Empirical model of variations in the helium 1083 nm emission. 2. Temperature

Based on the measurements of the ortho helium 1083 nm emission intensity during twilights and on the calculation of its variations depending on the solar zenith angle, the method for determining the atmospheric temperature at heights of 300–1000 km during the nighttime period of day has been developed, taking into account the diurnal and seasonal conditions.     

Empirical model of variations in the OI 630 nm emission. 1. Intensity

The empirical model of variations in the atomic oxygen emission intensity depending on different heliogeophysical conditions such as nighttime, lunar time, lunar phase age, season, year, and solar activity level during the 11-year cycle, as well as on cyclic aperiodic activity variations, level of geomagnetic disturbances, and their manifestations in the form of midlatitude subauroral red arcs, has been developed based on the long-term measurements of this emission intensity.     

Empirical model of variations in the helium 1083 nm emission. 1. Intensity

The model of variations in the orthohelium 1083 nm emission intensity has been constructed based on the measurements at different stations. The analytical approximations of the nighttime intensity variations depending on the phase age of the Moon, season, solar activity during the 11-year cycle, and geomagnetic disturbances are presented.     

Causes of <Emphasis Type="Italic">NmF</Emphasis>2 longitudinal variations at mid- and subauroral latitudes under summer nighttime conditions

The main factors controlling NmF2 longitudinal variations at mid- and subauroral latitudes have been studied. The data of the Intercosmos-19 topside sounding, obtained at high solar activity for summer nighttime conditions, have been used in the analysis. The contributions of the solar ionization, neutral wind, and temperature and composition of the thermosphere to NmF2 longitudinal variations have been estimated based on ionospheric models. It has been indicated that NmF2 variations in the unsunlit midlatitude ionosphere mainly depends on the residual electron density and its decay under the action of recombination. At subauroral latitudes under summer nighttime conditions, the ionosphere is partially sunlit, and ionization by solar radiation mainly contributes to NmF2 longitudinal variations, whereas the effect of the neutral wind is slightly less significant. These results also indicate how the contribution of different factors to NmF2 longitudinal variations changes at different latitudes.     

Experimental study of charge vertical transfer in surface air layer

The variability of air–earth electric currents in the lower 3-m air layer is analyzed in a complex with measurement data on the physical parameters that affect charge transfer in the atmosphere. Three types of air–earth current density profiles have been revealed during experimental observations in summer in Rostov region: (1) the current density decreases with an increase in the distance from the Earth’s surface and then stabilizes (nighttime conditions); (2) the current density increases with altitude up to 1 m and then decreases as altitude increases (day hours); (3) transient between types 1 and 2 that are observed in the morning and evening hours. The intensity of charge transfer in the surface air layer under the action of mechanical forces under different stratifications is estimated on the basis of data on altitude variations in the air–earth current density in view of the stationarity of electric processes and the constancy in the altitude of the total air–earth current density. Thermodynamic conditions are estimated with the use of wind velocity measurements and calculations of the turbulence factor and vertical component of the air temperature gradient.     

Temperature variations in the mesopause region according to the hydroxyl-emission observations at midlatitudes

The seasonal temperature variations in the mesopause region and the inter-day and nighttime temperature variability, the measure of which is standard deviations, have been studied based on the hydroxyl emission spectral observations at the Zvenigorod station of the Obukhov Institute of Atmospheric Physics in 2000–2011 and Institute of Solar Terrestrial Physics geophysical station (Tory) in 2008–2011. The long-term variations in all temperature variability parameters have been analyzed.     

Features of longitudinal variations in atmospheric temperature at heights of the radiating layer of 557.7-nm emission of atomic oxygen

On the basis of correlations between seasonal variations in the intensity and temperature of 557.7-nm emission, the mean monthly longitudinal variations in temperature are drawn. A comparison is performed with the data of interferometer and lidar measurements of temperature performed at various stations, as well as with the results of satellite studies. The dependences of the amplitudes of seasonal variations in temperature on latitude are obtained.     

