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Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance
B. Lin,L. Chambers,P. Stackhouse Jr.,B. Wielicki
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth's climate to the increase of CO2 concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO2 change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. Currently, there is a lack of high accuracy measurements of TOA radiation imbalance. Available estimations indicate that TOA net radiative heating to the climate system is about 0.85 W/m2. Based on this value, a positive climate feedback with a feedback coefficient ranging from 1.3 to 1.0 W/m2/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m2 TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.
The direct effect of aerosols on solar radiation based on satellite observations, reanalysis datasets, and spectral aerosol optical properties from Global Aerosol Data Set (GADS)
N. Hatzianastassiou,C. Matsoukas,E. Drakakis,P. W. Stackhouse Jr.
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: A global estimate of the seasonal direct radiative effect (DRE) of natural plus anthropogenic aerosols on solar radiation under all-sky conditions is obtained by combining satellite measurements and reanalysis data with a spectral radiative transfer model. The estimates are obtained with detailed spectral model computations separating the ultraviolet (UV), visible and near-infrared wavelengths. The global distribution of spectral aerosol optical properties was taken from the Global Aerosol Data Set (GADS) whereas data for clouds, water vapour, ozone, carbon dioxide, methane and surface albedo were taken from various satellite and reanalysis datasets. Using these aerosol properties and other related variables, we generate climatological (for the 12-year period 1984–1995) monthly mean aerosol DREs. The global annual mean DRE on the outgoing SW radiation at the top of atmosphere (TOA, ΔFTOA) is 1.62 Wm 2 (with a range of –10 to 15 Wm 2, positive values corresponding to planetary cooling), the effect on the atmospheric absorption of SW radiation (ΔFatmab) is 1.6 Wm 2 (values up to 35 Wm 2, corresponding to atmospheric warming), and the effect on the surface downward and absorbed SW radiation (Δ Fsurf, and ΔFsurfnet, respectively) is –3.93 and –3.22 Wm 2 (values up to –45 and –35 Wm 2, respectively, corresponding to surface cooling.) According to our results, aerosols decrease/increase the planetary albedo by –3 to 13% at the local scale, whereas on planetary scale the result is an increase of 1.5%. Aerosols can warm locally the atmosphere by up to 0.98 K day 1, whereas they can cool the Earth's surface by up to –2.9 K day 1. Both these effects, which can significantly modify atmospheric dynamics and the hydrological cycle, can produce significant planetary cooling on a regional scale, although planetary warming can arise over highly reflecting surfaces. The aerosol DRE at the Earth's surface compared to TOA can be up to 15 times larger at the local scale. The largest aerosol DRE takes place in the northern hemisphere both at the surface and the atmosphere, arising mainly at ultraviolet and visible wavelengths.
The direct effect of aerosols on solar radiation based on satellite observations, reanalysis datasets, and spectral aerosol optical properties from Global Aerosol Data Set (GADS)
N. Hatzianastassiou, C. Matsoukas, E. Drakakis, P. W. Stackhouse Jr., P. Koepke, A. Fotiadi, K. G. Pavlakis,I. Vardavas
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: A global estimate of the seasonal direct radiative effect (DRE) of natural plus anthropogenic aerosols on solar radiation under all-sky conditions is obtained by combining satellite measurements and reanalysis data with a spectral radiative transfer model and spectral aerosol optical properties taken from the Global Aerosol Data Set (GADS). The estimates are obtained with detailed spectral model computations separating the ultraviolet (UV), visible and near-infrared wavelengths. The global distribution of spectral aerosol optical properties was taken from GADS whereas data for clouds, water vapour, ozone, carbon dioxide, methane and surface albedo were taken from various satellite and reanalysis datasets. Using these aerosol properties and other related variables, we generate climatological (for the 12-year period 1984–1995) monthly mean aerosol DREs. The global annual mean DRE on the outgoing SW radiation at the top of atmosphere (TOA, ΔFTOA) is 1.62 W m 2 (with a range of 15 to 10 W m 2, negative values corresponding to planetary cooling), the effect on the atmospheric absorption of SW radiation (ΔFatmab) is 1.6 W m 2 (values up to 35 W m 2, corresponding to atmospheric warming), and the effect on the surface downward and absorbed SW radiation (ΔFsurf, and ΔFsurfnet, respectively) is 3.93 and 3.22 W m 2 (values up to 45 and 35 W m 2, respectively, corresponding to surface cooling). According to our results, aerosols decrease/increase the planetary albedo by 3 to 13% at the local scale, whereas on planetary scale the result is an increase of 1.5%. Aerosols can warm locally the atmosphere by up to 0.98 K day 1, whereas they can cool the Earth's surface by up to 2.9 K day 1. Both these effects, which can significantly modify atmospheric dynamics and the hydrological cycle, can produce significant planetary cooling on a regional scale, although planetary warming can arise over highly reflecting surfaces. The aerosol DRE at the Earth's surface compared to TOA can be up to 15 times larger at the local scale. The largest aerosol DRE takes place in the northern hemisphere both at the surface and the atmosphere, arising mainly at ultraviolet and visible wavelengths.
