Phase error sensitivity to the inversion strength and depth of the boundary layer in a conventionally neutral regime.

In outdoor sound propagation, the variation of wind speed with height plays an important role and a logarithmic profile is often assumed. This is an accurate description in a neutral boundary layer according to MOST. However, the neutral boundary layer can be either truly neutral or conventionally neutral depending on the stability condition at the top of the ABL. While the logarithmic profile is suitable in a truly neutral regime, the conventionally neutral is more commonly found. This regime is characterized by a stable stratification aloft that result in super geostrophic wind speed close to the top of the ABL and higher speed and steeper gradient close to the ground than predicted by the logarithmic profile. This work uses numerical simulations based on the Crank-Nicholson parabolic equation to derive the sensitivity of the phase to the ABL depth and inversion strength as a function of the distance from the source. The results show that a stronger inversion increases the phase differences that can be as large as 60^◦ already at 1 km from the source. Stronger inversions and a deeper ABL produce more complex interference on the ground, showing only after approximately 2 km, that affect both phase and magnitude.