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1.
We summarize the main features of the ionospheric F region as observed bythe Sondrestrom, Millstone Hill, Arecibo, and Jicamarca incoherent scatter radars during the 1–5May, 1995 CEDAR Storm Study interval. This paper apparently represents the first study of amajor storm interval using the current incoherent scatter radar chain supported by the U.S.National Science Foundation. We focus most attention on 2–3 May, and include additional datafrom IMP-8, the St. Johns magnetometer, SuperDARN, and global total electron content (TEC)maps from GPS. Three intervals of likely penetration of magnetospheric electric field from high tolow latitude are identified on 2 May. A unique feature of this storm are the strong daytimeequatorward wind surges in the neutral meridional wind observed at Millstone Hill. The first ofthese (at 14 UT on 2 May) is apparently due to a travelling atmospheric disturbance launched byintense frictional and Joule heating as observed at Sondrestrom. An evening enhancement in NmF2 (the dusk effect) is typically seen only on the first day of a geomagneticstorm. However, during this storm a strong dusk effect is seen at Millstone Hill on 2, 3, and 4May, associated with the equatorward wind surges. A penetrating eastward electric field alsocontributed to the dusk effect on 2 May. A large rise in hmF2 at Arecibo near0000 UT on 3 May is due to the same eastward electric field, which penetrates to the equator,causing a strong upward plasma drift at Jicamarca. This apparently results in a polewardexpansion of the equatorial anomaly zones as seen in GPS total electron content, and an increasein NmF2 at Arecibo to the largest value seen at midnight in several years.  相似文献   

2.
Longitudinal and local time variations in the structure of the equatorial anomaly under high solar activity in the equinox are considered according to the Intercosmos-19 topside sounding data. It is shown that the anomaly begins to form at 0800 LT, when the southern crest is formed. The development of the equatorial anomaly is associated with well-known variations in the equatorial ionosphere: a change in the direction of the electric field from the west to the east, which causes vertical plasma drift W (directed upward) and the fountain effect. At 1000 LT, both anomaly crests appear, but they become completely symmetrical only by 1400 LT. The average position of the crests increases from I = 20° at 1000 LT to I = 28° at 1400 LT. The position of the crests is quite strong, sometimes up to 15°, varies with longitude. The foF2 value above the equator and the equatorial anomaly intensity (EAI) at 1200–1400 LT vary with the longitude according to changes in the vertical plasma drift velocity W. At this time, four harmonics are observed in the longitudinal variations of W, foF2, and EAI. The equatorial anomaly intensity increases to the maximum 1.5–2 h after the evening burst in the vertical plasma drift velocity. Longitudinal variations of foF2 for 2000–2200 LT are also associated with corresponding variations in the vertical plasma drift velocity. The equatorial anomaly intensity decreases after the maximum at 2000 LT and the crests decrease in size and shift towards the equator, but the anomaly is well developed at midnight. On the contrary, after midnight, foF2 maxima in the region of the anomaly crests are farther from the equator, but this is obviously associated with the action of the neutral wind. At 0200 LT, in contrast to the morning hours, only the northern crest of the anomaly is clearly pronounced. Thus, in the case of high solar activity during the equinoxes, a well-defined equatorial anomaly is observed from 1000 to 2400 LT. It reaches the maximum at 2000 LT.  相似文献   

