磁正午附近极光强度与沉降粒子能量关系的参数模型

极光是日地能量耦合过程中粒子沉降到极区电离层的最直观表现,对于理解地球空间环境及预测空间天气具有重要作用.本文利用2003—2009年的北极黄河站的多波段地面极光观测,结合DMSP卫星粒子沉降探测,对磁正午附近的极光强度与沉降粒子沉降能量之间的关系进行了定量研究.统计结果表明,在10—13磁地方时(MLT)630.0 nm的极光发光占主导,以低能粒子沉降为主;而在13—14MLT,630.0 nm/427.8 nm极光强度比值降低,沉降粒子能量较高.另外,利用极光强度与沉降电子的能通量以及极光强度比值与平均能量之间的函数关系,初步建立了北极黄河站磁正午附近极光强度与沉降粒子能量关系的反演参数模型,为将来空间天气的监测服务.     

Peculiarities of electron precipitation in morning sector of auroral zone during geomagnetic storm

Summary The analysis of electron (E _e >30keV) and proton (E _p >150keV) precipitating fluxes measured on low altitude satellite Intercosmos-17 during the geomagnetic storm December 2, 1977 is presented. Particularly, the gap in electron precipitation on morning side at L=5÷6 is analyzed and discussed in terms of strong cyclotron diffusion.     

Intermittency of riometer auroral absorption observed at South Pole

Auroral radio-wave absorption values measured at South Pole for 3 years using a riometer are analyzed in order to test whether they show evidence of intermittency. The properties of the parameters of the probability density functions determined for several magnetic local time sectors are found to be significantly different. The probability density functions for the pre-midnight sector show the typical shape associated to intermittency. No results are given for the afternoon sector because few auroral absorption events meet the selection criteria to give statistically significant results. It is suggested that if the precipitating particle population responsible for the riometer auroral absorption shared the intermittency features of the absorption then the present results would allow the study of the properties of the induction component of magnetospheric turbulence.     

亚暴期间极光电集流带的变化

极光活动加剧和极光电集流增强是磁层-电离层能量耦合的两种重要表现形式,它们同为磁层带电粒子向电离层沉降的结果,但是变化规律却非常不同.本文用地基磁场资料,反演极区等效电流体系,研究地磁平静期和扰动期极光电集流带的运动特点.研究表明,Harang间断把极光电集流带分为两段：下午—黄昏段的东向电集流带较弱,而晨侧和子夜—凌晨段的西向电集流带较强.在亚暴膨胀相,随着AE指数增大,整个极光卵向赤道扩展,而极光电集流带却表现出分段差异的特点：下午—黄昏东向电集流带向低纬移动,晨侧西向电集流带也向赤道移动,而子夜—凌晨西向电集流带则向极移动.电动力学分析表明,在不同地方时段,控制电流的主要因素不同,因而,电流及其磁扰有不同的特点：下午—黄昏东向电集流和晨侧西向电集流组成了DP2电流体系,主要受控于磁层对流电场,反映了“驱动过程”的行为;而子夜—凌晨西向电集流是DP1电流体系的基本部分,主要受控于电导率,反映了“卸载过程”的特点.     

Modeling of nonstationary electron precipitation by the whistler cyclotron instability

We study a simple self-consistent model of a whistler cyclotron maser derived from the full set of quasi-linear equations. We employ numerical calculations to demonstrate dependencies of pulsation regimes of whistler-mode wave interactions with energetic electrons on plasma parameters. Possible temporal evolution of those regimes in real conditions is discussed; calculations are compared with case-study experimental data on energetic electron precipitation pulsations. A reasonable agreement of the model results and the observations has been found.     

日侧极光弧的发光强度与沉降电子能谱的相关关系

本文利用中国北极黄河站多波段全天空极光观测数据,选取稳定的日侧极光弧,统计研究了极光强度比I_557.7/I_630.0与极光发光强度I_557.7的相关关系.发现I_557.7在午前暖点和午后热点区附近出现极大值,分别为2.2 kR和2.9 kR;而I_630.0在磁正午出现极大值,为1.5 kR.当I_557.7从0.1 kR增加到10 kR时,极光强度比I_557.7/I_630.0也由0.2增加到9.结合DMSP卫星探测的沉降粒子能谱数据,找到17个DMSP卫星穿越黄河站上空极光弧的事件,共穿越40条极光弧.得到了沉降电子的平均能量正比于极光强度比I_557.7/I_630.0,沉降电子的总能通量正相关于极光强度I_557.7的关系式.利用该关系式反演所有极光弧的电子能谱,发现在午前和午后扇区,产生极光弧的沉降电子主要来源于等离子体片边界层;在高纬出现强度较弱的弧,对应等离子体幔区域.在磁正午附近,沉降电子的平均能量较低,极光弧处于低纬一侧,粒子源区主要是低纬边界层.

