ESTIMATING SURFACE LONGWAVE RADIATION AND APPLICATIONS TO HIGH LATITUDE ISSUES

Two models, with distinct advantages for calculating downwelling surface longwave (DSLW) radiation under all sky conditions are presented. Both models are driven with a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) level-3 cloud parameters and information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim model. To compute the clear sky component of DSLW the first model DSLW/UMD v1 utilizes a globally applicable parameterization. The second generation model DSLW/UMD v2 utilizes a two layer feed-forward artificial neural network with sigmoid hidden neurons and linear output neurons. When computing the cloud contribution to DSLW, DSLW/UMD v1 implements a commonly used statistical model to calculate cloud vertical height while in DSLW/UMD v2 the cloud base temperature is estimated by using an independent artificial neural network based on spatially and temporally co- located MODIS and Cloudsat Cloud Profiling Radar (CPR) and the Cloud-Aerosol Lidar and Infrared Pathfiner Satellite Observation (CALIPSO) Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. Daily average estimates of DSLW for 2003 to 2009 are compared against ground measurements from the Baseline Surface Radiation Network (BSRN) and show significant improvements over currently available model estimates. DSLW/UMD v2 as optimized for Polar Regions along with a UMD develop shortwave model are used to investigate the role of radiative components in Arctic sea ice anomalies. The correlation between downwelling surface longwave and shortwave radiation and sea ice anomaly for the period from 2003 to 2007 is investigated using the latest Moderate Resolution Imagining Spectroradiometer (MODIS) level-3 cloud parameters and information from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim model. All sky downwelling surface longwave radiation (DSLW), all sky downwelling shortwave radiation (DSSW), all sky total downwelling shortwave and longwave radiation (DSSW + DSLW), and cloud total cloud forcing are individually examined to determine their respective correlation to sea ice anomaly. It is determined that these radiation components are not the primary drivers for major sea ice anomalies that occur during the investigated time frame within the 120o E to 210o E region

The Mid-infrared Fine-structure Lines of Neon as an Indicator of Star For mation Rate in Galaxies

The fine-structure lines of singly ([Ne II] 12.8 micron) and doubly ([Ne III] 15.6 micron) ionized neon are among the most prominent features in the mid-infrared spectra of star-forming regions, and have the potential to be a powerful new indicator of the star formation rate in galaxies. Using a sample of star-forming galaxies with measurements of the fine-structure lines available from the literature, we show that the sum of the [Ne II] and [Ne III] luminosities obeys a tight, linear correlation with the total infrared luminosity, over 5 orders of magnitude in luminosity. We discuss the formation of the lines and their relation with the Lyman continuum luminosity. A simple calibration between star formation rate and the [Ne II]+[Ne III] luminosity is presented.Comment: To appear in ApJ. 8 page

Primordial helium recombination II: two-photon processes

Interpretation of precision measurements of the cosmic microwave background (CMB) will require a detailed understanding of the recombination era, which determines such quantities as the acoustic oscillation scale and the Silk damping scale. This paper is the second in a series devoted to the subject of helium recombination, with a focus on two-photon processes in He I. The standard treatment of these processes includes only the spontaneous two-photon decay from the 2^1S level. We extend this treatment by including five additional effects, some of which have been suggested in recent papers but whose impact on He I recombination has not been fully quantified. These are: (i) stimulated two-photon decays; (ii) two-photon absorption of redshifted HeI line radiation; (iii) two-photon decays from highly excited levels in HeI (n^1S and n^1D, with n>=3); (iv) Raman scattering; and (v) the finite width of the 2^1P^o resonance. We find that effect (iii) is highly suppressed when one takes into account destructive interference between different intermediate states contributing to the two-photon decay amplitude. Overall, these effects are found to be insignificant: they modify the recombination history at the level of several parts in 10^4.Comment: 19 pages, 11 figures, to be submitted to PR

Energy Access Scenarios to 2030 for the Power Sector in Sub-Saharan Africa

In order to reach a goal of universal access to modern energy services in Africa by 2030, consideration of various electricity sector pathways is required to help inform policy-makers and investors, and help guide power system design. To that end, and building on existing tools and analysis, we present several ‘high-level’, transparent, and economy-wide scenarios for the sub-Saharan African power sector to 2030. We construct these simple scenarios against the backdrop of historical trends and various interpretations of universal access. They are designed to provide the international community with an indication of the overall scale of the effort required. We find that most existing projections, using typical long-term forecasting methods for power planning, show roughly a threefold increase in installed generation capacity occurring by 2030, but more than a tenfold increase would likely be required to provide for full access – even at relatively modest levels of electricity consumption. This equates to approximately a 13% average annual growth rate, compared to a historical one (in the last two decades) of 1.7%.Energy Access, Power System Planning, Sub-Saharan Africa