3.
The variations in the density of the ionospheric F2 layer maximum (NmF2) under the action of the zonal plasma drift perpendicularly to the magnetic (B) and electric (E) fields in the direction geomagnetic west-geomagnetic east have been studied using the three-dimensional nonstationary theoretical model of electron and ion densities (N e and N i ) and temperatures (T e and T i ) in the low-latitude and midlatitude ionospheric F region and plasmasphere. The method of numerical calculations of N e , N i , T e , and T i , including the advantages of the Lagrangian and Eulerian methods, is used in the model. A dipole approximation of the geomagnetic field (B), taking into account the non-coincidence of the geographic and geomagnetic poles and differences between the positions of the Earth’s and geomagnetic dipole centers, is accepted in the calculations. The calculated NmF2 and altitudes of the F2 layer maximum (hmF2) have been compared with these quantities measured at 16 low-latitude ionospheric sounding stations during the geomagnetically quiet period October 11–12, 1958. This comparison made it possible to correct the input model parameters: the NRLMSISE-00 model [O], the meridional component of the neutral wind velocity according to the HWW90 model, and the meridional component of the equatorial plasma drift due to the electric field specified by the empirical model. It has been indicated that the effect of the zonal E × B plasma drift on NmF2 can be neglected under daytime conditions and changes in NmF2 and hmF2 under the action of this drift are insignificant under nighttime conditions north of 25° and south of ?26° geomagnetic latitude. The effect of the zonal E × B plasma drift on NmF2 and hmF2 is most substantial in the nightside ionosphere approximately from ?20° to 20° geomagnetic latitude, and the neglect of this drift results in an up to 2.4-fold underestimation of NmF2. The found dependence of the effect of the zonal E × B plasma drift on NmF2 and hmF2 on geomagnetic latitude is related to the longitudinal asymmetry of B, asymmetry of the neutral wind about the geomagnetic equator, and changes in the meridional E × B plasma drift at a change in geomagnetic longitude.  相似文献   

4.
Using model simulations, the morphological picture (revealed earlier) of the disturbances in the F 2 region of the equatorial ionosphere under quiet geomagnetic conditions (Q-disturbances) is interpreted. It is shown that the observed variations in the velocity of the vertical E × B plasma drift, related to the zonal E y component of the electric field, are responsible for the formation of Q-disturbances. The plasma recombination at altitudes of the lower part of the F 2 region and the dependence of the rate of this process on heliogeophysical conditions compose the mechanism of Q-disturbance formation at night. The daytime positive Q-disturbances are caused exclusively by a decrease in the upward E × B drift, and this type of disturbances could be related to the known phenomenon of counter electrojet. Possible causes of formation of the daytime negative Q-disturbances are discussed.  相似文献   

5.
Global electron content (GEC) as a new ionospheric parameter was first proposed by Afraimovich et al. [2006]. GEC is equal to the total number of electrons in the near-Earth space. GEC better than local parameters reflects the global response to a change in solar activity. It has been indicated that, during solar cycle 23, the GEC dynamics followed similar variations in the solar UV irradiance and F 10.7 index, including the 11-year cycle and 27-day variations. The dynamics of the regional electron content (REC) has been considered for three belts: the equatorial belt and two midlatitude belts in the Northern and Southern hemispheres (±30° and 30°–65° geomagnetic latitudes, respectively). In contrast to GEC, the annual REC component is clearly defined for the northern and southern midlatitude belts; the REC amplitude is comparable with the amplitude of the seasonal variations in the Northern Hemisphere and exceeds this amplitude in the Southern Hemisphere by a factor of ～1.7. The dayside to nightside REC ratio, R(t), at the equator is a factor of 1.5 as low as such a GEC ratio, which indicates that the degree of nighttime ionization is higher, especially during the solar activity maximum. The pronounced annual cycle with the maximal R(t) value near 8.0 for the winter Southern Hemisphere and summer Northern Hemisphere is typical of midlatitudes.  相似文献   

6.
Measurements from ground-based receiver chains of the global positioning system (GPS) and magnetometers of the Circum-pan Pacific Magnetometer Network (CPMN) in the west Pacific region during 1999–2003 are examined. The ionospheric total electron content (TEC) derived from the GPS receivers is used to observe the strength, location, and occurrence time of the equatorial ionization anomaly (EIA) crests, which resulted from the equatorial plasma E×B drift fountain. The magnetic field strength of CPMN is employed to monitor the equatorial electrojet (EEJ), and to further estimate the effectiveness of the E×B drift to the EIA crests. Results show that the strength and location of the EIA crests are proportional to the EEJ strength.  相似文献   

