The extended minimum of Solar Cycle 23, the extremely quiet solar-wind conditions prevailing, and the mini-maximum of Solar Cycle 24 drew global attention and many authors have since attempted to predict the amplitude of the upcoming Solar Cycle 25, which is predicted to be the third successive weak cycle; it is a unique opportunity to probe the Sun during such quiet periods. Earlier work has established a steady decline, over two decades, in solar photospheric fields at latitudes above $45^{\circ}$ and a similar decline in solar-wind micro-turbulence levels as measured by interplanetary scintillation (IPS) observations. However, the relation between the photospheric magnetic fields and those in the low corona/solar-wind are not straightforward. Therefore, in the present article, we have used potential-field source-surface (PFSS) extrapolations to deduce global magnetic-fields using synoptic magnetograms observed with National Solar Observatory (NSO), Kitt Peak, USA (NSO/KP) and Solar Optical Long-term Investigation of the Sun (NSO/SOLIS) instruments during 1975-2018. Furthermore, we have measured the normalized scintillation index [m] using the IPS observations carried out at the Institute of Space Earth Environment Research (ISEE), Japan during 1983-2017. From these observations, we have found that, since the mid-1990s, the magnetic-field over different latitudes at 2.5 $\rm R_{\odot}$ and 10 $\rm R_{\odot}$(extrapolated using PFSS method) has decreased by $\approx 11.3-22.2 \%$. In phase with the declining magnetic-fields, the quantity m also declined by $\approx 23.6 \%$. These observations emphasize the inter-relationship between the global magnetic-field and various turbulence parameters in the solar corona and solar wind.
Extensive interplanetary scintillation (IPS) observations at 327 MHz obtained between 1983 and 2009 clearly show a steady and significant drop in the turbulence levels in the entire inner heliosphere starting from around ~1995. We believe that this large-scale IPS signature, in the inner heliosphere, coupled with the fact that solar polar fields have also been declining since ~1995, provide a consistent result showing that the buildup to the deepest minimum in 100 years actually began more than a decade earlier.
Observations of interplanetary scintillation (IPS - the scintillation of compact radio sources due to density variations in the solar wind) enable the velocity of the solar wind to be determined, and its bulk density to be estimated, throughout the inner heliosphere. A series of observations using the Low Frequency Array (LOFAR - a radio telescope centred on the Netherlands with stations across Europe) were undertaken using this technique to observe the passage of an ultra-fast CME which launched from the Sun following the X-class flare of 10 September 2017. LOFAR observed the strong radio sou…
Observations of Interplanetary Scintillation (IPS) are an efficient remote-sensing method to study the solar wind and inner heliosphere. From 2016 to 2018, some distinctive observations of IPS sources like 3C 286 and 3C 279 were accomplished with the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single-dish telescope in the world. Due to the 270-1620 MHz wide frequency coverage of the Ultra-Wideband (UWB) receiver, one can use both single-frequency and dual-frequency analyses to determine the projected velocity of the solar wind. Moreover, based on the extraordinary…
The Sun affects the Earth's physical phenomena in multiple ways, in particular the material in interplanetary space comes from coronal expansion in the form of inhomogeneous plasma flow (solar wind), which is the primary source of the interplanetary medium. Ground-based Interplanetary Scintillation (IPS) observations are an important and effective method for measuring solar wind speed and the structures of small diameter radio sources. We discuss one mode of ground-based single-station observations: Single-Station Single-Frequency (SSSF) mode. To realize the SSSF mode, a new system has been es…
We outline a method of deriving one-dimensional phaseless visibility along solar wind direction from interplanetary scintillation power spectrum, together with the known visibility of a calibration source. The method is illustrated briefly. Details may be found in Edwin Jayaraj (1990).
