206 research outputs found
The Relation Between Magnetospheric State Parameters and the Occurrence of Plasma Depletion Events in the Night-Time Mid-Latitude F-Region
No full textStudies using all-sky imagers have revealed the presence of various ionospheric irregularities in the night-time mid-latitude F-region. The most prevalent and well known of these are the Medium Scale Traveling Ionospheric Disturbances (MSTIDs) that usually occur when the geomagnetic activity is low, and mid-latitude spread-F plumes that are often observed when the geomagnetic activity is high. The inverse and direct relations between geomagnetic activity (particularly Kp) and the occurrence rate of MSTIDs and midlatitude plumes, respectively, have been observed by several studies using different instruments. In order to understand the underlying causes of these two relations, it is illuminating to better characterize the occurrence of MSTIDs and plumes using multiple magnetospheric state parameters. Here we statistically compare multiple geomagnetic driver and response parameters (such as Kp, AE, Dst, and solar wind parameters) with the occurrence rates of night-time MSTIDs and plumes observed using an all-sky imager at Arecibo Observatory (AO) between 2003 and 2008. The results not only allow us to better distinguish MSTIDs and plumes, but also shed further light on the generation mechanism and electrodynamics of these two different phenomena occurring at night-time in the mid-latitude F-region
Modeling of Field-Aligned Guided Echoes in the Plasmasphere
No full textThe conditions under which high frequency (f>>f(sub uh)) long-range extraordinary-mode discrete field-aligned echoes observed by the Radio Plasma Imager (RPI) on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in the plasmasphere are investigated by ray tracing modeling. Field-aligned discrete echoes are most commonly observed by RPI in the plasmasphere although they are also observed over the polar cap region. The plasmasphere field-aligned echoes appearing as multiple echo traces at different virtual ranges are attributed to signals reflected successively between conjugate hemispheres that propagate along or nearly along closed geomagnetic field lines. The ray tracing simulations show that field-aligned ducts with as little as 1% density perturbations (depletions) and less than 10 wavelengths wide can guide nearly field-aligned propagating high frequency X mode waves. Effective guidance of wave at a given frequency and wave normal angle (Psi) depends on the cross-field density scale of the duct, such that ducts with stronger density depletions need to be wider in order to maintain the same gradient of refractive index across the magnetic field. While signal guidance by field aligned density gradient without ducting is possible only over the polar region, conjugate field-aligned echoes that have traversed through the equatorial region are most likely guided by ducting
The Virtual Wave Observatory (VWO): A Portal to Heliophysics Wave Data
No full textThe Virtual Wave Observatory (VWO) is one of the discipline-oriented virtual observatories that help form the nascent NASA Heliophysics Data environment to support heliophysics research. It focuses on supporting the searching and accessing of distributed heliophysics wave data and information that are available online. Since the occurrence of a natural wave phenomenon often depends on the underlying geophysical -- i.e., context -- conditions under which the waves are generated and propagate, and the observed wave characteristics can also depend on the location of observation, VWO will implement wave-data search-by-context conditions and location, in addition to searching by time and observing platforms (both space-based and ground-based). This paper describes the VWO goals, the basic design objectives, and the key VWO functionality to be expected. Members of the heliophysics community are invited to participate in VWO development in order to ensure its usefulness and success
The Virtual Wave Observatory (VWO)
No full textHeliophysics wave data are currently not easily searchable by computers, making identifying pertinent wave data features for analyses and cross comparisons difficult and laborious. Since wave data analysis requires specialized knowledge about waves, which spans the spectrum of microphysics to macrophysics, researchers having varied expertise cannot easily use wave data. To resolve these difficulties and to allow wave data to contribute more fully to Heliophysics research, we are developing a Virtual Wave Observatory (VWO) whose goal is to enable all Heliophysics wave data to become searchable, understandable and usable by the Heliophysics community. The VWO objective is to enable search of multiple and distributed wave data (from both active and passive measurements). This presentation provides and overview of the VWO, a new VxO component within the emerging distributed Heliophysics data and model environment
Specification of multiple geomagnetic responses to variable solar wind and IMF input
No full textAbstract. This paper shows that the state of the magnetosphere, resulting from continuous but variable forcing of the solar wind and the interplanetary magnetic field (IMF), can be empirically specified by a magnetospheric state vector Ψ, consisting of a set of hourly-averaged magnetospheric driver and response parameters. It is demonstrated that there exists a correspondence between the magnetospheric driver and multiple geomagnetic response parameters. This parameter correspondence allows different magnetopsheric states to be specified by means of a look-up table, provided that the relative time lags between various driver (e.g. Vsw, IMF) and response parameters (e.g. Kp, Dst, and AE) are taken into account. Using the magnetospheric state specifications, multi-scale geomagnetic responses can then be simultaneously prescribed statistically from their corresponding driver parameters. Magnetospheric state specifications have been determined by using magnetospheric state parameter data taken in 1970–2000. Their validities have been tested by specifying the multi-geomagnetic responses over three representative intervals: (1) a magnetic cloud event, (2) a period of multiple storms, and (3) the years of 2001 and 2002. For all the intervals, we have found good correlation (with r>0.75) between the prescribed and observed geomagnetic indices at hourly resolution, and the magnetospheric state specifications are thus validated.