油藏水驱开采时移地震监测岩石物理基础测量

岩石物理测量是油藏水驱开采时移地震监测的基础.在实验室对来自胜利油田的5块岩石样品模拟储层条件进行了水驱和气驱动态岩石物理弹性测量,重点分析了流体替换、温度、孔隙压力对岩石纵、横波速度的影响.实验表明,在水驱情形下,由于流体替换和温度、孔隙压力变化所引起的岩石纵横波速度的变化均很小,实施时移地震监测具有较大的风险性.相比之下,气驱可能引起较为明显的纵波速度变化,有利于时移地震监测的实施.进一步完善实验方法、丰富实验内容、是今后时移地震岩石物理实验研究的主要任务.     

THE MECHANISM OF DIURNAL VARIATION IN CONSECUTIVE APPARENT RESISTIVITY OBSERVATION

Parts of the consecutive apparent resistivity monitoring stations of China have recorded clear diurnal variations. The relative amplitudes of diurnal variations at these stations range from 1.3‰ to 5.8‰. The daily accuracies of apparent resistivity observation are better than 1‰, because the background electromagnetic noise is rather low at these stations. Therefore, the diurnal variations of apparent resistivity recorded at these stations are real phenomena. The diurnal variation shapes can be divided into two opposite types according to their characteristics. One type is that the apparent resistivity data decreases during the daytime but increases during the nighttime(Type 1). The other type is the apparent resistivity data increases during the daytime but decreases during the nighttime(Type 2). There is a correspondence between the diurnal and annual variation patterns of apparent resistivity. For the monitoring direction with diurnal variation of Type 1, the apparent resistivity decreases in summer and increases in winter. However, for the monitoring direction with diurnal variation of Type 2, the apparent resistivity increases in summer and decreases in winter. We take an analysis on the mechanism of apparent resistivity diurnal variation, combining the influence factors of water-bearing medium's resistivity, the electric structure of stations, and the apparent resistivity sensitivity coefficient(SC)theory. Intuitively, diurnal variation of apparent resistivity is caused by diurnal variation of medium resistivity in the measured area. The diurnal variation of medium resistivity will inevitably be caused by the factors with diurnal variation. Among the possible factors, there is diural variation in earth tide and temperature. Our analysis displays that apparent resistivity diurnal variation is not caused by the usually-believed earth tide, but by the ground temperature difference between daytime and nighttime. The earth tide strain is too small to cause remarkable effects on the apparent resistivity data. On the other hand, the daily tide strain has two peak-valley variations, and its phase and amplitude has a period of approximate 28 days. However, the apparent resistivity data do not show these corresponding features to earth tide. Furthermore, the detection range of current apparent resistivity stations is within a depth of several hundred meters. Within this depth range, the medium deformation caused by solid tide can be regarded as uniform change. Therefore, all monitoring directions and all stations will have the same pattern of diurnal variation. In general, the temperature increases in the daytime but decreases in the nighttime. For most water-bearing rock and soil medium, its resistivity decreases as temperature increases and increases as temperature decreases. Diurnal temperature difference affects about 0.4m of soil depth. Therefore, resistivity of this surface thin soil layer decreases in the daytime while increases in the nighttime. Under layered medium model, SC of each layer represents its contribution to the apparent resistivity. For the stations with positive SC of surface layer, apparent resistivity decreases in the daytime but increases in the nighttime. While for the stations with negative SC of surface layer, apparent resistivity diurnal variations display the opposite shape.     

ZH-1卫星得到的中国及邻区顶部电离层背景特征

利用ZH-1(CSES)卫星LAP载荷原位电子密度数据对中国及邻区(0°-54°N,70°-140°E)的顶部电离层背景分布及随季节变化进行了详细分析,研究结果显示:(1)研究区赤道异常的纬度延伸范围、随经度分布形态及它们的季节变化,具有与其他研究结果一致的规律性.(2)中纬度区,白天电子密度存在一个低值带,夜间电子密...     

