L. N. Garcia

On the origin of whistler mode radiation in the plasmasphere

[1] The origin of whistler mode radiation in the plasmasphere is examined from 3 years of plasma wave observations from the Dynamics Explorer and the Imager for Magnetopauseto-Aurora Global Exploration spacecraft. These data are used to construct plasma wave intensity maps of whistler mode radiation in the plasmasphere. The highest average intensities of the radiation in the wave maps show source locations and/or sites of wave amplification. Each type of wave is classified on the basis of its magnetic latitude and longitude rather than any spectral feature. Equatorial electromagnetic (EM) emissions (30–330 Hz), plasmaspheric hiss (330 Hz to 3.3 kHz), chorus (2–6 kHz), and VLF transmitters (10–50 kHz) are the main types of waves that are clearly delineated in the plasma wave maps. Observations of the equatorial EM emissions show that the most intense region is on or near the magnetic equator in the afternoon sector and that during times of negative Bz (interplanetary magnetic field) the maximum intensity moves from L values of 3 to <2. These observations are consistent with the origin of this emission being particle-wave interactions in or near the magnetic equator. Plasmaspheric hiss shows high intensity at high latitudes and low altitudes (L shells from 2 to 4) and in the magnetic equator with L values from 2 to 3 in the early afternoon sector. The longitudinal distribution of the hiss intensity (excluding the enhancement at the equator) is similar to the distribution of lightning: stronger over continents than over the ocean, stronger in the summer than in the winter, and stronger on the dayside than on the nightside. These observations strongly support lightning as the dominant source for plasmaspheric hiss, which, through particle-wave interactions, maintains the slot region in the radiation belts. The enhancement of hiss at the magnetic equator is consistent with particle-wave interactions. The chorus emissions are most intense on the morningside as previously reported. At frequencies from 10 to 50 kHz, VLF transmitters dominate the spectrum. The maximum intensity of the VLF transmitters is in the late evening or early morning with enhancements all along L shells from 1.8 to 3.

Observations of the latitudinal structure of plasmaspheric convection plumes by IMAGE‐RPI and EUV

Received 22 May 2002; revised 16 April 2003; accepted 2 May 2003; published 15 August 2003. [1] Recent IMAGE Extreme Ultraviolet Imager (EUV) observations showed the first global images of plasmaspheric convection plumes, which have been interpreted as the plasmaspheric tails predicted theoretically 3 decades earlier. Using observations by the IMAGE Radio Plasma Imager (RPI), we show that these convection plumes have large latitudinal extent. These results complement those recently made by others in correlating IMAGE EUV data with measurements of total electron content in the ionosphere. By correlating in situ RPI density measurements with global plasmaspheric EUV images, we have shown that apparently detached plasma structures, as appear in RPI dynamic spectrograms, are in many cases plasmaspheric convection plumes. The temporal separation between the RPI and EUVobservations help constrain the interpretation of one data set in the context of the other, thereby enabling an examination of the threedimensional plasma density structures outside the core plasmasphere. The data sets are mutually reinforcing because the data are collected within a few hours of one another. We used the EUV data to provide unambiguous identification of density enhancements in the region outside the plasmasphere and used the RPI data to obtain accurate number densities and extend information from the EUV data set by measuring densities below the EUV sensitivity threshold. INDEX TERMS: 2768 Magnetospheric Physics: Plasmasphere; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2730 Magnetospheric Physics: Magnetosphere—inner; 2788 Magnetospheric Physics: Storms and substorms; KEYWORDS: plasmasphere, plasmapause, inner magnetosphere, convection plumes, RPI, EUV

Enhanced high‐altitude polar cap plasma and magnetic field values in response to the interplanetary magnetic cloud that caused the great storm of 31 March 2001: A case study for a new magnetospheric index

[1] The magnetospheric electron number density and the magnetic field strength near 8 R E over the polar cap increased dramatically after the arrival of an interplanetary magnetic cloud on 31 March 2001. These parameters were determined with high accuracy from the plasma resonances stimulated by the Radio Plasma Imager (RPI) on Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) near apogee during both quiet (30 March 2001) and disturbed (31 March 2001) days. The quiet day and disturbed day values were each compared with magnetospheric magnetic field and electron density models; good agreement was found with the former but not the latter. The magnetospheric response was also expressed in terms of the ratio of the electron plasma frequency f pe to the electron cyclotron frequency f ce , which is proportional to the ratio of the electron gyroradius to the Debye radius. Simultaneous Wind measurements of the solar wind magnetic field strength, speed, and plasma density were used to calculate the solar wind quasi-invariant QI. This index is equivalent to the ratio of the solar wind magnetic pressure to the solar wind ram pressure or to the inverse of the magnetic Mach number squared. These nondimensional quantities, QI and f pe /f ce , have fundamental meanings in the solar wind MHD regime and in the relation between electric and magnetic forces on electrons in the magnetosphere, respectively. During the large 31 March 2001 storm, IMAGE was at the right place at the right time so as to enable comparisons between RPI f pe /f ce and Wind QI determinations. Both QI and f pe /f ce formed maxima during 6-hour observing intervals during this storm that were found to be highly correlated (87%) with a magnetospheric time lag of about 3 hours for f pe /f ce . These results, based on a detailed case study of this important event, suggest that the plasma parameter f pe /f ce may serve as a useful magnetospheric index.

