Spectral line widths are often observed to be larger than can be accounted for by thermal and instrumental broadening alone. This excess broadening is a key observational constraint for both nanoflare and wave dissipation models of coronal heating. Here we present a survey of non-thermal velocities measured in the high temperature loops (1–4 MK) often found in the cores of solar active regions. This survey of Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations covers 15 non-flaring active regions that span a wide range of solar conditions. We find relatively small non-thermal velocities, with a mean value of 17.6 ± 5.3 km s?1, and no significant trend with temperature or active region magnetic flux. These measurements appear to be inconsistent with those expected from reconnection jets in the corona, chromospheric evaporation induced by coronal nanoflares, and Alfvén wave turbulence models. Furthermore, because the observed non-thermal widths are generally small, such measurements are difficult and susceptible to systematic effects.
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机译：通常观察到谱线宽度大于仅通过热和仪器加宽可以解释的谱线宽度。这种过度加宽是对冠状加热的纳米耀斑和波耗散模型的关键观察约束。在这里，我们介绍了一个在高温回路（1-4 MK）中测得的非热速度的调查结果，该温度经常在太阳活动区的核心中发现。这项对Hinode极紫外成像光谱仪（EIS）观测的调查涵盖了15个无火的活动区域，这些活动区域跨越了广泛的太阳条件。我们发现相对较小的非热速度，平均值为17.6±5.3 km s？1，并且没有温度或活动区域磁通量的明显趋势。这些测量结果似乎与电晕中重新连接的射流，日冕纳米耀斑引起的色球蒸发以及Alfvén波湍流模型所预期的结果不一致。此外，由于观察到的非热宽度通常很小，因此这种测量很困难并且容易受到系统影响。
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