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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Persistent Longitudinal Variations of Plasma Density and DC Electric Fields in the Low Latitude Ionosphere Observed with Probes on the C/NOFS Satellite

Continuous measurements using in situ probes on consecutive orbits of the C/N0FS satellite reveal that the plasma density is persistently organized by longitude, in both day and night conditions and at all locations within the satellite orbit, defined by its perigee and apogee of 401 km and 867 km, respectively, and its inclination of 13 degrees. Typical variations are a factor of 2 or 3 compared to mean values. Furthermore, simultaneous observations of DC electric fields and their associated E x B drifts in the low latitude ionosphere also reveal that their amplitudes are also strongly organized by longitude in a similar fashion. The drift variations with longitude are particularly pronounced in the meridional component perpendicular to the magnetic field although they are also present in the zonal component as well. The longitudes of the peak meridional drift and density values are significantly out of phase with respect to each other. Time constants for the plasma accumulation at higher altitudes with respect to the vertical drift velocity must be taken into account in order to properly interpret the detailed comparisons of the phase relationship of the plasma density and plasma velocity variations. Although for a given period corresponding to that of several days, typically one longitude region dominates the structuring of the plasma density and plasma drift data, there is also evidence for variations organized about multiple longitudes at the same time. Statistical averages will be shown that suggest a tidal "wave 4" structuring is present in both the plasma drift and plasma density data. We interpret the apparent association of the modulation of the E x B drifts with longitude as well as that of the ambient plasma density as a manifestation of tidal forces at work in the low latitude upper atmosphere. The observations demonstrate how the high duty cycle of the C/NOFS observations and its unique orbit expose fundamental processes at work in the low latitude, inner regions of geospace.

Pfaff, R.↗
NASA NTRSDate not supplied

Seasonal and Dayurnal Planetary Albedo Variability from Six Years of DSCOVR EPIC Data

Deep Space Climate Observatory (DSCOVR) measurements of Earth’s reflected solar radiation from the Lissajous orbital position near the Lagrangian L1 point provide continuous monitoring of the Earth’s sunlit hemisphere. CERES-based angle models were used to convert the near-hourly reflected radiances of the EPIC images into a climate-style planetary albedo data-point over the sunlit hemisphere. Integration over the sunlit hemispheres averages out the meteorological weather noise, but retains the seasonal and planetary-scale variability. As the Earth rotates, this generates variations in the Earth’s planetary albedo that are precisely aligned in longitude, which constitutes the dayurnal cycle. This dayurnal variability in the planetary albedo arises from planetary-scale changes in cloud radiative properties that can be directly compared to similarly sampled climate GCM output data. Six years of EPIC data have been analyzed, showing characteristic patterns in the seasonal and dayurnal variability of the Earth’s planetary albedo. Much of the seasonal change in planetary albedo is associated with the changing DSCOVR viewing geometry and the change in solar declination. But throughout the year, the highest planetary albedos are observed over the Central Asia (Iraq) longitude, while the lowest planetary albedos occur over the Central Pacific longitude. For these longitudes, the relative seasonal changes in the planetary albedo are slowly varying and anti-correlated. Dayurnal amplitude maxima tend to occur during the July-September timeframe, with April-May and December exhibit distinct minima in the dayurnal amplitude. West Africa and the West Pacific longitudes likewise exhibit anti-correlated seasonal variability, while they also undergo anti-correlated short period oscillations. On the other hand, in nearby longitudes, there are short period spikes in planetary albedo of a few-days duration, as well as longer period oscillations that may range from a week to several months, that generally tend to be correlated.

Planetary Albedo↗
NASA NTRS1980

Discovery of a longitudinal asymmetry in the H Lyman-alpha brightness of Jupiter

A strong longitude variation in the midlatitude Lyman-alpha brightness of Jupiter has been discovered using data from the Voyager ultraviolet spectrometers. A minimum brightness of 14.4 kR was observed in the System III (1965) west longitude range 200-300 deg. The intensity rises to a broad peak of 19.6 kR near a longitude of 110 deg, a 36% increase over the minimum. This intensity 'bulge' was observed to rotate with the planet and appeared at the same longitude during both Voyager encounters, four months apart. This is a surprising discovery; no other planet studied to date has such a characteristic and the upper levels of the Jovian atmosphere were expected to be uniform in longitude. It is likely that a longitudinal asymmetry in charged particle precipitation leads to selective heating of the upper atmosphere and increased dissociation of H2, increasing the hydrogen column abundance. The resulting increase in resonant scattering could produce the observed intensity bulge.

