scholarly journals Drag-Based Model (DBM) Tools for Forecast of Coronal Mass Ejection Arrival Time and Speed

2021 ◽  
Vol 8 ◽  
Author(s):  
Mateja Dumbović ◽  
Jaša Čalogović ◽  
Karmen Martinić ◽  
Bojan Vršnak ◽  
Davor Sudar ◽  
...  
Keyword(s):  
Arrival Time ◽  
Single Point ◽  
Leading Edge ◽  
Observational Fact ◽  
1D Model ◽  
Self Similar ◽  
Key Aspects ◽  
Mass Ejection ◽  
Input Uncertainties ◽  
2D Model

Forecasting the arrival time of coronal mass ejections (CMEs) and their associated shocks is one of the key aspects of space weather research. One of the commonly used models is the analytical drag-based model (DBM) for heliospheric propagation of CMEs due to its simplicity and calculation speed. The DBM relies on the observational fact that slow CMEs accelerate whereas fast CMEs decelerate and is based on the concept of magnetohydrodynamic (MHD) drag, which acts to adjust the CME speed to the ambient solar wind. Although physically DBM is applicable only to the CME magnetic structure, it is often used as a proxy for shock arrival. In recent years, the DBM equation has been used in many studies to describe the propagation of CMEs and shocks with different geometries and assumptions. In this study, we provide an overview of the five DBM versions currently available and their respective tools, developed at Hvar Observatory and frequently used by researchers and forecasters (1) basic 1D DBM, a 1D model describing the propagation of a single point (i.e., the apex of the CME) or a concentric arc (where all points propagate identically); (2) advanced 2D self-similar cone DBM, a 2D model which combines basic DBM and cone geometry describing the propagation of the CME leading edge which evolves in a self-similar manner; (3) 2D flattening cone DBM, a 2D model which combines basic DBM and cone geometry describing the propagation of the CME leading edge which does not evolve in a self-similar manner; (4) DBEM, an ensemble version of the 2D flattening cone DBM which uses CME ensembles as an input; and (5) DBEMv3, an ensemble version of the 2D flattening cone DBM which creates CME ensembles based on the input uncertainties. All five versions have been tested and published in recent years and are available online or upon request. We provide an overview of these five tools, as well as of their similarities and differences, and discuss and demonstrate their application.

Microinstabilities and plasma waves at Near-Sun Solar Wind collisionless Shocks: Predictions for PSP and SO

2021 ◽  
Author(s):  
Zhongwei Yang ◽  
Shuichi Matsukiyo ◽  
Huasheng Xie ◽  
Fan Guo ◽  
Mingzhe Liu ◽  
...  
Keyword(s):  
Solar Wind ◽  
Shock Front ◽  
Leading Edge ◽  
Relativistic Electrons ◽  
Interplanetary Shocks ◽  
Particle In Cell ◽  
Drift Instability ◽  
Shock Simulation ◽  
Mass Ejection ◽  
The Impact

<p><span>Microinstabilities and waves excited at perpendicular interplanetary shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates obliquely to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. The impact of shock front rippling, Mach numbers, and dimensions on the ES wave excitation also will be discussed. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection–driven shocks in the near-Sun solar wind.</span></p>

The sheath region of April 2020 magnetic cloud and the associated energetic ions 

2021 ◽  
Author(s):  
Emilia Kilpua ◽  
Simon Good ◽  
Nina Dresing ◽  
Rami Vainio ◽  
Emma Davies ◽  
...  
Keyword(s):  
Flux Rope ◽  
Leading Edge ◽  
Heliospheric Current Sheet ◽  
Acceleration Process ◽  
Astrophysical Plasmas ◽  
Energetic Ions ◽  
Sheath Region ◽  
Open Questions ◽  
Mass Ejection

<p>Acceleration of energetic particles is a fundamental and ubiquitous mechanism in space and astrophysical plasmas. One of the open questions is the role of the sheath region behind the shock in the acceleration process. We analyze observations by Solar Orbiter, BepiColombo and the L1 spacecraft to explore the structure of a coronal mass ejection (CME)-driven sheath and its relation to enhancements of energetic ions that occurred on April 19-20, 2020. Our detailed analysis of the magnetic field, plasma and particle observations show that the enhancements were related to the Heliospheric Current Sheet crossings related to the reconnecting current sheets in the vicinity of the shock and a mini flux rope that was compressed at the leading edge of the CME ejecta. This study highlights the importance of smaller-scale sheath structures for the energization process. These structures likely formed already closer to the Sun and were swept and compressed from the upstream wind past the shock into the sheath. The upcoming observations by the recent missions (Solar Orbiter, Parker Solar Probe and BepiColombo) provide an excellent opportunity to explore further their role.  </p>

