Joint Physics Dept.–Inst. for Space Weather Sci. Colloquium

September 18, Thursday (** SPECIAL DAY**)

Inferring Reconnection Dynamics from the Fine Structure of Flare Ribbons

Dr. Joel Dahlin

U. of Maryland and GSFC

(Solar Physics, Host: Haimin Wang)

***UPDATED ROOM: 463 Tiernan (Old Phys Office)

**Special Time: 1pm - 2pm with 12:45 pm teatime

*** CORRECTED ZOOM Meeting ID for those who cannot attend in-person: 955 9399 6954

(APPROVAL by Prof Ahn REQUIRED for APPH/MTSE PhD Students to attend online)

*Password: check email or request from kenahn@njit.edu

Solar flares are spectacular manifestations of explosive energy release powered by magnetic reconnection. While the standard CSHKP model has proven highly successful in explaining key features of flare observations in terms of magnetic reconnection, many aspects of the energy release are not yet understood. In particular, the complex three-dimensional structure of the flare current sheet is thought to play important roles in particle acceleration and bursty energy release. Although direct diagnosis of the magnetic field dynamics in the corona remains highly challenging, rich information may be gleaned from flare ribbons, which represent the chromospheric imprints of reconnection in the corona. In particular, recent high-resolution imaging observations from solar telescopes including BBSO/GST, IRIS, and SST have revealed a diversity of fine structure in flare ribbons that hints at corresponding complexity in the reconnection region. We present high-resolution three-dimensional MHD simulations of an eruptive flare and describe our efforts to identify the imprints of current sheet dynamics on flare ribbon fine structure. In our model, the flare current sheet is highly turbulent and dominated by coherent magnetic structures known as plasmoids. We derive a model analogue for flare ribbons and demonstrate that the life cycle of a plasmoid manifests as a transient ‘spiral’ along the ribbon front. We show how fine-scale ribbon features may be used to constrain quantitative properties of the current sheet dynamics, and discuss implications for interpreting observations of fine structure in solar flares.