Sandel, B. R.↗
NASA NTRS1980

Corotating Birkeland currents in Jupiter's magnetosphere - An Io plasma-torus source

It is proposed that a persistent longitudinally asymmetric pattern of Birkeland (magnetic-field aligned) currents flow between the Jovian ionosphere and the plasma torus that encircles Jupiter near Io's orbit. A specific longitudinal sector of the torus (i.e., the active sector) contains more plasma and is therefore more massive than the rest of the torus. This asymmetry causes Birkeland currents to flow between Jupiter's ionosphere and the torus. The principal currents are confined to the longitude range of the active sector; an upper limit to their magnitude is approximately 5,000,000 A. Current flows upward from the ionosphere in the longitude range = 290 + or - 30 deg at the torus, which maps down the magnetic field lines in the northern hemisphere to a longitude range between 215 and 300 deg. Similarly, the downward Birkeland current, which flows between 230 + or - 30 deg at the torus, maps down to a longitude range within 180 and 215 deg at ionospheric heights in the northern hemisphere. The model also contains a possible weaker source in the southern hemisphere, removed approximately 180 deg in longitude from the primary northern-hemisphere source.

Dessler, A. J.↗
NASA NTRS1983

Coordinate systems

Jovian coordinate systems are different from those employed in the case of the earth. Latitude and longitude coordinates are usually established relative to some solid surface. Because Jupiter does not have a solid surface (at least none which is visible through the clouds), arbitrary, but convenient, coordinate grids have been prescribed. A spin equator is made out from observations of cloud motion, and the direction of the planetary spin axis is, therefore, determined with relatively good accuracy. The problem in establishing a Jupiter longitude system is that the mean rotation period of the clouds is a function of latitude. The solution selected was to define two separate longitude grids. A third longitude system became necessary with the detection of radio signals which gave evidence for a rotating planetary magnetic field. Attention is also given to orbital phase angle and longitude conventions for satellites, and two latitude systems for Jupiter

Dessler, A. J.↗
NASA NTRS2010

A Multi-Spacecraft View of Solar-Energetic-Particle Onsets in the 1977 November 22 Event

We examine the onset timing of solar energetic particles (SEPs) in the large ground-level event (GLE) of 1977 November 22 as observed from six spacecraft at four distinct solar longitudes. In most cases, it was possible to use velocity dispersion of the energetic protons to fix the solar particle release (SPR) time and the path-length traveled by the initial particle burst from each solar longitude. We find that the SPR times do depend upon solar longitude, being earliest for spacecraft that are magnetically well-connected to the source region, and later for longitudes on the flanks of the outward driven shock wave. The earliest SPR time occurs well after peak photon emission from the associated Ha flare. These observations are consistent with conclusions derived from single-longitude observations of different GLE events.

Reames, Donald V.↗
NASA NTRS2011

Strike-Slip Fault Patterns on Europa: Obliquity or Polar Wander?

Variations in diurnal tidal stress due to Europa's eccentric orbit have been considered as the driver of strike-slip motion along pre-existing faults, but obliquity and physical libration have not been taken into account. The first objective of this work is to examine the effects of obliquity on the predicted global pattern of fault slip directions based on a tidal-tectonic formation model. Our second objective is to test the hypothesis that incorporating obliquity can reconcile theory and observations without requiring polar wander, which was previously invoked to explain the mismatch found between the slip directions of 192 faults on Europa and the global pattern predicted using the eccentricity-only model. We compute predictions for individual, observed faults at their current latitude, longitude, and azimuth with four different tidal models: eccentricity only, eccentricity plus obliquity, eccentricity plus physical libration, and a combination of all three effects. We then determine whether longitude migration, presumably due to non-synchronous rotation, is indicated in observed faults by repeating the comparisons with and without obliquity, this time also allowing longitude translation. We find that a tidal model including an obliquity of 1.2?, along with longitude migration, can predict the slip directions of all observed features in the survey. However, all but four faults can be fit with only 1? of obliquity so the value we find may represent the maximum departure from a lower time-averaged obliquity value. Adding physical libration to the obliquity model improves the accuracy of predictions at the current locations of the faults, but fails to predict the slip directions of six faults and requires additional degrees of freedom. The obliquity model with longitude migration is therefore our preferred model. Although the polar wander interpretation cannot be ruled out from these results alone, the obliquity model accounts for all observations with a value consistent with theoretical expectations and cycloid modeling.

