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1.
Summary. Mean hourly values have been analysed month by month for a number of stations for which long runs of data are available. It is found that there is an annual variation in the M2 lunar tide, there being a global enhancement of the tide around January. There is also some evidence from the phase changes with latitude that, near the solstices, the lunar current system consists not of pairs of vortices, one in each hemisphere, but of single vortices with foci in the summer hemisphere. 相似文献
2.
全球低纬高原地区气候特征的初步研究 总被引：1，自引：0，他引：1
提出了全球１０大低纬高原和２０个著名春城的概念,给出了３５个有代表性的低纬高原气象站资料,通过分析气温和降水变化,得到低纬高原气候的共同特征是气温年较差小,四季如春,气温日较差大,一天分四季,降水适中,干湿季分明。主要气候类型是热带草原气候和高原型季风气候 相似文献
3.
《极地研究》1991,2(1):10-21
From the surface mass accumulation data in year of 1987/88, the distribution and variation of annual mass balance on Mizuho Plateau are discussed. The authors also analyze the effects of shortterm climatic and topographical variations on the mass balance. It is found that there are some differences in spatial distribution and annual average state in the year of 1987/88 and other years. Ia the area at elevation lower than 550 m near the coast, the mass balance appears to be negative. The annual mass balance over 80 km distance from S_(16) to inland is 0.84m snow depth. A low mass balance zone from 80 km site to Mizuho Station, is considered to be only 0.14 m snow depth. It is found from the comparison of mass balances that the mass-balance level on the glaciers in West China is 9 times higher than that on Mizuho Plateau, where the massbalance level appears to be low accumulative and low expensive, but inverse in middle and low latitude regions, such as on glaciers in West China. The effects of short-term 相似文献
4.
极区位于高纬度地区,极区航海图投影采用墨卡托投影时,图上极区附近变形较大,在极点处变形达到无穷大;采用极球面投影时,图上恒向线不是直线;心射切面投影不是正形投影,不能直接在图上量取方位和距离;兰伯特正形投影图上,经度是由角度表示,而不是真的经度;采用横轴墨卡托投影时,几乎所有的经线以及纬线在图上为曲线。以上常用的海图投影不利于船舶在极区安全航行,也不利于航海人员进行海图作业。针对此问题,将构建的伪经纬线网与经纬线网进行转换,通过Matlab得到基于伪经纬线网的横轴墨卡托投影图,此图具有类似于墨卡托海图的特点,图上极区变形失真小,图上伪经纬线的特点可方便极区海图作业。 相似文献
5.
本文利用南极长城站1987年4月至9月的地磁资料,分析了长城站地区冬季地磁S_q变化特征。分析结果表明:(1)南极长城站在初冬(4月)与冬末(9月)月份的S_q变化形态与北半球中纬度的北京地磁台的S_q变化形态基本相似,这可能是由中纬度电离层中的发电机电流所控制的。在仲冬月份(6月与7月),由于太阳紫外辐射效应减少,高纬度的地磁扰动占主导地位,反映出S_q变幅很小和以8小时以下的较短周期谐波起主要作用,(2)在初冬与冬末月份的S_q等效电流矢量,白天比黑夜大约5倍;其矢量方向在白天(08—15时)为顺时针,黑夜为反时针。在仲冬月由于电离层中电流的影响相对减弱,S_q等效电流矢量很小,白天与黑夜基本一样;其矢量分布方向与初冬和冬末的矢量方向不同,这可能是极区的电离层电流或场向电流的影响造成的。 相似文献
6.
Continental drift and true polar wandering 总被引：1，自引：0，他引：1
S. R. Dickman 《Geophysical Journal International》1979,57(1):41-50
Summary . Evidence in the form of 75 yr of ILS data is accumulating which suggests that true polar wander may be currently taking place. It seems likely that true wander of some magnitude must always accompany plate motions, but the extrapolated ILS rate is an order of magnitude larger than the rate of true polar wander deduced from palaeomagnetic data over the past 55 Myr. The conflict between palaeomagnetic and latitude data provides the motivation for investigating one possible excitation of polar wander, the mass redistribution which accompanies continental drift.
