Towards a new reference model of hmF2 for IRI

A numerical model of the peak height of the F2 layer, hmF2_top, is derived from the topside sounding database of 90,000 electron density profiles for a representative set of conditions provided by ISIS1, ISIS2, IK19 and Cosmos-1809 satellites for the period of 1969–1987. The model of regular hmF2 variations is produced in terms of local time, season, geomagnetic latitude, geodetic longitude and solar radio flux. No geomagnetic activity trends were discernible in the topside sounding data. The nighttime peak of hmF2_top evident for mid-latitudes disappears near the geomagnetic equator where a maximum of hmF2_top occurs at sunset hours when it can exceed 500 km at solar maximum. The hmF2 given by the IRI exceeds hmF2_top at the low solar activities. The hmF2_top, obtained by extrapolation of the first derivative of the topside profile to zero shows saturation similar to foF2 the greater the solar activity. The proposed model differs from hmF2 given by IRI based on M(3000)F2 to hmF2 conversion by empirical relationships in terms of foF2, foE and R12 with these quantities mapped globally by the ITU-R (former CCIR) from ground-based ionosonde data. The differences can be attributed to the different techniques of the peak height derivation, different epochs and different global distribution of the source data as well as the different mathematical functions involved in the maps and the model presentation.     

Time constants in the ionosphere from neural network models

Neural network (NN) models for the low latitude and the polar ionosphere from the D- to the F-region were developed which are based on incoherent scatter radar data from Arecibo and EISCAT Svalbard, respectively. The various geophysical input parameters defining the NN are not only the ones that represent the time one wants to predict, but also the geophysical conditions prior to the time of the prediction. The optimum length of these preceding periods are derived for the two models are different, but a period of 60 days is a compromise acceptable for both latitudes. Furthermore from the Arecibo data time constants of electron density decay after sundown are derived which – arguably – are also relevant elsewhere, including the polar latitudes. Whereas at all altitudes the electron densities decay exponentially after sundown, below 300 km there is an additional variation with solar zenith angle.     

Preliminary results of TEC measurements in Guwahati,India

A dual frequency GPS receiver was installed in Guwahati, India (latitude 26.2°N, longitude 91.75°E, dip +35°) in January 2006 in the framework of an Indian–Russian project of seismo-ionospheric effects searching and investigation. It is quite clear that manifestations of such effects should be strongly dependent (among others) on regional features of ionosphere. In our case formation of the equatorial anomaly will affect the results. So, the data of half a year of observations were analyzed to establish the behavior of Total Electron Content (TEC) in a region of Northern crest of the equatorial anomaly in quiet helio-geophysical conditions as a background for detecting the impact of effects from below.     

Initial results of the evaluation of IRI hmF2 performance for minima 22–23 and 23–24

The performance of the International Reference Ionosphere (IRI) in predicting the height of the maximum of electron density (hmF2) has been evaluated for similar geomagnetic latitudes stations in the northern hemisphere (NH) and southern hemisphere (SH), and for the last two minima. As truth-sites, the digisonde stations of Millstone Hill (42.6°N, 288.5°E), USA, and Grahamstown (33.3°S, 26.5°E), South Africa, were considered. A monthly averaged diurnal variation was obtained from all the observations and model output in the months studied, and the corresponding difference was also calculated. For this initial study data from summer and winter in the NH and SH were selected for the solstice comparison, and October data for both stations were used to represent equinox conditions. The choice of these periods depended on data availability and quality. The results show that for the earlier minimum in 1996, in general IRI hmF2 values are in reasonable agreement with the observations. The exceptions are October and December in the SH, where IRI hmF2 tends to high, particularly on the dayside, and also July for which the daytime measured values tend to be larger than the IRI ones. For the recent minimum in 2008, IRI tends to over-estimate the hmF2 in most of the observations. The results support the general assertion that thermospheric temperatures were cooler during the last solar minimum as a consequence of an unusually low, and extended, minimum in solar extreme-ultraviolet flux, and in response to continually increasing long-term trend in anthropogenic carbon dioxide. The cooler temperatures not only decrease density at a fixed height, but also make the corresponding contraction of the atmosphere lower the height of the F-region peak.     

