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1.
A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high Ap, index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly Kp indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.  相似文献   

2.
After discussing some examples of mid-latitude spread-Es this paper presents distributions showing the diurnal, annual and sunspot-cycle variations of this phenomenon. The variations are very similar to those found for mid-latitude spread-F. Also, a superposed-epoch analysis involving an investigation of spread-F occurrence relative to controls consisting of nights of high spread-Es occurrence showed a relationship of high significance. A similar analysis using spread-F occurrence relative to daytime spread-Es controls also suggested a relationship between these parameters. The results presented in this paper together with results from previous work suggest strongly that the two phenomena (spread-Es and spread-F) are produced by the same or similar disturbances. Also it seems likely that the disturbances responsible for spread-F during night hours are also present during daylight hours.  相似文献   

3.
The variation of the geomagnetic activity index Ap at the IMF sector boundaries (+ to ? and ? to +) has been studied for three solar cycles, separating data into vernal and autumnal equinoxes. It was found that a reported increase in Ap as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF Bz component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams.  相似文献   

4.
The problem of the ionospheric disturbances associated with geomagnetic storms is examined with the goal of searching for a relationship between the time-developments of the two phenomena. Faraday rotation measurements of total electron content (NT) are used to monitor the ionospheric F-region at a mid-latitude site, while a variety of geomagnetic parameters are examined as possible ways of following the geomagnetic variations. The ionospheric and geomagnetic data taken during 28 individual storms from 1967 to 1969 are used to search for a predictive scheme which can be tested using data from 17 storms in 1970. The specific aim is to find the geomagnetic parameter whose time-development can best forecast whether or not the ionospheric response will include an initial positive phase prior to the normally extended period of F-region depletions. Correlations between NT and the geomagnetic indices Kp, and equatorial Dst(H) prove to be wholly inadequate. The local times of main-phase-onset (MPO) determined from the equatorial Dst(H) indices as well as from local horizontal component data, also prove to be unsatisfactory. The best correlations are obtained using local measurements of the total geomagnetic field (F). These results show that a storm commencement (SC) will produce an enhancement in nt during the afternoon period following the SC unless there is an intervening post-midnight period with a strong depression of the geomagnetic field. Operationally this is taken to be a depression in F of at least 100γ near 03:00 LT  相似文献   

5.
Observation of ionograms recorded at about fifteen high latitude stations shows there the same morphological types of F-lacunae (disappearance of echoes from the F1, the F2 or the complete F-layer) as in Terre Adélie. The phenomenon is aestival and diurnal everywhere, but the shape of occurrence histograms varies from one station to another. A statistical study shows that the occurrence in the various stations (of the same hemisphere) is correlated, all the more as the considered stations have similar invariant latitudes. Occurrence is correlated with the daily index of magnetic activity Ap, a correlation which is maximum at about 75° invariant latitude and decreases on both sides. A study of particular events shows a clear relation between lacunae occurrence and the position and moving of the cleft (as deduced empirically from the Kp index), results which can be interpreted in terms of a previously described model.  相似文献   

6.
This paper describes occurrence probabilities and patterns of trans-equatorial proton (TEP), deuteron (TED) and helium (TEH) whistler from the ISIS-2 satellite in time compressed dynamic spectra. It is shown that the TEP whistlers have high occurrence probability in an active solar period, while the TED whistler has low occurrence probability. In a quiet solar period, the TEP whistler has a relatively lower occurrence probability than the TED whistler. The TEP whistler in a quiet solar period shows a strong seasonal variation. That is a higher occurrence probability in the winter than in the summer in the Northern Hemisphere. The curve of occurrence probability of the TED whistler has a valley (no occurrence) at the noon in a solar active period. The minimum occurrence probabilities, which depend on geomagnetic activity appear at about KP = 4-5. These phenomena seem to be explained by using the bouncing surface diagram of multicomponent and inhomogeneous plasmas with various proton density. The spectral pattern of trans-equatorial ion whistlers and calculation of an approximate equation with regard to deuteron effect show that relative proton densities to electrons NP/Ne decrease with increasing solar activity.  相似文献   

