Ionospheric Stations Research Articles

Ionospheric radio wave propagation finite element method modeling

In this work, a transionospheric propagation model is presented. The application analyzed here uses data from the Rome ionospheric station together with data from the theoretical IRI-95 and MSIS-E-90 models, in order to simulate the ionosphere. Using formulas from ionospheric propagation theory, these data form the wave equation, which is solved by means of the finite element method. Post-processing of the solution leads to the determination of the main wave propagation parameters.

Ionosphere dynamics over Europe and western Asia during magnetospheric substorms 1998–99

Abstract. The temporal and spatial behaviour of the ionospheric parameters foF2 and h'F during isolated substorms are examined using data from ionospheric stations distributed across Europe and western Asia. The main purpose is finding the forerunners of the substorm disturbances and a possible prediction of these disturbances. During the period from March 1998 to March 1999, 41 isolated substorms with intensities I = 60 - 400 nT were identified and studied. The study separated occasions when the local magnetometers were affected by the eastward electrojet (positive substorms) from those influenced by the westward electrojet (negative substorms). The deviations of the ionospheric parameters from their monthly medians (DfoF2 and Dh'F) have been used to determine the variations through the substorm. Substorm effects occurred simultaneously (< 1 h) across the entire observatory network. For negative substorms, DfoF2-values increase > 6 h before substorm onset, To, reaching a maximum 2–3 h before To. A second maximum occurs 1–2 h after the end of the substorm. The Dh'F values 3–4 h before To have a small minimum but then increase to a maximum at To. There is a second maximum at the end of the expansion phase before dh'F drops to a minimum 2–3 h after ending the expansion phase. For positive substorms, the timing of the first maximum of the dfoF2 and dh'F values depends on the substorm length – if it is longer, the position is closer to To. The effects on the ionosphere are significant: DfoF2 and Dh'F reach 2–3 MHz (dfoF2 = 50–70% from median value) and 50–70 km (D h'F = 20–30% from median value), respectively. Regular patterns of occurrence ahead of the first substorm signature on the magnetometer offer an excellent possibility to improve short-term forecasting of radio wave propagation conditions.Key words. Ionosphere (ionospheric disturbances) – Magnetospheric physics (storms and substorms) Radio science (ionospheric physics)

Long-term trends of <i>fo</i>F2 independent of geomagnetic activity

Abstract. A detailed analysis of the foF2 data at a series of ionospheric stations is performed to reveal long-term trends independent of the long-term changes in geomagnetic activity during the recent decades (nongeomagnetic trends). The method developed by the author and published earlier is used. It is found that the results for 21 out of 23 stations considered agree well and give a relative nongeomagnetic trend of -0.0012 per year (or an absolute nongeomagnetic trend of about -0.012 MHz per year) for the period between 1958 and the mid-nineties. The trends derived show no dependence on geomagnetic latitude or local time, a fact confirming their independence of geomagnetic activity. The consideration of the earlier period (1948–1985) for a few stations for which the corresponding data are available provides significantly lower foF2 trends, the difference between the later and earlier periods being a factor of 1.6. This is a strong argument in favor of an anthropogenic nature of the trends derived.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric disturbances; mid-latitude ionosphere)

Planetary electromagnetic waves in the ionospheric E-layer

The linear theory for the large-scale (λ>10 3 km) electromagnetic (EM) waves in the middle-latitude ionospheric E-layer is developed. The general dispersion relation for these waves is derived. It is shown that the latitudinal inhomogeneity of the geomagnetic field and the angular velocity of the Earth's rotation can lead to the appearance of wave modes in the form of slow and fast EM planetary waves. The slow mode is produced by the dynamo electric field and it represents a generalization of the ordinary Rossby type waves in a rotating atmosphere when the Hall effect in the E-layer is included. The fast mode is a new mode, which is associated with the oscillations of the ionospheric electrons frozen in the geomagnetic field. It represents the variation of the vortical electric field and it arises solely due to the latitudinal gradient of the external magnetic field. The basic characteristics of the wave modes, such as the wavelength, the frequency and the Rayleigh friction, are estimated. Other types of waves, termed slow magnetohydrodynamic (MHD) waves, which are insensitive to the spatial inhomogeneity of the Coriolis and Ampére forces are also reviewed. It is shown that they appear as an admixture of slow Alfvén (SA) and whistler type waves. Such waves can generate variations in the magnetic field from a few tenth to a few hundreds nT. It is stressed that the basic features of the considered waves agree with the general properties of the magnetic perturbations observed at the world network of magnetic and ionospheric stations.

