Intensity variations in the solar extreme ultraviolet spectrum observed by oso-1.
OSO observations of extreme UV radiation with application to identification of emission lines in spectral region 170-1400 angstroms
SOLAR RADIATION↗
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Intensity variations in the solar extreme ultraviolet spectrum observed by OSO-1.
OSO observations of EUV radiation applied to identification of emission lines in spectral region 170-1400 angstroms
OSO↗
Investigation of temporal variations of winds
Nighttime observations of upper atmospheric wind data to determine physical properties of atmosphere
Bedinger, J.↗
Observations of the stratospheric conductivity and its variation at three latitudes
Measurements from nine high-altitude balloon flights at altitudes ranging from 10 to 30 km have been obtained in order to study atmospheric conductivity variations on local and global scales. The conductivity profiles are not correlated with solar or cosmic ray activity, but they exhibit variations which appear to be dominated by local effects. Evidence is provided of stratospheric aerosol layers with number densities of the order of 1000/cu cm. It is suggested that global conductivity models employing latitudinal variations based on cosmic ray ionization alone may be improved by including the effects of latitudinal variations of temperature and aerosols.
Byrne, G. J.↗
Constraining the Global, Cloud-Free Reflected Solar Radiation Flux (RSRF) with Earth Observing System (EOS) Instruments
Variations in the top-of-atmosphere reflected solar radiation flux, and in the factors that determine its value, are among the most important diagnostic indicators of changes in Earth's energy balance. Data from the MISR (Multi-angle Imaging SpectroRadiometer), MODIS (Moderate-resolution Imaging Spectroradiometer), SAGE-3 (Stratospheric Aerosol and Gas Experiment), and CERES (Clouds and Earth's Radiant Energy System), all of which are spacecraft instruments scheduled for launch in 1999, will each constrain pieces of the RSRF budget. Prior to launch, we are performing studies to determine the sensitivity of these instruments to key factors that influence the cloud-free RSRF: aerosol optical depth, aerosol scattering properties, and surface visible bidirectional reflectance distribution function (BRDF). We are also assessing the ability of the aggregate of instruments to constrain the overall RSRF budget under natural conditions over the globe. Consider the MISR retrieval of aerosols: according to simulations over cloud-free, calm ocean, for pure particles with natural ranges of optical depth, particle size, and indices of refraction, MISR can retrieve column aerosol optical depth for all but the darkest particles, to an uncertainty of at most 0.05 or 20%, whichever is larger, even if the particle properties are poorly known. For one common particle type, soot, constraints on the optical depth over dark ocean are very poor. The simulated measurements also allow us to distinguish spherical from non-spherical particles, to separate two to four compositional groups based on indices of refraction, and to identify three to four distinct size groups between 0. 1 and 2.0 microns characteristic radius at most latitudes. Based on these results, we expect to distinguish air masses containing different aerosol types, routinely and globally, with multiangle remote sensing data. Such results far exceed current satellite aerosol retrieval capabilities, which provide only total optical depth for assumed particle properties; the new information will complement in situ data, which give details about aerosol size and composition locally. In addition, our team is using climatologies that reflect the constraints each instrument is expected to provide, along with ERBE (Earth Radiation Budget Experiment) data and a radiative transfer code, to study overall sensitivity to RSRF, helping us prepare for similar studies with new data from the EOS-era instruments.
Kahn, Ralph↗
Spacebased Observations of Oceanic Influence on the Annual Variation of South American Water Balance
The mass change of South America (SA) continent measured by the Gravity Recovery and Climate Experiment (GRACE) imposes a constraint on the uncertainties in estimating the annual variation of rainfall measured by Tropical Rain Measuring Mission (TRMM) and ocean moisture influx derived from QuikSCAT data. The approximate balance of the mass change rate with the moisture influx less climatological river discharge, in agreement with the conservation principle, bolsters not only the credibility of the spacebased measurements, but supports the characterization of ocean's influence on the annual variation of continental water balance. The annual variation of rainfall is found to be in phase with the mass change rate in the Amazon and the La Plata basins, and the moisture advection across relevant segments of the Pacific and Atlantic coasts agrees with the annual cycle of rainfall in the two basins and the Andes mountains.
