The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace. These processes are then to be interpreted in conjunction with results from the other ISTP spacecraft in order to discern the measurements and parameters for mass, momentum, and energy flow throughout geospace. This investigation will also contribute to observations of radio waves emitted in regions where the solar wind is accelerated. The WAVES investigation comprises several innovations in this kind of instrumentation: among which the first use, to our knowledge, of neural networks in real-time on board a scientific spacecraft to analyze data and command observation modes, and the first use of a wavelet transform-like analysis in real time to perform a spectral analysis of a broad band signal.

/pdf/waves-the-radio-and-plasma-wave-investigation-on-the-wind-ngfb2pv1t7.pdf

Waves: The Radio and Plasma Wave Investigation on the Wind Spacecraft

We present a comprehensive survey of 230 interplanetary CMEs (ICMEs) during 1995 – 2004 using Wind and ACE in situ observations near one AU, and examine the solar-cycle variation of the occurrence rate, shock association rate, scale size, velocity change, and other properties of ICMEs. The ICME occurrence rate increases (from 5 in 1996 to 40 in 2001) with solar activity; and 66% of all ICMEs occurred with shock(s). A compound parameter, the total pressure perpendicular to the magnetic field (Pt), i.e., the sum of magnetic and perpendicular plasma thermal pressures, assists us in effectively distinguishing ICMEs from other solar-wind structures such as stream interactions, and in quantifying the interaction strength. We interpret the characteristic signatures of the Pt temporal variation in terms of the inferred distance perpendicular to the flow to the center of the obstacle. Group 1 includes events that appear to be traversed near the ICME center, showing an apparent enhanced central Pt; Group 3 represents ICMEs passed far away from the center, displaying a rapid rise and then gradual decay in Pt; and Group 2 includes events with intermediate signatures. About 36% of 198 classifiable ICMEs are Group 1 events, consistent with the conventional wisdom that at one AU a magnetic cloud is found during crossings of only ~1/3 of ICMEs. Our set of Group 1 ICMEs and the set of magnetic clouds from other researchers have significant overlap and a similar solar-cycle dependence. The rough decline of the Group 1 fraction as solar activity increases, is consistent with rough increases of scale size, shock percentage, and peak Pt. These results call into question the need to have different mechanisms to create differently appearing ICMEs. Rather it is possible that all ICMEs have a central flux rope that is traversed about 33% of the time, but in the majority of cases is missed by the spacecraft.

/pdf/properties-of-interplanetary-coronal-mass-ejections-at-one-3wrd9f7j06.pdf

Properties of Interplanetary Coronal Mass Ejections at One AU During 1995 – 2004

A stream interaction region (SIR) forms when a fast solar stream overtakes a slow stream, leading to structure that evolves as an SIR moves away from the Sun. Based on Wind (1995 – 2004) and ACE (1998 – 2004) in situ observations, we have conducted a comprehensive survey of SIRs at one AU, including a separate assessment of the longer-lasting corotating interaction regions (CIRs) that recur on more than one solar rotation. In all there are 196 CIRs, accounting for about 54% of the 365 SIRs. The largest proportion of CIRs to SIRs (64%) appears in 1999, and the smallest proportion (49%) is in 2002. Over the ten years, the annual number of SIR events varies little, from 32 up to 45. On average, the occurrence rate of shocks at SIRs at one AU is about 24%. Seventy percent of the SIRs with shocks have only forward shocks, more than twice the percentage of SIRs with only reverse shocks. This preponderance of forward shocks is consistent with the deflections of forward and reverse shocks relative to the ecliptic plane. In order to help address the effect of SIRs and CIRs on geomagnetic activity, we determine the solar-cycle variation of the event duration, scale size, the change in velocity from slow stream to fast stream, and the solar-cycle variation of the maximum magnetic field, peak total perpendicular pressure, and other properties. These statistics also provide a baseline for future studies at other heliocentric distances and for validating heliospheric models.

/pdf/properties-of-stream-interactions-at-one-au-during-1995-2004-5f1e8fe8m8.pdf

Properties of stream interactions at one au during 1995 - 2004

[1] We apply the calibration method developed by Dulk et al. [2001] to the data from the Cassini/Radio and Plasma Wave Science (RPWS) High-Frequency Receiver in order to derive flux density measurements of six components of the Jovian low-frequency radio spectrum over the full frequency range of the instrument (3.5 kHz to 16.1 MHz). The estimated accuracy is better than 50%, i.e., much less than the intrinsic variations of the flux densities of these radiosources. It is mainly limited by the accuracy of the model used for the radio galactic background. Instrumental parameters such as the antennas' effective lengths and base capacitance are constrained in the calibration process. From 6 months of calibrated data centered on the Cassini-Jupiter flyby, we derive the average and peak Jovian radio spectrum between 3.5 and 16.1 MHz and its range of fluctuations, from which we deduce constraints on the beaming of the various radio components and estimate the power emitted by each component. Our calibration procedure also allows us to compare Cassini measurements of the Jovian radio spectrum with ground-based measurements performed, e.g., in Nancay above the ionospheric cutoff (10−15 MHz). It will be used to derive absolute flux measurements during the Saturn tour.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003JA010260

Jupiter's low-frequency radio spectrum from Cassini/Radio and Plasma Wave Science (RPWS) absolute flux density measurements

The demonstrated and developing methods for global magnetospheric imaging are presented and the scientific expectations of having global observations in conjunction with local measurements are discussed. The global observations of the previously invisible magnetosphere will provide the first look at the overall magnetosphere, its dynamics, and the interactions between its component parts. The capability of imaging magnetospheric plasmas marks the first occasion where an astrophysical plasma system which has been well characterized by in situ measurements, i.e., the earth's magnetosphere, can also be characterized globally by remote sensing.

Global magnetospheric imaging

ISEE observations of radiation at twice the solar wind plasma frequency.

Solar wind electron density and temperature over solar cycle 23: Thermal noise measurements on Wind

Propagation of terrestrial kilometric radiation through the magnetosheath - ISEE-3 observations

Terrestrial low-frequency bursts: Escape paths of radio waves through the bow shock

On October 1 1983, ISEE-3 crossed the earth's bow shock several times and entered the magnetosphere while continuously recording the nonthermal continuum (NTC) radio emission which is generated inside the magnetosphere. The effects of the solar wind, the bow shock, the magnetosheath, and the magnetopause on the propagation of the NTC are studied. On that day it is found that: (1) the relative values of the NTC low frequency cut-off in the solar wind and in the magnetosheath is due to an unusually high density overshoot in the bow shock, 7 to 11 times the solar wind density; (2) refraction at the interface between the magnetosheath and the solar wind can explain most of the decrease in the source angular size when the observer travels away from the earth; (3) plasma density irregularities in the magnetosheath cause considerable scattering of the NTC, and this effect gives a large apparent size to the NTC source when observed from inside the magnetosheath; and (4) the apparent source is also relatively large inside the magnetosphere, probably due to an approach to ray isotropy caused by oblique reflections from the magnetopause.

S. Hoang

Papers

ISEE observations of radiation at twice the solar wind plasma frequency.

Solar wind electron density and temperature over solar cycle 23: Thermal noise measurements on Wind

Propagation of terrestrial kilometric radiation through the magnetosheath - ISEE-3 observations

Terrestrial low-frequency bursts: Escape paths of radio waves through the bow shock

ISEE-3 observations of the earth's radio continuum through the bow shock and magnetosheath and in the magnetosphere