Exact and approximate methods for Alfvén waves in dissipative atmospheres
Abstract The Alfvén wave equation in a dissipative atmosphere has been solved exactly (Campos [1–3]) or using the phase mixing approximation (Heyvaerts and Priest , Nocera, Leroy and Priest ). In the present paper, we compare the phase mixing approximation, as it appears the reference above (which we designate henceforth HP), with an exact solution of the same model problem (Section 1). It is shown that: (Section 2) the dissipative Alfvén wave equation in HP is correct for the magnetic field perturbation, but not for the velocity perturbation; (Section 3) HP makes assumes implicitly that both the static viscosity and resistive diffusivities are constant, and omits restrictions on the external magnetic field, so that we redefine the atmospheric model which is the background for the wave propagation and dissipation; (Section 4) the phase mixing ‘ansatz’, when combined with the principle of superposition, which must hold for linear waves, is incompatible with Fourier analysis; (Section 5) the exact solution for dissipative Alfvén waves in an atmosphere, demonstrates the existence of a critical level, separating regions of dominant viscous and resistive dissipation; (Section 6) none of these properties is apparent in the phase mixing approximation, which can be compared with the exact solution if three restrictions are made: (i) high- or low-altitude i.e. far from the critical layer; (ii/iii) high-frequency and weak damping. Even under these restrictions no satisfactory agreement is found.
- NDSL :
유료 다운로드의 경우 해당 사이트의 정책에 따라 신규 회원가입, 로그인, 유료 구매 등이 필요할 수 있습니다. 해당 사이트에서 발생하는 귀하의 모든 정보활동은 NDSL의 서비스 정책과 무관합니다.
NDSL에서는 해당 원문을 복사서비스하고 있습니다. 위의 원문복사신청 또는 장바구니 담기를 통하여 원문복사서비스 이용이 가능합니다.
- 이 논문과 함께 출판된 논문 + 더보기