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We are engaged in testing gravitational theory by means of observations of objects in the solar system. This work tests the equivalence principle (EP), the Shapiro time delay, the advances of planetary perihelion, the possibility of a secular variation G(dot) in the 'gravitational constant' G, and the rate of the de Sitter (geodetic) precession of the Earth-Moon system. We describe here the results under this contract.
In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be " open " to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause significant observational consequences, such as growing postflare/CME loop system in the corona, separating bright flare ribbons in the chromosphere, and fast ejections of the plasma and the magnetic flux. An eruption on 2002 January 8 provides us a good opportunity to look into these observational signatures of and place constraints on the theories of eruptions. The event started with the expansion of a magnetic arcade over an active region, developed into a coronal mass ejection (CME), and left some thin streamer-like structures with successively growing loop systems beneath them. The plasma outflow and the highly ionized states of the plasma inside these streamer-like structures, as well as the growing loops beneath them, lead us to conclude that these structures are associated with a magnetic reconnection site, namely, the current sheet, of this eruptive process. We combine the data from the Ultraviolet Coronagraph Spectrometer, Large Angle and Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory, as well is from the Mauna Loa Solar Observatory Mark IV K-coronameter, to investigate the morphological and dynamical properties of this event, as well as the physical properties of the current sheet. The velocity and acceleration of the CME reached up to 1800 km/s and 1 km/sq s, respectively. The acceleration is found to occur mainly at the lower corona (<2.76 Solar Radius). The post-CME loop systems showed behaviors of both postflare loops (upward motion with decreasing speed) and soft X-ray giant arches (upward motion with constant speed, or acceleration) according to the definition of Svestka. In the current sheet, the presence of highly ionized ions, such as Fe(+17) and Ca(+13), suggests temperature as high as (3-4) x 10(exp 6) K, and the plasma outflows have speeds ranging from 300 to 650 km/s. Absolute elemental abundances in the current sheet show a strong first ionization potential effect and have values similar to those found in the active region streamers. The magnetic field strength in the vicinity of the current sheet is found to be of the order of 1 G.
Aboard the polar-orbiting SNPP satellite, the VIIRS instrument has been in operation since launch in October 2011. It is a visible and infrared radiometer with a unique panchromatic channel capability designated as a day-night band (DNB). This channel covers wavelengths from 0.5 to 0.9 µm and is designed with a near-constant spatial resolution for Earth observations 24 h a day. The DNB operates at 3 gain stages (low, middle, and high) to cover a large dynamic range. An onboard solar diffuser (SD) is used for calibration in the low gain stage, and to enable the derivation of gain ratios between the different stages. In this paper, we present the SNPP VIIRS DNB calibration performed by the NASA VIIRS characterization support team (VCST). The DNB calibration algorithms are described to generate the calibration coefficient look up tables (LUTs) for the latest NASA Level 1B Collection 2 products. We provide an evaluation of DNB on-orbit calibration performance. This activity supports the NASA Earth science community by delivering consistent VIIRS sensor data products via the Land Science Investigator-led Processing Systems, including the SD degradation applied for DNB calibrations in detector gain and gain ratio trending. The DNB stray light contamination and its correction are highlighted. Performance validations are presented using comparisons to the calibration methods employed by NOAA’s operational Interface Data Processing Segment. Further work on stray light corrections is also discussed.
In 2024 the Stratospheric Aerosol and Gas Experiment on the International Space Station (SAGE III/ISS) entered its eighth year of operations. Using a CCD spectrometer to observe solar and lunar occultations through Earth’s limb, the mission has retrieved tens of thousands of vertical profiles for ozone, aerosol, water vapor, and nitrogen dioxide. Retrieval algorithms are constantly under development to enhance these products. The next product version will improve upon previous versions by addressing problems with the aerosol extinction spectrum and recovering hundreds of profiles impeded by the recent proliferation of sunspots. Users of SAGE III/ISS data can also expect improvements to uncertainty estimates and a continued expansion of ancillary products.
