首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Humans on the earth have had an over-inflated view of how far the planet’s atmosphere extends into space. It turns out that the
Humans on the earth have had an over-inflated view of how far the planet’s atmosphere extends into space. It turns out that the
admin
2010-12-04
62
问题
Humans on the earth have had an over-inflated view of how far the planet’s atmosphere extends into space. It turns out that the ionosphere (电离层), the layer of electrically charged particles that comprises the outer atmosphere, is thinner than expected-and cooler.
Understanding the shape and size of the ionosphere is an important first step in figuring out how particularly dense regions within it may distort radio, radar and navigation signals. Such distortions can make communications and satellite-based systems less reliable.
"In order to predict how severe those distortions will be, it’s necessary to know how big those structures in the ionosphere are and where they exist," Roderick Hellis, with the Space sciences Center at the University of Texas in Dallas, told Discovery News.
Hellis and his colleagues have been using a suite of NASA instruments called CINDI, which fly on the U.S. Air Force Communication/Navigation Outage Forecast System (C/NOFS) satellite between 250 miles and 530 miles around the planet’s equator.
The researchers never expected to encounter the edge of Earth’s ionosphere at those altitudes, but that is exactly what happened during the summer of 2008, a time when the solar activity was unusually weak.
"It was a real combination of low solar activity and the satellite’s range," Hellis said. "We didn’t expect to be able to look at the top of the ionosphere in all places." Computer models based on previous research had predicted the ionosphere to be about 370 miles above Earth at night and about 620 miles up during the day--the variation due to temperature and other factors.
Instead, the CINDI team discovered that the transition between the ionosphere and space was about 250 miles above Earth at night and about 500 miles up during the day.
The ionosphere is primarily caused by extreme ultraviolet energy from the sun.
"It’s powerful enough that those photons (光子) can ionize (使……电离) atoms in Earth’s upper atmosphere," said David Hathaway, a solar physicist at NASA’s Marshall Space Flight Center in Huntsville, Ala. "When you have a geomagnetic disturbance or a solar flare going off, you can get an ionosphere that is uneven, which can cause problems with radio signals and GPS satellite signals, which have to pass through."
The findings were presented at the annual American Geophysical Union conference in San Francisco last month.
CINDI is an acronym for Coupled Ion Neutral Dynamics Investigation. The device works by separately measuring ionized and neutral particles at altitudes where the Air Force satellite flies. A similar device is on another polar-orbiting Air Force spacecraft.
The researchers hope to keep using CINDI as solar activity picks up in the sun’s new 11-year cycle. The next solar maximum is expected in late 2011 or 2012.
In order to predict distortions, scientists need to______.
选项
A、improve the severity of radio, radar and navigation signals
B、improve the accuracy of the satellite-based systems
C、study the charged particles in the ionosphere
D、study the thick regions in the ionosphere
答案
D
解析
第3段指出为了预测电离层对通讯的影响,科学家必须研究those structures,结合上一段可以知道those structures应指上一段提到的dense regions,故选D。
转载请注明原文地址:https://kaotiyun.com/show/8gs7777K
0
大学英语六级
相关试题推荐
Aresomepeoplebornclever,andothersbornstupidly?【S1】______Orisintelligencedeveloped
A、Congressionalsecretary.B、Congressman.C、Senator.D、Vicepresident.D
LondonisthecenteroftheinternationalartmarketandSothehy’s,whichhasits【B1B】______there,istheworld’sbiggestand
Do’sandTaboos:CulturalAspectsofInternationalBusiness—ByM.Ka
JosephWeizenbaum,professorofcomputerscienceatMIT,thinksthatthesenseofpoweroverthemachineultimatelycorruptsthe
Livelyargumentcentersaroundeffectofpubliccommunicationonaudiences,notonlyinmattersconcerningpublicopiniononpol
Super-kidsandSuperProblems—ByDavidElkindNot
Man,eveninthelowerstagesofdevelopment,possessesafacultywhich,forwantofabettername,IshallcallNumberSense.T
Itisobviousthat______(经济波动会影响人们的生活).
A、Becausetheyneedmoreproteinthanvegetablessupply.B、Becausetheycannotdigestvegetables.C、Becausetheyusemoreenergy
随机试题
根据公共政策目标所着眼的时间范围,可把公共政策目标分为()
对于血清中数种蛋白质抗原成分的分析,常可采用
女,35岁,5个月来间歇性胸背剧痛。体检:右侧下肢肌力Ⅳ度伴膝、踝反射亢进,Babinski征阳性。右踝振动觉消失,左胸下痛温觉消失。余神经系统无异常。胸椎平片无异常。可能诊断为
根据我国的会计相关法规,下列哪个单位不得使用中文以外其他语言文字编制会计记录?()
计划协调技术原理是首先应用网络图形式来表达一项计划中各种工作的先后顺序和相互关系。()
当物价上涨率高于财政收入增长率时,财政收入会出现()。
教育只能适应儿童的发展,而不能促进儿童的发展。()
个人独资企业解散后,按照《个人独资企业法》的规定,原投资人对企业存续期间的债务是否承担责任?()
下列各句中加下划线成语使用有误的一项是()。
(2013年上半年上午试题51)采用顺序表和单链表存储长度为n的线性序列,根据序号查找元素,其时间复杂度分别为________。
最新回复
(
0
)