7.
Temperature data collected over several years from rocket grenade and other experiments at Point Barrow (Alaska), Fort Churchill (Canada) and Wallops Island (Virginia) have been analysed to determine the effect of geomagnetic activity on the neutral temperature in the mesosphere and to study the latitudinal variation of this effect. An analysis carried out has revealed almost certainly significant correlations between the temperature and the geomagnetic indicies Kp and Ap at Fort Churchill and marginally significant correlations at Barrow and Wallops. This has also been substantiated by a linear regression analysis.The results indicate two types of interdependence between mesospheric temperature and geomagnetic field variations. The first type is the direct heating effect, during a geomagnetic disturbance, which has been observed in the present analysis with a time lag of 3–15 hr at the high latitudes and 36 hr at the middle latitudes. The magnitude of this heating effect has been found to decrease at the lower altitudes. The second type of interrelation which has been observed is temperature perturbations preceding geomagnetic field variations, both presumably caused by a disturbance in atmospheric circulation at these levels.  相似文献   

8.
We employ annually averaged solar and geomagnetic activity indices for the period 1960??C?2001 to analyze the relationship between different measures of solar activity as well as the relationship between solar activity and various aspects of geomagnetic activity. In particular, to quantify the solar activity we use the sunspot number R s, group sunspot number R g, cumulative sunspot area Cum, solar radio flux F10.7, and interplanetary magnetic field strength IMF. For the geomagnetic activity we employ global indices Ap, Dst and Dcx, as well as the regional geomagnetic index RES, specifically estimated for the European region. In the paper we present the relative evolution of these indices and quantify the correlations between them. Variations have been found in: i) time lag between the solar and geomagnetic indices; ii) relative amplitude of the geomagnetic and solar activity peaks; iii) dual-peak distribution in some of solar and geomagnetic indices. The behavior of geomagnetic indices is correlated the best with IMF variations. Interestingly, among geomagnetic indices, RES shows the highest degree of correlation with solar indices.  相似文献   

9.
Short-term variations δf0F2 in the values of the critical frequency of the ionospheric F2 region in middle latitudes due to solar and geomagnetic activities have been investigated. Diurnal and seasonal features of the energy flow from the auroral into midlatitude ionosphere are revealed. It is shown that they could be taken into account if instead of the 3-hour geomagnetic indices or their daily averages a new index is employed which characterizes the average level of geomagnetic activity over intervals of time no less than nine hours usually during the evening and night hours. A technique for short-term predicting δf0F2 in the midlatitude ionosphere is developed which employs the indices of solar and geomagnetic activities, and errors in the predictions are estimated.  相似文献   

10.
The propagation of the geomagnetic effect into the exosphere is investigated based on a free-flight particle kinetic model of exospheric densities and temperatures. Exobasic neutral gas conditions and their variations during a geomagnetic storm occurrence are adopted as given by the OGO-6 model. The contributions of particles originating at different exobasic locations to the density and temperature at exospheric regions are taken into account according to the time needed to reach these regions. A short-time geomagnetic variation of exobasic conditions is simulated by a Gaussianshaped Ap -index variation with an FWHM of 20 min. It is then shown that the relative amplitude and the half width of the geomagnetic density variation increase strongly with exospheric heights. The density peak and the main temperature peak are shown to be delayed by more than one and two hours, respectively, at heights above 10,000 km. The temperature variation changes from a singlepeaked to a double-peaked structure at greater exospheric heights. It is shown that the exospheric density response to geomagnetic disturbances is detectable in observations of the geocoronal He-1-584 Å resonance radiation.  相似文献   