On the ratio of P-wave to S-wave corner frequencies for shallow earthquake sources

1974 ◽  
Vol 64 (4) ◽  
pp. 1159-1180 ◽  
Author(s):  
F. A. Dahlen
Keyword(s):  
Single Point ◽  
Three Dimensional ◽  
P Wave ◽  
Corner Frequency ◽  
S Wave ◽  
Earthquake Sources ◽  
Kinematical Model ◽  
Self Similar ◽  
Smooth Deceleration ◽  
Shallow Focus

abstract We construct a theoretical three-dimensional kinematical model of shallow-focus earthquake faulting in order to investigate the ratio of the P- and S-wave corner frequencies of the far-field elastic radiation. We attempt to incorporate in this model all of the important gross kinematical features which would arise if ordinary mechanical friction should be the dominant traction resisting fault motion. These features include a self-similar nucleation at a single point, a subsonic spreading of rupture away from that point, and a termination of faulting by smooth deceleration. We show that the ratio of the P-wave corner frequency to the S-wave corner frequency for any model which has these features will be less than unity at all points on the focal sphere.

scholarly journals Planar magnetic structures in coronal mass ejection-driven sheath regions

2016 ◽  
Vol 34 (2) ◽  
pp. 313-322 ◽  
Author(s):  
Erika Palmerio ◽  
Emilia K. J. Kilpua ◽  
Neel P. Savani
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Leading Edge ◽  
Formation Mechanisms ◽  
Single Plane ◽  
Magnetic Structures ◽  
Automated Method ◽  
Mass Ejection ◽  
The Magnetic Field

Abstract. Planar magnetic structures (PMSs) are periods in the solar wind during which interplanetary magnetic field vectors are nearly parallel to a single plane. One of the specific regions where PMSs have been reported are coronal mass ejection (CME)-driven sheaths. We use here an automated method to identify PMSs in 95 CME sheath regions observed in situ by the Wind and ACE spacecraft between 1997 and 2015. The occurrence and location of the PMSs are related to various shock, sheath, and CME properties. We find that PMSs are ubiquitous in CME sheaths; 85 % of the studied sheath regions had PMSs with the mean duration of 6 h. In about one-third of the cases the magnetic field vectors followed a single PMS plane that covered a significant part (at least 67 %) of the sheath region. Our analysis gives strong support for two suggested PMS formation mechanisms: the amplification and alignment of solar wind discontinuities near the CME-driven shock and the draping of the magnetic field lines around the CME ejecta. For example, we found that the shock and PMS plane normals generally coincided for the events where the PMSs occurred near the shock (68 % of the PMS plane normals near the shock were separated by less than 20° from the shock normal), while deviations were clearly larger when PMSs occurred close to the ejecta leading edge. In addition, PMSs near the shock were generally associated with lower upstream plasma beta than the cases where PMSs occurred near the leading edge of the CME. We also demonstrate that the planar parts of the sheath contain a higher amount of strong southward magnetic field than the non-planar parts, suggesting that planar sheaths are more likely to drive magnetospheric activity.

Gravity currents with residual trapping

2008 ◽  
Vol 611 ◽  
pp. 35-60 ◽  
Author(s):  
M. A. HESSE ◽  
F. M. ORR ◽  
H. A. TCHELEPI
Keyword(s):  
Scaling Law ◽  
Leading Edge ◽  
Power Laws ◽  
Gravity Currents ◽  
Sharp Interface Model ◽  
Current Volume ◽  
Residual Trapping ◽  
Self Similar ◽  
Loss Term ◽  
Structural Closure

Motivated by geological carbon dioxide (CO2) storage, we present a vertical-equilibrium sharp-interface model for the migration of immiscible gravity currents with constant residual trapping in a two-dimensional confined aquifer. The residual acts as a loss term that reduces the current volume continuously. In the limit of a horizontal aquifer, the interface shape is self-similar at early and at late times. The spreading of the current and the decay of its volume are governed by power-laws. At early times the exponent of the scaling law is independent of the residual, but at late times it decreases with increasing loss. Owing to the self-similar nature of the current the volume does not become zero, and the current continues to spread. In the hyperbolic limit, the leading edge of the current is given by a rarefaction and the trailing edge by a shock. In the presence of residual trapping, the current volume is reduced to zero in finite time. Expressions for the up-dip migration distance and the final migration time are obtained. Comparison with numerical results shows that the hyperbolic limit is a good approximation for currents with large mobility ratios even far from the hyperbolic limit. In gently sloping aquifers, the current evolution is divided into an initial near-parabolic stage, with power-law decrease of volume, and a later near-hyperbolic stage, characterized by a rapid decay of the plume volume. Our results suggest that the efficient residual trapping in dipping aquifers may allow CO2 storage in aquifers lacking structural closure, if CO2 is injected far enough from the outcrop of the aquifer.

