Energetic Particle Population in the Heliosphere

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Dictionary of Geophysics, Astrophysic, and Astronomy.pdf

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				energetic storm particles
	Energetic Particle Population in the Heliosphere

Popu-	temporal	spatial	energy	acceleration
lation	scales	scales	range	mechanism

GCR	continuous	global	GeV to > TeV	diffusive shock
AGCR	continuous	global	10 – 100 MeV	shock?
SEP	?	?	keV – 100 MeV	reconnection, stochastic
			selective heating, shock
ESP	days	extended	keV – 10 MeV	diffusive shock,
			shock-drift, stochastic
RII	27 days	extended	keV – 10 MeV	diffusive shock
PBSP	continuous	local	keV – MeV	diffusive shock, shock drift

with the solar cycle. The anomalous component stems from originally neutral particles which became ionized as they traveled through interplanetary space towards the sun. The now charged particles are then convected outwards with the solar wind and are accelerated at the termination shock, the outer boundary of the heliosphere.

3.Solar energetic particles (SEP) are accelerated in solar ﬂares, their injection therefore is point-like in space and time. Energies extend up to about 100 MeV, occasionally even into the GeV range. In this case, particles can also be observed from the ground (see ground level event). Properties of solar energetic particles differ, depending on whether the parent ﬂare was gradual or impulsive. See gradual ﬂare, impulsive ﬂare.

4.Energetic storm particles (ESP) are accelerated at interplanetary shocks. Originally, ESPs were thought to be particle enhancements related to the passage of an interplanetary shock. The name was chosen to reﬂect their association with the magnetic storm observed as the shock hits the Earth’s magnetosphere. Today, we understand the particle acceleration at the shock, their escape and the subsequent propagation through interplanetary space as a continuous process lasting for days to weeks until the shock ﬁnally stops accelerating particles. See energetic storm particles.

5.Recurrent intensity increases (RII) are due to particles accelerated at the shocks around corotating interaction regions (CIRs). The energetic particles can even be observed remote from these co-rotating shocks at distances where the shocks have not yet been formed or at higher solar latitudes when a spacecraft is well above the streamer belt where the CIR form. See corotating interaction region.

6. Planetary bow shock particles (PBSP) Particles accelerated at a planetary bow shock are a local particle component with energies extending up to some 10 keV. An exception is the Jovian magnetosphere where electrons are accelerated up to about 10 MeV. With a suitable magnetic connection between Earth and Jupiter, these Jovian electrons can be observed even at Earth’s orbit.

energetic storm particles Particles accelerated at an interplanetary shock. The name stems from the ﬁrst observations of shock-accelerated particles: around the time of shock passage at the Earth when the interaction between the shock and the magnetosphere caused a geomagnetic storm, an increase in particle intensities could be observed, which was termed energetic storm particles.

Originally, the term referred to a bump in the intensity on the decaying ﬂank of a solar energetic particle event. In protons up to energies of a few hundred keV, such a bump lasted for some hours around the time of shock passage. Energetic storm particles are observed only at quasi-parallel shocks, where they are accelerated by diffusive shock acceleration. At quasiperpendicular shocks, on the other hand, short shock-spikes, lasting only for some 10 min, are observed at the time of shock passage. Thus, the appearance of the shock accelerated particles strongly depends on the local angle θ Bn between the magnetic ﬁeld direction and the shock normal and the dominant acceleration mechanism related to this local geometry.

Today, the term energetic storm particles is often is used in a broader context and basically refers to the fact that part or all of the observed

energy

particles are accelerated at a traveling interplanetary shock. Such intensity increases can be observed in electrons as well as nuclei with electron increases predominately up to energies of some 10 keV or occasionally up to a few MeV and proton increases up to some MeV, at strong shocks even up to about 100 MeV.

In contrast to energies up to some hundred keV, in these higher energies no obvious dependence of the intensity time proﬁle on the local geometry, that is the angle θ Bn, can be seen and therefore no distinction in shock spikes and shock bumps related to quasi-perpendicular and quasi-parallel shocks can be observed. In the MeV range, particles are much faster than the shock and therefore easily escape from the shock front. Thus, the intensity time proﬁle at the observer’s site does not reﬂect the local properties of the shock and the associated particles but samples particles accelerated at the shock during its propagation from the sun to the observer. Thus, the intensity proﬁle can be interpreted as a superposition of particles continuously accelerated at the outward propagating shock and their subsequent propagation through interplanetary space. Since the acceleration efﬁciency of the shock changes as it propagates outward and the magnetic connection (see cobpoint) of the observer to the shock moves eastward along the shock front into regions of different acceleration efﬁciency, for different locations of the observer with respect to the shock different intensity proﬁles result. Therefore, in the MeV range, the appearance of the energetic particle event does not depend on local geometry but on the location of the observer relative to the shock. This dependence, of course, is modiﬁed by the characteristics of the shock, in particular its ability to accelerate particles and the radial and azimuthal variations of this acceleration efﬁciency.

