Ionospheric Stations Research Articles

Ionospheric effetcs of an intense geomagnetic storm

An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of 15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms proposed to explain the F2 region behaviour during disturbed conditions is considered.

Modeling of ionospheric parameter variations in East Asia during the moderate geomagnetic disturbances

The results of modeling of ionospheric disturbances observed in the East Asian region during moderate storms are presented. The numerical model for ionosphere–plasmasphere coupling developed at the ISTP SB RAS is used to interpret the data of observations at ionospheric stations located in the longitudinal sector of 90–130°E at latitudes from auroral zone to equator. There is obtained a reasonable agreement between measurements and modeling results for winter and equinox. In the summer ionosphere, at the background of high ionization by the solar EUV radiation in the quiet geomagnetic period the meridional thermospheric wind strongly impacts the electron concentration in the middle and auroral ionosphere. The consistent calculations of the thermospheric wind permit to obtain the model results which are closer to summer observations. The actual information about the space-time variations of thermosphere and magnetosphere parameters should be taken into account during storms.

Solar activity variations of ionosonde measurements and modeling results

The time series of hourly electron density profiles N(h) obtained at several mid-latitude stations in Europe have been used to obtain N(h) profiles on a monthly basis and to extract both the expected bottomside parameters and a proxy of the ionospheric variability as functions of time and height. With these data we present advances on a “Local Model” technique for the parameters B0 and B1, its applicability to other ionospheric stations, to other bottomside ionospheric parameters, and to modeling the time/height variability of the profile. The Local Model (LM) is an empirical model based on the experimental results of the solar activity dependence of the daily and seasonal behavior of the above parameters. The LM improves the IRI-2001 prediction of the B0 and B1 by factor of two at mid-latitudes. Moreover, the LM can be used to simulate other ionospheric parameters and to build mean N(h) profiles and the deviations from them. The modeling of both the average N(h) profiles and their deviations is an useful tool for ionospheric model users who want to know both the expected patterns and their deviations.

Automatic scaling of critical frequency foF2 and MUF(3000)F2: A comparison between Autoscala and ARTIST 4.5 on Rome data

The performances of Autoscala and ARTIST 4.5 were comparatively evaluated using a large database of 6098 ionograms recorded from September 2005 to June 2006 by the digisonde DPS4 at the Rome ionospheric station. Results of comparisons between automatically and manually scaled data are shown for both programs highlighting the different behaviors. The Autoscala and ARTIST 4.5 values of foF2 and MUF(3000)F2 both agree with the hand‐scaled values for ∼95% of ionograms. For the other ∼5% of ionograms, which the manual scaler classed as unscalable, ARTIST 4.5 usually gave invalid results, whereas Autoscala usually gave no result. The data recorded by the ionosondes DPS4 (interpreted by ARTIST 4.5) and AIS‐INGV (interpreted by Autoscala) during three geomagnetic storms were also analyzed. Ionograms with typical errors both for Autoscala and ARTIST 4.5 are displayed.

Spatial correlation of foF2 and vTEC under quiet and disturbed ionospheric conditions: A case study

The spatial variations of the ionospheric F2-layer vertical incidence critical frequency (foF2) and GPS-derived vertical total electron content (vTEC) under geomagnetically quiet and disturbed days are examined using measurements from the latitudinal and longitudinal chains of ionospheric stations and GPS receivers over the European area. Plots produced for January 2005 are used to discuss temporal structures in terms of the prevailing solar-terrestrial conditions. Then the line trends procedure has been applied to simultaneous data collected from a limited number of measuring stations during quiet monthly median ionospheric conditions as well as during the storm period of 16–23 January 2005. The procedure is explained involving an application of the least squares method to define latitudinal and longitudinal dependence of foF2 and vTEC at different locations. Examples of coefficients of determination thereby produced show that the linear regression equations are very helpful in predicting longitudinal and latitudinal vTEC and foF2 variations during the quiet as well as disturbed ionospheric conditions.

