10:45 AM - 12:15 PM
[AAS02-P01] Research on the physical mechanism of the marine boundary layer and the distribution of atmospheric duct height
Keywords:Atmospheric duct, Evaporation duct, Over-The-Horizontal radar, WRF model, PJ model, Radio occultation
Atmospheric duct effect is the main reason for long-range detection of over-the-horizon (OTH) radar, whether it is an evaporation duct that occurs in the ocean or an elevated duct that occurs at high altitude, it may make electromagnetic waves propagate farther distances with smaller path loss, to achieve the purpose of beyond visual range. Besides, the atmospheric duct effect has affected by atmospheric boundary layer parameters greatly. Therefore, how to predict the atmospheric environment effectively will be the key to the operation of the OTH radar. In addition, it is difficult to obtain real time atmospheric profile due to ships performing missions at sea, so U.S. navy has developed P-J model that can estimate the parameters of the evaporation duct based on the ship’s meteorological observation data. However, if this model needs to be used to the sea around Taiwan, some testing and validation are required to meet the actual situation.
In this study, the offshore buoys and the sounding data of UAV and FORMOSAT-7 were been used to calculate seasonal characteristics of atmospheric ducts in the offshore sea around Taiwan. The results shows that the evaporation duct height in the southeastern sea area is higher in autumn and winter, and the average value is slightly higher than that in other sea areas. Although the inversion method of FORMOSAT-7 get high accuracy profiles of air pressure and temperature, it were not good for the low-level water vapor pressure profile, and the inversion of modified refractive index profile (M-profile) cannot interpret the duct. Furthermore, we use UAV with “storm tracker” (an ultra-lightweight radiosonde) to collect atmospheric boundary layer parameters offshore, and find that the evaporation duct occur probability reach up to 90% during 15th to 18th August 2022. We also find the water vapor pressure profile has a sharp change below 40 meters, which is consistent with the change trend of the M-profile when duct occur. Finally, we compared the duct height which simulated by P-J model with the UAV measured value, and find that when the air temperature near the sea is lower than the sea temperature, it is roughly close (RMSE is 5.9). It also shows that when high-level temperature inversion occurs, the simulated duct height will much smaller than measured value because of the environment is not conducive to the vertical mixing of water vapor.
In this study, the offshore buoys and the sounding data of UAV and FORMOSAT-7 were been used to calculate seasonal characteristics of atmospheric ducts in the offshore sea around Taiwan. The results shows that the evaporation duct height in the southeastern sea area is higher in autumn and winter, and the average value is slightly higher than that in other sea areas. Although the inversion method of FORMOSAT-7 get high accuracy profiles of air pressure and temperature, it were not good for the low-level water vapor pressure profile, and the inversion of modified refractive index profile (M-profile) cannot interpret the duct. Furthermore, we use UAV with “storm tracker” (an ultra-lightweight radiosonde) to collect atmospheric boundary layer parameters offshore, and find that the evaporation duct occur probability reach up to 90% during 15th to 18th August 2022. We also find the water vapor pressure profile has a sharp change below 40 meters, which is consistent with the change trend of the M-profile when duct occur. Finally, we compared the duct height which simulated by P-J model with the UAV measured value, and find that when the air temperature near the sea is lower than the sea temperature, it is roughly close (RMSE is 5.9). It also shows that when high-level temperature inversion occurs, the simulated duct height will much smaller than measured value because of the environment is not conducive to the vertical mixing of water vapor.