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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Geotail Measurements Compared with the Motions of High-Latitude Auroral Boundaries during Two Substorms

Geotail plasma and field measurements at -95 R(sub E) are compared with extensive ground-based, near-Earth, and geosynchronous measurements to study relationships between auroral activity and magnetotail dynamics during the expansion phases of two substorms. The studied intervals are representative of intermittent, moderate activity. The behavior of the aurora and the observed effects at Geotail for both events are harmonized by the concept of the activation of near-Earth X lines (NEXL) after substorm onsets, with subsequent discharges of one or more plasmoids down the magnetotail. The plasmoids must be viewed as three-dimensional structures which are spatially limited in the dawn-dusk direction. Also, reconnection at the NEXL must proceed at variable rates on closed magnetic field lines for significant times before beginning to reconnect lobe flux. This implies that the plasma sheet in the near-Earth magnetotail is relatively thick in comparison with an embedded current sheet and that both the NEXL and distant X line can be active simultaneously. Until reconnection at the NEXL engages lobe flux, the distant X line maintains control of the poleward auroral boundary. If the NEXL remains active after reaching the lobe, the auroral boundary can move poleward explosively. The dynamics of high-latitude aurora in the midnight region thus provides a means for monitoring these processes and indicating when significant lobe flux reconnects at the NEXL.

Maynard, N. C.↗
NASA NTRS1998

EGRET Sources at Intermediate Galactic Latitudes

During the period 15 March 1992 through 31 October 1997, 12 papers using ROSAT data, supported in part by this grant, were published in referred journals, and one paper was published in a conference proceedings. Their bibliographical references are listed in the Appendix, and the abstracts of these papers are given in the next 13 sections of this report. Finally, a summary of the work completed to date on the newest project, for which ROSAT data are still being received, is given in the section entitled "EGRET Sources at Intermediate Galactic Latitude".

Halpern, Jules P.↗
NASA NTRS1997

Layering in halocarbons, methane, nitrous oxide, ozone, and water vapour over mid-latitudes

The purpose of the balloon flights performed in March 1993 from Aire-sur-Adour (France) was to measure trace gases in the polar vortex during a dynamically active period. These balloon flights revealed coincident layering in long-lived tropospheric source gases. A layer of mid-latitude air, enriched in trace gases, was detected at sampled levels near 15 mbar. High resolution advection models, fine scale distributions of ozone, nitrous oxide, methane, and halocarbons were constructed. The calculations showed how air enriched in trace gases is sampled near 15 mbar when a filament of such air is drawn into the outer portion of the vortex.

Orsolini, Yvan J.↗
NASA NTRS1993

The Effects of Neutral Inertia on Ionospheric Currents in the High-Latitude Thermosphere Following a Geomagnetic Storm

Results of an experimental and theoretical investigation into the effects of the time dependent neutral wind flywheel on high-latitude ionospheric electrodynamics are presented. The results extend our previous work which used the National Center for Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) to theoretically simulate flywheel effects in the aftermath of a geomagnetic storm. The previous results indicated that the neutral circulation, set up by ion-neutral momentum coupling in the main phase of a geomagnetic storm, is maintained for several hours after the main phase has ended and may dominate height-integrated Hall currents and field-aligned currents for up to 4-5 hours. We extend the work of Deng et al. to include comparisons between the calculated time-dependent ionospheric Hall current system in the storm-time recovery period and that measured by instruments on board the Dynamics Explorer 2 (DE 2) satellite. Also, comparisons are made between calculated field-aligned currents and those derived from DE 2 magnetometer measurements. These calculations also allow us to calculate the power transfer rate (sometimes called the Poynting flux) between the magnetosphere and ionosphere. The following conclusions have been drawn: (1) Neutral winds can contribute significantly to the horizontal ionospheric current system in the period immediately following the main phase of a geomagnetic storm, especially over the magnetic polar cap and in regions of ion drift shear. (2) Neutral winds drive Hall currents that flow in the opposite direction to those driven by ion drifts. (3) The overall morphology of the calculated field-aligned current system agrees with previously published observations for the interplanetary magnetic field (IMF) B(sub Z) southward conditions, although the region I and region 2 currents are smeared by the TI(ICM model grid resolution. (4) Neutral winds can make significant contributions to the field-aligned current system when B(sub Z) northward conditions prevail following the main phase of a storm, but can account for only a fraction of the observed currents. (5) DE 2 measurements provide a demonstration of "local" (satellite-altitude) flywheel effects. (6) On the assumption that the magnetosphere acts as an insulator, we calculate neutral-wind-induced polarization electric fields of approx. 20-30 kV in the period immediately following the geomagnetic storm.

