How the Assumed Size Distribution of Dust Minerals Affects the Predicted Ice Forming Nuclei

The formation of ice in clouds depends on the availability of ice forming nuclei (IFN). Dust aerosol particles are considered the most important source of IFN at a global scale. Recent laboratory studies have demonstrated that the mineral feldspar provides the most efficient dust IFN for immersion freezing and together with kaolinite for deposition ice nucleation, and that the phyllosilicates illite and montmorillonite (a member of the smectite group) are of secondary importance.A few studies have applied global models that simulate mineral specific dust to predict the number and geographical distribution of IFN. These studies have been based on the simple assumption that the mineral composition of soil as provided in data sets from the literature translates directly into the mineral composition of the dust aerosols. However, these tables are based on measurements of wet-sieved soil where dust aggregates are destroyed to a large degree. In consequence, the size distribution of dust is shifted to smaller sizes, and phyllosilicates like illite, kaolinite, and smectite are only found in the size range 2 m. In contrast, in measurements of the mineral composition of dust aerosols, the largest mass fraction of these phyllosilicates is found in the size range 2 m as part of dust aggregates. Conversely, the mass fraction of feldspar is smaller in this size range, varying with the geographical location. This may have a significant effect on the predicted IFN number and its geographical distribution.An improved mineral specific dust aerosol module has been recently implemented in the NASA GISS Earth System ModelE2. The dust module takes into consideration the disaggregated state of wet-sieved soil, on which the tables of soil mineral fractions are based. To simulate the atmospheric cycle of the minerals, the mass size distribution of each mineral in aggregates that are emitted from undispersed parent soil is reconstructed. In the current study, we test the null-hypothesis that simulating the presence of a large mass fraction of phyllosilicates in dust aerosols in the size range 2 m, in comparison to a simple model assumption where this is neglected, does not yield a significant effect on the magnitude and geographical distribution of the predicted IFN number. Results from sensitivity experiments are presented as well

How the Emitted Size Distribution and Mixing State of Feldspar Affect Ice Nucleating Particles in a Global Model

The effect of aerosol particles on ice nucleation and, in turn, the formation of ice and mixed phase clouds is recognized as one of the largest sources of uncertainty in climate prediction. We apply an improved dust mineral specific aerosol module in the NASA GISS Earth System ModelE, which takes into account soil aggregates and their fragmentation at emission as well as the emission of large particles. We calculate ice nucleating particle concentrations from K-feldspar abundance for an active site parameterization for a range of activation temperatures and external and internal mixing assumption. We find that the globally averaged INP concentration is reduced by a factor of two to three, compared to a simple assumption on the size distribution of emitted dust minerals. The decrease can amount to a factor of five in some geographical regions. The results vary little between external and internal mixing and different activation temperatures, except for the coldest temperatures. In the sectional size distribution, the size range 24 micrometer contributes the largest INP number

Soil Dust Aerosols and Wind as Predictors of Seasonal Meningitis Incidence in Niger

Background: Epidemics of meningococcal meningitis are concentrated in sub-Saharan Africa during the dry season, a period when the region is affected by the Harmattan, a dry and dusty northeasterly trade wind blowing from the Sahara into the Gulf of Guinea. Objectives: We examined the potential of climate-based statistical forecasting models to predict seasonal incidence of meningitis in Niger at both the national and district levels. Data and methods: We used time series of meningitis incidence from 1986 through 2006 for 38 districts in Niger. We tested models based on data that would be readily available in an operational framework, such as climate and dust, population, and the incidence of early cases before the onset of the meningitis season in January–May. Incidence was used as a proxy for immunological state, susceptibility, and carriage in the population. We compared a range of negative binomial generalized linear models fitted to the meningitis data. Results: At the national level, a model using early incidence in December and averaged November–December zonal wind provided the best fit (pseudo-R2 = 0.57), with zonal wind having the greatest impact. A model with surface dust concentration as a predictive variable performed indistinguishably well. At the district level, the best spatiotemporal model included zonal wind, dust concentration, early incidence in December, and population density (pseudo-R2 = 0.41). Conclusions: We showed that wind and dust information and incidence in the early dry season predict part of the year-to-year variability of the seasonal incidence of meningitis at both national and district levels in Niger. Models of this form could provide an early-season alert that wind, dust, and other conditions are potentially conducive to an epidemic

Predicting the mineral composition of dust aerosols: Insights from elemental composition measured at the Izaña Observatory

