Strong vertical thermodynamic gradients in the atmospheric boundary layer produce non-standard refractivity gradients that significantly impact the performance of radio frequency systems. The four dimensional nature of surface layers, mixing layers, entrainment layers, and internal layers lead to corresponding four dimensional engineering demands on Navy radar and communication systems. This seminar will describe, through measurements and mesoscale numerical weather prediction modeling, the relationship between refractivity and atmospheric boundary layer structures. The resulting engineering impacts will be briefly demonstrated.