Abstract
Evaporation duct is a layer above the ocean surface due to the inherent humidity inversion at the air-sea boundary layer. The formation of the duct depends on meteorological factors near the ocean surface and is affected by weather process above the ocean. The presence of this duct can have profound effects on over-water electromagnetic propagation at microwave bands. However, the information on evaporation duct features during the period of typhoon is limited. Here we show the impact of a typhoon on evaporation duct using the typhoon Parpiroon occurred in 2012 as an example. It is very interesting to find that there is an “evaporation duct eye” with very low evaporation duct height in the eye of typhoon. The trajectory of the typhoon center is almost consistent with that of the evaporation duct height minimum center during the typhoon Parpiroon. This is also confirmed by 19 more typhoons over northwest Pacific Ocean in 2018. Furthermore, we found that the low wind speed in the typhoon center is the primary cause of this interesting phenomenon. Our results demonstrate the characteristics of evaporation duct distribution during the typhoon process and illustrate the correlation between typhoon trajectory and evaporation duct height minimum center trajectory.
Highlights
Evaporation ducts are formed due to the inherent humidity inversion at air-sea boundary
The National Centers for Environmental Prediction (NCEP) Climate Forecast System Version 2 (CFSV2) dataset during typhoon Prapiroon was obtained from the Computational and Information Systems Laboratory (CISL) Research Data Achieve managed by National Center for Atmospheric Research (NCAR)’s data support section
The physical principle of this interesting phenomenon was illustrated based on the evaporation duct model and it is found that the low wind speed in the typhoon center is the primary cause
Summary
Evaporation ducts are formed due to the inherent humidity inversion at air-sea boundary. The air in contact with the sea is saturated with water vapor and the water vapor decreases approximately as a logarithmic function of height, creating an evaporation duct structure [1], [2]. Evaporation ducts impact electromagnetic propagation significantly at microwave frequencies greater than 0.5 GHz [3]. The trapping layer of an evaporation duct behaves like a waveguide and can lead to decreased propagation loss at microwave frequencies and an extended radar detection range [4]–[7]. The height at which a radio wave’s curvature equals the Earth curvature is defined as the evaporation duct height (EDH) [8], [9].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
