Mult-wavelength radar performance modeling during an extreme clear air propagation event over the Persian Gulf

Non-standard radio frequency (RF) propagation extends for hundreds of kilometers over the water when surface ducts are formed due to offshore flow of warm and dry air over colder sea surfaces. Surface ducts are created when the vertical gradient of modified refractivity (dM/dz) is less than zero. The vertical gradient of M is dependent on the vertical gradient of potential temperature (dθ/dz) and the vertical gradient of water vapor mixing ratio (dw/dz) as shown in equation 1. Depending on temperature and relative humidity, the w gradient term can be two to six times the θ gradient term.