The mass redistribution arises mainly because of the contrasting density structure of oceanic and continental regions. The change in the inertia tensor resulting from 106 yr of plate motions is found to be negligibly small; even consideration of episodic plate movements, anelasticity, or a decoupled lithosphere cannot boost the effect to the ILS rate of polar wander. These conclusions are strengthened by the fact that any one of several absolute plate velocity models, based on extremely diverse assumptions, yields the same results.
In contrast, preliminary findings regarding the effect of Pleistocene deglaciation activities on the inertia tensor reveal that such non-isostatic phenomena may have a large influence on polar wander. 相似文献
The mass redistribution arises mainly because of the contrasting density structure of oceanic and continental regions. The change in the inertia tensor resulting from 10
In contrast, preliminary findings regarding the effect of Pleistocene deglaciation activities on the inertia tensor reveal that such non-isostatic phenomena may have a large influence on polar wander. 相似文献
7.
ZHANG Mingjun DONG Lei WANG Shengjie ZHAO Aifang QIANG Fang SUN Meiping WANG Qiong 《地理学报》2014,24(5):833-844
Based on the radiosonde data observed at 14 stations in Southwest China from 1960 to 2010, as well as the corresponding surface air temperature, the long-term change of free-air 0℃ isotherm height in Southwest China and the relationships between surface air temperature and 0℃ isotherm height are discussed. The results indicated that the spatial distribution of 0℃ isotherm height is generally related with latitude, but the huge massif or plateau may complicate the latitude pattern. The two main regimes influencing the spatial patterns of 0℃ isotherm height in Southwest China are latitude and huge massif. The annual 0℃ isotherm height has increased by 35 m per decade in the recent decades, which is statistically significant at the 0.001 level. Generally, the increasing trend can be examined for each seasonal series, especially in winter (53 m per decade). The diversity of trend magnitudes for annual and seasonal series can also be detected at a spatial view, but generally 0℃ isotherm height correlated well with surface air temperature. 相似文献
8.
CHARACTERISTICS OF Sq VARIATION OF GEOMAGNETIC FIELD AT THE GREAT WALL STATION, ANTARCTICA IN WINTER 
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下载免费PDF全文 《极地研究》1991,2(1):53-59
In this paper the characteristics of Sq variation of geomagnetic field in the region of the Chinese Great Wall Station (CGWS), Antarctica, in winter are analyzed from geomagnetic data obtained at the Geomagnetic Observatory of CGWS. The result enables us to reveal the following aspects: (1) The pattern of Sq variation at CGWS in early (Apr.) and Late winter (Sep.) is similar to that at Beijing Geomagnetic Observatory (BJO) at the middle latitude in the Northern Hemisphere. It may be controlled by the midlatitudinal ionospheric dynamo current. Amplitude of Sq variation is very small, and the harmonics in 8 hours or shorter periods in midwinter (June and July) is predominant because of the decreased effect of solar ultraviolet radiation and the dominant geomagnetic disturbance at high latitudes. (2) The vectors of Sq-equivalent current in the daytime are about five times more than that in the night. The direction of the vectors is clockwise in the daytime (08-15h) and counterclockwise in the night in earl 相似文献
9.
P. N. Mayaud 《Geophysical Journal International》1978,55(1):193-201
Summary. This investigation concerns both the annual variation and the daily variation of the Dst index for 18 years. The data display a 6-month wave, a 12-month wave and a 24-hr wave the phase of which apparently does not vary in the course of the year. This contrasts with the variations observed with planetary indices derived from subauroral K indices, which undergo a modulation in sin2 ΨM (ΨM is the angle between the solar wind and the dipole axis) with the well-known change in phase of the daily variation from one solstice to another. The origin of the 6-month wave is attributed to the mechanism suggested by Malin & Isikara: the 6-month variation of the mean latitude of the ring current. The 12-month wave may be due to the northern latitude of most of the Dst observatories. The daily variation is probably due to the asymmetric part of the ring current which is not averaged out because of the non-uniform longitudinal distribution of the Dst observatories. 相似文献
10.
