Physics of the Solar Corona

Shklovskii, I. S.

doi:10.1119/1.1973875

Cited by 20 publications

(26 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Observations in the wings of He at 14h19 m indicated the presence within it of Doppler shifts both + and -. Filament activity prior to the onset of a flare is a well-observed phenomenon (SMITH and RAMSEY, 1964). It should be noted that the 18 MHz record which had been undisturbed during earlier hours developed a 'noise storm' or series of many bursts at 13h30mUT and continued to be disturbed until 20h15 m UT.…”

Section: Relation Of H~ Flare-emission To Filament Activitymentioning

confidence: 99%

The proton flare of August 28, 1966

Dodson

Hedeman

1968

Sol Phys

View full text Add to dashboard Cite

The proton flare of August 28, 1966 began on Ha records at 15h21m35 ~ UT. It presented an unusually complex development with flare emission occurring in two distinct plages. The brightest part of the flare attained maximum intensity, 152 % of the continuum, between 15h30 TM and 15h32 m UT. Photometric measurements show that a long-enduring part of the flare continued to decline in intensity until at least 21h20 TM UT.The flare developed first in parts of the plages that were near the extremities of a filament and a complex system of curvilinear absorption structures, possibly an eruptive prominence in projection. During the rise to maximum intensity a large expanding feature moved southward from the site of the flare with a velocity ~ 700 km/sec. Its appearance on monochromatic records of the chromosphere made in the center of Hc~ and 0.5 A on either side was consistent with the effect of an advancing phenomenon that induces a small shift of the Hc~ absorption line, first to longer, and then to shorter wavelengths.Two bright flare-filaments were obvious aspects of the event by 15~128m and dominated the main phase of the flare. Loop-type prominences were observed in absorption as early as 15h40 m. General Description of Outbreak and Development of the H~ FlareThe proton flare of August 28, 1966 (Imp. 2B or greater, N22 E05) occurred in two well-defined plages, each with separate spot groups, and presented an unusually complex development. The first evidence of flare-emission on the He patrol films of the McMath-Hulbert Observatory (0.5 A band pass) occurred at 15h21 m35 s UT ** when a small area, region 1 in Figure 1A, on the North side of filament F ( Figure 1B) suddenly increased in intensity. Thirty seconds later another small point, region 2, directly across the filament and on the South side was also the site of flare-emission. These two initial brightenings were in the plage surrounding the dying/3 spot group (Mt. Wilson No. 16111) that preceded by approximately 15 ~ the large/37 spot (Mt. Wilson No. 16114) near which the principal He emission of this proton flare would occur. By 15h22m35 S flare-emission had started at regions 3 and 4 within the large bright plage surrounding the/~7 spot. The flare then broke out in numerous small bright points, some of which are indicated in Figure 1. Intensity increased rapidly at 15h24 TM and 15h25 m UT and maximum intensity was reached between 15h3ff n and 15h32 m UT. (See Figure 2.)The regions of enhanced emission for this flare fall naturally into two parts, the

show abstract

Section: Relation Of H~ Flare-emission To Filament Activitymentioning

confidence: 99%

The proton flare of August 28, 1966

Dodson

Hedeman

1968

Sol Phys

View full text Add to dashboard Cite

show abstract

“…The ratio n w /n e of neutral hydrogen strongly determines whether these temperature increases would be observable: if n w /n e 10 −6 , as predicted by the static, fluid ionisation balance calculations (Shklovskii 1965;Gabriel 1971;Fontenla et al 1990Fontenla et al , 1991Fontenla et al , 1993Cranmer 2000) discussed in Sections 3.1 and 3.3, then (9) predicts that LH drive will not produce observable temperature enhancements at large coronal heights. Indeed, only if n w /n e 10 −2 and v A 1000 km s −1 , would T obs increase significantly above the local temperature ≈10 6 K. Limitations to our current knowledge of n w /n e are listed in Section 3.3.…”

Section: High Coronal Reconnection Sitesmentioning

confidence: 99%

“…It appears that this question cannot be answered definitively at present. Reasons for this are: (1) Ionisation calculations for the corona (Shklovskii 1965;Gabriel 1971;Fontenla et al 1990Fontenla et al , 1991Fontenla et al , 1993Cranmer 2000), balancing collisional ionisation with radiative recombination, yield ratios n n /n e ≈ 2 × 10 −5 for T e = 10 5 K and ≈(0.1-1) × 10 −6 for T e 10 6 K. (2) The observed properties of prominences imply that significant amounts of neutral gas with T 8000 K can persist stably to such altitudes, in which case the ionisation balance calculations yield n w /n e ≈ 1 (Fontenla et al 1990(Fontenla et al , 1991(Fontenla et al , 1993, albeit without satisfactory theoretical explanation. (3) To my knowledge, kinetic calculations of ion, electron, and neutral distribution functions coupled by charge-exchange, Coulomb, and ordinary collisions, radiative ionisation and recombination do not yet exist for the transition from the collisional photosphere to the collisionless corona even in the steady state limit, let alone the nonequilibrium limit that includes the effects of spicules, magnetic activity, network evolution, multiple generations of charge-exchange, etc.…”