Validation of AVHRR and TMI-derived sea surface temperature in the northern South China Sea

Satellite-derived SSTs are validated in the northern South China Sea (NSCS) using in situ SSTs from the drifting buoys and well-calibrated sensors installed on Research/Vessel(R/V) Shiyan 3. The satellite SSTs are Advanced Very High Resolution Radiometer (AVHRR) daytime SST, AVHRR nighttime SST, Tropical rainfall Measuring Mission Microwave Imager (TMI) daytime SST and TMI nighttime SST. Availability of satellite SST, which is the ratio that the number of available satellite SST to the total ocean pixels in NSCS is calculated; annual average SST availabilities of AVHRR daytime SST, AVHRR nighttime SST, TMI daytime SST and TMI nighttime SST are 68.42%, 69.99%, 56.57% and 52.80%, respectively. Though the TMI SST availability is nearly constant throughout the year, the variations of the AVHRR SST availability are much larger because of seasonal variations of cloud cover in NSCS. Validation of the satellite-derived SSTs shows that bias±standard deviation (STD) of AVHRR SST is −0.43±0.76 and −0.33±0.79 °C for daytime and nighttime, respectively, and bias±STD of TMI SSTs is 0.07±1.11 and 0.00±0.97 °C for daytime and nighttime, respectively. It is clear that AVHRR SSTs have significant regional biases of about −0.4 °C against the drifting buoy SSTs. Differences between satellite-derived−in situ SSTs are investigated in terms of the diurnal SST cycle. When satellite-derived wind speeds decrease down below 6 m/s, the satellite SSTs become higher than the corresponding in situ SSTs, which means that the SST difference (satellite SST−Buoy SST) is positive. This wind-speed dependence of the SST difference is consistent with the previous results, which have mentioned that low wind speed coupled with clear sky conditions (high surface solar radiation) enhance the diurnal SST amplitude and the bulk-skin temperature difference.     

Empirical model of variations in the emission of the infrared atmospheric system of molecular oxygen: 1. Intensity

On the basis of the data of ground-based spectrometric observations in Zvenigorod (55.7°N, 36.8°E) and published results of measurements of the intensity of the Infrared Atmospheric system of molecular oxygen obtained at other stations, empirical relations describing variations in the intensity of the 1.58-μm emission for various solar and geophysical conditions are calculated.     

High altitude observations of electron temperature and a possible north–south asymmetry

Measurements of electron temperature made by the thermal electron energy distribution (TED) instrument on board the EXOS-D (Akebono) satellite have been analysed. From the data taken between 1989 and 1995, averaged daytime and nighttime temperature profiles for different geophysical conditions have been produced. These profiles represent the averaged thermal electron temperature between 1000 and 8000 km altitude for conditions of high (F10.7>150) and low (F10.7<120) solar activity. Results indicate that increased solar activity has a marked effect on the electron temperature. At 8000 km altitude, the typical low-latitude daytime electron temperature is around 8000 K. The nighttime electron temperature at 8000 km is around 4000 K. The averaged daytime difference between high and low solar activity conditions is around 1000 K at altitudes above 2500 km. Between 1000 and 2000 km altitude this situation is reversed, and the electron temperature is comparatively higher during periods of low solar activity during both day and night. Composition changes in the region are proposed as a mechanism for this reversal. In addition, there is evidence of an asymmetry in thermal electron temperature between the northern and southern hemispheres. The averaged electron temperature is found to be comparatively higher in the northern hemisphere during the daytime and comparatively higher in the southern hemisphere during the nighttime. This difference between hemispheres is particularly evident during the nighttime, and during the rapid heating and cooling periods around sunrise and sunset. Possible reasons for the asymmetry are discussed. Profiles are also presented for conditions of high (Ap>30) and low (Ap<20) magnetic activity. Analysis has confirmed that geomagnetic activity has little effect on electron temperature below L=2.2.     

