An inverted U burst with equally developed ascending and descending branches observed by Giant Ukrainian Radio Telescope (GURT) on 18 April 2017 in meter wavelengths band is discussed. This U burst was attributed to the high coronal loop above the limb active region NOAA 12651. Under the assumption that, associated with the burst, the coronal loop confines isothermal plasma stratified according to a Boltzmann density relation, the geometrical and physical parameters of the loop were estimated. According to our model coronal loops may contain plasma which is up to 20 times denser than the surrounding coronal plasma. In general the proposed model gives the relation between the plasma temperature and the height of the loop in such a way that under the given parameters of the associated U burst, higher loops contain cooler plasma and vice versa. An alternative method of coronal loop height determination was suggested. Assuming that the observed U burst and the preceding type III burst were generated by the same exciter we define the height of the loop from the delay of the former with respect to the latter at certain frequency. We show that defining of coronal loops heights by another independent method, e.g. interferometric or tied-array imaging may solve the uncertainty of the inside-the-loop plasma temperature determination.

中文翻译：

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与高日冕环相关的太阳 U 型爆发

讨论了由乌克兰巨型射电望远镜 (GURT) 于 2017 年 4 月 18 日在米波段观测到的具有同等发展的上升和下降分支的倒 U 型爆发。这个 U 型爆发归因于 NOAA 12651 肢体活动区上方的高日冕环。 在与爆发相关的假设下，日冕环限制了根据玻尔兹曼密度关系分层的等温等离子体，环的几何和物理参数估计。根据我们的模型，日冕环可能包含比周围日冕等离子体密度高 20 倍的等离子体。一般来说，所提出的模型给出了等离子体温度和回路高度之间的关系，在给定的相关 U 爆发参数下，较高的回路包含较冷的等离子体，反之亦然。建议了另一种确定冠状环高度的方法。假设观察到的 U 脉冲串和前面的 III 型脉冲串是由同一个激励器产生的，我们根据前者相对于后者在特定频率下的延迟来定义环路的高度。我们表明，通过另一种独立的方法（例如干涉测量或系阵列成像）定义日冕环高度可以解决环内等离子体温度确定的不确定性。