Numerical hydrodynamics of the jet phenomena in the solar atmosphere

Abstract

One-dimensional hydrodynamic simulations of surges are performed in order to make clear their origin and structure. Surges are regarded as the jets resulting from a sudden pressure increase at the base of the model atmosphere. The height of the explosion (h ₀), which is measured from the level of τ₅₀₀₀ = 1, is regarded as a free parameter. Another free parameter is the strength of the sudden pressure increase (p/p ₀) at h ₀. Simulations are performed for values in the ranges of 540 km ≤ h ₀ ≤ 1920 km and 3 ≤ p/p ₀ ≤ 30. It was found that for a fixed p/p ₀ there exists a critical height (h _c ) in h ₀, which separates the jet (surge) models into two types. For h ₀ > h _c , jets are produced directly by the pressure gradient force near h ₀, and made of the matter ejected from the explosion itself. The essential hydrodynamic structure of this type is the same as that in a shock tube (this type is called ‘shock tube’ type). For h ₀ < h _c , jets are not the direct results of the pressure enhancement, but are produced by the shock wave which are generated by the pressure enhancement and which has propagated through the chromosphere (this type is called the ‘crest shock’ type). It is shown that the critical height (h _c ) ranges from 1000 km to 1500 km for 3 ≤ p/p ₀ ≤ 30. General properties of both types are investigated in detail. The results are compared with observations and it is concluded that small surges associated with Ellerman bombsbelong to the ‘crest shock’ type, i.e. they are produced by the shock wave.