Modifiedrefractivity(M)profileisanimportantparametertodescribetheatmosphericrefractionenvironment,aswellasakeyfactorinuniquelyevaluatingelectromagneticpropagationeffects.Inordertoimprovethemodel-derivedMprofileinstable(especiallyverystable)conditions,threenonlinearsimilarityfunctions,namelyBH91,CB05,SHEBA07,areintroducedinthispapertoimprovetheoriginalBabin_V25model,andtheperformancesofthesemodifiedmodelsareverifiedbasedonthehydrometeorologicalobservationsfromtowerplatforms,whicharefinallycomparedwiththeoriginalBabin_V25modelandLocal_HYQ92model.Resultsshowthatintroducingnonlinearsimilarityfunctionscansignificantlyimprovethemodel-derivedMprofile;especially,thenewlydevelopedSHEBA07functionsmanagetoreducethepredictedrootmeansquare(rms)differencesofMandMslope(forboth0-5mand5-40m)by64.5%,16.6%,and60.4%,respectivelyinstableconditions.Unfortunately,thisimprovedmethodreactslittleontheevaporationductheight;incontrast,Local_HYQ92modeliscapableofreducingthepredictedrmsdifferencesofM,Mslope(forboth0-5mand5-40m),andevaporationductheightby76.7%,40.2%,83.7%,and58.0%respectively.Finally,anewrecommendationismadetoapplyLocal_HYQ92andBabin_SHEBA07inverystableconditionsconsideringthatMslopeismoreimportantthanevaporationductheightandabsoluteMvalueinuniquelydeterminingelectromagneticpropagationeffects.
