Investigating jets in the lower-to-mid solar atmosphere : observations & numerical simulations

• Main Author: Scullion, Eamon
• Published: University of Sheffield 2010
• Subjects: 523.58
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556987

Understanding the fine structures and transient phenomena associated with the origins of the fast solar wind, in the lower-to-mid solar atmosphere, remains one of the biggest unanswered questions in solar physics today. A variety of jet-like transient events appear in cool plasmas in the form of spicules, macrospicules and surges. Transient and explosive jet-like phenomena are not only dominant in the lower solar atmosphere in UV and EUV temperatures but, also, in the mid-to-upper coronal atmosphere at X-Ray (10-300 key) and soft X-ray (1-10 key) temperatures. The recent launch of highly tuned space observatories, such as Hinode (2006) and STEREO (2007) and more recently SDO (2010), provide a wealth of data concerning the complex dynamics ongoing within the thin band of atmosphere above the photospheric surface of the Sun. In the lower-to-mid solar atmosphere the hot and the cold plasma are separated at the solar transition region. Beneath this layer mass and energy are coupled from the solar interior into the hot outer solar atmosphere via a number of different physical mechanisms which are controlled by either wave-driven or magnetic reconnect ion driven processes. Spicules are one of the most common features in the lower-to-mid solar atmosphere and have recently become the subject of significant debate with regard to their principle formation mechanisms. The spicule family tree can be classified into three branches, namely, type-I, type-II and macrospicule. Both type-I spicules and macrospicules are generally believed to be formed through unique processes. Type-I spicules are wave driven and macrospicules are driven by an explosive magnetic reconnect ion process. The recently discovered type-II spicules (2007) pose an interesting problem such that they are thought to exhibit characteristics from both models. Consequently, type-II spicules are interesting for a number of reasons, i.e., they might address the long standing questions concerning the origin of the fast solar wind and the coronal heating problem. In this thesis we examine the nature of spicular structures in the lower-to-mid solar atmosphere through observational analysis with supporting numerical simulations (via SAC: Sheffield Advanced Code: Shelyag et al, 2008). The observational approach is two-fold, involving a spectroscopic study of jets observed in polar coronal holes, for both on-disk and off-limb events, as well as, a multi-instrumental imaging approach involving recently launched instruments. The numerical simulations are three-fold. We will investigate the wave-driven model behind type-I spicule formation in 3D. the process of magnetic flux emergence in the solar chromosphere in 2.5D to understand the process leading to macrospicule formation and magnetic reconnection in 2.5D in order to investigate type-II spicule formation. In supporting our numerical models with high spatial, temporal and spectral resolution observations we have discovered a number of interesting phenomena. Firstly, we have modelled the formation of transition region quakes (TRQs). We have evaluated the response of the transition region to the propagation of p-modes from the lower chromosphere and acoustic wave energy transmission in 3D. Secondly, we have simulated convection flows associated with type-I spicules in the corona, which is the first example of any convection based process in the corona. In this spectroscopic analysis, we successfully isolated an important criteria in controlling the heating potential of macrospicules, i.e., the helicity of the magnetic flux emergence.