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 i…
Interplanetary scintillation (IPS) is a useful tool for detecting coronal mass ejections (CMEs) throughout interplanetary space. Global magnetohydrodynamic (MHD) simulations of the heliosphere, which are usually used to predict the arrival and geo-effectiveness of CMEs, can be improved using IPS data. In this study, we demonstrate an MHD simulation that includes IPS data from multiple stations to improve CME modelling. The CMEs, which occurred on 09-10 September 2017, were observed over the period 10-12 September 2017 using the Low-Frequency Array (LOFAR) and IPS array of the Institute for Spa…
Understanding the mechanism(s) of the solar wind acceleration is important in astrophysics and geophysics. A promising model of the solar wind acceleration is known as the wave/turbulence-driven (WTD) model, in which Alfvén waves feed energy to the solar wind. In this study, we tested the WTD model with global measurement of wind speed from interplanetary scintillation (IPS) observations. For Carrington rotations in minimal and maximal activity phases, we selected field lines calculated by the potential-field source-surface method in high- and mid-latitudes and compared the simulated and obser…
The 3D structure of solar wind and its evolution in time is needed for heliospheric modeling and interpretation of energetic neutral atoms observations. We present a model to retrieve the solar wind structure in heliolatitude and time using all available and complementary data sources. We determine the heliolatitude structure of solar wind speed on a yearly time grid over the past 1.5 solar cycles based on remote-sensing observations of interplanetary scintillations, in situ out-of-ecliptic measurements from Ulysses, and in situ in-ecliptic measurements from the OMNI-2 database. Since the in s…
Coronal mass ejections (CMEs) cause various disturbances of the space environment; therefore, forecasting their arrival time is very important. However, forecasting accuracy is hindered by limited CME observations in interplanetary space. This study investigates the accuracy of CME arrival times at the Earth forecasted by three-dimensional (3D) magnetohydrodynamic (MHD) simulations based on interplanetary scintillation (IPS) observations. In this system, CMEs are approximated as spheromaks with various initial speeds. Ten MHD simulations with different CME initial speed are tested, and the den…
Recent coordinated observations of interplanetary scintillation (IPS) and stereoscopic heliospheric imagers (HIs) are significant to continuously track the propagation and evolution of solar eruptions throughout interplanetary space. In order to obtain a better understanding of the observational signatures in these two remote-sensing techniques, the magnetohydrodynamics of the macro-scale interplanetary disturbance and the radio-wave scattering of the micro-scale electron-density fluctuation are coupled and investigated using a newly-constructed multi-scale numerical model. This model is then …
Coronal mass ejections (CMEs) cause disturbances in the environment of the Earth when they arrive at the Earth. However, the prediction of the arrival of CMEs still remains a challenge. We have developed an interplanetary scintillation (IPS) estimation system based on a global magnetohydrodynamic (MHD) simulation of the inner heliosphere to predict the arrival time of CMEs. In this system, the initial speed of a CME is roughly derived from white light coronagraph observations. Then, the propagation of the CME is calculated by a global MHD simulation. The IPS response is estimated by the three-…
The LOw Frequency ARray (LOFAR) is a next-generation radio telescope which uses thousands of stationary dipoles to observe celestial phenomena. These dipoles are grouped in various 'stations' which are centred on the Netherlands with additional 'stations' across Europe. The telescope is designed to operate at frequencies from 10 to 240\,MHz with very large fractional bandwidths (25-100%). Several 'beam-formed' observing modes are now operational and the system is designed to output data with high time and frequency resolution, which are highly configurable. This makes LOFAR eminently suited fo…
Interplanetary Scintillation (IPS) induces intensity fluctuations in small angular size astronomical radio sources via the distortive effects of spatially and temporally varying electron density associated with outflows from the Sun. These radio sources are a potential foreground contaminant signal for redshifted HI emission from the Epoch of Reionisation (EoR) because they yield time-dependent flux density variations in bright extragalactic point sources. Contamination from foreground continuum sources complicates efforts to discriminate the cosmological signal from other sources in the sky. …