Ionospheric specification and forecasting based on observations from European ionosondes participating in DIAS project

There are two main objectives of the DIAS (European Digital Upper Atmosphere Server) project. First, it establishes a pan-European repository of raw and derived digital data describing the state of ionospheric part of the upper atmosphere, which is capable of ingesting real-time information and maintaining historical data collections provided by most operating ionospheric stations in Europe. Second, the DIAS system produces and distributes, based on the raw data collection, several operational products required by various user groups for ionospheric nowcasting, prediction and forecasting purposes. The project completed on May 2006 and the DIAS server operates since then continuously. The basic products that are delivered are real-time and historical ionograms from all DIAS-affiliated ionospheric stations, frequency plots and maps of the ionosphere over Europe based on the foF2, M(3000)F2, MUF and electron density parameters, as well as long term prediction and short term forecasting up to 24 hour ahead.

Long-term trends in the ratio of the daytime and nighttime values of foF2

The consideration of the relation between the daytime and nighttime values of the critical frequency F2, foF2 of the ionospheric F2 layer, started in the previous publication of the authors, is continued. The main regularities in variations in the correlation coefficient R(foF2) characterizing this relation are confirmed using larger statistical material (more ionospheric stations and longer observational series). Long-term trends in the R(foF2) value are found: at all stations the negative value of R(foF2) increases with time after 1980.

Ionospheric disturbances in the East-Asian region during geomagnetic storm in November, 2004

Results of the study into variations of the ionospheric parameters during the intense geomagnetic storm on November 7–11, 2004 in the 20–80°N, 80–160°E sectors are presented. These used data from ionospheric stations and total electron content (TEC) measurements obtained from the network of the GPS ground-based receivers and the receiver onboard the CHAMP satellite. Periods of total absorption and blanketing sporadic E layers were observed at high latitudes, whereas long-lasting negative disturbances which are typical of geomagnetic storms of high intensity were detected at midlatitudes. In the afternoon hours of local time on November 8, 2004, a large-scale ionospheric disturbance was detected on the basis of foF2 and TEC measurements. The disturbance was propagating southwestward at a mean velocity of about 200 m/s. Comparison of the relative amplitude of this large-scale disturbance according to the total electron content (∼70%) and foF2 (∼80%) measurements made it possible to assume that the disturbance was extended in height. A similar disturbance of smaller intensity was observed on November 10.

Neural network-based prediction techniques for global modeling of M(3000)F2 ionospheric parameter

In recent times neural networks (NNs) have been employed to solve many problems in ionospheric predictions. This paper illustrates a new application of NNs in developing a global model of the ionospheric propagation factor M(3000)F2. NNs were trained with daily hourly values of M(3000)F2 from various ionospheric stations spanning the period 1964–1986 with the following temporal and spatial input parameters: Universal Time, geographic latitude, magnetic inclination, magnetic declination, solar zenith angle, day of the year, A16 index (a 2-day running mean of the 3-h planetary magnetic ap index), R2 index (a 2-month running mean of sunspot number), and the angle of meridian relative to the subsolar point. The performance of the NNs was verified by comparing the predicted values of M(3000)F2 with observed values from a few selected ionospheric stations and the IRI (International Reference Ionosphere) model (CCIR M(3000)F2 model) predicted values. The results obtained compared favourably with the IRI model. Based on the error differences, the result obtained justifies the potential of the NN technique for the predictions of M(3000)F2 values on a global scale.

What do we know of the long-term change of the Earth’s ionosphere?

