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1.
This study analyzes the TEC data during 1998–2007, observed by the AREQ (16.5°S, 71.5°W) GPS station to investigate the equatorial ionospheric variations under geomagnetic quiet-conditions. The diurnal TEC values generally have a maximum value between 1330 and 1500 LT and a minimum around 0500 LT. For the seasonal variation, the semi-annual variation apparently exists in the daytime TEC with two peaks in equinoctial months. In contrast, this semi-annual variation is not found in the nighttime. Furthermore, the results of the annual variation show that the correlation between the daytime TEC value and the solar activity factor is highly positive.  相似文献   

2.
张强  赵齐乐 《地球物理学报》2019,62(12):4493-4505
2016年2月,武汉大学卫星导航定位技术研究中心(Wuhan University, WHU)正式成为新的国际GNSS服务组织(International GNSS Services, IGS)电离层联合分析中心(Ionosphere Associate Analysis Center, IAAC).本文首次系统地评估和分析了武汉大学IGS电离层分析中心自2016年日常化运行以来(2016年1月到2018年9月,太阳活动低年)的全球电离层产品的精度,并与其他六家IAACs (CODE、JPL、ESA、UPC、EMR和CAS)进行了比较分析.结果表明:WHU的全球电离层产品能够长期稳定且有效地监测全球电离层总电子含量(Total Electron Content, TEC)的时空变化;和IGS综合全球电离层产品比较,WHU的模型均方根误差和CODE、JPL相差不大,均值约为1.4 TECU,产品一致性优于其他IAACs;和GPS实测电离层TEC比较,WHU的模型内符合精度和CODE基本相当,均值约为1.4 TECU,且与电离层活动水平和地理纬度存在显著的相关性;和Jason-2测高卫星VTEC比较,WHU的全球电离层产品的系统性偏差均值约为-0.7 TECU,在不同纬度约为-3.0到1.0 TECU,且与地理纬度存在近似抛物线函数的关系;WHU的模型外符合精度和CODE、JPL以及CAS基本一致,均值约为2.9 TECU,且在中高纬度地区优于低纬度地区,北半球优于南半球.  相似文献   

3.
To study the occurrence characteristics of equatorial spread-F irregularities and their latitudinal extent, simultaneous digital ionosonde data (January–December 2001) from Trivandrum (8.2°N), Waltair (17.7°N) and Delhi (28.6°N) and 4 GHz scintillation data from Sikandarabad (26.8°N) and Chenglepet (10.4°N), and 250 MHz scintillation data from Bhopal (23.2°N) for equinoxes period are analysed. It is noted that except summer months, occurrence of spread F is always maximum at Trivandrum, minimum at Delhi and moderate at Waltair. During equinoxes and winter months. Their occurrences at higher latitude station are always conditional to their prior occurrences at lower latitudes indicating their association with the generation of equatorial plasma bubble and associated irregularities. Scintillation occurrences also follow the similar pattern. During the summer months, the spread-F occurrences are highest at equatorial location Trivandrum, moderate at Delhi and minimum at Waltair and seem to be caused by irregularities generated locally especially over Delhi.To gain forecasting capability, night-to-night occurrences of spread-F/scintillation at these locations are examined in relation to post sunset rise of h’F and upward ExB drift velocity over the magnetic equator using Trivandrum ionosonde data. It is noted that except the summer months, the spread-F at Trivandrum, Waltair and Delhi are observed only when equatorial ExB (h’F) is more than about 15 m/s (325 km), 20 m/s (350 km) and 25 m/s (375 km), respectively. With these threshold values their corresponding success rate of predictions are more than 90%, 50% and 15% at the respective locations. Whereas in the case of GHz scintillations near equator are observed only when ExB (h’F) is more than 15 m/s (325 km), whereas for low latitude, the same should be 30 m/s (400 km) and their success rate of prediction is about 90% and 30%, respectively. The intensity of 4 GHz scintillation at low latitude is also found to be positively correlated with equatorial upward ExB drift velocity values, whereas correlation is poor with that of equatorial scintillations. In conclusions, near magnetic equator threshold values of ExB or h’F can be successfully used for the night-to-night prediction of spread-F/scintillations occurrences, whereas these are necessary but not sufficient for their prediction at higher latitudes. For that some other controlling parameters like background electron density, neutral winds, gravity waves, etc. should also be examined.  相似文献   