Primordial helium recombination. I. Feedback, line transfer, and continuum opacity

Precision measurements of the cosmic microwave background temperature anisotropy on scales ℓ>500 will be available in the near future. Successful interpretation of these data is dependent on a detailed understanding of the damping tail and cosmological recombination of both hydrogen and helium. This paper and two companion papers are devoted to a precise calculation of helium recombination. We discuss several aspects of the standard recombination picture, and then include feedback, radiative transfer in He i lines with partial redistribution, and continuum opacity from H i photoionization. In agreement with past calculations, we find that He ii recombination proceeds in Saha equilibrium, whereas He i recombination is delayed relative to Saha due to the low rates connecting excited states of He i to the ground state. However, we find that at z<2200 the continuum absorption by the rapidly increasing H i population becomes effective at destroying photons in the He i 21Po-11S line, causing He i recombination to finish around z≃1800, much earlier than previously estimated

Independent Emission and Absorption Abundances for Planetary Nebulae

Emission-line abundances have been uncertain for more than a decade due to unexplained discrepancies in the relative intensities of the forbidden lines and weak permitted recombination lines in planetary nebulae (PNe) and H II regions. The observed intensities of forbidden and recombination lines originating from the same parent ion differ from their theoretical values by factors of more than an order of magnitude in some of these nebulae. In this study we observe UV resonance line absorption in the central stars of PNe produced by the nebular gas, and from the same ions that emit optical forbidden lines. We then compare the derived absorption column densities with the emission measures determined from ground-based observations of the nebular forbidden lines. We find for our sample of PNe that the collisionally excited forbidden lines yield column densities that are in basic agreement with the column densities derived for the same ions from the UV absorption lines. A similar comparison involving recombination line column densities produces poorer agreement, although near the limits of the formal uncertainties of the analyses. An additional sample of objects with larger abundance discrepancy factors will need to be studied before a stronger statement can be made that recombination line abundances are not correct.Comment: 19 pages, 13 figures, accepted by ApJ. Preprint utilizes emulateapj.cls v. 12/01/06 (included

Non-LTE Models and Theoretical Spectra of Accretion Disks in Active Galactic Nuclei. IV. Effects of Compton Scattering and Metal Opacities

We extend our models of the vertical structure and emergent radiation field of accretion disks around supermassive black holes described in previous papers of this series. Our models now include both a self-consistent treatment of Compton scattering and the effects of continuum opacities of the most important metal species (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni). With these new effects incorporated, we compute the predicted spectrum from black holes accreting at nearly the Eddington luminosity (L/L_Edd = 0.3) and central masses of 10^6, 10^7, and 10^8 M_sun. We also consider two values of the Shakura-Sunyaev alpha parameter, 0.1 and 0.01. Although it has little effect when M > 10^8 M_sun, Comptonization grows in importance as the central mass decreases and the central temperature rises. It generally produces an increase in temperature with height in the uppermost layers of hot atmospheres. Compared to models with coherent electron scattering, Comptonized models have enhanced EUV/soft X-ray emission, but they also have a more sharply declining spectrum at very high frequencies. Comptonization also smears the hydrogen and the He II Lyman edges. The effects of metals on the overall spectral energy distribution are smaller than the effects of Comptonization for these parameters. Compared to pure hydrogen-helium models, models with metal continuum opacities have reduced flux in the high frequency tail, except at the highest frequencies, where the flux is very low. Metal photoionization edges are not present in the overall disk-integrated model spectra. In addition to our new grid of models, we also present a simple analytic prescription for the vertical temperature structure of the disk in the presence of Comptonization, and show under what conditions a hot outer layer (a corona) is formed.Comment: 22 pages, Latex. 19 figures. Uses corrected version of emulateapj.sty and apjfonts.sty (included). Accepted for publication in Ap

Optimization of the Culture Medium Composition to Improve the Production of Hyoscyamine in Elicited Datura stramonium L. Hairy Roots Using the Response Surface Methodology (RSM)