11.
The seasonal variation of the geomagnetic activity shows two sharp maxima (in March and September) and two broader minima (in June and December). It can only poorly be described by a double sine wave. The double phase wave of geomagnetic activity can be transformed - by vertical mirroring of the half year part between the maxima - into a single phase wave, which is represented well by a single sine function. This function is determined here for C i (the daily international character figure of geomagnetic activity) and for A p (the equivalent daily amplitude, based on K p, the geomagnetic planetary three-hour-range indices), for both in their ratios to the mean value over the year and then averaged over many years. To remove part of the irregularities the daily values of C i and A p were corrected for solar activity and reduced to quiet Sun circumstances. Mirroring back to the double phase function the geomagnetic variation is then represented by $$Ci({\text{or }}Ap) = Cm({\text{or }}Ap,m) - |A{\text{ sin}}(\lambda - \varphi )|$$ , in which m means the mirror value, A is the amplitude of the single sine curve, λ runs parallel to the Sun's longitude, ? is the phase constant and the bars indicate the absolute value. The data of the first maximum of the seasonal variation was found to vary between March 18 and 28 for different groups of years. The sharpness of the maxima may point out a resonance in the interaction between the solar wind and the magnetosphere. In the appendix the relation \(Ci = aR^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} + b\) (R being the relative sunspot number) is brought forward. The values of the parameter b through the eleven-year period reveal an increasing influence of sunspot-free regions towards the minimum.  相似文献   

12.
The influence of active processes on the Sun and their response on the dynamics of Earth’s artificial satellites has been investigated. The relationship between the characteristics of solar activity and variations of the periods P of the orbital motion of Earth’s artificial satellites has been found. These variations mainly indicate the variations in the Earth’s atmosphere density caused by solar activity (index F10.7) and geomagnetic activity (ΣKp index). High values of the correlation coefficients between P and F10.7 (–0.77…–0.91) and between P and ΣKp (–0.67…–0.89) exhibit significant effect of solar and geomagnetic activity on the orbital periods of satellites.  相似文献   

13.
The data from observations of the geomagnetic field, ionospheric parameters and atmospheric emissions, carried out at four midlatitude station in Bulgaria are analysed. The observations refer to the geomagnetic disturbance on 28/30 October 1973 (Kpmax = 7) and also to a very quiet period before it. It is shown that all four geomagnetic substorms during the night of 29/30 October influenced the midlatitude F-region. This is indicated by a lowering of the height of the F-region by ca. 50–70 km. Owing to this downward drift of ionisation the dissociative recombination and the intensity of the red line is accordingly increased. As an explanation of this phenomenon we suggest the action of the electric fields, which can at the same time be transported from the magnetosphere to the ionosphere.  相似文献   

14.
Magnetic field intensity of the horizontal component (H) data measured from Magnetic Data Acquisition System (MAGDAS) at Ilorin (geographic latitude: 8.47°N, geographic longitude: 4.68°E, geomagnetic latitude: 1.82°S, geomagnetic longitude: 78.6°S), Nigeria in the year 2009 (a low activity year) was used to study the diurnal, monthly-median and standard deviation of the solar quiet of the horizontal component (S q H). The diurnal variation of S q H and its corresponding monthly median variation (MS q H) shows minima values at pre-sunrise hours between 0500 and 0600 LT. The S q H value shows a daytime maximum variation range between 20 and 91 nT and a nighttime minimum variation range from 1 to 4 nT. The occurrences of daytime maxima of the S q H values that were observed in all the months are between the hours of 1000 and 1200 LT. The daytime maximum of the MS q H values from the entire months were seen at 1100 LT with exceptions of January and December. The month of October has the highest value (61 nT) and the lowest value was observed in December (35 nT). It is clearer that the range in maximums of S q H and MS q H variations during the daytime period in all the months is greater than the range in minimums observed at nighttime period (post-sunset and pre-sunrise). The monthly standard deviation (STD) depicts the index of variability of all the day-to-day variations in each month. Counter electrojet (CEJ) events were observed in the morning and as well during the evening hours. The magnitudes and frequencies of CEJ events during the evening hours are greater than that of the morning hours. CEJ seen during the morning period around 0500–0600 LT is the consequence of late reversals of nighttime westward currents to daytime eastward currents. A semi-annual variation with peak values during March, April, September and October was observed. Seasonal variation that was characterized with CEJ was also investigated.  相似文献   

