第22与23周磁静日北京台银河宇宙线周日变化与半日变化特征

利用快速傅里叶变换及其计算功率谱的方法研究了第22和23周磁静日北京宇宙线台站记录的银河宇宙线强度的周日变化与半日变化，计算结果表明，在两个太阳活动周交替时，银河宇宙线的周日变化与半日变化特征消失，在太阳活动低年逐渐向高年过度时，首先出现的是周日变化。半日变化特征出现要滞后于周日变化，22周太阳活动高年看不出周日变化，而23周太阳活动的高年周日变化非常显著，22周太阳活动的下降期。只有周日变化而无半日变化。这是分析北京宇宙线台近2个太阳活动周数据得到的新结果。     

武汉上空中层顶区域潮汐的MF雷达观测

利用武汉中频雷达观测数据进行分析,研究2至3月份武汉上空中层顶潮汐结构及其随高度和时间变化的特性.用Lomb-Scargle周期图方法计算的水平风场动态功率谱表明,武汉上空存在持续的周日潮汐,是中层顶区域风场结构的主要成分.周日潮的平均振幅随高度的增加呈先增后减的趋势.大多数情况下,潮汐谱峰对应的频率与定义值有一定的偏移.周日潮水平扰动速度矢量随时问和高度变化的轨迹表明,经向分量的相位比纬向分量的相位超前,潮汐能量向上传播,对应于向下的相位传播速度.计算得出的经向分量和纬向分量的垂直相速度分别为1.10和1.15 km/h.      

用整数小波变换进行无失真SAR图像压缩

介绍了利用提升方案(lifting scheme)构造小波变换的3个主要优点,给出了几个整数到整数可逆小波变换对,讨论了SAR图像的特点,提出了一种利用整数到整数小波变换进行无失真SAR图像压缩的方法.该方法具有速度快、可进行同址运算和能进行分级传输等特点.比较了对ERS-1单视SAR图像和IEEE标准测试图的压缩结果,表明性能要略优于DPCM(Differential Pulse Code Modulation)方法,且只须对单视SAR图像作一级小波分解,分解级数增加会使压缩效果变差.     

Solar EUV energy budget of the thermosphere

Using the accumulation of experimental data and theoretical studies conducted on the terrestrial thermosphere since the mid seventies, we have re-evaluated the channels by which solar UV energy is transferred to the atmosphere. As an outcome of this evaluation we have redetermined the solar EUV heating efficiency for the thermosphere and find this to be considerably different from that established in earlier studies. The heating efficiency has strong altitude, solar cycle and diurnal dependencies. The values of this parameter vary from less than 10% to greater than 100%, with peak midday values of 50–55% In recent papers we have presented the results of this new UV heating efficiency determination using a steady state solution of the ionospheric model. In this paper we present the results obtained solving a time dependent model over a diurnal cycle. The time dependent effects are found to be significant, with certain longlived species acting as temporary reservoirs of latent heat that is released to the neutral atmosphere at later times.     

北京地区电离层电子含量的某些特性

从对1980年至今的北京电离层电子含量的常规观测资料分析发现:电离层电子含量(IEC)的周日变化曲线除了绝大多数呈单峰变化外, 还有非扰动状态下的周日双峰变化、夜增长现象以及日出后不久的次极大正午之后的主极大等.本文着意于报道北京地区的IEC双峰特性和夜增现象及其随太阳活动的周期变化, 并与其它报道进行比较.      

Effects of CME and CIR induced geomagnetic storms on low-latitude ionization over Indian longitudes in terms of neutral dynamics

This paper presents the response of the ionosphere during the intense geomagnetic storms of October 12–20, 2016 and May 26–31, 2017 which occurred during the declining phase of the solar cycle 24. Total Electron Content (TEC) from GPS measured at Indore, Calcutta and Siliguri having geomagnetic dips varying from 32.23°N, 32°N and 39.49°N respectively and at the International GNSS Service (IGS) stations at Lucknow (beyond anomaly crest), Hyderabad (between geomagnetic equator and northern crest of EIA) and Bangalore (near magnetic equator) in the Indian longitude zone have been used for the storms. Prominent peaks in diurnal maximum in excess of 20–45 TECU over the quiet time values were observed during the October 2016 storm at Lucknow, Indore, Hyderabad, Bangalore and 10–20 TECU for the May 2017 storm at Siliguri, Indore, Calcutta and Hyderabad. The GUVI images onboard TIMED spacecraft that measures the thermospheric O/N₂ ratio, showed high values (O/N₂ ratio of about 0.7) on October 16 when positive storm effects were observed compared to the other days during the storm period. The observed features have been explained in terms of the O/N₂ ratio increase in the equatorial thermosphere, CIR-induced High Speed Solar Wind (HSSW) event for the October 2016 storm. The TEC enhancement has also been explained in terms of the Auroral Electrojet (AE), neutral wind values obtained from the Horizontal Wind Model (HWM14) and equatorial electrojet strength from magnetometer data for both October 2016 and May 2017 storms. These results are one of the first to be reported from the Indian longitude sector on influence of CME- and CIR-driven geomagnetic storms on TEC during the declining phase of solar cycle 24.     

