Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical...Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper：（1） great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;（2） westerly duct theory,which suggests a ＂corridor＂ through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;（3） energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;（4） equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and（5） meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.展开更多
Because of its potential applications in agriculture, environment monitoring and so on, wireless underground sensor network（WUSN） has been researched more and more extensively in recent years. The main and most impo...Because of its potential applications in agriculture, environment monitoring and so on, wireless underground sensor network（WUSN） has been researched more and more extensively in recent years. The main and most important difference of WUSN to terrestrial wireless sensor network（WSN） is the channel characteristics, which determines the design methodology of it. In this paper, the propagation character of electromagnetic（EM） wave in the near surface WUSN is analyzed, as well as the path loss model of it is given. In addition, the influence of human＇s ankle to the channel characteristics of near surface WUSN is investigated by electromagnetic theory analysis, simulation and experiment. A novel path loss model of near surface WUSN which takes the interference of human＇s ankle into consideration is proposed. It is verified that the existing of human above the WUSN system may cause additional attenuation to the signal of near surface WUSN which propagates as lateral wave along the ground. Moreover, the relation of the attenuation and operating frequency is deduced, which gives a reference to extend the frequency band applied in WUSN.展开更多
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2014CB953900)National Natural Science Foundation of China(41375081)+1 种基金LASW State Key Laboratory Special Fund(2013LASW-A05)China Meteorological Administration Special Public Welfare Research Fund(GYHY201406018)
文摘Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper：（1） great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;（2） westerly duct theory,which suggests a ＂corridor＂ through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;（3） energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;（4） equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and（5） meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.
基金supported by the National Natural Science Foundation of China(61001120)
文摘Because of its potential applications in agriculture, environment monitoring and so on, wireless underground sensor network（WUSN） has been researched more and more extensively in recent years. The main and most important difference of WUSN to terrestrial wireless sensor network（WSN） is the channel characteristics, which determines the design methodology of it. In this paper, the propagation character of electromagnetic（EM） wave in the near surface WUSN is analyzed, as well as the path loss model of it is given. In addition, the influence of human＇s ankle to the channel characteristics of near surface WUSN is investigated by electromagnetic theory analysis, simulation and experiment. A novel path loss model of near surface WUSN which takes the interference of human＇s ankle into consideration is proposed. It is verified that the existing of human above the WUSN system may cause additional attenuation to the signal of near surface WUSN which propagates as lateral wave along the ground. Moreover, the relation of the attenuation and operating frequency is deduced, which gives a reference to extend the frequency band applied in WUSN.