New Opportunities for a Historic Spacecraft

On 10 August 2014, an extraordinary spacecraft will return to Earth after having been away for 30 years. Plans are emerging and actions are being taken to reactivate the International Sun-Earth Explorer 3 (ISEE 3, later renamed the International Cometary Explorer (ICE)) and enable it to gather new scientific data. The NASA–European Space Agency ISEE pioneered the multipoint approach to studying solar-terrestrial connections. ISEE 1 and ISEE 2 were launched in 1977, and ISEE 3 was launched in 1978. These spacecraft were designed to explore the relationship between the incoming solar wind (sampled by ISEE 3) and Earth’s magnetosphere (sampled by ISEE 1 and ISEE 2). ISEE 3 is notable for many space firsts. It was the first spacecraft in a “halo orbit” around the Sun-Earth L1 libration point. Later, it became the first spacecraft to intercept a comet when, after being renamed ICE, it was sent to comet Giacobini-Zinner in 1985. After a distant encounter with Halley’s comet in 1986, ISEE 3/ICE continued on its heliocentric orbit. In August 2014, this trajectory will bring the spacecraft on a close approach with Earth and will provide an opportunity to return it to active service. The spacecraft carries 13 plasma, high-energy particle, field, and wave sensors, most of which were still functional as of 1999. The current health of these instruments needs to be evaluated, but a test in 2008 confirmed ISEE 3/ICE’s location and clearly detected the spacecraft carrier signal. The spacecraft has sufficient fuel (approximately 150 meters per second of change in velocity (∆V) capability) to send it back to L1. Much of the documentation from the initial mission programming was lost, but members of the original team are now working on rebuilding the commands necessary for spacecraft control and data acquisition. Once these commands are rebuilt, the Deep Space Network will be used to communicate with the spacecraft and determine instrument health. Demonstrating that we can communicate with the spacecraft and that it is sufficiently healthy is a crucial step toward a new mission in 2014. On what new adventures do we send our venerable explorer? One option is that it could return to the L1 halo orbit. Much more is known about space weather now than was known 30 years ago. Even so, multipoint space weather monitoring and research are more important than ever, and this spacecraft is an exceptional candidate to serve as a space weather monitor providing complementary and cost-effective measurements of the solar wind. However, ISEE 3/ICE can serve many more purposes. Controlling this comparatively simple spacecraft, now well beyond warranty, would be an ideal training opportunity for young scientists and engineers. A single PC, for example,

Full-scale time domain modeling of the interaction of HF waves with the topside ionosphere

We use a time domain simulation to study the interaction of high frequency wave with the topside ionosphere. The ionosphere density profile is derived from X-mode ionogram data obtained from satellite topside sounding. In the simulation, we observe the reflection of L-O and R-X modes at different altitudes and large amplitude electrostatic field generation at the reflection altitude of L-O mode. These electrostatic fields of Langmuir type have amplitude several times of the injected wave field amplitude and can be important in heating local electrons. The full-scale time domain modeling allows us to understand the propagation, reflection, coupling and mode conversion of HF wave.

Space-borne radio-sounding investigations facilitated by the Virtual Wave Observatory (VWO)

The goal of the Virtual Wave Observatory (VWO) is to provide user-friendly access to heliophysics wave data [1]. While the VWO initially emphasized the vast quantity of wave data obtained from passive receivers, the VWO infrastructure can also be used to access active sounder data sets. Here we demonstrate the application of the VWO capabilities to data from the Alouette/ISIS topside sounders. The sounders were designed to produce analog data records that were displayed in the ionogram format on 35 mm film [2]. This format required manual inspection to convert the ionospheric-reflection traces to topside electron-density profiles Ne(h). Due to cost considerations, not all of the topside-sounder data from this highly successful program, which spanned nearly three decades, were used to produce 35-mm film ionograms. In addition, not all of the 35-mm film ionograms were manually scaled to produce Ne(h) profiles. A data preservation effort, including analog-to-digital conversion of the topside-sounder data, was performed on a subset of the original telemetry tapes to produce a half-million Alouette-2, ISIS-1, and ISIS-2 digital topside-sounder ionograms [3]. The digital format allowed (1) an automatic scaling technique to be developed in order to more efficiently produce topside Ne(h) profiles [4] and (2) efficient data search capabilities (see http://nssdc.gsfc.nasa.gov/space/isis/isis-status.html). Here we emphasize the latter capability to demonstrate the desirability of gaining access to the actual ionograms for investigations of both natural and sounder-stimulated plasma-wave phenomena. By this demonstration, we wish to encourage investigators to make other valuable space-borne sounder data sets accessible via the VWO.