North-south asymmetries of solar particle events in upper stratospheric ozone

Stratospheric ozone depressions, following intense solar particle events (SPE) observed by the backscattered ultraviolet (BUV) experiment on the Nimbus-4 satellite, indicate the existence of distinct asymmetries between the Northern and Southern Hemispheres. These asymmetries are observed in the magnitude of the depressions above the 5-mb level, their temporal variations, and the spatial (i.e., latitude and longitude) dependence of these variations. Possible causes of asymmetries, shown by two events on 4 August 1972 and 25 January 1971, can be attributed to: (1) tilt of the interplanetary magnetic field (IMF) with respect to the Earth's dipole magnetic field which influences the precipitation of energetic solar particles into the polar atmospheres; (2) differences in ozone chemistry caused by the large change in atmospheric temperature between summer and winter hemispheres; (3) seasonal differences of the stratosphere's dynamic states which are affected by upward propagating planetary waves in winter in contrast to the relatively undisturbed zonal flow in summer; (4) topographic asymmetry between Northern and Southern Hemispheres.These effects are shown by three-dimensional plots of the events in geographic coordinates and by color contour plots of the stratospheric ozone distributions in geomagnetic and geographic polar coordinates, respectively.     

Synthesis of γ-Mg2SiO4

Magnesium orthosilicate with spinel structure (γ-Mg₂SiO₄) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001Å. X-ray powder diffraction pattern revealed a significant difference between γ-Mg₂SiO₄ and other γ-M₂SiO₄ spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg₂SiO₄ spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels.     

Cyclotron side-band emissions from ring-current electrons

VLF-emissions with subharmonic cyclotron frequency from magnetospheric electrons have been detected by the S³-A satellite (Explorer 45) whose orbit is close to the magnetic equatorial plane where the wave-particle interaction is most efficient. These emissions are observed during the main phase of a geomagnetic storm in the nightside of the magnetosphere outside of the plasmasphere around L = 3–5. The emissions consist essentially of two frequency regimes, one below the equatorial electron gyro-frequency, , and the other above . The emissions below are whistler mode and there is a sharp band of “missing emissions” along . The emissions above are electrostatic mode and the frequency ranges up to . It is concluded that these emissions are generated by the enhanced relativity low energy (1–5 keV) ring current electrons, penetrating into the nightside magnetosphere during the main phase of a magneto storm. Although the high energy (50–350 keV) electrons showed remarkable changes of pitch angle distribution, their associations with VLF-emissions are not so significant as those of low energy electrons.     

Research on the evolution law of permafrost under the influence of urbanization based on remote sensing technology

The permafrost of Mohe County and its suburbs in the Daxing′an Mountains has been influenced by the urbanization. Remote sensing, GIS technology and numerical simulation was used to study the temperature variations of permafrost with the changes in surface vegetation that cover Mohe County and suburban areas, and the law of permafrost degradation on the study area was analyzed. The research results show that the urban area of the study area increased 114.42%from 2000 to 2016, and the urbanization process is continuing to accelerate. The Normalized Difference Vegetation Index map of 2017 in Mohe County and its suburbs was studied and the maximum proportion of vegetation coverage was different in the four seasons. The numerical calculation model results show that the permafrost temperature change in the study area cyclically fluctuates in a cosine form. The annual variation curve of permafrost temperature gradually decreased and its accompanying phase lag increased with depth. The annual temperature change value with the different depths of the town was greater than the natural ground. The maximum permafrost thawing depths of the town and natural ground were 4.2 m and 2.82 m in 50 a, and the degradation rates of the two permafrost are, respectively, 0.88 cm/a and 0.46 cm/a. These results show that urbanization has accelerated the degradation of permafrost.     

