rewrite the content according to APA style Clear-air echoes at centimeter wavelengths are mainly believed to be caused by insects and birds because of two evidence the isotropic turbulence and the str

Clear-air echoes at centimeter wavelengths are predominantly attributed to insects and birds due to two pieces of evidence: isotropic turbulence and the atmospheric structure constant. Kolmogorov's theory posits that turbulence is homogenous and isotropic, which implies that the turbulence scattering intensity in the horizontal and vertical planes is consistent. Therefore, if turbulence were the cause of the echo, the turbulence differential reflectivity Z_DR would be zero. The second piece of evidence comes from the structure constant, which can be converted from the reflectivity factor and refractive index structure constant using Bragg scattering formula. The atmospheric structure constant C_n^2 calculated from clear-air echoes surpasses the upper range of observed values.