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Relation between magnetospheric state parameters and the occurrence of plasma depletion events in the nighttime midlatitude<i>F</i>region
No full textISIS Topside-Sounder Plasma-Wave Investigations as Guides to Desired Virtual Wave Observatory (VWO) Data Search Capabilities
No full textMany plasma-wave phenomena, observed by space-borne radio sounders, cannot be properly explained in terms of wave propagation in a cold plasma consisting of mobile electrons and infinitely massive positive ions. These phenomena include signals known as plasma resonances. The principal resonances at the harmonics of the electron cyclotron frequency, the plasma frequency, and the upper-hybrid frequency are well explained by the warm-plasma propagation of sounder-generated electrostatic waves, Other resonances have been attributed to sounder-stimulated plasma instability and non-linear effects, eigenmodes of cylindrical electromagnetic plasma oscillations, and plasma memory processes. Data from the topside sounders of the International Satellites for Ionospheric Studies (ISIS) program played a major role in these interpretations. A data transformation and preservation effort at the Goddard Space Flight Center has produced digital ISIS topside ionograms and a metadata search program that has enabled some recent discoveries pertaining to the physics of these plasma resonances. For example, data records were obtained that enabled the long-standing question (several decades) of the origin of the plasma resonance at the fundamental electron cyclotron frequency to be explained [Muldrew, Radio Sci., 2006]. These data-search capabilities, and the science enabled by them, will be presented as a guide to desired data search capabilities to be included in the Virtual Wave Observatory (VWO)
A new mechanism of symmetry of current-voltage characteristics for high-k dielectric capacitor structures
No full textHistorically, there has been a controversy regarding whether the leakage current versus voltage (I-V) relationship is governed by the Schottky mechanism or by the Poole-Frenkel (P-F) mechanism for several decades. For the P-F mechanism, the I-V characteristics is expected to be symmetrical. In this paper, the author points out that there is an extra mechanism for symmetrical I-V characteristics.Published versio
Time correlation of low-altitude relativistic trapped electron fluxes with solar wind speeds
No full textWe present the results from a study of time correlation between the low-altitude relativistic trapped electron fluxes and the solar wind speeds. Our trapped electron observations in the energy range of 0.19–3.2 MeV were obtained by the OHZORA spacecraft in an altitude range of 350–850 km, near a solar minimum period (1984–87). The solar wind data with a 5-minute time resolution were obtained from IMP-8 observations. Linear correlation analyses between the two data sets have been performed for relative time lags varying from 12 minutes to 60 days. The 2.5–day, 13-day, 27-day and 54-day correlation peaks previously reported for energetic electrons near geosynchronous orbits are clearly seen in our results. However, the use of higher time resolution solar wind data than in previous studies allows correlation analyses to be performed at shorter time lags. We report here that correlation at shorter time lags (<10 hrs) exists and that while such correlation is stronger than those observed at longer lag times, it can not be entirely attributed to storm or substorm injections. The correlation is also found to decrease with drift shell magnetic equatorial radii, rt. In addition, local-time and radial variations in the responses of different drift shells to solar wind speed enhancements indicate that the energetic electron population enters the inner magnetosphere predominantly through the midnight sector.We thank the NASA National Space Science Data Center (NSSDC) for providing the OHZORA and IMP-8 data used in this study. We are also indebted to Dr. T. Kohno and K. Nagata for archiving their HEP data from OHZORA at the NSSDC. Work by L. C. Tan at RSTX was supported by NASA contract NAS5-97059.https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/98GL0171
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