Deng, W.↗
NASA NTRS1998

Temperature climatology of the middle atmosphere from long-term lidar measurements at mid- and low-latitudes

The temperature structure of the middle atmosphere has been studied for several decades using a variety of techniques. However, temperature profiles derived from lidar measurements can provide improved vertical resolution and accuracy. Lidars can also provide long-term data series relatively absent of instrumental drift, and integration of the measurements over several hours removes most of the gravity wave-like short-scale disturbances. This paper describes a seasonal climatology of the middle atmosphere temperature derived from lidar measurements obtained at several mid- and low-latitude locations. Results from the following lidars, which have all obtained a long-term measurement record, were used in this study: the two Rayleigh lidars of the Service d'Aeronomie du CNRS, France, located at the Observatoire de Haute Provence (OHP, 44.0 deg N) and at the Centre d'Essais des Landes (CEL, 44.0 deg N), the two Rayleigh/Raman lidars of the Jet Propulsion Laboratory, USA, located at Table Mountain, California (TMF, 34.4 deg N) and at Mauna Loa, Hawaii (MLO, 19.5 deg N), and the Colorado State University, USA, sodium lidar located at Fort Collins, Colorado (CSU, 40.6 deg N). The overall data set extends from 1978 to 1997 with different periods of measurements depending on the instrument. Three of the instruments are located at primary or complementary stations (OHP, TMF, MLO) within the Network for Detection of Stratospheric Change (NDSC). Several aspects of the temperature climatology obtained by lidar in the middle atmosphere are presented, including the climatological temperature average through the year; the annual and semi-annual components, and the differences compared to the CIRA-86 climatological model.

McDermid, I. Stuart↗
NASA NTRS2000

Investigating the Role of the Earth's Ionosphere in Space Weather: Modeling and Observations of High-Latitude Ionospheric Outflows

We will present what we believe to be the first reported observations of up- and downflows of topside ionospheric thermal plasmas from multiple near-simultaneous tracks through the high-latitude topside ionosphere. From several Southern polar passes, it has been possible to construct plots of field-aligned flows of 0+ observed by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft near 5000 km altitude together with vertical ion flow observations from one or more DMSP spacecraft near 800 km altitude. We also will present simultaneous observations of POLAR auroral LTVI images with field-aligned flows. We will further show new fluid-kinetic simulations of auroral ionospheric flows in the altitude range 120 km to several R-E as subjected to the synergistic auroral effects of soft electron precipitation, transverse wave-driven ion heating, and hot plasma-driven electric potentials.

Horwitz, J. L.↗
NASA NTRS2000

Near-Simultaneous POLAR and DMSP Measurements of Topside Ionospheric Up and Down Flows at High Latitudes

We will present what we believe to be the first reported observations of up- and downflows of topside ionospheric thermal plasmas from multiple near-simultaneous tracks through the high-latitude topside ionosphere. From several Southern polar passes, it has been possible to construct plots of field-aligned flows of 0+ observed by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft near 5000 km altitude together with vertical ion flow observations from one or more DMSP spacecraft near 800 km altitude. These observations provide a glimpse of the wide-spread upward and downward ionospheric ion flows over the broad polar region along multiple distinct satellite tracks. For the instances where DMSP and POLAR cross nearly the same field lines at the 800 and 5000 kin altitudes, we will show ion parameter measurements at these to altitudes in comparison to Dynamic Fluid-Kinetic(DyFK) transport simulations of anticipated altitude profiles of these parameters.

Zeng, W.↗
NASA NTRS2000

Estimation of Aerosol Direct Radiative Effects Over the Mid-Latitude North Atlantic from Satellite and In Situ Measurements

We estimate solar radiative flux changes due to aerosols over the mid-latitude North Atlantic by combining optical depths from AVHRR measurements with aerosol properties from the recent TARFOX program. Results show that, over the ocean the aerosol decreases the net radiative flux at the tropopause and therefore has a cooling effect. Cloud-free, 24-hour average flux changes range from -9 W/sq m near the eastern US coast in summer to -1 W/sq m in the mid-Atlantic during winter. Cloud-free North Atlantic regional averages range from -5.1 W/sq m in summer to -1.7 W/sq m in winter, with an annual average of -3.5 W/sq m. Cloud effects estimated from ISCCP data, reduce the regional annual average to -0.8 W/sq m. All values are for the moderately absorbing TARFOX aerosol (omega(0.55 microns) = 0.9); values for a nonabsorbing aerosol are approx. 30% more negative. We compare our results to a variety of other calculations of aerosol radiative effects.

