磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法

本文采用国际地磁参考场(1980IGRF,n=8)磁力线经验公式和三层模式电离层,结合哨声波沿磁力线传播所需电子浓度的横向梯度,给出了磁纬10°以下哨声路径纬度和所需抬升因子积分中值的估算方法;从而得出:(1)哨声色散值D不仅与电离层N_mF2正相关,而且与h_mF2也有明显相关性.当路径纬度ф₉₀≤10.5°(IGRF,n=8,下同)时,D与h_mF2负相关;>12时,正相关;在10.5°—12°之间时,正或负相关取决于路径顶点高度与h_m之差值.估算表明,三亚(磁纬7.04°N)收到的哨声中路径纬度ф₉₀≤10.5。的占94.5%,D与h_mF2负相关,这与观测结果一致.(2)所需抬升因子积分中值一般在7—31%之间.      

海南岛三亚哨声观测资料的初步分析

本文主要介绍1983年初在海南岛三亚观测哨声的部分结果.记录到大量哨声,其中包括短哨、多源哨和多路哨;约有10%的哨声下截频在0.8kc/s左右.经分析发现:(1)三亚哨声几乎全部出现在f₀F₂下降的过程中,哨声出现率的峰值在f₀f₂下降最快处,即电子浓度下降变化急剧处;(2)哨声活动和磁暴的关系与中高纬有所不同,存在明显的相反情况.      

电离层离子丰度对哨声传播经度效应的影响

Iss-b卫星探测结果表明,|电离层离子丰度呈现经度变化.本文选取较真实的电离层模型参数,对130°E和114°E两个子午面内传播的低纬哨声进行了射线跟踪.我们发现,由于[O~+],[He~+]和[H~+]决定的电子浓度垂直梯度的经度变化,导致哨声传播特性的经度效应,使得130°E比114°E内传播的低纬哨声更好地满足透射条件:|μsinδ|≤1.与电子浓度的水平梯度的影响比较,离子丰度决定的电子浓度垂直梯度随经度的变化使哨声传播产生的经度效应明显得多.武昌(地理30.5°N,114.6°E;地磁19.3°N).和鹿儿岛(31.5°N,130.8°E;20.5°N)两台站观测到的哨声出现率的经度效应证实了本文的理论预言.     

地磁场模式对低纬哨声射线追迹计算的影响

考虑到低纬地磁场与偶极子磁场偏离较大, 本文用国际参考场(n=6)进行了低纬哨声射线追迹计算.结果表明, 在约9°N和12°N处有两个很窄的哨声波非导传播出口点, 相应射线起点都在雷电活动区.哨声波非导传播出口的截止纬度约在8—9°N处.计算结果也较满意地解释了低纬哨声色散值和f₀/F₂正相关的事实.      

重庆与兰州电离层Es出现率的比较研究

对重庆(29.5,106.6)与兰州(36,103.9)f₀E_s>5MHz的Es出现率和E层临界频率f₀E进行了详细对比研究.结果表明:(1)此两地Es出现率的变化特征显著.白天重庆高于兰州;晚上则正相反.(2)出现率的这种变化与Es环境电离密度的变化趋势十分一致.(3)上述特征的形成,除了此两地纬度上的差异外,与兰州地处地磁S_q电流系的焦点很有关系.      

武昌上空Es—s的形态与出现规律

本文对武昌上空电离层E_s-s的形态与出现规律进行了考察与统计分析。 该地区的E_s-s描迹清晰、出现频繁.表明E_s-s既不单是磁扰的伴随现象,也不仅为极光地带与地磁赤道地区所特有。 该地区的E_s-s多出现于磁静日的白天.其出现率分别于地方时间九、十点(对于日变化)和夏季月份(对于年变化)达到最大;对于这一特征,既看不出地磁变化的影响,也看不出太阳活动的控制。     

哨声模波通过低纬电离层传播的某些特征

本文采用IGRF(1980)模型进行了哨声模三维射线跟踪计算, 研究了夜间哨声通过低纬电离层传播的射线与波法的特征.着重讨论了形成非导管哨声可透射路径的条件、射线的聚焦效应及射线的低纬截止.数值计算得到路径终纬度截止约在倾角纬度10.7°N.      

合肥地区日落哨的分析

本文根据1986年初合肥地区(地理纬度31.73°N,经度117.15°E;地磁纬度20.60°N)哨声观测资料,分析和计算了日落哨导管的抬升因子、吸收系数和导管寿命.      

