62 research outputs found
Prediction of geomagnetic storm strength from inner heliospheric in situ observations
Prediction of the effects of coronal mass ejections (CMEs) on Earth strongly depends on knowledge of the interplanetary magnetic field southward component, B z . Predicting the strength and duration of B z inside a CME with sufficient accuracy is currently impossible, forming the so-called B z problem. Here, we provide a proof-of-concept of a new method for predicting the CME arrival time, speed, B z , and resulting disturbance storm time (Dst) index on Earth based only on magnetic field data, measured in situ in the inner heliosphere (<1 au). On 2012 June 12â16, three approximately Earthward-directed and interacting CMEs were observed by the Solar Terrestrial Relations Observatory imagers and Venus Express (VEX) in situ at 0.72 au, 6° away from the SunâEarth line. The CME kinematics are calculated using the drag-based and WSAâEnlil models, constrained by the arrival time at VEX, resulting in the CME arrival time and speed on Earth. The CME magnetic field strength is scaled with a power law from VEX to Wind. Our investigation shows promising results for the Dst forecast (predicted: â96 and â114 nT (from 2 Dst models); observed: â71 nT), for the arrival speed (predicted: 531 ± 23 km sâ1; observed: 488 ± 30 km sâ1), and for the timing (6 ± 1 hr after the actual arrival time). The prediction lead time is 21 hr. The method may be applied to vector magnetic field data from a spacecraft at an artificial Lagrange point between the Sun and Earth or to data taken by any spacecraft temporarily crossing the SunâEarth line
Combined Multipoint Remote and In Situ Observations of the Asymmetric Evolution of a Fast Solar Coronal Mass Ejection
We present an analysis of the fast coronal mass ejection (CME) of 2012 March
7, which was imaged by both STEREO spacecraft and observed in situ by
MESSENGER, Venus Express, Wind and Mars Express. Based on detected arrivals at
four different positions in interplanetary space, it was possible to strongly
constrain the kinematics and the shape of the ejection. Using the white-light
heliospheric imagery from STEREO-A and B, we derived two different kinematical
profiles for the CME by applying the novel constrained self-similar expansion
method. In addition, we used a drag-based model to investigate the influence of
the ambient solar wind on the CME's propagation. We found that two preceding
CMEs heading in different directions disturbed the overall shape of the CME and
influenced its propagation behavior. While the Venus-directed segment underwent
a gradual deceleration (from ~2700 km/s at 15 R_sun to ~1500 km/s at 154
R_sun), the Earth-directed part showed an abrupt retardation below 35 R_sun
(from ~1700 to ~900 km/s). After that, it was propagating with a quasi-constant
speed in the wake of a preceding event. Our results highlight the importance of
studies concerning the unequal evolution of CMEs. Forecasting can only be
improved if conditions in the solar wind are properly taken into account and if
attention is also paid to large events preceding the one being studied
ElEvoHI : A NOVEL CME PREDICTION TOOL FOR HELIOSPHERIC IMAGING COMBINING AN ELLIPTICAL FRONT WITH DRAG-BASED MODEL FITTING
This article has an erratum: DOI 10.3847/0004-637X/831/2/210In this study, we present a new method for forecasting arrival times and speeds of coronal mass ejections (CMEs) at any location in the inner heliosphere. This new approach enables the adoption of a highly flexible geometrical shape for the CME front with an adjustable CME angular width and an adjustable radius of curvature of its leading edge, i.e., the assumed geometry is elliptical. Using, as input, Solar TErrestrial RElations Observatory (STEREO) heliospheric imager (HI) observations, a new elliptic conversion (ElCon) method is introduced and combined with the use of drag-based model (DBM) fitting to quantify the deceleration or acceleration experienced by CMEs during propagation. The result is then used as input for the Ellipse Evolution Model (ElEvo). Together, ElCon, DBM fitting, and ElEvo form the novel ElEvoHI forecasting utility. To demonstrate the applicability of ElEvoHI, we forecast the arrival times and speeds of 21 CMEs remotely observed from STEREO/HI and compare them to in situ arrival times and speeds at 1 AU. Compared to the commonly used STEREO/HI fitting techniques (Fixed-phi, Harmonic Mean, and Self-similar Expansion fitting), ElEvoHI improves the arrival time forecast by about 2 to +/- 6.5 hr and the arrival speed forecast by approximate to 250 to +/- 53 km s(-1), depending on the ellipse aspect ratio assumed. In particular, the remarkable improvement of the arrival speed prediction is potentially beneficial for predicting geomagnetic storm strength at Earth.Peer reviewe
Magnetic Fluctuations and Turbulence in the Venus Magnetosheath and Wake
Recent research has shown that distinct physical regions in the Venusian
induced magnetosphere are recognizable from the variations of strength and of
wave/fluctuation activity of the magnetic field. In this paper the statistical
properties of magnetic fluctuations are investigated in the Venusian
magnetosheath, terminator, and wake regions. The latter two regions were not
visited by previous missions. We found 1/f fluctuations in the magnetosheath,
large-scale structures near the terminator and more developed turbulence
further downstream in the wake. Location independent short-tailed non-Gaussian
statistics was observed.Comment: 16 pages, 4 figure
Ensemble Prediction of a Halo Coronal Mass Ejection Using Heliospheric Imagers
