Improvement to the Evaporation Duct Model by Introducing Nonlinear Similarity Functions in Stable Conditions

Modified refractivity (M) profile is an important parameter to describe the atmospheric refraction environment, as well as a key factor in uniquely evaluating electromagnetic propagation effects. In order to improve the model-derived M profile in stable (especially very stable) conditions, three nonlinear similarity functions, namely BH91, CB05, SHEBA07, are introduced in this paper to improve the original Babin_V25 model, and the performances of these modified models are verified based on the hydrometeorological observations from tower platforms, which are finally compared with the original Babin_V25 model and Local_HYQ92 model. Results show that introducing nonlinear similarity functions can significantly improve the model-derived M profile; especially, the newly developed SHEBA07 functions manage to reduce the predicted root mean square (rms) differences of M and M slope (for both 0–C5 m and 5–C40 m) by 64.5%, 16.6%, and 60.4%, respectively in stable conditions. Unfortunately, this improved method reacts little on the evaporation duct height; in contrast, Local_HYQ92 model is capable of reducing the predicted rms differences of M, M slope (for both 0–C5 m and 5–C40 m), and evaporation duct height by 76.7%, 40.2%, 83.7%, and 58.0% respectively. Finally, a new recommendation is made to apply Local_HYQ92 and Babin_SHEBA07 in very stable conditions considering that M slope is more important than evaporation duct height and absolute M value in uniquely determining electromagnetic propagation effects.