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Study of large forbush decrease events of solar cycle 23rd

机译：太阳周期第23次大前冲减少事件的研究

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In the descending phase of 23rd solar cycle about 10 exceptionally large (with > 10 % magnitude) Forbush decrease (FD) events have been observed. Of these, selecting five FD events recorded by Moscow neutron monitor station, in the same year 2005 i.e. on 18 January, 15 May, 17 July, 24 August and 11 September 0f 2005, we have investigated their properties in terms of their origin (solar sources), temporal evolution and relation with interplanetary and geomagnetic parameters. The 7-day cosmic ray intensity (CRI) variation with the variation in solar wind velocity, total interplanetary magnetic field B, its southward component Bz, Dst and Kp indices have been analysed to see the changes taking place in the magnetosphere and geospace. The passage of interplanetary (IP) shock and arrival of storm sudden commencement (SSC) was also examined during the onset of FDs. The cause of sudden depression in CRI near the Earth was traced back by noting the activities of the Sun two–three days before the occurrence of FD. For this, the data of Sunspot number, Sunspot area, eruption of Coronal Mass Ejection (CME), associated solar flare and their location on solar disc, all are thoroughly studied. The presence of interplanetary counterpart of CME (ICME/magnetic cloud) is also looked for to get the exact reason of shielding of cosmic rays. It is concluded from this comprehensive study that - Large FDs are caused due to fast halo CMEs associated by intense solar flares, there is abrupt rise in interplanetary parameters before the main phase of FDs, and such events are always accompanied with major geomagnetic storms which can be used for space weather prediction.
机译：在第23个太阳周期的下降阶段，观察到大约10个异常大（幅度大于10％）的前冲下降（FD）事件。其中，从2005年同年，即2005年1月18日，5月15日，7月17日，8月24日和9月11日0f，莫斯科中子监测站记录的5个FD事件中，我们调查了它们的性质（太阳）源），时间演化以及与行星际和地磁参数的关系。分析了7天的宇宙射线强度（CRI）随太阳风速，总行星际磁场B，其南向分量Bz，Dst和Kp指数的变化，以了解磁层和地球空间中的变化。在FD发作期间还检查了行星际（IP）冲击的通过和风暴突然开始（SSC）的到来。注意到FD发生前两到三天太阳的活动，可以追溯到地球附近CRI突然降低的原因。为此，对黑子数，黑子面积，日冕物质喷发（CME）爆发，相关的太阳耀斑及其在太阳盘上的位置等数据进行了全面研究。还寻找CME（ICME /磁云）行星际对应物的存在，以获取屏蔽宇宙射线的确切原因。从这项综合研究得出的结论是：-大型FD是由强烈的太阳耀斑引起的快速光晕CME引起的，FD的主要阶段之前行星际参数突然上升，并且此类事件总是伴随着重大的地磁风暴，用于太空天气预报。

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