A. D. Akchurin

The influence of lower atmosphere dynamics on the mid-latitude sporadic E-layer

Abstract The relationship between the occurrence of intense sporadic-E layers and features of tropospheric weather has been investigated. It has been found that, as certain features of the tropospheric pressure field (as identified from meteorological charts) develop over specific geographic regions, the probability of intense sporadic-E layers increases. Investigating the 500 mb chart has shown that the probability of occurrence of intense sporadic-E layers increases in response to distortion of patterns of zonal westerly flows.

Use of the Hough transform for the propagation mode extraction

This paper proposes the method of propagation mode extraction on ionograms with the help of the Hough transform. Usually, the Hough transform for ionogram processing is used at the step of track autoscaling, when propagation modes already extracted. Authors propose a method for image binarization based on the application of abnormal sample extraction method which allows to use of the Hough transform for propagation mode extraction. The experimental verification of the effectiveness of the proposed method is conducted. The ionogram processing approach can also be used to the element extraction on the images with the same properties.

Determination of maximum usable frequencies based on frequency characteristics of sporadic layer obtained by vertical sounding

It is analyzed determining methods and calculation techniques of MEs coefficient - converting the frequency characteristics of Es-layer by vertical sounding (VS) to maximum usable frequencies (MUF) of Es layer at oblique incidence (OI). Correction coefficient K, caused by the difference in technical provision of ionosonde and radio-line, and depending on the choice of threshold detection of Es-signal amplitude, introduces for determining of MUF Es. Revealed changes of correction coefficient from the type of Es-layer. For signal level appropriate to -30 dB, correction coefficient K for type c of Es layer equal 1.31, f type - 2.15, l type - 1.54, h type - 1.38. It is explained not only by geometrical factors, but also by changes in Es-layer structure, depending on the height of its location, and the magnitude of background ionization, which leads to daily changes of correction coefficient at fixed levels of Es-layer reflection coefficient. Changes in K coefficient during the day are considerable, since its value from night to day reduced by 1.3 times on Moscow-Kazan line. When the sensitivity of ionosphere station and radio-line are close, the value of K coefficient should not be significantly different from unit. This situation was checked by probing at sliding frequency on the Moscow-Kazan line. Found that at approximately same power of VS and OI stations the experimental distribution of K coefficient with standart deviation of 0.14, the same as calculation obtained by simulation modeling based on cloud model layer with parameters obtained from temporal variations of frequency fbEs.

Observation of irregularities dynamics by vertical and quasi-vertical sounding

Based on comparative analysis of the A and H plots collected from the ionograms of vertical and quasi vertical sounding you can get information about spatial and temporal changes. The ionosonde sensitivity to irregularities ΔN / N ~5*10, sensing period 1 minute, distance between ionosondes 30 km. It is allows to investigate fast-flowing (with periods of 5-20 min) and small-scale irregularities of the ionosphere.

Effects of planetary waves in parameters of the midlatitude sporadic E layer

The spatial structure of the planetary waves in the frequency parameters of the sporadic E layer have been studied based on an analysis of the 30-year series of the ionospheric data for the midlatitude region of the Northern Hemisphere, which made it possible to observe the planetary waves with zonal wavenumbers 1, 2, and 3. The characteristic periods of existence have been revealed for these waves, and the seasonal distributions of these periods have been constructed. These waves can be considered among quasistationary formations according to their character; i.e., these waves are stationary or slowly move during long time intervals but can abruptly change the initial phase during 1–2 days. Two clearly defined zones between 30°–60° E and 210°–240° E have been detected as a result of an analysis of the longitudinal belts where an abrupt change in the initial phases of these waves is most frequent.

Spring stratospheric circulation transition and mid-latitude sporadic E-layer

Abstract Using ionospheric data from a 32-year period for 8 mid-latitude stations within the European part of Russia, the dependence of intensity of an sporadic-E layer during the summer period on the start date of the spring seasonal transition of zonal circulation in the stratosphere was investigated. In those years with an early circulation transition, the sporadic-E layer intensity was increased by a factor 1.5 compared with years with a late circulation transition.