AR_final file_2018-19

Figure 20: Left panel: AIA 171 ∼ Angstrom image showing the transient brightening, which are located with arrows. The FOV of EIS, IRIS and XRT FOV are highlighted with red, green and yellow boxes, respectively. The vertical blue line located the IRIS slit position. Right panel: The loops are brightened up due to the transient brightening. The images show the loops at their peak brightening in different panels as labelled. hensive measure of the energetics of such bright- enings. The measurements show that the DEM weighted temperatures of these transients are in the range log T ( K ) = 6 . 2 − 6 . 6 with radiative energies ∼ 10 24 − 25 ergs and densities approximately equal to a few times 10 9 cm − 3 . Further study of energy loss using these results showed that the dominant mech- anism of energy loss for all the identified brighten- ings is conduction rather than radiation, which is usually believed (See Figure 21). Mg II line intensities in quiet-Sun and coronal Holes Coronal holes (CH) and quiet Sun (QS)regions are two areas on the Sun, which are uniquely identified in coronal images. However, they are hardly dis- tinguishable in the chromosphere and photosphere. From the point of view of using Mg II indices as proxies for modelling the Sun-climate relation- ships, it is crucial to understand the behaviour of the Mg II line in coronal holes and quiet Sun re- gions at chromospheric heights. Pradeep Kayshap, Durgesh Tripathi , Sami K. Solanki and Hardi Peter have used the high-resolution spectra that are obtained by the Interface Region Imaging Spec- trometer (IRIS). Just by visual inspection as well as from the over-all distribution, they find that the distribution of intensities of Mg II lines is very sim- ilar in coronal holes as well as in the transition region. However, after invoking the magnetic field, it is found that Mg II intensities are significantly lower in CH than in QS for the areas with similar magnetic flux density (see Figure 22). The wing in- tensities that represent the photospheric emission, however, do not show such behaviour. This analy- sis further reveals that the difference between Mg II intensities in coronal holes and quiet Sun increases with increasing magnetic flux density. These find- ings have significant importance for using Mg II index as a proxy for the modelling of solar spectral irradiance as well as the general supply of mass and energy from the lower atmosphere to the upper. ( 87 )