Papers by Stanimir Stankov
Russian Meteorology and Hydrology
SWIPPA (Space Weather Impact on Precise Positioning Applications) is a project initiated by the G... more SWIPPA (Space Weather Impact on Precise Positioning Applications) is a project initiated by the German Aerospace Center (DLR) and co-sponsored by the European Space Agency (ESA). The project aims at establishing, operating, and evaluating a specific space-weather monitoring service that can possibly lead to improving the precise positioning applications based on Global Navigation Satellite Systems (GNSS). Reported here is the current status of SWIPPA, detailed are the products and services that are currently available in a high resolution operational mode.
It is well recognized that the space weather can induce severe ionosphere perturbations and can c... more It is well recognized that the space weather can induce severe ionosphere perturbations and can cause serious technological problems in the Global Navigation Satellite Systems (GNSS). On the other hand, the ionosphere also plays an active role in the complex Sun-Earth relationship and the space weather manifestation. Highly dynamical and strong deviations of the ionosphere electron density structure may cause range errors by rapid phase and amplitude fluctuations of the satellite signal. Therefore, in order to efficiently operate and further improve the functionality of such systems, key information on the ionosphere condition is needed, particularly when the ionosphere is disturbed.
The ionospheric influence on reference networks has been proven at daily and longer-term levels a... more The ionospheric influence on reference networks has been proven at daily and longer-term levels and can be a significant error factor. The impact is noticeably stronger during ionospheric perturbations and storms, which raises the question about reliability of GNSS reference networks during such unfavourable conditions.
Planetary and Space Science, 2005
Presented is a new method for retrieving the topside electron density distribution from space-bas... more Presented is a new method for retrieving the topside electron density distribution from space-based observations of the total electron content. By assuming an adequate topside density distribution, the profile reconstruction technique utilizes ionosonde and oxygen-hydrogen ion transition level measurements for uniquely determining the unknown ion scale heights and the corresponding ion and electron density profiles. The method is tested on actual measurements from the CHAMP satellite. Important applications are envisaged, such as developing and evaluating empirical and theoretical ionosphere-plasmasphere models. r
Journal of Atmospheric and Solar-Terrestrial Physics, 2006
The knowledge of the scale height in the topside ionosphere region remains rather poor due to the... more The knowledge of the scale height in the topside ionosphere region remains rather poor due to the insufficient observations carried so far. To advance this knowledge, presented here is a new method of retrieving the topside ionospheric scale height based on radio occultation observations onboard low-earth-orbiting satellites. The scale height, well known for its dependence on the temperatures and masses of the ionospheric constituents, understandably experiences large spatial and temporal variability. With the help of the CHAMP satellite's occultation experiment, analysed is the scale height behaviour with respect to solar and geomagnetic activity, local time, season, longitude and latitude. The expected strong dependence on temperature has been confirmed; however, it has been found that this dependence is not straightforward but more complex and clearly affected by other factors. For example, while the daytime scale height values increase at higher solar activity, the night-time values do not show such a trend. The seasonal dependence proved to be strong with summer-time values significantly higher than winter-time numbers. Also, there is no common pattern for the diurnal variations: sometimes daytime values are higher, sometimes the night-time values dominate; large differences are detected from season to season and from latitude to latitude. Generally, the scale increases at higher latitudes, although a few differences do exist. No major longitudinal and hemispheric differences have been detected so far. Based on the accumulated data, a first attempt has been made to empirically simulate the scale height value at 425 km altitude; as input parameters, the model respects the local time, latitude, and season. The scale height model can be implemented into the electron density profile retrieval procedure by delivering an improved initial guess. r
Annales Geophysicae, 2005
The ionospheric plasma can significantly influence the propagation of radio waves and the ionosph... more The ionospheric plasma can significantly influence the propagation of radio waves and the ionospheric disturbances are capable of causing range errors, rapid phase and amplitude fluctuations (radio scintillations) of satellite signals that may lead to degradation of the system performance, its accuracy and reliability. The cause of such disturbances should be sought in the processes originating in the Sun. Numerous studies on these phenomena have been already carried out at a broad international level, in order to measure/estimate these space weather induced effects, to forecast them, and to understand and mitigate their impact on present-day technological systems.
Advances in Space Research, 2006
To better and faster quantify the strength and impact of the ionospheric perturbations, we propos... more To better and faster quantify the strength and impact of the ionospheric perturbations, we propose a new index for operational use in communication/navigation systems. Presented here is the analysis of selected events of strong disturbances observed with techniques based on Global Navigation Satellite Systems (GNSS) in order to show some insufficiencies when using existing geomagnetic indices. We found that the GNSS Total Electron Content (TEC) measurements and/or derivatives are outstanding candidates for defining a new ionospheric perturbation index, more specialised and therefore more effective. It is believed that the standardization and usage of the proposed perturbation index, together with other indices of similar nature, can prove helpful in reducing the space weather impact on the GNSS-based navigation and positioning.
Advances in Space Research, 1994
A mathematical model is used to study the relative abundance of H + and He + ions in the topside ... more A mathematical model is used to study the relative abundance of H + and He + ions in the topside ionosphere. It is found that the daytime light-ion densities are strongly coupled with the neutral densities. This fact arises difficulties in modelling the ion composition for IRI without taking into account any particular reference atmosphere. As an example, the transition heights between O+-H + and O+-He + are shown, plotted against the neutral densities. The supposed linear dependance gives a clear evidence that all light-ion ionization below these heights will experience stronger influence by the neutral atmosphere.
Advances in Space Research, 2006
The plasma scale height is one of the important ionospheric characteristics due to its intrinsic ... more The plasma scale height is one of the important ionospheric characteristics due to its intrinsic connection to the ionospheric plasma temperature and composition, and thus to the shape of the electron density profile. Therefore, the knowledge of the plasma scale height values and variation is of crucial importance when addressing several open scientific and technological questions such as the upper ionosphere temperature balance, ion composition, storm dynamics, etc. While the plasma scale height value in the bottomside ionosphere can be deduced directly and reliably enough by vertical incidence sounding, the plasma scale height in the topside ionosphere is difficult to obtain. The ionospheric radio occultation (IRO) technique, based on low-earth-orbiting (LEO) satellites, is capable of delivering valuable information on the topside plasma scale height behaviour and of providing a rich database for consequent development of new empirical models of the plasma scale height and density. The purpose of this paper is to present a new procedure for retrieval of the topside plasma scale height value from IRO measurements by the LEO satellite CHAMP. First results from the analysis of the topside plasma scale height's temporal and spatial variations are also provided.
A new formula of the electron density profiles above the peak height is introduced. The formula i... more A new formula of the electron density profiles above the peak height is introduced. The formula is based on the Epstein layer and depends on the O + and H + scale heights and the O + -H + transition level. Both scale heights have a ratio 1:16 reduced by a factor representing the change from magnetic field line direction to vertical direction. The bottom-side part of TEC (profile calculations using foF2, M 3000 F2 and foE) is subtracted from the GPS-measured TEC at the same location. The topside TEC, together with the empirically obtained O + -H + transition level, are then used to deduce the unknown scale heights. The method is demonstrated on genuine data covering low and high solar activity conditions.
SWIPPA (Space Weather Impact on Precise Positioning Applications of GNSS) is a project, initiated... more SWIPPA (Space Weather Impact on Precise Positioning Applications of GNSS) is a project, initiated by the German Aerospace Centre (DLR), aiming at establishing a specific space weather service for improving current Global Navigation Satellite System (GNSS) applications. This project is considered a substantial part of the preparations for future European Space Weather Programme and GALILEO services.
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Papers by Stanimir Stankov