Ivan Kutiev

A new method for reconstruction of the vertical electron density distribution in the upper ionosphere and plasmasphere

Ground-based ionosphere sounding measurements alone are incapable of reliably modeling the topside electron density distribution above the F layer peak density height. Such information can be derived from Global Positioning System (GPS)-based total electron content (TEC) measurements. A novel technique is presented for retrieving the electron density height profile from three types of measurements: ionosonde (foF2, foE, M3000F2, hmf2), TEC (GPS-based), and O+-H+ ion transition level. The method employs new formulae based on Chapman, sech-squared, and exponential ionosphere profilers to construct a system of equations, the solution of which system provides the unknown ion scale heights, sufficient to construct a unique electron density profile at the site of measurements. All formulae are based on the assumption of diffusive equilibrium with constant scale height for each ion species. The presented technique is most suitable for middle- and high-geomagnetic latitudes and possible applications include: development, evaluation, and improvement of theoretical and empirical ionospheric models, development of similar reconstruction methods utilizing low-earth-orbiting satellite measurements of TEC, operational reconstruction of the electron density on a real-time basis, etc.

Autocorrelation method for temporal interpolation and short-term prediction of ionospheric data

An autocorrelation method is developed for temporal interpolation and short-term prediction of ionospheric characteristics. The ionospheric data are considered as a realization of a periodic process with randomly dispersed measured values superimposed on it. The autocorrelation function or its nonnalized autocorrelation coefficients are determined from the measured data over a period of 20–30 days, and on that basis an autocorrelation model is obtained. This model is then used to interpolate the missing values in the monthly tables of ionospheric characteristics, here called “gaps.” The interpolation at a given hour is performed by calculating weighting coefficients for the neighboring measured values. The procedure selects those measurement values around the gap which have the highest autocorrelation coefficients. The model can be used to extrapolate (predict) the data, treating the prediction period (usually 24 hours) as a gap placed at the end of the available data. The method also calculates the so-called prediction error, which is found to be close to the standard deviation of the measured data. The interpolation and prediction error are estimated to be less than 12% in the case of ƒoF2.

Modeling of midlatitude F region response to geomagnetic activity

An empirical model is developed to describe the variations of midlatitude F region ionization along all longitudes within the dip latitude band (30°-55°N), induced by geomagnetic activity, by using the relative deviations (Φ) of the Fregion critical frequency f 0 F 2 from its monthly median. The geomagnetic activity is represented by the Kp index. The main statistical relationship between Φ and Kp is obtained by using 11 years of data from 26 midlatitude ionosondes. The statistical analysis reveals that the average dependence of Φ on Kp is quadratic, the average response of the ionosphere to geomagnetic forcing is delayed with a time constant T of about 18 hours, and the instantaneous distribution of Φ along local times can be assumed sinusoidal. A continuity equation is written for Φ with the production term being a function of Kp modulated by a sinusoidal function of local time and the loss term proportional to Φ with a loss coefficient β=1/T. A new, modified function of geomagnetic activity (K f ) is introduced, being proportional to Φ averaged over all longitudes. The model Φ is defined by two standing sinusoidal waves with periods of 24 and 12 hours, rotating synchronously with the Sun, modulated by the modified function K f . The wave amplitudes and phases, as well as their average offset, are obtained by fitting to the data. A new error estimate called prediction efficiency (Peff) is used, which assigns equal weights to the model errors at all deviations of data from medians. The prediction efficiency estimate gives a gain of accuracy of 29%.

Analytical expression of O+H+ ion transition surface for use in IRI

A global surface of O+H+ transition level is constructed, based on published data from OGO-6, Intercosmos-2, Alouette-1, ISS-b, and TAIYO satellites. This surface covers ±60° dipole latitude, all longitudes, two levels of solar activity, summer and winter solstices, and 00 and 12 hours local time. The surface is used as input data to a mathematical model which calculates transition levels in 5-dimensional space: sunspot number (R), month (M), local time (LT), dipole latitude (DL), and longitude (LONG). This model is based on a generalized multivariable polynomial, using a system of linearly independent functions. Model transition levels are compared with averaged data from AE-E and AE-C, as well as rocket measurements from Vertical-6 and Vertical-10. The obtained analytical expression can be directly used in IRI.

