Impact of Typhoon on Evaporation Duct in the Northwest Pacific Ocean

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.