Modelling the direct effect of aerosols in the solar near-infrared on a planetary scale
N. Hatzianastassiou, C. Matsoukas, A. Fotiadi, P. W. Stackhouse Jr., P. Koepke, K. G. Pavlakis,I. Vardavas
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2007,
Abstract: We used a spectral radiative transfer model to compute the direct radiative effect (DRE) of natural plus anthropogenic aerosols in the solar near-infrared (IR), between 0.85–10 μm, namely, their effect on the outgoing near-IR radiation at the top of atmosphere (TOA, ΔFTOA), on the atmospheric absorption of near-IR radiation (ΔFatmab) and on the surface downward and absorbed near-IR radiation (ΔFsurf, and ΔFsurfnet, respectively). The computations were performed on a global scale (over land and ocean) under all-sky conditions, using detailed spectral aerosol optical properties taken from the Global Aerosol Data Set (GADS) supplemented by realistic data for the rest of surface and atmospheric parameters. The computed aerosol DRE, averaged over the 12-year period 1984–1995 for January and July, shows that on a global mean basis aerosols produce a planetary cooling by increasing the scattered near-IR radiation back to space by 0.48 W m 2, they warm the atmosphere by 0.37 W m 2 and cool the surface by decreasing the downward and absorbed near-IR radiation at surface by 1.03 and 0.85 W m 2, respectively. The magnitude of the near-IR aerosol DRE is smaller than that of the combined ultraviolet (UV) and visible DRE, but it is still energetically important, since it contributes to the total shortwave (SW) DRE by 22–31%. The aerosol-produced near-IR surface cooling combined with the atmospheric warming, may affect the thermal dynamics of the Earth-atmosphere system, by increasing the atmospheric stability, decreasing thus cloud formation, and precipitation, especially over desertification threatened regions such as the Mediterranean basin. This, together with the fact that the sign of near-IR aerosol DRE is sometimes opposite to that of UV-visible DRE, demonstrates the importance of performing detailed spectral computations to provide estimates of the climatic role of aerosols for the Earth-atmosphere system. This was demonstrated by sensitivity tests revealing very large differences (up to 300%) between aerosol DREs computed using detailed spectral and spectrally-averaged aerosol optical properties. Our model results indicate thus that the aerosol direct radiative effect on the near-IR radiation is very sensitive to the treatment of the spectral dependence of aerosol optical properties and solar radiation.
Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance
B. Lin, L. Chambers, P. Stackhouse Jr., B. Wielicki, Y. Hu, P. Minnis, N. Loeb, W. Sun, G. Potter, Q. Min, G. Schuster,T.-F. Fan
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth's climate to the increase of CO2 concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO2 change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. In this study, the TOA imbalance value of 0.85 W/m2 is used. Note that this imbalance value has large uncertainties. Based on this value, a positive climate feedback with a feedback coefficient ranging from 1.3 to 1.0 W/m2/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m2 TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.
The Formation of Kappa-Distribution Accelerated Electron Populations in Solar Flares
Nicolas H. Bian,A. Gordon Emslie,Duncan J. Stackhouse,Eduard P. Kontar
Physics , 2014, DOI: 10.1088/0004-637X/796/2/142
Abstract: Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration of electrons in the presence of Coulomb collisions. If electron escape from the acceleration region can be neglected, the electron distribution function is determined by a balance between diffusive acceleration and collisions. Such a scenario admits a stationary solution for the electron distribution function that takes the form of a kappa distribution. We show that the evolution toward this kappa distribution involves a "wave front" propagating forwards in velocity space, so that electrons of higher energy are accelerated later; the acceleration time scales with energy according to $\tau_{\rm acc} \sim E^{3/2}$. At sufficiently high energies escape from the finite-length acceleration region will eventually dominate. For such energies, the electron velocity distribution function is obtained by solving a time-dependent Fokker-Planck equation in the "leaky-box" approximation. Solutions are obtained in the limit of a small escape rate from an acceleration region that can effectively be considered a thick target.
Equations of state and stability of MgSiO$_3$ perovskite and post-perovskite phases from quantum Monte Carlo simulations
Yangzheng Lin,R. E. Cohen,Stephen Stackhouse,Kevin P. Driver,Burkhard Militzer,Luke Shulenburger,Jeongnim Kim
Physics , 2014, DOI: 10.1103/PhysRevB.90.184103
Abstract: We have performed quantum Monte Carlo (QMC) simulations and density functional theory (DFT) calculations to study the equations of state of MgSiO$_3$ perovskite (Pv) and post-perovskite (PPv), up to the pressure and temperature conditions of the base of Earth's lower mantle. The ground state energies were derived using QMC and the temperature dependent Helmholtz free energies were calculated within the quasi-harmonic approximation and density functional perturbation theory. The equations of state for both phases of MgSiO$_3$ agree well with experiments, and better than those from generalized gradient approximation (GGA) calculations. The Pv-PPv phase boundary calculated from our QMC equations of states is also consistent with experiments, and better than previous LDA calculations. We discuss the implications for double crossing of the Pv-PPv boundary in the Earth.
