Spacecraft Radio Frequency Fluctuations in the Corona: a Messenger-Helios Composite Study
Abstract
Dissipation of locally generated slow compressive waves may play a role in Alfven wave heating and acceleration of the corona. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FF) that encode the coronal electron number density disturbances, allowing exploration of coronal acoustic or slow magnetoacoustic wave models. FF observations from MESSENGER 2009 and HELIOS 1975-1976 superior conjunctions were combined to produce a composite view of equatorial region FF near solar minimum over solar offset range 1.4-25 Rs. We present a model of FF based on randomized compressive waves aligned with the coronal radial magnetic structure and traveling at the sonic speed. The model intrinsically includes anisotropic features at low solar offset on the basis of magnetically controlled flux tube dimensions. Agreement between the observations and the modeled FF over solar offset up to 12 Rs supports the possibility that magnetically guided slow compressive waves are ubiquitous in the inner coronal regions pertinent to slow solar wind formation and initial acceleration.
- Publication:
-
Solar Heliospheric and INterplanetary Environment (SHINE 2018)
- Pub Date:
- July 2018
- Bibcode:
- 2018shin.confE.249W