低纬100—200km间电子数密度的变化

利用光化平衡模式计算了低纬100—200km间白天电子数密度的变化。求得E-F₁谷区的谷深,谷宽、谷高的变化特征。获得如下结果:a.太阳活动明显影响电子数密度随高度及太阳天顶角的变化,发现太阳活动指数与电子数密度间不仅存在正相关,而且存在负相关;b.太阳活动明显影响E-F₁谷区的形态。在一定太阳活动条件下,对同一太阳赤纬和地理纬度,谷深、谷宽与太阳天顶角的关系难以用一简单函数来表示;c.太阳耀斑、地磁活动对该区电子密度有明显影响;d.在讨论100—200km间电子密度时不能忽略O+（2P）和NO的光电离率。      

磁暴期间甚低纬哨声的导管传播

对磁暴期间甚低纬哨声导管传播的机理进行了初步的讨论，根据暴时低纬哨声的特点，认为暴时出现的扩展哨、多跳回波是沿东向扰动电场导致的场列电离增强路径传播的。对在东向电场影响下低纬Ｆ层的数值模拟表明，东向电场导致的场列电离增强结构有利于哨声的捕获和传播。     

Rare observation of daytime whistlers at very low latitude (L = 1.08)

The source region and propagation mechanism of low latitude whistlers (Geomag. lat. <30°) have puzzled scientific community for last many decades. In view of recent reports, there is consensus on the source region of low latitude whistlers in the vicinity of the conjugate point. But the plausible conditions of ionospheric medium through which they travel are still uncertain. In addition to that, the whistlers in daytime are never observed at geomagnetic latitudes less than 20°. Here, for the first time, we present a rare observations of whistlers during sunlit hours from a very low-latitude station Allahabad (Geomag. Lat: 16.79°N, L = 1.08) in India on 04 February 2011. More than 90 whistlers are recorded during 1200–1300 UT during which the whole propagation path from lightning source region to whistler observation site is under sunlit. The favorable factors that facilitated the whistlers prior to the sunset are investigated in terms of source lightning characteristics, geomagnetic and background ionospheric medium conditions. The whistler activity period was found to be geomagnetically quiet. However, a significant suppression in ionospheric total electron content (TEC) compared to its quiet day average is found. This shows that background ionospheric conditions may play a key role in low latitude whistler propagation. This study reveals that whistlers can occur under sunlit hours at latitudes as low as L = 1.08 when the source lightning and ionospheric medium characteristics are optimally favorable.     

One-to-one relationship between low latitude whistlers and conjugate source lightning discharges and their propagation characteristics

One-to-one relation with its causative lightning discharges and propagation features of night-time whistlers recorded at low-latitude station, Allahabad (geomag. lat. 16.05°N, L = 1.08), India, from continuous observations made during 1–7 April, 2011 have been studied. The whistler observations were made using the Automatic Whistler Detector (AWD) system and AWESOME VLF receiver. The causative lightning strikes of whistlers were checked in data provided by World-Wide Lightning Location Network (WWLLN). A total of 32 whistlers were observed out of which 23 were correlated with their causative lightnings in and around the conjugate location (geom. lat. 9.87°S) of Allahabad. A multi-flash whistler is also observed on 1 April with dispersions 15.3, 17.5 and 13.6 s^1/2. About 70% (23 out of 32) whistlers were correlated with the WWLLN detected causative lightnings in the conjugate region which supports the ducted mode of propagation at low latitude. The multi-flash and short whistlers also propagated most likely in the ducted mode to this station.     

Characteristics of low-latitude whistlers and their relation with f0F2 and magnetic activity

Some results obtained from the characteristics of low-latitude whistlers received at Wuchang (Geomag. Lat. 19.2°N), Zhanjiang (9.8°N) and Yulin (6.4°N) are presented. The observations cover three years at Wuchang, two years at Zhanjiang, one year at Yulin.     

Simultaneous observations of some unusual whistlers and VLF hiss emission at a low L-value (L = 1.17)

The purpose of this paper is to describe some unusual whistlers (doublets and triplets) and VLF hiss emission recorded simultaneously on February 18, 1998 during nighttime at a low latitude Indian ground station Jammu (geomag. lat., 22° 26′ N; L = 1.17), and to make some discussions about their origin. The detailed structures of the observed VLF hiss emission clearly show that these emissions confined to a narrow continuous frequency band. Some times the frequency of hiss band oscillates and subsequently touches the upper edge of the first whistler component of the doublet. Detailed structures of the dynamic spectra of whistler and VLF hiss emission are briefly presented. From the dispersion analysis of the whistler doublets and triplets, it is found that the individual whistlers of the doublets and triplets simultaneously observed on the same day are one-hop whistlers having propagation path along higher and closely spaced L-values. Our result also shows that VLF hiss has been generated in the equatorial region of higher L-values. Generation and propagation mechanisms are briefly discussed.     

哨声波的自聚焦(Ⅱ)——当磁层对波有放大作用时的讨论

本文指出, 当磁层对波有放大作用时, 哨声波的自聚焦容易发生;当磁层对波有吸收时, 哨声波的自聚焦不容易发生.