Abstract Details


Name: Ananya Hore
Affiliation: Department of Physics, Indian Institute of Science, Bangalore
Conference ID: TVS202510114
Title: Relevant Spatial Scale of the Global Solar Surface and Atmospheric Magnetic Field During Cycle 24
Authors and Co-Authors: Ananya Hore
Abstract Type: Contributory Presentation
Abstract: Physical processes within the Sun generate structures over a wide range of spatial scales, both on the photosphere and in the overlying atmosphere. Understanding these phenomena necessitates identifying the relevant spatial scales governing magnetic activity. Sunspot diameters (approximately 10-200 Mm) require relatively higher spatial resolution (minimum degree, l = 63 in spherical harmonics, widely used in modal decomposition) compared to the background large-scale diffused surface magnetic field. Similarly, coronal structures range from current sheets in flares (less than 1 Mm) to streamers spanning nearly half a hemisphere. Here, we present a quantitative mathematical study of appropriate length scales essential for global field evolution on the surface and in the corona. Surface and coronal magnetic fields are analyzed using spherical harmonic-based modal decomposition of full-disk magnetograms from SOHO/MDI and SDO/HMI spanning solar cycle 24 (2009-2020), with coronal fields obtained via PFSS extrapolations. Analysis of mode contributions, effective degree and unsigned magnetic flux indicates that even with degree less than 30 (approximately 146 Mm), most of the photospheric contribution is retained, with dominant contributions restricted to effective degrees 7-19 (minimum scale of 220 Mm). The coronal magnetic field is primarily determined by photospheric field distribution. Excluding transients like CMEs, large-scale quasi-static coronal features such as streamers are well represented by l= 7, implying the reduced influence of individual sunspots with height. Furthermore, both mode contribution and effective degree decline with altitude, and beyond 1.5 solar radius, the field predominantly exhibits dipolar, quadrupolar or octopolar characteristics. This quantitative analysis underscores the relevance of earlier low-resolution observations in global simulations, even though the community emphasizes assimilating high-resolution data. It also highlights that low-resolution stellar magnetic field measurements can still yield valuable insights into atmospheric and planetary impacts.