Observation and Modeling of the Solar Wind Turbulence Evolution in the Sub-Mercury Inner Heliosphere

This letter exploits the radial alignment between the Parker Solar Probe and BepiColombo in late 2022 February, when both spacecraft were within Mercury's orbit. This allows the study of the turbulent evolution, namely, the change in spectral and intermittency properties, of the same plasma parcel during its expansion from 0.11 to 0.33 au, a still unexplored region. The observational analysis of the solar wind turbulent features at the two different evolution stages is complemented by a theoretical description based on the turbulence transport model equations for nearly incompressible magnetohydrodynamics. The results provide strong evidence that the solar wind turbulence already undergoes significant evolution at distances less than 0.3 au from the Sun, which can be satisfactorily explained as due to evolving slab fluctuations. This work represents a step forward in understanding the processes that control the transition from weak to strong turbulence in the solar wind and in properly modeling the heliosphere. &nbsp;</p

Linking Small-scale Solar Wind Properties with Large-scale Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar Orbiter Observations

The solar wind measured in situ by Parker Solar Probe in the very inner heliosphere is studied in combination with the remote-sensing observation of the coronal source region provided by the METIS coronagraph aboard Solar Orbiter. The coronal outflows observed near the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and 6.3 R⊙ above the eastern solar limb, can be associated with the streams sampled by PSP at 0.11 and 0.26 au from the Sun, in two time intervals almost 5 days apart. The two plasma flows come from two distinct source regions, characterized by different magnetic field polarity and intensity at the coronal base. It follows that both the global and local properties of the two streams are different. Specifically, the solar wind emanating from the stronger magnetic field region has a lower bulk flux density, as expected, and is in a state of well-developed Alfv&eacute;nic turbulence, with low intermittency. This is interpreted in terms of slab turbulence in the context of nearly incompressible magnetohydrodynamics. Conversely, the highly intermittent and poorly developed turbulent behavior of the solar wind from the weaker magnetic field region is presumably due to large magnetic deflections most likely attributed to the presence of switchbacks of interchange reconnection origin. &nbsp;</p

Lower-thermosphere–ionosphere (LTI) quantities: current status of measuring techniques and models

The lower-thermosphere&ndash;ionosphere (LTI) system consists of the upper atmosphere and the lower part of the ionosphere and as such comprises a complex system coupled to both the atmosphere below and space above. The atmospheric part of the LTI is dominated by laws of continuum fluid dynamics and chemistry, while the ionosphere is a plasma system controlled by electromagnetic forces driven by the magnetosphere, the solar wind, as well as the wind dynamo. The LTI is hence a domain controlled by many different physical processes. However, systematic in situ measurements within this region are severely lacking, although the LTI is located only 80 to 200&thinsp;km above the surface of our planet. This paper reviews the current state of the art in measuring the LTI, either in situ or by several different remote-sensing methods. We begin by outlining the open questions within the LTI requiring high-quality in situ measurements, before reviewing directly observable parameters and their most important derivatives. The motivation for this review has arisen from the recent retention of the Daedalus mission as one among three competing mission candidates within the European Space Agency (ESA) Earth Explorer 10 Programme. However, this paper intends to cover the LTI parameters such that it can be used as a background scientific reference for any mission targeting in situ observations of the LTI. &nbsp;</p

A Compact Five-Channel VLF Wave Receiver for CubeSat Missions

Very low frequency (VLF) waves play an important role in controlling the evolution of energetic electron distributions in near-Earth space. This paper describes the design of a VLF receiver for the Climatology of Anthropogenic and Natural VLF Wave Activity in Space (CANVAS) CubeSat mission, designed to make continuous observations of VLF waves in low-Earth orbit originating from lightning and ground-based transmitters. The CANVAS VLF receiver will observe five components of VLF waves in the 0.3–40 kHz frequency range, using three orthogonal magnetic search coils deployed on the end of a 1-meter carbon fiber boom and four deployable electric field antennas operated as two orthogonal dipoles. Together, these five wave components will be used to calculate real and imaginary spectral matrix components using real-time fast Fourier transforms calculated in an onboard FPGA. Spectral matrix components will be averaged to obtain 1 second time resolution and frequency resolution better than 10%. The averaged spectral matrix will be used to determine the complete set of wave parameters, including Poynting flux, polarization, planarity, and k-vector direction. CANVAS is currently in the manufacturing and assembly phase and is planned to launch at the end of 2022

Electrostatic Solitary Waves in the Solar Wind: Evidence for Instability at Solar Wind Current Sheets

A strong spatial association between bipolar electrostatic solitary waves (ESWs) and magnetic current sheets (CSs) in the solar wind is reported here for the first time. This association requires that the plasma instabilities (e.g., Buneman, electron two stream) which generate ESWs are preferentially localized to solar wind CSs. Distributions of CS properties (including shear angle, thickness, solar wind speed, and vector magnetic field change) are examined for differences between CSs associated with ESWs and randomly chosen CSs. Possible mechanisms for producing ESW-generating instabilities at solar wind CSs are considered, including magnetic reconnection