Rhoden, Alyssa Rose↗
DOE OSTI2025

Using Temporal Information from Human Mobility Data to Detect Anchor Points

Spatiotemporal mobility data are available in massive quantities, but large quantities of data typically include fewer variables or data fields. Often, the only available fields are User ID, Longitude, Latitude, Timestamp (ULLT). This raises an important question: how much can we infer about human mobility patterns using only these four fields? With ULLT data, we do not know individuals' socioeconomic status information or when they are visiting their anchor points (AP) or locations (such as homes, places of employment, or schools), and it is a modern challenge to use this data to infer these characteristics. When detecting anchor locations with limited input information, verification and validation (VV) are significant challenges. This paper addresses the problem of identifying individuals' anchor locations using only temporal information from spatiotemporal datasets with limited attributes. Our approach does not explicitly use latitude and longitude during analysis. Locationbased information is only employed in the preprocessing stage to identify periods of movement (trips) and stops (dwelling). Beyond this step, all analysis is based on temporal patterns. In theory, if stops and dwell times could be detected through alternative means, our method could function entirely without location-based input. We demonstrate this methodology on the 2017 National Household Travel Survey (NHTS) data, because it includes a carefully designed and collected time use survey with representative sampling and labeled ground truth. The high-quality survey data allows us to test the accuracy of our methods because NHTS contains intended place labels and agent/user characteristics. We have also applied our validated AP identification algorithm on very large-scale GPS based trajectory data for Patterns-of-Life (PoL) assessment and other applications, but due to space limit that could not be presented here.

McBride, Liz [ORNL] (ORCID:0000000286925869)↗
DOE OSTI2024

Parallax-corrected VISST-derived pixel-level products from satellite GOES-16

The NASA Langley group led by William Smith produced GOES-16 satellite cloud retrievals over an approximate 10 by 10 degree region over the CACTI field campaign location. These retrievals are described here: https://www.arm.gov/capabilities/vaps/visst and are available for download here . They use algorithms historically called VISST that are now referred to as SatCORPS. More information can be found in Trepte et al. (2019), Minnis et al. (2021), and Yost et al. (2021). If using this dataset, please cite these references, the CACTI VISST dataset DOI found at the download link above, and this dataset’s DOI. The CACTI VISST pixel-level retrievals are on a 2 km spatial grid and available every 15 minutes (every 10 minutes late in the campaign), producing 21,765 files for the entire field campaign between October 2018 and April 2019. They are not corrected for parallax error, which is an offset in the actual geographical location of a cloud above the surface due to the satellite viewing the cloud partly from the side off nadir. This dataset applies a correction for parallax using the location relative to the satellite and the retrieved cloud top height above the surface, which allows the dataset to be geo-located with surface-based observations. The parallax correction for each location depends on the longitude, latitude and cloud top height above ground level (AGL) for that longitude and latitude in the original VISST files. The cloud top height AGL requires first computing the surface elevation at each VISST grid point. Data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) Global Digital Elevation Map Version 3 at 30-m resolution is projected onto the VISST grid using conservative coarsening (conserving surface elevation) in the xESMF Python package. The surface elevation is then subtracted from the VISST-retrieved cloud top height above mean sea level. These cloud top heights AGL are then combined with longitude and latitude to estimate the latitude and longitude corrections. Due to variability in cloud top height, the parallax shifts produce an irregular grid of values since higher cloud tops are shifted further than lower cloud tops. A ball tree-based neighbor search with Haversine distance is performed using the Python-based scikit-learn library to find the nearest VISST grid point to each parallax correction-shifted point. The data value of the shifted point is then assigned to that VISST grid point. In this manner, the irregular geographical shifts to correct for parallax are projected back to the rectilinear VISST grid. Because relatively higher clouds should obscure lower clouds, the variable values for the highest cloud top are preferentially chosen if two or more values are assigned to a grid point. The parallax correction should be viewed as an improved but still imperfect estimation of the cloud top locations, largely because the cloud top height is an imperfect retrieval. Please see the attached README document for further information. Users are encouraged to contact the authors with any additional questions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1972

