Decay of magnetohydrodynamic turbulence in the expanding solar wind: WIND observations

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F67985815%3A_____%2F24%3A00604407" target="_blank" >RIV/67985815:_____/24:00604407 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/68378289:_____/24:00601023

Výsledek na webu

<a href="https://hdl.handle.net/11104/0361804" target="_blank" >https://hdl.handle.net/11104/0361804</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1051/0004-6361/202450811" target="_blank" >10.1051/0004-6361/202450811</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Decay of magnetohydrodynamic turbulence in the expanding solar wind: WIND observations

Popis výsledku v původním jazyce

We have studied the decay of turbulence in the solar wind. Fluctuations carried by the expanding wind are naturally damped because of flux conservation, slowing down the development of a turbulent cascade. The latter also damps fluctuations but results in plasma heating. We analyzed time series of the velocity and magnetic field (v and B, respectively) obtained by the WIND spacecraft at 1 au. Fluctuations were recast in terms of the Elsasser variables, z(+/-) = v +/- B/root 4 pi rho, with rho being the average density, and their second- and third-order structure functions were used to evaluate the Politano-Pouquet relation, modified to account for the effect of expansion. We find that expansion plays a major role in the Alfvénic stream, those for which z(+) >> z(-). In such a stream, expansion damping and turbulence damping act, respectively, on large and small scales for z(+), and also balance each other. Instead, z(-) is only subject to a weak turbulent damping because expansion is a negligible loss at large scales and a weak source at inertial range scales. These properties are in qualitative agreement with the observed evolution of energy spectra that is described by a double power law separated by a break that sweeps toward lower frequencies for increasing heliocentric distances. However, the data at 1 au indicate that injection by sweeping is not enough to sustain the turbulent cascade. We derived approximate decay laws of energy with distance that suggest possible solutions for the inconsistency: in our analysis, we either overestimated the cascade of z(+/-) or missed an additional injection mechanism, for example, velocity shear among streams.

Název v anglickém jazyce

Decay of magnetohydrodynamic turbulence in the expanding solar wind: WIND observations

Popis výsledku anglicky

We have studied the decay of turbulence in the solar wind. Fluctuations carried by the expanding wind are naturally damped because of flux conservation, slowing down the development of a turbulent cascade. The latter also damps fluctuations but results in plasma heating. We analyzed time series of the velocity and magnetic field (v and B, respectively) obtained by the WIND spacecraft at 1 au. Fluctuations were recast in terms of the Elsasser variables, z(+/-) = v +/- B/root 4 pi rho, with rho being the average density, and their second- and third-order structure functions were used to evaluate the Politano-Pouquet relation, modified to account for the effect of expansion. We find that expansion plays a major role in the Alfvénic stream, those for which z(+) >> z(-). In such a stream, expansion damping and turbulence damping act, respectively, on large and small scales for z(+), and also balance each other. Instead, z(-) is only subject to a weak turbulent damping because expansion is a negligible loss at large scales and a weak source at inertial range scales. These properties are in qualitative agreement with the observed evolution of energy spectra that is described by a double power law separated by a break that sweeps toward lower frequencies for increasing heliocentric distances. However, the data at 1 au indicate that injection by sweeping is not enough to sustain the turbulent cascade. We derived approximate decay laws of energy with distance that suggest possible solutions for the inconsistency: in our analysis, we either overestimated the cascade of z(+/-) or missed an additional injection mechanism, for example, velocity shear among streams.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10308 - Astronomy (including astrophysics,space science)

Projekt

—

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2024

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Astronomy & Astrophysics

ISSN

0004-6361

e-ISSN

1432-0746

Svazek periodika

690

Číslo periodika v rámci svazku

Oct.

Stát vydavatele periodika

FR - Francouzská republika

Počet stran výsledku

13

Strana od-do

A265

Kód UT WoS článku

001332213700022

EID výsledku v databázi Scopus

2-s2.0-85207953364