Bergstrom, Robert W.↗
NASA NTRS1999

Origin and Variability of Upper Tropospheric Nitrogen Oxides and Ozone at Northern Mid-Latitudes

Measurements of NO(x) and ozone performed during the NOXAR project are compared with results from the coupled chemistry-climate models ECHAM4.L39(DLR)/CHEM and GISS-model. The measurements are based on flights between Europe and the East coast of America and between Europe and the Far East in the latitude range 40 deg N to 65 deg N. The comparison concentrates on tropopause altitudes and reveals strong longitudinal variations of seasonal mean NO,, of 200 pptv. Either model reproduced strong variations 3 km below but not at the tropopause, indicating a strong missing NO(x) or NO(y) sink over remote areas, e.g. NO(x) to HNO3 conversion by OH from additional OH sources or HNO3 wash-out. Vertical profiles show maximum NO(x) values 2-3 km below the tropopause with a strong seasonal cycle. ECHAM4.L39(DLR)/CHEM reproduces a maximum, although located at the tropopause with a less pronounced seasonal cycle, whereas the GISS model reproduces the seasonal cycle but not the profile's shape due to its coarser vertical resolution. A comparison of NO(x) frequency distributions reveals that both models are capable of reproducing the observed variability, except that ECHAM4.L39(DLR)/CHEM shows no very high NO(x) mixing ratios. Ozone mean values, vertical profiles and frequency distributions are much better reproduced in either model, indicating that the NO(x) frequency distribution, namely the most frequent NO(x) mixing ratio, is more important for the tropospheric photochemical ozone production than its mean value. Both models show that among all sources, NO(x) from lightning contributes most to the seasonal cycle of NO(x) at tropopause altitudes. The impact of lightning in the upper troposphere on NO(x) does not vary strongly with altitude, whereas the impact of surface emissions decreases with altitude. However, the models show significant differences in lightning induced NO(x) concentrations, especially in winter, which may be related to the different treatment of the lower stratospheric coupling between dynamics and chemistry.

Grewe, V.↗
NASA NTRS2000

Multiple Satellite Observations of High-Latitude Ionospheric Outflows

We will present reported observations of up- and down-flows of topside ionospheric thermal plasmas from multiple near-simultaneous tracks through the high-latitude topside ionosphere. From several Southern polar passes, it has been possible to construct plots of field-aligned flows of O+ observed by the Thermal Ion Dynamics Experiment(TIDE) on the POLAR spacecraft near 5000 km altitude together with vertical ion flow observations from one or more DMSP spacecraft near 800 km altitude. We will also involve simulations from our Dynamic Fluid-Kinetic(DyFK) modeling of polar plasma transport and display resulting altitude profiles of ion parallel velocities and densities, and overlay those profiles with the "conjunction" measurements by DMSP(800 km) and POLAR(approx. 5000 km altitude). We also will present simultaneous observations of POLAR auroral UVI images with field-aligned flows.

Horwitz, J.↗
NASA NTRS2000

The Density-Potential (N(sub e)-V(sub s/c)) Relation in the High-Latitude Prenoon Ionosphere

Sounding of the Cleft Ion Fountain Energization Region (SCIFER) Thermal Electron Capped Hemisphere Spectrometer (TECHS) data are used to study the plasma density, spacecraft potential relation (N(sub e)-V(sub s/c)) in the prenoon topside auroral and cleft ionosphere during a period of low solar activity. The SCIFER TECHS data show a power-law electron temperature dependence on ambient density across the transition from positive to negative spacecraft potential values in the high-latitude ionosphere. The illuminated ionospheric N(sub e)-V(sub s/c) relation is numerically modeled by imposing equilibrium of current flowing to/from the conductive surfaces of the payload. This modeling demonstrates a strong dependence of spacecraft potential on electron temperature across a wide range of densities. This electron temperature dependence is especially significant in the negative spacecraft potential regime. SCIFER TECHS observations of the N(sub e)-V(sub s/c) relation are used to extend the previous magnetospheric observation-model results to the higher density ionospheric regime.

Adrian, M. L.↗
NASA NTRS1999

Characterization of Terrain in the Mars Surveyor 2001 Landing Site Latitude and Elevation Region Using Mapping Phase Mars Global Surveyor MOC Images

One of the original objectives of the Mars Orbiter Camera (MOC), as proposed in 1985, was to acquire observations to be used in assessing future spacecraft landing sites. Images obtained by the Mars Global Surveyor MOC since March 1999 provide the highest resolution views (1.5-4.5 m/pixel) of the planet ever seen. We have been examining these new data to develop a general view of what Mars is like at meter-scale within the latitudes and elevations that are accessible to the Mars Surveyor 2001 lander. Our goal is to provide guidance to the 2001 landing site selection process, rather than to use MOC images to recommend a specific landing site.

Malin, M. C.↗
NASA NTRS2001

What is the Relationship Between Heavy Ion Outflow and High-Latitude Energetic Particle Precipitation?