The Solar TErrestrial RElations Observatory (STEREO) and its heliospheric imagers (HIs) have provided us the possibility to enhance our understanding of the interplanetary propagation of coronal mass ejections (CMEs). HIâbased methods are able to forecast arrival times and speeds at any target and use the advantage of tracing a CME's path of propagation up to 1 AU and beyond. In our study, we use the ELEvoHI model for CME arrival prediction together with an ensemble approach to derive uncertainties in the modeled arrival time and impact speed. The CME from 3 November 2010 is analyzed by performing 339 model runs that are compared to in situ measurements from linedâup spacecraft MErcury Surface, Space ENvironment, GEochemistry, and Ranging and STEREOâB. Remote data from STEREOâB showed the CME as halo event, which is comparable to an HI observer situated at L1 and observing an Earthâdirected CME. A promising and easy approach is found by using the frequency distributions of four ELEvoHI output parameters, drag parameter, background solar wind speed, initial distance, and speed. In this case study, the most frequent values of these outputs lead to the predictions with the smallest errors. Restricting the ensemble to those runs, we are able to reduce the mean absolute arrival time error from 3.5 ± 2.6 to 1.6 ± 1.1 hr at 1 AU. Our study suggests that L1 may provide a sufficient vantage point for an Earthâdirected CME, when observed by HI, and that ensemble modeling could be a feasible approach to use ELEvoHI operationally
Prediction of the in situ coronal mass ejection rate for solar cycle 25: Implications for parker solar probe in situ observations
The Parker Solar Probe (PSP) and Solar Orbiter missions are designed to make groundbreaking observations of the
Sun and interplanetary space within this decade. We show that a particularly interesting in situ observation of an
interplanetary coronal mass ejection (ICME) by PSP may arise during close solar flybys (<0.1 au). During these
times, the same magnetic flux rope inside an ICME could be observed in situ by PSP twice, by impacting its frontal
part as well as its leg. Investigating the odds of this situation, we forecast the ICME rate in solar cycle 25 based on
two models for the sunspot number (SSN): (1) the forecast of an expert panel in 2019 (maximum SSN = 115), and
(2) a prediction by McIntosh et al. (2020, maximum SSN = 232). We link the SSN to the observed ICME rates in
solar cycles 23 and 24 with the Richardson and Cane list and our own ICME catalog, and calculate that between
one and seven ICMEs will be observed by PSP at heliocentric distances <0.1 au until 2025, including 1Ï
uncertainties. We then model the potential flux rope signatures of such a double-crossing event with the
semiempirical 3DCORE flux rope model, showing a telltale elevation of the radial magnetic field component BR,
and a sign reversal in the component BN normal to the solar equator compared to field rotation in the first
encounter. This holds considerable promise to determine the structure of CMEs close to their origin in the solar
corona
Intermittent turbulence, noisy fluctuations and wavy structures in the Venusian magnetosheath and wake
Recent research has shown that distinct physical regions in the Venusian
induced magnetosphere are recognizable from the variations of strength of the
magnetic field and its wave/fluctuation activity. In this paper the statistical
properties of magnetic fluctuations are investigated in the Venusian
magnetosheath and wake regions. The main goal is to identify the characteristic
scaling features of fluctuations along Venus Express (VEX) trajectory and to
understand the specific circumstances of the occurrence of different types of
scalings. For the latter task we also use the results of measurements from the
previous missions to Venus. Our main result is that the changing character of
physical interactions between the solar wind and the planetary obstacle is
leading to different types of spectral scaling in the near-Venusian space.
Noisy fluctuations are observed in the magnetosheath, wavy structures near the
terminator and in the nightside near-planet wake. Multi-scale turbulence is
observed at the magnetosheath boundary layer and near the quasi-parallel bow
shock. Magnetosheath boundary layer turbulence is associated with an average
magnetic field which is nearly aligned with the Sun-Venus line. Noisy magnetic
fluctuations are well described with the Gaussian statistics. Both
magnetosheath boundary layer and near shock turbulence statistics exhibit
non-Gaussian features and intermittency over small spatio-temporal scales. The
occurrence of turbulence near magnetosheath boundaries can be responsible for
the local heating of plasma observed by previous missions
Using Solar Orbiter as an upstream solar wind monitor for real time space weather predictions
Coronal mass ejections (CMEs) can create significant disruption to human
activities and systems on Earth, much of which can be mitigated with prior
warning of the upstream solar wind conditions. However, it is currently
extremely challenging to accurately predict the arrival time and internal
structure of a CME from coronagraph images alone. In this study, we take
advantage of a rare opportunity to use Solar Orbiter, at 0.5\,AU upstream of
Earth, as an upstream solar wind monitor. We were able to use real time science
quality magnetic field measurements, taken only 12 minutes earlier, to predict
the arrival time of a CME prior to reaching Earth. We used measurements at
Solar Orbiter to constrain an ensemble of simulation runs from the ELEvoHI
model, reducing the uncertainty in arrival time from 10.4\,hours to 2.5\,hours.
There was also an excellent agreement in the profile between Solar
Orbiter and Wind spacecraft, despite being separated by 0.5\,AU and
10 longitude. Therefore, we show that it is possible to predict not
only the arrival time of a CME, but the sub-structure of the magnetic field
within it, over a day in advance. The opportunity to use Solar Orbiter as an
upstream solar wind monitor will repeat once a year, which should further help
assess the efficacy upstream in-situ measurements in real time space weather
forecasting
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