Popular summary.Aerosols, tiny solid or liquid particles suspended in the atmosphere, were once only a side note in the Atmospheric Sciences. Today we realize the importance of aerosols in instigating or mitigating climate change, in modifling clouds and large-scale precipitation patterns and in affecting human health. Unlike greenhouse gases, which are well-mixed and long-lasting in the atmosphere, aerosols are temporally and spatially variable with lifetimes of a few days to a few weeks. Their transient natures make aerosols difficult to characterize and their effects on climate, hydrology and health difficult to model. Satellites provide the best means to observe the global aerosol system and narrow the uncertainties associated with aerosol characterization, but the satellite observations must be sufficiently accurate to be useful. The MODerate resolution Imaging Spectroradiometer (MODIS) aboard both NASA's Terra and Aqua satellites provides a unique tool to discern the global impact of aerosols. The products derived from MODIS data include aerosol optical thickness, which is a measure of aerosol amount, as well as products that describe the size of the aerosol particles. The MODIS aerosol retrievals are continuously evaluated against ground-truth of an existing global network of highly accurate instruments (AERONET). The results show an accuracy for the MODIS aerosol products that will sufficiently narrow the uncertainty of global aerosol characterization. Furthermore, the MODIS derivation of aerosol particle size aids in discriminating between man-made aerosol and naturally produced aerosols. This is a major step forward in narrowing the uncertainties associated with estimating the total anthropogenic effect on climate.
This paper presents a detailed assessment of the ability of the 240 Skyrme interaction parameter sets in the literature to satisfy a series of criteria derived from macroscopic properties of nuclear matter in the vicinity of nuclear saturation density at zero temperature and their density dependence, derived by the liquid-drop model, in experiments with giant resonances and heavy-ion collisions. The objective is to identify those parametrizations which best satisfy the current understanding of the physics of nuclear matter over a wide range of applications. Out of the 240 models, only 16 are shown to satisfy all these constraints. Additional, more microscopic, constraints on the density dependence of the neutron and proton effective mass β-equilibrium matter, Landau parameters of symmetric and pure neutron nuclear matter, and observational data on high-and low-mass cold neutron stars further reduce this number to 5, a very small group of recommended Skyrme parametrizations to be used in future applications of the Skyrme interaction of nuclear-matter-related observables. Full information on partial fulfillment of individual constraints by all Skyrme models considered is given. The results are discussed in terms of the physical interpretation of the Skyrme interaction and the validity of its use in mean-field models. Future work on application of the Skyrme forces, selected on the basis of variables of nuclear matter, in the Hartree-Fock calculation of properties of finite nuclei, is outlined.
 The recently released Collection 5 Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products provide a consistent record of the Earth's aerosol system. Comparing with ground-based AERONET observations of aerosol optical depth (AOD) we find that Collection 5 MODIS aerosol products estimate AOD to within expected accuracy more than 60% of the time over ocean and more than 72% of the time over land. This is similar to previous results for ocean and better than the previous results for land. However, the new collection introduces a 0.015 offset between the Terra and Aqua global mean AOD over ocean, where none existed previously. Aqua conforms to previous values and expectations while Terra is higher than what had been expected. The cause of the offset is unknown, but changes to calibration are a possible explanation. Even though Terra's higher ocean AOD is unexpected and unexplained, we present climatological analyses of data from both sensors. We find that the multiannual global mean AOD at 550 nm over oceans is 0.13 for Aqua and 0.14 for Terra, and over land it is 0.19 in both Aqua and Terra. AOD in situations with 80% cloud fraction are twice the global mean values, although such situations occur only 2% of the time over ocean and less than 1% of the time over land. Aerosol particle size associated with these very cloudy situations does not show a drastic change over ocean, but does over land. Regionally, aerosol amounts vary from polluted areas such as east Asia and India, to the cleanest regions such as Australia and the northern continents. As AOD increases over maritime background conditions, fine mode aerosol dominates over dust over all oceans, except over the tropical Atlantic downwind of the Sahara and during some months over the Arabian Sea.
