The equatorial anomaly and atmospheric winds
Equatorial anomaly and atmospheric winds in F 2 region
Mayr, H. G.↗
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Geopotential models in the Australian region
The ability of three high-order geopotential models (OSU81, GPM2 and OSU86E) to recover the gravity anomaly field (delta g) in the Australian region was tested. The region was divided into 2 x 2 deg blocks, and the mean and rms of the residual gravity (delta g measured - delta g modeled) was found to estimate the fit of the model to the point gravity data. The results showed that OSU81 and GPM2 performed similarly, recovering the delta g with a mean value of less than plus or minus 5 mGal in 63 and 70 percent of the blocks, respectively. However, both these models achieved a fit of worse that was plus or minus 13 mGal in 6 to 7 percent of cases. These were in areas either on or near the coast, or in the Central Australian region, inferring that for a precise geoid slope determination in these regions, a detailed analysis of delta g in region is needed. On the other hand, OSU86E produced a very good result, having a mean fit of less than plus or minus 5 mGal in 80 percent of the blocks, and worse than plus or minus 13 mGal in only 1 percent of cases. The rms values for this model were also improved over the other two models, indicating that for applications requiring highest precision, the preferred model is OSU86E.
Kearsley, A. H. W.↗
The Vega balloon experiment - Initial results from the global radio tracking
A unique global array of 20 radio telescopes provided 24-h telemetry acquisition of meteorological data from the Vega balloons and differential VLBI measurements of their trajectories. Initial Doppler-tracking analysis indicates mean zonal wind velocities of 69 + or - 1 and 66 + or - 1 m/sec at the Vega 1 and Vega 2 float heights, and discloses an anomaly in the Vega 2 trajectory above the mountains in Aphrodite Terra.
Preston, R. A.↗
Time-Variable Gravity Signal due to Extratropic Pacific Water Mass Redistribution
Using the satellite-laser-ranging (SLR) data, Cox and Chao [2002] reported the detection of a large post-1998 anomaly (in the form of a positive jump) in the time series of Earth s lowest-degree gravity harmonic 52, or the dynamic oblateness. Among several groups now examining the mass redistribution in the global geophysical fluids in search of the cause(s), we report here a temporally coinciding anomalies found in the extratropic north + south Pacific basins. Clearly seen in the leading EOFPC mode for extratropic Pacific, these anomalies occurred in sea-surface height, sea-surface temperature, and temperature- and salinity-depth profiles. We based our analysis on two different data sources: TOPEX/Poseidon altimetry, and the ECCO ocean general circulation model output assimilating T/P data. The magnitude of these changes, when converted to equivalent J2 change, appears to be a few times too small to explain the observed J2 directly. These findings, and the fact that the anomalies occurred following the strong 1997-98 El Nino, suggest strong geophysical connection of the interannual-to-decadal variation of 52 with the Pacific Decadal Oscillation (PDO) and the ultimate global-change processes that cause PDO. More work is underway, and additional independent data sources are examined, paying close attention to the fact that the J2 anomaly has been reversing back to normal since 2001. These include: (1) cryospheric contributions (melting of glaciers and ice sheets); (2) land hydrological contributions; (3) polar sea influences ( e g , via deep flow); (4) fluid flow in Earth's core; (5) time-variable gravity signals from SLR in higher harmonic degree/order, including J3,J4, (2,1), and (2,2) coefficients, considering their lower signal-to-noise ratios; (6) Earth rotation data in terms of length-of-day and polar motion.
Chao, B. F.↗
THE ELECTRON DENSITY DISTRIBUTION IN THE F SUB 2 LAYER OF THE IONOSPHERE IN WINTER
Electron density distribution in the f-2 layer of the ionosphere in winter, and the relation of the enhanced ionization to the so-called winters anomaly
F LAYER↗
Element Mapping in Anhydrous IDPs: Identification of the Host Phases of Major/Minor Elements as a Test of Nebula Condensation Models
Many anhydrous interplanetary dust particles (IDPs) are the most pristine samples of primitive solar system dust currently available for laboratory analysis. Their primitive nature is demonstrated by: 1) the high content of moderately volatile elements, indicating they have not been heated significantly since formation, 2) the absence of hydrated material, indicating they never experienced aqueous processing, 3) the presence of unequilibrated mineral assemblages, 4) the presence of large isotopic anomalies (e.g., D and 15N enrichment), in these IDPs.
Flynn, G. J.↗
Voyager spacecraft electrostatic discharge testing
The program of environmental testing undergone by the Voyager spacecraft in order to simulate the transient voltage effects of electrostatic discharges expected in the energetic plasma environment of Jupiter is reported. The testing consists of studies of the electrostatic discharge characteristics of spacecraft dielectrics in a vacuum-chamber-electron beam facility, brief piece part sensitivity tests on such items as a MOSFET multiplexer and the grounding of the thermal blanket, and assembly tests of the magnetometer boom and the science boom. In addition, testing of a complete spacecraft was performed using two arc sources to simulate long and short duration discharge sources for successive spacecraft shielding and grounding improvements. Due to the testing program, both Voyager 1 and Voyager 2 experienced tolerable electrostatic discharge-caused transient anomalies in science and engineering subsystems, however, a closer duplication of the spacecraft environment is necessary to predict and design actual spacecraft responses more accurately.