7.
The total electron content (TEC) of the equatorial ionosphere is controlled by photochemical processes as well as the transport of the ionospheric plasma near the magnetic equator. The transport phenomenon is initiated by the vertical drift driven by the eastward electric field, which also drives the Equatorial Electrojet. The empirical relation between the Equatorial Electrojet and the anomaly component of the equatorial TEC has already been established. Taking this relation as a reference, a simplified physical model of the anomaly component of equatorial TEC is obtained as a function of Equatorial Electrojet. Influence of other factors like the solar incidence angle and the solar flux are also considered here and the extent of their influence are also investigated. This has been done using TEC data obtained from dual frequency GPS receivers during the low solar activity period of 2005. The derived model is based on the physics of the underlying fountain effect and matches with the observed empirical relation to a fair extent. Obtained results are found to corroborate with previous findings and these physical model values are found to have improved correlation with the observed data than the reference empirical relation. This establishes the conformity between the EEJ based ionospheric model and the physical phenomenon of the fountain effect.  相似文献   

8.
Equations of regression are derived for the intense magnetic storms of 1957?2016. They reflect the nonlinear relation between Dstmin and the effective index of geomagnetic activity Ap(τ) with a timeweighted factor τ. Based on this and on known estimations of the upper limit of the magnetic storm intensity (Dstmin =–2500 nT), the maximal possible value Ap(τ)max ~ 1000 nT is obtained. This makes it possible to obtain initial estimates of the upper limit of variations in some parameters of the thermosphere and ionosphere that are due to geomagnetic activity. It is found, in particular, that the upper limit of an increase in the thermospheric density is seven to eight times larger than for the storm in March 1989, which was the most intense for the entire space era. The maximum possible amplitude of the negative phase of the ionospheric storm in the number density of the F2-layer maximum at midlatitudes is nearly six times higher than for the March 1989 storm. The upper limit of the F2-layer rise in this phase of the ionospheric storm is also considerable. Based on qualitative analysis, it is found that the F2-layer maximum in daytime hours at midlatitudes for these limiting conditions is not pronounced and even may be unresolved in the experiment, i.e., above the F1-layer maximum, the electron number density may smoothly decrease with height up to the upper boundary of the plasmasphere.  相似文献   

9.
Results of the study of the behavior of the F 2 region and topside ionosphere during the magnetic storm on November 7–10, 2004, which was a superposition of two sequent Severe magnetic disturbances (Kp = 9–) are presented. The observations were conducted by the incoherent scatter radar at Kharkov. Considerable effects of a negative ionospheric disturbance are registered, including a decrease in the electron density in the F 2-layer maximum by a factor of 6–7 and of the total electron content up to a height of 1000 km by a factor of 2, a lifting up of the ionospheric F 2 layer by 300 km at night and by 150–180 km in the daytime, unusual nighttime heating of the plasma with an increase of the ion and electron temperatures up to 2000 and 3000 K, respectively, and a decrease in the relative density of hydrogen ions N(H+)/N e by a factor of up to 3.5 because of the emptying of the magnetic flux tube passing over Kharkov. The effects usually observed in the high-latitude ionosphere, including the coherent echoes, are detected during the main phase of the storm. The results obtained manifest a shift of the large-scale structures of the high-latitude ionosphere (the auroral oval, main ionospheric trough, hot zone, etc.) down to latitudes close to the latitude of the Kharkov radar.  相似文献   

10.
The equatorial ionosphere responses over Brazil to two intense magnetic storms that occurred during 2001 are investigated. The equatorial ionization anomaly (EIA) and variations in the zonal electric field and meridional winds at different storms phases are studied using data collected by digisondes and GPS receivers. The difference between the F layer peak density (foF2) at an equatorial and a low latitude sites was used to quantify the EIA; while the difference between the true heights (hF) at the equatorial and an off-equatorial site was used to calculate the magnetic meridional winds. The vertical drift was calculated as dhF/dt. The results show prompt penetration electric fields causing unusual early morning development of the EIA, and disturbed dynamo electric field producing significant modification in the F region parameters. Variations to different degrees in the vertical drift, the thermospheric meridional winds and the EIA developments were observed depending on the storm phases.  相似文献   

