北极地区海雾数值模拟及其电波衰减研究

Numerical simulation of Arctic sea fog and radio wave attenuation

北极地区气候恶劣,但提供了北美洲、欧洲北部和亚洲北部国家之间最短交通往来路径,因此具有重要的战略地位。北极航行需要气象、导航、通讯、雷达等方面的保障,北极海雾降低了海上能见度,会使航行船只迷失方向造成搁浅、碰撞等重大事故,并引发大气波导超视距、毫米波严重衰减等电波传播现象。本文根据全球再分析数据,基于适合北极地区的中尺度大气数值模式,通过改进Noah陆面过程方案、长波辐射方案(RRTMG方案)等设置,成功模拟了我国第四次北极考察期间在北冰洋遇见的某次浓雾及其演变发展,并基于米氏(Mie)散射和瑞利(Rayleigh)散射理论评估了其对毫米波和远红外波段上的单位距离衰减值。对于毫米波段两代表频率(频段高低端100 GHz和30 GHz),在频率30 GHz,单位距离衰减值随海雾含水量增大逐渐增大,但变化平缓;在频率100 GHz,单位距离衰减值随海雾含水量增大迅速增大。对于红外波段两代表波长(波段高低端0.1 cm和50μm),在波长0.1 cm,单位距离衰减值随海雾含水量逐渐增大但变化平缓;在波长50μm,衰减值随海雾含水量增大迅速增大,单位距离衰减值可迅速增大到几百dB·km^(-1),两波长的衰减值相差很大。对于相同液态含水量雾区的单位距离衰减值来说,远红外衰减值远远大于毫米波衰减值,毫米波频段高低端和红外波段波长最高端0.1 cm衰减值一般在几dB以下,而红外波段波长最低端50μm衰减值在几百dB,与其他波段相比单位距离衰减值甚大,Polar WRF模式能够模拟获取较准确的北极海雾特性,也能够用于评估北极海雾对电磁波传播衰减以及对无线电信息系统特性的时空影响。

The Arctic region has a harsh climate and an important strategic location.The shortest straight distance between countries in North America,northern Europe and northern Asia is the path through the Arctic.Meteorological,navigation,communication,radar and other support are needed during the Arctic cruises.Arctic sea fog,which reduces the visibility at sea,can cause ships to lose their routes resulting in serious accidents such as grounding and collision.Sea fog can also cause radiowave propagation phenomena,such as atmospheric ducting over the horizon and serious attenuation of millimeter waves.Using the global reanalysis data,based on the mesoscale atmospheric numerical model suitable for the Arctic region,this paper successfully simulated the Arctic fog and its evolution and development encountered in the 4th Chinese National Arctic Research Expedition in the Arctic Ocean by improving the Noah land surface process scheme,the long wave radiation scheme(RRTMG scheme)and other settings.Based on Mie scattering theory and Rayleigh scattering theory,the unit distance attenuation values for millimeter wave and far infrared band were evaluated.For the two representative frequencies in the millimeter wave band(100 GHz and 30 GHz at the high and low ends of the frequency band),the attenuation value increased gradually with the water content of sea fog at the 30 GHz,but the change was gentle.At 100 GHz,the attenuation value increased rapidly with the water content of sea fog.For the two representative wavelengths of the infrared band(0.1 cm and 50μm at the high and low ends of the band),the attenuation value increased gradually with the water content of sea fog at the wavelength of 0.1 cm,but the change was slow.At the wavelength of 50μm,the attenuation value increased rapidly to hundreds of dB·km^(-1) with the water content of sea fog.The attenuation values of the two wavelengths differed greatly.For the same water content fog area,the far infrared attenuation value per kilometer was far greater than that of the millimeter wave.The attenuation values of high and low end of the millimeter wave band and at the highest end of the infrared wave band(0.1 cm)were generally less than a few tens of dB·km^(-1),while the attenuation value at 50μm,the lowest end of the infrared wave band,was several hundred dB·km^(-1),which was much larger than other bands.The Polar WRF model can simulate and obtain more accurate characteristics of Arctic sea fog.The model can also be used to evaluate the spatial and temporal effects of Arctic sea fog on electromagnetic wave propagation attenuation and radio information system characteristics.