4.
The ionospheric slab thickness, the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), is closely related to the shape of the ionospheric electron density profile Ne (h) and the TEC. Therefore, the ionospheric slab thickness is a significant parameter representative of the ionosphere. In this paper, the continuous GPS observations in South Korea are firstly used to study the equivalent slab thickness (EST) and its seasonal variability. The averaged diurnal medians of December–January–February (DJF), March–April–May (MAM), June–July–August (JJA) and September–October–November (SON) in 2003 have been considered to represent the winter, spring, summer and autumn seasons, respectively. The results show that the systematic diurnal changes of TEC, NmF2 and EST significantly appeared in each season and the higher values of TEC and NmF2 are observed during the equinoxes (semiannual anomaly) as well as in the mid-daytime of each season. The EST is significantly smaller in winter than in summer, but with a consistent variation pattern. During 14–16 LT in daytime, the larger EST values are observed in spring and autumn, while the smaller ones are in summer and winter. The peaks of EST diurnal variation are around 10–18 LT which are probably caused by the action of the thermospheric wind and the plasmapheric flow into the F2-region.  相似文献   

5.
Temporal mass variations in the continental hydrosphere and in the atmosphere lead to changes in the gravitational potential field that are associated with load-induced deformation of the Earth’s crust. Therefore, models that compute continental water storage and atmospheric pressure can be validated by measured load deformation time series. In this study, water mass variations as computed by the WaterGAP Global Hydrology Model (WGHM) and surface pressure as provided by the reanalysis product of the National Centers for Environmental Prediction describe the hydrological and atmospheric pressure loading, respectively. GPS observations from 14 years at 208 stations world-wide were reprocessed to estimate admittance factors for the associated load deformation time series in order to determine how well the model-based deformation fits to real data. We found that such site-specific scaling factors can be identified separately for water mass and air pressure loading. Regarding water storage variation as computed by WGHM, weighted global mean admittances are 0.74 ± 0.09, 0.66 ± 0.10, 0.90 ± 0.06 for the north, east and vertical component, respectively. For the dominant vertical component, there is a rather good fit to the observed displacements, and, averaged over all sites, WGHM is found to slightly overestimate temporal variations of water storage. For Europe and North America, with a dense GPS network, site-specific admittances show a good spatial coherence. Regarding regional over- or underestimation of WGHM water storage variations, they agree well with GRACE gravity field data. Globally averaged admittance estimates of pre-computed atmospheric loading displacements provided by the Goddard Geodetic VLBI Group were determined to be 0.88 ± 0.04, 0.97 ± 0.08, 1.13 ± 0.01 for the north, east and vertical, respectively. Here, a relatively large discrepancy for the dominant vertical component indicates an underestimation of corresponding loading predictions.  相似文献   

6.
The GPS-derived total electron content (TEC) and NmF2 are measured at the Chung-Li ionosonde station (24.9°N, 121°E) in order to study the variations in slab thickness (τ) of the ionosphere at low-latitudes ionosphere during 1996–1999, corresponding to half of the 23rd solar cycle. This study presents the diurnal, seasonal, and solar flux variations in τ for different solar phases. The seasonal variations show that the average daily value is greater during summer and the reverse is true during equinox in the equatorial ionization anomaly (EIA) region. Moreover, the τ values are greater during the daytime (0800–1600 LT) and nighttime (2000–0400 LT) for summer and winter, respectively. The diurnal variation shows two abnormal peaks that appear during the pre-sunrise and post-sunset hours. The peak values decrease as the sunspot number increases particularly for the pre-sunrise peak. Furthermore, the variation in the F-peak height (hpF2) indicates that a thermospheric wind toward the equator leads to an increase in hpF2 and an enhancement in τ during the pre-sunrise period. Furthermore, the study shows the variations of τ values for different geophysical conditions such as the geomagnetic storm and earthquake. A comprehensive discussion about the relation between τ and the geophysical events is provided in the paper.  相似文献   

7.
We investigate the effects of penetration electric fields, meridional thermospheric neutral winds, and composition perturbation zones (CPZs) on the distribution of low-latitude plasma during the 7–11 November 2004 geomagnetic superstorm. The impact on low-latitude plasma was assessed using total electron content (TEC) measurements from a latitudinally distributed array of ground-based GPS receivers in South America. Jicamarca Radio Observatory incoherent scatter radar measurements of vertical E×B drift are used in combination with the Low-Latitude IONospheric Sector (LLIONS) model to examine how penetration electric fields and meridional neutral winds shape low-latitude TEC. It is found that superfountain conditions pertain between ～1900 and 2100 UT on 9 November, creating enhanced equatorial ionization anomaly (EIA) crests at ±20° geomagnetic latitude. Large-amplitude and/or long-duration changes in the electric field were found to produce significant changes in EIA plasma density and latitudinal location, with a delay time of ～2–2.5 h. Superfountain drifts were primarily responsible for EIA TEC levels; meridional winds were needed only to create hemispherical crest TEC asymmetries. The [O/N2] density ratio (derived from the GUVI instrument, flown on the TIMED satellite) and measurements of total atmospheric density (from the GRACE satellites), combined with TEC measurements, yield information regarding a likely CPZ that appeared on 10 November, suppressing TEC for over 16 h.  相似文献   