This document is the fourth quarter progress report for year two on contract NAW-99002 'What is the relationship between heavy ion outflow and high latitude energetic particle precipitation'. In this project we are studying the relationship between the fluxes, mean energies, and field-aligned flow speeds of escaping suprathermal H+ and O+ measured by the TEAMS instrument on FAST and the energy flux of precipitating electrons obtained form the LBHL images taken by the Ultraviolet Imagery (UVI) camera on the Polar spacecraft. We have analyzed data from three time intervals, 7-11 Feb, 25-31 Jan, and 1-6 Feb 1997. We find that there indeed is a relationship between the O+ escape fluxes and the intensity of the aurora at the foot point of the field line. The time delay between an auroral intensification and the corresponding increase in escape flux is very short, only a few minutes. At low auroral luminosity the relationship between escape flux and luminosity appears to break down due possibly to the lack of sensitivity of the auroral emissions to large fluxes of low energy electrons.

Wilson, Gordon R.↗
NASA NTRS2001

Magnetic Field Structure of Pressure Balanced Structures from Ulysses High Latitudes Observations

Ulysses observations showed that pressure balance structures (PBSs) are a common feature in the high-latitude solar winds near the solar minimum. On the other hand, coronal plumes are common in polar coronal holes near the solar minimum. It is therefore considered that the PBSs would be remnants of plumes. Several detailed studies of the PBSs have been made from Ulysses/SWOOPS observations, but study of their magnetic structures has not yet been done. The study of the magnetic structure is important because previous observations and theoretical models of plumes indicate that they are related to the network activity such as magnetic reconnection on the photosphere. We have investigated the magnetic structures of the PBSs with Ulysses magnetometer and SWOOPS data. We have found that magnetic reversals in radial magnetic field take place while the spacecraft passes through most of the PBSs These magnetic reversals have been interpreted as large amplitude Alfv/'enic fluctuations but our results suggest that Ulysses is also traversing current sheets of plasmoids associated with network activity at the base of plumes.

Yamauchi, Y.↗
NASA NTRS2000

Land Use Effects on Atmospheric C-13 Imply a Sizable Terrestrial CO2 Sink in Tropical Latitudes

Records of atmospheric CO2 and 13-CO2, can be used to distinguish terrestrial vs. oceanic exchanges of CO2 with the atmosphere. However, this approach has proven difficult in the tropics, partly due to extensive land conversion from C-3 to C-4 vegetation. We estimated the effects of such conversion on biosphere-atmosphere C-13 exchange for 1991 through 1999, and then explored how this 'land-use disequilibrium' altered the partitioning of net atmospheric CO2 exchanges between ocean and land using NOAA-CMDL data and a 2D, zonally averaged atmospheric transport model. Our results show sizable CO2 uptake in C-3-dominated tropical regions in seven of the nine years; 1997 and 1998, which included a strong ENSO event, are near neutral. Since these fluxes include any deforestation source, our findings imply either that such sources are smaller than previously estimated, and/or the existence of a large terrestrial CO2 sink in equatorial latitudes.

Townsend, Alan R.↗
NASA NTRS2001

What is the Relationship Between Heavy Ion Outflow and High-Latitude Energetic Precipitation?

Second quarter progress report for year 3 on contract NASW-99002 "What is the Relationship between heavy ion outflow and high latitude energetic particle precipitation". In this Project we are studying the relationship between the fluxes, mean energies, and field-aligned flow speeds of escaping suprathermal H+ and 0+ measured by the TEAMS instrument on FAST and the energy flux of precipitating electrons obtained from the LBHL images taken by the UVI camera on POLAR. In this portion of the project we are using UVI images to tell us when substorm onsets occur and how the auroral zone changes during the course of a substorm. We are correlating this information with TEAMS flux measurements made over the auroral zone at times close to these substorms. The goal is to understand how the flux of suprathermal ion outflow varies with substorm phase.

Wilson, Gordon R.↗
NASA NTRS2001

Relation Between Pressure Balance Structures and Polar Plumes from Ulysses High Latitude Observations

Ulysses observations have shown that pressure balance structures (PBSs) are a common feature in high-latitude, fast solar wind near solar minimum. Previous studies of Ulysses/SWOOPS plasma data suggest these PBSs may be remnants of coronal polar plumes. Here we find support for this suggestion in an analysis of PBS magnetic structure. We used Ulysses magnetometer data and applied a minimum variance analysis to discontinuities. We found that PBSs preferentially contain tangential discontinuities, as opposed to rotational discontinuities and to non-PBS regions in the solar wind. This suggests that PBSs contain structures like current sheets or plasmoids that may be associated with network activity at the base of plumes.

Yamauchi, Y.↗