An instrument for DC electric field and AC electric and magnetic field measurements aboard ‘Intercosmos-Bulgaria-1300’ satellite

Abstract The instrument IESP-IPMP represents the complex unit measuring the vector of the DC electric field, the vectors of the electric and magnetic field in the frequency range of 0.2 – 6.5 Hz (wave form), autocorrelation functions of waves with frequencies of 0.1 – 5 kHz, and wave amplitudes in 8 bandpass channels. Some results are shown and compared in the various frequency ranges.

Empirical modelling of ionospheric storms at midlatitudes

Abstract The reaction of the F-layer to geomagnetic storms is studied between 35° and 55° (dipole latitude) with as indicator the relative deviation of foF2 to its monthly median. A longitude/UT Fourier development yields the longitudinally averaged offset, the diurnal and the semidiurnal wave. These are evaluated in terms of the total energy input into the auroral thermosphere (“Power Index” P) as solutions of a continuity equation written for this ionospheric characteristic. Production, loss and drift terms are introduced in the equation, representing the main physical processes controlling the ionospheric disturbances during storms. The ionospheric characteristic is presented as the sum of the average offset and the slowly rotating standing wave. The expression matches the data satisfactorily for storms in the summer hemisphere, while in winter there is significant discrepancy, possibly as a consequence of interhemispheric influences.

GPS observations of post-storm TEC enhancements at low latitudes

In a previous work (J. Geophys. Res., 110(A01308), 1–11, 2005), the authors developed an original approach to the processing of total electron content (TEC) data obtained by GPS signals from the Japan receiver network. This approach includes removing the diurnal and seasonal variation carried by 27-day medians and the solar rotation periodicity. The relative deviations of TEC from the median—from all measured locations at a given hour—were then approximated by a regression line along the main prolongation of the Japan islands, between latitudes 24° and 45°N. The two variables of the regression line, the average value at the center and the slope were obtained as a time series, and their behavior during geomagnetic storms in the period 2000–2002 were analyzed. One interesting result was the observed enhancement of TEC at the end of the recovery phase of the storms. The slope variations clearly showed that this enhancement started from the south and was interpreted as a poleward expansion of equatorial crest. In the present paper we further analyze this post-storm phenomenon, adding foF2 data from Japanese Kokubunji and Okinawa ionosondes. We also show the latitude extension of the poleward expansion by using lat/UT contour plots. The results confirm that most of the post-storm TEC enhancements are part of the equatorial crest region which extends poleward during nighttime. In some cases, the enhanced TEC structures develop by separating from the crest region. Daytime TEC enhancements were also observed. Their structures are not confined to the equatorial crests region, but occupy the whole latitude range considered in this study. TEC post-storm enhancements were generally found to be in agreement with foF2 variations.

European ionospheric forecast and mapping

Abstract A new technique is developed for forecasting and instantaneous mapping of the ionospheric parameters over Europe, based on analytical presentation of the mapped quantities. The diurnal and seasonal variations of the ionospheric foF2 and M(3000)F2 parameters are represented by a modified version of the regional model ISIRM adjusted to the past measured data. An autoregressive extrapolation of the data from the past month enables the 15-day-ahead forecast of the quiet ionospheric distribution to be performed. In addition, the short-term variations due to geomagnetic activity are defined as a plane surface superimposed on the quiet distribution. This correction is obtained by two plane characteristics as functions of the geomagnetic three-hour Kp index. In this way the 24-hour forecast can be obtain during quiet as well as disturbed ionospheric conditions. The corresponding EIFM software provides a variety of options to perform the short-term forecast depending on availability of the measured ionospheric data and predicted Kp values.

Positive phase of ionospheric storms and its connection with the dayside cusp

Comparaisons de sondages ionospheriques verticaux avec des modeles de circulations thermospheriques dans les regions polaires. On confirme un resultat anterieur concernant la connexion de la phase positive des orages ionospheriques avec le cornet polaire diurne

Electron temperature distribution in the inner plasmasphere I (mid and low latitudes)

Abstract With a special set of planar probes, the Japanese satellite, AKEBONO has continued electron temperature (Te) measurement up to the height of ∼10000 km in all latitude ranges, since its launch in 1989. Although the data are still being analyzed and the results obtained so far are preliminary, we discuss the height profiles in the latitude range which is lower than 60 degrees, in terms of local time, geomagnetic latitude and seasonal variations. Although quite a large amount of theoretical work on the thermal structure of the high altitude has been done so far, the results obtained by means of the satellite AKEBONO, present a first systematic picture of the inner plasmasphere of the earth.