11.
A possibility of estimating the local value of the plasma frequency of the F2 layer ionospheric maximum (subionospheric region) according to the multifrequency sounding data of the arctic ionosphere from high-elliptical spacecrafts was considered. The data in the form of the frequency dependence of the group path of the sounding signal, the transionogram, were synthesized in the results of mathematical modeling. The energetic potential of proposed method, the wave field mode structure, and uncertainty of the critical frequency estimation according to the measured cut-off frequencies of magnetoionic components of the transionogram were analyzed. It was shown that the expected potential uncertainty of foF2 estimation is somewhat higher than that for the case of maximum reliable ground based data, but it is, in general, substantially less than the methods that use measurements of the total electron content in GPS technology. We discussed physical feasibility for a realization of the method for ionospheric state diagnostics.  相似文献   

12.
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13.
The changes of the ionospheric electric field before and after four huge earthquakes, which include the Ms 8.7 earthquake of 2004 and the Ms 8.5 earthquake of 2005 in Sumatra of Indonesia, the Ms 8.0 Wenchuan earthquake of 2008 in China, the Ms 8.8 earthquake of 2010 in Chile, and their strong aftershocks are studied in this paper. The significant results revealed that the power spectral density of low-frequency electric field below 20 Hz in the ionosphere, a kind of electromagnetic radiation phenomena, increased abnormally before and after the earthquakes and partially corresponded to the increased power spectral density of the low-frequency geoelectric field in time. This research preliminarily indicates that the low-frequency electromagnetic radiation during the imminent stages before such earthquakes could be detected by the observation of the ionospheric electric field. However, the spatial, temporal, and intensive complexities of the electric field anomalies in the ionosphere before earthquakes have come in sight also.  相似文献   

14.
The expression for the increment of instability and decrement of diffusion damping of gradient drift waves for ionospheric altitudes above the F 2 layer maximum is obtained. The gradient drift instability is used to interpret the observations of spread F in the region of large-scale horizontal irregularities of the electron density. Two types of such irregularities observed on board the Intercosmos-19 (IC-19) satellite in the region of low latitudes (a peak of the density in the dusk ionosphere and a trough of the density in the dawn ionosphere) are considered. It is shown that the observed gradients of the density and electric field values in the dawn and dusk ionospheric sectors are quite sufficient for the instability development criterion to be satisfied in both considered cases.  相似文献   

15.
We have studied changes in the ionosphere prior to strong crustal earthquakes with magnitudes of М ≥ 6.5 based on the data from the ground-based stations of vertical ionospheric sounding Kokobunji, Akita, and Wakkanai for the period 1968–2004. The data are analyzed based on hourly measurements of the virtual height and frequency parameters of the sporadic E layer and critical frequency of the regular F2 layer over the course of three days prior to the earthquakes. In the studied intervals of time before all earthquakes, anomalous changes were discovered both in the frequency parameters of the Es and F2 ionospheric layers and in the virtual height of the sporadic E layer; the changes were observed on the same day at stations spaced apart by several hundred kilometers. A high degree of correlation is found between the lead-time of these ionospheric anomalies preceding the seismic impact and the magnitude of the subsequent earthquakes. It is concluded that such ionospheric disturbances can be short-term ionospheric precursors of earthquakes.  相似文献   

16.
Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they affect the normal eastward Sq field. This paper presents an analysis of ground magnetic field and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground field and ionospheric electrodynamic data leads to the identification of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric field during the pre-sunrise hours (0400–0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the time-interval 0800–0950 UT. Subsequent to the change in hF during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric field. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The H variations observed at the equator are the sum of the following components: SR, DP, DR, DCF and DT.  相似文献   