Whittlesey, A.↗
DSS command software update
The modifications, additions, and testing results for a version of the Deep Space Station command software, generated for support of the Voyager Saturn encounter, are discussed. The software update requirements included efforts to: (1) recode portions of the software to permit recovery of approximately 2000 words of memory; (2) correct five Voyager Ground data System liens; (3) provide capability to automatically turn off the command processor assembly local printer during periods of low activity; and (4) correct anomalies existing in the software.
Stinnett, W. G.↗
Detailed gravity anomalies from Geos 3 satellite altimetry data
Detailed gravity anomalies are computed from a combination of Geos 3 satellite altimeter and terrestrial gravity data using least-squares principles. The mathematical model used is based on the Stokes' equation modified for a nonglobal solution. Using Geos 3 data in the calibration area, the effects of several anomaly parameter configurations and data densities/distributions on the anomalies and their accuracy estimates are studied. The accuracy estimates for 1 deg x 1 deg mean anomalies from low density altimetry data are of the order of 4 mgal. Comparison of these anomalies with the terrestrial data and also with Rapp's data derived using collocation techniques show rms differences of 7.2 and 4.9 mgal, respectively. Indications are that the anomaly accuracies can be improved to about 2 mgal with high density data. Estimation of 30 in. x 30 in. mean anomalies indicates accuracies of the order of 5 mgal. Proper verification of these results will be possible only when accurate ground truth data become available.
Gopalapillai, G. S.↗
Multiwavelength Characterization of an ACT-Selected, Lensed Dusty Star-Forming Galaxy at zeta 2.64
We present C I(21) and multi-transition C-12 O observations of a dusty star-forming galaxy, ACT J2029+0120,which we spectroscopically confirm to lie at zeta = 2.64. We detect CO(3-2), CO(5-4), CO(7-6), CO(8-7), and C I(2-1) at high significance, tentatively detect HCO+(4-3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4-3) and CS(7-6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG Seyfert or QSO host object in the taxonomy of the Herschel Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T approximately 117 K and n(sub H2) approximately 10(exp5) cm(exp -3), most consistent with a ULIRGQSO object and the presence of high-density tracers. We also find that the velocity width of the C I line is potentially larger than seen in all CO transitions forth is object, and that the L'(sub Ci(2-1))/L'(sub CO(3-2))ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.
Roberts-Borsani, G. W.↗
Numerical models of mantle convection
An overview of numerical methods describing the structure and dynamics of the mantle is presented with attention given to novel 3D modeling techniques. The paper reviews 3D spherical and Cartesian models for constant viscosity emphasizing the assumptions regarding style of convection, time dependence, and implications for the mantle. Similarly treated are 3D Cartesian models with temperature-dependent viscosities, and briefly examined are models that are based on compressibility, nonlinear viscosity, or plates. Extensive illustrations are presented detailing: (1) temperature variations from models of 3D thermal convection in spherical shells; (2) thermal anomalies in equatorial cross sections; and (3) temperature variations in a spherical shell heated from within. The discussion relates the numerical results of the models with real mantle-convection events, and the simulations are shown to yield increasingly realistic representations of material behavior.
Schubert, G.↗
A factor of 2 reduction in theoretical F2 peak electron density due to enhanced vibrational excitation of N2 in summer at solar maximum
The degree to which the O(+) + N2 reaction rate is increased as a result of enhanced vibrational excitation of the N2 molecule in the thermosphere was investigated. It is found that the reaction rate may be sufficiently elevated in summer at solar maximum to decrease the peak O(+) density by a factor of 2, but there is only a small reduction in the winter peak density. Therefore the vibrational excitation of N2 acts to increase the magnitude of the seasonal anomaly. This work emphasizes the need for more laboratory work to clear up uncertainties in some of the key parameters.
Richards, P. G.↗
A harmonic analysis of lunar gravity
An improved model of lunar global gravity has been obtained by fitting a sixteenth-degree harmonic series to a combination of Doppler tracking data from Apollo missions 8, 12, 15, and 16, and Lunar Orbiters 1, 2, 3, 4, and 5, and laser ranging data to the lunar surface. To compensate for the irregular selenographic distribution of these data, the solution algorithm has also incorporated a semi-empirical a priori covariance function. Maps of the free-air gravity disturbance and its formal error are presented, as are free-air anomaly and Bouguer anomaly maps. The lunar gravitational variance spectrum has the form V(G; n) = O(n to the -4th power), as do the corresponding terrestrial and martian spectra. The variance spectra of the Bouguer corrections (topography converted to equivalent gravity) for these bodies have the same basic form as the observed gravity; and, in fact, the spectral ratios are nearly constant throughout the observed spectral range for each body. Despite this spectral compatibility, the correlation between gravity and topography is generally quite poor on a global scale.