Influence of solar wind parameters on ground magnetic field near equator during intense storms

Using a simple time-lagged correlation technique, present study aims to identify the solar wind (SW) parameter, which is better associated with the ground magnetic field variations of shorter time duration near equator, during intense geomagnetic storms. It is found that out of all SW parameters, successively occurring enhancements in the SW dynamic pressure have substantial influence on the horizontal component of magnetic field at ground. Present analysis reveals a time lag of ~30–45 min between the SW pressure changes seen at L1 location and ground magnetic field variations, and hence providing a good approximation of an averaged propagation time during entire storm interval; the time lag varies with solar wind velocity. Separate study during day and nighttime suggests that the SW dynamic pressure enhancements recorded by the dayside outer magnetospheric satellite have impact on the ground horizontal magnetic field measurements near equator, irrespective of day or nighttime.     

Difference between the spectra of acoustic gravity waves in daytime and nighttime hours due to nonequilibrium effects in the atmosphere

The singularities of the wave disturbance spectra of the nonequilibrium atmosphere in the range of acoustic gravity waves (AGWs) have been analyzed. Using the dispersion ratio for AGWs in the nonequilibrium atmosphere, it has been established that the spectra in the daytime and nighttime hours are different and this difference, caused by a nonequilibrium spectrum sensitivity to atmospheric temperature, can reach several percent in certain atmospheric regions. For the spectrum of the equilibrium model of the atmosphere, the difference between the daytime and nighttime spectra makes up several fractions of percent. As a result of the spectral treatment of variations in pressure and intensity of cosmic rays (CRs), it has been found out that the daytime AGW spectrum is higher-frequency than the nighttime spectrum. A comparison of the theoretical calculations of the AGW spectrum with observations has made it possible to distinguish the effect of nonequilibrium in the AGW spectral composition.     

Seasonal and nighttime behaviors of emissions of hydroxyl and the atmospheric system of molecular oxygen of the midlatitude mesopause

Based on observations of mesopause emissions, namely, emissions of hydroxyl (band (6-2)) and molecular oxygen (band (0-1) of the atmospheric system), their systematic nighttime and seasonal variations are determined at Zvenigorod Observatory in 2000–2008. It is shown that the intensity of hydroxyl emission decreases during the entire night or first half-night, probably due to the influence of the chemical sink of atomic oxygen on the nighttime behavior of hydroxyl emission. The nighttime behavior of the intensity of molecular oxygen emission is explained by the action of atmospheric tides. The seasonal behavior of emissions is characterized by two minima, in April–May and December; it is caused by the annual behavior of the atomic oxygen content, temperature, and atmospheric density in the emitting layer. Based on the emission data, we determined the seasonal variations of atomic oxygen at heights of ∼87 km (maximum of hydroxyl emission) and ∼95 km (maximum of molecular oxygen emission).     

The nighttime winter anomaly (NWA) effect in the american sector as a consequence of interhemispheric ionospheric coupling

The nighttime winter anomaly (NWA) effect was observed during solar minimum conditions at the American sector by means of ionospheric electron content and vertical sounding measurements in Havana (Cuba). An effective interhemispheric transport of plasma is suggested to explain enhanced northern nighttime ionization during winter solstice. To elucidate this effect, an adequate physicalnumerical model of the coupled system ionosphere-plasmasphere is presented and applied to a corotating tube of plasma at L=1.5 in the American sector. The NWA can be explained by theoretically derived higher tube content during the December solstice and accordingly by more intense nighttime fluxes from the plasmasphere, compared to the June solstice.     

