Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTurbulent Proton Heating Rate in the Solar Wind from $5$ to $45~R_{odot}$
112
0
0.0
(
0
)
Added by
Kantepalli Sasikumar Raja
Publication date
2021
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Various remote sensing observations have been used so far to probe the turbulent properties of the solar wind. Using the recently reported density modulation indices that are derived using angular broadening observations of Crab Nebula during 1952 - 2013, we measured the solar wind proton heating using the kinetic $rm Alfvacute{e}n$ wave dispersion equation. The estimated heating rates vary from $approx 1.58 times 10^{-14}$ to $1.01 times 10^{-8} ~rm erg~ cm^{-3}~ s^{-1}$ in the heliocentric distance range 5 - 45 $rm R_{odot}$. Further, we found that heating rates vary with the solar cycle in correlation with density modulation indices. The models derived using in-situ measurements (for example, electron/proton density, temperature, and magnetic field) that the recently launched Parker Solar Probe observes (planned closest perihelia $rm 9.86~ R_{odot}$ from the center of the Sun) are useful in the estimation of the turbulent heating rate precisely. Further, we compared our heating rate estimates with the one derived using previously reported remote sensing and in-situ observations.
rate research
Read More
We obtain scatter broadened images of the Crab Nebula at 80 MHz as it transits through the inner solar wind in June 2016 and 2017. These images are anisotropic, with the major axis oriented perpendicular to the radially outward coronal magnetic field. Using these data, we deduce that the density modulation index (delta N_e/N_e) caused by turbulent density fluctuations in the solar wind ranges from 1.9 times 10^{-3} to 7.7 times 10^{-3} between 9-20 R_{odot}. We also find that the heating rate of solar wind protons at these distances ranges from 2.2 times 10^{-13} to 1.0 times 10^{-11} ~erg~cm^{-3}~s^{-1}. On two occasions, the line of sight intercepted a coronal streamer. We find that the presence of the streamer approximately doubles the thickness of the scattering screen.
We investigate how the proton distribution function evolves when the protons undergo stochastic heating by strong, low-frequency, Alfven-wave turbulence under the assumption that $beta$ is small. We apply our analysis to protons undergoing stochastic heating in the supersonic fast solar wind and obtain proton distributions at heliocentric distances ranging from 4 to 30 solar radii. We find that the proton distribution develops non-Gaussian structure with a flat core and steep tail. For $r >5 R_{rm S}$, the proton distribution is well approximated by a modified Moyal distribution. Comparisons with future measurements from emph{Solar Probe Plus} could be used to test whether stochastic heating is occurring in the solar-wind acceleration region.
The fast solar winds high speeds and nonthermal features require that significant heating occurs well above the Suns surface. Two leading theories have seemed incompatible: low-frequency Alfvenic turbulence, which transports energy outwards but struggles to explain the observed dominance of ion over electron heating; and high-frequency ion-cyclotron waves (ICWs), which explain the heating but lack an obvious source. We unify these paradigms via the novel helicity barrier mechanism. Using six-dimensional plasma simulations, we show that in imbalanced turbulence (as relevant to the solar wind) the helicity barrier limits electron heating by inhibiting the turbulent cascade of energy to the smallest scales. The large-scale energy grows in time to eventually generate high-frequency fluctuations from low-frequency turbulence, driving ion heating by ICWs. The resulting turbulence and ion distribution function provide a compelling match to in-situ observations from Parker Solar Probe and other spacecraft, explaining, among other features, the steep transition range in the magnetic spectrum.
We report analysis of sub-Alfvenic magnetohydrodynamic (MHD) perturbations in the low-b{eta} radial-field solar wind using the Parker Solar Probe spacecraft data from 31 October to 12 November 2018. We calculate wave vectors using the singular value decomposition method and separate the MHD perturbations into three types of linear eigenmodes (Alfven, fast, and slow modes) to explore the properties of the sub-Alfvenic perturbations and the role of compressible perturbations in solar wind heating. The MHD perturbations there show a high degree of Alfvenicity in the radial-field solar wind, with the energy fraction of Alfven modes dominating (~45%-83%) over those of fast modes (~16%-43%) and slow modes (~1%-19%). We present a detailed analysis of a representative event on 10 November 2018. Observations show that fast modes dominate magnetic compressibility, whereas slow modes dominate density compressibility. The energy damping rate of compressible modes is comparable to the heating rate, suggesting the collisionless damping of compressible modes could be significant for solar wind heating. These results are valuable for further studies of the imbalanced turbulence near the Sun and possible heating effects of compressible modes at MHD scales in low-b{eta} plasma.
The Kelvin-Helmholtz instability (KHI) is a nonlinear shear-driven instability that develops at the interface between shear flows in plasmas. KHI has been inferred in various astrophysical plasmas and has been observed in situ at the magnetospheric boundaries of solar-system planets and through remote sensing at the boundaries of coronal mass ejections. While it was hypothesized to play an important role in the mixing of plasmas and in triggering solar wind fluctuations, its direct and unambiguous observation in the solar wind was still lacking. We report in-situ observations of ongoing KHI in the solar wind using Solar Orbiter during its cruise phase. The KHI is found in a shear layer in the slow solar wind in the close vicinity of the Heliospheric Current Sheet, with properties satisfying linear theory for its development. An analysis is performed to derive the local configuration of the KHI. A 2-D MHD simulation is also set up with empirical values to test the stability of the shear layer. In addition, magnetic spectra of the KHI event are analyzed. We find that the observed conditions satisfy the KHI onset criterion from the linear theory analysis, and its development is further confirmed by the simulation. The current sheet geometry analyses are found to be consistent with KHI development. Additionally, we report observations of an ion jet consistent with magnetic reconnection at a compressed current sheet within the KHI interval. The KHI is found to excite magnetic and velocity fluctuations with power-law scalings that approximately follow $k^{-5/3}$ and $k^{-2.8}$ in the inertial and dissipation ranges, respectively. These observations provide robust evidence of KHI development in the solar wind. This sheds new light on the process of shear-driven turbulence as mediated by the KHI with implications for the driving of solar wind fluctuations.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