Section: High Coronal Acceleration Events Involving Reconnectionmentioning

confidence: 99%

“…for T e = (1-2) × 10 6 K (Shklovskii 1965;Gabriel 1971;Fontenla et al 1990Fontenla et al , 1991Fontenla et al , 1993Cranmer 2000). Moreover, since the collision frequency decreases rapidly above the photosphere, so that kinetic effects should be included rather than assuming fluid theory and very small collisional mean free paths relative to plasma scale lengths, and since the chromosphere is likely not in equilibrium due to the dynamic effects of spicules, explosive events, EUV blinkers (Harrison 1997;Harrison et al 1999), and magnetic activity, even higher levels of neutrals can be expected, at least sometimes, in these regions.…”

Section: Chromospheric and Transition Region Eventsmentioning

confidence: 99%

See 1 more Smart Citation

Lower Hybrid Drive in Solar Magnetic Reconnection Regions: Implications for Electron Acceleration and Solar Heating

Cairns

2001

Publ. – Astron. Soc. Aust

View full text Add to dashboard Cite

Lower hybrid (LH) drive involves the resonant acceleration of electrons parallel to the magnetic field by lower hybrid waves, often driven by ions with ring or ring-beam distributions. Charge-exchange between hydrogen atoms and protons with relative motions perpendicular to the magnetic field leads to ring distributions of pickup ions, with concomitant perpedicular ion ‘heating’. This paper considers the combination of LH drive and charge-exchange in the outflow regions of magnetic reconnection sites in the solar chromosphere and lower corona, showing that the combined mechanism naturally predicts major perpendicular ion heating and parallel electron acceleration, and exploring the mechanism’s relevance to specific solar reconnection phenomena, heating of the solar atmosphere, and production of energetic electrons that generate solar radio emission. Although primarily qualitative, analysis shows that the mechanism has numerous attractive aspects, including perpendicular ion heating that increases linearly with ion mass, parallel electron acceleration, predicted ion and electron temperatures that span those of the chromosphere and lower corona, and parallel electron speeds spanning those for type III bursts. Applications to chromospheric explosive events and low-lying active regions, and to heating the chromosphere, appear particularly suitable. Sweeping of plasma frozen-in to chromospheric and coronal magnetic field lines across the neutral atmosphere due to motions of sub-photospheric fields represents an obvious and important generalisation of the mechanism away from reconnection sites. The requirements that the neutrals not be strongly collisionally coupled to the plasma and that sufficient neutrals are available for charge-exchange restricts the LH drive mechanism to above the photosphere but below where the corona is essentially fully ionised. LH drive may thus be important in heating the chromosphere and low corona while other heating mechanisms dominate at higher altitudes. Although attractive thus far, quantitative analyses of LH drive in these contexts are necessary before definitive conclusions are reached.

show abstract

“…20 The computational process to invert the K-coronal brightness to derive the electron density is described in detail in Baumbach 21 and Shklovskii. 22 Van de . The dark spot on the moon is the area where the speck of dust is seen in Fig.…”

Section: Measuring the Electron Density Using The Polarization Cameramentioning

confidence: 99%

Replacing the polarizer wheel with a polarization camera to increase the temporal resolution and reduce the overall complexity of a solar coronagraph

Reginald

Gopalswamy

Yashiro

et al. 2017

J. Astron. Telesc. Instrum. Syst

View full text Add to dashboard Cite

"Replacing the polarizer wheel with a polarization camera to increase the temporal resolution and reduce the overall complexity of a solar coronagraph," J. Astron. Telesc. Instrum. Syst. 3(1), 014001 (2017), doi: 10.1117/1.JATIS.3.1.014001. Abstract. Experiments that require linearly polarized brightness measurements, traditionally have obtained three successive images through a linear polarizer that is rotated through three well-defined angles and the images are combined to get the linearly polarized brightness. This technique requires a mechanism to hold the linear polarizer in place and to precisely turn it through the three angles. Obviously, the temporal resolution is lost in such a scenario, since the three images that are used to derive the linearly polarized brightness are taken at three different times. Specifically, in a dynamic corona that is in constant reshaping of its structures, the linearly polarized brightness image produced in this manner may not yield true values all around the corona. In this regard, with the advent of the polarization camera, the linearly polarized brightness can be measured from a single image. This also eliminates the need for a linear polarizer and the associated rotator mechanisms and can contribute toward lower weight, size, power requirements, overall risk of the instrument, and most importantly, increase the temporal resolution. We evaluate the capabilities of a selected polarization camera and how these capabilities could be tested in a ground experiment conducted in conjunction with a total solar eclipse. The ground experiment requires the measurement of the linearly polarized brightness, also known as K-corona, in a corona that also contains unpolarized brightness, known as F-corona, in order to measure three important physical properties pertaining to coronal electrons, namely, the electron density, electron temperature, and the electron speed.

show abstract

Physics of the Solar Corona

Cited by 20 publications

References 0 publications

The proton flare of August 28, 1966

The proton flare of August 28, 1966

Lower Hybrid Drive in Solar Magnetic Reconnection Regions: Implications for Electron Acceleration and Solar Heating

Replacing the polarizer wheel with a polarization camera to increase the temporal resolution and reduce the overall complexity of a solar coronagraph

Contact Info

Product

Resources

About