Bills, B. G.↗
Venus gravity - A harmonic analysis and geophysical implications
An improved theoretical model of Venusian global gravity has been obtained by fitting a tenth degree spherical harmonic series to 78 orbital arcs of Doppler tracking data from the Pioneer Venus Orbiter. Maps of the free-air anomaly and its formal error are presented. Isostatic anomaly and 'Geoid' maps are also presented, and their geophysical implications are discussed in details. Comparison with equivalent resolution topographic models reveals a strong correlation between long wavelength gravity and the topography of Venus. Analysis of the second degree harmonics showed two aspects of the orientation of the inertial axes of Venus: (1) a significant (about three degrees) departure of the axis of greatest inertia from the rotational axis; and (2) a near alignment of the axis of least inertia with the location of the subterrestrial point at the time of the next inferior conjunction with earth (December 16, 2101). A series of contour maps of the Venusian free-air anomalies is provided.
Mottinger, N. A.↗
In-flight radiation measurements on STS-60
A joint investigation between the United States and Russia to study the radiation environment inside the Space Shuttle flight STS-60 was carried out as part of the Shuttle-Mir Science Program (Phase 1). This is the first direct comparison of a number of different dosimetric measurement techniques between the two countries. STS-60 was launched on 3 February 1994 in a nearly circular 57 degrees x 353 km orbit with five U.S. astronauts and one Russian cosmonaut for 8.3 days. A variety of instruments provided crew radiation exposure, absorbed doses at fixed locations, neutron fluence and dose equivalent, linear energy transfer (LET) spectra of trapped and galactic cosmic radiation, and energy spectra and angular distribution of trapped protons. In general, there is good agreement between the U.S. and Russian measurements. The AP8 Min trapped proton model predicts an average of 1.8 times the measured absorbed dose. The average quality factor determined from measured lineal energy, y, spectra using a tissue equivalent proportional counter (TEPC), is in good agreement with that derived from the high temperature peak in the 6LiF thermoluminescent detectors (TLDs). The radiation exposure in the mid-deck locker from neutrons below 1 MeV was 2.53 +/- 1.33 microSv/day. The absorbed dose rates measured using a tissue equivalent proportional counter, were 171.1 +/- 0.4 and 127.4 +/- 0.4 microGy/day for trapped particles and galactic cosmic rays, respectively. The combined dose rate of 298.5 +/- 0.82 microGy/day is about a factor of 1.4 higher than that measured using TLDs. The westward longitude drift of the South Atlantic Anomaly (SAA) is estimated to be 0.22 +/- 0.02 degrees/y. We evaluated the effects of spacecraft attitudes on TEPC dose rates due to the highly anisotropic low-earth orbit proton environment. Changes in spacecraft attitude resulted in dose-rate variations by factors of up to 2 at the location of the TEPC.
NASA Discipline Radiation Health↗
Magnetic field in Le Monnier Bay according to data of Lunokhod 2
Results of the first traverse measurement of the magnetic field on the surface of the moon are analyzed. The mean value of the magnetic field in the portion of Le Monnier Bay investigated is estimated at 20 to 30 gammas. An anomaly of the field was disclosed, which is confined to craters that exceed 50 meters in size.
Dolginov, S. S.↗
Development of a model of atmospheric oxygen variations to estimate terrestrial carbon storage and release
Two years of work has been completed towards the development of a model of atmospheric oxygen variations on seasonal to decadal timescales. During the first year we (1) constructed a preliminary monthly-mean climatology of surface ocean oxygen anomalies, (2) began modeling studies to assess the importance of short term variability on the monthly-mean oxygen flux, and (3) conducted preliminary simulations of the annual mean cycle of oxygen in the atmosphere. Most of the second year was devoted to improving the monthly mean climatology of oxygen in the surface ocean.
Najjar, Raymond G.↗
A compositional study of the aristarchus region of the moon using near-infrared reflectance spectroscopy
Newly obtained near-infrared reflectance spectra for features on or near the Aristarchus Plateau demonstrate the diversity of compositions in the region. Highland units are of three probable compositions: a feldspar and clinopyroxene assemblage; a probable clinopyroxene, olivine, and possibly feldspar assemblage; and an assemblage composed of olivine or olivine and feldspar. The feldspar-clinopyroxene assemblage is tentatively correlated with the major Th anomaly centered on Aristarchus crater. The regional pyroclastic deposits on the plateau are composed of greater than 90 percent Fe(2+)-bearing glass. The Aristarchus cratering event fully penetrated any mare or pyroclastics in the target. Evidence for mare-related material is found in the ejecta on the mare side of the mare-plateau contact.
Lucey, P. G.↗