tailieunhanh - Astrophysics and Space Science Proceedings Phần 3

Thay đổi rất nhỏ, nhưng quan trọng trong biên độ chu kỳ mặt trời thường được quan sát thấy từ một chu kỳ khác, và các mô hình dựa trên hoặc là biến động ngẫu nhiên, hoặc phản hồi phi tuyến, hoặc thời gian trì hoãn động lực tồn tại để giải thích sự biến đổi trong biên độ chu kỳ (cho tổng quan, xem Charbonneau 2005. Nghe Đọc ngữ âm Xếp hạng bản dịch | 92 D. Nandy Origin of Grand Minima Small but significant variations in solar cycle amplitude is commonly observed from one cycle to another and models based on either stochastic fluctuations or nonlinear feedback or time-delay dynamics exist to explain such variability in cycle amplitude for overviews see Charbonneau 2005 Wilmot-Smith et al. 2006 . However most models find it difficult to switch off the sunspot cycle completely for an extended period of time - such as that observed during the Maunder minimum -and subsequently recover back to normal activity. Two important and unresolved questions in this context are what physical mechanism stops active region creation completely and how does the dynamo recover from this quiescent state. The first question is the more vexing one and still eludes a coherent and widely accepted explanation. The second question is less challenging in my opinion the answer possibly lies in the continuing presence of another a-effect could be the traditional dynamo a-effect suggested by Parker which can work on weaker sub-equipartition toroidal fields - to slowly build up the dynamo amplitude to eventually recover the sunspot cycle from a Maunder-like grand minima. These are speculative ideas and one thing that can be said with confidence at this writing is that we are just scratching the surface as far as the physics of grand minima like episodes is concerned. Parametrization of Turbulent Diffusivity Typically in many dynamo models published in the literature the coefficient of turbulent diffusivity employed is much lower than that suggested by mixing-length theory about 1013 cm2 s-1 Christensen-Dalsgaard et al. 1996 . This is done to ensure that the flux transport in the SCZ in advection dominated . meridional circulation is the primary flux transport process . There are many disadvantages to using a higher diffusivity value in these dynamo models. Usage of higher diffusivity values makes the flux transport process diffusion