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  • 1
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    On the sensitivity of droplet size relative dispersion to warm cumulus cloud evolution (2012)
    Wiley
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    Publication Date: 2012-07-12
    Description: Relative dispersion (ε), defined as the ratio between cloud droplet size distribution width (σ) and cloud droplet average radius (〈r〉), is a key factor used to parameterize various cloud processes in global circulation models (GCMs) and bulk microphysical scheme models (BSMs). Recent studies indicate that the impact of aerosol loading (N) and atmospheric thermodynamic conditions on ε are far from fully understood. Currently, a fixed value per hydrometeor type is used in most BSMs and GCMs, which imposes significant limitations on our ability to model and predict cloud processes and their impact on the environment, on regional to global scales. In this study, we use a detailed bin microphysics single cloud model to investigate the combined impact of atmospheric thermodynamic conditions and N on ε, in warm cumulus clouds. As initial conditions, we used different lapse-rates combined with 8 scenarios of aerosol loading, representing very clean (N = 25 cm−3) to heavily polluted (N = 1600 cm−3) conditions. Moreover, the results are analyzed per cloud evolutionary stage according to the dominance of microphysical processes. The use of this method indicated a different pattern of ε at each stage. Specifically, during the mature stage fitting of ε to rv is relatively resilient to changes in the environmental conditions. Such findings suggest a new view of the effect of aerosols on clouds, via changes in the cloud evolution patterns and a new approach to parameterization of ε based on rv, which can significantly improve the prediction of cloud processes by GCMs and BSMs.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Modification of the National Weather Service Distributed Hydrologic Model for subsurface water exchanges between grids (2011)
    Wiley
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    Publication Date: 2011-06-29
    Description: To account for spatial variability of precipitation, as well as basin physiographic properties, the National Weather Service (NWS) has developed a distributed version of its hydrologic component, termed the Hydrology Laboratory-Research Distributed Hydrologic Model (HL-RDHM). Because channels are the only source of water exchange between neighboring computational elements, the absence of such exchange has been identified as a weakness in the model. The primary objective of this paper is to modify the model structure to account for subsurface water exchanges without dramatically altering the conceptual framework of the water balance module. The subsurface exchanges are established by partitioning the slow response components released from the lower layer storages into two parts: the first part involves the grid's conceptual channel, while the second is added to the lower layer storages of the downstream pixel. Realizing the deficiency of the water balance module to locate the lower zone layers in sufficient depths, a complementary study is conducted to test the feasibility of further improvement in the modified model by equally shifting downward the lower zone layers of all pixels over the basin. The Baron Fork at Eldon, Oklahoma, is chosen as the test basin. Ten years of grid-based multisensor precipitation data are used to investigate the effects of the modification, plus shifting the lower zone layers on model performance. The results show that the modified-shifted HL-RDHM can markedly improve the streamflow simulations at the interior point, as well as very high peak-flow simulations at the basin's outlet.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Precipitation-generated oscillations in open cellular cloud fields (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-08-13
    Description: Cloud fields adopt many different patterns that can have a profound effect on the amount of sunlight reflected back to space, with important implications for the Earth's climate. These cloud patterns can be observed in satellite images of the Earth and often exhibit distinct cell-like structures associated with organized convection at scales of tens of kilometres. Recent evidence has shown that atmospheric aerosol particles-through their influence on precipitation formation-help to determine whether cloud fields take on closed (more reflective) or open (less reflective) cellular patterns. The physical mechanisms controlling the formation and evolution of these cells, however, are still poorly understood, limiting our ability to simulate realistically the effects of clouds on global reflectance. Here we use satellite imagery and numerical models to show how precipitating clouds produce an open cellular cloud pattern that oscillates between different, weakly stable states. The oscillations are a result of precipitation causing downward motion and outflow from clouds that were previously positively buoyant. The evaporating precipitation drives air down to the Earth's surface, where it diverges and collides with the outflows of neighbouring precipitating cells. These colliding outflows form surface convergence zones and new cloud formation. In turn, the newly formed clouds produce precipitation and new colliding outflow patterns that are displaced from the previous ones. As successive cycles of this kind unfold, convergence zones alternate with divergence zones and new cloud patterns emerge to replace old ones. The result is an oscillating, self-organized system with a characteristic cell size and precipitation frequency.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Feingold, Graham -- Koren, Ilan -- Wang, Hailong -- Xue, Huiwen -- Brewer, Wm Alan -- England -- Nature. 2010 Aug 12;466(7308):849-52. doi: 10.1038/nature09314.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, Colorado 80305, USA. graham.feingold@noaa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20703303" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 4
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    Smoke and pollution aerosol effect on cloud cover (2006)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2006-07-15
    Description: Pollution and smoke aerosols can increase or decrease the cloud cover. This duality in the effects of aerosols forms one of the largest uncertainties in climate research. Using solar measurements from Aerosol Robotic Network sites around the globe, we show an increase in cloud cover with an increase in the aerosol column concentration and an inverse dependence on the aerosol absorption of sunlight. The emerging rule appears to be independent of geographical location or aerosol type, thus increasing our confidence in the understanding of these aerosol effects on the clouds and climate. Preliminary estimates suggest an increase of 5% in cloud cover.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kaufman, Yoram J -- Koren, Ilan -- New York, N.Y. -- Science. 2006 Aug 4;313(5787):655-8. Epub 2006 Jul 13.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA/Goddard Space Flight Center, 613.2, Greenbelt, MD 20771, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16840661" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 5