Inviscid hypersonic flow on cusped concave surfaces

1966 ◽  
Vol 24 (1) ◽  
pp. 99-112 ◽  
Author(s):  
Philip A. Sullivan
Keyword(s):  
Shock Wave ◽  
Surface Pressure ◽  
Leading Edge ◽  
Pressure Change ◽  
Inviscid Flow ◽  
Small Region ◽  
The Body ◽  
Cubic Surface ◽  
Self Similar ◽  
Similar Solutions

An analysis of the exact equations of the inviscid flow of a perfect gas over cusped concave bodies is described. The field is examined in the limit of infinite free-stream Mach numberM∞. The slope of the shock wave in a small region adjacent to the leading edge is strongly dependent onM∞, while much further downstream the shock-wave slope is controlled primarily by the body slope. Consequently the region near the leading edge introduces into the field downstream a thin layer of gas, adjacent to the body, where the entropy is much lower than that of the gas above it. This layer is so dense that the gas velocity along it is not appreciably slowed by the pressure gradient along the body. However, it is so thin that there is little pressure change across it.The well-known self-similar solutions to the hypersonic small-disturbance equations have previously only been used to study the flow on blunted slender convex surfaces. They are known to behave singularly at the body. It is shown that there is a region on concave power-law shapes where the self-similar solutions are the correct first approximation to the exact inviscid equations in the limitM∞→ ∞; and that, further, they predict the correct first-order surface pressure.Numerical results for surface pressure from the similar solutions are presented, and comparisons are made with certain approximate theories available for more general shapes. Pressure measurements taken on a cubic surface in the Imperial College gun tunnel are presented and compared with the theoretical distributions.

Using STEREO-HI beacon data to predict CME arrival time and speed with the ELEvoHI model

2020 ◽  
Author(s):  
Maike Bauer ◽  
Tanja Amerstorfer ◽  
Jürgen Hinterreiter ◽  
Christian Möstl ◽  
Jackie A. Davies ◽  
...  
Keyword(s):  
Real Time ◽  
Coronal Mass Ejections ◽  
Arrival Time ◽  
Geomagnetic Storms ◽  
Leading Edge ◽  
Science Data ◽  
Electrical Devices ◽  
Using Data ◽  
Heliospheric Imager

<div> <div> <div> <div> <p>Coronal mass ejections (CMEs) may induce strong geomagnetic storms which have a significant impact on satellites in orbit as well as electrical devices on Earth’s surface. If we want to be able to mitigate the potentially devastating consequences which strong CMEs might have on Earth, developing models which accurately predict their arrival time is an integral step. The Ellipse Evolution model based on Heliospheric Imager observations (ELEvoHl) predicts the arrival of coronal mass ejections using data from STEREO’s HI instruments. HI data is available as high-resolution science data, which is downlinked every few days and low-resolution beacon data, which is downlinked in near real-time. Therefore, to allow for real time predictions of CME arrivals, beacon data must be used. We study different data reduction procedures to improve the quality of the measurements and compile the resulting images into time-elongation plots (J-plots). We track the leading edge of each selected CME event by hand, resulting in a series of time-elongation points which function as input for the ELEvoHI model. We compare the resulting predictions to those obtained using science data in terms of accuracy and errors of the predicted arrival time and speed.</p> </div> </div> </div> </div>

scholarly journals Non-Self-Similar Dead-Core Rate for the Fast Diffusion Equation with Dependent Coefficient

2014 ◽  
Vol 2014 ◽  
pp. 1-5
Author(s):  
Liping Zhu ◽  
Zhengce Zhang
Keyword(s):  
Diffusion Equation ◽  
Single Point ◽  
Fast Diffusion ◽  
Fast Diffusion Equation ◽  
Dead Core ◽  
Core Profile ◽  
Self Similar ◽  
Similar Solutions ◽  
Compactness Arguments ◽  
Core Problem

We consider the dead-core problem for the fast diffusion equation with spatially dependent coefficient and show that the temporal dead-core rate is non-self-similar. The proof is based on the standard compactness arguments with the uniqueness of the self-similar solutions and the precise estimates on the single-point final dead-core profile.

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