北极地区以南生成并向北移动进入极区的气旋,在移动发展过程中常伴随大风、降水和升温等过程,对中低纬度地区物质和热量向极地输送起着重要作用,并对极区大气、海洋和海冰的变化产生一定影响。基于欧洲中期天气预报中心(ECMWF)发布的1979—2015年的海平面气压再分析数据产品,利用气旋自动识别和追踪算法,开展气旋的识别和追踪,获得向极跨越70°N气旋的数量、强度、活动轨迹及北向运动纬距等主要特征如下:该类气旋在数量上,春、冬季多于夏、秋季,年总数量和春、秋、冬季均呈减少趋势;强气旋易发于冬季,弱气旋多发于夏季;该类气旋活动轨迹,冬季集中分布在海上,夏季在陆地上;该类气旋北向运动纬距整体平均为9.2°,冬季平均最大,为10.2°,夏季平均最小,为7.3°;在年际变化上,年平均和春、冬季平均呈增长趋势,夏、秋季平均呈减少趋势;在年代际变化上,年平均和夏、冬季平均从1979—1988年到1989—1998年阶段都是减小的,到1999—2008年阶段是增大的,其后再减小,春、秋季则无明显趋势变化。 相似文献
11.
Mingjun Zhang Lei Dong Shengjie Wang Aifang Zhao Fang Qiang Meiping Sun Qiong Wang 《地理学报(英文版)》2014,24(5):833-844
Based on the radiosonde data observed at 14 stations in Southwest China from 1960 to 2010, as well as the corresponding surface air temperature, the long-term change of free-air 0℃ isotherm height in Southwest China and the relationships between surface air temperature and 0℃ isotherm height are discussed. The results indicated that the spatial distribution of 0℃ isotherm height is generally related with latitude, but the huge massif or plateau may complicate the latitude pattern. The two main regimes influencing the spatial patterns of 0℃ isotherm height in Southwest China are latitude and huge massif. The annual 0℃ isotherm height has increased by 35 m per decade in the recent decades, which is statistically significant at the 0.001 level. Generally, the increasing trend can be examined for each seasonal series, especially in winter （53 m per decade）. The diversity of trend magnitudes for annual and seasonal series can also be detected at a spatial view, but generally 0℃ isotherm height correlated well with surface air temperature. 相似文献
12.
20 0 0年 7月 ,太阳表面发生了一系列的耀斑与日冕物质抛射事件 ,最大耀斑能级达X5 .7/3 B。地球表面发生相应特大磁暴 ,Dst指数最大负偏达 - 3 0 0 n T。中国南极中山站地处极隙区纬度 ,白天位于磁层极隙区 ,夜间位于极盖区 ,以多种高空大气物理观测设备详细记录了该磁暴过程。对有关数据的分析表明 ,高能粒子引起电离层吸收急剧增加 ,测高仪数据两天多信号空白 ,宇宙噪声吸收显著增加 ;地磁 Pc3 /5脉动增加与行星际磁场南向分量密切对应 ,显示行星际磁流体波对激发磁层脉动的贡献 ;磁暴主相期间 ,Pc3 /5脉动大幅度增加 ;极区地磁水平分量随南向行星际磁场变化 ,但滞后近 8小时 ;Dst指数与南向行星际磁场密切相关 ,磁暴受控于高度负偏的南向行星际磁场 相似文献
13.
利用南极地磁资料研究了地磁扰日变化ＳＤ场特征。１）ＳＤ场变化不如Ｓｑ场变化规则,无明显的昼夜差异;太阳活动高年（１９９１年）比下降年（１９９４年）ＳＤ场变化更强烈。２）极隙区中山站ＳＤ场变幅比亚极光区长城站和北半球低纬区北京台的ＳＤ场变幅大１０倍以上。３）中山站Ｓ０Ｄ（Ｈ）变化呈“正弦波”形态,与长城站和北京台Ｓ０Ｄ（Ｈ）变化形态相反。４）中山站Ｓ０Ｄ等效电流矢量在早晨－下午（０２～１５ｈ）矢量方向为反时针西向,下午－夜间（１５～０２ｈ）矢量方向为顺时针东向,这是由极区东向、西向电射流和极区电流涡旋所引起;长城站与北京台Ｓ０Ｄ等效电流矢量很小,这是由极区东向和西向电射流的影响所致。 相似文献
14.
塔克拉玛干地区近四十年来的干湿变化 总被引：4，自引：1，他引：3
本文利用塔克玛干,周围山区、及相邻地区的４８个气象站近４０年的降水资料,分析塔克拉玛干地区年与四季干湿变化的阶段与周期,与与周围山区及相邻地区进行相关性分析。 相似文献
15.