多年冻土区土壤多环芳烃污染研究进展

多环芳烃（polycyclic aromatic hydrocarbons,PAHs）是一种难降解、毒性强的致癌性污染物,其广泛分布于各环境介质中,陆地环境中90%的PAHs累积在土壤中。随着资源的开发,由油品泄漏、垃圾渗滤、污水排放等行为造成的多年冻土区PAHs土壤污染问题日益突显,并且在气候变化背景下,多年冻土中的PAHs具有重新释放而造成二次污染的风险,多年冻土区土壤多环芳烃污染分布特征和迁移规律研究对评估多年冻土区生态环境风险,防治土壤持久性有机物污染,保障广大多年冻土居民生命健康安全具有重要意义。通过回顾目前国内外多年冻土区土壤中PAHs污染的相关研究,分析发现多年冻土区未受污染的土壤中PAHs的污染水平远低于中低纬度人口密集区域,可代表地球土壤中PAHs的背景值;高纬度或高海拔的地理位置以及严寒的气候使得冻土区土壤中PAHs一个普遍且最重要的来源是大气远距离传输;活动层的冻融作用主要通过改变土壤理化性质和控制水分运移方向影响PAHs在多年冻土区土壤中的垂向分布特征,多年冻土的低渗透性具有阻碍PAHs垂向迁移的作用。综合分析已有研究成果,表明目前冻土区土壤PAHs污染研究还是大量集中于表层土壤中的污染分布调查和来源解析,而关于PAHs在活动层和多年冻土层中的垂向迁移研究还仅限于对其在土壤剖面中分布状况的解释性分析,冻融作用对PAHs在土壤中的迁移、转化和归宿的影响机制还不清楚。未来多年冻土区土壤中PAHs的研究将集中于迁移转化机理与污染治理技术两方面,针对PAHs在多年冻土区土壤中迁移行为的模拟模型亟待研究开发,以实现PAHs污染储量和迁移通量的定量预测;此外,多年冻土区土壤污染问题的深入研究还需要紧密联系多圈层、多界面、多介质、多要素以及多目标污染物而开展。     

VLF-emissions associated with ring current electrons: Off-equatorial observations

The combination of a small inclination of the orbit (～4°) with the tilt angle (～11°) of the Earth's magnetic dipole axis enabled the S³-A satellite (Explorer 45) to make simultaneous observations of magnetospheric VLF-emissions and the associated enhancement of ring current electrons not only at the magnetic equator but also up to 15° geomagnetic latitudes. Microdensitometer scanning of the wideband data of these emissions reveals that the band of missing emission in the off-equatorial whistler mode emissions (chorus) appears at $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ and that the intensities of the off-equatorial emission above $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ are very weak in contrast to those of the near equatorial emissions, where $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ is the equatorial electron gyrofrequency corresponding to the local gyrofrequency f_H at the satellite. Ray-tracing of whistler mode waves produced by the enhanced ring-current electrons at the geomagnetic equator just outside of the plasmapause has shown that some of these waves are reflected from high latitudes back to the Equator inside the source region. This process had been previously speculated to explain the formation of the bimodal intensity distribution with a gap at half the gyrofrequency (the two-band chorus) in the equatorial emission data. The intensities of those reflected waves, however, are shown to be insufficient to explain the observed emissions below $\text{f}{}_{\mathrm{<mtext>Ho</mtext>}}\text{2}$ at the Equator. These results indicate that the superposition of two types of emissions produced by the same processes but from different locations is not the main mechanism for the formation of the two-band chorus and that the dominant sources of these choruses are located around ± 5° geomagnetic latitude.     

A calculation of auroral hiss with improved models for geoplasma and magnetic field

