scholarly journals Enhanced Radio Source Scintillation due to Comet Austin (1989c1)

1991 ◽  
Vol 44 (5) ◽  
pp. 565 ◽  
Author(s):  
P Janardhan ◽  
SK Alurkar ◽  
AD Bobra ◽  
OB Slee
Keyword(s):  
Solar Wind ◽  
Radio Source ◽  
Electron Density ◽  
Density Variation ◽  
Scintillation Index ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
Electron Density Variation ◽  
Comet Halley

Enhanced scintillations in the direction of the quasar 2204+29 (3C441) were observed on 13 May 1990 when the tail of Comet Austin passed in front of it. Comparison with previous observations at 103, 327 and 408 MHz of Comet Halley and at 408 MHz of Comet Wilson show that proper occultation geometry is essential for observing enhanced scintillations. It has been shown that the solar elongation ? during such observations should be large, typically greater than 60� and in no case less than 30� at 103 MHz. At the time of the occultation the scintillation index (r.m.s./mean source flux) was greater than that expected for this source by a factor of 3. The r.m.s. electron density variation /IN, at a distance of 0�9 A.U. from the sun and 7�3� downstream of the nucleus, was found to be 6 cm-3 as compared with 1 cm-3 for the normal solar wind at 1 A.U. The corresponding scale sizes of the turbulence were found to be much finer than normally found in interplanetary scintillation (IPS) caused by the solar wind.

scholarly journals Radio Source Scintillations Through Comet Tails Revisited: Comet Wilson (1987)

1990 ◽  
Vol 43 (6) ◽  
pp. 801 ◽  
Author(s):  
OB Slee ◽  
AD Bobra ◽  
D Waldron ◽  
J Lim
Keyword(s):  
Solar Wind ◽  
Transition Region ◽  
Large Scale ◽  
Fold Increase ◽  
Density Variation ◽  
Scintillation Index ◽  
Small Scale ◽  
Negative Results ◽  
Electron Density Variation ◽  
Scale Turbulence

Observations of the quasars 0606-795 and 0637-752 as the tail of Comet Wilson swept across them on May 1 and May 2, 1987, showed a three-fold increase in scintillation index over that of nearby compact radio sources outside the tail. Two scintillation regimes have been identified: (1) small-scale turbulence of 10-40 km develops near the tail-axis; (2) large-scale turbulence of 90-350 km is present in the off-axis transition region between the tail plasma and solar wind. At a distance 0�12 AU downstream from the nucleus the r.m.s. electron-density variation in these turbules is 4-8 cm-3 on axis and 0�8-1� 7 cm-3 in the transition region between the tail and the solar wind. The reported negative results from earlier comets are shown to be of doubtful significance.

Preliminary Observations of the Effects of a Corotating Stream on Interplanetary Scintillation

1968 ◽  
Vol 1 (4) ◽  
pp. 142-145 ◽  
Author(s):  
P. A. Dennison ◽  
M. Wiseman
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Sunspot Number ◽  
Interplanetary Medium ◽  
Scintillation Index ◽  
Small Scale ◽  
Flare Activity ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
Valuable Method

Since its discovery in 1964, interplanetary scintillation has become recognized as a valuable method for investigating the solar wind and the small-scale structure of the interplanetary medium. A particular advantage of the method lies in the ability to study those regions of the medium outside the plane of the ecliptic. To date little has been written about the relation between interplanetary scintillation and solar activity, although regular observations of the source 3C48 during 1965-6 have indicated that a small correlation may exist between the scintillation index and sunspot number. It also appears that anomalous increases in the scintillation index are, on occasion, related to strong flare activity on the Sun.

scholarly journals EISCAT measurements of solar wind velocity and the associated level of interplanetary scintillation

2002 ◽  
Vol 20 (9) ◽  
pp. 1279-1289 ◽  
Author(s):  
R. A. Fallows ◽  
P. J. S. Williams ◽  
A. R. Breen
Keyword(s):  
Solar Wind ◽  
Wind Velocity ◽  
Solar Wind Velocity ◽  
Solar Wind Plasma ◽  
Scintillation Index ◽  
Line Of Sight ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
Interplanetary Physics ◽  
Eiscat Measurements

Abstract. A relative scintillation index can be derived from EISCAT observations of Interplanetary Scintillation (IPS) usually used to study the solar wind velocity. This provides an ideal opportunity to compare reliable measurements of the solar wind velocity derived for a number of points along the line-of-sight with measurements of the overall level of scintillation. By selecting those occasions where either slow- or fast-stream scattering was dominant, it is shown that at distances from the Sun greater than 30 RS , in both cases the scintillation index fell with increasing distance as a simple power law, typically as R-1.7. The level of scintillation for slow-stream scattering is found to be 2.3 times the level for fast-stream scattering.Key words. Interplanetary physics (solar wind plasma)

scholarly journals Power Spectral Analysis of Enhanced Scintillation of Quasar 3C459 Due to Comet Halley

1992 ◽  
Vol 45 (1) ◽  
pp. 115 ◽  
Author(s):  
P Janardhan ◽  
SK Alurkar ◽  
AD Bobra ◽  
OB Slee ◽  
D Waldron
Keyword(s):  
Solar Wind ◽  
Spectral Analysis ◽  
Power Spectral Analysis ◽  
Density Variation ◽  
Scale Size ◽  
Power Spectral ◽  
Plasma Tail ◽  
Halley's Comet ◽  
Electron Density Variation ◽  
Comet Halley

The radio source 2314+038 (3C459) showed enhanced scintillations on three days at a solar elongation of about 90� as the plasma tail of Halley's Comet swept across it on six days during 16-21 December 1985. If we assume that the plasma velocities in the tail were not constant everywhere, but increased linearly from about 50 kms-1 at the tail axis to the normal average solar wind velocity of 400 kms-1 at the edges where the tail merged with the solar wind, a power spectral analysis of the scintillations shows two ranges of the rms electron density variation t:..N and scale size a. In particular, these are a fine scale zone near the axis where a is in the range 9 to 27 km and t:..N in the range 2 to 5 cm -3 and a zone near the edges with a and t:..N in the ranges 100 to 265 km and 0�4 to 0�8 cm-3 respectively. The assumption of a single velocity of 100 kms-1 throughout the tail shows similar fine scales near the tail axis and large scales near the edges. The scale sizes in that case range from about 18 km at the axis to about 70 km at the edges, corresponding to t:..N of 3�3 and 0�85 cm-3 respectively. A comparison with the results obtained by Slee et al. (1987) shows that there is no radial variation of t:..N. The tail-lag is seen to playa crucial role in determining the correct occulting geometry and the path of the source through the tail.

A Biological System Producing a Self-Assembling Cholesteric Protein Liquid Crystal

1971 ◽  
Vol 8 (1) ◽  
pp. 93-109
Author(s):  
A. C. NEVILLE ◽  
B. M. LUKE
Keyword(s):  
Liquid Crystal ◽  
Electron Density ◽  
Electron Micrographs ◽  
Self Assembly ◽  
Liquid Crystalline ◽  
Density Variation ◽  
Self Assembling ◽  
The Matrix ◽  
Electron Density Variation ◽  
Helicoidal Structure

The protein in the oothecal glands of praying mantids (Sphodromantis tenuidentata, Miomantis monacha) exists in the form of lamellar liquid crystalline spherulites, which coalesce as they flow out of a punctured gland tubule. Electron micrographs of sections of these spherulites after fixation show parabolic patterns of an electron-light component, set in a continuous matrix of protein. Such patterns arise in helicoidal systems (e.g. arthropod cuticle) and microdensitometric scans of the matrix show a rhythmical electron-density variation consistent with helicoidal structure. Double spiral patterns identical to those seen in liquid crystal spherulites are illustrated. These properties resemble those of cholesteric liquid crystals. The constructional units appear to be molecular rather than fibrillar as described by previous authors. The helicoidal architecture arises by self-assembly in the gland lumen. Lamellar surface structures self-assembled spontaneously on glass coverslips when the protein was left to stand for several days. When heated to 55 °C, the birefringent liquid crystalline protein abruptly changes to an isotropic gel, with associated loss of parabolic patterning in electron micrographs and of the rhythmical electron-density variation on microdensitometric scans. This behaviour is compared to the formation of gelatin from collagen, in terms of the randomization of an originally ordered secondary structure.

scholarly journals Investigation of the Electron Density Variation During the 21 August 2017 Solar Eclipse

2018 ◽  
Vol 45 (3) ◽  
pp. 1253-1261 ◽  
Author(s):  
B. W. Reinisch ◽  
P. B. Dandenault ◽  
I. A. Galkin ◽  
R. Hamel ◽  
P. G. Richards
Keyword(s):  
Electron Density ◽  
Solar Eclipse ◽  
Density Variation ◽  
Electron Density Variation

scholarly journals Interplanetary Scintillation - Preliminary Observations at 103 MHz

1980 ◽  
Vol 91 ◽  
pp. 405-408
Author(s):  
S. K. Alurkar ◽  
R. V. Bhonsle
Keyword(s):  
Solar Wind ◽  
Solar Wind Plasma ◽  
Scintillation Index ◽  
Interplanetary Scintillation ◽  
Antenna Aperture ◽  
Scale Size ◽  
Intensity Fluctuations

A 3-station interplanetary scintillation (IPS) observatory is being developed mainly with a view to study the solar wind plasma. The first IPS telescope operating at 103 MHz at Thaltej near Ahmedabad has been put into regular operation since April 1979. With only half the antenna aperture (≃2500 m2) presently in use, observations of 8-10 sources are being made to calculate scintillation index, temporal spectrum of intensity fluctuations and scale size of density irregularities.

scholarly journals EISCAT measurements of the solar wind

1996 ◽  
Vol 14 (12) ◽  
pp. 1235-1245 ◽  
Author(s):  
A. R. Breen ◽  
W. A. Coles ◽  
R. R. Grall ◽  
M. T. Klinglesmith ◽  
J. Markkanen ◽  
...  
Keyword(s):  
Solar Wind ◽  
Slow Solar Wind ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
Final Velocity ◽  
Flow Vector ◽  
Fast Wind ◽  
Interaction Regions ◽  
Slow Wind ◽  
Eiscat Measurements

Abstract. EISCAT observations of interplanetary scintillation have been used to measure the velocity of the solar wind at distances between 15 and 130 R⊙ (solar radii) from the Sun. The results show that the solar wind consists of two distinct components, a fast stream with a velocity of ~800 km s–1 and a slow stream at ~400 km s–1. The fast stream appears to reach its final velocity much closer to the Sun than expected. The results presented here suggest that this is also true for the slow solar wind. Away from interaction regions the flow vector of the solar wind is purely radial to the Sun. Observations have been made of fast wind/slow wind interactions which show enhanced levels of scintillation in compression regions.

scholarly journals Observations of interplanetary scintillation in China

2012 ◽  
Vol 8 (S294) ◽  
pp. 487-488
Author(s):  
Li-Jia Liu ◽  
Bo Peng
Keyword(s):  
Solar Wind ◽  
Interplanetary Medium ◽  
Interplanetary Space ◽  
Solar Wind Speed ◽  
Small Diameter ◽  
Primary Source ◽  
Radio Sources ◽  
The Sun ◽  
Interplanetary Scintillation ◽  
The Earth

AbstractThe Sun affects the Earth in multiple ways. In particular, the material in interplanetary space comes from coronal expansion in the form of solar wind, which is the primary source of the interplanetary medium. Ground-based Interplanetary Scintillation (IPS) observations are an important and effective method for measuring solar wind speed and the structures of small diameter radio sources. In this paper we will discuss the IPS observations in China.

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