A physical model for palaeosecular variation 总被引：1，自引：0，他引：1
Summary. A new model to describe the latitude dependence of the angular dispersion of the palaeomagnetic field (palaeosecular variation) is developed following previous models, but with crucial differences. It is shown that if the probability distribution of virtual geomagnetic poles (VGPs) is circularly symmétric about the rotation axis then the geométry of the distribution of field directions is latitude dependent. This has a significant effect on the latitude dependence of dispersion and is accounted for in the model. The dipole and non-dipole parts of the field are not artificially separated but are intimately linked through an observationally determined relation that the time averaged intensity of the non-dipole field is dependent upon the intensity of the dipole field. It is shown that a consequence of this relation is that no knowledge of the probability distribution of the geomagnetic dipole moment is required. This is a fundamental improvement over previous models.
The model provides excellent fits to the palaeodata and, unlike previous models, is not inconsistent with the latitude variation of the non-dipole field dispersion determined from the present field. For the past 5 Ma the point estimate of the VGP dispersion due to dipole wobble is 7.2° and of the VGP dispersion at the equator due to variation in the non-dipole field is 10.6°. This estimate of the dispersion due to variation in the non-dipole field is in excellent agreement with the value predicted from an analysis of the variation in field intensities over the same period. Fits of the model to data from earlier periods indicate that dispersion due to variation in the non-dipole field is essentially independent of the geomagnetic reversal rate while dipole wobble is positively correlated with reversal rate. 相似文献
The model provides excellent fits to the palaeodata and, unlike previous models, is not inconsistent with the latitude variation of the non-dipole field dispersion determined from the present field. For the past 5 Ma the point estimate of the VGP dispersion due to dipole wobble is 7.2° and of the VGP dispersion at the equator due to variation in the non-dipole field is 10.6°. This estimate of the dispersion due to variation in the non-dipole field is in excellent agreement with the value predicted from an analysis of the variation in field intensities over the same period. Fits of the model to data from earlier periods indicate that dispersion due to variation in the non-dipole field is essentially independent of the geomagnetic reversal rate while dipole wobble is positively correlated with reversal rate. 相似文献
16.
A series of solar flare and coronal mass ejection (CME) event occurred in July 2000, particularly the largest flare (X5.7/3B) with CME on 14th of July since 1989, which stimulated a great geomagnetic storm with D st index reaching -300 nT. A number of data have been obtained from the Chinese Antarctic Zhongshan Station (ZHS, INT Lat. 74.5°, L≈14), which is located at cusp latitude, and from the ACE satellite. After analyzing these data we have got the results as follows: a lot of solar high energy particles penetrated into the polar ionosphere and ionized it, which significantly increased the cosmic noise absorption (CNA) and blanked the DPS-4 data for more than two days. The magnetic pulsation in Pc 3/5 frequency band on the ground has a high relation with the fluctuation of interplanetary magnetic field (IMF) B z, which shows the contribution of interplanetary magnetohydrodynamical (MHD) waves to the Pc 3/5 pulsation on the ground. The Pc 3/5 pulsation was intensified much during the great magnetic storm. The H component of the magnetic field at ZHS varied with the southern value of IMF B z but lagged behind for about 8 10 h. While D st index responded to the variation of the IMF B z very quickly, which suggested that the magnetic storm occurred at low latitude firstly and then effected the ionospheric current at high latitude. 相似文献
17.
Summary. A simplified model of the solar quiet-time ionospheric current system is used to calculate the induced currents in a model earth. The conductivity is assumed to be constant below a depth of about 400 km and zero above that depth. The current induced in the north—south conductivity anomaly under the Rocky Mountains is then estimated from the time-varying potential difference between points at 30 and 45° latitude at the surface of the conducting sphere. The purpose of these calculations is to investigate whether variations in the latitude of the northern hemisphere current system vortex will substantially alter the relationship between the observed magnetic field components at the Earth's surface and the local magnetic field gradient caused by the conductivity anomaly. We find that a 10° shift in the latitude of the ionospheric current focus causes a change of 6 per cent or less in the transfer function from the field components to the gradient in the total field. Thus such latitude shifts cannot explain much of the magnetic field gradient variation at periods near 24 hr that has been observed near Boulder, Colorado. 相似文献
18.
