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
2023-12-18
34
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 magnetic-polarity 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 solarphysics: 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. Modem 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] The author focuses primarily on ______.
选项
A、two competing scientific models concerning the sun’s magnetic field
B、an overview of some recent scientific developments in solar physics
C、the reasons why a problem in solar physics has not yet been solved
D、the difficulties involved in linking terrestrial climate with solar activity
答案
D
解析
转载请注明原文地址:https://tihaiku.com/zcyy/3284187.html
相关试题推荐
WhathappenedtothefourremaininglawyersafterPatrick’sdisappearance?[br]
WhathappenedtothefourremaininglawyersafterPatrick’sdisappearance?[br]
WhathappenedtothefourremaininglawyersafterPatrick’sdisappearance?[br]
Scobielikedtohavehistelescopeinbedbecause______.[br]Scobiethoroughly
Therecentsurgeinoilpricestoroughly$55abarrelteachessomeusefulle
Therecentsurgeinoilpricestoroughly$55abarrelteachessomeusefulle
ThefirstdecadesoftheRomanEmpirewerethegoldenageofLatinliterature
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
Ithasbeenknownformanydecadesthattheappearanceofsunspotsisroughly
随机试题
Thelong,wetsummerhereinthenortheasternU.S.notwithstanding,there’sa
假设你是Harry,给超市经理写封投诉信。内容包括:1.昨天你在超中购物时,发现所售牛奶过期;2.向售货员反映情况,对方只顾聊天,置之不理;
在ISO的OSI模型中,为数据分组提供在网络中路由功能的是(3)。A.物
分红寿险和健康险保单在世界各地都很普遍。在分红寿险中,下列选项不是分红最常见的红
医德义务对医务人员职责的规定包括的两个方面内容是A.权利与义务 B.荣誉与幸福
端子箱竣工(预)验收标准卡中,密封检查要求端子箱内电缆孔洞应用无机堵料封堵,必要
小儿的生理特点有A.脏腑娇嫩 B.发育迅速 C.发病较快 D.对外界适应能
()是指对股票进行估值时,对可比较的或者代表性的公司进行分析,以获得估值基础。A
A.眶下区弥漫性水肿 B.以下颌角为中心的红肿可伴有明显的开口受限 C.下颌
【背景资料】 某机场场道土基为盐渍土。机场于2011年8月正式开始飞行区跑道加
最新回复
(
0
)