energy Work, or the ability to do a particular amount of work. Energy is usually categorized as either kinetic (the energy of actual mass motion), or potential (stored energy, which can be used eventually to cause mass motion). Thermal energy is recognized as kinetic energy of molecular or atomic structures, i.e., it is motion on the small scale. Thermal energy can be extracted from heated systems provided there is a difference of the average molecular or atomic kinetic

energy. Such a difference is equivalent to a difference in temperature. Potential energy exists in many forms: gravitational (a rock poised at the top of a hill), electrical (an electron situated at the negative terminal of the battery). In classical electromagnetism, there is an energy associated with static electric and magnetic ﬁelds in vacuum: Energy = 21 0E2 + 21 B2/µ0, where 0 is the permittivity and µ0 is the magnetic susceptibility. The presence of polarizable materials modiﬁes these expressions by replacing the vacuum 0 by a permittivity speciﬁc to the material, and by replacing the vacuum µ0 by a value µ speciﬁc to the material. The units of energy (and work) in metric systems are ergs: 1 erg = 1 dyne · cm (the work done by moving a force of 1 dyne through a distance of 1 cm), and Joules: 1 Joule = 107 ergs. Since the unit of power is watts: 1 watt = 1J/sec, derived units of energy are often in use. For instance, the kilowatt hour = 103 watts × 3600 sec = 3.6×106J. Another energy unit is the calorie, deﬁned as the energy required to raise the temperature of 1 gm of water 1◦K from a temperature of 15◦C = 288.15K; 1 calorie = 4.18674 J. The dieting “Calorie,” properly written capitalized, is 1,000 calories. In the British system, the basic unit of work is the foot-pound. The British system unit analogous to the calorie is the British thermal unit (Btu), approximately the energy to raise 1 lb of water 1◦F. The precise relation is 1 Btu = 251.996 calories.

energy-containing scale As the energy content at scales larger than the system and below the Kolmogorov scale vanishes, the turbulent kinetic energy spectrum has a maximum. The range of the spectrum that contains the signiﬁcant part of the turbulent energy is referred to as the energy-containing scale. The aim of eddy-resolving models is to describe the turbulent ﬂow down to the resolution of the energycontaining scales in order to capture most parts of the kinetic energy of the system.

energy conversion efﬁciency In oceanography, the rate of chemical energy accumulation per unit volume divided by the rate of absorption of light energy by phytoplankton per unit volume; it is linearly related to quantum yield.

entropy

energy grade line A visual representation of the energy in a ﬂow. Indicates the sum of the velocity head, V 2/2g, elevation, and pressure head, p/γ , for the ﬂow, where V is the ﬂow speed, g is the acceleration of gravity, p is pressure, and γ is the unit weight (weight per unit volume) of the ﬂuid.

energy-momentum relations — special relativity In special relativity physical laws must be the same in reference systems moving uniformly with respect to each other; that is, they must be invariant under Lorentz Transformations. In special relativity time is not an absolute variable, and therefore special relativity is mathematically described through a fourdimensional spacetime with time as the ﬁrst coordinate in addition to the three spatial coordinates. In order for the Lorentz electromagnetic force to be incorporated into a law of mechanics that is invariant under Lorentz transformations, and for the mechanics law to also reduce to Newton’s law at low velocities, a fourcomponent relativistic momentum vector is deﬁned such that the ﬁrst component equals the energy of a given particle and the other three components equal the momentum components of the particle. Since the four-vector scalar product is invariant under Lorentz transformations, one obtains the relativistic relationship between the energy and the momentum of a particle by calculating the four-vector scalar product of the four-vector momentum with itself.

energy per unit length (cosmic string) In the framework of a cosmological model with the generation of topological defects, a cosmic string is an approximation of a vacuum vortex defect in terms of a line-like structure, conﬁned to a two-dimensional world sheet. For a complete macroscopic description (as opposed to microscopic, in terms of relevant ﬁelds like the Higgs ﬁeld and other microscopic ﬁelds coupled to it) we need to know quantities such as the string tension T and the energy per unit length U (often denoted µ in the literature). For a microscopic model, speciﬁed by its Lagrangian, we can compute its energy-momentum tensor T µν by standard methods. Given the cylindrical symmetry of the string conﬁguration, the energy

per unit length is calculated as

U = 2π rdrT tt ,

where T tt is the time-time component of the energy-momentum tensor. See equation of state (cosmic string), Goto–Nambu string, tension (cosmic string), wiggle (cosmic string).

