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-XRT observations of AR 11089. On the left is a frame from the observing sequence. On the right are light curves from three different locations in the core of the active region. Intensities are in DN s −1 per pixel. The dashed horizontal line is the median intensity for the period shown. The dotted horizontal lines are ±20% of the median. The solid vertical line corresponds to the time of the image. The emission in the core of the active region is relatively constant, with a variability of 20% or less. Transient events with relatively short lifetimes ( 900 s) are also observed. The electronic version of the manuscript includes a movie of these data.
Source publication
We present observations of high temperature emission in the core of a solar
active region using instruments on Hinode and SDO. These multi-instrument
observations allow us to determine the distribution of plasma temperatures and
follow the evolution of emission at different temperatures. We find that at the
apex of the high temperature loops the em...
Context in source publication
Context 1
... mentioned previously, the primary strength of the XRT is the ability to observe high temperature emission over a wide field of view at relatively high cadence. This is illustrated in Figure 3, where light curves from several positions in the core of the active region are shown. Each light curve is from a single pixel, there is no spatial averaging. ...
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Citations
... We model a coronal loop of total length 90Mm and use the same nanoflare train as inCargill et al. (2015), consisting of 23 square wave heating pulses over an 8 hour period, as shown in the upper panel ofFigure 4.1. This set up is representative of the modelling challenge faced when trying to understand the heating of the core loops found in active regions (e.g.Warren et al., 2011Warren et al., , 2012. Each nanoflare lasts 200s and they cover a range of magnitudes of heating, each with an energy dependent waiting time between events. ...
This thesis presents a new computationally efficient method for modelling the response of the solar corona to the release of energy. During impulsive heating events, the coro- nal temperature increases which leads to a downward heat flux into the transition region (TR). The plasma is unable to radiate this excess conductive heating and so the gas pres- sure increases locally. The resulting pressure gradient drives an upflow of dense material, creating an increase in the coronal density. This density increase is often called chromo- spheric evaporation. A process which is highly sensitive to the TR resolution in numerical simulations. 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. The outcome is that with an under-resolved TR, major errors occur in simulating the coronal density evo- lution. We address this problem by treating the lower transition region as a discontinuity that responds to changing coronal conditions through the imposition of a jump condition that is derived from an integrated form of energy conservation. In this thesis, it is shown that this method permits fast and accurate numerical solutions in both one-dimensional and multi-dimensional simulations. By modelling the TR with this appropriate jump condition, we remove the influence of poor numerical resolution and obtain the correct evaporative response to coronal heating, even when using resolutions that are compatible with multi-dimensional magnetohydrodynamic simulations.
Magnetically, the Sun can be compartmentalized into boxes around active regions that can be modeled separately, since the mean magnetic field strength in the surrounding Quiet Sun regions and in coronal holes is about three orders of magnitude lower. An example of a (dipolar) active region is shown in Fig. 8.1, as observed with HMI/SDO and AIA/SDO in various wavelengths.
