Abstract Details
| Name: Abhishek Johri Affiliation: NCRA-TIFR Conference ID: ASI2017_425 Title : Acceleration and evolution of solar energetic particle events in the Sun-Earth distance. Authors and Co-Authors : Prof. P.K. Manoharan, RAC, NCRA-TIFR Abstract Type : Oral Abstract Category : Sun and the Solar System Abstract : Solar energetic particle (SEP) refers to the high energy (keV to GeV energies) charged particles (\textit{e.g.,} electrons, protons, alpha etc.), coming from the Sun as a result of solar activity. The physics of SEP production, acceleration and propagation in the interplanetary space is rather complex and not well understood. They originate in the solar atmosphere (chromosphere or corona or both) and then are accelerated all the way from the Sun to the Earth. Near--earth spacecraft observations of these SEP events, broadly categorises them into two classes as reviewed by Reames (1999) viz; impulsive and gradual. Impulsive events are believed to be accelerated in rapid and short--lived ($\leqslant$30 minutes) solar flares whereas gradual SEP events are found to be well correlated with coronal mass ejections (CMEs) and their charge states suggests their origin in solar corona and acceleration due to shocks driven by fast (V $\gtrsim 700$ kms$^{-1}$) CMEs. Here, we present the preliminary results on the spectral evolution of SEP events in the Sun--Earth distance. We have analysed the energy spectrum (assuming Flux $\propto$ Energy$^{-\gamma}$: $\gamma$ being the spectral index) for 73 SEP in 10--100, 10--060, and 10--050 MeV energy ranges. Our findings are [1] SEP spectrum gets steeper from the peak of SEP event to shock arrival time near Earth space (i.e., at 1 AU), [2] It is important to mention that steepening is caused by the high energy part of the spectrum. [3] Spectral indices in the 10--060 and 10--050 MeV ranges are more correlated then 10--100 and 10--050 MeV ranges. [4] Spectral indices do not correlate with the 11--year solar cycle but maximum to minimum value of spectral index varies from one phase of solar cycle to another. |