105 research outputs found
Spitzer measurements of atomic and molecular abundances in the Type IIP SN 2005af
We present results based on Spitzer Space Telescope mid-infrared (3.6-30
micron) observations of the nearby IIP supernova 2005af. We report the first
ever detection of the SiO molecule in a Type IIP supernova. Together with the
detection of the CO fundamental, this is an exciting finding as it may signal
the onset of dust condensation in the ejecta. From a wealth of fine-structure
lines we provide abundance estimates for stable Ni, Ar, and Ne which, via
spectral synthesis, may be used to constrain nucleosynthesis models.Comment: ApJ Letters (accepted
Impact of urban canopy meteorological forcing on aerosol concentrations
The regional climate model RegCM4 extended with the land surface model CLM4.5
was coupled to the chemistry transport model CAMx to analyze the impact of
urban meteorological forcing on surface fine aerosol (PM2.5)
concentrations for summer conditions over the 2001–2005 period, focusing on
the area of Europe. Starting with the analysis of the meteorological
modifications caused by urban canopy forcing, we found a significant increase
in urban surface temperatures (up to 2–3 K), a decrease of specific humidity (by
up to 0.4–0.6 gkg−1), a reduction of wind speed (up to −1 ms−1) and an enhancement of vertical turbulent diffusion coefficient
(up to 60–70 m2s−1).These modifications translated into significant changes in surface aerosol
concentrations that were calculated by a cascading experimental approach.
First, none of the urban meteorological effects were considered. Then, the
temperature effect was added, then the humidity and the wind, and finally, the
enhanced turbulence was considered in the chemical runs. This facilitated the
understanding of the underlying processes acting to modify urban aerosol
concentrations. Moreover, we looked at the impact of the individual aerosol
components as well. The urbanization-induced temperature changes resulted in
a decrease of PM2.5 by −1.5 to −2 µg m−3, while decreased
urban winds resulted in increases by 1–2 µg m−3. The enhanced
turbulence over urban areas resulted in decreases of PM2.5 by −2 µg m−3. The combined effect of all individual impact depends on
the competition between the partial impacts and can reach up to −3 µg m−3 for some cities, especially when the temperature impact was stronger
in magnitude than the wind impact. The effect of changed humidity was found
to be minor. The main contributor to the temperature impact is the
modification of secondary inorganic aerosols, mainly nitrates, while the wind
and turbulence impact is most pronounced in the case of primary aerosol (primary
black and organic carbon and other fine particle matter). The overall as well
as individual impacts on secondary organic aerosol are very small, with the
increased turbulence acting as the main driver. The analysis of the vertical
extent of the aerosol changes showed that the perturbations caused by urban
canopy forcing, besides being large near the surface, have a secondary
maximum for turbulence and wind impact over higher model levels, which is
attributed to the vertical extent of the changes in turbulence over urban
areas. The validation of model data with measurements showed good agreement,
and we could detect a clear model improvement in some areas when including
the urban canopy meteorological effects in our chemistry simulations.</p
Improved Laboratory Transition Probabilities for Neutral Chromium and Re-determination of the Chromium Abundance for the Sun and Three Stars
Branching fraction measurements from Fourier transform spectra in conjunction
with published radiative lifetimes are used to determine transition
probabilities for 263 lines of neutral chromium. These laboratory values are
employed to derive a new photospheric abundance for the Sun: log (Cr
I) = 5.640.01 (). These Cr I solar abundances do
not exhibit any trends with line strength nor with excitation energy and there
were no obvious indications of departures from LTE. In addition, oscillator
strengths for singly-ionized chromium recently reported by the FERRUM Project
are used to determine: log (Cr II) = 5.770.03 (). Transition probability data are also applied to the spectra of three
stars: HD 75732 (metal-rich dwarf), HD 140283 (metal-poor subgiant), and CS
22892-052 (metal-poor giant). In all of the selected stars, Cr I is found to be
underabundant with respect to Cr II. The possible causes for this abundance
discrepancy and apparent ionization imbalance are discussed.Comment: 44 pages, 6 figure
Land–atmosphere interactions in sub-polar and alpine climates in the CORDEX flagship pilot study Land Use and Climate Across Scales (LUCAS) models – Part 1: Evaluation of the snow-albedo effect
