Plasmas/Plasma objects

Representation of upper-atmospheric lightning and electrical-discharge phenomena are displayed. Credit: Abestrobi.{{free media}}

A plasma object may be simply an object consisting of mobile charged particles. The percentage of neutral particles is often ignored.

Plasmas

Plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms (reduce or increase the number of electrons in them), thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions.

For plasma to exist, ionization is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e., response to magnetic fields and high electrical conductivity). The degree of ionization, α is defined as α = n_i/(n_i + n_a) where n_i is the number density of ions and n_a is the number density of neutral atoms. The electron density is related to this by the average charge state <Z> of the ions through n_e = <Z> n_i where n_e is the number density of electrons.

"Plasma is the fourth state of matter, consisting of electrons, ions and neutral atoms, usually at temperatures above 10⁴ degrees Kelvin." "The sun and stars are plasmas; the earth's ionosphere, Van Allen belts, magnetosphere, etc., are all plasmas. Indeed, plasma makes up much of the known matter in the universe."

Elves

"A third phenomenon was discovered in video from the STS-41 mission (October 1990) in the lower ionosphere directly above an active thunderstorm. It consisted of a large horizontal brightening several hundred kilometers across at the altitude of the airglow layer. In 1995, Lyons and associates confirmed the existence of this type of very brief brightening which they named Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources (ELVES)."

"When the lightning phenomena were viewed from a different vantage point - from above the thunderstorms (e.g., from space, aircraft or mountaintop) - new discoveries were made and insights gained into the upper atmospheric optical flashes now commonly referred to as sprites, jets, starters, and ELVES."

"There are no historical reports from eyewitnesses describing the phenomenon that is now called "Emission of Light and Very Low Frequency Perturbations From Electro-magnetic Pulse Sources" or ELVES (Lyons and Nelson, 1995). The one millisecond lifetime of this phenomenon explains why there have been no eyewitness accounts describing a brief flash that would fill the entire night sky for any observer within a 100 km radius from the causative lightning flash. Inan (1990) and Inan et al. (1991) predicted the existence of strong Joule heating of the base of the ionosphere by the electromagnetic pulses of natural lightning."

"After fifteen sprites and one jet had been identified in the shuttle video, a distinctively different event was discovered in shuttle video acquired on October 7, 1990 directly above an active thunderstorm off the coast of French Guyana (Boeck et al., 1992). A large horizontal flash appeared at the altitude of the airglow layer. It occurred in the video field before the appearance of main lightning flash in a thunderstorm that was near the limb of the Earth. They concluded that the causative lightning flash occurred slightly after the video scan passed the location of the storm image. There was a clear view of the mesosphere below the airglow layer, but there was no indication of a sprite in the video sequence (although a sprite event was captured 4½ hours earlier under similar moonlight conditions). A search of the shuttle video failed to produce a second example of this type of horizontal flash. Since it was clear that this was not an example of a sprite or a jet, the observations were published on the basis of this single example. The video was presented at the 1991 Spring AGU meeting (Boeck et al., 1991a) as well as at the Aerospace Lightning Conference (Boeck et al., 1991b). To promote a better understanding of these new phenomena as seen from space, Vaughan distributed a number of video tapes to various researchers who had express an interest in the phenomena. Seminars based on the video tape observations were given at Los Alamos National Laboratory and Stanford University. Researchers at both of these institutions have made major contributions to the theory of Sprite and ELVES phenomena."

"Several years passed before there was a second successful measurement of the ELVES phenomenon. On June 23, 1995 Lyons et al. (1995) and Fukunishi et al. (1996) confirmed the existence of a flash similar to the airglow flash seen earlier in the shuttle data, and Lyons et al. (1995) gave it the name Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources (ELVES). Lyons presented video images captured by a low-light-level TV camera sited near Ft. Collins, Colorado. The ELVES phenomenon has a characteristic event duration of one millisecond (Fukunishi, 1996)."

Sprites

This is the first color image of a sprite. Credit: Eastview.{{free media}}

"The phenomenon, now known as a sprite, was first accidently documented on ground based videotape recordings on the night of July 6, 1989. Video observations from the space shuttle acquired from 1989 through 1991 provided 17 additional examples to confirm the existence of the sprites phenomenon."

"Throughout the historical scientific literature, there are sprinklings of eyewitness accounts of unusual "lightning" observed in the clear air above nighttime thunderstorms. The descriptions use phases such as "continuous darts of light... ascended to a considerable altitude, resembling rockets more than lightning." (MacKenzie and Toynbee, 1886), "a luminous trail shot up to 15 degrees or so, about as fast as, or faster than, a rocket" (Everett, 1903), "a long weak streamer of a reddish hue" (Malan, 1937), "flames appearing to rise from the top of the cloud" (Ashmore, 1950), or "the discharge assumed a shape similar to roots of a tree in an inverted position" (Wood, 1951). Partly because these eyewitness reports of unusual "lightning" appearing above thunderstorms were never captured on film, the lightning science community generally ignored them. The lack of an established vocabulary and the existence of several distinctive phenomena contributed to the variation in the verbal descriptions."

