Work Package 4 - Space plasma parameters from COSMOS-900 and DEMETER data


Objectives

The main objectives of WP4 were:

  1. Finding out whether or not characteristic oscillations of ionospheric plasma related to seismic activity exist.
  2. If the answer to the first question is positive, then to determine the main characteristics of these oscillations, their extension in time and space, and if they are magnetically controlled.
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Description

Although the seismic effects in the Earth ionosphere have been studied for a number of years, a set of parameters that may be used to characterize the processes and hence used as earthquake predictors has not been determined since the most of the reports are in the form of case-studies, and convincing statistics for observed earthquake-related effects are still missing.

Most of essential observations of ionosphere-related seismic effects were obtained from the data of the DEMETER satellite that was specially designed for seismic research and launched into a sun-synchronous 10-22h LT polar circular orbit with an altitude of about 700 km.

The COSMOS-900 data set includes simultaneous measurements of two plasma parameters, electron density and temperature; the time-spatial variations and fluctuations of these parameters and their various combinations can be considered as possible seismic-sensitive parameter candidates for the earthquake precursors. A statistical analysis of the COSMOS-900 data set can provide a statistically significant new insight into the mechanism of seismo-ionospheric effects. In contrast to DEMETER, the COSMOS-900 orbit can provide more possibilities for seismic studies due to the all-local time (0-24h LT) coverage and lower altitudes (500 km at the start of the mission and ~350 km at the end). The possibility of combining this data with that of DEMETER will contribute to the solution of this problem significantly.

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Highlights

Task 4.2 - Preparation of COSMOS-900 observational databank

The Russian COSMOS 900 satellite was launched on April 30th, 1977 into a circular, polar orbit whose height was allowed to decrease during the mission from an initial 500 km down to around 330km. The mission ended on September 11th, 1979 after 2.5 years in orbit. COSMOS-900 carried a suite of plasma instruments, capable of measuring the density and temperature of both ions and electrons. Despite being copied and recopied to newer media in the early 80's and 90's only part of the raw data from the ZAP-4 operational mode are available for processing and analysis. Task 4.2 involved the processing and cleaning of the raw data to generate a fully calibrated set of measurements of the ion density, electron temperature, and spacecraft potential that may be used for further analysis.

Changes in wave power spectra

Figure 4.1: Examples of byte errors in the parameter data. Erroneous values appear as outliers in the dataset as indicated by the arrows.

The reprocessing task was applied to OVF version of the data that was written to CD in the early 90’s. Each of the 298 data files that could be processed contains data from several orbits. These files were separated into separate, time continuous sections for further processing. It was only possible to extract three parameters, the ion density, electron temperature, and spacecraft potential from these files. Once the parameters were extracted, the resulting data sets were cleaned. This process involves the removal of erroneous data points that have been corrupted by either satellite hardware effects, transmission problems, during onboard storage, or during the multiple copying processes. Firstly, the measurement time was validated to ensure that it corresponded to an actual period of operation of the satellite. Any incorrectly time tagged data values were deleted. Secondly, data with byte errors in the parameter values were selected and deleted. Such values typically occur as outliers when the data are plotted. Examples are shown in Figure 4.1.

Once the data were cleaned, a data bank was created. The measurements of ion density, electron temperature, and spacecraft potential were supplemented with ephemeris data to give the location of the measurements and also various geophysical parameters that can be used to provide information regarding the state of the solar wind and the geomagnetic environment.

Task 4.3 - Development of data processing methods

Once the datasets from DEMETER and COSMOS-900 had been validated for scientific analysis several software tools were produced to visualise the data, perform searches within the data set to identify sections of data that occur in the vicinity of large earthquakes, and perform a frequency-time analysis of the data.

Changes in wave power spectra

Figure 4.2: Measurements of the ion density and spatial and temporal locations of the satellite tracks with respect to earthquake epicentres.

Figure 4.2 shows an example of the tool created to search for satellite passes in conjunction with the occurrence of earthquakes. The list on the right allows the user to select the satellite passes closest to the earthquake epicenter whilst the plots of the left display (from top to bottom) the ion density measured on the selected orbital passes, the latitude and longitude of the satellite track together with the location of the epicentres of earthquakes that occurred within a month of the satellite passage, and the temporal location of the satellite passage with respect to the time of the earthquake events.

The second tool enables the user to extract data from a single passage of the satellite, perform a wavelet based frequency-time analysis of the data and display the results. An example of the output is shown in Figure 4.3. From top to bottom the panels show the measurements of the ion density, its wavelet spectrogram, and vertical and horizontal cuts through the spectrogram at the location indicated by the crosshairs.

Task 4.4 - Interpretation of results

Using the above mentioned tools, plasma data from the DEMETER and COSMOS-900 satellites were analysed to investigate the occurrence of periodicities in the plasma measurements and their relation to the occurrence of earthquakes.

Changes in wave power spectra

Figure 4.3: Example of the frequency-time analysis of the ion density.

The conclusions of this study were as follows:

  1. Seismic effects exist in all plasma parameters. They are most pronounced in the plasma density, less so in the electron temperature. They are not observed in the spacecraft potential.
  2. Seismic effects are most pronounced during nighttime periods at altitudes of the F2 region.
  3. In most cases the seismic effects cause the wave-like variations with characteristic time scales S=300-450 s - about 5-8 min (frequencies F=012-0.2 min-1 ).
  4. These wave-like variations are field-aligned and usually cover a spatial area of Δλ=±25-30° (longitude) and Δφ=±40° (latitude).
  5. Within the F2 region the seismic-related wave-like variations were observed for around 3-4 days before and after the earthquake.
  6. Similar variations were also observed by DEMETER (700 km altitude).
  7. In addition to the wave-like variations, local seismic effects may appear in the form either of sharp increases (piston-like variation) or local depressions of the density over the EQ epicenter.
  8. The analysis suggests a possible candidate for the signature of an EQ precursor: the appearance of wave-like variation with characteristic scales S=300-450 s.
  9. The seismic wave-like variations are likely to be caused by dynamic wave-like processes in neutral atmosphere.
  10. Local seismic-related piston-like variations are most probably caused by sharp appearance of EQ-related transverse electric fields that cause the plasma drift upward (for eastward E-field) or downward (for westward E-field).
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Reports

D4.1 DEMETER data bank on Ne, Te and decision of possibility of its use for analysis.
D4.2 Preparation of COSMOS-900 observational data bank for space and spectral analysis and development of the relevant software.
D4.3 Development of data processing methods for plasma parameters analysis for correlation with seismic activity
D4.4 Interpretation of obtained results

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