8.
The global ionospheric total electron content maps (GIMs) provide integrated electron densities between the ground and the GPS satellite altitude (20,200 km). Satellite altimeter ionospheric delay corrections require integrated electron densities between the ground and altimeter satellite altitude. In the case of the Geosat Follow-On (GFO) spacecraft, flying at 800 km, we estimated that using GIM TEC data alone, up to a 2 cm path delay can be introduced into the GFO measurements for high solar activity period by not taking into account the electron content above this altitude. Furthermore, the GIMs can have errors of 20–30 TECU in low latitudes for high solar activity in areas where there is little GPS data (such as over the oceans). In this paper, we describe the results of ingesting GIM TEC data into the International Reference Ionosphere model (IRI-95) to mitigate these two effects.  相似文献   

9.
We present the first measurement of polar mesospheric cloud (PMC) occurrence frequency over the diurnal cycle from a satellite. The observations are made during the 2007 northern hemisphere PMC season by the Spatial Heterodyne IMager for MEsospheric Radicals (SHIMMER), which views the limb near 309 nm typically between 34 and 98 km. The PMC diurnal variation is derived between 50 and 58°N, where local times at the tangent point precess by ～30 min/day allowing for observations between 0330 and 2130 local time during the PMC season. We find that the occurrence frequencies exhibit a strong semidiurnal behavior with peaks near 0600 and 1800 local time and a minimum between 0900 and 1600 during which they are on average an order of magnitude less. The semidiurnal dependence is strongly correlated with concurrent ground-based measurements of meridional winds and temperatures measured at the same latitude. Our results for PMC frequency over the diurnal cycle can be used to help reconcile observations from other satellites that only permit cloud measurements at discrete local times.  相似文献   

10.
The gravitational effects of water storage variations driven by local precipitation events are modeled for the Walferdange Underground Laboratory for Geodynamics (WULG) in the Grand Duchy of Luxembourg. A modified mass continuity model is implemented, which uses rainfall data from Walferdange as input. In the absence of soil moisture and groundwater level information, the model is empirically parameterized. Model outputs are compared to the gravity time series registered with the Observatory Superconducting Gravimeter CT040 located in the WULG. We find that the model explains 77% of the gravity residuals. In addition, a statistical analysis is carried out to determine the relationship between precipitation, gravity variations and water level changes in the nearby Alzette River. A time delay of 88 ± 34 min between the maximum variation rates of the water level and gravity signal has been calculated. The signals have an admittance of 45 ± 5 cm μGal?1.  相似文献   

11.
The characteristics (annual and diurnal cycle, polarity, multiplicity and first stroke peak current) of ∼4.3×106 cloud-to-ground flashes recorded in the Iberian Peninsula during the first decade of measurements of the lightning detection network installed in Spain are analyzed. The mean monthly variation shows maximum lightning activity between May and September, while minimum values are observed in January and February. The mean diurnal cycle shows maximum values at 1700 LT and minimum values at around 1000 LT. The average maximum flash density (not corrected for detection efficiency) is 2.1 flashes km−2 year−1. Maximum lightning activity is associated with mountainous areas. The effect of the Mediterranean Sea is also seen. The percentage of positive flashes is 9%, although this changes over the year from 6.5% in June to 22.6% in January. The average multiplicity is found to be 2.0 for the negative flashes and 1.1 for the positive flashes, and the percentages of single-stroke flashes are 53.6% and 89%, respectively. The monthly distribution of multiplicity for negative flashes peaks in the summer and minimum values are found in the winter. The multiplicity of the positive flashes does not seem to be function of the month. The median (mean) first stroke peak currents are found to be 23.5 kA (27.3 kA) for the negative flashes and 35.3 kA (47.1 kA) for the positive flashes. For both polarities, the peak current is higher in the summer than in the winter. The percentage of positive flashes and the mean peak currents for negative flashes are higher over the sea areas than over land.  相似文献   