We discuss the detection and evolution of a complex series of transient and quasi-static solar wind structures in the days following the well-known comet 2P / Encke tail disconnection event in April 2007. The evolution of transient solar wind structures ranging in size from < 105 km to > 106 km was characterized using one-minute time resolution observation of Interplanetary Scintillation (IPS) made using the European Incoherent SCA Tter (EISCA T) radar system. Simultaneously, the global structure and evolution of these features was characterized by the Heliospheric Imagers (HI) on the Solar TE…
We report on a measurement of interplanetary scintillation (IPS) using the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. Although this proof-of-concept observation utilised just 3 seconds of data on a single source, this is nonetheless a significant result, since the exceptional wide field of view of ASKAP, and this validation of its ability to observe within 10 degrees of the Sun, mean that ASKAP has the potential to observe an interplanetary coronal mass ejection (CME) after it has expanded beyond the field of view of white light coronagraphs, but long before it has r…
We present observations of high-amplitude rapid (2 s) variability toward two bright, compact extragalactic radio sources out of several hundred of the brightest radio sources in one of the 30x30 deg MWA Epoch of Reionization fields using the Murchison Widefield Array (MWA) at 155 MHz. After rejecting intrinsic, instrumental, and ionospheric origins we consider the most likely explanation for this variability to be interplanetary scintillation (IPS), likely the result of a large coronal mass ejection propagating from the Sun. This is confirmed by roughly contemporaneous observations with the Oo…
In this paper, we review the preliminary results on the propagation effects and interplanetary consequences of fast and wide coronal mass ejection (CME) events, occurred during 18--25 June 2015, in the Sun-Earth distance range. The interplanetary scintillation (IPS) images reveal that the large-scale structures of CME-driven disturbances filled nearly the entire inner heliosphere with a range of speeds, $\sim$300--1000 {\kmps}. The comparison of speed data sets, from IPS technique results in the inner heliosphere and {\it in-situ} measurements at 1 AU, indicates that the drag force imposed by …
First results of sub-arcsecond scale objects identified with ASKAP using interplanetary scintillation
CSIRO, Space and Astronomy（澳大利亚联邦科学与工业研究组织，空间与天文）；Sydney Institute for Astronomy, School of Physics A28, The University of Sydney（悉尼大学，物理学院A28，悉尼天文研究所）；School of Physics, The University of Newcastle（纽卡斯尔大学，物理学院）
Interplanetary scintillation-informed heliospheric modelling for the MeerKAT Pulsar Timing Array 4.5 yr dataset
Swinburne University of Technology（斯威本科技大学）；OzGrav: The ARC Centre of Excellence for Gravitational Wave Discovery（引力波发现ARC卓越中心）；CSIRO, Space and Astronomy（CSIRO空间与天文学部）
Comparison is carried out of the long term variation of the year averaged solar wind speed and interplanetary scintillation index with the variations of Wolf's numbers and A_P indexes of geomagnetic activity for the data of 20-24 solar activity cycles. It is shown that the slow non-monotonous trend in the scintillation parameters at middle and high heliolatitudes exists with the typical scale of order of century cycle. Correlation between the variations of Wolf's numbers and anomalies of the air temperature is analyzed for long data series from 1610 up to the present time. Possible application…
We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the H-alpha observations of the flare events made with a 15 cm solar tower telescope at ARIES, Nainital, India. The propagation characteristics of the CMEs have been derived from the three-dimensional images of the solar wind (i.e., density and speed) obtained from the interplane…
This paper presents a preliminary analysis of the turbulence spectrum of the solar wind in the near-Sun region R < 50 Rs, obtained from interplanetary scintillation measurements with the Ooty Radio Telescope at 327 MHz. The results clearly show that the scintillation is dominated by density irregularities of size about 100 - 500 km. The scintillation at the small-scale side of the spectrum, although significantly less in magnitude, has a flatter spectrum than the larger-scale dominant part. Furthermore, the spectral power contained in the flatter portion rapidly increases closer to the Sun. Th…