enthalpy An extensive thermodynamic potential H given by

H = U − P V ,

where U is the internal energy, P is the pressure, and V is the volume of the system. The change of the enthalpy is the maximum work that can be extracted from a reversible closed system at constant P . For a reversible process at constant S and P , work stored as enthalpy can be recovered completely.

entrainment Jets and plumes, moving through ﬂuid at rest, have the tendency to entrain ambient ﬂuid into the ﬂow. The rate ∂Q/∂x [m2s−1], at which the volume ﬂow Q [m3s−1] increases per unit distance x [m], is called the entrainment rate. The most customary parameterization of the entrainment rate is ∂Q/∂x = ERu (Morton, 1959), where R and u are circumference and velocity of the ﬂow Q. The nondimensional proportionality factor E is called the entrainment coefﬁcient, which increases as the gradient Richardson number Ri decreases. This implies that entrainment is more efﬁcient for large velocity differences and small density differences. Often entrainment involves the transport of one substance in another, such as suspended particles in a current, or parcels of moist air in dry winds.

entropy That thermodynamic potential deﬁned by the exact differential

dS = dQ/T ,

where dQ is a reversible transfer of heat in a system, and T is the temperature at which the transfer occurs. Entropy is conceptually associated with disorder; the greater the entropy the less ordered energy is available.

environmental lapse rate

environmental lapse rate To a cloud or a rising parcel of air, the actual variation rate with height of temperature and moisture conditions in the atmosphere surrounding it. The overall average rate is a decrease of about 6.5 K/km, but the rate varies greatly from region to region, air stream to air stream, season to season. An inverse environmental lapse rate is a negative environmental lapse rate (temperature increase with height).

eolian Refers to wind-related processes or features. Wind is created when different regions of an atmosphere experience temperature and/or pressure differences, causing the atmosphere to move in an attempt to average out these differences. Wind is a major agent of erosion, reducing rocks to sand and dust and transporting the material between locations. Eolian erosional features include yardangs and ventifacts. Eolian depositional features include dunes, ergs, and loess. Eolian material can be transported by saltation, suspension, traction, or impact creep.

eon Often used in place of 1 billion (109) years.

EOP See earth orientation parameters.

Eötvös experiment Baron Loránd Eötvös measured the dependence of gravitational acceleration on the chemical composition of matter. He used a torsion pendulum to measure the difference δg of the acceleration of samples at the end of the two arms. By 1922, these measurements established to the precision δg/g 10−9 that the acceleration is independent of the chemical composition. (More recent measurements by Dicke and Braginski have improved this precision to 10−12). The Eötvös experiment provides the experimental support for the geometrical nature of the gravitational interaction, as predicted by the theory of general relativity.

epeiric sea An inland sea with limited connection to the open ocean that is shallow, typically with depths less than 250 m.

ephemeris A book or set of tables predicting the location in the sky of planets and satellites.

ephemeris time (ET) Uniform time based on seconds having the duration they did on 0.5 January 1900, since seconds based upon the Earth’s rotation generally lengthen with time (see Universal Time). Prior to 1972, accurate measurements of the motions of the moon and planets provided the best measure of time, superior to any laboratory clock. Ephemeris Time was thus deﬁned as a continuous measure of time based on these motions, although, technically, its deﬁnition rested on Simon Newcomb’s theory of the motion of the sun. Ephemeris Time, which came into usage in 1956, was replaced by Dynamical Time in 1984. The two systems coexisted from 1977 to 1984. Ephemeris Time was used, in the obvious way, as the basis of the ephemeris second, which is the direct ancestor of the SI second; i.e., the SI second was matched as well as possible to the ephemeris second.

epicenter Point on the Earth’s surface above the initial earthquake rupture.

epicentral distance The distance of an observation point at the Earth’s surface from the epicenter of an earthquake. It is expressed either as a length S along the great circle path between the observation point and the epicenter or as an angle F = S/R, where R is the average radius of the earth.

epicycle Secondary circle along which the planet moves in the Ptolemaic (geocentric) description of the solar system. The epicycle center moves along a larger circle called the deferent. This combination can explain the retrograde motion of the planets. See deferent, geocentric, retrograde motion.

Epimetheus Moon of Saturn, also designated SXI. Discovered by Walker, Larson, and Fountain in 1978 and conﬁrmed in 1980 by Voyager 1. It is a co-orbital partner of Janus. Its orbit has an eccentricity of 0.009, an inclination of 0.34◦,

and a semimajor axis of 1.51 × 105 km. Its size is 72 × 54 × 49 km, its mass, 5.6 × 1017 kg, and

its density 0.7 g cm−3. It has a geometric albedo of 0.8, and orbits Saturn once every 0.694 Earth days.

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