In this paper, long-term change of the Earth’s ionosphere is discussed. It can most effectively be studied by means of ionospheric parameters recorded on ionograms obtained by vertical incidence sounding of the ionosphere. These measurements supply the longest ionospheric data series recorded by the greatest number of ionospheric stations. It has been found that in the F2 region long-term changes are due to geomagnetic activity and dynamical processes, from the 1970s effect of greenhouse gases is dominant [Mikhailov, A.V. Ionospheric long-term trends: can the geomagnetic control and the greenhouse hypothesis be reconciled? Ann. Geophys. 24, 2533–2541, 2006]. Spatial variation of hmF2 trends may be related to up- and downwelling at the neighbourhood of the boundary continent-sea. In the E and F1 regions, the sign of the foE, foF1 and h′E corrected trends, foF1 and foE increasing, h′E decreasing hint at greenhouse effect, which results in enhanced electron density and reduced height due to shrinking of the atmosphere as a consequence of cooling. Long-term changes in the lower ionosphere studied by LF phase height and ionospheric absorption measurements can be attributed to the effect of greenhouse gases [Bremer, J., Berger, U. Mesospheric temperature trends derived from ground-based LF phase-height observations at mid-latitudes: comparison with model simulations. J. Atmos. Solar-Terr. Phys. 64, 805–816, 2002].

Investigation on Properties of Ionospheric Es Layer in Hainan Region

利用中国科学院空间科学与应用研究中心海南电离层观测站DPS-4电离层测高仪2002年3月至2005年2月的观测数据,对太阳活动下降期间海南地区上空发生的偶发E层(Es)的逐年变化和季节变化进行了统计分析.主要结果表明,在这3年中海南地区Es事件出现次数逐年增加;Esr,Esq出现最频繁,其次是Esr,而Esc和Esf出现次数较少,出现次数最少的是Esh;Es事件在夏季出现最为频繁,秋季和冬季次之,春季最为稀少;各季节不同类型Es事件的出现率也不同,其中Esl和Esq一般在各季节占主导地位,Esr其次,Esc,Esf和Esh出现次数较少,尤其是Esf在秋季几乎没有出现.这些结果对于进一步研究Es产生的物理机制提供了探测基础,同时对于电离层空间天气预报模型的建立也具有重要的意义.

Monitoring and Forecasting the Ionosphere Over Europe: The DIAS Project

Knowledge of the state of the upper atmosphere, and in particular its ionospheric part, is very important in several applications affected by space weather, especially the communications and navigation systems that rely on radio transmission. To better classify the ionosphere and forecast its disturbances over Europe, a data collection endeavour called the European Digital Upper Atmosphere Server (DIAS) was initiated in 2004 by a consortium formed around several European ionospheric stations that transmit in real-time ionospheric parameters automatically scaled. The DIAS project is a collaborative venture of eight institutions funded by the European Commission eContent Programme. The project seeks to improve access to digital information collected by public European institutes and to expand its use. The main objective of the DIAS project is to develop a pan-European digital data collection describing the state of the upper atmosphere, based on real-time information and historical data collections provided by most of the operating ionospheric stations in Europe. Various groups of users require data specifying upper atmospheric conditions over Europe for nowcasting and forecasting purposes. The DIAS system is designed to distribute such information. The successful operation of DIAS is based on the effective use of observational data in operational applications through the development of new added-value ionospheric products and services that best fit the needs of the market. DIAS is a unique European system, and its continuous operation will efficiently support radio propagation services with the most reliable information. DIAS began providing services to users in August 2006. The Need for Accurate Ionospheric Products Radio frequency communications and satellite positioning and navigation systems are applications most affected by ionospheric disturbances. Such disturbances can cause drastic and large-scale changes in the usable ranges of high frequency (HF) or below HF bands affecting standard ground-to-ground and submarine communication systems. The characteristics of an ionospheric propagation channel, whether it is HF or transionospheric frequencies, are highly variable on timescales ranging from a few seconds to the 11-year solar cycle. Even during its quietest periods, the Sun produces electromagnetic radiation and solar wind, both of which can affect a variety of geomagnetic and ionospheric phenomena, which in turn affect radio waves propagating through the ionosphere. Hence day-to-day and hour-to-hour changes in propagation channel characteristics can occur.

