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1.
In this paper, we investigate the solar flare effects of the ionosphere at middle latitude with a one-dimensional ionosphere theoretical model. The measurements of solar irradiance from the SOHO/Solar EUV Monitor (SEM) and GOES satellites have been used to construct a simple time-dependent solar flare spectrum model, which serves as the irradiance spectrum during solar flares. The model calculations show that the ionospheric responses to solar flares are largely related to the solar zenith angle. During the daytime most of the relative increases in electron density occur at an altitude lower than 300 km, with a peak at about 115 km, whereas around sunrise and sunset the strongest ionospheric responses occur at much higher altitudes (e.g. 210 km for a summer flare). The ionospheric responses to flares in equinox and winter show an obvious asymmetry to local midday with a relative increase in total electron content (TEC) in the morning larger than that in the afternoon. The flare-induced TEC enhancement increases slowly around sunrise and reaches a peak at about 60 min after the flare onset.  相似文献   

2.
The ground track of the annular eclipse of 3 October 2005 crossed the Iberian Peninsula. The main objective of this work was to analyze the variability of the solar irradiance and the total ozone column during the course of this event at El Arenosillo (Southwestern Spain). For achieving this goal, two Kipp & Zonen broadband radiometers (one for measuring total solar irradiance and other for measuring ultraviolet erythemal solar irradiance), one NILU-UV multi-band instrument and one Brewer spectroradiometer were used in this work. Total irradiance (310–2800 nm), and ultraviolet erythemal radiation (UVER) were recorded at a high frequency of 5 s, showing a strong reduction (higher than 80%) of the irradiance at the maximum solar obscuration which was of 79.6%. The irradiance decrease during the course of the eclipse was positively correlated with the percentage of eclipse obscuration, showing a very high agreement (R2～0.99). The irradiance recorded at selected wavelengths from the NILU-UV instrument shows a more pronounced decrease in the UV irradiance at the lower wavelengths during the solar eclipse. Finally, the evolution of the total ozone column (TOC) derived from Brewer and NILU instruments during the eclipse presented an opposite behavior: while the Brewer derived TOC values increase about 15 DU, the NILU derived TOC values decrease about 11 DU. This opposite behavior is mainly related to an artifact in the spectral irradiances recorded by the two instruments.  相似文献   

3.
The total electron content (TEC) is a key ionospheric parameter for various space weather applications. Over the last decade an extensive database of TEC measurements has become available from both space- and ground-based observations, and these measurements have established the general morphology of the global TEC distributions. In particular, the TOPEX TEC measurements have shown strong longitudinal variations of TEC in addition to the observed day-to-day variabilities. To better understand the observed TEC variations and to better guide its modeling, we have studied the sensitivity of quiet-time TEC to the following key atmospheric and ionospheric parameters: neutral density, neutral wind, plasma temperatures, plasmaspheric flux, and the O+–O collision frequency. These parameters are often only roughly known and can cause large uncertainties in model results. For this study, we have developed a numerical mid-latitude ionospheric model, which solves the momentum and continuity equations for the O+ density and a simplified set of equations for the H+ density. To obtain TEC, the calculated ion densities have been integrated from the bottom altitude (100 km) to the altitude of the TOPEX satellite (1336 km). Our study shows that during the day the neutral wind and the neutral composition have the most important effect on TEC. In particular, the zonal component of the neutral wind can have a large effect on TEC in the southern hemisphere where the magnetic declination angle is large. During the night, most of the above-mentioned parameters can play a significant role in the TEC morphology, except for the plasma temperature, which has only a small effect on TEC. Finally, the TEC varies roughly linearly with respect to all of the parameters except for the neutral wind.  相似文献   