Formation of polarization jet during injection of ions into the inner magnetosphere

Long-lasting ground based measurements of a polarization jet (PJ) by the latitudinal chain of ionospheric stations in Yakutia (3 < L < 5; MLT = UT + 9 h) and by 5 subauroral Russian stations were analyzed. A number of cases were found when PJ was recorded simultaneously with energetic ion observations by AMPTE/CCE and INTERBALL 2. The data comparison shows that at least in the considered cases of strong magnetic substorms, PJ was accompanied by strong injection of ions with the energy of ∼ 20 – 50 keV and intensity of ∼ 10 6 cm −2 c −1 ster −1 keV −1. Close to the injection region in the near midnight sector no ion dispersion was observed, but in the evening sector nose events were detected. In accordance with a mechanism suggested by Southwood and Wolf (1978) PJ was observed near the equatorial boundary of energetic ion penetration into the magnetosphere. Measurements by ionosondes at different longitudes show that the westward velocity of the front of PJ development is close to the gradient drift velocity of 20 keV ions (forming nose events). Thus, the physical mechanism of PJ formation due to energetic ion injection during a strong substorm burst is experimentally confirmed. Satellite measurements show that in the near midnight sector energetic ions reach the shell L = 3.0 in 20 – 30 minutes after a substorm commencement with AE > 500 nT.

Diurnal Variation of Gravity Wave Activity at Midlatitudes in the Ionospheric F Region

We investigate the short-term fluctuations in the period range from 15 to 180 minutes in the electron density variations of the F region ionosphere. Electron density profiles obtained at the ionospheric stations of Pruhonice (49.9° N, 14.5° E) and Ebro (40.8° N, 0.5° E) at five minute time sampling have been used for this analysis. The diurnal changes of the activity of the acoustic gravity wave fluctuations (AGW) show a clear enhancement during and several hours after sunrise. The periods of such AGW's are about 60 to 75 minutes and these waves propagates vertically through the ionosphere from a source located at an altitude of 180-220 km. The most likely source for these events seems to be passage of the Solar terminator.

Morphologies of Global Ionospheric Disturbances During Geomagnetic Disturbance Events of Different Type

AbstractUsing the observational data from the global ionospheric stations, we analyzed the morphologies of global ionospheric F2‐layer (f0F2 and hmF2) disturbance during five different type geomagnetic disturbance events. The main results show that: for magnetic storms with delayed main phase, types S(C) and S(E), the middle–high latitude ionosphere demonstrates the evident positive phase disturbance first and the following negative phase disturbance is evidently delayed; the negative phase disturbance covers a wide region, even extends into low–latitudes, lasts a longer time, and recovers very slowly, in which the disturbance of type S(C) is more evident. For magnetic storm with no–delayed main phase, types S(A), S(B) and S(D), the ionospheric positive phase disturbance at high–latitudes lasts a shorter time, even does not appear at all, and the following middle–high latitude ionospheric negative phase disturbance starts, develops, and recovers rapidly. The intensity of magnetic storm main phase has certain effect on the intensity, development and periods of ionospheric negative phase disturbance. The ionospheric disturbances at high–latitudes have the evident local time effect in the recovery phase of storm with no delayed main phase. The local time effect is enhanced with the reduction of latitude, and evidently affects the ionosphere disturbances at middle–low latitudes. Generally, There are great differences for the ionospheric disturbances at different latitude regions, which reflect the interactions of the different physical processes.

Mid-latitude effects of the May 15, 1997 magnetic storm

We investigate the May 15, 1997 magnetic storm effects on the mid- and low-latitude ionosphere. The study is based on using the data from three chains of ionospheric stations located approximately along the meridians 20°, 140° and 280°E in the geomagnetic latitude range 13–65°N. Variations in f 0F2 are considered. Estimates of the zonal electric fields are made. Results of our analysis show that the main ionospheric effects of the storm under consideration are: (1) long-lasting intense negative disturbances during the storm main and recovery phases at subauroral and mid-latitudes; (2) positive disturbances at stations of the European and American chains observed prior to the storm, regardless of the local time; (3) a positive peak of Δ f 0F2 at stations of the Asian chain during the storm main phase in the evening hours; (4) a similarity of the form of the Δ f 0F2-variations at different latitudes and (5) the largest effect on the F region is observed at the Asian chain. The resulting differences of the Δ f 0F2-variations can be driven both by the local time of the sudden storm commencement and by magnetic dip. It is not mere chance that the largest differences are observed along the meridian 140°E where the difference between the geographic and magnetic poles is the largest.