15.
Jovian decametric radio wave emissions that were observed at Goddard Space Flight Center, U.S.A. for a period from 1 October to 31 December, 1974 and data obtained at Mt Zao observatory, Tohoku University, Japan, for a period from 14 July to 6 December, 1975 have been used to investigate the relationship of the occurrence of the Jovian decametric radio waves (JDW), from the main source, to the geomagnetic disturbance index, ΣKp. The dynamic cross-correlation between JDW and ΣKp indicates an enhanced correlation for certain values of delay time. The delay time is consistent with predicted values based on a model of rotating turbulent regions in interplanetary space associated with two sector boundaries of the interplanetary magnetic field, i.e. the rotating sector boundaries of the interplanetary magnetic field first encounter the Earth's magnetosphere producing the geomagnetic field disturbances, and after a certain period, they encounter the Jovian magnetosphere. There are also cases where the order of the encounter is opposite, i.e. the sector boundaries encounter first Jovian magnetosphere and encounter the Earth's magnetosphere after a certain period.  相似文献   

16.
The geomagnetic Kp-index data for the 1932–1969 period have been investigated by means of a modified power spectrum technique on the basis of overlapping 2-yr intervals. The observed 27-, and 13.5-day periodicities show an obvious solar cycle dependence through the whole period concerned. Also, periodicities in the range of 9?4 days have been observed through years of minimum and decreasing phases of solar activity. The periodicities observed are found to be related to the existence of variations in the interplanetary medium structure which modulates the geomagnetic activity.  相似文献   

17.
The low energy (1–20 keV) detector registering particles onboard the polar-orbiting low altitude (~ 850 km) DMSP-F2 and -F3 satellites also records high energy electrons penetrating the detector walls. Thus we can study the dynamics of this electron population at L = 3.5, during isolated periods of magnetospheric substorms identified by the indices of auroral electrojet (AE), geomagnetic (Kp) and ring current (Dst). Temporal changes in the electron flux during the substorms are observed to be an additional contribution riding over the top of the pre-storm (or geomagnetically quiet-time) electron population ; the duration of the interval of intensity variation is observed to be about the same as that of the enhancement of the AE index. This indicates the temporal response of the outer radiation belt to the substorm activity, since the observation was made in the “horns” of the outer radiation belt. The observed enhanced radiation at low altitude may associate with the instantaneous increase and/or dumping of the outer radiation belt energetic electrons during each isolated substorm activity.  相似文献   

18.
From an analysis of K-indices at three low latitude stations it is shown that the geomagnetic response to the passage of a sector boundary depends both on the nature of the boundary and on the phase of solar activity. Larger geomagnetic response is associated with (+ ?) boundary especially during conditions of low solar activity. A marked difference, especially for the (? +) boundary in the nature of the geomagnetic response between pre-1957 and post-1957 data is clearly demonstrated. Study of the geomagnetic response for separate UT intervals reveals that the effect due to different UT diurnal variations of activity on days of opposite polarity are manifested more clearly in association with post-boundary periods.  相似文献   

19.
We suggest geoeffective independent parameters that can be calculated on the basis of conventional measurements of the solar wind, which allows them to be used to forecast space weather. We present the results of our analysis of the ground variations in planetary geomagnetic activity (K p ) and geoeffective parameters calculated on the basis of solar wind and interplanetary magnetic field measurements in the Earth’s orbit for the period 1964–1996 by taking into account the change in the orientation of the geomagnetic moment during the Earth’s diurnal and annual motions.  相似文献   

20.
《Planetary and Space Science》2007,55(10):1218-1224
In this paper, we report the results derived from a statistical analysis of whistlers recorded at Varanasi during the period January 1990–December 1999. The monthly occurrence rate shows a maximum during January to March. In order to study the role of geomagnetic disturbance on the whistler occurrence rate, we have used the KP index and its variation. It is found that the occurrence probability monotonically increases with ∑KP (daily sum) values. It is found that, when ∑KP>20, the occurrence rate is greater than the average value, in good agreement with results reported by other workers. In addition, we also present the probability of the observation of whistlers during weak/intense geomagnetic storms and also during the main phase and recovery phase of geomagnetic storms.  相似文献   

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