Diurnal variation of earth radiation budget components above Africa and the neighboring Atlantic Ocean; Changes between 1983 and 1985, estimated from METEOSAT observations adjusted to ERBS data

METEOSAT observations in the thermal infrared “window” and “water vapor” channels, as well as in the visible channel, reveal diurnal variations over large areas which remain significant in the monthly means. The variations in the infrared correspond to diurnal cycles in the surface skin temperature (over land) and in cloud cover (over both land and sea) at various levels, and they must appear as a more or less significant diurnal variation in the integrated longwave emission to space of the Earth-atmosphere system. The diurnal cycle in the reflected shortwave radiation is influenced by these meteorological variations as well as by the astronomical cycle and the anisotropic reflectance. These must be taken into account in studies of Earth Radiation Budget variations. Using nearly simultaneous and spatially coincident pixel data from the ERBE scanner on ERBS and from METEOSAT in November 1984, we construct provisional transfer functions relating the narrow-band METEOSAT infrared observations to the longwave radiant exitance at the top of the atmosphere. We apply these transfer functions to the METEOSAT ISCCP B2 data sets for the summers of 1983–1985, and compare the resulting longwave radiant exitance estimates, with particular attention to the diurnal variation, which should be relatively insensitive to the inaccuracy inherent in applying the provisional (November 1984) transfer functions to the 1983–1985 data.     

Transient variations of vertical total electron content over some African stations from 2002 to 2012

This paper presents the vertical total electron content vTEC variations for three African stations, located at mid-low and equatorial latitudes, and operating since more than 10 years. The vTEC of the middle latitude GPS station in Alexandria, Egypt (31.2167°N; 29.9667°E, geographic) is compared to the vTEC of two others GPS stations: the first one in Rabat/Morocco (33.9981°N; 353.1457°E, geographic), and the second in Libreville/Gabon (0.3539°N; 9.6721°E, geographic). Our results discussed the diurnal, seasonal, and solar cycle dependences of vTEC at the local ionospheric conditions, during different phases of solar cycle in the light of the classification of Legrand and Simon. The vTEC over Alexandria exhibits the well-known equinoctial asymmetry which changes with the phases of the solar cycle; the spring vTEC is larger than that of autumn during the maximum, decreasing and minimum phases of solar cycle 23. During the increasing phase of solar cycle 24, it is the contrary. The diurnal variation of the vTEC presents multiple maxima during the equinox from 2005 to 2008 and during the summer solstice from 2006 to 2012. A nighttime vTEC enhancement and winter anomaly are also observed. During the deep solar minimum (2006–2009) the diurnal variation of the vTEC observed over Alexandria is similar to the diurnal variation observed during quiet magnetic period at equatorial latitudes. We observed also that the amplitude of vTEC at Libreville is larger than the amplitude of vTEC observed at Alexandria and Rabat, indeed Libreville is near the southern crest of the Equatorial Ionization anomaly. Finally, the correlation coefficient between vTEC and the sunspot number Rz is high and changes with solar cycle phases.     

北京上空冬季潮汐波活动特征全天时激光雷达探测研究

利用北京延庆子午工程激光雷达对北京上空钠层进行长期连续观测,分析研究钠层及其相关参数的周日变化.提取钠层各个高度上的相位信息,与同时段经向风潮汐信息进行比较发现:在各个高度上,二者周日相位数值基本一致.半日相位对比结果表明,虽然存在差异,但整体仍保持较好的一致性.此外,从2014年至2016年每年10月到第二年1月共4个月的钠层连续观测数据中提取钠层周日和半日的振幅和相位,探究北京上空冬季的潮汐特征.结果显示:周日潮的相位自上向下传播,且无明显的季节变化特征,其垂直波长在40～50km的范围;周日潮较强,半日潮较弱.      

Use of meteosat ISCCP B2 data for the study of interannual variations of climatic elements in Africa

Composite monthly images corresponding to West African rainy seasons of 1983, 1984, and 1985, have been constructed from ISCCP B2 Meteosat data. Average and standard deviation images from thermal infrared and water vapor channels are studied. In the thermal infrared, differences between the three years appear principally in the mean structure of the ITCZ, North-South extend, northward boundary, longitudinal variations of the convection. In the water vapor channel, well defined “dry” areas appear, showing the location and extent of subsidence regions on a large scale. These locations and extents also vary from year to year.     

