V.I.Shishov, S.A.Tyul’bashev, I.V.Chashei, I.A.Subaev, K.A.Lapaev

INTERPLANETARY AND IONOSPHERE SCINTILLATION MONITORINGOF RADIO SOURCES ENSEMBLE AT THE SOLAR ACTIVITY MINIMUM

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

Abstract

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 (

IPP

IPP,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 (

Ion

Ion,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.

Radio occultation solar wind study

Radio occultation — since 1952, VitkevichPhase, frequency, amplitude modulationAmplitude modulation — IPS, since 1964Scintillation index m2 = < I - <I>>2 / <I>2 IPS - Sources with angular size less or order of 0''.1 arc secIonospheric scintillation — all radio sources Weak IPS: m2 << 1Strong IPS: m = 1 — point source, m < 1 - source with finite angular sizeMapping of turbulent interplanetary plasma — great number of natural sourcesFirst modification: observation of sources with known angular structureObservation of sources ensemble — statistical approach

Radiotelescope BSA LPIFrequency 111 MHz, frequency band 600 кHz, sampling rate 10 Hz16 beams, strip 8o in declination , 24 hours in right ascension Monitoring observation series: 2006, 18.11-30.12; 2007, 11.06-18.06; 2008, 20.10-4.11Several hundreds of scintillating sources during 24 hours

Observations, period of low solar activity

Processing

Measurable — radio flux variations

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.

Example of initial record

Mean daily variance, IPS

Mean daily variance, Ion Scint

Day to day variance, IPS

Day to day variance, Ion Scint

Dependence on elongation, IPS

Heliospheric current sheet, 2008

Conclusions

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.