"[Boccippio et al., 1994] has shown that these bright discharges are associated with large amplitude return strokes bringing positive charge downward. In fact, a positive return stroke accompanied the only MLE sprite recorded within range of a ground based lightning detection network. The videos showed that additional discharges continued in the clouds after a sprite for a total mean time of a second, which can be interpreted as evidence for a continuing current. All together, this was strong evidence that the sprite above the thunderstorm was caused, directly or indirectly, by an energetic lightning discharge."

The "range to the sprites was well over 1000 kilometers [...] The width of the sprites varied considerably from very thin or even several thin filaments to broad columns some kilometers across, while the bright "head" (when visible) had dimensions on the order of kilometers."

"The optical and RF measurements collected during the 1994 field campaign rapidly uncovered the basic properties of sprites (Lyons, 1994; Lyons and Williams, 1994; Lyons et al., 1994; Sentman et al., 1994; Sentman et al., 1995; Wescott et al., 1994; Lyons et al., 1995a,b). Other workers (e.g., Boccippio, 1994) established the causal association of sprites with positive cloud-to-ground lightning discharges."

Sprites "are typically associated with low flash rate cells [...] The shuttle videos established that lightning directly or indirectly causes sprites."

The first "color image of a sprite [...] was obtained during a 1994 NASA/University of Alaska aircraft campaign to study sprites. The event was captured using an intensified color TV camera. The red color was subsequently determined to be from nitrogen fluorescent emissions excited by a lightning stroke in the underlying thunderstorm."

Blue jets

"In the summer of 1994, Wescott and associates (Wescott et al., 1994; Wescott et al., 1995a,b) confirmed the existence of jets and named the phenomena blue jets when they recorded a very active thunderstorm in Arkansas, USA using both a low-light-level monochrome and a color video cameras. The video was collected during a nighttime research flight using two aircraft that were flying around the thunderstorm. During this flight, color video imagery established that jets are blue in color and sprites are red. A total of 52 jets were seen during a 20-minute time span. The jets developed over several video frames, with a characteristic time of the order of 100 ms and propagation speeds similar to that of a step leader process (i.e., ~ 105 m/s). The video released after this flight proved to be a turning point in establishing wide interest in these phenomena. The spectacular multiple close-up images of these jets completely overshadowed the single, poorly resolved jet observation from the space shuttle."

Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. In addition, whereas red sprites tend to be associated with significant lightning strikes, blue jets do not appear to be directly triggered by lightning (they do, however, appear to relate to strong hail activity in thunderstorms). They are also brighter than sprites and, as implied by their name, are blue in color. The color is believed to be due to a set of blue and near-ultraviolet emission lines from neutral and ionized molecular nitrogen.

Blue starters

Blue "starters (Wescott et al., 1995) [are] an upward moving luminous phenomenon closely related to blue jets."

Gigantic jets

This is a gigantic jet observed over a thunderstorm. Credit: Welias.{{free media}}

File:Gigantic jet near Phillipines.png

This is an image of a gigantic jet above a thunderstorm near the Philippines. Credit: H. T. Su, R. R. Hsu, A. B. Chen, Y. C. Wang, W. S. Hsiao, W. C. Lai, L. C. Lee, M. Sato & H. Fukunishi.{{fairuse}}

"On February 02, 2014, the Oro Verde Observatory (República Argentina) reported 10 or more gigantic jet event[s] observed over a thunderstorm in Entre Ríos south. Storm center [is] located at 33°S, 60°W, near the Rosario city."

Each gigantic "jet could transfer 30 coulombs of negative charge from the clouds to the ionosphere (H T Su et al. 2003 Nature 423 974)."

"During a thunderstorm in the South China Sea in July 2002, Su and co-workers used low-light-level cameras to photograph the clouds every 17 milliseconds. The five jets they observed - dubbed carrot-jets or tree-jets according to their shapes - were visible for some tens of milliseconds. But crucially, the team also detected simultaneous bursts of radio waves in four of the five cases, which indicates that the jets had transferred significant amounts of charge. The thunderclouds were at an altitude of 16 km."

"Such electromagnetic bursts have only previously been linked with powerful lightning strikes, which are known to transfer large quantities of charge. But [lightning may not have] triggered the radio waves they detected, since the local lightning detection network registered no strikes at the times of the jets."

On the left is an image of a fully developed gigantic jet above a thunderstorm near the Philippine.

Theoretical plasma objects

Def. a "state of matter consisting of [partially] fully ionized gas" is called a plasma.

Def. an ionized gas consisting of positive ions and free electrons in proportions resulting in more or less no overall electric charge is called a plasma.

Def. an object consisting of particles in which > 50 % are ions and electrons is called a plasma object.