E. C. Butcher 《Geophysical Journal International》1982,69(1):101-111
Summary. From a study of 'abnormal quiet days' (AQDs) along the 0° meridian between 14 and 60° N, it was found (Butcher & Brown) that the minimum in H at stations on the poleward side of the Sq ( H ) focus was formed by a small negative substorm event when the normal Sq ( H ) amplitude was reduced by a superposed northward field.
In this paper we consider both the AQD event and the superposed northward field as a function of longitude and also consider in more detail the latitude variation of the superposed northward field. From such a study it is concluded that: (1) the AQD event is definitely due to a small magnetospheric substorm event; (2) the superposed northward field varies smoothly with longitude falling to zero some 110° from the longitude of its maximum amplitude; (3) the superposed northward field has a variation with geomagnetic latitude tending to zero near 20° and 70°N with a maximum near 55° N in summer and 35° N in winter; (4) there is some evidence that the effect of the IMF penetrates into the mid-latitude E-region and its effect is latitude-dependent. Although the evidence supports the suggestion that the currents responsible for the superposed northward field flow in the E-region no suggestion as to the origin of the driving force of the currents is forthcoming. 相似文献
In this paper we consider both the AQD event and the superposed northward field as a function of longitude and also consider in more detail the latitude variation of the superposed northward field. From such a study it is concluded that: (1) the AQD event is definitely due to a small magnetospheric substorm event; (2) the superposed northward field varies smoothly with longitude falling to zero some 110° from the longitude of its maximum amplitude; (3) the superposed northward field has a variation with geomagnetic latitude tending to zero near 20° and 70°N with a maximum near 55° N in summer and 35° N in winter; (4) there is some evidence that the effect of the IMF penetrates into the mid-latitude E-region and its effect is latitude-dependent. Although the evidence supports the suggestion that the currents responsible for the superposed northward field flow in the E-region no suggestion as to the origin of the driving force of the currents is forthcoming. 相似文献
19.
本文利用南极中山站的数字式电离层垂直测高仪１９９５年的频高图资料，对中山站上空冬季电离层的一些平均特性进行了初步分析。中山站冬季电离层Ｆ层很不稳定，其日变化比较明显，ｆｏＦ２的月中值在０９００ＵＴ出现极大并在１４００ＵＴ附近出现次极大。最大值在０９００ＵＴ（磁中午）附近，这是极隙区软电子沉降、极区等离子体对流和光辐射电离效应等诸多因素综合作用的结果，形成了所谓的磁中午异常。在２０００～０１００ＵＴ之间ｆｏＦ２数值较小，可能是由于这段时间中山站正处于电离层极洞区域。Ｅｓ层几乎每天都可以观测到，在１７００ＵＴ附近出现机率较高，并且ｆｏＥｓ数值较大，多数为极光型Ｅｓ，主要是由于极光粒子沉降引起的。电离层Ｅ层的变化相对平缓。 相似文献
20.
A generalized database of global palaeomagnetic data from 3719 lava flows and thin dykes of age 0–5 Ma has been constructed for use with a relational database management system. The database includes all data whose virtual geomagnetic poles (VGP) lie within 45 of the spin axis and can be used for studies of palaeosecular variation and for geomagnetic field modelling. Because many of these data were collected and processed more than 15–20 years ago, each result has been characterized according to the demagnetization procedures carried out. Analysis of these data in terms of the latitude variation of the angular dispersion of VGPs (palaeosecular variation from lavas) strongly suggests that careful data selection is required and that many of the older studies may need to be redone using more modern methods. Differences between the angular dispersions for separate normal- and reverse-polarity data sets confirm that many older studies have not been adequately cleaned magnetically. Therefore, the use of the database for geomagnetic field modelling should be carried out with some caution. Using a VGP cut-off angle that varies with latitude, the best data set consists of 2636 results that show a smooth increase of VGP angular dispersion with latitude. Model G for palaeosecular variation, which is based on modelling of the antisymmetric (dipole) and symmetric (quadrupole) dynamo families, provides a good fit to these results. 相似文献