Frank Hill/National Solar Observatory

A Study of Seismic Signatures of Active Regions in Farside Imaging for

Applications to Space-Weather

The investigators will conduct a comprehensive statistical study of the relation between

the holographic seismic signatures of active regions and their magnetic and intensity

configurations for further improvements in imaging active regions on the Sun's far

surface and further extension of farside imaging to space weather and other applications.

The program we propose consists of two substantial parts: 1) Improvements in the

calibrations of holographic seismic images based on the evaluation of nearside signatures,

and 2) Application of holographic diagnostics, both nearside and farside, to simulations

of active regions to be produced by a closely related program.

This study can be regarded as a continuation of a NASA-supported research that has

extended farside imaging techniques to GONG observations covering the entire far

hemisphere of the Sun and has substantially improved the quality of the original farside

images, which initially covered less than half of the Sun's far hemisphere. The early

stages of Part (1) have already commenced under the current NASA program, which is

about to expire. This is based on the relatively simple assumption that the farside

signature characterizes an "acoustic Wilson depression" proportional to the square

magnetic field alone, which is already recognized as inadequate. The new program will

take into account field inclination, and intensity and the underlying thermal anomalies

these may signify in plages and sunspots. A realistic interpretation of the farside seismic

signatures is crucial for improved space-weather applications, particularly for our

understanding of the connection between farside signatures and prospects for major flares

and Coronal Mass Ejections (CME). Part (2) will be conducted in close collaboration

with CoIs at NWRA and Stanford, who will produce simulations of active regions for

control applications of our farside imaging techniques. These are essential for a working

assessment of the diffuse artifacts projected into farside images by active regions on the

Sun's near surface. A comprehensive determination of the diffuse artifact is crucial to a

practical extrapolation of changes in the global coronal magnetic field and the impact of

active regions that emerge on the Sun's far surface, including an assessment of prospects

for large flares and CMEs. It is, moreover, essential to the application of farside imaging

to solar irradiance forecasting, which it is now heavily in demand. The program we

propose will be conducted with CoIs and collaborators doing closely related theoretical

modeling and simulations at NWRA and Stanford. We will also work closely with

collaborators at LASP and the SOHO/SWAN project who are working on visible and UV

irradiance forecasting.