     

The size of the auroral belt during magnetic storms

Using the auroral boundary index derived from DMSP electron precipitation data and the Dst index, changes in the size of the auroral belt during magnetic storms are studied. It is found that the equatorward boundary of the belt at midnight expands equatorward, reaching its lowest latitude about one hour before Dst peaks. This time lag depends very little on storm intensity. It is also shown that during magnetic storms, the energy of the ring current quantified with Dst increases in proportion to L_e^–3, where L_e is the L-value corresponding to the equatorward boundary of the auroral belt designated by the auroral boundary index. This means that the ring current energy is proportional to the ion energy obtained from the earthward shift of the plasma sheet under the conservation of the first adiabatic invariant. The ring current energy is also pronortional to E_mag, the total magnetic field energy contained in the spherical shell bounded by L_e and L_eq, where L_eq corresponds to the quiet-time location of the auroral precipitation boundary. The ratio of the ring current energy E_R to the dipole energy E_mag is typically 10%. The ring current leads to magnetosphere inflation as a result of an increase in the equivalent dipole moment.     

Mesospheric observations with the EISCAT UHF radar during polar cap absorption events: 3. Comparison with simultaneous EISCAT VHF measurements

Mesospheric observations were obtained by the EISCAT UHF and VHF radars during the solar proton event of March 1990. We present the first comparison of incoherent-scatter spectral measurements from the middle mesosphere using simultaneous, co-located observations by the two radars. VHF spectra observed with a vertical antenna were found to be significantly narrower than model predictions, in agreement with earlier UHF results. For antenna pointing directions that were significantly away from the vertical, the wider VHF radar beam gave rise to broadening of the observed spectra due to vertical shears in the horizontal wind. In this configuration, UHF spectral measurements were found to be more suitable for aeronomical applications. Both radar systems provide consistent and reliable estimates of the neutral wind. Spectral results using both the multipulse and pulse-to-pulse schemes were intercompared and their suitability for application to combined mesosphere - lower thermosphere studies investigated.     

On the importance of auroral processes in the Universe

Acceleration of charged particles in magnetic field-aligned electric potential differences at Earth and at the outer planets in the solar system is summarized and its general importance in the Universe is briefly discussed.The role of field-aligned currents, driven by parallel electric fields, in causing filamentary structure in stellar atmospheres is briefly reviewed.The differences between auroral optical emissions at various planets are summarized.The important role of field-aligned potential differences in the generation of AKR and corresponding emissions from other objects is discussed.Finally, aurora-associated processes for ejection of planetary plasma into space are briefly reviewed.     

低太阳活动期间极区ELDI的EISCAT/ESR雷达观测

本文利用2009—2011年EISCAT/ESR雷达的场向观测数据,统计研究了低太阳活动期间极区E层占优电离层(ELDI)事件的发生规律及其主要特征.地面雷达观测表明,极区ELDI表现出明显的季节变化特征:在冬季和早春发生率较高.EISCAT雷达(极光椭圆纬度)观测到的ELDI多出现在磁午夜扇区,平均持续30 min;ESR雷达(极尖/极隙区纬度)观测到的ELDI多出现在磁正午附近,平均持续14 min,表现出与之前无线电掩星观测结果不一致的日变化特征.在ELDI事件期间,两处雷达观测到的电离层NmE/NmF2比值和E层厚度都没有表现出显著的空间差异.事例分析证实E层电子增强和F层电子密度耗空都能够独立地导致ELDI,然而,统计分析表明上述两个过程对ELDI的形成都起着不可或缺的作用.     

极光沉降粒子能量与AE、Dst指数的相关分析

对NOAA的POES系列极轨卫星观测得到的1978年以来近30年的极光沉降粒子半球能量的估算值EPI(Estimated Power Input)数据进行了分析,结果表明,极光沉降粒子有显著的春秋分峰值的年变化特征,并且有冬季半球沉降能量较大的南北半球不对称性.对EPI的时均值Pa与地磁指数AE、D_st的相关分析得到,Pa与AE的相关系数为0.76,Pa与D_st的相关系数为-0.55.把南北半球的时均值SPa,NPa数据分别与AE,D_st指数做相关,发现SPa与AE的相关性稍高于NPa的,SPa和NPa与D_st的相关性近似.当时延τ=0时,AE与Pa的相关最好,表明全球极光沉降粒子和极光电集流的变化同步;当D_st滞后于Pa,时延τ=1~2 h,Pa与D_st的相关最好,并且时延τ为6～8 h,Pa与D_st的相关都好于无时延的水平.     

Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam

We investigate the influence of magnetic mirroring and elastic and inelastic scattering on the angular redistribution in a proton/hydrogen beam by using a transport code in comparison with observations. H-emission Doppler profiles viewed in the magnetic zenith exhibit a red-shifted component which is indicative of upward fluxes. In order to determine the origin of this red shift, we evaluate the influence of two angular redistribution sources which are included in our proton/hydrogen transport model. Even though it generates an upward flux, the redistribution due to magnetic mirroring effect is not sufficient to explain the red shift. On the other hand, the collisional angular scattering induces a much more significant red shift in the lower atmosphere. The red shift due to collisions is produced by < 1 -keV protons and is so small as to require an instrumental bandwidth <0.2nm. This explains the absence of measured upward proton/hydrogen fluxes in the Proton I rocket data because no useable data concerning protons < 1 keV are available. At the same time, our model agrees with measured ground-based H-emission Doppler profiles and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the profile. Our results suggest that Doppler profile measurements with higher spectral resolution may enable us to quantify better the angular scattering in proton aurora.     

Seasonal variations in the parameters of the effects of noon absorption recovery during PCA

During many PCAs at auroral zone stations in the daytime, a smooth decrease in the absorption, called the noon recovery effect, is observed. The manifestation of this effect in PCA events registered at various seasons of the year (in spring, summer, and fall under a completely illuminated ionosphere and in winter under a completely (or partially) dark ionosphere) is analyzed in this paper. In the summer PCA, the amplitude of the noon recovery (the strongest decrease in the absorption in the hours close to the noon) and the frequency of occurrence of this effect are lower than in equinox conditions. A decrease in temperature and the enhanced content of water vapor in the upper mesosphere in summer as compared to the equinox seasons are the main factors governing the small amplitude of the noon recovery in summer PCA. Using experimental and calculated data, the presence of the noon recovery effect in winter PCA is found for the first time. In winter PCA, the absorption variation during noon recovery has a complicated shape: a smooth decrease in the daytime hours and a short-term (pulse-type) increase in the absorption in the local noon. This increase is caused by the fact that the ionosphere over auroral stations in the winter season is illuminated for a short time interval (around the local noon), which causes a sharp increase in the absorption. The amplitude of the noon recovery in winter PCA is higher than in equinox and summer PCA.     

地球辐射带能量电子通量在不同地磁活动下的统计分析

利用大约15个月的CRRES卫星MEA能量电子观测数据,分别在地磁活动平静(0≤Kp)、中等(3≤Kp≤6)及强烈(6)的条件下,选取电子能量为148 keV, 509 keV, 1090 keV, 1581 keV的辐射带能量电子通量进行统计分析,得到了不同地磁活动条件下地球辐射带高能电子通量在(L, MLT)空间的全球分布模型.结果表明,在2的磁层区域,高能电子通量分布在不同的地磁活动指数Kp条件下差别明显;在12~18 MLT时段内高能电子的通量明显增大.     

Negative ions in the auroral mesosphere during a PCA event around sunset

This is a study of the negative ion chemistry in the mesosphere above Tromsø using a number of EISCAT observations of high energy proton precipitation events during the last solar maximum, and in particular around sunset on 23 October, 1989. In these conditions it is possible to look at the relative importance of the various photodetachment and photodissociation processes controlling the concentration of negative ions. The data analysed are from several UHF GEN11 determinations of the ion-plasma ACF together with the pseudo zero-lag estimate of the ‘raw’ electron density, at heights between 55 km and 85 km, at less than 1 km resolution. The power profiles from the UHF are combined with the 55-ion Sodankylä model to obtain consistent estimates of the electron density, the negative ion concentrations, and the average ion mass with height. The neutral concentrations and ion temperature are given by the MSIS90 model. These parameters are then used to compare the calculated widths of the ion-line with the GEN11 determinations. The ion-line spectrum gives information on the effects of negative ions below 70 km where they are dominant; the spectral width is almost a direct measure of the relative abundance of negative ions.     

