Dalia Buresova

DOES THE QBO AND THE MT. PINATUBO VOLCANIC ERUPTION. AFFECT THE GRAVITY WAVE ACTIVITY IN THE LOWER IONOSPHERE

All existing data (∼6 years) on gravity wave activity, inferred from the nighttime A3 (oblique incidence on the ionosphere) radio wave absorption measurements in the lower ionosphere on 270 kHz at Průhonice in Central Europe, have been exploited to get information on the effects of QBO phases and the Mt. Pinatubo volcanic eruption on the gravity wave activity in the winter half of the year. There appears to be an enhancement of gravity wave activity in the two winters just after the strong volcanic eruption of Mt. Pinatubo. This enhancement is remarkable for long-period waves (T=2–3 hours). No clear effect of the phase of QBO on the level of gravity wave activity has been found; a possible effect of QBO on the correlations between gravity wave activities in individual period bands is indicated. The results are limited by a relatively short data series; however, no more data will he available.

Results of foF2 Data Testing With the UNDIV Program

The prediction of critical frequency foF2 is of great importance in the area of short-wave telecommunication and ionospheric modelling. The test study of foF2 data should enable the validity of data used inPRIMEmap generating and testing to be checked. The preliminary results show that some data should not be used because they could affect the latest results ofPRIMEmap generating, testing and improving.

APPLICATION OF DIGITAL FILTERS TO CHECK QUALITY OF THE AUTOMATICALLY SCALED IONOGRAMS

Abstract The ionospheric observatory Pruhonice serves to monitor the state of ionosphere using ground-based vertical sounding instrument - the Digisonde DPS-4D. Measured ionograms are automatically evaluated (scaled) and basic characteristics are derived. The ionograms and the scaled parameters are sent to the international databases. Especially during disturbed conditions the automatic scaling could give unreliable results. This paper presents simple method how to detect accidental errors in automatic scaling based on the parameters derived from ionograms and on an application of the finite impulse response filters.

An analysis of the scale height at the F2-layer peak over three middle-latitude stations in the European sector

This paper presents the results of an analysis of the variations of the scale height at the F2-layer peak (Hm) under different seasonal and solar-activity conditions. The database includes hourly Hm values derived from ionograms recorded at three middle-latitude stations in the European sector: El Arenosillo (37.1°N; 353.3°E), Ebro (40.8°N, 0.5°E) and Pruhonice (50.0°N; 15.0°E). The results show that, in general: (1) Hm exhibits diurnal variation with higher values during daytime than during night-time and secondary peaks around sunrise and sunset; (2) during winter time the scale height is lower than in summer time; (3) the scale heights increase with increasing solar activity; (4) Hm decreases when the latitude increases; (5) Hm shows a low correlation with the F2-region peak parameters NmF2 and hmF2 and a high correlation with the thickness parameter B0 and the equivalent slab thickness EST; (6) the day-to-day variability is greater at low solar activity than at high solar activity—it reaches maximum values around sunrise or sunset and it is lower around midnight than around noon at low solar activity. The results of this study are similar to those reported by other authors and can be useful for estimating the topside ionosphere from bottomside measurements and modelling.

Do CRISTA Experiment/Campaign Data Represent a Typical Situation or Not?

Data from four A3 radio wave circuits in central Europe are used to analyse the representativeness of the ionization and gravity wave activity pattern in the lower ionosphere (∼85 – 100 km) in the CRISTA experiment interval (3 – 12 November 1994) for the given conditions. It has been found that the CRISTA experiment interval was run under conditions, which are highly representative both of October – November 1994 and autumn, low-moderate solar activity, the descending phase of solar cycle conditions, i.e. CRISTA measurements may be considered to provide values identical with, or close to climatological values (at least for central Europe, h = 85 – 100 km).

Comparison of parametric methods for radar signal processing

The paper deals with comparison of parametric power spectral density methods for the utilization in the meteorological radar. Type of the considered radar is pulse radar of frequency modulated pulses. We have compared duration of signal processing requested by single methods involved in the test. The methods used are the Auto Regressive (AR) model, MUSIC method, Eigen Vector algorithm and CAPON. Duration of signal processing is important for regular measurements of the radar. The best results we obtained for the AR model.

Pilot Ionosonde Network for Identification of Traveling Ionospheric Disturbances

Travelling Ionospheric Disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves (AGWs). Their identification and tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although various techniques have been proposed to measure TID characteristics, their real-time implementation still has several difficulties. In this contribution, we present a new technique, based on the analysis of oblique Digisonde-to-Digisonde (D2D) “skymap” observations, to directly identify TIDs and specify the TID wave parameters based on the measurement of angle-of-arrival, Doppler frequency, and time-of-flight of ionospherically reflected high-frequency (HF) radio pulses. The technique has been implemented for the first time for the Net-TIDE project with data streaming from the network of European Digisonde DPS4D observatories. The performance is demonstrated during a period of moderate auroral activity, assessing its consistency with independent measurements such as data from auroral magnetometers and electron density perturbations from Digisondes and GNSS stations. Given that the different types of measurements used for this assessment were not made at exactly the same time and location, and that there was insufficient coverage in the area between the AGW sources and the measurement locations, we can only consider our interpretation as plausible and indicative for the reliability of the extracted TID characteristics. In the framework of the new TechTIDE project (European Commission H2020), a retrospective analysis of the Net-TIDE results in comparison with those extracted from GNSS TEC-based methodologies is currently being attempted, and the results will be the objective of a follow up paper.