Ⅱ-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 49 (2016)

Box-model
composition
Box-modelsimulation
simulationfor
forvariation
variationofof atmosphericatmospheric chemicalchemical composition
causedby solarsolar energetic
energetic particles
particles
caused byY. Nakai,*1 Y. Motizuki,*1 M. Maruyama,*1 H. Akiyoshi,*1,*2 and T. Imamura*2
The atmospheric effect of energetic particles from thegiant solar flares (solar energetic particles: SEPs) has been
attracting attention in recent years. High-energy protons inSEPs can intrude down to the stratosphere and cause
dissociation of nitrogen molecules in the middle atmosphere.
This induced an increase in reactive odd nitrogen species(NOy) and decrease in ozone through subsequent chemical
reactions over a period lasting longer than the SEP events,
which typically continue for 3-7 days. The concentration
variations of several chemical species with SEP events havebeen observed, and related simulations have beenattempted.1-3)
We have investigated the variation of chemicalcomposition induced by SEP protons using the box-model
simulation, which includes multitudinous reactions forvarious ionic and neutral chemical species in the middle
atmosphere, but no transport processes.4,5) The box-model
simulations in the altitude range of 20-65 km were applied
to the SEP event in October-November 2003. In thissimulation, we adopted 77 chemical species including both
positive and negative ions and 482 chemical reactions
including various types of ionic reactions for the gas phasechemistry in the middle atmosphere.5) The simulation wasperformed using commercial software (FACSIMILE,MCPA Software Ltd).
The prompt products generated through radiolysis
processes by the SEP protons induce subsequent ionic andneutral reactions (SEP-induced reactions). Thus, theproduction rates of the prompt products are estimated using
the G-values (amount of products per absorbed energy of100 eV)6,7) under the assumption that the yield of theprompt products is determined only with the energy depositin the air. The day-by-day energy deposits with two peaks
during the SEP event were estimated through thecalculation of daily ion-pair creation rate by the SEP
protons2). We also assume that the prompt products arecharged and neutral products generated from nitrogen andoxygen molecules.4,5)
Figure 1 shows the preliminary results of the energy
deposit rate in a unit volume of the air, the variation of theozone concentration (ΔO3), and that of the NOy
concentration (ΔNOy) at a 50km altitude in the northern
polar region for the SEP event in October-November 2003.
The variation of each chemical species induced by SEP
protons was estimated as the difference between the result
considering both SEP-induced and photochemical reactions
and that considering only photochemical reactions using thesame initial condition. The ΔO3 responds to the increase in＊1＊2

RIKEN Nishina Center
National Institute for Environmental Studies- 132 -Figure 1. Preliminary results for the energy deposit rate in aunit volume of the air, the variation of the ozone
concentration and that of NOy at a 50km altitude, caused bySEP protons. The SEP event started on October 28, 2003.
energy deposit very quickly. After the SEP event, the ΔO3
increases again but does not completely recover to thepre-event value. On the other hand, ΔNOy increases during
the SEP event and recovers very slowly after the event,maintaining its value for a few weeks or more. The
depletion of ozone after the SEP event presumably remains
because of the ozone consumption in the catalytic reaction
cycle involving NOy.
In near future, the variations estimated by the box-model
for a short term will be input into a three-dimensional
chemical climate model8) as instantaneous perturbation forinvestigation of the global and long-term influence.
References1)   B. Funke et al., Atmos. Chem. Phys. 11, 9089 (2011);
2)   C.H. Jackman et al., Atmos. Chem. Phys. 8, 765 (2008).
3)   P.T. Verronen et al., Geophys. Res. Lett. 35, L20809 (2008).
4)   K. Sekiguchi et al., RIKEN Accel. Prog. Rep. 46, 124 (2013).
5)   Y. Nakai et al., RIKEN Accel. Prog. Rep. 48, 168 (2015).
6)   C. Willis and A. W. Boyd, Int. J. Radiat. Phys. Chem. 8, 71(1976).
7)   H. Mätzing, Adv. Chem. Phys. LXXX, 315 (1991).
8)   H. Akiyoshi et al., J. Geophys. Res., in press.