Intensities of auroral hiss generated by the Cerenkov radiation process by electrons in the lower magnetosphere are calculated with respect to a realistic model of the Earth's magnetosphere. In this calculation, the magnetic field is expressed by the “Mead-Fairfield Model” (1975), and a static model of the iono-magnetospheric plasma distribution is constructed with data accumulated by recent satellites (Alouette-I, -II, ISIS-I, OGO-4, -6 and Explorer 22). The energy range of hiss producing electrons and the frequency range of the calculated VLF are 100–200 keV, and 2–200 kHz, respectively. Intensities with a maximum around 20 kHz, of the order of 10^?14 W/m²/Hz¹ at the ground seem to be ascribable to the incoherent Cerenkov emission from soft electrons with a differential energy spectrum E^?2 having an intensity of the order of 10⁸cm^?2/sec/sr/eV at 100 eV. It is shown that the frequency of the maximum hiss spectral density at geomagnetic latitudes 80° on the day-side and 70° on the night-side is around 20 kHz for the soft spectrum (～E^?2) electrons, which shifts toward lower frequency (～10 kHz) for a hard spectrum (～E^?1·2) electrons. The maximum hiss intensity produced by soft electrons is more than one order higher than that of hard electron produced hiss. The higher rate of hiss occurrence in the daytime side, particularly in the soft electron precipitation zone in the morning sector, and the lesser occurrence of auroral hiss in night-time sectors must be, therefore, due to the local time dependence of the energy spectra of precipiating electrons rather than the difference in the geomagnetic field and in the geoplasma distributions.     

Annual and semiannual oscillations of stratospheric ozone

The global structures of annual oscillation (AO) and semiannual oscillation (SAO) of stratospheric ozone are examined by applying spherical harmonic analysis to the ozone data obtained from the Nimbus-7 solar backscattered UV-radiation (SBUV) measurements for the period November 1978 to October 1980. Significant features of the results are: (1) while the stratospheric ozone AO is prevalent only in the polar regions, the ozone SAO prevails both in the equatorial and polar stratospheres; (2) the vertical distribution of the equatorial ozone SAO has a broad maximum of the order of 0.5 (mixing ratio in g/g) and the maximum appears earlier at high altitude (shifting from May [and November] at 0.3 mb [60 km] to November [and May] at 40 mb); (3) above the 40 km level, the maximum of the polar ozone SAO shifts upward towards later phase with altitude with a rate of approximately 10 km/month in both hemispheres; (4) vertical distributions of the polar ozone AOs and SAOs show two peaks in amplitude with a minimum (nodal layer) in between and a rapid phase change with altitude takes place in the respective nodal layers; and (5) the heights of the ozone AO- and SAO-peaks decrease with latitude. The main part of AOs and SAOs of stratospheric ozone including hemispheric asymmetries is ascribable to: (i) temperature dependent ozone photochemistry in the upper stratosphere and mesosphere, (ii) variations of radiation field in the lower stratosphere affected by the annual cycle of solar illumination and temperature in the upper stratosphere and (iii) meridional ozone transport by dynamical processes in the lower stratosphere.     

Stratospheric ozone response to a solar proton event: Hemispheric asymmetries

Ozone depression in the polar stratosphere during the energetic solar proton event on 4 August 1972 was observed by the backscattered ultraviolet (BUV) experiment on the Nimbus 4 satellite. Distinct asymmetries in the columnar ozone content, the amount of ozone depressions and their temporal variations above 4 mb level (38 km) were observed between the two hemispheres. The ozone destroying solar particles precipitate rather symmetrically into the two polar atmospheres due to the geomagnetic dipole field These asymmetries can be therefore ascribed to the differences mainly in dynamics and partly in the solar illumination and the vertical temperature structure between the summer and the winter polar atmospheres. The polar stratosphere is less disturbed and warmer in the summer hemisphere than the winter hemisphere since the propagation of planetary wave from the troposphere is inhibited by the wind system in the upper troposphere, and the air is heated by the prolonged solar insolation. Correspondingly, the temporal variations of stratospheric ozone depletion and its recovery appear to be smooth functions of time in the (northern) summer hemisphere and the undisturbed ozone amount is slighily, less than that of its counterpart. On the other hand, the tempotal variation of the upper stratospheric ozone in the winter polar atmosphere (southern hemisphere) indicates large amplitudes and irregularities due to the disturbances produced by upward propagating waves which prevail in the polar winter atmosphere. These characteristic differences between the two polar atmospheres are also evident in the vertical distributions of temperature and wind observed by balloons and rocker soundings.