rainfall annual cycle↗
A Comparison of MERRA and NARR Reanalysis Datasets with the DOE ARM SGP Continuous Forcing data
In this study, the atmospheric state, precipitation, cloud fraction, and radiative fluxes from Modern Era Retrospective-analysis for Research and Applications (MERRA) and North American Regional Reanalysis (NARR) are collected and compared with the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) continuous forcing during the period 1999-2001. For the atmospheric state, the three datasets have excellent agreement for the horizontal wind components and air temperature. NARR and ARM have generally good agreement for humidity, except for several biases in the PBL and in the upper troposphere. MERRA, on the other hand, suffers from a year-round negative bias in humidity except for the month of June. For the vertical pressure velocity, significant differences exist with the largest biases occurring during the spring upwelling and summer downwelling periods. Although NARR and MERRA share many resemblances to each other, ARM outperforms these reanalyses in terms of correlation with cloud fraction. Because the ARM forcing is constrained by observed precipitation that gives the adequate mass, heat, and moisture budgets, much of the precipitation (specifically during the late spring/early summer) is caused by smaller-scale forcing that is not captured by the reanalyses. Both NARR and MERRA capture the seasonal variation of CF observed by ARM radar-lidar and GOES with high correlations (0.92-0.78), but having negative biases of 14% and 3%, respectively. Compared to the ARM observations, MERRA shows a better agreement for both SW and LW fluxes except for LW-down (due to a negative bias in water vapor), NARR has significant positive bias for SW-down and negative bias for LW-down under clear- and all-sky conditions . The NARR biases result from a combination of too few clouds and a lack of sufficient extinction by aerosols and water vapor in the atmospheric column. The results presented here represent only one location for a limited time period, and more comparisons at different locations and longer time period are needed.
Kennedy, Aaron D.↗
Observations of Tidallly Coherent Diurnal and Semidiurnal Variations in the Geocenter
The center of mass of the Earth, about which a satellite orbits, is determined by the mass distribution of the solid Earth, the oceans, and the atmosphere.
Diurnal↗
On the total energy output of the nova outburst
It is shown that the postmaximum decline in optical light during the outburst of a normal classical nova is caused by a shift in the wavelength of maximum energy to the ultraviolet. The constant-luminosity phase which was directly observed in Nova FH Ser 1970 may, therefore, be common to all novae, regardless of speed class. This implies that all speed classes of novae have similar energy budgets and that it is the total energy involved in the outburst which produces the variation in the observed characteristics of the novae. Recent thermonuclear runaway models for the outburst also show an extended period of high luminosity and high effective temperature following the initial outburst.
Gallagher, J. S.↗
Analysis of Suomi - NPP VIIRS Vignetting Functions Based on Yaw Maneuver Data
The Suomi NPP Visible Infrared Imager Radiometer Suite (VIIRS) reflective bands are calibrated on-orbit via reference to regular solar observations through a solar attenuation screen (SAS) and diffusely reflected off a Spectralon (Registered Trademark) panel. The degradation of the Spectralon panel BRDF due to UV exposure is tracked via a ratioing radiometer (SDSM) which compares near simultaneous observations of the panel with direct observations of the sun (through a separate attenuation screen). On-orbit, the vignetting functions of both attenuation screens are most easily measured when the satellite performs a series of yaw maneuvers over a short period of time (thereby covering the yearly angular variation of solar observations in a couple of days). Because the SAS is fixed, only the product of the screen transmission and the panel BRDF was measured. Moreover, this product was measured by both VIIRS detectors as well as the SDSM detectors (albeit at different reflectance angles off the Spectralon panel). The SDSM screen is also fixed; in this case, the screen transmission was measured directly. Corrections for instrument drift and degradation, solar geometry, and spectral effects were taken into consideration. The resulting vignetting functions were then compared to the pre-launch measurements as well as models based on screen geometry.
Xiong, Xiaoxiong↗
Downward shift of the acceleration/injection region during solar flares
Simultaneous observations of impulsive hard X-rays and type III radio bursts associated with two recent solar flares have been analyzed in order to study the characteristic increase in the starting frequency of fast-drift type III bursts during the impulsive phase. The time variation of the starting frequency has been found to be similar to that of approximately 35 keV X-rays, especially during the increasing phase. A similar variation has been observed for the low frequency cutoff of these bursts. The observations are consistent with a systematic downward shift of the electron acceleration/injection region during the impulsive phase of a solar flare.