武汉上空中层和低热层大气潮汐的流星雷达观测

武汉流星雷达是2002年元月建成的我国第一部全天空流星雷达，本文对2002年2月19日到7月31日流星雷达观测的潮汐的讨论表明，武汉中层顶以周日潮汐为潮汐运动的主要分量，它的强度远大于半日潮汐，周日潮汐和半日潮汐的波源都在80km以下．周日潮汐分量在3、4月份最强，并且经向分量略强于纬向分量．两个分量的峰值在约95km处出现，分别达到44m／s和60m／s．半日潮的最大值24m／s出现在4月初约93km处．周日潮汐和半日潮汐的振幅和相位随时间呈现出拟周期变化的特征，这可能是潮汐与行星波非线形相互作用的结果．观测结果与GSWM模型的比较表明，GSWM模型在相位随高度变化趋势上与观测结果一致，但模型的周日潮相位比观测约超前1—2h，半日潮相位约滞后1—4h．在周日潮汐较强的月份，模型与观测有较大的差异，观测的幅度通常在95km附近有极大值，而模型并没有极大值．GSWM模型对半日潮的幅度的估计通常过小，观测的半日潮汐幅度有时甚至超过模型值的一倍以上．     

Periodic variations of ionization rate in the low and middle atmosphere

The cosmic ray ionization source functions which were obtained using a simplified extensive air shower model are used to calculate the eleven year cycle, seasonal and diurnal variations of ionization rate in the low and middle atmosphere. The ionization source function, as a function of the penetrating depth and the energy of cosmic ray particles, is the ionization rate per unit depth for a unit flux of incoming cosmic ray particles with certain energy.The calculation of the eleven year cycle variation of ionization rate in the low and middle atmosphere due to the modulation of galactic cosmic ray intensity by solar activity shows that the amplitude is larger at a higher magnetic latitude and is generally larger at higher altitudes. The relative amplitude of fluctuation of the ionization peak value (at altitudes near 15 km) is up to 45% in the magnetic polar region. The ionization rate, due to the seasonal variation of the atmospheric density, varies from several per cent below the ionization peak to several tens per cent above the peak. This seasonal variation of ionization rate reaches 35% at 70 km. The diurnal variation of atmospheric densities caused by atmospheric tidal oscillation can produce a diurnal variation of the ionization rate to an amplitude of several per cent at altitudes above 40 km. The diurnal oscillation is less than 1% below 35 km.     

Low altitude dose measurements from APEX, CRRES and DMSP

Dosimeter data taken on the APEX (1994–1996), CRRES (1990–1991) and DMSP (1984–1987) satellites have been used to study the low altitude (down to 350 km) radiation environment. Of special concern has been the inner edge of the inner radiation belt due to its steep gradient. We have constructed dose models of the inner edge of the belt from all three spacecraft and put them into a personal computer utility, called APEXRAD, that calculates dose for user-selected orbits. The variation of dose for low altitude, circular orbits is given as a function of altitude, inclination and particle type. Dose-depth curves show that shielding greater than 1/4 in Al is largely ineffectual for low altitude orbits. The contribution of outer zone electrons to low altitude dose is shown to be important only for thin shields and to have significant variation with magnetic activity and solar cycle.     

Application of neural networks to South African GPS TEC modelling

The propagation of radio signals in the Earth’s atmosphere is dominantly affected by the ionosphere due to its dispersive nature. Global Positioning System (GPS) data provides relevant information that leads to the derivation of total electron content (TEC) which can be considered as the ionosphere’s measure of ionisation. This paper presents part of a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. The South African GPS receiver network is operated and maintained by the Chief Directorate Surveys and Mapping (CDSM) in Cape Town, South Africa. Vertical total electron content (VTEC) was calculated for four GPS receiver stations using the Adjusted Spherical Harmonic (ASHA) model. Factors that influence TEC were then identified and used to derive input parameters for the NN. The well established factors used are seasonal variation, diurnal variation, solar activity and magnetic activity. Comparison of diurnal predicted TEC values from both the NN model and the International Reference Ionosphere (IRI-2001) with GPS TEC revealed that the IRI provides more accurate predictions than the NN model during the spring equinoxes. However, on average the NN model predicts GPS TEC more accurately than the IRI model over the GPS locations considered within South Africa.     