) is small, potentially allowing reconstruction of past shifts in tropospheric oxidation pathways from ice cores. Assuming a Rayleigh-type process we find fractionation constants ε of −60±15‰, 8±2‰ and 1±1‰, for δ 15 N, δ 18 O and 17 O, respectively. A photolysis model yields an upper limit for the photolytic fractionation constant 15 ε of δ 15 N, consistent with lab and field measurements, and demonstrates a high sensitivity of 15 ε to the incident actinic flux spectrum. The photolytic 15 ε is process-specific and therefore applies to any snow covered location. Previously published 15 ε values are not representative for conditions at the Earth surface, but apply only to the UV lamp used in the reported experiment (Blunier et al., 2005;Jacobi et al., 2006). Depletion of oxygen stable isotopes is attributed to photolysis followed by isotopic exchange with water and hydroxyl radicals. Conversely, 15 N enrichment of the NO
The effect of anthropogenic aerosols on clouds is one of the most important and least understood aspects of human-induced climate change. Small changes in the amount of cloud coverage can produce a climate forcing equivalent in magnitude and opposite in sign to that caused by anthropogenic greenhouse gases, and changes in cloud height can shift the effect of clouds from cooling to warming. Focusing on the Amazon, we show a smooth transition between two opposing effects of aerosols on clouds: the microphysical and the radiative. We show how a feedback between the optical properties of aerosols and the cloud fraction can modify the aerosol forcing, changing the total radiative energy and redistributing it over the atmospheric column.
Abstract. Gas and particle measurements are described for optically thick regional hazes, dominated by aged smoke from biomass buming, in the cermdo and rain forested regions of Brazil. The hazes tended to be evenly mixed from the surface to the trade wind inversion at 34 km in altitude. The properties of aged gases and particles in the regional hazes were significantly different from those of young smoke (<4 min old). As the smoke aged, the total amount of carbon in non-methane hydrocarbon species (C
Abstract. Here we report the measurement of the comprehensive isotopic composition (δ15N, Δ17O and δ18O) of nitrate at the air–snow interface at Dome C, Antarctica (DC, 75°06' S, 123°19' E), and in snow pits along a transect across the East Antarctic Ice Sheet (EAIS) between 66° S and 78° S. In most of the snow pits, nitrate loss (either by physical release or UV photolysis of nitrate) is observed and fractionation constants associated are calculated. Nitrate collected from snow pits on the plateau (snow accumulation rate below 50 kg m−2 a−1) displays average fractionation constants of (−59±10) ‰, (+2.0±1.0) ‰ and (+8.7±2.4)‰ for δ15N, Δ17O and δ18O, respectively. In contrast, snow pits sampled on the coast show distinct isotopic signatures with average fractionation constants of (−16±14) ‰, (−0.2±1.5) ‰ and (+3.1±5.8) ‰, for δ15N, Δ17O and δ18O, respectively. Our observations corroborate that photolysis (associated with a 15N / 14N fractionation constant of the order of –48 ‰ according to Frey et al. (2009) is the dominant nitrate loss process on the East Antarctic Plateau, while on the coast the loss is less pronounced and could involve both physical release and photochemical processes. Year-round isotopic measurements at DC show a~close relationship between the Δ17O of atmospheric nitrate and Δ17O of nitrate in skin layer snow, suggesting a photolytically driven isotopic equilibrium imposed by nitrate recycling at this interface. Atmospheric nitrate deposition may lead to fractionation of the nitrogen isotopes and explain the almost constant shift of the order of 25 ‰ between the δ15N values in the atmospheric and skin layer nitrate at DC. Asymptotic δ15N(NO3−) values calculated for each snow pit are found to be correlated with the inverse of the snow accumulation rate (ln(δ15N as. + 1) = (5.76±0.47) &cdot; (kg m−2 a−1/ A) + (0.01±0.02)), confirming the strong relationship between the snow accumulation rate and the degree of isotopic fractionation, consistent with previous observations by Freyer et al. (1996). Asymptotic Δ17O(NO3−) values on the plateau are smaller than the values found in the skin layer most likely due to oxygen isotope exchange between the nitrate photoproducts and water molecules from the surrounding ice. However, the apparent fractionation in Δ17O is small, thus allowing the preservation of a portion of the atmospheric signal.
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