###### Abstract
In 1969, [PERSON] summarized progress in the field of radar backscattering from refractive index irregularities in clear air and described their relationship to atmospheric structure and turbulence [11]. His study showed that the relationship between microstructure and atmospheric mean fields can be illustrated for a simplified situation in the stable regime, from which it can be concluded that strong clear-air turbulence will be associated with zones of increased refractive index variability and enhanced radar returns. Four years later, his team summarized and discussed the experimental progress made since 1969, showing how the echo patterns obtained could be used to interpret multiple layering, gravity waves, internal fronts, and the details of dynamic instability and turbulence generation in stably stratified shear layers [12]. This research laid the theoretical foundations of Bragg clear-air scattering. Bragg scattering has also been discussed in detail in some studies, but there has been no substantial update of the theory. However, the field of wireless communications, which is similar to that of radar, proposes a new mechanism. In respect of communication, tropospheric scattering (also known as troposcatter) has been suggested as an efficient propagation method by the Radiocommunication Sector of the International Telecommunication Union. This is the mechanism by which microwave radio systems inadvertently achieve beyond-the-horizon communications [13]. According to the currently accepted theory of tropospheric scattering, information transfer is the result of the combination of the following three models [14]: the reflective layer model [15], scattering from turbulence [16], and reflections from an exponential atmosphere [17]. By comparing tropospheric scattering with radar theories, it is clear that Bragg scattering and Fresnel scattering involve backward scattering forms of turbulent scattering and reflections from an exponential atmosphere, respectively. However, little attention has been paid to the connection between tropospheric scattering and clear-air echoes. The reflecting layer model, one of the three mechanisms of tropospheric scattering, has been forgotten in the study of clear-air echoes. This has led to a large number of studies based on an incomplete scattering theory of the clear-air echo. Researchers generally base their studies of meteorological clear-air echoes exclusively on Bragg scattering and isotropic turbulence. [PERSON] and [PERSON] argued that scattering is due to refractive index fluctuations on a scale of one-half the wavelength due to isotropic turbulence [18]. [PERSON] stated in his book that observed clear-air echoes are much larger than the value that the atmospheric structure constant can provide, if only conventional Bragg scattering is considered [19]. [PERSON] et al. performed radar reflectivity comparisons of clear-air echoes in Florida and Colorado at wavelengths of 3, 5, and 10 cm, and concluded that insects are primarily responsible for the clear-air echoes in the mixed boundary layer [2]. They also concluded that at and above the top of the well-mixed boundary layer, Bragg scattering dominates and is frequently observed in the S-band. However, although earlier studies have suggested that their conclusions apply only to isotropic turbulence, the statistical results of many studies do not take into account the effects produced by non-isotropic turbulence because no new theories have been proposed. Thus, this study focuses on the relationship between radar clear-air echoes and tropospheric scattering. In this study, we introduce the theory of tropospheric from over-the-horizon communication into atmospheric physics. The aim is to extend the set of scattering mechanisms of turbulence. Radar is treated as a self-transmitting and self-receiving wireless communication system, which allows us to explain troposcatter in the atmosphere. This approach provides a new perspective on the study of clear-air scattering in atmospheric physics.