International Ultraviolet Explorer measurements of Mg II h and k emission fluxes are presented for 30 F and G stars that are on or near the main sequence and compared with Wilson's measurements of the Ca II H and K fluxes in these stars. The survey includes a large proportion of stars with very low chromospheric activity as well as 111 Tau, X(1) Ori and other examples of strong chromospheric emission. Emission cores are presented in all of the stars observed. A sharp lower limit to the flux in the cores of the k lines implies the existence of a minimum level of chromospheric activity in which the k line flux is a constant fraction of stellar luminosity. Reduction of Wilson's values to absolute fluxes produces a close correlation between Mg and Ca strength with possibly some dependence on color. For the most active stars, the Mg k and Ca fluxes are consistent with the presence of solar plage covering up to one half of the stellar surface. However, the ratio of k to h in these stars is much less than this simple interpretation predicts.
Volume mixing ratio profiles of HCl, HOCl, ClNO3, CH3Cl, CFC-12, CFC-11, CCl4, HCFC-22, and CFC-113 were measured simultaneously from 9 to 38 km by the Jet Propulsion Laboratory MkIV Fourier Transform Infrared solar absorption spectrometer during two balloon flights from Fairbanks, Alaska (64.8 N), on May 8 and July 8, 1997. The altitude variation of total organic chlorine (CCly) total inorganic chlorine (Cly), and the nearly constant value (3.7 +/- 0.2 ppbv) of their sum (Cl(sub TOT)) demonstrates that the stratospheric chlorine species available to react with O3 are supplied by the decomposition of organic chlorinated compounds whose abundances are well quantified. Measured profiles of HCl and ClNO3 agree well with profiles found by photochemical model (differences < 10% for altitudes below 35 km) constrained by various other constituents measured by MkIV. The production of HCl by ClO + OH plays a relatively small role in the partitioning of HCl and ClNO3 for the sampled air masses. However, better agreement with the measured profiles of HCl and ClNO3 is obtained when this source of HCl is included in the model. Both the measured and calculated [ClNO3]/[HCl] ratios exhibit the expected near linear variation with [O3]2/[CH4] over a broad range of altitudes. MkIV measurements of HCl, ClNO3, and CC1y agree well with ER-2 in situ observations of these quantities for directly comparable air masses. These results demonstrate good understanding of the budget of stratospheric chlorine and that the partitioning of inorganic chlorine is accurately described by photochemical models that employ JPL97 reaction rates and production of HCl from ClO + OH for the environmental conditions encountered: relatively warm temperatures, long periods of solar illumination, and relatively low aerosol surface areas.
Chondrule formation experiments suggest that the B/Li ratios of synthesized chondrules are always lower than that of the starting material, and that the B/Li ratios systematically decrease with decreasing cooling rates at constant temperature. Additional information is contained in the original extended abstract.
In real world operation, low-frequency oscillations associated with plant-level voltage control of inverter-based resources (IBRs) have been a concern of grid operators. Here, this research aims to demonstrate and analyze the effect of plant-level voltage control on system stability and potential interactions among IBRs. The experiment results of a 13.2-kV system interconnected with two IBRs—a 1-MW battery energy storage system (BESS) and a 430-kW solar photovoltaic (PV) plant—are presented. Both 0.5-Hz and 3-Hz oscillations become visible at certain conditions. The phenomenon is further explained by use of a feedback system consisting of the plant-level droop control and the effect of reactive power or var injection on voltage. The main components of the block diagram are obtained via frequency scan measurements. The analysis offers an understanding of the main contributors and other influencing factors of the 3-Hz and 0.5-Hz modes. It also reveals the role of the volt-var droop gain, the low-pass filter time constant, and the system impedance in stability.
The objective of this research is to conduct various fault simulation studies for diagnosing the type and location of faults in the power distribution system. Different types of faults are simulated at different locations within the distribution system and the faulted waveforms are monitored at measurable nodes such as at the output of the DDCU's. These fault signatures are processed using feature extractors such as FFT and wavelet transforms. The extracted features are fed to a clustering based neural network for training and subsequent testing using previously unseen data. Different load models consisting of constant impedance and constant power are used for the loads. Open circuit faults and short circuit faults are studied. It is concluded from present studies that using features extracted from wavelet transforms give better success rates during ANN testing. The trained ANN's are capable of diagnosing fault types and approximate locations in the solar dynamic power distribution system.