Medium-term ionospheric precursors to strong earthquakes

[1] An attempt is made to determine the most typical changes in parameters of the ionospheric F2 and Es layers during the 7 days prior to an earthquake. Earthquakes with magnitudes M > 6 in the Pacific region in the vicinity of Japan are considered. Hourly measurement data at Kokubunji ionospheric station for 40 earthquakes with epicenter distances R < 1000 km are used. Seismoionospheric disturbances are detected on the basis of analysis of the derivations of current values of the ionospheric layer parameters from the running medians. A method of identification of precursors on the basis of some set of morphological signs is proposed. It is shown that different times of appearance of precursors are caused by their dependence on the magnitude of the coming earthquakes and the distance from the observational point to the epicenter. For M = 6 − 7 and R < 600 km this time is from 1 to 6 days. Empirical dependencies of the time of appearance of ionospheric precursors and the value of seismogenic disturbances in ionospheric layer parameters are obtained and may be used for prediction purposes.

Large-scale disturbances of auroral origin during strong magnetic storms of October 29–31, 2003, and November 7–11, 2004, according to the data of the GPS network and ionosondes

The intensity of large-scale traveling ionospheric disturbances (LS TIDs), registered according to measurements of the total electron content (TEC) during the magnetic storms of October 29–31, 2003, and November 7–11, 2004, has been compared with that of local electron density disturbances. The data of TEC measurements at ground-based GPS receivers located near the ionospheric stations and the corresponding values of the critical frequency of the ionospheric F region (foF2) were used for this purpose. The variations in TEC and foF2 were similar for all events mentioned above. The previous assumption that the region of thickness 150–200 km in the vicinity of the ionospheric F region mainly contributes to TEC modulation was confirmed for the cases when the electron density disturbance at an F region maximum was not more than 50%. However, this region probably becomes more extensive in vertical when the electron density disturbance in the vicinity of the ionospheric F region is about 85%.

Ionospheric disturbances in the east-Asian region during the geomagnetic period in November 2004

Results of the studies of ionospheric parameter variations during the intense geomagnetic storm on November 7–11, 2004, in the 20°–80° N, 60°–180° E sector are presented. The data of ionospheric stations and the results of total electron content (TEC) measurements at the network of the GPS ground-based receivers and of the GPS receiver onboard the CHAMP satellite were used. Periods of total absorption and blanketing sporadic E layers were observed at high latitudes, whereas durable negative disturbances typical of geomagnetic storms of high intensity were detected at midlatitudes. In the afternoon hours of local time on November 8, 2004, a large-scale ionospheric disturbance of a frontal type was detected on the basis of foF2 and TEC measurements. The disturbance propagated southwestward at a mean velocity of about 200 m/s. The comparison of the relative amplitude of this large-scale disturbance according to the total electron content (∼70%) and foF2 (∼80%) measurements made it possible to assume a large vertical scale of the disturbance.

Applying artificial neural network to derive long‐term foF2 trends in the Asia/Pacific sector from ionosonde observations

An artificial neural network (ANN) method is first used for deriving long‐term trends of the F2‐layer critical frequency (foF2) at 19 ionospheric stations in the Asia/Pacific sector. It is found that the ANN method can eliminate the geomagnetic activity effect on foF2 more effectively than usual regression methods. Of the selected 19 stations, there are significant long‐term trends corresponding to a confidence level ≥90% at 14 stations and 12 of these stations present negative trends. An average trend of −0.05% per year in the selected area can be obtained if the 12 stations with significant negative long‐term trends be considered. No pronounced diurnal and latitudinal effects in trends and no uniform pattern of seasonal variation in most stations are detected. The long‐term trends for low latitude and equatorial stations differ from other stations suggest that some special dynamical processes may take effects in the equatorial anomaly region. Many factors which can influence ionosphere, such as the greenhouse effect, solar and geomagnetic activity, and neutral background gas, might contribute to the trend.