Regional variations of dust mineral composition are fundamental to climate impacts but generally neglected in climate models. A challenge for models is that atlases of soil composition are derived from measurements following wet sieving, which destroys the aggregates potentially emitted from the soil. Aggregates are crucial to simulating the observed size distribution of emitted soil particles. We use an extension of brittle fragmentation theory in a global dust model to account for these aggregates. Our method reproduces the size-resolved dust concentration along with the approximately size-invariant fractional abundance of elements like Fe and Al in the decade-long aerosol record from the Izaña Observatory, off the coast of West Africa. By distinguishing between Fe in structural and free forms, we can attribute improved model behavior to aggregation of Fe and Al-rich clay particles. We also demonstrate the importance of size-resolved measurements along with elemental composition analysis to constrain models.This research was supported by the Department of Energy (DE-SC0006713), the NASA Modeling, Analysis and Prediction Program, and the Aerosol Global Atmospheric Watch program of Izaña Observatory, which has been funded by AEMET and several research projects of the Ministry of Economy and Competitiveness of Spain and the European Regional Development Fund (ERDF) including POLLINDUST (CGL2011-26259) and AEROATLAN (CGL2015-66229-P)

Dangerous human-made interference with climate: a GISS modelE study

We investigate the issue of "dangerous human-made interference with climate" using simulations with GISS modelE driven by measured or estimated forcings for 1880–2003 and extended to 2100 for IPCC greenhouse gas scenarios as well as the "alternative" scenario of Hansen and Sato (2004). Identification of "dangerous" effects is partly subjective, but we find evidence that added global warming of more than 1°C above the level in 2000 has effects that may be highly disruptive. The alternative scenario, with peak added forcing ~1.5 W/m2 in 2100, keeps further global warming under 1°C if climate sensitivity is ~3°C or less for doubled CO2. The alternative scenario keeps mean regional seasonal warming within 2σ (standard deviations) of 20th century variability, but other scenarios yield regional changes of 5–10σ, i.e. mean conditions outside the range of local experience. We conclude that a CO2 level exceeding about 450 ppm is "dangerous", but reduction of non-CO2 forcings can provide modest relief on the CO2 constraint. We discuss three specific sub-global topics: Arctic climate change, tropical storm intensification, and ice sheet stability. We suggest that Arctic climate change has been driven as much by pollutants (O3, its precursor CH4, and soot) as by CO2, offering hope that dual efforts to reduce pollutants and slow CO2 growth could minimize Arctic change. Simulated recent ocean warming in the region of Atlantic hurricane formation is comparable to observations, suggesting that greenhouse gases (GHGs) may have contributed to a trend toward greater hurricane intensities. Increasing GHGs cause significant warming in our model in submarine regions of ice shelves and shallow methane hydrates, raising concern about the potential for accelerating sea level rise and future positive feedback from methane release. Growth of non-CO2 forcings has slowed in recent years, but CO2 emissions are now surging well above the alternative scenario. Prompt actions to slow CO2 emissions and decrease non-CO2 forcings are required to achieve the low forcing of the alternative scenario

Mars Atmosphere Simulations With ROCKE-3D: Nonlinear Dust Cycle Behavior Linked to Dust Radiative Effect

&amp;lt;p&amp;gt;We present simulation results of the dust cycle on Mars using the NASA Goddard Institute for Space Studies (GISS) ROCKE-3D [1] general circulation model with radiatively active dust aerosol tracers. Dust aerosols are represented by a sectional scheme that partitions the simulated dust mass into eight size classes, covering a total size range from 0.1 to 32 &amp;amp;#956;m particle diameter. The model simulates emission from sources, advection, and turbulent, gravitational, and wet deposition of dust. The strength of the dust cycle can be calibrated with a global factor for the dust emission. ROCKE-3D is coupled to the Suite of Community Radiative Transfer codes based on Edwards and Slingo (SOCRATES) [2,3], which applies Mie theory to calculate scattering and absorption of radiation by aerosols. We carried out a series of experiments over 11 Mars years, for which we varied the strength of the dust cycle, and for radiatively active and inactive dust. The simulated dust aerosol optical depths were compared to gridded retrievals of the dust AOD from measurements over 11 years [4, 5]. We find that the dust cycle displays nonlinear behavior with the strength of emission, when the dust is radiatively active, which is absent for radiatively inactive dust. When the dust cycle strength exceeds a certain threshold the simulated mean annual cycle of dust starts to exhibit features that are similar to the observed mean annual cycle. We hypothesize that feedbacks involving the dust radiative effect introduce important non-linearities, which are essential for reproducing and understanding the observed dust cycle on Mars.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;References: [1] Way, M. J. et al. (2017) ApJS, 231, 12.&amp;lt;br&amp;gt;[2] Edwards, J. M. (1996), JAtS, 53, 1921.&amp;lt;br&amp;gt;[3] Edwards, J. M., &amp;amp; Slingo, A. (1996), QJRMS, 122, 689.&amp;lt;br&amp;gt;[4] Montabone, L. et al. (2015) Icarus, 251, 65.&amp;lt;br&amp;gt;[5] Montabone, L. et al. (2020) JGR Planets, 2019JE006111.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;</jats:p

Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust

&lt;p&gt;&lt;em&gt;The composition of soil dust aerosols derives from the mineral abundances in the parent soils&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;that vary across dust source regions. Nonetheless, Earth system models (ESMs) have traditionally represented&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;mineral dust as a globally homogeneous species. The growing interest in modeling dust mineralogy, facilitated&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;by the recognized sensitivity of the dust climate impacts to composition, has motivated state-of-the-art ESMs to&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;incorporate the mineral speciation of dust along with its effect upon the dust direct radiative effect (DRE). In&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;this work, we enable the NASA Goddard Institute for Space Studies ModelE2.1 to calculate the shortwave (SW)&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;DRE accounting for the regionally varying soil mineralogy. Mineral&ndash;radiation interaction at solar wavelengths&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;is calculated according to two alternative coupling schemes: (1) external mixing of three mineral components&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;that are optically distinguished, one of which contains embedded iron oxides; (2) a single internal mixture of&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;all dust minerals with a dynamic fraction of iron oxides that varies regionally and temporally. We link dust absorption&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;to the fractional mass of iron oxides based on recent chamber measurements using natural dust aerosol&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;samples. We show that coupled mineralogy overall enhances the scattering by dust, and thus the global cooling,&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;compared to our control run with globally uniform composition. According to the external mixing scheme, the&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;SW DRE at the top of atmosphere (TOA) changes from -0.25 to -0.30 W m-&lt;/em&gt;&lt;span&gt;&lt;em&gt;2&lt;/em&gt;&lt;/span&gt;&lt;em&gt;, corresponding to a change in&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;the net DRE, including the longwave effect, from -0.08 to -0.12 W m-&lt;/em&gt;&lt;span&gt;&lt;em&gt;2&lt;/em&gt;&lt;/span&gt;&lt;em&gt;. The cooling increase is accentuated&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;when the internal mixing scheme is configured: the SW DRE at the TOA becomes -0.34 W m-&lt;/em&gt;&lt;span&gt;&lt;em&gt;2 &lt;/em&gt;&lt;/span&gt;&lt;em&gt;with a net DRE&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;of -0.15 W m-&lt;/em&gt;&lt;span&gt;&lt;em&gt;2&lt;/em&gt;&lt;/span&gt;&lt;em&gt;. The varying composition modifies the regional distribution of single scattering albedo (SSA),&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;whose variations in specific regions can be remarkable (above 0.03) and significantly modify the regional SW&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;DRE. Evaluation against the AErosol RObotic NETwork (AERONET) shows that explicit representation of soil&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;mineralogy and its regional variations reduces the low bias of model dust SSA while improving the range of&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;variability across stations and calendar months. Despite these improvements, the moderate spatiotemporal correlation&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;with AERONET reveals remaining modeling challenges and the need for more accurate measurements&lt;/em&gt;&lt;/p&gt; &lt;p&gt;&lt;em&gt;of mineral fractions in soils.&lt;/em&gt;&lt;/p&gt;&lt;p&gt;The following archives contain the software code and analysis data used in the article: "Observationally constrained regional variations of shortwave absorption by iron oxides emphasize the cooling effect of dust" by V. Obiso, M. Gon&ccedil;alves Ageitos, C. P&eacute;rez Garc&iacute;a-Pando, J. P. Perlwitz, G. L. Schuster, S. E. Bauer, C. Di Biagio, P. Formenti, K. Tsigaridis and R. L. Miller (ACP, 2024).&lt;/p&gt; &lt;p&gt;&nbsp;&lt;/p&gt; &lt;p&gt;Specifically, the three files contain the version of GISS ModelE used in this work (&lt;em&gt;Obiso_etal_ACP_2024.ModelE_Source_Code_20240312.zip&lt;/em&gt;), the required input files for the model (&lt;em&gt;Obiso_etal_ACP_2024.ModelE_Input_Files_20240312.zip&lt;/em&gt;) and the whole package of analysis scripts and input data, including instructions for the user, for generating all the figures of the article (&lt;em&gt;Obiso_etal_ACP_2024.Analysis_Scripts_Data_20240306.tgz&lt;/em&gt;).&lt;/p&gt

GISS‐E2.1: Configurations and Climatology

Abstract This paper describes the GISS‐E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS‐E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden‐Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks