Chashei I 1 ., Glubokova 1,2 S., Glyantsev 1,2 А ., Tyul’bashev 1 , S. , Shishov 1 , V.

Interplanetary scintillation of strong sources during the descending phase near the

minimum of 23 solar activity cycle

Chashei I1., Glubokova1,2 S., Glyantsev1,2 А., Tyul’bashev1, S., Shishov1, V.

1. Pushchino Radio Astronomy Observatory2. Pushchino State University

Introduction

• Radio waves from space radio sources propagate through interplanetary plasma. The interplanetary scintillation (IPS) is fluctuation of space radio sources flux density, caused by fluctuation of interplanetary plasma density. Scintillation observations allow to derive information on solar wind spatial structure and large scale disturbances.

Introduction

• The scintillation observations are carrying out in monitoring regime by the radio telescope BSA (Big Scanning Array) of Lebedev Physical Institute from 2006 to present time. The aim is detection of large scale disturbances in the solar wind.

• Present work contains IPS data two strong scintillating radio sources 3C048 and 3C298 near the minimum of solar activity cycle 23.

• This data allow to draw some conclusions about the global solar wind structure.

• In addition this data may be used for the observations calibration of weaker radio sources.

The observations parameters

• Central frequency: 111 MHz• Wave bandwidth: 600 kHz• The effective area of the array in the zenith direction: 20 000 – 25 000 square meters.• The array beams system includes 16 beams, covering

the sky strip with width about 8 degrees in declination during 24 hours in right ascension.

• Data are related to the time interval: from Sep 2006 to March 2007 for 3C 298 and from March to Oct 2007 for 3C 48 at the descending phase near solar activity minimum.

The example of IPS record for the source 3C298

The example of IPS record for the source 3C48

Scintillation index

• The scintillation index is the r.m.s. source intensity

variance normalized to average intensity. • Here I is intensity, t is time, m is scintillation

index.

The scintillation index dependence on the elongation angle sine for 3C298

The heliolatitude dependence of the line of sight proximate

point for the source 3C298

The heliolatitude dependence of the line of sight proximate

point for the source 3C48

The scintillation index dependence on the elongation angle sine for 3C48

Power-density spectrum is Fourier transform of intensity autocorrelation function

Here I is intensity, t is time, В is autocorrelation function, М is power-density spectrum.

The power-density spectrum of the 3C298 scintillation

The power-density spectrum of the 3C48 scintillation

Solar wind velocity estimates using the width of IPS temporal spectrum

Here υ is the solar wind velocity, F0 is the spectrum break frequency, λ is the wavelength, z0 cos ε is the distance from the scattering sheet (z0 = 1 a. u. ), ε is the source elongation angle.

The comparison of the derived solar wind velocity with values found from IPS measurements at spaced radio

telescopes (University of Nagoya, www.stelab.nagoya-u.ac.jp) for 3C298

The comparison of the derived solar wind velocity with values found from IPS measurements at spaced radio

telescopes (University of Nagoya, www.stelab.nagoya-u.ac.jp) for 3C48

Conclusions

• The analysis has been carried out for data, derived from observation series of scintillation of the strong compact radio sources 3C 48 and 3C 298 at 111 MHz during one year (from Sep. 2006 to Oct. 2007) near the solar activity minimum. In this time interval the interplanetary plasma was quiet, significant disturbances in scintillation level and in solar wind velocities were not detected.

• The radial dependences of scintillation index have been obtained, which are more weak than the dependence m(sin )-3/2expected for the spherically symmetrical model of solar wind. The difference can be explained by the existence of the low-latitude plasma sheet with higher turbulence level (the heliospheric current sheet).

• Velocities of the plasma irregularities have been derived from the temporal scintillation power spectra. The good agreement with the values derived from instantaneous measurements at spaced radio telescopes has been shown. Observation at single radio telescope may be used for solar wind velocity monitoring.

• In general, these results agree with the typical for solar activity minimum bi-modal solar wind spatial structure with slow dense wind at low heliolatitudes and fast lower density wind at middle and high heliolatitudes.

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