Comparison between Single- and Multi-Station
IPS Measurements

Aguilar-Rodriguez, Ernesto*; Mejia-Ambriz, Julio**.
*UNAM-MEXART, México
**University of California, San DiegoTwo ways to determinate solar wind velocity byIPS observations● Multi-station: The solar wind speed is derived by measuring theradiation pattern delay between separated stations (∼ 100 km).

● Single-station: Determination of solar wind speeds by fitting asolar wind velocity model to the observed power spectrum of IPS.

General methodology to get the IPS observed
power spectra(1) Divide the time series into
subintervals of 512 points each(2) Take the FFT to get the power
spectra of each subinterval.
Spectra having high noise
at high frequencies are discarded
log-log(3) Take the sum of these power
spectra to yield the total
observed power spectrum

General methodology to get the IPS observed
power spectra(1) Divide the time series into
subintervals of 512 points each(2) Take the FFT to get the power
spectra of each subinterval.
Spectra having high noise
at high frequencies are discarded
log-log(3) Take the sum of these power
spectra to yield the total
observed power spectrum

General methodology to obtain solar windvelocities: Single-station IPS technique
The modelVersion:
Isotropic solar
wind and nocontribution ofthe inner scale

Two examples of themodel using typicalparameters

Spectra at 327 MHz
are around 1.5X wider
than those observed at
140 MHz.

General methodology to obtain solar windvelocities: Single-station IPS techniqueFit a model of the power spectra in the region of IPS contribution (~0.2 to~2 Hz). Best fitting is obtained by minimizing the chi-square distribution:To associate an error to the velocities, we fix all the other parameters and find where its chisquared distribution becomes quadruple from the minimum value as v is varied.

Case of single-station study: MEXART and SWIFT(Toyokawa array) of STELMEXART
17 observations of 3C48 at 140 MHz to obtain solar wind speeds by applying the singlestation technique. The observations were carried out during the minimum and maximum
for solar cycle 24, at elongation angles 21° – 63° (0.37-0.89 AU).
(i) The α parameter is fixed assuming solar cycle dependence. α=3.8 for the minimum andα=3.3 for the maximum (Manoharan, Kojima, and Misawa, JGR, 1994; Glubokova,Chashei, and Tyul’bashev, Adv Astron Space Phys, 2012).
(ii) We fit the model to the observed power spectra using 2 free parameters: V and Θ.
(iii) We use the average of Θ from the previous fittings (‹Θ›=170 mas).
(iv) We fix all the parameters and find V.
SWIFT
We take 20 available observations of 3C48 obtained at 327 MHz at dates near to theselected observations of MEXART, and we apply the same steps above (‹Θ›=120 mas).

MEXART and SWIFT(Toyokawa array) ofSTEL
Comparison of IPS powerspectra.
Quasi-simultaneousobservations (8 hours ofdifference). As expected thespectra observed with SWIFT(327 MHz) are around 1.5X
wider than those observed with
MEXART (140 MHz).

MEXART-140 MHz

SWIFT-327 MHz

Comparison of simultaneous observations:
STEL (multi-station) vs SWIFT-STEL (single-station)
12 observations. Velocities match very well, except for one observation in April 2013
which may be related to a combination of fast and slow solar wind at different
positions on the line of sight (Moran et al., Ann Geophysicae, 2000).

velocity (km/s)

Observations carried out for 6 months:
Single-station 327 MHz, SWIFT-STEL ( * )Single-station 140 MHz, MEXART ( ◊ )Multi-station 327 MHz, STEL ( ∆ )day/time of the month

Case of single-station study: Big Scanning Array(BSA). Puschino Radioastronomy Observatory
3C48

STEL, multi-station (~ 17 hours later)v = 569 ± 3.
Data provided courtesy of S. Tyul’bashev

111MHz

3C147

STEL, multi-station (~ 7 hours before)
V = 461 ± 1.

General results and comments• We focus on the single-station technique to obtain solar wind speeds with IPS
remote sensing observations.
• The reported solar wind velocities at 140 MHz are the first remote sensing results
determined with MEXART.
• Measurements using the single-station technique with SWIFT and those frommulti-site (STEL) agree very well.
• Taking the speeds measured by STEL (multi-site) as the actual values, the relative
error of measurements with SWIFT (single-station) have an average of ∼ 8%. The
fitting error using the chi-square distribution is ∼13%.
• Taking the average speed measured by STEL and SWIFT (8 hours of difference)as the actual value, the resulting average relative difference error for MEXART is ∼11%. The fitting chi-square distribution error is ∼13%.