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Research at St Andrews

Craig David Johnston

Person

Craig David Johnston
Postal address:
School of Mathematics and
Statistics
North Haugh
St Andrews
United Kingdom

Email: cdj3@st-andrews.ac.uk

Direct phone: +44 (0)1334 463756

Research overview

My research involves the development of a numerical method to model the mass exchange that takes place in the Sun's atmosphere, between the corona and chromosphere, in response to coronal heating. During impulsive heating events, an increase in the coronal density occurs because the increased coronal temperature leads to an excess downward heat flux that the transition region (TR) is unable to radiate. This creates an enthalpy flux from the TR to the corona. The density increase is often called chromospheric evaporation. Sufficiently high resolution of the TR is essential in numerical simulations in order to obtain the correct coronal density. If the resolution is not adequate, then the downward heat flux jumps over the TR and deposits the heat in the chromosphere, where it is radiated away. This leaves little excess energy to drive an upward enthalpy flux and so the upflows are underestimated, leading to major errors in simulating the coronal density evolution. To deal with this problem we have developed a new approach which models the Transition Region using an Adaptive Conduction (TRAC) method that acts to broaden any unresolved parts of the atmosphere. We have shown that this approach, referred to as TRAC, successfully removes the influence of numerical resolution on the coronal density response to heating while maintaining high levels of agreement with fully resolved models, even when using the coarse spatial resolutions that are typically achieved in multi-dimensional MHD codes.

 

More information on my current research activities is available on my personal website.

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