17.
A comparison between the modeled NmF2 and hmF2 and NmF2 and hmF2, which were observed by the Kokubunji, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders and by the middle and upper (MU) atmosphere radar, have been used to study the time-dependent response of the low-latitude ionosphere to geomagnetic forcing during a time series of geomagnetic storms from 22 to 26 April 1990. The reasonable agreement between the model results and data requires the modified equatorial meridional E×B plasma drift, the modified HWM90 wind, and the modified NRLMSISE-00 neutral densities. We found that changes in a flux of plasma into the nighttime equatorial F2-region from higher L-shells to lower L-shells caused by the meridional component of the E×B plasma drift lead to enhancements in NmF2 close to the geomagnetic equator. The equatorward wind-induced plasma drift along magnetic field lines, which cross the Earth equatorward of about 20° geomagnetic latitude in the northern hemisphere and about −19° geomagnetic latitude in the southern hemisphere, contributes to the maintenance of the F2-layer close to the geomagnetic equator. The nighttime weakening of the equatorial zonal electric field (in comparison with that produced by the empirical model of Fejer and Scherliess [Fejer, B.G., Scherliess, L., 1997. Empirical models of storm time equatorial zonal electric fields. J. Geophys. Res. 102, 24047–24056] or Scherliess and Fejer [Scherliess, L., Fejer, B.G., 1999. Radar and satellite global equatorial F region vertical drift model. J. Geophys. Res. 104, 6829–6842) in combination with corrected equatorward nighttime wind-induced plasma drift along magnetic field lines in the both geomagnetic hemispheres are found to be the physical mechanism of the nighttime NmF2 enhancement formation close to the geomagnetic equator over Manila during 22–26 April 1990. The model crest-to-trough ratios of the equatorial anomaly are used to study the relative role of the main mechanisms of the equatorial anomaly suppression for the 22–26 April 1990 geomagnetic storms. During the most part of the studied time period, a total contribution from geomagnetic storm disturbances in the neutral temperature and densities to the equatorial anomaly changes is less than that from meridional neutral winds and variations in the E×B plasma drift. It is shown that the latitudinal positions of the crests are determined by the E×B drift velocity and the neutral wind velocity.  相似文献   

18.
Variations in the frequency of occurrence of riometer absorption, minimum frequency of reflection of the ionospheric F layer, minimum height, and height of maximum electron density of the ionospheric F layer near the solar minimum have been studied. Application of the superposed epoch technique has detected the Moon phase effect on these ionospheric parameters. This effect was: three events per day in the occurrence of riometer absorption, 0.056 MHz in the minimum frequency of reflection of the F layer, and 2.6 and 6.7 km, in the change of the minimum height of reflection and height of reflection from the region with maximum electron density of the ionospheric F layer, respectively. The lunar tide action changes the ionospheric conductivity and, thus, influences the current systems of the magnetosphere. Through changes of magnetospheric currents, the Moon phase effect is exhibited in the Ap and Dst indices and is 4.3 and 4.25 nT, respectively.  相似文献   

19.
The observations of the effects of the partial (about 77%) solar eclipse (SE) of March 29, 2006, in the ionospheric plasma are presented. The experimental data were obtained using the Kharkov incoherent scatter radar. At the moment of the maximum phase of SE, a decrease in the critical frequency of the ionospheric F 2 layer by 18%, a depletion of the density in the F 2 layer maximum by 33%, and an increase in the maximum height z m by 30 km were observed. The solar eclipse caused a decrease in the electron and ion temperatures by 150–300 and 100–200 K, respectively, within the height range 210–490 km. An increase in the relative density of the hydrogen ions during the maximum phase of SE by 20–25% within the height range 900–1200 km is detected. Calculations of the parameters of dynamical processes and thermal regime of the ionospheric plasma during SE are performed.  相似文献   

20.
The results of observations of the total electron content (TEC) in periods of storm disturbances of meteorological situation are presented in the paper. The observational results have shown that a passage of a meteorological storm is accompanied by a substantial decrease in values of TEC and critical frequencies of the ionospheric F2 region. The decreases in values of these ionospheric parameters reach 50% and up to 30% in TEC and critical frequency of the F2 layer, respectively, as compared to meteorologically quiet days. Based on qualitative analysis, it is found that the processes related to formation of local regions of thermospheric heating due to a dissipation of AGW coming into the upper atmosphere from the region of the meteorological disturbance in the lower atmosphere are a possible cause of these ionospheric disturbances.  相似文献   

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