Remote sensing of coccolithophore blooms

CZCS and AVHRR images have been used to study the spatial, temporal and spectral development of coccolithophore blooms in the NE Atlantic. It is suggested that variations in colour and reflectance in the images are due to differences in the relative concentrations of coccolithophore cells and detached plates. Also the formation and disappearance of an intense bloom in the English Channel is related to changes in water-column stability during the spring-neap tidal cycle.     

An observation of snow melting process from remotely sensed data

Observations of satellite images have shown that the snow melting in mountainous area proceeds more repidly in the east-facing slope of the valley than in the west-facing one. The energy for melting snow consists of the total from the atmosphere and from the solar rays. The diurnal variation of the solar energy into the snow in the east-facing slope differs from that in the west-facing slope. This causes the heighest value of the instantaneous energy for melting snow to occur in the west-facing surface. As one of the reasons for the above tendency, the difference of the heighest value to melt snow may be taken into account.     

In situ results on the variation of neutral atmospheric hydrogen at venus

The concentrations of neutral hydrogen within the atmosphere of Venus are investigated for the period 1979–1980. During this period, the planet made nearly three orbits about the Sun, so that nearly three complete diurnal cycles were observed from the Pioneer Venus Orbiter (PVO). Values of n(H) are derived from in-situ ion and neutral composition measurements from the Orbiter Ion Mass Spectrometer (OIMS) and the Orbiter Neutral Mass Spectrometer (ONMS) using a charge exchange relationship involving O⁺, H⁺, O and CO₂. The dawn bulge in the diurnal distribution of n(H), reported from the first diurnal cycle by Brinton et al., is found to persist with n(H) peaking at levels near 2 - 5 × 10⁷/cm³ at altitudes below 165 km. At peak levels, the bulge exhibits a concentration ratio up to 400/1 relative to dayside values. Large day to day variations of up to a factor of five in n(H) are frequently encountered, and are attributed to perturbations induced by the solar wind interaction. These short term variations, plus a suggestion of some local time variation in the bulk location, make precise assessment of interannual variations in the n(H) difficult. Between the first diurnal cycle in early 1979 and the third in mid 1980, the decline in solar euv flux was of the order of 10% or less. Allowing for uncertainties due to short term variations, no clear evidence is found for an interannual variation in the hydrogen concentrations.     

海南地区电离层闪烁观测与GISM模式预测的比较分析

为了获得全球电离层闪烁模式GISM在中国低纬地区预测的精度和可靠性,利用海南三亚GPS电离层闪烁监测系统一年的观测数据与模式预测结果进行对比分析.结果表明,在太阳活动低年,GISM能较好地反映海南地区电离层闪烁的季节变化、日变化和空间分布特性;对于季节变化,模式与观测结果在中等强度闪烁条件下较为相符,而在强闪烁和弱闪烁条件下有不同程度的偏差;模式预测的闪烁日变化与实际观测基本一致,但在闪烁发生率出现最大值的时间上模式预测要滞后约1 h左右;在电离层闪烁发生率的空间分布上,模式预测与实际观测较为相符,即海南地区南面电离层闪烁发生率高于北面.      

Observing the earth radiation budget from satellites: Past,present, and a look to the future

Satellite measurements of the radiative exchange between the planet Earth and space have been the objective of many experiments since the beginning of the space age in the late 1950's. The on-going mission of the Earth Radiation Budget (ERB) experiments has been and will be to consider flight hardware, data handling and scientific analysis methods in a single design strategy. Research and development on observational data has produced an analysis model of errors associated with ERB measurement systems on polar satellites. Results show that the variability of reflected solar radiation from changing meteorology dominates measurement uncertainties. As an application, model calculations demonstrate that measurement requirements for the verification of climate models may be satisfied with observations from one polar satellite, provided we have information on diurnal variations of the radiation budget from the ERBE mission.     

Behavior of the equivalent slab thickness over three European stations

The total electron content (TEC) derived from the global positioning system (GPS) and the F2-layer peak electron density obtained from Digisonde data have been used to study the diurnal, seasonal and solar activity variations of the ionospheric equivalent slab thickness (τ) over three European stations located at Pruhonice (50.0°N, 15.0°E), Ebro (40.8°N, 0.5°E) and El Arenosillo (37.1°N, 353.3°E). The diurnal variation of the τ is characterized by daytime values lower than nighttime ones for all seasons at low solar activity while daytime values larger than nighttime characterizes the diurnal variation for summer at high solar activity. A double peak is noticeable at dusk and at dawn, better expressed for winter at low solar activity. The seasonal variations of τ depend on local time and solar activity, the daytime values of τ increases from winter to summer whereas nighttime values of τ show the opposite. The effect of the solar activity on τ depends on local time and season, there being very sensitive for winter nighttime values of τ. The results of this study are compared with those presented by other authors.