Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F68378289%3A_____%2F21%3A00552241" target="_blank" >RIV/68378289:_____/21:00552241 - isvavai.cz</a>

Výsledek na webu

<a href="https://hal-obspm.ccsd.cnrs.fr/obspm-03368166/file/chane21_overexpansion_CME_23May02_final.pdf" target="_blank" >https://hal-obspm.ccsd.cnrs.fr/obspm-03368166/file/chane21_overexpansion_CME_23May02_final.pdf</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1051/0004-6361/202039867" target="_blank" >10.1051/0004-6361/202039867</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

Popis výsledku v původním jazyce

Context. From May 24–25, 2002, four spacecraft located in the solar wind at about 1 astronomical unit (au) measured plasma densitiesnone to two orders of magnitude lower than usual. The density was so low that the flow became sub-Alfvénic for four hours, and thenAlfvén Mach number was as low as 0.4. Consequently, the Earth lost its bow shock, and two long Alfvén wings were generated.nAims. This is one of the lowest density events ever recorded in the solar wind at 1 au, and the least documented one. Our goal is tonunderstand what caused the very low density.nMethods. Large Angle and Spectrometric Coronagraph (LASCO) and in situ data were used to identify whether something unusualnoccurred that could have generated such low densitiesnResults. The very low density was recorded inside a large interplanetary coronal mass ejection (ICME), which displayed a long,nlinearly declining velocity profile, typical of expanding ICMEs. We deduce a normalised radial expansion rate of 1.6. Such a strongnexpansion, occurring over a long period of time, implies a radial size expansion growing with the distance from the Sun to the powern1.6. This can explain a two-orders-of-magnitude drop in plasma density. Data from LASCO and the Advanced Composition Explorernshow that this over-expanding ICME was travelling in the wake of a previous ICME.nConclusions. The very low densities measured in the solar wind in May 2002 were caused by the over-expansion of a large ICME.nThis over-expansion was made possible because the ICME was travelling in a low-density and high-velocity environment present innthe wake of another ICME coming from a nearby region on the Sun and ejected only three hours previously. Such conditions are verynunusual, which explains why such very low densities are almost never observed.

Název v anglickém jazyce

Over-expansion of a coronal mass ejection generates sub-Alfvénic plasma conditions in the solar wind at Earth

Popis výsledku anglicky

Context. From May 24–25, 2002, four spacecraft located in the solar wind at about 1 astronomical unit (au) measured plasma densitiesnone to two orders of magnitude lower than usual. The density was so low that the flow became sub-Alfvénic for four hours, and thenAlfvén Mach number was as low as 0.4. Consequently, the Earth lost its bow shock, and two long Alfvén wings were generated.nAims. This is one of the lowest density events ever recorded in the solar wind at 1 au, and the least documented one. Our goal is tonunderstand what caused the very low density.nMethods. Large Angle and Spectrometric Coronagraph (LASCO) and in situ data were used to identify whether something unusualnoccurred that could have generated such low densitiesnResults. The very low density was recorded inside a large interplanetary coronal mass ejection (ICME), which displayed a long,nlinearly declining velocity profile, typical of expanding ICMEs. We deduce a normalised radial expansion rate of 1.6. Such a strongnexpansion, occurring over a long period of time, implies a radial size expansion growing with the distance from the Sun to the powern1.6. This can explain a two-orders-of-magnitude drop in plasma density. Data from LASCO and the Advanced Composition Explorernshow that this over-expanding ICME was travelling in the wake of a previous ICME.nConclusions. The very low densities measured in the solar wind in May 2002 were caused by the over-expansion of a large ICME.nThis over-expansion was made possible because the ICME was travelling in a low-density and high-velocity environment present innthe wake of another ICME coming from a nearby region on the Sun and ejected only three hours previously. Such conditions are verynunusual, which explains why such very low densities are almost never observed.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10305 - Fluids and plasma physics (including surface physics)

Projekt

<a href="/cs/project/GA18-05285S" target="_blank" >GA18-05285S: Magnetosferické emise typu EMIC</a><br>

Návaznosti

I - Institucionalni podpora na dlouhodoby koncepcni rozvoj vyzkumne organizace

Rok uplatnění

2021

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

647

Číslo periodika v rámci svazku

Mar 26

Stát vydavatele periodika

FR - Francouzská republika

Počet stran výsledku

12

Strana od-do

A149

Kód UT WoS článku

000636920700001

EID výsledku v databázi Scopus

2-s2.0-85103480384