Interplanetary Medium

Owing to our dependance on spaceborne technology, an awareness of disturbances in the near-Earth space environment is proving to be increasingly crucial. Earth-directed Coronal mass ejections (CMEs) emanating from the
Sun are the primary drivers of space weather disturbances. Studies of CMEs, their kinematics, and their near-Earth effects are therefore gaining in importance.

The effect of CMEs near the Earth is often manifested as transient decreases in galactic cosmic ray intensity, which are called Forbush decreases (FDs). In this thesis we probe the structure of CMEs and their associated shocks using FD observations by the GRAPES-3 muon telescope at Ooty. We have established that the cumulative diffusion of galactic cosmic rays into the CME is the dominant mechanism for causing FDs (Chapter 3).

This diffusion takes place through a turbulent sheath region between the CME and the shock. One of our main results concerns the turbulence level in this region. We have quantitatively established that cross-field diffusion aided by magnetic field turbulence accounts for the observed lag between the FD and the magnetic field enhancement of the sheath region (Chapter 4).

We have also investigated the nature of the driving forces acting on CMEs in this thesis. Using CME data from the SECCHI coronagraphs aboard STEREO sapcecraft, we have found evidence for the non-force-free nature of the magnetic field configuration inside these CMEs, which is the basis for
the (often-invoked) Lorentz self-force driving (Chapter 5).

Taken together the work presented in this thesis is a comprehensive attempt to characterise CME propagation from typical coronagraph fields of view to the Earth.

The main data on observations of the Sun, interplanetary medium, and magnetosphere, obtained mainly by home researchers during the strongest magnetic storm of November 20, 2003 (Dst=-472 nT), are presented in the work. This period corresponds ...

We have developed a new three-dimensional magnetohydrodynamic (MHD) solar wind model coupled to the Space Weather Modeling Framework (SWMF) that solves for the different electron and proton temperatures. The collisions between the electrons and protons are taken into account as well as the anisotropic thermal heat conduction of the electrons. The solar wind is assumed to be accelerated by the Alfvén waves. In this paper, we do not consider the heating of closed magnetic loops and helmet streamers but do address the heating of the protons by the Kolmogorov dissipation of the Alfvén waves in open field-line regions. The inner boundary conditions for this solar wind model are obtained from observations and an empirical model. The Wang-Sheeley-Arge model is used to determine the Alfvén wave energy density at the inner boundary. The electron density and temperature at the inner boundary are obtained from the differential emission measure tomography applied to the extreme-ultraviolet images of the STEREO A and B spacecraft. This new solar wind model is validated for solar minimum Carrington rotation 2077 (2008 November 20 through December 17). Due to the very low activity during this rotation, this time period is suitable for comparing the simulated corotating interaction regions (CIRs) with in situ ACE/WIND data. Although we do not capture all MHD variables perfectly, we do find that the time of occurrence and the density of CIRs are better predicted than by our previous semi-empirical wind model in the SWMF that was based on a spatially reduced adiabatic index to account for the plasma heating.

In this work we study the temporal variation of the heliospheric termination shock radius using in-ecliptic combined measurements from different spacecraft at 1 AU near the Earth. The results show that the radius of the heliospheric termination shock varies in time with a period of 11 years. During some 11-year time periods the shock radius anti-correlates with the solar cycle activity, specifically with the sunspot number. The average radius is approximately 115 AU with minimum value ∼ 80 AU and maximum value ∼150 AU. These values are the upper limits since we do not take into account the charge exchange effects of solar wind with the interstellar neutrals. We also compare the results with those from other spacecraft (Helios 1 and Voyager 2). We find that Helios 1 measurements give almost the same result as the one obtained from measurements at 1 AU while Voyager 2 measurements give a heliospheric termination shock radius approximately 15 AU lower.

AbstractDuring the Earth swing-by of the Cassini spacecraft, a worldwide program of data-gathering was undertaken to define the prevailing interplanetary and geophysical conditions. This included observations of the interplanetary medium, outer magnetosphere, geostationary orbit, UV aurora, geomagnetic disturbance, and ionospheric flow. These data show that during the Cassini outbound passage through the geomagnetic tail the magnetosphere underwent two complete “classic” substorm cycles. The global data are used to set the Cassini data into a context which allows a much fuller interpretation. The pass took place through the dawn tail, where previous Geotail observations indicate that the plasma sheet usually remains ‘stationary’ at expansion phase onset. Reconnection and plasmoid formation are typically dusk and midnight phenomena. The Cassini observations nevertheless show a marked response of the plasma sheet both to the growth phase (thinning), and expansion phase onset (expansion without heating). Subsequent impulsive expansion of the substorm into the Cassini sector, however, resulted in the prompt appearance of reconnection-related phenomena (earthward flowing plasma and strongly disturbed fields), though the spacecraft footprint remained poleward of the intense UV auroras. Due to continuing strong southward-directed IMF during the expansion phases, a quasi-equilibrium appears to have formed between dayside and near-Earth nightside reconnection for ∼30 min after onset. Auroral zone recovery began about ∼10 min after a northward turn of the interplanetary magnetic field (IMF) to nearer-zero values in each case. A net closure of open flux then ensued, leading to deflation of the tail lobe field, ‘dipolarization’ of the near-Earth tail plasma sheet field, simultaneous reduction in the earthward plasma sheet flow and the flow in the nightside ionosphere, and displacement of the ground-based disturbance to high latitudes.