12.
《Journal of Geodynamics》2010,49(3-5):253-259
We observe the Earth tidal fields at diurnal and semi-diurnal periods using Kinematic Precise Point Positioning (KPPP) GPS analysis. Our KPPP GPS solutions compare well with super-conducting gravimeter (SG) observations and a theoretical Earth tidal model, that includes both ocean tide loading model and body tides. We make a high resolution map of the observed Earth tidal response fields using the Japanese GEONET GPS network which consists of 1200 sites. We find that: (1) the average phase of GPS data lags 0.11 ± 0.04° from our theoretical Earth tidal model, (2) the average amplitude ratio between GPS and the theoretical Earth tidal model is 1.007 ± 0.003, (3) the amplitude in the Kyushu district is about 1.0–1.5 ± 0.3% larger than in the Hokkaido district, and (4) the amplitude at the Japan Sea side is about 0.5 ± 0.2% larger than that at the Pacific Ocean side. These results suggest that we may be able to place constraints on Earth structure using GPS-derived tidal information.  相似文献   

13.
The ionospheric responses to a large number (116) of moderate (?50≥Dst>?100 nT) geomagnetic storms distributed over the period (1980–1990) are investigated using total electron content (TEC) data recorded at Calcutta (88.38°E, 22.58°N geographic, dip: 32°N). TEC perturbations exhibit a prominent dependence on the local times of main phase occurrence (MPO). The storms with MPO during daytime hours are more effective in producing larger deviations and smaller time delays for maximum positive deviations compared to those with nighttime MPO. Though the perturbations in the equinoctial and winter solstitial months more or less follow the reported climatology, remarkable deviations are detected for the summer solstitial storms. Depending on the local times of MPO, the sunrise enhancement in TEC is greatly perturbed. The TEC variability patterns are interpreted in terms of the storm time modifications of equatorial electric field, wind system and neutral composition.  相似文献   

14.
The Qujialing site is a representative Neolithic archaeological site in the middle reaches of the Yangtze River, China. Absence of suitable material for radiocarbon dating in this region makes the timing of the similar sites difficult. Here we applied optically stimulated luminescence (OSL–SAR) and thermoluminescence (TL–SAR) techniques to date the archaeological and natural deposits from the Qujialing site with known age, testing the techniques on samples at archaeological sites in this region. The results showed that the luminescence properties of quartz from sediment and baked earth samples are very similar. The quartz OSL ages obtained for a sediment sample and a baked earth sample from the cultural layer are 5.4 ± 0.3 and 5.1 ± 0.3 ka, respectively. The quartz TL age of the baked earth sample is 5.6 ± 0.5 ka. These dates are consistent with the calibrated radiocarbon ages (4.9 ± 0.1 and 5.1 ± 0.1 ka cal BP (±1σ)) of the two charcoal samples from the cultural layer at a nearby locality, and are also in agreement with the age of Qujialing culture period. The results indicate that the OSL dating techniques can be applied to date similar archaeological sites in the middle reaches of the Yangtze River, China.  相似文献   

15.
We analyze the longest temperature series from Prague, Bologna and Uccle. We partition daily minimum and maximum temperatures and their differences in two subsets as a function of high vs low solar activity, using the superimposed epochs method. Differences display patterns with significant amplitudes and time constants ～3 months. These are recognized in all stations and are stable against a change in the analyzed period. Amplitude of variations is ～1 °C. Differences between average annual values corresponding to high vs low activity periods are also ～1 °C. Solar activity may account for these long-term temperature variations. These variations also present local characteristics, which may render identification of a global correlation delicate. We discuss possible physical mechanisms by which solar variation could force climate changes (e.g. through solar activity itself, the EUV part of the solar flux, cosmic rays, the downward ionosphere-earth current density, etc.).  相似文献   

16.
《Marine pollution bulletin》2014,78(1-2):274-281
Nine macroalgal blooms were studied in five coastal lagoons of the SE Gulf of California. The nutrient loads from point and diffuse sources were estimated in the proximity of the macroalgal blooms. Chlorophyll a and macroalgal biomass were measured during the dry, rainy and cold seasons. Shrimp farms were the main point source of nitrogen and phosphorus loads for the lagoons. High biomasses were found during the dry season for phytoplankton at site 6 (791.7 ± 34.6 mg m−2) and during the rainy season for macroalgae at site 4 (296.0 ± 82.4 g m−2). Depending on the season, the phytoplankton biomass ranged between 40.0 and 791.7 mg m−2 and the macroalgal biomass between 1 and 296.0 g m−2. The bulk biomass (phytoplankton + macroalgal) displayed the same tendency as the nutrient loads entering the coastal lagoons. Phytoplankton and macroalgal biomass presented a significant correlation with the atomic N:P ratio.  相似文献   

