35 research outputs found
Reconstructing solar wind inhomogeneous structures from stereoscopic observations in white-light: Small transients along the Sun-Earth line
The Heliospheric Imagers (HI) on board the two spacecraft of the Solar
Terrestrial Relations Observatory (STEREO) provided white-light images of
transients in the solar wind from dual perspectives from 2007 to 2014. In this
paper, we develop a new method to identify and locate the transients
automatically from simultaneous images from the two inner telescopes, known as
HI-1, based on a correlation analysis. Correlation coefficient (cc) maps along
the Sun-Earth line are constructed for the period from 1 Jan 2010 to 28 Feb
2011. From the maps, transients propagating along the Sun-Earth line are
identified, and a 27-day periodic pattern is revealed, especially for
small-scale transients. Such a periodicity in the transient pattern is
consistent with the rotation of the Sun's global magnetic structure and the
periodic crossing of the streamer structures and slow solar wind across the
Sun-Earth line, and this substantiates the reliability of our method and the
high degree of association between the small-scale transients of the slow solar
wind and the coronal streamers. Besides, it is suggested by the cc map that
small-scale transients along the Sun-Earth line are more frequent than
large-scale transients by a factor of at least 2, and that they quickly
diffused into background solar wind within about 40 Rs in terms of the
signal-to-noise ratio of white-light emissions. The method provides a new tool
to reconstruct inhomogeneous structures in the heliosphere from multiple
perspectives.Comment: 24 pages, 9 figures, to be published on Journal of Geophysical
Research - Space Physic
Recommended from our members
A signature of 27-day solar rotation in the concentration of metallic ions within the terrestrial ionosphere
We present observations during the interval 2006-2014 of 27-day and 13.5-day periodic oscillations in the ionospheric sporadic E (Es) layer. This is a thin, dense layer composed of metallic ions in the Earth's upper atmosphere between 90 and 130 km. Lomb-Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and GPS/GNSS radio occultations are associated with high-speed solar winds generated from persistent coronal holes on successive 27-day solar rotations. The 27-day and 13.5-day oscillations in the Es layers are dependent on latitude, showing a higher magnitude of periodicities at low-latitudes between 0 {15 and high-latitudes between 45 {90 (10%{14%) than those at mid-latitudes between 15 {45 (4%{10%). The 27-day and 13.5-day oscillations in the high-latitude Es layers correlate well with the geomagnetic activity Dst and Ap indices, and these periodic oscillations become more signi cant at the solar maximum (2000{2003, and 2011{2014) than the solar minimum
Recommended from our members
Modelling the observed distortion of multiple (ghost) CME fronts in STEREO Heliospheric imagers
In this work, we have, for the first time, applied the interpretation of multiple ghost-fronts to two synthetic CMEs propagating within a structured solar wind using the HUXt solar wind model. The two coronal mass ejections (CMEs) occurred on 2012 June 13-14 showing multiple fronts in images from STEREO HIs. The HUXt model is used to simulate the evolution of these CMEs across the inner heliosphere as they interacted with structured ambient solar wind. The simulations reveal that the evolution of CME shape is consistent with observations across a wide range of solar latitudes and that the manifestation of multiple `ghost-fronts' within HIs field of view is consistent with the positions of the nose and
flank of the same CME structure. This provides further conformation that the angular separation of these features provides information on the longitudinal extent of a CME. For one of the CMEs considered in this study, both simulations and observations show that a concave shape develops within the outer CME front. We conclude that this distortion results from latitudinal structure in the ambient solar wind speed. The work emphasizes that the shape of the CME cannot be assumed to remain a coherent geometrical shape during its propagation in the heliosphere. Our analysis demonstrates that the presence of `ghost' CME fronts can be used to infer the distortion of CMEs by ambient solar wind structure as a function of both latitude and longitude. Those information have potential to improve the forecasting of space weather events at Earth
Recommended from our members
Interhemispheric transport of metallic ions within ionospheric sporadic E layers by the lower thermospheric meridional circulation
Long-lived metallic ions in the Earth’s atmosphere/ionosphere have been investigated for many decades. Although the seasonal variation in ionospheric ‘sporadic E’ layers was first observed in the 1960s, the mechanism driving the variation remains a long-standing mystery. Here we report a study of ionospheric irregularities using scintillation data from COSMIC
satellites and identify a large-scale horizontal transport of long-lived metallic ions, combined with the simulations of the Whole Atmosphere Community Climate Model with the chemistry of metals and ground-based observations from two meridional chains of stations from 1975–2016. We find that the lower thermospheric meridional circulation influences the meridional
