Ⅱ-7. Astrophysics and Astro-Glaciology

RIKEN Accel. Prog. Rep. 50 (2017)

Box-model simulation for inﬂuence of solar proton events on themiddle atmosphere
Y. Nakai,∗1 Y. Motizuki,∗1,∗2 M. Maruyama,∗1 Y. Hasebe,∗1,∗2 H. Akiyoshi,∗1,∗3 and T. Imamura∗3
In a solar proton event (SPE), high-energy particles
precipitate into the atmosphere. A part of the high energy particles can induce an increase in the concentrations of radicals, such as odd nitrogen radicals (NOx)and odd hydrogen radicals (HOx), through ionic andneutral reactions in the middle atmosphere. Furthermore, ozone depletion through subsequent reactions
with radicals lasts longer than the SPE. The concentration variations of trace gas components with SPEs
have been observed and numerical simulation studies
have been performed.1–5)
We have developed a box-model of multitudinousand homogeneous gas phase reactions of ionic and neutral chemical species in the middle atmosphere, but
without transport processes, to investigate the variation of trace gas composition induced by SPEs.6–8)
We adopted 79 chemical species including positive andnegative ions and 608 chemical reactions including various types of ionic and neutral reactions in the latest
version of the box-model. The detailed numbers ofadopted chemical species and chemical reactions arelisted in Tables 1 and 2, respectively. The simulations
were performed using commercial software (FACSIMILE, MCPA Software Ltd).
Figure 1 shows the result for the variation of ozone
concentration at an altitude of 50km in the northern
polar region for an SPE known as the “Halloween”
event, which occurred in October-November 2003. The
solid line corresponds to the result of full calculation,and the dashed line corresponds to that of a calculation
conducted by taking account only of neutral-species
production in initial radiolysis processes. The diﬀerence between the two results indicates that ion production in initial radiolysis processes and subsequentionic reactions are important in the quick ozone depletion in the SPE. In both cases, diurnal oscillations ofconcentrations are observed.
In the near future, the variations estimated by thebox-model simulation during an SPE will be input intoa three-dimensional chemical climate model9) as perturbations to investigate the spatial and temporal atTable 1. The number of chemical species adopted in thismodel.
Neutral species
Positively charged species
Negatively charged species
Total adopted species
∗1∗2
∗345
171779RIKEN Nishina Center
Department of Physics, Saitama Univ.
National Institute for Environmental Studies- 143 -

mospheric inﬂuence of the SPE through transport processes, aerosol formation, and so on.

Fig. 1. Variation of the ozone concentration at an altitude of 50km in the northern polar region for the “Halloween” SPE in October-November 2003 (See text).
Table 2. The number of reactions adopted in this modelfor each reaction type.
Reaction typeRadioysis (initial processes in SPE)
Positive ion-neutral reactions
Negative ion-neutral reactions
Electron attachment on neutral species
Collisional and associative detachment
Electron-positive ion recombinations
Ion-ion recombinations
Photodissociation of negative ionsa
Photo-detachment of electronsa
Solar UV photolysis of neutral species
Neutral reactions
Total adopted reactions# of reactions
1249
6581526285
3524116608

a Applied only above 70km.

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