Separating Nightside Interplanetary and Ionospheric Scintillation with LOFAR

TL;DR

This paper demonstrates the first LOFAR observations of night-side interplanetary scintillation, distinguishing it from ionospheric effects, and confirms the presence of IPS with high time cadence data, supporting prior MWA findings.

Contribution

It introduces high time cadence LOFAR observations of night-side IPS and compares them with MWA data to verify the interplanetary origin of scintillation signals.

Findings

LOFAR successfully detects night-side IPS.

High time cadence data helps differentiate IPS from ionospheric scintillation.

Results are consistent with slow solar wind and CME observations.

Abstract

Observation of interplanetary scintillation (IPS) beyond Earth-orbit can be challenging due to the necessity to use low radio frequencies at which scintillation due to the ionosphere could confuse the interplanetary contribution. A recent paper by Kaplan {\it et al} (2015) presenting observations using the Murchison Widefield Array (MWA) reports evidence of night-side IPS on two radio sources within their field of view. However, the low time cadence of 2\,s used might be expected to average out the IPS signal, resulting in the reasonable assumption that the scintillation is more likely to be ionospheric in origin. To verify or otherwise this assumption, this letter uses observations of IPS taken at a high time cadence using the Low Frequency Array (LOFAR). Averaging these to the same as the MWA observations, we demonstrate that the MWA result is consistent with IPS, although some contribution from the ionosphere cannot be ruled out. These LOFAR observations represent the first of night-side IPS using LOFAR, with solar wind speeds consistent with a slow solar wind stream in one observation and a CME expecting to be observed in another.