transport and seasonal variations of metallic ions within sporadic E layers. The winter-to-summer, meridional velocity of ions is estimated to vary between -1.08 and 7.45 m/s at altitudes of 107–118 km between 10�–60�N latitude. Our results not only provide strong support for the lower thermospheric meridional circulation predicted by a whole atmosphere chemistry-climate model, but also emphasise the influences of this winter-to-summer circulation on the large-scale interhemispheric transport of composition in the thermosphere/ionosphere
Recommended from our members
Using "ghost front" to predict the arrival time and speed of CMEs at Venus and Earth
Using in-situ measurements and remote-sensing observations, we study two Coronal Mass Ejections
(CMEs) that left the Sun on 13-14 June 2012 and impacted both Venus and Earth while the planets
were in close radial alignment. The two CMEs generate multiple fronts in STEREO/HI images,
which can also be observed in ‘J-map’ as bifurcated features. We present the ‘ghost front’ model to
combine remote observations from STEREO/SECCHI and in-situ observations from the Wind and
VEX spacecraft, and to derive the kinematics and propagation directions of the CMEs. By fitting the
observations of multiple fronts to a kinematically evolving flux rope (KEFR) model and assuming the
CMEs undergo deceleration through frictional drag with a steady-state solar wind, we confirm that
the outer and inner fronts of the CMEs as detected in HI images are consistent with peaks in Thomson
scattered light returned from the flank and nose of a single front for each CME. An interaction takes
place between the CME-1 and CME-2 that can be observed in the HI-1 field of view before CME-1
encounters Venus. The multi-point in-situ observations of the shock-CME interaction event serve as
further evidence of the interaction between CMEs. The arrival times calculated from the ghost-front
model are within 2.5 hours of those observed at VEX and Wind. Our analysis indicates that ghost
fronts could provide information about the longitudinally-extended shape of the CME in the field of
view of HI-1, which can be used to improve the forecast of ICME arrival time at Earth
Main Cause of the Poloidal Plasma Motion Inside a Magnetic Cloud Inferred from Multiple-Spacecraft Observations
Although the dynamical evolution of magnetic clouds (MCs) has been one of the foci of interplanetary physics for decades, only few studies focus on the internal properties of large-scale MCs. Recent work by Wang et al. (J. Geophys. Res.120, 1543, 2015) suggested the existence of the poloidal plasma motion in MCs. However, the main cause of this motion is not clear. In order to find it, we identify and reconstruct the MC observed by the Solar Terrestrial Relations Observatory (STEREO)-A, Wind, and STEREO-B spacecraft during 19 – 20 November 2007 with the aid of the velocity-modified cylindrical force-free flux-rope model. We analyze the plasma velocity in the plane perpendicular to the MC axis. It is found that there was evident poloidal motion at Wind and STEREO-B, but this was not clear at STEREO-A, which suggests a local cause rather than a global cause for the poloidal plasma motion inside the MC. The rotational directions of the solar wind and MC plasma at the two sides of the MC boundary are found to be consistent, and the values of the rotational speeds of the solar wind and MC plasma at the three spacecraft show a rough correlation. All of these results illustrate that the interaction with ambient solar wind through viscosity might be one of the local causes of the poloidal motion. Additionally, we propose another possible local cause: the existence of a pressure gradient in the MC. The significant difference in the total pressure at the three spacecraft suggests that this speculation is perhaps correct
Recommended from our members
The dynamic evolution of multipoint interplanetary coronal mass ejections observed with BepiColombo, Tianwen-1, and MAVEN
We present two multipoint interplanetary coronal mass ejections (ICMEs) detected by the Tianwen-1 and Mars Atmosphere and Volatile Evolution spacecraft at Mars and the BepiColombo (0.56 au ∼0.67 au) upstream of Mars from 2021 December 5 to 31. This is the first time that BepiColombo is used as an upstream solar wind monitor ahead of Mars and that Tianwen-1 is used to investigate the magnetic field characteristics of ICMEs at Mars. The Heliospheric Upwind Extrapolation time model was used to connect the multiple in situ observations and the coronagraph observations from STEREO/SECCHI and SOHO/LASCO. The first fast coronal mass ejection event (∼761.2 km s−1), which erupted on December 4, impacted Mars centrally and grazed BepiColombo by its western flank. The ambient slow solar wind decelerated the west flank of the ICME, implying that the ICME event was significantly distorted by the solar wind structure. The second slow ICME event (∼390.7 km s−1) underwent an acceleration from its eruption to a distance within 0.69 au and then traveled with the constant velocity of the ambient solar wind. These findings highlight the importance of background solar wind in determining the interplanetary evolution and global morphology of ICMEs up to Mars distance. Observations from multiple locations are invaluable for space weather studies at Mars and merit more exploration in the future