Electron temperature variations at the F2 layer peak height during the space weather month of September 1999

Data from 23 ionospheric stations are used for September 1999 to produce the electron temperature, Te, at the F2 layer peak height, hmF2, on the base of empirical relation between Te and the electron density, Ne, at a given height for a given index of solar radio flux (Brace and Theis, 1978, 1984). Daily and monthly Te minimum, mean, and maximum are then evaluated for each station. Near the solar maximum monthly Te(min) is about 1470°K while the monthly Te(max), occurring during sunrise, varies with location in a wide range from 1900 to 3900°K. A new weighted scheme is suggested for forecast of magnetic activity 3 h in advance by accumulation of selected magnetic indices ranked by decreasing order for 12 hrs preceding given time of observation. By using the daily Te values, cold and hot ionospheric days during the month have been defined: the magnetic activity does not influence Te at low and equatorial latitudes while at mid-latitudes a high degree of correlation is found between the F2 peak plasma heating and weighted accumulation of the magnetic indices. The most important effect of Te heating at sunrise is observed at high latitudes during the recovery phase of magnetic storm and sub-storm.

Neural-network-based prediction techniques for single station modeling and regional mapping of the &amp;lt;I&amp;gt;fo&amp;lt;/I&amp;gt;F2 and M(3000)F2 ionospheric characteristics

Abstract. In this work, Neural-Network-based single-station hourly daily foF2 and M(3000)F2 modelling of 15 European ionospheric stations is investigated. The data used are neural networks and hourly daily values from the period 1964- 1988 for training the neural networks and from the period 1989-1994 for checking the prediction accuracy. Two types of models are presented for the F2-layer critical frequency prediction and two for the propagation factor M(3000)F2. The first foF2 model employs the E-layer local noon calculated daily critical frequency (foE12) and the local noon F2- layer critical frequency of the previous day. The second foF2 model, which introduces a new regional mapping technique, employs the Juliusruh neural network model and uses the E-layer local noon calculated daily critical frequency (foE12), and the previous day F2-layer critical frequency measured at Juliusruh at noon. The first M(3000)F2 model employs the E-layer local noon calculated daily critical frequency (foE12), its ± 3 h deviations and the local noon cosine of the solar zenith angle (cos c12). The second model, which introduces a new M(3000)F2 mapping technique, employs Juliusruh neural network model and uses the E-layer local noon calculated daily critical frequency (foE12), and the previous day F2-layer critical frequency measured at Juliusruh at noon.

Solar Cycle variations of ƒ&amp;lt;i&amp;gt;o&amp;lt;/i&amp;gt;F2 from IGY to 1990

Abstract. Noontime monthly median values of F2-layer critical frequency foF2 (m) for some ionospheric stations representing low- and mid-latitudes are examined for their dependence on solar activity for the years 1957 (IGY) to 1990. This is the period for which ionospheric data in digital form is available in two CD-ROMs at the World Data Center, Boulder. It is observed that at mid-latitudes, foF2 (m) shows nearly a linear relationship with R12 (the 12-month running average of the Zurich sunspot number), though this relation is nonlinear for low-latitudes. These results indicate some departures from the existing information often used in theoretical and applied areas of space research.Key words. Ionosphere (equatorial ionosphere; mid-latitude ionosphere; modelling and forecasting)

Low latitude ionospheric effects near longitude 120°E during the great geomagnetic storm of july 2000

A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about −300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120°E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O2 or N2 to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in f0F2 during these days, and the diurnal variation of f0F2 was less clear than before.

Changes in the F1 region electron density during geomagnetic storms at low solar activity

This paper attempts to demonstrate the changes in the F1 layer ionization during geomagnetic storm. To analyze the behavior of F1 region, we have selected eight rather strong geomagnetic storms that occurred in different seasons in 1994–1997. Their course was similar and there were at least three quiet days before each event. The electron density profiles for these events, derived from all the available ionograms of the Pruhonice station (50°N, 14.6°E), were analyzed in order to investigate electron density variability at heights of 160–190 km. Spring/autumn asymmetry of the effects in F1 region is found. We observed no significant effect of an ionospheric storm in electron density in the F1 region during spring geomagnetic storms, while there is a substantial effect in autumn at 180 and 190 km heights. We have compared our results with those obtained from ionograms of some other European ionospheric stations. In general, the F1 region appears to be much more stable than the F2 layer during ionospheric storms. Substantial intra-hour variability was found in NmF2 during geomagnetic storms in daytime, while it was very weak on the storm maximum day in F1 layer.