We report radial speed evolution of interplanetary coronal mass ejections (ICMEs) detected by the SOHO/LASCO coronagraph, interplanetary scintillation (IPS) at 327 MHz, and in-situ observations. In this study, we analyze solar wind disturbance factor (g-value) data derived from IPS observations during 1997-2009 covering nearly the whole period of Solar Cycle 23. By comparing observations from the SOHO/LASCO, IPS, and in situ, we then identify 39 ICMEs that could be analyzed carefully. Here, we define two speeds V_SOHO and V_bg, which are initial speed of ICME and the speed of the background so…
We operate the six German stations of the LOw Frequency ARray as standalone telescopes to observe more than 100 pulsars every week. To date, we have collected almost four years of high-quality data at an unprecedented weekly cadence. This allows us to perform a wide variety of analyses aimed at characterising the magnetoionic plasma crossed by pulsar radiation. In particular, our studies are focused on electron density variations in the interstellar and interplanetary media, the Galactic and interplanetary magnetic field, scintillation, and extreme scattering events. Here we report the first r…
Interplanetary coronal mass ejections (ICMEs) have complex magnetic and density structures, which is the result of their interaction with the structured solar wind and with previous eruptions. ICMEs are revealed by in situ measurements and in the past five years, through remote-sensing observations by heliospheric imagers. However, to understand and analyze these observations often requires the use of numerical modeling. It is because no instruments can yet provide a simple view of ICMEs in two or three dimensions. Numerical simulations can be used to determine the origin of a complex ejecta o…
We use dual-site radio observations of interplanetary scintillation (IPS) with extremely long baselines (ELB) to examine meridional flow characteristics of the ambient fast solar wind at plane-of-sky heliocentric distances of 24-85 solar radii (R\odot). Our results demonstrate an equatorwards deviation of 3-4° in the bulk fast solar wind flow direction over both northern and southern solar hemispheres during different times in the declining phase of Solar Cycle 23.
In-situ measurements carried out by spacecraft in radial alignment are critical to advance our knowledge on the evolutionary behavior of coronal mass ejections (CMEs) and their magnetic structures during propagation through interplanetary space. Yet, the scarcity of radially aligned CME crossings restricts investigations on the evolution of CME magnetic structures to a few case studies, preventing a comprehensive understanding of CME complexity changes during propagation. In this paper, we perform numerical simulations of CMEs interacting with different solar wind streams using the linear forc…
Despite helium abundance (AHe = nH/nHe) is ~ 8 % at the solar photospheric/chromospheric heights, AHe can be found to exceed 8% in interplanetary coronal mass ejections (ICMEs) on many occasions. Although various factors like interplanetary shocks, chromospheric evaporation and "sludge removal" have been separately invoked in the past to address the AHe enhancements in ICMEs, none of these processes could explain the variability of AHe in ICMEs comprehensively. Based on extensive analysis of 275 ICME events, we show that there is a solar activity variation of ICME averaged AHe values. The inve…
We study solar modulation of galactic cosmic rays (GCRs) during the deep solar minimum, including the declining phase, of solar cycle 23 and compare the results of this unusual period with the results obtained during similar phases of the previous solar cycles 20, 21, and 22. These periods consist of two epochs each of negative and positive polarities of the heliospheric magnetic field from the north polar region of the Sun. In addition to cosmic ray data, we utilize simultaneous solar and interplanetary plasma/field data including the tilt angle of the heliospheric current sheet. We study the…
Observations of the fluctuations in Interplanetary Magnetic Field around L1 point during the solar transient events of 2024 with MAG payload onboard Aditya-L1 spacecraft
We report kinematic properties of slow interplanetary coronal mass ejections (ICMEs) identified by SOHO/LASCO, interplanetary scintillation, and in-situ observations, and propose a modified equation for the ICME motion. We identify seven ICMEs between 2010 and 2011, and examine them with 39 events reported in our previous work. We examine 15 fast (V_SOHO - V_bg > 500 km/s), 25 moderate (0 km/s <= V_SOHO - V_bg <= 500 km/s), and 6 slow (V_SOHO - V_bg < 0 km/s) ICMEs, where V_SOHO and V_bg are the initial speed of ICMEs and the speed of the background solar wind, respectively. For slow ICMEs, we…