An overview of radar soundings of the martian ionosphere from the Mars Express spacecraft

The Mars Express spacecraft carries a low-frequency radar called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) that is designed to study the subsurface and ionosphere of Mars. In this paper, we give an overview of the ionospheric sounding results after approximately one year of operation in orbit around Mars. Several types of ionospheric echoes are commonly observed. These include vertical echoes caused by specular reflection from the horizontally stratified ionosphere; echoes from a second layer in the topside ionosphere, possibly associated with O⁺ ions; oblique echoes from upward bulges in the ionosphere; and a variety of other echoes that are poorly understood. The vertical echoes provide electron density profiles that are in reasonable agreement with the Chapman photo-equilibrium model of planetary ionospheres. On the dayside of Mars the maximum electron density is approximately 2 × 10⁵ cm⁻³. On the nightside the echoes are often very diffuse and highly irregular, with maximum electron densities less than 10⁴ cm⁻³. Surface reflections are sometimes observed in the same frequency range as the diffuse echoes, suggesting that small isolated holes exist in the nightside ionosphere, possibly similar to those that occur on the nightside of Venus. The oblique echoes arise from upward bulges in the ionosphere in regions where the crustal magnetic field of Mars is strong and nearly vertical. The bulges tend to be elongated in the horizontal direction and located in regions between oppositely directed arch-like structures in the crustal magnetic field. The nearly vertical magnetic field lines in the region between the arches are thought to connect into the solar wind, thereby allowing solar wind electrons to heat the lower levels of the ionosphere, with an attendant increase in the scale height and electron density.     

A new global F2 peak electron density model for the International Reference Ionosphere (IRI)

A new neural network (NN) based global empirical model for the F2 peak electron density (NmF2) has been developed using extended temporal and spatial geophysical relevant inputs. Measured ground based ionosonde data, from 84 global stations, spanning the period 1995 to 2005 and, for a few stations from 1976 to 1986, obtained from various resources of the World Data Centre (WDC) archives (Space Physics Interactive Data Resource SPIDR, the Digital Ionogram Database, DIDBase, and IPS Radio and Space Services) have been used for training a NN. The training data set includes all periods of quiet and disturbed magnetic activity. A comprehensive comparison for all conditions (e.g., magnetic storms, levels of solar activity, season, different regions of latitudes, etc.) between foF2 value predictions using the NN based model and International Reference Ionosphere (IRI) model (including both the International Union of Radio Science (URSI) and International Radio Consultative Committee (CCIR) coefficients) with observed values was investigated. The root-mean-square (RMS) error differences for a few selected stations are presented in this paper. The results of the foF2 NN model presented in this work successfully demonstrate that this new model can be used as a replacement option for the URSI and CCIR maps within the IRI model for the purpose of F2 peak electron density predictions.     

COST 296 action results for space weather ionospheric monitoring and modelling

COST 296 Action refers to the project on Mitigation of Ionospheric Effects on Radio Systems (MIERS) in the framework of European Cooperation in Science and Technology (COST), which is one of the longest-running European instruments supporting cooperation among scientists and researchers across Europe. The main objective of the MIERS project has been to develop an increased knowledge of the effects imposed by the ionosphere on practical radio systems, and for the development and implementation of techniques to mitigate the harmful effects of the ionosphere on such systems. This paper highlights COST 296 Action results that have been achieved during its lifetime period of February 2005–February 2009 with emphasis on space weather ionospheric monitoring and modelling.     

空间太阳能发电和微波与电离层相互作用

本文第一部分研究了空间太阳能热发电，基于所提的评价动力系统的准则，比较了三种热力学系统，并给出了一些参数变化对闭式回热Ｂｒａｙｔｏｎ循环系统的影响，本文第二部分对微波速对电离层中电子的加速和受热进行了数值研究，得出了一些结果。