4.
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   

5.
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   

6.
The total solar eclipse of 29 March, 2006 which was visible at Ibadan (7.55°N, 4.56°E), south-western Nigeria was utilized to document atmospheric surface-layer effects of the eclipse for the first time in Nigeria. The meteorological parameters measured are global radiation, net radiation, wind speed (at different heights), atmospheric pressure and soil temperature (5, 10 and 30 cm), moisture and heat flux and rainfall. The results revealed remarkable dynamic atmospheric effects. The observations showed that the incoming solar radiation, net radiation and air temperature were significantly affected.There was an upsurge of wind speed just before the first contact of the eclipse followed by a very sharp decrease in wind speed due to the cooling and stabilization of the atmospheric boundary layer. The atmospheric pressure lags the eclipse maximum by 1 h 30 min, while the soil temperature at 5 and 10 cm remain constant during the maximum phase of the eclipse.  相似文献   

7.
An annular eclipse occurred over Europe in the morning hours of 3 October 2005. The well-defined obscuration function of the solar radiation during the eclipse provided a good opportunity to study the ionospheric/thermospheric response to solar radiation changes. Since the peak electron density behavior of the ionospheric F2 layer follows the local balance of plasma production, loss and transport, the ionospheric plasma redistribution processes significantly affect the shape of the electron density profile. These processes are discussed here based on a comparison of vertical incidence sounding (VS) and vertical total electron content (TEC) data above-selected ionosonde stations in Europe. The equivalent slab thickness, derived with a time resolution of 10 min, provides relatively good information on the variation of the electron density profile during the eclipse. The computations reveal an increased width of the ionosphere around the maximum phase. As indicated by the available measurements over Spain, the photo production is significantly reduced during the event leading to a slower increase of the total ionization in comparison with the neighboring days. The supersonic motion of the Moon's cool shadow through the atmosphere may generate atmospheric gravity waves that propagate upward and are detectable as traveling ionospheric disturbances at ionospheric heights. High-frequency (HF) Doppler shift spectrograms were recorded during the eclipse showing a distinct disturbance along the eclipse path. Whereas the ionosonde measurements at the Ebro station/Spain in the vicinity of the eclipse path reveal the origin of the wave activity in the lower thermosphere below about 180 km altitude, the similar observations at Pruhonice/Czech Republic provide arguments to localize the origin of the abnormal waves in the middle atmosphere well below the ionospheric heights. Although ionosonde and HF Doppler measurements show enhanced wave activity, the TEC data analysis does not, which is an indication that the wave amplitudes are too small for detecting them via this interpolation method. The total ionization reduces up to about 30% during the event. A comparison with similar observations from the solar eclipse of 11 August 1999 revealed a quite different ionospheric behavior at different latitudes, a fact that needs further investigation.  相似文献   

8.
2009年7月22日上午发生的日全食是21世纪持续时间最长的日全食,其全食带覆盖了中国中部的K江流域,为研究日全食对电离层的影响提供了一次难得的机会,为此本文通过卡尔曼滤波算法实现了实时求解TEC和GPS系统硬件延迟,为实时监测日全食期间电离层变化提供了绝对的电离层TEC.采用上海和浙江区域内GPS网的观测数据,建立了...  相似文献   

9.
We present the results derived from measuring fundamental parameters of the ionospheric response to the August 11, 1999 total solar eclipse. Our study is based on using the data from about 100 GPS stations located in the neighborhood of the eclipse totality phase in Europe. The eclipse period was characterized by a low level of geomagnetic disturbance (Dst-variation from −10 to −20 nT), which alleviated significantly the problem of detecting the ionospheric response to the eclipse. Our analysis revealed a well-defined effect of a decrease (depression) of the total electron content (TEC) for all GPS stations. The delay between minimum TEC values with respect to the totality phase near the eclipse path increased gradually from 4 min in Greenwich longitude (10:40 UT, LT) to 8 min at the longitude 16° (12:09 LT). The depth and duration of the TEC depression were found to be 0.2–0.3 TECU and 60 min, respectively. The results obtained in this study are in good agreement with earlier measurements and theoretical estimates.  相似文献   

