Method for analyzing tidal characteristics of accidental E-layer critical frequency

Abstract

The invention provides a novel analysis method for tidal characteristics of accidental E-layer critical frequency. According to the technical scheme, the method comprises the following steps: step 1, acquiring a critical frequency time sequence of an accidental layer E from foundation observation stations distributed globally; step 2, boundary influence removal is carried out on the obtained critical frequency time sequence of the accidental E layer; and step 3, performing wavelet transformation on the prolonged critical frequency time sequence to obtain a wavelet coefficient matrix without boundary influence, and recording the column number of the wavelet coefficient matrix A as N0. And 4, in the wavelet coefficient matrix A, recording the total column number meeting the tidal characteristics (including half-day tidal characteristics and full-day tidal characteristics) as N1, and calculating R = N1 / N0. The generation frequency of the half-day tidal characteristic or the full-day tidal characteristic can be obtained according to the numerical value of R. The generation frequency calculated by the method is high in precision.

Description

Technical Field

[0001] The invention relates to the technical field of ionospheric irregular bodies, and in particular to the study of the occurrence law of an ionospheric irregular body. Background Art

[0002] The sporadic E layer is a thin cloud structure with enhanced electron density existing in the E layer of the ionosphere. It has attracted the interest of scientists since its discovery. Decades of research have given us a better understanding of its formation mechanism. At present, the most widely accepted formation mechanism of the sporadic E layer in the ionosphere in the mid-latitude region is the wind shear theory, that is, the shear of the horizontal wind field in the vertical direction causes the metal ions to produce a polymerization effect under the combined action of collision and Lorentz force, forming a relatively stable "dense" plasma thin layer structure. Since tidal wind is the main source of wind shear required for the formation of the sporadic E layer in the mid-latitude region, the critical frequency of the sporadic E layer in the mid-latitude region shows obvious tidal wind characteristics, among which the diurnal tidal characteristics and semi-diurnal tidal characteristics are particularly obvious.

[0003] Studying the changes in the critical frequency of the sporadic E layer is of great significance to the transmission of electromagnetic signals such as satellite communications. In previous studies, the tidal characteristics of the sporadic E layer were studied based on Fourier transform, which resulted in only focusing on whether the tidal characteristics of the sporadic E layer existed in a certain period of time, but not on its duration. The defects of the above research methods have a great impact on the forecast accuracy of the empirical forecast model. Summary of the invention

[0004] The present invention proposes a new analysis method for the tidal characteristics of the sporadic E-layer critical frequency, introduces wavelet transform, and simultaneously obtains the time domain and frequency domain information of the critical frequency time series of the sporadic E-layer, thereby providing more accurate reference information for the empirical forecasting model.

[0005] The technical solution steps of the present invention are as follows:

[0006] Step 1: Acquire ionospheric altimeter data from ground-based observation stations distributed around the world. The data used in the present invention is the critical frequency time series of the sporadic E layer in the ionospheric altimeter data.

[0007] Step 2: Remove the boundary influence from the critical frequency time series of the sporadic E layer. The method adopted by the present invention is to extend the time series.

[0008] Step 3: Perform wavelet transform on the extended critical frequency time series, remove the wavelet transform coefficients of the extended part, and obtain the wavelet coefficient matrix without boundary influence. The number of columns of the above wavelet coefficient matrix A is denoted as N0.

[0009] Step 4: In the wavelet coefficient matrix A, the total number of columns that meet the tidal characteristics (including semi-diurnal tidal characteristics and diurnal tidal characteristics) is recorded as N1. The calculation method of N1 is as follows:

[0010] Let T be 12h and 24h respectively, and calculate the occurrence frequency R at each value of T:

[0011] The initial value of N1 is 0. The column A(:, j) of A is regarded as a function. If A(:, j) takes the local maximum value at time T, then N1 = N1 + 1. Repeat the above operation until A is traversed.

[0012] R=N1 / N0.

[0013] From the above calculation, we can know that if T=12h, then R is the frequency of occurrence of semi-diurnal tide in sporadic E layer; if T=24h, then R is the frequency of occurrence of diurnal tide in sporadic E layer.

