Characteristics of Electromagnetic Wave Ducts in Different Geographical Locations

Electromagnetic (EM) waves are used in communications and in remote sensing including weather radar. Environmental factors can affect how these waves travel through the atmosphere. The refractivity properties of a layer of atmosphere impact how much the EM wave bends as it traverses through the layer. The magnitude of refractivity is related to changes in temperature and moisture with height. A wave duct describes conditions where waves bend downward more than the curvature of the earth, allowing the waves to travel further than when a duct is not present.

To determine where and when wave ducts are present, we calculate modified refractivity from profiles of temperature and moisture from ~5 hPa vertical resolution upper air soundings archived at the National Centers for Environmental Information. This study compiles information from various regions around the world to look for patterns in the frequency, height, and strength of EM wave ducts from different times of the year and different times of the day. Most wave ducts are between 80 m and 250 m in thickness. Thinner wave ducts tend to have weaker strengths while thicker wave ducts have a wide range of duct strengths. This information will aid in improving understanding of how wave duct characteristics vary in different conditions.