Investigation of daily variations of cosmic ray fluxes in the beginning of 24 th solar activity cycle. Ashot Chilingarian, Bagrat Mailyan. IHY-ISWI Regional Meeting, 7-13 September 2009, Šibenik, Croatia. Why does daily variation of cosmic rays exist ?.
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Investigation of daily variations of cosmic ray fluxes in the beginning of 24th solar activity cycle
Ashot Chilingarian, Bagrat Mailyan
IHY-ISWI Regional Meeting, 7-13 September 2009, Šibenik, Croatia
A three-dimensional form of the Parker spiral that results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium
Daily variations understood to result from a combination of inward diffusion along the spiral interplanetary magnetic field and outward convection by the solar wind.
If we decompose cosmic ray flux into
radial and tangential components,
radial flux of galactic cosmic rays will be
compensated by solar wind convective outflow.
Tangential component, due to Earth’s rotation, causes variation with maximum at 18:00 local time.
G.F. Krymsky, 1964.
This data is consistent with baloon-borne experiment B.E.S.S., recently reported at 31st International Cosmic Ray Conference
T.Hams et al., Short-term and diurnal proton flux variation during the BESS-Polar I balloon flight, Proceedings of 31st ICRC, Lodz, Poland
Data and methodology
For daily variation studies, we use one-month time series taken from May 2008 until January, 2009.
Data from the SEVAN Aragats (located at 3200m)
is available from October 2008.We took data of SEVAN Yerevan from January and February 2009.
Data from SEVAN Bulgaria and SEVAN Croatia - from December 2008.
Daily data were fitted by the harmonic approximation function for each day of selected
period and then obtained amplitudes and phases were averaged
f(ti) = A + B.cos(wti + Y)
The quality of fit, difference between experimental data and the fit is calculated
As we can see the amplitude of variation is
about 0.24% and phase is 3.307 in radians,
which corresponds to 11:22 in UT or 15:21
in local time.
After fitting the 11 May, 2008 data of Moscow, Alma-Ata and
Nor Amberd monitors the following values of
amplitudes were obtained – 0.47%, 0.20% and 0.24% respectively.
Phases in local time for these monitors are 14:53, 15:25 and 15:21 respectively.
To describe daily variations of muons with energies > 5 GeV,
data were fitted by sum cosines with 24 and 12 hour periods.
New Particle Detector Network for Solar Physics and Space Weather research
Different coincidences of SEVAN detector correspond to different species of secondary cosmic rays