Isotopic composition of precipitation during strong El Niño–Southern Oscillation events in the Southeast Region of Brazil

Equatorial Pacific sea surface temperature variations interact with processes of atmospheric circulation, creating conditions for the occurrence of El Niño–Southern Oscillation (ENSO). ENSO events represent the most important interannual phenomena affecting climate patterns worldwide and causing significant socio‐economic impacts. In the Brazilian territory, ENSO leads to an increase in drought episodes in the north‐eastern region and an increase in precipitation in the southern region, whereas the effects over the south‐east region are yet not well understood. The main goal of this study is to compare variations of isotopic composition in precipitation across the south‐east portion of the Brazilian territory during two very strong ENSO events: 1997–1998 (ENSO 1) and 2014–2016 (ENSO 2). Daily isotopic records, available from the Global Network of Isotopes in Precipitation database for ENSO 1, and samples collected during ENSO 2 were used to compare the influence of both events on the isotopic composition of precipitation. Seasonal variations indicated more depleted precipitation during the wet seasons (δ¹⁸O = ?5.4 ± 4.0‰) and enriched precipitation during the dry seasons (δ¹⁸O = ?2.8 ± 2.3‰). Observed rainfall variations were associated with atmospheric large‐scale processes and moisture transport from the Amazon region, whereas extreme values (enriched or depleted) appear to be associated with particular convective and stratiform precipitation events. Overall, more depleted isotopic composition of precipitation (δ¹⁸O = ?4.60‰) and higher d‐excess (up to +15‰) were observed during the dry season of ENSO 1 when compared with ENSO 2 dry season (δ¹⁸O‰ = ?2.80‰, d‐excess lower than +14‰). The latter is explained by greater atmospheric moisture content, particularly associated with recycling of transpiration fluxes from the Amazon region, during dry season of ENSO 1. No significant differences for δ¹⁸O and δ²H were observed during the wet season; however, d‐excess from ENSO 2 was greater than ENSO 1, due to the slightly greater atmospheric moisture content and very strong upward motion observed. Our findings highlight the opportunity that environmental isotopes offer towards understanding hydrometeorological processes, particularly, the evolution of extreme climatic events of global resonance such as ENSO.     

Strong localized variations of the low-altitude energetic electron fluxes in the evening sector near the plasmapause

Specific type of energetic electron precipitation accompanied by a sharp increase in trapped energetic electron flux are found in the data obtained from low-altitude NOAA satellites. These strongly localized variations of the trapped and precipitated energetic electron flux have been observed in the evening sector near the plasmapause during recovery phase of magnetic storms. Statistical characteristics of these structures as well as the results of comparison with proton precipitation are described. We demonstrate the spatial coincidence of localized electron precipitation with cold plasma gradient and whistler wave intensification measured on board the DE-1 and Aureol-3 satellites. A simultaneous localized sharp increase in both trapped and precipitating electron flux could be a result of significant pitch-angle isotropization of drifting electrons due to their interaction via cyclotron instability with the region of sharp increase in background plasma density.     

Formation of homogeneous regions for regional frequency analysis of extreme precipitation events in the Czech Republic

Extreme high precipitation amounts are among environmental events with the most disastrous consequences for human society. This paper deals with the identification of ‘homogeneous regions’ according to statistical characteristics of precipitation extremes in the Czech Republic, i.e. the basic and most important step toward the regional frequency analysis. Precipitation totals measured at 78 stations over 1961–2000 are used as an input dataset. Preliminary candidate regions are formed by the cluster analysis of site characteristics, using the average-linkage clustering and Ward’s method. Several statistical tests for regional homogeneity are utilized, based on the 10-yr event and the variation of L-moment statistics. In compliance with results of the tests, the area of the Czech Republic has been divided into four homogeneous regions. The findings are supported by simulation experiments proposed to evaluate stability of the test results. Since the regions formed reflect also climatological differences in precipitation regimes and synoptic patterns causing high precipitation amounts, their future application may not be limited to the frequency analysis of extremes.     

Possible evidence for partial demagnetization of electrons in the auroral E-region plasma during electron gas heating

A previous study, based on incoherent and coherent radar measurements, suggested that during auroral E-region electron heating conditions, the electron flow in the auroral electrojet undergoes a systematic counterclockwise rotation of several degrees relative to the E×B direction. The observational evidence is re-examined here in the light of theoretical predictions concerning E-region electron demagnetization caused by enhanced anomalous cross-field diffusion during strongly-driven Farley-Buneman instability. It is shown that the observations are in good agreement with this theory. This apparently endorses the concept of wave-induced diffusion and anomalous electron collision frequency, and consequently electron demagnetization, under circumstances of strong heating of the electron gas in the auroral electrojet plasma. We recognize, however, that the evidence for electron demagnetization presented in this report cannot be regarded as definitive because it is based on a limited set of data. More experimental research in this direction is thus needed.