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The Mexican Array Radio Telescope (MEXART), located in the state of Michoacan in Mexico, has been operating in an analog fashion, utilizing a Butler Matrix to generate fixed beams on the sky, since its inception. Calibrating this instrument has proved difficult, leading to loss in sensitivity. It was also a rigid setup, requiring manual intervention and tuning for different observation requirements. The Radio Frequency (RF) system has now been replaced with a digital one. This digital backend is a hybrid system utilizing both FPGA-based technology and GPU acceleration, and is capable of automatically calibrating the different rows of the array, as well as generating a configurable number of frequency-domain synthesized beams to towards selected locations on the sky. A monitoring and control system, together with a full-featured web-based front-end, has also been developed, greatly simplifying the interaction with the instrument. This paper presents the design, implementation and deployment of the new digital backend, including preliminary analysis of system performance and stability.

The fluid dynamics of a straight tundish was studied when Ar-gas was fed through the bottom, using mathematical simulation. Flow rates of 15 and 40 liters/min of argon in three locations into the tundish – near input steel, center, and near output steel – were analyzed. A stochastic model was employed for determining statistically the particle amount (emulating alumina particles) in the inclusions removal. From these calculations and those of the Residence Time Distribution (RTD) curves, we found a direct relationship to improve steel quality. Specifically, removal of the smaller nonmetallic inclusions was significantly enhanced for cases with the lowest dead volume fraction; they correspond to those of the highest averaged residence time. Therefore, it was found that it is even possible to reduce argon consumption and still obtain good results of steel cleanness.

Interplanetary shocks in the heliosphere modify the solar wind through which they pass. In particular, shocks play an important role in particle acceleration. During the extended solar minimum (2007–2010) STEREO observed 65 forward shocks driven by stream interactions (SI), with magnetosonic Mach numbers Mms ≈ 1.1–4.0 and shock normal angles θBN ~ 20–87°. We analyze the waves associated with these shocks and find that the region upstream can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) waves (f ~ 10−2–10−1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. We find that when the Mach number (Mms) is low and the shock is quasi-perpendicular ( θBN > 45°) whistler waves remain close to the shock. As Mms increases, the shock profile changes and can develop a foot and overshoot associated with ion reflection and gyration. Whistler precursors can be superposed on the foot region, so that some quasi-perpendicular shocks have characteristics of both subcritical and supercritical shocks. When the shock is quasi-parallel ( θBN

Complex Structures (CSs) formed by the interaction of magnetic cloud (MC)-like structures with other transients (e.g., another MC, a stream interaction region, or a fast stream of solar wind) were frequently observed in the interplanetary space by STEREO spacecraft during the solar minimum 23 and the rising phase of the solar cycle 24. Here we report the presence of low-frequency waves (LFWs) inside some isolated MCs (IMCs) and inside the CSs observed by STEREO during such period (2007–2011). It is important to study in detail the properties of waves in space plasmas since particle distribution functions can be modified by wave-particle interactions. We compare wave characteristics within IMCs with those waves observed inside CSs. Both left-handed (LH) and right-handed (RH), near-circularly polarized, transverse and almost parallel-propagating LFWs (around the proton cyclotron frequency) were sporadically observed inside both IMCs and CSs. In contrast, compressive mirror-mode waves (MMs) were observed only within CSs. We studied local plasma conditions inside the IMCs and CSs to gain insight about wave origin: most of the MMs within CSs were observed in regions with enhanced plasma beta (β>1); the majority of the LH waves were found in low beta plasmas (β

This paper introduces and describes the radio and plasma wave investigation on the STEREO Mission: STEREO/WAVES or S/WAVES. The S/WAVES instrument includes a suite of state-of-the-art experiments that provide comprehensive measurements of the three components of the fluctuating electric field from a fraction of a hertz up to 16 MHz, plus a single frequency channel near 30 MHz. The instrument has a direction finding or goniopolarimetry capability to perform 3D localization and tracking of radio emissions associated with streams of energetic electrons and shock waves associated with Coronal Mass Ejections (CMEs). The scientific objectives include: (i) remote observation and measurement of radio waves excited by energetic particles throughout the 3D heliosphere that are associated with the CMEs and with solar flare phenomena, and (ii) in-situ measurement of the properties of CMEs and interplanetary shocks, such as their electron density and temperature and the associated plasma waves near 1 Astronomical Unit (AU). Two companion papers provide details on specific aspects of the S/WAVES instrument, namely the electric antenna system (Bale et al., Space Sci. Rev., 2007) and the direction finding technique (Cecconi et al., Space Sci. Rev., 2007).