Changing structures of summertime heatwaves over China during 1961–2017

Despite the prevalence of artificial separation of daytime and nighttime hot extremes, they may actually co-occur or occur sequentially. Considering their potential lead-lag configuration, this study identified an entire heatwave period as consecutive days with either daytime or nighttime hot extremes and investigated the changes of the prevalence and sequence of daytime and nighttime hot extremes during heatwaves over China from 1961 to 2017. It was found that the majority(82%) of heatwaves were compound heatwaves that had both daytime and nighttime hot extremes exceeding the 90 th percentile-based thresholds, while only 7%(11%) were purely daytime(nighttime) heatwaves that contained only daytime(nighttime) hot extremes. During the entire periods of compound heatwaves, daytime hot extremes usually occurred one day or a few days before nighttime hot extremes, which was in accordance with the daily variations in radiation and meteorological conditions, such as the increasing surface humidity and cloud cover, and decreasing solar radiation during the entire heatwave periods. From 1961 to2017, compound heatwave numbers exhibited the sharpest increase with a statistically significant trend of 0.44 times decade-1, in contrast to an insignificant trend of 0.00 times decade-1 for purely daytime heatwaves and a significant trend of 0.09 times decade-1 for purely nighttime heatwaves. Within the compound heatwave periods, hot nights were starting earlier and ending later, and numbers of concurrent daytime-nighttime hot extremes increased significantly at 0.20 days decade-1. In particular,urban area were not only subject to increasingly more frequent and longer compound heatwaves, but also to more occurrences of concurrent daytime-nighttime hot extremes with more serious impact. This study provides instructions for researchers to customize and select appropriate heatwave indices.     

Plasmaspheric electron content (PEC) over low latitude regions around the magnetic equator in the Indian sector during different geophysical conditions

The variation of plasmaspheric electron content (PEC) is an important parameter for studying the effects of space weather events in the low latitude ionosphere. In the present study, the vertical TEC (VTEC) measurements obtained from co-located dual-frequency Global Positioning System (GPS) and Coherent Radio Beacon Experiment (CRABEX) systems have been used. The daytime PEC variations under different geophysical conditions have been estimated (around the magnetic equator) over the Indian sector, for the first time. The first observations of the nighttime PEC variations over the Indian sector are also estimated from the simultaneous measurements of Faraday rotation, differential Doppler and modulation phase delay made using the CRABEX system on-board the Indian geostationary satellite GSAT2. The study shows that the PEC varies over a range of 10–22% (of the total electron content (TEC)) during daytime of magnetically quiet period. There is an increase in PEC with latitude during magnetically quiet period. During a magnetically disturbed period of 9 November 2004, the PEC increased to ∼30% of the TEC over the magnetic equatorial location of Trivandrum (8.5°N, 76.9°E, dip 0.5°N), while at Bangalore (13°N, 78°E, dip 10°N) it showed a large depletion. The implications of the new observations are discussed.     

Evidence of tidal perturbations in the middle atmosphere over Southern Tropics as deduced from LIDAR data analyses

Systematic measurements of the middle-atmosphere temperature by a RAYLEIGH LIDAR located at La Réunion Island (20.8°S–55.5°E) has led to a preliminary study of the tidal effects in the height range of 30–70 km. Two analysis methods able to estimate the mean nighttime evolution of the temperature have been compared. Method 1 consists in averaging the temperature deviations from the nightly mean over several successive nights of measurement for given local solar times (LST); method 2 consists in averaging the raw data over the period of observation for given LST and in deriving afterwards the mean nighttime evolution of the temperature profiles. Some consistent LST-related structures have been observed with both methods, though better results have been obtained with method 1. One possible explanation for the differences between the two methods is the use of a series of data ranging from 4 to 8 h/night, depending on the meteorological conditions. In contrast to method 2, method 1 allows to correct the mean temperature for a given night, when the measurement window is different from night to night. Method 1 has been applied to two time series recorded in October and November 1995. The results clearly show the presence of tidal components with a downward phase propagation, specifically a warmer early night and a colder midnight in the stratosphere and the lower mesosphere. This behaviour is consistent with other LIDAR measurements made at similar latitudes in the Northern Hemisphere. In addition, a close comparison with the Global-Scale Wave Model (GSWM) tidal model predictions has also pointed out some similarities. Yet, large discrepancies in magnitude are also observed: as already reported in previous studies, the amplitudes predicted by GSWM are more than two times smaller compared to the corresponding values observed with the LIDAR.