10.
This paper documents the effect of the annular solar eclipse of 15 January 2010 on the lower atmospheric boundary layer dynamics over a complex terrain environment at Gadanki (13.5°N, 79.2°E,) using a suite of instruments namely automatic weather station, mini boundary layer mast (15 m), Doppler SODAR, GPS radiosonde and ozonesonde observations. The net heating rates are estimated using radiative transfer algorithm before, during and after the eclipse. Effect on soil temperature is seen clearly up to 20 cm depth and at all the levels up to 15 m. Decrease in the thermal plume level, a dip in the surface layer and a strong vertical downdrafts (subsidence) are noticed during the peak eclipse. Upper layer winds did not show any variation during the eclipse. It is also found to have pronounced effect on all the surface meteorological parameters for a two-day period.  相似文献   

11.
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   

12.
The morphology of averaged diurnal variations of total electron content (TEC) under quiet helio-geomagnetic conditions for all latitudinal bands and various longitudes has been studied using Global Ionospheric Maps (GIMs) datasets. The diurnal TEC variation maximum is generally registered at 14–15 LT. The maximum is 38±5, 14±2, 10±2 TECU (TECU is generally accepted TEC unit) at the equatorial, middle and high latitudes. The nighttime TEC minimum is within 5–7 TECU regardless of a season, latitude and longitude. At the equatorial latitudes TEC exhibits the most significant daily/season variations and the asymmetry of its behavior in the hemispheres near the equinox. Abnormal diurnal TEC variations (evening maximum, near-noon minimum) are observed at middle and high latitudes in summer due to atmospheric wind effects. The comparison of the averaged diurnal TEC variations with the behavior of the ionospheric F2-layer critical frequency indicated that GIMs describe daily/annual TEC variations reasonably well.  相似文献   

13.
The present work integrates ground-based ionosphere measurements using very-low-frequency radio transmissions with satellite measurements of the total electron content to draw common conclusions about the possible impact that the Mw6.1 earthquake that took place in Greece on January 26, 2014, had on the ionosphere.Very-low-frequency radio signals reveal the existence of an ∼4-day anomaly in the wavelet spectra of the signals received inside the earthquake preparation zone and a significant increase in the normalized variance of the signals prior to the earthquake (approximately 1 day before).Through total electron content analysis, it was possible to identify a clear anomaly from 15:00 until 20:00 UT on the day before the earthquake that appears again on the day of the earthquake between 07:00 UT and 08:00 UT. The anomalous values reach TEC1Sigma ∼4.36 and 3.11, respectively. Their spatial and temporal distributions give grounds to assume a possible link with the earthquake preparation. The geomagnetic, solar and weather conditions during the considered period are presented and taken into account.This work is an initial and original step towards a multi-parameter approach to the problem of the possible earthquake-related effects on the ionosphere joining observations made from both ground stations and satellites. A well-founded knowledge of these phenomena is clearly necessary before dealing with their application to earthquake prediction purposes.  相似文献   

14.
Electron and ion temperature (Te and Ti) data observed using RPA on board SROSS C2 satellite are investigated for the variation with local time, season, latitude (0–30°N geographic) over a half of a solar cycle (1995–2000). The nighttime Te (∼1000 K) is independent of the season and the solar flux whereas Ti exhibits positive correlation with the solar activity during all three seasons. In the early morning hours during summer, Te is higher by ∼500 K than other seasons in all three levels of solar activity. During winter and equinox in the early morning hours, Te and Ti are higher during low solar activity, showing a negative correlation with solar flux. During daytime, the Ti increases with the solar flux in winter and summer solstice, but is independent in equinox. IRI underestimates Te and Ti during the morning period by 50–75% in the equatorial and near-equatorial stations during all levels of solar activities.  相似文献   