Aims. We investigate the characteristics of energetic electron beams, plasma turbulence and radio emission from interplanetary shock waves. Methods. Numerical calculations of spectra and Landau damping of hot plasma eigen oscillations in the magnetic field are used. Results. It is shown that the longitudinal wave spectrum, excited in the solar wind plasma, extends with the increase of the refractive index n over range of values n >10. This result allows us to explain the broad band of emission, the constant value of the average ratio of frequency-band to radio emission frequency from interplanetary shock wave fronts, and to estimate the electron beam density and amplitude of Langmuir waves at the shock. It is shown that a spectrum of radio emission is determined by the spectrum of Langmuir waves excited upstream of the interplanetary shock wave by heated electrons escaping from the shock wave front.

We use STEREO data to study shocks driven by stream interactions and the waves associated with them. During the years of the extended solar minimum 2007-2010, stream interaction shocks have Mach numbers between 1.1-3.8 and θBn ∼20-86°. We find a variety of waves, including whistlers and low frequency fluctuations. Upstream whistler waves may be generated at the shock and upstream ultra low frequency (ULF) waves can be driven locally by ion instabilities. The downstream wave spectra can be formed by both, locally generated perturbations, and shock transmitted waves. We find that many quasiperpendicular shocks can be accompanied by ULF wave and ion foreshocks, which is in contrast to Earth's bow shock. Fluctuations downstream of quasi-parallel shocks tend to have larger amplitudes than waves downstream of quasi-perpendicular shocks. Proton foreshocks of shocks driven by stream interactions have extensions dr ≤0.05 AU. This is smaller than foreshock extensions for ICME driven shocks. The difference in foreshock extensions is related to the fact that ICME driven shocks are formed closer to the Sun and therefore begin to accelerate particles very early in their existence, while stream interaction shocks form at ∼1 AU and have been producing suprathermal particles for a shorter time.

We study suprathermal electron distributions (E > 80 eV) in regions adjacent to interplanetary (IP) shocks driven by interplanetary coronal mass ejections (ICMEs). The shocks were observed by the two STEREO spacecraft during the years 2007-2010, hence during the minimum and at the beginning of the rising phase of the current solar cycle. All the ICMEs were isolated events, meaning that the shocks were produced only due to interactions of the ICMEs with the solar wind. We find that suprathermal electron pitch angle distributions (PADs) in regions adjacent to ICME driven IP shocks vary from shock to shock. At some shocks, these electrons show the "usual" isotropic halo and a narrow, field-aligned strahl. The PADs upstream and downstream of these shocks differ only in the width of the strahl, with the later being wider in the downstream regions. In other cases we observe unusual downstream conical distributions at intermediate angles (between 0 and 90 or 90 and 180° PA), counterstreaming electrons at the shock transitions and downstream PADs without the strahl component. Here we present two shocks from our sample with such unusual electrons distributions, not reported in the literature.

We analyze the properties of 98 weak interplanetary shocks measured by the dual STEREO spacecraft over approximately 3 years during the past solar minimum. We study the occurrence of whistler waves associated with these shocks, which on average are high beta shocks (0.2 60 deg.). The wave propagation with respect to the shock-normal direction has no preferred direction and varies similarly to the upstream case. It is possible that downstream fluctuations are generated by ion relaxation as suggested in previous hybrid simulation shocks.

