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In this study, we investigate the energy partition of four confined circular-ribbon flares (CRFs) that occurred close to solar disk center. The flares are observed simultaneously by the Solar Dynamics Observatory (SDO), the Geostationary Operational Environmental Satellites (GOES), and the Ramaty Hight Energy Solar Spectroscopic Imager (RHESSI). We calculate different energy components, including the radiative outputs in the ranges 1 – 8 Å, 1 – 70 Å, and 70 – 370 Å, total radiative loss, peak thermal energy derived from GOES and RHESSI, nonthermal energy in flare-accelerated electrons, and magnetic free energy before the flares. It is found that the values of energy components increase systematically with the flare class, indicating that more energy is involved in larger flares. The magnetic free energies ( E m a g ) are larger than the nonthermal energies ( E n t h ) and radiative outputs, which is consistent with the magnetic nature of flares. The ratio E n t h E m a g of the four flares, being 0.70 – 0.76, is considerably higher than that of eruptive flares. Hence, this ratio may serve as an important factor for discriminating confined from eruptive flares. The nonthermal energies are sufficient to provide the heating requirements including the peak thermal energy and radiative loss. Our findings impose constraints on theoretical models of confined CRFs and have potential implications on space weather forecast. [ABSTRACT FROM AUTHOR]

Flare kernels brighten simultaneously in all Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) channels making it difficult to determine their temperature structure. The Interface Region Imaging Spectrograph (IRIS) is able to spectrally resolve Fe XXI emission from cold chromospheric brightenings, so it can be used to infer the amount of Fe XXI emission in the 131 Å AIA channel. We use observations of two small solar flares seen by IRIS and SDO to compare the emission measures (EMs) deduced from the IRIS Fe XXI line and the AIA 131 Å channel to determine the fraction of Fe XXI emission in flare kernels in the 131 Å channel of AIA. Cotemporal and cospatial pseudo-raster AIA images are compared with the IRIS results.We use multi-Gaussian line fitting to separate the blending chromospheric emission so as to derive Fe XXI intensities and Doppler shifts in IRIS spectra.We define loop and kernel regions based on the brightness of the 131 Å and 1600 Å intensities. In the loop regions the Fe XXI EMs are typically 80% of the 131 Å values, and range from 67% to 92%. Much of the scatter is due to small misalignments, but the largest site with low Fe XXI contributions was probably affected by a recent injection of cool plasma into the loop. In flare kernels the contribution of Fe XXI increases from less than 10% at the low-intensity 131 Å sites to 40−80% in the brighter kernels. Here the Fe XXI is superimposed on bright chromospheric emission and the Fe XXI line shows blueshifts, sometimes extending up to the edge of the spectral window, 200 km s−1. The AIA 131 Å emission in flare loops is due to Fe XXI emission with a 10−20% contribution from continuum, Fe XXIii, and cooler background plasma emission. In bright flare kernels up to 52% of the 131 Å is from cooler plasma. The wide range seen in the kernels is caused by significant structure in the kernels, which is seen as sharp gradients in Fe XXI EM at sites of molecular and transition region emission. [ABSTRACT FROM AUTHOR]