Kane, S. R.↗
Cometary nucleus and active regions
On the basis of the icy conglomerate model of cometary nuclei, various observations demonstrate the spotted nature of many or most nuclei, i.e., regions of unusual activity, either high or low. Rotation periods, spin axes and even precession of the axes are determined. The observational evidence for variations in activity over the surfaces of cometary nuclei are listed and discussed. On June 11 the comet IRAS-ARAKI-ALCOCK approached the Earth to a distance of 0.031 AU, the nearest since C/Lexell, 1770 I, providing a unique opportunity for near-nucleus observations. Preliminary analysis of these images establishes the spin axis of the nucleus, with an oblioquity to the orbit plane of approximately 50 deg, and a lag angle of sublimation approximately 35 deg from the solar meridian on the nucleus. Asymmetries of the inner coma suggests a crazy-quilt distribution of ices with differing volatility over the surface of the nucleus. The observations of Comet P/Homes 1892 III, exhibiting two 8-10 magnitude bursts, are carefully analyzed. The grazing encounter produced, besides the first great burst, an active area on the nucleus, which was rotating retrograde with a period of 16.3hr and inclination nearly 180 deg. After the first burst the total magnitude fell less than two magnitudes from November 7 to November 30 (barely naked eye) while the nuclear region remained diffuse or complex, rarely if ever showing a stellar appearance. The fading was much more rapid after the second burst. The grazing encounter distributed a volume of large chunks in the neighborhood of the nucleus, maintaining activity for weeks.
Whipple, F. L.↗
Ultraviolet and visual variability of Theta CrB during a normal B-phase following a shell phase (1980-1985)
Based on far-UV and visual observations made between 1980 and 1985, the phenomena characterizing the end of a shell phase of Theta-CrB, and the normal B-phase following it, are described as part of a long-term study of Be stars. The strength, shape, and velocity of the C IV, Si IV, and Al III resonance lines, and the Fe III lines of low excitation, show associated variability patterns over the whole range of ionization observable in the IUE and visual spectra. The observed variability pattern consists of a one-year narrow-line stage where the lines show narrow absorption cores close to rest wavelength, a two-year series of abrupt changes between a weak and a strong line, and a damping out of these variations leaving the observed spectrum in a lower ionization state. The existence of a phase-lag between similar phenomena occurring in the superionized and subionized/normally ionized regions, is noted.
Doazan, V.↗
Data Assimilation and Uncertainties in Early Solar Cycle Predictions
Stochastic nature of solar activity variations together with our limited knowledge of the dynamo mechanism and subsurface dynamics causes uncertainty in predictions of the solar cycle. For improving the physics-‐based predictions we can take advantage of the mathematical data assimilation approach that allows us to take into account both, observational errors and model uncertainties, and provide estimates of the next solar cycle along with prediction uncertainties. In this study we use the Parker's migratory dynamo model together with the equation of magnetic helicity balance, which reproduces main properties of the sunspot cycles and allow us to minimize discrepancies between the observed global activity variations and the model solution. The test simulation runs show that a reliable prediction can be obtained for two phases of preceding solar cycle: 1) if the polar field reversals shortly after the solar maxima (strong toroidal field and weak poloidal field), and 2) during the solar minima (strongest poloidal and weak toroidal fields). The early estimate of Cycle 25 obtained by this method shows that this cycle will start in 2019 – 2020, reach the maximum in 2023 – 2024, and that the mean sunspot number at the maximum will be about 90 (for the v2.0 sunspot number series).
Data Assimilation↗
Earthquake recurrence on the southern San Andreas modulated by fault-normal stress
Earthquake recurrence data from the Pallett Creek and Wrightwood paleoseismic sites on the San Andreas fault appear to show temporal variations in repeat interval. We investigate the interaction between strike-slip faults and auxiliary reverse and normal faults as a physical mechanism capable of producing such variations. Under the assumption that fault strength is a function of fault-normal stress (e.g. Byerlee's Law), failure of an auxiliary fault modifies the strength of the strike-slip fault, thereby modulating the recurrence interval for earthquakes. In our finite element model, auxiliary faults are driven by stress accumulation near restraining and releasing bends of a strike-slip fault. Earthquakes occur when fault strength is exceeded and are incorporated as a stress drop which is dependent on fault-normal stress. The model is driven by a velocity boundary condition over many earthquake cycles. Resulting synthetic strike-slip earthquake recurrence data display temporal variations similar to observed paleoseismic data within time windows surrounding auxiliary fault failures. Our simple model supports the idea that interaction between a strike-slip fault and auxiliary reverse or normal faults can modulate the recurrence interval of events on the strike-slip fault, possibly producing short term variations in earthquake recurrence interval.
