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V.I.Shishov, S.A.Tyul’bashev, I.V.Chashei, I.A.Subaev, K.A.Lapaev Pushchino Radioastronomy Observatory, Astrospace Center, Lebedev Physical Institute, Russian Academy of Sciences.
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Pushchino Radioastronomy Observatory,
Astrospace Center, Lebedev Physical Institute, Russian Academy of SciencesINTERPLANETARY AND IONOSPHERE SCINTILLATION MONITORINGOF RADIO SOURCES ENSEMBLE AT THE SOLAR ACTIVITY MINIMUM
Results are presented of twenty-four-hour interplanetary and ionosphere scintillation monitoring obtained in Pushchino Radioastronomy Observatory during three observation series: between November 18 and December 30, 2006; between June 11 and June 18, 2007; between October 20 and November 4, 2008. Observations were carried out simultaneously in 16 beams of radio telescope BSA LPI (Big Scanning Array of Lebedev Physical Institute) at the frequency 111 MHz. All the sources with scintillating flux greater than 0.2 Jn were recorded in the range of declination from +3о to +10о by observations in the years 2006, 2008 and from 21o to 28o in the year 2007. The values of radio source flux fluctuations temporal structure functions were measured at the temporal lags 0.1 s, 1 s and 10 s, which characterize noise, interplanetary scintillation and ionosphere scintillation, respectively. About 1,000 scintillating radio sources were observed every day. The number of sources N (IPPIPP,0) with scintillating flux IPP greater than the given value IPP,0 in the sky area with sizes 8o in declination and 0.5 hours in right ascension was used as the parameter describing turbulent interplanetary plasma. This parameter is shown to be proportional to mean scintillation index of radio sources statistical ensemble in the given sky area. Similarly, the parameter N (IonIon,0) was introduced for description of turbulent ionosphere. Mean twenty-four hours temporal dependence of scintillation index is found. Weak from day to day variations of scintillation index were observed. In general, interplanetary plasma, as well ionosphere were in quiet state during the observation periods. Unusually weak dependence of scintillation index on the position of the sources relative to the Sun were observed in the year 2008 at very deep solar activity minimum. Such a weak dependence can be explained by strong concentration of absolute solar wind turbulence level to the solar equatorial plane.Abstract
Phase, frequency, amplitude modulation
Amplitude modulation — IPS, since 1964
Scintillation index m2 = < I - <I>>2 / <I>2
IPS - Sources with angular size less or order of 0''.1 arc sec
Ionospheric scintillation — all radio sources
Weak IPS: m2 << 1
Strong IPS: m = 1 — point source, m < 1 - source with finite angular size
Mapping of turbulent interplanetary plasma — great number of natural sources
First modification: observation of sources with known angular structure
Observation of sources ensemble — statistical approachRadio occultation solar wind study
Frequency 111 MHz, frequency band 600 кHz, sampling rate 10 Hz
16 beams, strip 8o in declination , 24 hours in right ascension
Monitoring observation series:
2006, 18.11-30.12; 2007, 11.06-18.06; 2008, 20.10-4.11
Several hundreds of scintillating sources during 24 hoursObservations, period of low solar activity
Flux structure function
DI(, t) = <[I(t + ) - I(t)]2> (averaging over time 1 min):
D(0.1s) = noise;
D(1s) = IPS + noise;
D(10s) = Ion Scint + IPS + noise
Beam filter — detection of sources
Statistical parameter N - number of sources with scintillating flux greater than
0.25 Jn in the sky area 8o in declination and 0.5 hours in right ascension.
N proportional to <m2> , if sources ensemble is uniform.Processing
Dependences of scintillation index on day time were found in the period of low solar activity for IPS and Ion Scint.
Variations of scintillation parameters from day to day are sufficiently weak.
Interplanetary plasma and ionosphere were in a quiet state during 2006-2008.
Very weak 2008 radial dependence of scintillation index is caused by strong concentration of interplanetary plasma to solar equatorial plane, probably, showing presence of heliospheric current sheet. Extension of slab above equatorial plane is about 0.15 AU at heliocentric distance 0.8 AU.Conclusions