15.
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   

16.
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   

17.
A study on variability of the equatorial ionosphere was carried out at fixed heights below the F2 peak for two different levels of solar activity. The study covered height range of 100 km up to the peak of F2 layer using a real height step increase of 10 km. The variability index used is the percentage ratio of standard deviation over the average value for the month. Daytime minimum variability of between 3% and 10% was observed at height range of about 150–210 km during low solar activity and between 2% and 7% at height range of 160–220 km during high solar activity. The nighttime maximum of between 70% and 187% was observed at height range of about 210–250 km during low solar activity and between 42% and 127% at height range of 210–250 km during high solar activity. The height range at which daytime minimum was observed falls within the F1 height of the ionosphere. The result obtained is consistent with previous works carried out in the low latitude locations for American sector.  相似文献   

18.
During the total solar eclipse on July 22, 2009 in Wuhan, the joint observation test of Na layer and ionosphere was conducted by using the daytime observation atmospheric lidar and the GPS ionosphere detector. The results show that the full width at half maximum (FWHM) of Na layer density slightly narrowed during the total solar eclipse and broadened after the eclipse, while the height of Na peak slightly decreased in the eclipse and increased after the eclipse. These implying that Na layer changes reflect the rapid process of sunrise and sunset. The ionosphere total electron content (TEC) and the sky background light noise also presented an obvious fluctuation characteristic with the changes of solar irradiation during the process of total solar eclipse. The difference lies in that the changes of FWHM of Na layer atoms are much slower than that of ionosphere, the reason for this might be that the Na layer, after being disturbed by the total solar eclipse, will generate a series of complicated photochemical reactions and momentum transport processes, and then recombine the Na atoms. The Na atoms to be detected by the lidar need a lag process, which rightly conforms to the theoretical simulated results.  相似文献   

19.
We report observations of seasonal and local time variation of the averaged electron and iron concentrations, as well as simultaneous measurements of the two species, above the Arecibo Observatory (18.35°N, 66.75°N), Puerto Rico. The average Fe profile between 21:00 and 24:00 LT has a single peak at about 85 km with the exception of the summer when an additional peak exists at about 95 km. The higher Fe peak in the summer is correlated with higher electron concentrations in this season. The three nights of simultaneous measurements of electron and iron concentrations show that narrow layers of Fe and electrons are well correlated. Comparison of the climatological and simultaneous Fe and electron data suggests that recombination of Fe+ plays an important role in determining the Fe profile in the upper part of the Fe layer. Above 93 km, the Fe concentration appears to increase after sunset if the electron concentration exceeds about 4000 electrons cm−3. The average rate of Fe production is about 0.1 atom cm−3 s−1 for all seasons at 100 km in the early evening hours. A chemical model reveals that the concentration of Fe+ must be 50–80% of the total ionization over Arecibo for typical equinox conditions to explain the observed rate of Fe production. These high relative Fe+ concentrations are consistent with in situ observations that Fe+ is usually the dominant ion in sporadic E layers in the nighttime lower E region. This suggests that the source of Fe+ is provided by sporadic E layers descending over Arecibo after sunset. The Fe density between 80 and 85 km decreases during the night, for all seasons. This is attributed to the formation of stable molecular Fe species, such as FeOH, due to the increase in O3 and decrease in atomic O and H during the night at these altitudes.  相似文献   

20.
The observations of the upper mesosphere region (∼95 km altitude) in the period of 27–30 March 2006 using mesopause oxygen rotational temperature imager (MORTI) at Almaty (43.03°N, 76.58°E) are presented in this report to illustrate the mesosphere response to the solar eclipse (SE) event, which occurred on 29 March 2006. The nighttime volume emission rates and rotational temperatures, obtained from MORTI measurements, show appreciable differences in the pattern of wave-like oscillations observed during the period of interest. These oscillations are possibly due to the SE. Using a periodogram method the spectra of the observed wave-like oscillations, observed in the mesosphere, are examined. A physical mechanism is proposed to interpret the effects observed in terms of the mesosphere response to the total SE.  相似文献   

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