Solar flares produce increases in coherent-scatter power from the mesosphere due to the increase in free electrons produced by X-ray photoionization. Thirteen such power enhancements were observed at Urbana. When such an enhancement occurs at an altitude containing a turbulence layer with constant strength, the relative enhancement of electon density is estimated from the enhancement in power. Such estimates of enchanced electron density are compared with estimates of the X-ray photoionization at that altitude, deduced from geostationary satellite measurements. It is found that possible types ion-chemical reaction scheme may be distinguished, and the nonflare ion-pair production function may be estimated. The type of ion-chemical scheme and the nonflare ion-production function are shown to depend on the solar zenith angle.
Highly supercritical compressible convection is simulated in a two-dimensional domain in which the upper half is unstable to convection while the lower half is stably stratified. This configuration is an idealization of the layers near the base of the solar convection zone. Once the turbulent flow is well developed, a toroidal magnetic field B sub tor is introduced to the stable layer. The field's evolution is governed by an advection-diffusion-type equation, and the Lorentz force does not significantly affect the flow. After many turnover times the field is stratified such that the absolute value of B sub tor/rho is approximately constant in the convective layer, where rho is density, while in the stable layer this ratio decreases linearly with depth. Consequently most of the magnetic flux is stored in the overshoot layer. The inclusion of rotation leads to travelling waves which transport magnetic flux latitudinally in a manner reminiscent of the migrations seen during the solar cycle.
High efficiency silicon solar cells are characterized using current-voltage curves, electroluminescence imaging, impedance spectroscopy, capacitance transients, microwave photoconductive decay, and time-resolved photoluminescence imaging. The sample set is composed of cells from different manufacturers and includes an n-type silicon heterojunction (SHJ), an n-type passivated emitter rear totally diffused (PERT), and five different p-type passivated emitter rear contact (PERC) cells. Carrier lifetimes, both photoconductivity and photoluminescence, are measured co-located with the light excitation pulse and within the cell but away from the light spot. Luminescence intensity and excess carrier lifetimes correlate to cell voltage. The capacitance transient time constants correlate to the capacitance values extracted from impedance spectroscopy.
The amplified spontaneous emission (ASE) from a long pulse, solar-simulating radiation pumped iodine laser amplifier is studied. The ASE threshold pump intensity is almost proportional to the inverse of the laser gain length when the gas pressure is constant in the laser tube.
This study focuses on the effects of summertime stratocumulus over the eastern Pacific. This cloud is linked to the semi-permanent sub-tropical highs that dominate the low-level circulation over the Pacific and Atlantic. Subsidence on the eastern flank of these highs creates an inversion based about 800 m above sea level that caps moist air near the surface. This air overlies cool waters driven by upwelling along the coastal regions of North America. Strong surface north-westerlies mix the boundary layer enough to saturate the air just below the capping inversion. Widespread stratocumulus is thus formed. All calculations were carried out using the GENESIS general circulation model that was run at MSFC. Among the more important properties of the model is that it includes radiative forcing due to absorption of solar radiation and the emission of infrared radiation, interactive clouds (both stratocumulus and cumulus types), exchanges of heat and moisture with the lower boundary. Clouds are interactive in the sense that they impact the circulation by modifying the fields of radiative heating and turbulent fluxes of heat and moisture in the boundary layer. In turn, clouds are modified by the winds through the advection of moisture. In order to isolate the effects of mid- and high-latitude stratocumulus, two runs were made with the model: one with and the other without stratocumulus. The runs were made for a year, but with perpetual July conditions, i.e., solar forcing was fixed. The diurnal solar cycle, however, was allowed for. The sea surface temperature distribution was fixed in both runs to represent climatological July conditions. All dependent variables were represented at 12 surfaces of constant sigma = p/p(sub O), where p is pressure and p(sub O) is surface pressure. To facilitate analysis, model output was transformed to constant pressure surfaces. Structures no smaller in size than 7.5 degrees longitude and 4.5 degrees in latitude were resolved. Smaller features of the circulation were parameterized. The model thus captures synoptic- and planetary-scale circulation features.