Recurrent active regions related to metric radio continuum emissions and the interplanetary magnetic sector structure

Active heliographic longitudes at the sun are investigated by using the observational data for long-lived metric continuum noise sources. It is shown that, for the period from 1963 to 1969, the number of such longitudes was four in general and these longitudes were very stable for this radio activity since 1963. A discussion is given on the relationship between those longitudes and the sector structure of the interplanetary magnetic field.

Sakurai, K.↗
NASA NTRS1974

Magnetic coordinates for the Pioneer 10 Jupiter encounter

The magnetic coordinates of the Pioneer 10 spacecraft and the five innermost satellites are reported for the Jupiter encounter. The D sub 2 offset is used to make the calculations. Magnetic coordinates are needed for the interpretation of the trapped particle measurements, including the absorption effects of the satellites. Contours of constant field magnitude and magnetic latitude are given at the surface of Jupiter for the D sub 2 model. The system 3 longitude of a spacecraft at Jupiter is derived, and formulas given for the relationships between system 1, 2, and 3 longitudes. The longitude of the magnetic dipole increases by about 3 deg per year, due to the inaccurate rotation rate used to define system 3 longitude.

Mead, G. D.↗
NASA NTRS1974

Magnetic coordinates for the Pioneer 10 Jupiter encounter

The magnetic coordinates of the Pioneer 10 spacecraft and the five innermost satellites are given around the time of Jupiter encounter, Dec. 1-8, 1973. The D sub 2 offset dipole model of Smith et al. (1974) is used to make the calculations. Magnetic coordinates are needed for the interpretation of the trapped particle measurements, including the absorption effects of the satellites. Contours of constant field magnitude and magnetic latitude are given at the surface of Jupiter for the D sub 2 model. The system III longitude of a spacecraft at Jupiter is derived, and formulas are given for the relationships between system I, II, and III longitudes. The longitude of the magnetic dipole increases by about 3 deg/yr, owing to the inaccurate rotation rate used to define system III longitude.

Mead, G. D.↗
NASA NTRS1978

Global morphology of nitric oxide in the lower E region

Measurements of nitric oxide at 105 km by the ultraviolet nitric oxide experiment on Atmosphere Explorer C are presented. The amount of nitric oxide in the lower E region is shown to depend on latitude, longitude, and magnetic activity. Near the equator the density at the peak of the NO layer is typically about 2 x 10 to the 7th power/cu cm and varies little with longitude or magnetic activity, except during major storms. At high latitudes (up to 68 deg geographic latitude), peak densities are typically 2 or 3 times larger and much more variable. A longitudinal dependence is found in both geographic and geomagnetic coordinates, with minimum densities found near 45 deg E geomagnetic longitude and maxima near 135 deg W geomagnetic longitude. At 40 deg dip latitude the half amplitude is about 30%.

Cravens, T. E.↗
NASA NTRS1978

Frequency and time dependence of the Jovian decametric radio emissions - A nineteen-year high-resolution study

A nineteen-year catalog of observations has permitted detailed comparison of Jovian source characteristics at 10 frequencies from 5.6 to 30 MHz. The spectral morphology of Jupiter's decameter-wavelength radio sources was studied by means of high-resolution histograms of occurrence probability for intervals as small as 2 deg in Jovian system III longitude and the departure of Io from superior geocentric conjunction. Longitude histograms clearly exhibit a substantial shift in the source A and source B positions between 15 and 10 MHz. Similar diagrams isolate the dependence of each source on the position of Io, illustrating changes with frequency in the structures and sizes of the main probability maxima and in the positions of surrounding secondary peaks. Individual frequency probability histograms for both longitude and Io phase reveal new phenomena, such as a bridge of radiation through source B longitudes connecting sources A and C at 15 MHz and spectral modification of portions of the Io-related source B peak.

