Separating Nightside Interplanetary and Ionospheric Scintillation With Lofar

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 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.

Interplanetary Scintillation with the Murchison Widefield Array I: a sub-arcsecond survey over 900 deg2 at 79 and 158 MHz

“…For the source shown in Figure 1, ν 0 is 0.3 Hz (0.25 Hz in the lower band), and α is approximately 4.5. This is consistent with the findings of Fallows et al (2013) and (Tokumaru et al 2011) at slightly higher frequencies, and Kaplan et al (2015) (see also Fallows et al 2016) in their investigations of night-side IPS.…”

“…In particular, there has been a proliferation of all-sky surveys with these new instruments including the MWA GLEAM Survey (Wayth et al 2015;Hurley-Walker et al 2017), and MSSS with LOFAR (Heald et al 2015), as well as the alternative data release of the TGSS, conducted with the GMRT (Intema et al 2017), and a redux (Lane et al 2014) of VLSS (Cohen et al 2007) conducted with the VLA. In addition, IPS has already been detected and studied with both LOFAR (Fallows et al 2013(Fallows et al , 2016 and the MWA (Kaplan et al 2015).…”

Single‐Site IPS Power Spectra Analysis for Space Weather Products Using Cross‐Correlation Function Results From EISCAT and MERLIN IPS Data

“…We are aware that the autocorrelation function problems could likely be improved/corrected by manually adjusting the high‐pass filter to a higher value which attenuates the system noise in the spectrum as well as aids in cutting out ionospheric scintillation contributions (e.g., Fallows et al, , and references therein). However, since one of the drivers of this paper is to look at the space weather operations element and in IPS's role in space weather operations, the automated option was used as this is how it would be if implemented in a real‐time/near‐real‐time operational system.…”

Radio observatories and instrumentation used in space weather science and operations

“…The system is operated by the Netherlands Institute for Radio Astronomy (ASTRON), observes in the frequency range of 10-240 MHz, and is used for a variety of astrophysical science use cases, including research into the epoch of reionization (Patil et al, 2017), pulsar and fast transient observations (Stappers et al, 2011), and large-scale radio surveys (Shimwell et al, 2017), among many others. LOFAR is also involved in solar physics and space weather research, including both quiet and active Sun, heliospheric, and ionospheric observations (e.g., Fallows et al, 2013Fallows et al, , 2016Morosan et al, 2014;Vocks et al, 2018). However, it does not observe the Sun or heliosphere constantly and therefore cannot function as a space weather facility for monitoring or forecasting.…”