A New Formula for Computing Minimum Trapped Frequency of Evaporation Duct

In the past, the minimum trapped frequency formula of evaporation duct is obtained under the assumption of linear attenuation, while the profile of actual evaporation duct is linear-logarithmic, which leads to the calculation error of the formula. Based on the integral minimum trapped frequency formula, the calculation results under different stability conditions considering the logarithmic evaporation duct profile are simulated and analyzed. And the minimum trapped frequencies of different evaporation duct heights under neutral conditions are obtained. Then, a new formula for computing minimum trapped frequency of evaporation duct is obtained by using the least square method. Considering the logarithmic modified refractive index profile, the new formula significantly reduces the prediction error of minimum trapped frequency compared with the integral calculation res ult.