首页
登录
职称英语
It has been known for many decades that the appearance of sunspots is roughly
It has been known for many decades that the appearance of sunspots is roughly
游客
2023-12-17
7
管理
问题
It has been known for many decades that the appearance of sunspots is roughly periodic, with an average cycle of eleven years. Moreover, the incidence of solar flares and the flux of solar cosmic rays, ultraviolet radiation, and X-radiation all vary directly with the sunspot cycle. But after more than a century of investigation, the relation of these and other phenomena, known collectively as the solar-activity cycle, to terrestrial weather and climate remains unclear. For example, the sunspot cycle and the allied magneticpolarity cycle have been linked to periodicities discerned in records of such variables as rainfall, temperature, and winds. Invariably, however, the relation is weak, and commonly of dubious statistical significance.
Effects of solar variability over longer terms have also been sought. The absence of recorded sunspot activity in the notes kept by European observers in the late seventeenth and early eighteenth centuries has led some scholars to postulate a brief cessation of sunspot activity at that time ( a period called the Maunder minimum). The Maunder minimum has been linked to a span of unusual cold in Europe extending from the sixteenth to the early nineteenth centuries. The reality of the Maunder minimum has yet to be established, however, especially since the records that Chinese naked-eye observers of solar activity made at that time appear to contradict it. Scientists have also sought evidence of long-term solar periodicities by examining indirect climatological data, such as fossil records of the thickness of ancient tree rings. These studies, however, failed to link unequivocally terrestrial climate and the solar-activity cycle, or even to confirm the cycle’s past existence.
If consistent and reliable geological or archaeological evidence tracing the solar-activity cycle in the distant past could be found, it might also resolve an important issue in solar physics, how to model solar activity. Currently, there are two models of solar activity. The first supposes that the Sun’s internal motions (caused by rotation and convection) interact with its large-scale magnetic field to produce a dynamo, a device in which mechanical energy is converted into the energy of a magnetic field. In short, the Sun’s large-scale magnetic field is taken to be self-sustaining, so that the solar-activity cycle it drives would be maintained with little overall change for perhaps billions of years. The alternative explanation supposes that the Sun’s large-scale magnetic field is a remnant of the field the Sun acquired when it formed, and is not sustained against decay. In this model, the solar mechanism dependent on the Sun’s magnetic field runs down more quickly. Thus, the characteristics of the solar-activity cycle could be expected to change over a long period of time. Modern solar observations span too short a time to reveal whether present cyclical solar activity is a long-lived feature of the Sun, or merely a transient phenomenon. [br] On which of the following assumptions is based the belief that tree-ring thickness shows links between solar periodicity and terrestrial climate?
选项
A、Solar-activity cycle existed in its present form during the period in question.
B、Average tree-ring thickness varies from species to species.
C、Tree-ring thickness varies with changes in terrestrial climate.
D、Both terrestrial climate and solar-activity cycle affect treering thickness.
答案
C
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3280803.html
相关试题推荐
Whichofthefollowingwordscontainsoneboundmorpheme?A、Disappearance.B、Unto
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
Therecentsurgeinoilpricestoroughly$55abarrelteachessomeusefulles
Therecentsurgeinoilpricestoroughly$55abarrelteachessomeusefulles
Afterdecadesofexodus,thetideofIrishmigrationtookadefinitiveturn
Afterdecadesofexodus,thetideofIrishmigrationtookadefinitiveturn
Forthefirsttimeindecades,researchersarereportingasignificantdrop
Forthefirsttimeindecades,researchersarereportingasignificantdrop
随机试题
Anewstudyfoundthatinner-citykidslivinginneighborhoodswithmoregre
(1)InarecentbookentitledThePsychicLifeofInsects,ProfessorBouvier
Thejobinterviewisthemomentoftruthinjobhunting.Inadditiontohow
幂级数在(0,+∞)内的和函数S(x)=_________.
维生素E含量最低的食物是( )。A.麦胚 B.花生油 C.豆类 D.鱼类
女性,45岁,诉有下坠感,有尿液漏出。查体宫颈已脱出阴道口,阴道前壁显露于阴道口
缺失,可摘局部义齿设计为隙卡,PI卡环,舌杆连接。增加间接固位体的最佳位置是A.
实贷实付的关键是让贷款人按照贷款合同的约定用途使用贷款资金,减少贷款挪用的风险
债券本期收益率的计算公式是()。A、票面收益/市场价格 B、票面收益/债
在建设工程监理招标过程中,通过资格预审可以实现( )的目的。A.排除不合格的投标
最新回复
(
0
)