Palmer, Randy↗
Understanding variation in salamander ionomes: A nutrient balance approach
1. Ecological stoichiometry uses information on a few key biological elements (C, N and P) to explain complex ecological patterns. Although factors driving variation in these elements are well established, expanding stoichiometric principles to explore dynamics of the many other essential elements comprising biological tissues (i.e. the ionome) is needed to determine their metabolic relationships and better understand biological control of elemental flows through ecosystems. 2. Here in this paper, we report observations of ionomic variation in two species of salamander (Ambystoma opacum and A. talpoideum) across ontogenic stages using specimens from biological collections of two wetlands sampled over a 30-year period. This unique data set allowed us to explore the extent of ionomic variation between species, among ontogenic stages, between sites and through time. 3. We found species- and, to a lesser extent, site-specific differences in C, N and P along with 13 other elements forming salamander ionomes but saw no evidence of temporal changes. Salamander ionomic composition was most strongly related to ontogeny with relatively higher concentrations of many elements in adult males (i.e. Ca, P, S, Mg, Zn and Cu) compared to metamorphic juveniles, which had greater amounts of C, Fe and Mn. 4. In addition to patterns of individual elements, covariance among elements was used to construct multi-elemental nutrient balances, which revealed differences in salamander elemental composition between species and sites and changes in elemental proportions across ontogenic development. These multi-elemental balances distinguished among species-site-ontogenic stage groups better than using only C, N and P. 5. Overall, this study highlights the responsiveness of consumer ionomes to life-history and environmental variation while reflecting underlying relationships among elements tied to biological function. As such, ionomic studies can provide important insights into factors shaping consumer elemental composition and for predicting how these changes might affect higher-order ecological processes.
59 BASIC BIOLOGICAL SCIENCES↗
Comets
Vacuum ultraviolet observations from sounding rockets and satellite observatories of the gaseous comae of several comets are reviewed. The earliest of these led to discovery of the hydrogen envelope extending for millions of km from the nucleus. Subsequent observations of H I Lyman alpha, the OH (0,0 band and the oxygen resonance triplet provided strong evidence for the water-ice model of the cometary nucleus. Several species were discovered in the coma including C, C(+), CO, S, and CS. High resolution spectroscopy and the spatial variation of the observed emissions provide means to elucidate the production and excitation mechanisms of these species. The similarity of the spectra of the half dozen comets observed to date argues for a common, homogeneous composition (with the exception of dust and CO) of the cometary ice and a minimal effect on the neutral species due to molecular collisions in the inner coma.
Wilkening, L. L.↗
Highly resolved Eulerian simulations of fuel spray transients in single and multi-hole injectors: Nozzle flow and near-exit dynamics
In high pressure fuel injectors, needle opening and closing transients cause complex off-design fluid dynamics behaviors that profoundly impact the spray and mixture formation processes. These dynamics are completely different from what is known to occur in steady state conditions. In this study, diesel spray transients have been investigated in single-hole and 3-hole nozzles, encompassing internal and external nozzle flow and including needle motion, performing highly resolved (2.5 μm) computational fluid dynamics (CFD) simulations. We focused on end-of-injection (EOI) and start-of-injection (SOI) processes, in order to provide insights in to the physics. The liquid fuel, vapor and gas species are modeled with a single-fluid multiphase mixture approach, with diffuse interface, and with large eddy simulations (LES) of the turbulence. Occurrence of phase change due to cavitation is accounted for, and the spray dispersion is described with a turbulent dispersion model. Detailed needle motion data and orifice internal surface are available from xray synchrotron source measurements carried out at Argonne National Laboratory, and shared through the Engine Combustion Network (ECN) community. Simulations are compared against x-ray phase contrast imaging and radiography of the internal and near-exit flow, in addition to optical microscopy data of the near-exit sprays. Simulation results are found to agree well with available experimental data, and are able to realistically capture local and global features. The simulations allow to gain insight into the physics of gas ingestion and dribbles at EOI, for different hole diameters, operating conditions and number of holes. At SOI, timing of liquid appearance out of the injector and spray tip penetration are adequately predicted, by using the EOI flow field as in-nozzle initialization, and by prescribing the measured tip needle displacement with an informed effective valve opening point inferred from the x-ray observations. Lastly, the variation of spreading angle over time is also discussed in detail for the multi-hole case, including hole-to-hole variations. Due to real geometry features and asymmetric needle motion with eccentric components, it is found that the three holes exhibit swirling flows of increasing intensity as the lift decreases, causing the near cone angle to open and spread, in a quasi-hollow cone structure. These features are not observed in axial single-hole injectors because of their relative simplicity and intrinsic symmetry.
42 ENGINEERING↗