Traditionally, optimization in biological analyses has been carried out by monitoring the influence of one factor at a time; this technique is called one-variable-at-a-time. The disadvantage of this technique is that it does not include any interactive effects among the variables studied and requires a large number of experiments. Therefore, in recent years, the Response Surface Methodology (RSM) has become the most popular optimization method. It is an effective mathematical and statistical technique which has been widely used in optimization studies with minimal experimental trials where interactive factors may be involved. This present study follows on from our previous work, where RSM was used to optimize the B5 medium composition in [NO3−], [Ca2+] and sucrose to attain the best production of hyoscyamine (HS) from the hairy roots (HRs) of Datura stramonium elicited by Jasmonic Acid (JA). The present paper focuses on the use of the RSM in biological studies, such as plant material, to establish a predictive model with the planning of experiments, analysis of the model, diagnostics and adjustment for the accuracy of the model. With the RSM, only 20 experiments were necessary to determine optimal concentrations. The model could be employed to carry out interpolations and predict the response to elicitation. Applying this model, the optimization of the HS level was 212.7% for the elicited HRs of Datura stramonium, cultured in B5-OP medium (optimized), in comparison with elicited HRs cultured in B5 medium (control). The optimal concentrations, under experimental conditions, were determined to be: 79.1 mM [NO3−], 11.4 mM [Ca2+] and 42.9 mg/L of sucrose

An evaluation of IASI-NH\u3csub\u3e3\u3c/sub\u3e with ground-based Fourier transform infrared spectroscopy measurements

Global distributions of atmospheric ammonia (NH3) measured with satellite instruments such as the Infrared Atmospheric Sounding Interferometer (IASI) contain valuable information on NH3 concentrations and variability in regions not yet covered by ground-based instruments. Due to their large spatial coverage and (bi-)daily overpasses, the satellite observations have the potential to increase our knowledge of the distribution of NH3 emissions and associated seasonal cycles. However the observations remain poorly validated, with only a handful of available studies often using only surface measurements without any vertical information. In this study, we present the first validation of the IASI-NH3 product using ground-based Fourier transform infrared spectroscopy (FTIR) observations. Using a recently developed consistent retrieval strategy, NH3 concentration profiles have been retrieved using observations from nine Network for the Detection of Atmospheric Composition Change (NDACC) stations around the world between 2008 and 2015. We demonstrate the importance of strict spatio-temporal collocation criteria for the comparison. Large differences in the regression results are observed for changing intervals of spatial criteria, mostly due to terrain characteristics and the short lifetime of NH3 in the atmosphere. The seasonal variations of both datasets are consistent for most sites. Correlations are found to be high at sites in areas with considerable NH3 levels, whereas correlations are lower at sites with low atmospheric NH3 levels close to the detection limit of the IASI instrument. A combination of the observations from all sites (Nobs = 547) give a mean relative difference of −32.4 ± (56.3) %, a correlation r of 0.8 with a slope of 0.73. These results give an improved estimate of the IASI-NH3 product performance compared to the previous upper-bound estimates (−50 to +100 %)

Molecular and Atomic Excitation Stratification in the Outflow of the Planetary Nebula M27

High resolution spectroscopy with FUSE and STIS of atomic and molecular velocity stratification in the nebular outflow of M27 challenge models for the abundance kinematics in planetary nebulae. The simple picture of a very high speed (~ 1000 km/s), high ionization, radiation driven stellar wind surrounded by a slower (~ 10 km/s) mostly molecular outflow, with low ionization and neutral atomic species residing at the wind interaction interface, is not supported... We find ...there is a fast (33 -- 65 km/s) low ionization zone, surrounding a slower (<~ 33 km/s) high ionization zone and, at the transition velocity (33 km/s), vibrationally excited H_2 is intermixed with a predominately neutral atomic medium... Far-UV continuum fluorescence of H_2 is not detected, but Lyman alpha (Lya) fluorescence is present. The diffuse nebular medium is inhospitable to molecules and dust. Maintaining the modest equilibrium abundance of H_2 (N(H_2)/N(HI) << 1) in the diffuse nebular medium requires a source of H_2, mostly likely the clumpy nebular medium. The stellar SED shows no signs of reddening (E(B-V) < 0.01), but paradoxically measurements of Ha/Hb ... indicate E(B-V) ~ 0.1. ...the apparent enhancement of Ha/Hb in the absence of dust may result from a two step process of H_2 ionization by Lyman continuum (Lyc) photons followed by dissociative recombination (H_2 + gamma -> H_2^+ + e -> H(1s) + H (nl)), which ultimately produces fluorescence of Ha and Lya. In the optically thin limit at the inferred radius of the velocity transition we find dissociation of H_2 by stellar Lyc photons is an order of magnitude more efficient than spontaneous dissociation by far-UV photons. We suggest that the importance of this H_2 destruction process in HII regions has been overlooked.Comment: In emulateapj 2 column, 28 pages total, 18 figures. Accepted for publication in the Astrophysical Journal on 5 January 2007. Abstract abridge