An evaporation duct prediction model coupled with the MM5
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An evaporation duct prediction model coupled with the MM5 JIAO Lin1*, ZHANG Yonggang1 1 Department of Military Oceanography, Dalian Naval Academy, Dalian 116018, China
Received 31 March 2014; accepted 26 January 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2015
Abstract
Evaporation duct is an abnormal refractive phenomenon in the marine atmosphere boundary layer. It has been generally accepted that the evaporation duct prominently affects the performance of the electronic equipment over the sea because of its wide distribution and frequent occurrence. It has become a research focus of the navies all over the world. At present, the diagnostic models of the evaporation duct are all based on the Monin-Obukhov similarity theory, with only differences in the flux and character scale calculations in the surface layer. These models are applicable to the stationary and uniform open sea areas without considering the alongshore effect. This paper introduces the nonlinear factor av and the gust wind item wg into the Babin model, and thus extends the evaporation duct diagnostic model to the offshore area under extremely low wind speed. In addition, an evaporation duct prediction model is designed and coupled with the fifth generation mesoscale model (MM5). The tower observational data and radar data at the Pingtan island of Fujian Province on May 25–26, 2002 were used to validate the forecast results. The outputs of the prediction model agree with the observations from 0 to 48 h. The relative error of the predicted evaporation duct height is 19.3% and the prediction results are consistent with the radar detection. Key words: evaporation duct diagnosis, mesoscale model (MM5), evaporation duct prediction model, numerical simulation Citation: Jiao Lin, Zhang Yonggang. 2015. An evaporation duct prediction model coupled with the MM5. Acta Oceanologica Sinica, 34(5): 46–50, doi: 10.1007/s13131-015-0666-z
1 Introduction Evaporation duct is a kind of abnormal refractive structure in marine boundary layer; it affects the propagation of electromagnetic wave on the sea. The study shows that the propagation characteristics of electromagnetic wave will be changed and the distribution of propagation energy will be changed and the propagation path will be bended in the evaporation duct. Part of electromagnetic wave will be trapped into the duct layer and forms the over–horizon propagation. Because of the turbulent characteristics in marine boundary layer, the instantaneous value of meteorological element is difficult to measure. As a result, it is not recommended to adopt the method of building the profile of the atmospheric refractive index to determine the evaporation duct height. Based on similarity theory in the surface layer, the macroscopic measurement method of the hydrological and meteorological elements is used to calculate the evaporation duct height. However, due to the lack of initial field data and vertical resolution in the past weather forecasting model, whose output of the bottom level is
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