Ludmila A. Leonovich

Determining parameters of large-scale traveling ionospheric disturbances of auroral origin using GPS-arrays

Abstract The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS-arrays whose elements can be selected from a large set of GPS stations forming part of the International GPS Service network. The method was used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The North-American sector where many GPS stations are available, and also the time interval 00:00–06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough with a conspicuous southward wall in the range of geographic latitudes 50–60° and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 h and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000–3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it ‘curled’ to the west in longitude where the local time was around afternoon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.

Ionospheric effects of the solar flares of September 23, 1998 and July 29, 1999 as deduced from global GPS network data

Abstract This paper presents data from first global positioning system (GPS) measurements of global response of the ionosphere to solar flares of September 23, 1998 and July 29, 1999. The analysis used novel technology of a global detection of ionospheric effects from solar flares as developed by one of the authors (Afraimovich, Radio Sci. 35 (2000) 1417). The essence of the method is that use is made of appropriate filtering and a coherent processing of variations in total electron content (TEC) in the ionosphere which is determined from GPS data, simultaneously for the entire set of visible (over a given time interval) GPS satellites at all stations used in the analysis. It was found that fluctuations of TEC, obtained by removing the linear trend of TEC with a time window of about 5 min, are coherent for all stations and the line-of-sight to the GPS satellites on the dayside of the Earth. The time profile of TEC responses is similar to the time behavior of hard X-ray emission variations during flares if the relaxation time of electron density disturbances in the ionosphere of order 50–100 s is introduced. No such effect on the nightside of the Earth has been detected yet.

Simultaneous radio and optical observations of the mid-latitude atmospheric response to a major geomagnetic storm of 6–8 April 2000

Basic properties of the mid-latitude traveling ionospheric disturbances (TIDs) during the maximum phase of a major magnetic storm of 6 –8 April 2000 are shown. Total electron content (TEC) variations were studied by using data from GPS receivers located in Russia and Central Asia. The nightglow response to this storm at mesopause and termospheric altitudes was also measured by optical instruments FENIX located at the observatory of the Institute of Solar-Terrestrial Physics (51:9 ◦ N; 103:0 ◦ E), and MORTI located at the observatory of the Institute of Ionosphere (43:2 ◦ N; 77:0 ◦ E). Observations of the O (557:7 and 630:0 nm) emissions originating from atmospheric layers centered at altitudes of 90 and 250 km were carried out at Irkutsk and of the O2(b 1 + g −X 3 − g ) (0-1) emission originating from an atmospheric layer centered at altitude of 94 km was carried out at Almaty. Our radio and optical measurement network observed a storm-induced solitary large-scale wave with duration of 1 h and a wave front width of no less than 5000 km, while it traveled equatorward with a velocity of 200 m=s from 62 ◦ Nt o 38 ◦ N geographic latitude. The TEC disturbance, basically displaying an electron content depression in the maximum of the F2 region, reveals a good correlation with growing nightglow emission, the temporal shift between the TEC and emission variation maxima being diAerent for diAerent altitudes. A comparison of the auroral oval parameters with dynamic spectra of TEC variations and optical 630 nm emissions in the frequency range 0.4 –4 mHz (250 –2500 s periods) showed that as the auroral oval expands into mid-latitudes, also does the region with a developed medium-sale and small-scale TEC structure. c

The use of the international GPS network as the global detector (GLOBDET) simultaneously observing sudden ionospheric disturbances

We developed a new technology for global detection of ionospheric disturbances, on the basis of phase measurements of the total electron content (TEC) along the line-of-sight (LOS) between the receiver on the ground and transmitters on the GPS satellites using an international GPS networks. Temporal dependencies of TEC with the time resolution of 30 s are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of visible satellites. These series are subjected to filtering in the selected range of oscillation periods using known algorithms for spatio-temporal analysis of signals. An analysis is made of the possibilities of using the GLOBDET when detecting the ionospheric response of solar flares. In this case it is best to make the coherent summation of the filtered series of TEC. Because of a statistical independence of the background fluctuations, the signal/noise ratio, when the flare effect is detected, is increased due to a coherent processing by at least the times, where N is the number of LOS.

Observation of large-scale traveling ionospheric disturbances of auroral origin by global GPS networks

The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS arrays whose elements can be selected from a large set of GPS stations forming part of the international GPS network. The method was used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The North-American sector where many GPS stations are available, and also the time interval 00:00–06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough (MIT) with a conspicuous southward wall in the range of geographic latitudes 50–60° and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 hour and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000–3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it ‘curled’ to the west in longitude where the local time was around noon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.

Ionospheric effects of the solar flares as deduced from global GPS network data

Abstract Results derived from analysing the ionospheric response to faint and bright solar flares are presented. The analysis used novel technology of a global detection of ionospheric effects from solar flares as developed by the authors (Afraimovich, 2000a; Afraimovich, 2000b), on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. The essence of the method is that use is made of appropriate filtering and a coherent processing of variations in the TEC which is determined from GPS data, simultaneously for the entire set of visible GPS satellites at all stations used in the analysis. This technique is useful for identifying the ionospheric response to faint solar flares (of X-ray class C) when the variation amplitude of the TEC response to separate line-on-sight (LOS) is comparable to the level of background fluctuations. The dependence of the TEC variation response amplitude on the flare location on the Sun is investigated.

Novel technology for detecting atmospheric disturbances using GPS. Instantaneous response of the ionosphere to a sudden commencement of the strong magnetic storms

Abstract We developed a new technology for global detection of atmospheric disturbances, on the basis of phase measurements of the total electron content (TEC) using the international GPS network. Temporal dependencies of TEC are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of visible satellites. These series are subjected to filtering in the selected range of oscillation periods using known algorithms for spatiotemporal analysis of signals. An “instantaneous” ionospheric response to the sudden commencement of the strong magnetic storms were detected. On the dayside of the Earth the largest value of the net response amplitude was found to be of order 0.4 TECU (2–3 % of the background TEC value), and the delay with respect to the SSC in mid-latitudes was about 360 s. In higher latitudes the delay goes up to 15 min. On the nightside these values are 0.2 TECU and 30 min, respectively. The velocity of the traveling disturbance from the middle to high latitudes on the dayside as well as from the dayside to the nightside was about 10–20 km/s.

Aeronomic effects of the solar flares in the topside ionosphere

We obtained that according to the GPS data at altitudes of the topside ionosphere (h >300 km) a flare is able to cause a decrease of the electron content. Using the theoretical model it is shown that the intense transport of O+ ions into the above-situated plasma caused by a sharp increase in the ion production rate and thermal expansion of the ionospheric plasma is a cause of the formation of the negative disturbance in the electron concentration in the topside ionosphere.