The solar wind magnetic cloud of October 18–20, 1995: effect on ionosphere of the Russian Asian region

Based on data from a chain of ionospheric stations we investigate the response of ionospheric parameters to the magnetic storm of October, 18-23, 1995. During this storm an abrupt decrease in critical frequencies to 35-45% in the F-region in the daytime hours and intense sporadic E-layers of the auroral type at night were recorded by the entire chain of stations. The analysis of experimental data suggests that the trough boundaries are displaced as far as 41 ° magnetic latitude. © 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

Variability and magnetic storm effects in equatorial electron density profile

Abstract The variability of electron density at fixed heights in the bottom-side ionosphere is investigated at an equatorial ionospheric station in the African continent. Data used are for the representative months of each of the seasons of the years at two solar activity periods and for all 24 hours of the day. The index used is the standard deviation from the average profile of ten non-storm days of the months, obtained with the ARP technique. The morphology of the variability is described and the departure of magnetic storm day's profiles from the average profile for non-storm conditions is investigated for specific storms.

Evaluation of the ionospheric noise and variability within the hour by 5 minutes ionospheric soundings

The actual future needs in radio propagation predictions are short-term ionospheric forecasting and now-casting. These are often given at standard hours, but in order to improve the reliability and the accuracy of forecasting, the variability within-the-hour and the so-called “intrinsic noise” of the ionosphere cannot be neglected anymore. Values of foF2 and MUF(3000)F2, obtained in 5-minutes vertical sounding campaigns, performed at Rome and Juliusruh ionospheric stations during different seasons and different levels of solar activity, are analysed and the results are discussed.

Long term trend in the high latitude ionosphere

The long-term variability of the critical frequency of the F2 ionospheric layer, f0F2, has been investigated as a possible indicator of the increasing greenhouse effect. The preliminary results obtained by analysing 34 years of data from high latitude ionospheric stations in the Southern Hemisphere have shown a decreasing of the plasma frequency according to what predicted by theoretical model calculations.

Ground-based observations of the March 26, 1976 magnetospheric storm

Abstract An analysis has been made from a geophysical complex operating during magnetospheric storm, with the purpose to study ground level manifestations of such disturbances and of the recovery process of prestorm conditions. The maps of electrojets were constructed with data from the magnetometer chains located on the Yakutsk (130° E) and Norilsk (90° E) meridians. The analysis of variations of ionospheric parameters were conducted from three ionospheric stations of Yakutsk (Tixie, Zhigansk, and Yakutsk), and two of Norilsk (Dixon and Norilsk) meridians and of Arkhangelsk (40° E). The conclusions are made that strong disturbances in the magnetic field are governed by universal time and observed over an extensive range of longitudes, week disturbances are operated by local time and latitude of observation.

Formation of a Polarization Jet during the Expansion Phase of a Substorm: Results of Ground-Based Measurements

The ground-based polarization jet measurements at the Yakutsk ionosphere station (L= 3.0) for the years 1989–1991 (110 events) are compared with variations of the AE-index and with parameters of the local magnetic activity. It is shown that polarization jet development in the near midnight sector can occur during a period of no longer than 10 min on the expansion phase of a substorm. The formation of the polarization jet is accompanied by a specific magnetic field variation corresponding in shape to a fast passage of the Harang Discontinuity above the station. Statistical data are given on ground level observations of the polarization jet, which are close to those measured from satellites. The mean delay (averaged over the full data bank) between the onset of a substorm with AE≥ 500 nT and the moment of the polarization jet appearance at L= 3.0 is equal to 0.5 h near midnight and to 1.0 – 1.5 h in the evening sector. Estimations show that the duration of the polarization jet formation when energetic ions are injected into the Harang Discontinuity region above the ground station can last for about 10 min, and during this time the Harang Discontinuity can be shifted to the west. This is in qualitative agreement with the described observations.

Longitudinal variation of critical frequencies in polar F-region

Based on data from a network of ionospheric stations located in the range of geographic longitudes 19°–285° and invariant latitudes 53°–70°N we have investigated diurnal behaviour variations in F2-layer critical frequencies for different seasons and different levels of solar activity. The study revealed that the longitudinal effect in diurnal f o F2 variations is most conspicuous in the summertime at the invariant latitude about 55–57°N and manifests itself in the shift of the f o F2 maximum into the evening and night-time hours on the Yakutsk (129.6°) and Ottawa (284°) meridians in the region of westward declination. It is likely that such a behaviour of f o F2 is conditioned by a change in the dynamic regime of the high-latitude ionosphere associated with the magnetic anomaly.