We report observations of a steady 20 year decline of solar photospheric fields at latitudes $\geq$45${^{o}}$ starting from $\sim$1995. This prolonged and continuing decline, combined with the fact that Cycle 24 is already past its peak, implies that magnetic fields are likely to continue to decline until $\sim$2020, the expected minimum of the ongoing solar Cycle 24. In addition, interplanetary scintillation (IPS) observations of the inner heliosphere for the period 1983--2013 and in the distance range 0.2--0.8 AU, have also shown a similar and steady decline in solar wind micro-turbulence le…
The ratio of the rms electron density fluctuations to the background density in the solar wind (density modulation index, $ε_{N} \equiv Δ{N}/N$) is of vital importance in understanding several problems in heliospheric physics related to solar wind turbulence. In this paper, we have investigated the behavior of $ε_{N}$ in the inner-heliosphere from 0.26 to 0.82 AU. The density fluctuations $Δ{N}$ have been deduced using extensive ground-based observations of interplanetary scintillation (IPS) at 327 MHz, which probe spatial scales of a few hundred km. The background densities ($N$) have been de…
In this paper, I review the results of 3-D evolution of the inner heliosphere over the solar cycle #23, based on observations of interplanetary scintillation (IPS) made at 327 MHz using the Ooty Radio Telescope. The large-scale features of solar wind speed and density turbulence of the current minimum are remarkably different from that of the previous cycle. The results on the solar wind density turbulence show that (1) the current solar minimum is experiencing a low level of coronal density turbulence, to a present value of ~50% lower than the previous similar phase, and (2) the scattering di…
X-ray emission generated through solar-wind charge exchange (SWCX) is known to contaminate X-ray observation data, the amount of which is often significant or even dominant, particularly in the soft X-ray band, when the main target is comparatively weak diffuse sources, depending on the space weather during the observation. In particular, SWCX events caused by interplanetary coronal mass ejections (ICMEs) tend to be spectrally rich and to provide critical information about the metal abundance in the ICME plasma. We analyzed the SN1006 background data observed with Suzaku on 2005 September 11 s…
The ngVLA has the potential to play a significant role in characterizing properties of the outer corona and the heating and acceleration of the solar wind into the inner heliosphere. In particular, using distant background sources to transilluminate the foreground corona and solar wind, a variety of radio propagation phenomena can be used to map plasma properties as a function of solar elongation and position angle throughout the solar cycle. These include angular broadening, interplanetary scintillations, and differential Faraday rotation, which can be used to map the solar wind velocity, det…
Observation of Interplanetary Scintillation (IPS) provides an important and effective way to study the solar wind and the space weather. A series of IPS observations were conducted by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The extraordinary sensitivity and the wide frequency coverage make FAST an ideal platform for IPS studies. In this paper we present some first scientific results from FAST observations of IPS with the L-band receiver. Based on the solar wind velocity fitting values of FAST observations on September 26-28, 2020, we found that the velocity decreases …
Radio Wave Propagation as a Probe of the Solar Corona and Solar Wind
Indian Institute of Astrophysics（印度天体物理研究所）；Indian Institute of Science Education and Research（印度科学教育与研究学院）；Physical Research Laboratory（物理研究实验室）；University of Glasgow（格拉斯哥大学）
We have studied the relationship between the solar-wind speed $[V]$ and the coronal magnetic-field properties (a flux expansion factor [$f$] and photospheric magnetic-field strength [$B_{\mathrm{S}}$]) at all latitudes using data of interplanetary scintillation and solar magnetic field obtained for 24 years from 1986 to 2009. Using a cross-correlation analyses, we verified that $V$ is inversely proportional to $f$ and found that $V$ tends to increase with $B_{\mathrm{S}}$ if $f$ is the same. As a consequence, we find that $V$ has extremely good linear correlation with $B_{\mathrm{S}}/f$. Howev…