Rapid, low-input, low-bias construction of shotgun fragment libraries by high-density in vitro transposition
Andrew Adey, Hilary G Morrison, Asan, Xu Xun, Jacob O Kitzman, Emily H Turner, Bethany Stackhouse, Alexandra P MacKenzie, Nicholas C Caruccio, Xiuqing Zhang, Jay Shendure
Genome Biology , 2010, DOI: 10.1186/gb-2010-11-12-r119
Abstract: Massively parallel DNA sequencing methods are rapidly achieving broad adoption by the life sciences research community [1,2]. As the productivity of these platforms continues to grow with hardware and software optimizations, the bottleneck experienced by researchers is increasingly at the front end (the construction of sequencing libraries) and at the back end (data analysis and interpretation) rather than in the sequencing itself.The input material for commonly used platforms, such as the Illumina Genome Analyzer [3], the Roche (454) Genome Sequencer [4], the Life Technologies SOLiD platform [5], as well as for 'real-time' third-generation sequencers such as Pacific Biosciences [6], consists of complex libraries of genome- or transcriptome-derived DNA fragments flanked by platform-specific adaptors. The standard method for constructing such libraries is entirely in vitro and typically includes fragmentation of DNA (mechanical or enzymatic), end-polishing, ligation of adaptor sequences, gel-based size-selection, and PCR amplification (Figure 1a). This core protocol may be preceded by additional steps depending on the specific application, such as cDNA synthesis for RNA-seq libraries [7].Although generally effective, several aspects of the standard method are throughput-limiting or otherwise suboptimal. These include: (1) Labor: there are several labor-intensive enzymatic manipulations with obligate clean-up steps. (2) Time: the protocol requires 6-10 hours from beginning to end, often including an overnight incubation. (3) Automation: although 96-plex, semi-automated processing has been achieved by large-scale genome centers [8], many researchers lack access to the requisite robotic liquid handling systems and/or instruments for parallelized mechanical fragmentation. (4) Sample indexing: incorporation of barcoded adaptors, which enable concurrent analysis of multiple samples and post-sequencing deconvolution, still requires most steps to be carried out on individual
In vivo testing of a bone graft containing chitosan, calcium sulfate and osteoblasts in a paste form in a critical size defect model in rats  [PDF]
Jerome G. Saltarrelli Jr., Debi P. Mukherjee
Journal of Biomedical Science and Engineering (JBiSE) , 2009, DOI: 10.4236/jbise.2009.21005
Abstract: Bone loss associated with musculoskeletal trauma or metabolic diseases often require bone grafting. The supply of allograft and auto-graft bones is limited. Hence, development of synthetic bone grafting materials is an active area of research. Chitosan, extracted from chitin present in crawfish shells, was tested as a de-livery vehicle for osteoblasts in a 2-3 mm size defect model in rats. Twenty-seven male Lewis rats, divided into three groups with sacrifice intervals of 3, 6 & 9 months were used. In the experimental samples, a critical size defect was filled with chitosan bone graft paste and fixed with a plate, while in the operated control group, a critical size defect was repaired only by a plate (no paste was applied). An unoperated control group was also included. Bone growth was evaluated histologically by examining undecal-cified and decalcified stained sections. The fe-murs were also examined non-destructively by micro-computed tomography (礐T). Defects filled with chitosan bone graft paste demon-strated superior healing across all time periods compared to unfilled defects as examined by histology and micro-computed tomography. Crawfish chitosan has successfully been used as a cell delivery system for osteoblasts for use as a synthetic bone graft material.
Entecavir for treatment of chronic hepatitis B: A clinical update for the treatment of patients with decompensated cirrhosis  [PDF]
P. Patrick Basu, Robert S. Brown Jr.
Open Journal of Internal Medicine (OJIM) , 2012, DOI: 10.4236/ojim.2012.22012
Abstract: The introduction of nucleos(t)ide analogues for the treatment of chronic hepatitis B virus (HBV) infection was transformative in reducing morbidity and mortality. Entecavir, a potent selective nucleoside analogue first approved in 2005 for treatment of chronic HBV, is associated with significant antiviral, biochemical, serologic, and histologic responses. Rapid reductions in HBV DNA levels, low risk of resistance development, and a favorable adverse event profile have contributed to its clinical usefulness. Re-cent developments in the use of entecavir have increased its utility in the management of difficult-to-treat patients with chronic HBV, including those patients with decompensated liver disease. Recent studies in this population have demonstrated that entecavir 1.0 mg/d given for up to 48 weeks had superior antiviral activity when compared with adefovir and was generally safe and well tolerated. Long-term outcomes of entecavir in difficult-to-treat populations are eagerly anticipated.
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