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We report on X-ray spectral and timing results of the new black hole candidate (BHC) MAXI J1659-152 with the orbital period of 2.41 hours (shortest among BHCs) in the 2010 outburst from 65 Rossi X-ray Timing Explorer (RXTE) observations and 8 simultaneous Swift and RXTE observations. According to the definitions of the spectral states in Remillard & McClintock (2006), most of the observations have been classified into the intermediate state. All the X-ray broadband spectra can be modeled by a multi-color disk plus a power-law with an exponential cutoff or a multi-color disk plus a Comptonization component. During the initial phase of the outburst, a high energy cutoff was visible at 30-40 keV. The innermost radius of the disk gradually decreased by a factor of more than 3 from the onset of the outburst and reached a constant value of 35 d(sub 10)cos(i sup −1/2) km, where d(sub 10) is the distance in units of 10 kpc and i is the inclination. The type-C quasi-periodic oscillation (QPO) frequency varied from 1.6 Hz to 7.3 Hz in association with a change of the innermost radius, while the innermost radius remained constant during the type-B QPO detections at 1.6-4.1 Hz. Hence, we suggest that the origin of the type-B QPOs is different from that of type-C QPOs, the latter of which would originate from the disk truncation radius. Assuming the constant innermost radius in the latter phase of the outburst as the innermost stable circular orbit, the black hole mass in MAXI J1659-152 is estimated to be 3.6-8.0 solar mass for a distance of 5.3-8.6 kpc and an inclination angle of 60-75 degrees.
Symbiotic stars in which the symbiotic phenomenon is powered solely by accretion, often at an average rate that is higher than in cataclysmic variable stars, provide an important opportunity to diagnose boundary layers around disk-accreting white dwarfs. Here, we investigate SU Lyncis (SU Lyn), a recently discovered example of a purely accretion-powered symbiotic star, using the first reliable X-ray spectroscopy, obtained with NuSTAR, and ultraviolet (UV) photometry obtained with Swift. SU Lyn has hard, thermal, X-ray emission that is strongly affected by a variable local absorber that has little impact on the UV emission. Its X-ray spectrum is described well using a plasma cooling from kT ≈ 21 keV, with a 3-30 keV luminosity of approximately 4.9 × 10(exp 32) erg s(exp -1). The spectrum is also consistent with the presence of reflection with an amplitude of 1.0, although in that case, the bestfit plasma temperature is 20%-25% lower. The UV to X-ray luminosity ratio of SU Lyn changed significantly between 2015 and 2016. We interpret this as a consequence of a drop by almost 90% in the accretion rate. Whereas the UV luminosity of the disk responded linearly, the luminosity of the optically thin (hard X-ray) emission from the boundary layer remained roughly constant because the boundary layer changed from partially optically thick to almost completely optically thin. Under this interpretation, we place a lower limit on the white dwarf mass of 0.7 solar mass (0.8 solar mass if we neglect reflection).
High efficiency silicon solar cells are characterized using current-voltage curves, electroluminescence imaging, impedance spectroscopy, capacitance transients, microwave photoconductive decay, and time-resolved photoluminescence imaging. The sample set is composed of cells from different manufacturers and includes an n-type silicon heterojunction (SHJ), an n-type passivated emitter rear totally diffused (PERT), and five different p-type passivated emitter rear contact (PERC) cells. Carrier lifetimes, both photoconductivity and photoluminescence, are measured co-located with the light excitation pulse and within the cell but away from the light spot. Luminescence intensity and excess carrier lifetimes correlate to cell voltage. The capacitance transient time constants correlate to the capacitance values extracted from impedance spectroscopy.