[1] In this work we study the waves in regions adjacent to ten interplanetary (IP) shocks formed by the interactions between interplanetary coronal mass ejections and the solar wind. We analyze the STEREO data for the years 2007–2010. Shocks in our sample have low magnetosonic Mach numbers (Mms ≤ 2.3), their criticality ratios range between 0.8 and 2.3 and θBn are between 38° and 85°. We find ultra-low frequency (ULF, 0.01 Hz–0.05 Hz) waves and higher-frequency (HF, ≥ 1 Hz) whistler precursors upstream of these shocks. Downstream of them we observe irregular ULF fluctuations and regular HF waves with similar frequencies as in the upstream case. We find that IP shocks with relatively small Mms can excite waves in large regions in front of them (2.2 × 10−3 AU–4.6 × 10−3 AU), thereby forming large ULF wave foreshocks. We do not find any evidence for the steepening of these waves. We do observe suprathermal (E ≤ 30 keV) proton foreshocks upstream of some of the shocks in the sample. The extensions of suprathermal proton foreshocks range between 0.02 AU and 0.1 AU. However, not all foreshocks with suprathermal ions show ULF waves or vice versa. The extensions of ULF and proton foreshocks can be very different. Enhanced ULF waves and suprathermal protons can be observed upstream of local quasi-perpendicular shocks. We propose that the observed discordance between the shock geometries and the presence of the foreshock phenomena may be explained in terms of temporal and spatial variations of the local geometry of the IP shocks.

We investigate the characteristics of interplanetary (IP) shock waves associated with a stream interaction region (SIR) observed during April 21–24, 2007 by STEREO‐A/B, WIND and ACE spacecraft. During the years 2007–2008 STEREO‐A observed 43 and STEREO‐B crossed 41 shocks. As IP shocks propagate, they encounter solar wind with different characteristics (density, speed) and different orientations of the ambient magnetic field. Hence, it is expected that shock profiles will vary strongly through the space. We use magnetic field and plasma data to study shock structure, strength and orientation. In this example of a SIR we find that the characteristics of the shocks change dramatically from one region to another, the shock structure can be quasi‐perpendicular as observed in one spacecraft and quasi‐parallel when crossed at other point. Low frequency waves with different characteristics appear upstream and downstream of forward and reverse shocks. In this example the region upstream of the forward quasi‐perpe...

International audience; We report on the properties of radio-quiet (RQ) and radio-loud (RL) coronal mass ejections (CMEs) that are fast and wide (FW). RQ CMEs lack type II radio bursts in the metric and decameter-hectometric (DH) wavelengths. RL CMEs are associated with metric or DH type II bursts. We found that ~40% of the FW CMEs from 1996 to 2005 were RQ. The RQ CMEs had an average speed of 1117 km s-1 compared to 1438 km s-1 for the RL, bracketing the average speed of all FW CMEs (1303 km s-1). The fraction of full halo CMEs (apparent width=360deg) was the largest for the RL CMEs (60%), smallest for the RQ CMEs (16%), and intermediate for all FW CMEs (42%). The median soft X-ray flare size for the RQ CMEs (C6.9) was also smaller than that for the RL CMEs (M3.9). About 55% of RQ CMEs were back sided, while the front-sided ones originated close to the limb. The RL CMEs originated generally on the disk with only ~25% being back sided. The RQ FW CMEs suggest that the Alfvén speed in the low-latitude outer corona can often exceed 1000 km s-1 and can vary over a factor of >=3. None of the RQ CMEs was associated with large solar energetic particle events, which is useful information for space weather applications.

[1] We report on a study of type II radio bursts from the Wind/WAVES experiment in conjunction with white-light coronal mass ejections (CME) from the Solar and Heliospheric Observatory (SOHO). The type II bursts considered here have emission components in all the spectral domains: metric, decameter-hectometric (DH) and kilometric (km), so we refer to them as m-to-km type II bursts. CMEs associated with the m-to-km type II bursts were more energetic than those associated with bursts in any single wavelength regime. CMEs associated with type II bursts confined to the metric domain were more energetic (wider and faster) than the general population of CMEs but less energetic than CMEs associated with DH type II bursts. Thus the CME kinetic energy seems to organize the life time of the type II bursts. Contrary to previous results, the starting frequency of metric type II bursts with interplanetary counterparts seems to be no different from that of type II bursts without interplanetary counterparts. We also verified this by showing that the average CME height at the onset time of the type II bursts is the same for the two metric populations. The majority (78%) of the m-to-km type II bursts were associated with solar energetic particle (SEP) events. The solar sources of the small fraction of m-to-km type II bursts without SEP association were poorly connected to the observer near Earth. Finally, we found that the m-to-km type II bursts were associated with bigger flares compared to the purely metric type II bursts.