. The positive (negative) net forcing at the TOA (surface) is due to the dominance of longwave (shortwave) forcing. Both the TOA and surface forcings are in a range of 0–20 W m−2, depending on the optical depths of thin cirrus clouds.

The clear‐sky aerosol top of atmosphere shortwave (SW) and longwave (LW) radiative effects over the Saharan desert (15–30°N, 10°W–30°E) are investigated based entirely on the satellite observations of aerosol optical thickness (AOT), surface albedo, surface temperature, surface emissivity, atmospheric water vapor content, and SW/LW fluxes. The Ozone Monitoring Instrument (OMI) on Aura and the Multi‐angle SpectroRadiometer (MISR) on Terra satellite are used to estimate AOT at 558 nm (EAOT) for June to September, 2005–2006 when the predominant aerosol type is dust. We then use these EAOT values in conjunction with broadband measurements from the Clouds and the Earth's Radiant Energy System (CERES) to calculate the top‐of‐atmosphere SW and LW flux radiative effect due to these aerosols. The difference in SW flux between desert surface and dust aerosols is found to be negligible due to the high surface reflectance over the Sahara desert. The instantaneous area‐averaged LW radiative effect is calculated as +11.4 Wm−2 with radiative efficiencies ranging from +11 to +26 Wm−2/AOT. The results indicate that net radiative effect of dust over the Sahara desert is dominated by the longwave effect in contrast to oceans where the shortwave effect dominates.