Intense solar energetic particle (SEP) events data, associated with ground level enhancements (GLEs), occurred during 1989 to 2006 have been obtained from the spectrometers on board GOES spacecraft in the energy range 10-100 MeV. The interplanetary effects of these events and their associated coronal mass ejections (CMEs) have been provided by the LASCO/SOHO coronagraph images in the field of view of 2-30 {\rsun} and the interplanetary scintillation images from the Ooty Radio Telescope in the heliocentric distance range of $\sim$40-250 R$_\odot$. The comparison between the radial evolution of …
We perform a validation study of the latest version of the Alfvén Wave Solar atmosphere Model (AWSoM) within the Space Weather Modeling Framework (SWMF). To do so, we compare the simulation results of the model with a comprehensive suite of observations for Carrington rotations representative of the solar minimum conditions extending from the solar corona to the heliosphere up to the Earth. In the low corona ($r < 1.25$ \Rs), we compare with EUV images from both STEREO-A/EUVI and SDO/AIA and to three-dimensional (3-D) tomographic reconstructions of the electron temperature and density based on…
The modeling of the heliosphere requires continuous three-dimensional solar wind data. The in-situ out-of-ecliptic measurements are very rare, so that other methods of solar wind detection are needed. We use the remote-sensing data of the solar wind speed from observations of interplanetary scintillation (IPS) to reconstruct spatial and temporal structures of the solar wind proton speed from 1985 to 2013. We developed a method of filling the data gaps in the IPS observations to obtain continuous and homogeneous solar wind speed records. We also present a method to retrieve the solar wind densi…
Two new interplanetary technologies have advanced in the past decade to the point where they may enable exciting, affordable missions that reach further and faster deep into the outer regions of our solar system: (i) small and capable interplanetary spacecraft and (ii) light-driven sails. Combination of these two technologies could drastically reduce travel times within the solar system. We discuss a new paradigm that involves small and fast moving sailcraft that could enable exploration of distant regions of the solar system much sooner and faster than previously considered. We present some o…
Treatments of the radio scattering due to density turbulence in the solar wind typically employ asymptotic approximations to the phase structure function. We use a general structure function (GSF) that straddles the asymptotic limits and quantify the relative error introduced by the approximations. We show that the regimes where GSF predictions are accurate than those of its asymptotic approximations is not only of practical relevance, but are where inner scale effects influence the estimate of the scatter-broadening. Thus we propose that GSF should henceforth be used for scatter broadening ca…
In this paper, we review the results of interplanetary scintillation (IPS) observations made with the legacy system of the Ooty Radio Telescope (ORT) and compare them with the possibilities opened by the upgraded ORT, the Ooty Wide Field Array (OWFA). The stability and the sensitivity of the legacy system of ORT allowed the regular monitoring of IPS on a grid of large number of radio sources and the results of these studies have been useful to understand the physical processes in the heliosphere and space weather events, such as coronal mass ejections, interaction regions and their propagation…
Automatic Detection of Interplanetary Coronal Mass Ejections in Solar Wind In Situ Data
Space Research Institute, Austrian Academy of Sciences（奥地利科学院空间研究所）；Zentralanstalt für Meteorologie und Geodynamik（奥地利气象与地球动力学中央研究所）；Know-Center GmbH（Know-Center有限公司）；Institute of Physics, University of Graz（格拉茨大学物理研究所）；Institute of Interactive Systems and Data Science, Graz University of Technology（格拉茨工业大学交互系统与数据科学研究所）；Washington University in St. Louis（圣路易斯华盛顿大学）；AI AUSTRIA（奥地利人工智能协会）
The sun as an oscillator produces frequencies which propagate in the heliosphere, via solar wind, to the terrestrial magnetosphere. We searched for those frequencies in the parameters of the near Earth solar plasma and the geomagnetic indices for the past four solar cycles. The solar wind parameters used in this work are the interplanetary magnetic field, plasma beta, Alfven Mach number, solar wind speed, plasma temperature, plasma pressure, plasma density and the geomagnetic indices DST, AE, Ap and Kp. We found out that each parameter of the solar wind exhibit certain periodicities which diff…