Cambridge Atmospheric and Space Science Series Physics of the Space Environment Tamas I. Gombosi ... Physics of the Space Environment This book provides a comprehensive introduction to the physical phenomena that result from the interaction of the Sun and the planets - ...

Major solar eruptive events consisting of both a large flare and a near simultaneous large fast coronal mass ejection (CME), are the most powerful explosions and also the most powerful and energetic particle accelerators in the solar system, producing solar energetic particles (SEPs) up to tens of GeV for ions and 10s-100s of MeV for electrons. The intense fluxes of escaping SEPs are a major hazard for humans in space and for spacecraft. Furthermore, the solar plasma ejected at high speed in the fast CME completely restructures the interplanetary medium, producing the most extreme space weather in geospace, at other planets, and in the heliosphere. Thus, the understanding of the flare/CME energy release process and of the related particle acceleration processes in SEEs is a major goal in Heliophysics. Here we present a concept for a Solar Eruptive Events (SEE) mission, consisting of a comprehensive set of advanced new instruments on the single spacecraft in low Earth orbit, that foc...

Commission 49 covers research on the solar wind, shocks and particle acceleration, both transient and steady-state, e.g., corotating, structures within the heliosphere, and the termination shock and boundary of the heliosphere. During the last three years there was considerable progress made in studies of solar energetic particles, compositional and other signatures in the heliosphere, solar wind pickup ions, the termination shock, which was finally crossed by a spacecraft, and the boundary between the heliosphere and interstellar medium, and in solar wind modeling and space weather. These topics have been summarized here in five articles, each with extensive references that will guide the reader who wants further details. Observations from the following spacecraft have extensively used during this period: Ulysses, Cassini, Voyager 1 and 2, MESSENGER, ACE, Genesis, SOHO, Wind, and RHESSI.

Fast CME/shocks propagating in the interplane-tary medium can generate kilometric Type II (km-TII) radioemissions at the local plasma frequency and/or its harmonic,so these radio emissions provide a means of remotely track-ing CME/shocks. We apply a new analysis technique, us-ing the frequency drift of km-TII spectrum obtained by theThermal Noise Receiver (TNR) of the WIND/WAVES exper-iment, to infer, at some adequate intervals, the propagationspeed of six CME/shocks. We combine these results withpreviously reported speeds from coronagraph white lightand interplanetary scintillation observations, and in-situ mea-surements, to study the temporal speed evolution of the sixevents. The speed values obtained by the km-TII analysis arein a reasonable agreement with the speed measurements ob-tained by other techniques at different heliocentric distanceranges. The combination of all the speed measurements showa gradual deceleration of the CME/shocks as they propagateto 1AU. This new technique can be useful in studying theevolution of fast CME/shocks when adequate intervals ofkm-TII emissions are available.

We study the propagation of coronal mass ejections (CMES) from near the Sun to 1 AU by comparing results from two different models: a 1-D, hydrodynamic, single-fluid, numerical model (González-Esparza et al., 2003a) and an analytical model to study the dynamical evolution of supersonic velocity's fluctuations at the base of the solar wind applied to the propagation of CMES (Cantó et al., 2002). Both models predict that a fast CME moves initially in the inner heliosphere with a quasi-constant velocity (which has an intermediate value between the initial CME velocity and the ambient solar wind velocity ahead) until a `critical distance' at which the CME velocity begins to decelerate approaching to the ambient solar wind velocity. This critical distance depends on the characteristics of the CME (initial velocity, density and temperature) as well as of the ambient solar wind. Given typical parameters based on observations, this critical distance can vary from 0.3 to beyond 1 AU from the Sun. These results explain the radial evolution of the velocity of fast CMEs in the inner heliosphere inferred from interplanetary scintillation (IPS) observations (Manoharan et al., 2001, 2003, Tokumaru et al., 2003). On the other hand, the numerical results show that a fast CME and its associated interplanetary (IP) shock follow different heliocentric evolutions: the IP shock always propagates faster than its CME driver and the latter begins to decelerate well before the shock.

The notion that plasma shocks in astrophysical settings can and do accelerate charged particles to high energies is not a new one. However, in recent years considerable progress has been achieved in understanding the role particle acceleration plays both in astrophysics and in the shock process itself. In this paper we briefly review the history and theory of shock acceleration, paying particular attention to theories of parallel shocks which include the backreaction of accelerated particles on the shock structure. We discuss in detail the work that computer simulations, both plasma and Monte Carlo, are playing in revealing how thermal ions interact with shocks and how particle acceleration appears to be an inevitable and necessary part of the basic plasma physics that governs collisionless shocks. We briefly describe some of the outstanding problems that still confront theorists and observers in this field.

Since its switch-on in Oct. 90, the Kiel Electron Telescope onboard Ulysses has detected many quiet time increases of the flux of 3-30 MeV electrons, known to originate from Jupiter. We report on the long term variations of this flux for the Ulysses ecliptic journey, and at the beginning of the out of ecliptic phase. They are well accounted for