[0014] The purpose of the present invention is to propose an analysis method for the tidal characteristics of the critical frequency time series of the sporadic E layer based on wavelet transform. Based on the result of wavelet transform, the frequency and time information of the original time series are quantified simultaneously, so as to define the occurrence frequency of the tidal characteristics of the sporadic E layer. This method calculates the occurrence frequency with higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a flow chart of the present invention;

[0016] Figure 2 Changes in the incidence of diurnal tidal characteristics of sporadic E-layers in winter at Okinawa Station, Japan from 1997 to 2022 DETAILED DESCRIPTION

[0017] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0018] The data of the ionospheric altimeter are obtained from ground-based observation stations distributed around the world. The data used in the present invention is the critical frequency time series of the sporadic E layer in the ionospheric altimeter data. First, the occurrence frequency R of the sporadic E layer in the winter between 1997 and 2022 at the Okinawa station in Japan is calculated as an example. The winter time is from December to February of the following year. Secondly, the occurrence frequency R of the sporadic E layer in the summer between 1997 and 2022 at the Okinawa station in Japan is calculated as an example. The summer time is from June to August each year.

[0019] First, the critical frequency time series of the sporadic E layer obtained at the Okinawa station in Japan in winter each year is used to remove the boundary influence. The method adopted by the present invention is to extend the time series, and the extended time series is from November to March of the following year. Then, the extended critical frequency time series is subjected to wavelet transform, and the wavelet transform coefficients of the extended part are removed to obtain the wavelet coefficient matrix without boundary influence. The number of columns of the above wavelet coefficient matrix A is recorded as N0. Finally, in the wavelet coefficient matrix A, the total number of columns that meet the full-day tidal characteristics is obtained and recorded as N1, R=N1 / N0, and R is the frequency of occurrence of the full-day tidal characteristics of the sporadic E layer in winter from 1997 to 2022 at the Okinawa station in Japan. The calculation method for summer is the same as that for winter, and its extended time series is from May to September each year.

[0020] The frequency of occurrence of sporadic E-layer diurnal tidal characteristics in winter and summer from 1997 to 2022 is shown in Figure 2. Figure 2 As shown, the red curve represents the frequency of occurrence in summer, and the blue curve represents the frequency of occurrence in winter. The ordinate is the calculated frequency of occurrence R, and the abscissa is the year. In practice, the frequency of occurrence of the full-day tidal characteristics in winter should be greater than the frequency of occurrence of the full-day tidal characteristics in summer. The calculation results of the present invention confirm this point, indicating the accuracy of the calculation results of the present invention.

Claims

1. A method for analyzing tidal characteristics of sporadic E-layer critical frequency, characterized in that: The steps include: Step 1: Obtain the data of the ionospheric altimeter and obtain the critical frequency time series of the sporadic E layer in the ionospheric altimeter data; Step 2: Remove the boundary effect from the critical frequency time series of the sporadic E layer. Step 3: Perform wavelet transform on the critical frequency time series obtained after processing in step 2, remove the wavelet transform coefficients of the extended part, and obtain the wavelet coefficient matrix without boundary influence. The wavelet coefficient matrix is ​​denoted as A, and the number of columns is N0; Step 4: In the wavelet coefficient matrix A, the total number of columns that meet the tidal characteristics is recorded as N1, and the calculation method of N1 is as follows: Let T be 6h, 8h, 12h, and 24h respectively, and calculate the occurrence frequency R at each value of T, where h refers to the time unit hour: The initial value of N1 is 0. The column A(:, j) of A is regarded as a function. If A(:, j) takes the local maximum value at time T, then N1 = N1 + 1. Repeat the above operation until A is traversed. Let R = N1 / N0; If T=6h, R is the frequency of occurrence of quarter-diurnal tide of sporadic E layer; if T=8h, R is the frequency of occurrence of one-third-diurnal tide of sporadic E layer; if T=12h, R is the frequency of occurrence of semi-diurnal tide of sporadic E layer; if T=24h, R is the frequency of occurrence of full-diurnal tide of sporadic E layer.

2. The method for analyzing tidal characteristics of sporadic E-layer critical frequency according to claim 1, characterized in that: The critical frequency time series of the sporadic E layer is processed to remove the boundary effect by extending the time series.

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