Thieman, J. R.↗
NASA NTRS1979

Decametric radio measurement of Jupiter's rotation period

Results of determinations of Jupiter's average decametric-wave rotation period are reported. The residual longitude drift of 18, 20 and 22.2 GHz emission observed at stations in Florida and Chile was calculated from measurements of the longitudes of source A peak centers for apparitions separated by 12 years; the drift was assumed to be the longitude shift which maximizes the cross correlation of histograms of occurence probability as a function of System III (1957.0) central meridian longitude. The weighted mean rotation period observed is 9 h 55 min 29.689 sec (standard deviation 0.005 sec), which is 0.022 sec less than the System III (1965) value. It is suggested that, if measurements are continued through the next maximum of Jovicentric earth declination, a secular drift in Jupiter's magnetic field may be observable.

May, J.↗
NASA NTRS1981

A comparison of the thermal and radar characteristics of Mars

Results of thermal infrared sensing and radar observations of the Martian surface are compared for the region centered on +22 deg latitude. Values of the apparent thermal inertia of the surface were derived from surface brightnesses observed by the Viking Orbiter Infrared Thermal Mapper, while radar cross sections were obtained in earth-based experiments at wavelengths of 3.8, 12.5 and 70 cm. A correlation between the thermal inertia and radar cross section values is observed which is strongest with the 70-cm radar data except between longitudes of 10 and 90 deg, where a slight anticorrelation is found. The mixing of small (much less than 70 cm) rocks into a surface of fine material can account for the data between 90 and 370 deg longitude, with as much as 50% of the surface covered by rock in Syrtis Major, Isidis Planitia and parts of Elysium Planitia, and little or no rock cover near Olympus Mons, Elysium Mons, and Amazonis Planitia. The remaining longitudes may be explained in terms of the effects of atmospheric dust on the surface temperature or the effects of local variations in large-scale roughness or scattering from rocks. Data from the 90 to 370 deg longitude region are consistent with the division of the Martian surface into two types of terrain, possibly related to the erosional or depositional nature of the regions.

Jakosky, B. M.↗
NASA NTRS1981

Auroral arc electrodynamic parameters measured by AE-C and the Chatanika radar

Auroral arc electrodynamic parameters are studied using coordinated measurements between the AE-C satellite and the Chatanika radar. On January 4, 1978, the spacecraft twice crossed an east-west aligned auroral arc at widely spaced longitudes, spanning more than 3 hours in local time. The Chatanika radar was scanning in elevation at a magnetic longitude equidistant from the two AE-C crossings. The electric field pattern around this arc was remarkably similar at the three longitudes. Equatorward of the arc the north-south field was very intense (greater than approximately 60 mV/m), whereas poleward of the arc it was small (approximately 10 mV/m). The east-west field was small and almost constant across the arc. The same arc was observed by the radar for about 1 hour, and this electric field pattern did not change, even though the arc location, intensity, and width changed substantially. For a given electric field the AE-C measured ion temperature was substantially different during each of the arc crossings. This dissimilarity is attributed to differences in the F region neutral wind at the two longitudes. It is shown that the electric field variations are consistent with the existence of polarization charges within the arc, even though the electric field remained small poleward of the arc.

Beaujardiere, O. D. L.↗
NASA NTRS1988

Determination of rock type on Mercury and the moon through remote sensing in the thermal infrared

Thermal infrared emission spectra of the moon and Mercury have been obtained using the Si:As photoconductor and circular variable filter at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Lunar spectra from 7.2 to 12.2 microns for two different locations in the south polar highlands have Christiansen frequency peaks at 8.1 microns and 7.9 microns, respectively. This indicates different compositions at the two locations; mafic in the first case, more felsic in the second. Emission spectra from Mercury are not as spatially localized,; however, the longitude of maximum contribution to the spectrum can be calculated from thermal models of the earth-facing disk. Results for areas centered at two longitudes have been obtained. Two locations in the intercrater plains were observed. At 40-deg longitude (very near the crater Homer), a peak at 7.9 microns indicates mafic igneous rock type. Spectra emanating from 46-deg longitude have peaks at 7.8 microns, indicating a region borderline between mafic and intermediate composition.

Tyler, Ann L.↗