It "is possible to virtually stop and maintain a slow, (many Hubble times!) steady collapse of a compact physical plasma object outside of its Schwarzschild radius with photon pressure generated by synchrotron radiation from an equipartition surface magnetic field. To control the rate of collapse, the object must radiate at the local Eddington limit, but from a highly redshifted surface. [...] There is recent evidence for the presence of such extreme magnetic fields in gravitational collapse. Equipartition magnetic fields have been implicated as the driver of GRB 021206 [Coburn & Boggs 2003] and fields much in excess of those expected from mere flux compression during stellar collapse have been found in magnetars [Ibrahim, Swank & Parke 2003]. Kluzniak and Ruderman [1998] have described the generation of ∼ 10¹⁷ G magnetic fields via differential rotation in neutron stars."

Neutrals

Main resources: Radiation astronomy/Neutrals and Neutrals astronomy

A hot plasma ion 'steals' charge from a cold neutral atom to become an Energetic Neutral Atom (ENA). Credit Mike Gruntman.{{free media}}

The ENA leaves the charge exchange in a straight line with the velocity of the original plasma ion. Credit: Mike Gruntman.{{free media}}

"In 1951, prior to the Space Age, the existence of energetic neutral hydrogen atoms (as high as 70 keV in energy) in space plasma was discovered."

"ENA imaging permits study of the ways in which our entire plasma environment -- including the magnetopause, ring current, plasmasphere, auroral zones, plasma sheet, and the ionosphere -- reacts to the changing conditions of the solar wind (Williams, 1990)."

X-rays

Main resources: Radiation astronomy/X-rays and X-ray astronomy

File:The bay Perseus galaxy cluster.jpg

A wave of hot gas twice as wide as the Milky Way galaxy called "the bay" (ovaled) roils the nearby Perseus galaxy cluster. Credit: Stephen Walker et al./NASA Goddard Space Flight Center.{{fairuse}}

"The wave [of hot gas ovaled in the image on the right], which measures 200,000 light-years across, likely formed billions of years ago, after a neighboring cluster clipped Perseus."

"Most of the observable matter within galaxy clusters is superheated gas that glows in X-ray wavelengths."

"The bay generates no emissions, so — unlike some other features in the massive gas field — its origins don't trace back to activity of the supermassive black hole at the core of Perseus' central galaxy, NGC 1275."

"And the bay's shape doesn't match those predicted by computer models that simulate normal gas sloshing."

"Galaxy cluster mergers represent the latest stage of structure formation in the cosmos."

"Hydrodynamic simulations of merging clusters allow us to produce features in the hot gas and tune physical parameters, such as the magnetic field."

"Then we can attempt to match the detailed characteristics of the structures we observe in X-rays."

"We think the bay feature we see in Perseus is part of a Kelvin-Helmholtz wave, perhaps the largest one yet identified, that formed in much the same way as the simulation shows."

"We have also identified similar features in two other galaxy clusters, Centaurus and Abell 1795."

Dominant group

Main resource: Dominant group

A magnetohydrodynamics (MHD) and chemical comet-coma model is applied to describe and analyze the plasma flow, magnetic field, and ion abundances in Comet Halley. A comparison of model results is made with the data from the Giotto mission.

"In the second dominant group of ions we generally see more discrepancies in the model and the HIS data".

The principal application of the dominant group concept is to the ion density measurements at or within 1500 km of the comet nucleus, where "the model abundances for the light ions, up to 21 amu, are in very good agreement with the 1500 km observations."

The comparison between model and measurements "generally becomes worse as one considers higher molecular masses and greater distance from the [comet] nucleus."

"In fact, observations of the volatiles in 9P/Tempel 1 indicate that the abundance ratios for most species in the ejecta are in the range of those found for the dominant group of Oort Cloud comets (Mumma et al. 2005), implying that many short-period comets maintain the components they had on leaving the trans-Neptunian region at 1 m of depth from the surface, even after numerous perihelion passages."

"In particular, the O isotopic ratios of the dominant Group 1 grains (Figure 4) are consistent both with spectroscopic observations of O-rich red giants and AGB stars (Harris & Lambert 1984) and with model calculations of dredge-up processes in these stars (labeled curve in Figure 4) (Boothroyd & Sackmann 1999, Dearborn 1992, El Eid 1994)."

"The dominant group of detectable eclipsing binaries consists of two detached main-sequence stars." "In the case of survey model 1 and a flat initial mass ratio distribution, this subgroup of systems accounts for 60% of the population of detectable eclipsing binaries." "In this exploratory study we used the BiSEPS binary population synthesis code to estimate the number of eclipsing binaries and single stars detectable in the Galactic disc by an idealised Super-WASP exoplanet transit survey."

Filaments

File:Solar filament.jpg

This solar filament, some 350,000 kilometres long, erupted from the surface of the Sun on 31 August. Credit: NASA.{{fairuse}}

"This solar filament, some 350,000 kilometres long, erupted from the surface of the Sun on 31 August. Seen in the extreme ultraviolet by NASA’s Solar Dynamics Observatory satellite, the eruption became a coronal mass ejection moving at about 1,400 kilometres per second — its particles grazed Earth’s magnetosphere several days later, sparking an auroral display."

Hypotheses

Main resource: Hypotheses

1. A plasma object has at least 2 % electrons or positive ions per total number of particles.

See also

• Lightning
• Sun