Near-real time foF2 predictions using neural networks

This paper describes the use of the neural network (NN) technique for the development of a near-real time global foF2 (NRTNN) empirical model. The data used are hourly daily values of foF2 from 26 worldwide ionospheric stations (based on availability) during the period 1976–1986 for training the NN and between 1977 and 1989 for verifying the prediction accuracy. The training data set includes all periods of quiet and disturbed geomagnetic conditions. Two categories of input parameters were used as inputs to the NN. The first category consists of geophysical parameters that are temporally or spatially related to the training stations. The second category, which is related to the foF2 itself, consists of three recent past observations of foF2 (i.e. real-time foF2 (F 0), 2 h (F −2) and 1 h (F −1) prior to F 0) from four control stations (i.e. Boulder (40.0°N, 254.7°E), Grahamstown (33.3°S, 26.5°E), Dourbes (50.1°N, 4.6°E) and Port Stanley (51.7°S, 302.2°E). The performance of the NRTNN was verified under both geomagnetically quiet and disturbed conditions with observed data from a few verification stations. A comparison of the root mean square error (RMSE) differences between measured values and the NRTNN predictions with our earlier standard foF2 NN empirical model is also illustrated. The results reveal that NRTNN will predict foF2 in near-real time with about 1 MHz RMSE difference anywhere on the globe, provided real time data is available at the four control stations. From the results it is also evident that in addition to the geophysical information from any geographical location, recent past observations of foF2 from these control stations could be used as inputs to a NN for near-real time foF2 predictions. Results also reveal that there is a temporal correlation between measured foF2 values at different locations.

Planetary statistics of the critical frequency of the ionospheric F 2 region during catastrophic earthquakes

The statistics of the relative variations (δfoF2) in the critical frequency of the ionospheric F2 region during catastrophic earthquakes with magnitude M ≥ 6 at 70 vertical sounding (VS) automatic ionospheric stations (AISs) of the global network is considered. Five-day periods including 70 such situations have been selected for 1981 and 1983–1985. Five sets of 24 foF2 measurements from 3 days before to a day after the earthquake instant are formed for each AIS. The number of AISs, for which the fourth statistical invariant is above the significance level (E ≥ 1), has been analyzed. It has been indicated that the histogram deformation at the set of AISs is substantial a day before earthquakes.

Progress in studies of the trends in the ionosphere F region

A detailed analysis of the hmF2 data obtained at the network of ionospheric stations is performed to reveal long-term trends independent of the geomagnetic activity variations during the recent decades (nongeomagnetic trends). The method developed and tested by the author earlier is applied. Unlike the results on foF2 published by the author earlier, the picture of hmF2 trends is not homogeneous. For 17 ionospheric stations positive significant trends are obtained. Six stations give negative trends in hmF2. For three stations no trends were derived. The behavior of the positive trends is considered. It is shown that these trends depend neither on geomagnetic latitude nor on local time, both facts confirming their independence of geomagnetic activity. The averaging of the positive trends over all 17 stations gives a relative trend of 0.0011 per year with the standard deviation of 0.0005. At the average height of the F2 layer of about 300 km this means an increase in hmF2 by 0.33 km per year. Possible interpretations of the obtained trends in foF2 and hmF2 from the point of view of anthropogenic changes in the thermosphere are considered.

Response of ionosphere to the great geomagnetic storm of September 1998: Observation and modeling

We present the results derived from investigating of the ionospheric effects of the great geomagnetic storm on September 24–27, 1998 based on analyzing the data obtained at ionospheric stations located in the region of Siberia and the Far East. For the sake of comparison we have also introduced the data from some European stations. In addition to the vertical-incidence sounding data the measurements from the Irkutsk incoherent scatter radar are used. It is obtained that the intense negative disturbances during the main phase of the storm are observed at all stations under investigation. A comparison of the foF2 variations for the two meridians shows that even with a relatively small difference of longitudes (45°), the recovery phase has substantial differences of ionospheric disturbances. On September 26, the positive disturbances are observed and persist the following day at all stations except Salekhard and the Norilsk chain. At the Norilsk chain and at Salekhard the negative disturbances recurred after positive disturbances. The sign reversal of disturbance during the recovery phase extends over in the further displacement from the west to the east. An interpretation of the measurements includes their comparing with the results of calculations in terms of a numerical model of the ionosphere and plasmasphere. The modeling results are in the satisfied agreement with the measurements. According to the model calculations the sign of the ionospheric disturbance is changed from negative to positive as the result of combined effects of corpuscular and photo ionization. The sign of ionospheric disturbance is determined by a local time at which the magnetic storm has begun.