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    Smoke invigoration versus inhibition of clouds over the Amazon (2008)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2008-08-16
    Description: 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Koren, Ilan -- Martins, J Vanderlei -- Remer, Lorraine A -- Afargan, Hila -- New York, N.Y. -- Science. 2008 Aug 15;321(5891):946-9. doi: 10.1126/science.1159185.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Environmental Sciences, Weizmann Institute, Rehovot 76100, Israel.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18703738" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 6
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    Measurement of the effect of Amazon smoke on inhibition of cloud formation (2004)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2004-02-28
    Description: Urban air pollution and smoke from fires have been modeled to reduce cloud formation by absorbing sunlight, thereby cooling the surface and heating the atmosphere. Satellite data over the Amazon region during the biomass burning season showed that scattered cumulus cloud cover was reduced from 38%in clean conditions to 0%for heavy smoke (optical depth of 1.3). This response to the smoke radiative effect reverses the regional smoke instantaneous forcing of climate from -28 watts per square meter in cloud-free conditions to +8 watts per square meter once the reduction of cloud cover is accounted for.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Koren, Ilan -- Kaufman, Yoram J -- Remer, Lorraine A -- Martins, Jose V -- New York, N.Y. -- Science. 2004 Feb 27;303(5662):1342-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉NASA Goddard Space Flight Center (GSFC), Greenbelt, MD 20771, USA. ilank@climate.gsfc.nasa.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/14988557" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 7
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    Directional Derivatives of Ray Velocity in Anisotropic Elastic Media (2018)
    Oxford University Press
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    Publication Date: 2018
    Description: 〈span〉〈div〉Summary〈/div〉Two-point boundary-value ray tracing in anisotropic elastic media, based on the ray bending method, is a highly nonlinear problem. It can be solved by the Newton method, which requires first and second spatial, directional and mixed derivatives of the ray (group) velocity at each node along a trial ray trajectory between two fixed endpoints. The second derivatives also provide the curvature components of the propagating wavefronts and thus make it possible to compute dynamic characteristics (e.g. geometrical spreading) along the rays, as well as paraxial rays and beams. We have developed an original novel methodology for obtaining analytically these spatial/directional gradient vectors and spatial/directional/mixed Hessian matrices for general anisotropic (triclinic) media. The derivatives for higher ‘crystal’ symmetry classes, such as transverse isotropy, orthorhombic, and monoclinic media (including those with tilted symmetry axes or planes) are explicitly provided; each is followed by a numerical example. We validate our exact analytic derivatives by comparing them to numerical approximations computed with finite difference schemes.〈/span〉
    Print ISSN: 2051-1965
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Spatial boundaries of Aerosol Robotic Network (AERONET) observations over the Mediterranean basin (2016)
    Wiley
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    Publication Date: 2016-02-19
    Description: Accurate knowledge of aerosol variability on a relatively high spatio-temporal scale is needed for better assessment of aerosol radiative effects and aerosol-climate interactions. We investigated the spatial boundaries of the Aerosol Robotic Network (AERONET) observations over the Mediterranean basin using a statistical approach. We used 13 years (2002-2014) of aerosol optical depth (AOD) measurements from the Moderate-resolution Imaging Spectroradiometer (MODIS) and 15 AERONET sites around the Mediterranean basin. The gridded correlation maps show moderate to high correlations (R 〉 0.5) around each AERONET site up to ~200-500 km radius depending on location. Such analyses provide information on the spatial domain in which the AERONET measurements can be reliably used per site. The statistical model provides a better daytime AOD product on finer temporal resolution with higher spatial coverage as compared to using AERONET/MODIS observations separately. The findings from this study can be useful for the assimilation-based model forecasting of aerosol properties.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Cell biology. Promoting tumorigenesis by suppressing autophagy (2012)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2012-11-20
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Koren, Itay -- Kimchi, Adi -- New York, N.Y. -- Science. 2012 Nov 16;338(6109):889-90. doi: 10.1126/science.1230577.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Molecular Genetics. Weizmann Institute of Science, Rehovot 76100, Israel. itay.koren@weizmann.ac.il〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23161981" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Apoptosis Regulatory Proteins/*metabolism ; *Autophagy ; Cell Transformation, Neoplastic/*metabolism ; Humans ; Membrane Proteins/*metabolism ; Proto-Oncogene Proteins c-akt/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 10
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    From aerosol-limited to invigoration of warm convective clouds (2014)
    American Association for the Advancement of Science (AAAS)
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    Publication Date: 2014-06-07
    Description: Among all cloud-aerosol interactions, the invigoration effect is the most elusive. Most of the studies that do suggest this effect link it to deep convective clouds with a warm base and cold top. Here, we provide evidence from observations and numerical modeling of a dramatic aerosol effect on warm clouds. We propose that convective-cloud invigoration by aerosols can be viewed as an extension of the concept of aerosol-limited clouds, where cloud development is limited by the availability of cloud-condensation nuclei. A transition from pristine to slightly polluted atmosphere yields estimated negative forcing of ~15 watts per square meter (cooling), suggesting that a substantial part of this anthropogenic forcing over the oceans occurred at the beginning of the industrial era, when the marine atmosphere experienced such transformation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Koren, Ilan -- Dagan, Guy -- Altaratz, Orit -- New York, N.Y. -- Science. 2014 Jun 6;344(6188):1143-6. doi: 10.1126/science.1252595.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth and Planetary Sciences, Weizmann Institute, Rehovot 76100, Israel. ilan.koren@weizmann.ac.il. ; Department of Earth and Planetary Sciences, Weizmann Institute, Rehovot 76100, Israel.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24904161" target="_blank"〉PubMed〈/a〉
    Keywords: *Aerosols ; Atmosphere/*chemistry ; *Climate Change ; *Environmental Pollution ; Hot Temperature
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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