17.
The brittle/ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary. In this study we examine the slip history of the large-scale Naxos/Paros extensional fault system (NPEFS), Cyclades, Greece, by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime. Based on apatite and zircon fission-track (AFT and ZFT) and (U–Th)/He dating we observe variable slip rates across the brittle/ductile transition on Naxos. ZFT and AFT ages range from 11.8 ± 0.8 to 9.7 ± 0.8 Ma and 11.2 ± 1.6 to 8.2 ± 1.2 Ma and (U–Th)/He zircon and apatite ages are between 10.4 ± 0.4 to 9.2 ± 0.3 Ma and 10.7 ± 1.0 to 8.9 ± 0.6 Ma, respectively. On Paros, ZFT and AFT ages range from 13.1 ± 1.4 Ma to 11.1 ± 1.0 Ma and 12.7 ± 2.8 Ma to 10.5 ± 2.0 Ma while the (U–Th)/He zircon ages are slightly younger between 8.3 ± 0.4 Ma and 9.8 ± 0.3 Ma. All ages consistently decrease northwards in the direction of hanging wall transport. Most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of ∼ 6–8 km Myr− 1 on the NPEFS across the brittle/ductile transition. Even the intrusion of a large granodiorite body into the narrowing fault zone at ∼ 12 Ma on Naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate. The data also show that the NPEFS accomplished a minimum total offset of ∼ 50 km between ∼ 16 and 8 Ma.  相似文献   

18.
《Continental Shelf Research》2008,28(18):2594-2600
We analyzed the temporal and vertical distribution of biogenic (BSi) and lithogenic (LSi) silica, and diatom abundance in the upwelling center off Concepción, Chile, from April 2004 to May 2005. Measurements were performed at the FONDAP COPAS Time Series Station 18 (36°30.8′S, 73°07.7′W; 88 m water depth), and were combined with primary production estimates and river runoff data to assess the relationships between water column BSi and primary production, and between LSi and river runoff. Throughout the sampling period, water-column-integrated (0–80 m) BSi averaged 252±287 mmol m−2, and was about six times higher than average LSi (44±30 mmol m−2). The highest water column BSi observed during the upwelling season (786±281 mmol m−2) coincided with increments in total diatom abundance, and high integrated chlorophyll a concentration and primary production. In contrast, LSi was nearly two times higher in winter (85±43 mmol m−2) than the annual average, in agreement with the period of substantial discharges from the Itata and Bio-Bio rivers. The observed temporal patterns in BSi and LSi are coincident with primary production-related factors and riverine outflow, respectively, suggesting that the BSi and LSi pools are separate. With respect to the vertical distribution in the water column, most of the BSi and diatoms were found in surface waters (0–30 m depth), whereas LSi was most abundant at depth. Our study attempts to make an inventory of both BSi and LSi in the water column off Concepción, and gives the present-day background information necessary to assess potential future changes in the hydrological cycle that, in turn, may induce modifications in the Si path from the watersheds to the ocean.  相似文献   

19.
In this paper, the total electron content (TEC) data from eight global positioning system (GPS) stations of the EUREF network, provided by IONOLAB (Turkey), were analyzed using discrete Fourier analysis to investigate the TEC variations over the Mediterranean before and during the strong earthquake of 12th October 2013, which occurred west of Crete, Greece. In accordance with the results of similar analyses in the area, the main conclusions of this study are the following: (a) TEC oscillations in a broad range of frequencies occur randomly over an area of several hundred km from the earthquake and (b) high frequency oscillations (f ⩾ 0.0003 Hz, periods T ⩽ 60 m) may point to the location of the earthquake with questionable accuracy. The fractal characteristics of the frequency distribution may point to the locus of the earthquake with higher accuracy. We conclude that the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanism through acoustic or gravity waves could explain this phenomenology.  相似文献   

20.
In this study, we present new GPS observations in Azerbaijan to provide an improved basis for determining the distribution of crustal deformation throughout the country and surrounding areas. The deformation field in the region has been analyzed with a dense GPS network configuration and a reliable quantification of the ongoing deformation was achieved. Results show that while contraction is dominant over the whole region, it is mostly concentrated on the middle and eastern parts of Caucasus Thrust Fault reaching up to 6.4 ± 0.2 mm/yr and Lesser Caucasus Fault does no accommodate more than 1–2 mm/yr of contraction. New network also clearly substantiates that the West Caspian Fault, which is a continuation of Caucasus Thrust Fault in the south, accommodates right-lateral slip rates of 7.1 ± 0.3 mm/yr in addition to 5.5 ± 0.3 mm/yr contraction rates.  相似文献   

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