Interplanetary and Interstellar Dust Observed by the Wind/WAVES Electric Field Instrument

Observations of hypervelocity dust particles impacting the Wind spacecraft are reported here for the first time using data from the WindWAVES electric field instrument. A unique combination of rotating spacecraft, amplitude-triggered high-cadence waveform collection, and electric field antenna configuration allow the first direct determination of dust impact direction by any spacecraft using electric field data. Dust flux and impact direction data indicate that the observed dust is approximately micron-sized with both interplanetary and interstellar populations. Nanometer radius dust is not detected by Wind during times when nanometer dust is observed on the STEREO spacecraft and both spacecraft are in close proximity. Determined impact directions suggest that interplanetary dust detected by electric field instruments at 1 AU is dominated by particles on bound trajectories crossing Earths orbit, rather than dust with hyperbolic orbits

Prediction of plasmaspheric hiss spectral classes

We present a random forests machine learning model for prediction of plasmaspheric hiss spectral classes from the Van Allen Probes dataset. The random forests model provides accurate prediction of plasmaspheric hiss spectral classes obtained by the self organizing map (SOM) unsupervised machine learning classification technique. The high predictive skill of the random forests model is largely determined by the distinct and different locations of a given spectral class (&ldquo;no hiss&rdquo;, &ldquo;regular hiss&rdquo;, and &ldquo;low-frequency hiss&rdquo;) in (MLAT, MLT, L) coordinate space, which are the main predictors of the simplest and most accurate base model. Adding to such a base model any other single predictor among different magnetospheric, geomagnetic, and solar wind conditions provides only minor and similarly incremental improvements in predictive skill, which is comparable to the one obtained when including all possible predictors, and thus confirming major role of spatial location for accurate prediction. &nbsp;</p

Electric and magnetic radial diffusion coefficients using the Van Allen probes data

ULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc-5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift-averaged power spectral densities are used to derive the magnetic and the electric component of the radial diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving radial diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes radial diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates

The CANVAS Mission: Quantifying the Very-Low-Frequency Radio Energy Input from the Ground into the Earth\u27s Magnetosphere

Very-low-frequency (VLF) electromagnetic waves, emitted by ground-based sources including lightning and VLF transmitters, can impact the lower ionosphere and magnetosphere through their interaction with the local plasma and energetic particle environments. Quantifying the impacts of these waves requires an accurate assessment of the propagation and attenuation of these waves. The Climatology of Anthropogenic and Natural VLF wave Activity in Space (CANVAS) mission is designed to measure VLF waves in low Earth orbit originating from these ground-based sources. The mission aims to characterize the VLF environment in low Earth orbit to address two main goals: i) constrain the VLF wave injection from the ground into the magnetosphere, and ii) improve models of VLF wave attenuation during propagation through the ionosphere. CANVAS will measure VLF waves using three search coil magnetometers and two electric field dipole antennas that comprise its payload. The search coils are integrated into a 3D-printed Carbon PEEK holder, along with the magnetic field preamplifier board. The search coil system is deployed 1 meter from the spacecraft using a carbon fiber deployable boom, in order to isolate the sensitive search coils from spacecraft noise. The electric field system is composed of four 40 cm monopole antennas, making two orthogonal dipole antennas, integrated into the spacecraft “crown”, along with a custom preamplifier circuit for each monopole. The payload is completed by a custom analog receiver board, providing amplification, anti-alias filtering, and centering for the analog-to-digital converters (ADCs); and a custom digital board, which includes an FPGA for onboard signal processing. Spectral data spanning 0.3–40 kHz are saved at 1-second cadence, providing a continuous “fast survey” data mode for the duration of the mission. The CANVAS spacecraft is a 4U CubeSat, 10 × 10 × 45 cm and under 6 kg. In addition to the 1-meter deployable carbon fiber boom and electric field antennas, the spacecraft incorporates deployable solar panels and a monopole antenna for UHF communications. Data is downlinked in S-band. The spacecraft structure and avionics are custom-designed and built at CU Boulder, while the radios and attitude determination and control system (ADCS) are vendor-supplied components. The CANVAS mission is designed to operate at ∼500 km altitude in a moderate-inclination orbit (∼50 degrees), to ensure global coverage of lightning-generating regions; most lightning globally is confined to within ±50 degrees latitude. Spectra at 1-second cadence account for ∼424 MB of data per day, after housekeeping and encoding overhead. A one-year mission will ensure seasonal coverage to observe the Marshall 1 36th Annual Small Satellite Conference variability in global lightning activity. This paper presents a detailed overview of the CANVAS science goals, payload, spacecraft, and mission. The instrument is now completed and undergoing functional testing and performance characterization, and the spacecraft is beginning integration, expected to be completed in Fall 2022. The CANVAS mission will be ready to launch in early 2023