Seasonal snow cover plays a major role in the climate system of the Northern Hemisphere via its effect on land surface albedo and fluxes. In climate models the parameterization of interactions between snow and atmosphere remains a source of uncertainty and biases in the representation of local and global climate. Here, we evaluate the ability of an ensemble of regional climate models (RCMs) coupled with different land surface models to simulate snow–atmosphere interactions over Europe in winter and spring. We use a previously defined index, the snow-albedo sensitivity index (SASI), to quantify the radiative forcing associated with snow cover anomalies. By comparing RCM-derived SASI values with SASI calculated from reanalyses and satellite retrievals, we show that an accurate simulation of snow cover is essential for correctly reproducing the observed forcing over middle and high latitudes in Europe. The choice of parameterizations, and primarily the choice of the land surface model, strongly influences the representation of SASI as it affects the ability of climate models to simulate snow cover accurately. The degree of agreement between the datasets differs between the accumulation and ablation periods, with the latter one presenting the greatest challenge for the RCMs. Given the dominant role of land surface processes in the simulation of snow cover during the ablation period, the results suggest that, during this time period, the choice of the land surface model is more critical for the representation of SASI than the atmospheric model
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Advances in air quality research – current and emerging challenges
© Author(s) 2022. This work is distributed under the Creative Commons Attribution 4.0 License. https://creativecommons.org/licenses/by/4.0/This review provides a community’s perspective on air quality research focusing mainly on developmentsover the past decade. The article provides perspectives on current and future challenges as well asresearch needs for selected key topics. While this paper is not an exhaustive review of all research areas in thefield of air quality, we have selected key topics that we feel are important from air quality research and policy perspectives. After providing a short historical overview, this review focuses on improvements in characterizingsources and emissions of air pollution, new air quality observations and instrumentation, advances in air qualityprediction and forecasting, understanding interactions of air quality with meteorology and climate, exposure andhealth assessment, and air quality management and policy. In conducting the review, specific objectives were(i) to address current developments that push the boundaries of air quality research forward, (ii) to highlightthe emerging prominent gaps of knowledge in air quality research, and (iii) to make recommendations to guidethe direction for future research within the wider community. This review also identifies areas of particular importancefor air quality policy. The original concept of this review was borne at the International Conferenceon Air Quality 2020 (held online due to the COVID 19 restrictions during 18–26 May 2020), but the articleincorporates a wider landscape of research literature within the field of air quality science. On air pollutionemissions the review highlights, in particular, the need to reduce uncertainties in emissions from diffuse sources,particulate matter chemical components, shipping emissions, and the importance of considering both indoor andoutdoor sources. There is a growing need to have integrated air pollution and related observations from bothground-based and remote sensing instruments, including in particular those on satellites. The research shouldalso capitalize on the growing area of low-cost sensors, while ensuring a quality of the measurements which areregulated by guidelines. Connecting various physical scales in air quality modelling is still a continual issue,with cities being affected by air pollution gradients at local scales and by long-range transport. At the same time,one should allow for the impacts from climate change on a longer timescale. Earth system modelling offers considerablepotential by providing a consistent framework for treating scales and processes, especially where thereare significant feedbacks, such as those related to aerosols, chemistry, and meteorology. Assessment of exposureto air pollution should consider the impacts of both indoor and outdoor emissions, as well as application of moresophisticated, dynamic modelling approaches to predict concentrations of air pollutants in both environments.With particulate matter being one of the most important pollutants for health, research is indicating the urgentneed to understand, in particular, the role of particle number and chemical components in terms of health impact,which in turn requires improved emission inventories and models for predicting high-resolution distributions ofthese metrics over cities. The review also examines how air pollution management needs to adapt to the abovementionednew challenges and briefly considers the implications from the COVID-19 pandemic for air quality.Finally, we provide recommendations for air quality research and support for policy.Peer reviewe
- …