2003年7月3日夜間，五分山氣象雷達在臺灣海峽北部觀測到寬約100km、長約300km 且強度為45dBZ的線狀回波。它近似滯留在同一地區長達12小時以上。雷達影像之柱狀結構類似於對流系統的垂直結構，但其回波強度在垂直方向卻顯示出不連續性。此外，均勻的頻譜寬表示該區大氣環境是穩定的且沒有顯著的亂流存在。 這段期間，水平解析度5km的紅外線衛星並沒有觀測到這種長生命期且有組織的雲系。同樣現象的觀測，也無法在水平解析度5km的熱帶?雨觀測計畫的降水雷達(Precipitation Radar of Tropical Rainfall Measuring Mission, TRMM/PR)或是在水平解析度1km的中解析度影像光譜儀(Moderate-resolution Imaging Spectroradiometer, MODIS)等衛星中獲得。它們的觀測資料顯示臺灣地區當時是晴空無雲且沒降水。 依據美國環境預報中心每六小時之全球分析場(National Center of Environmental Prediction/Global Final Analysis, NCEP/FNL)，臺灣鄰近地區的對流可用位能(convective available potential energy, CAPE)值相當的微弱且屬於微弱沉降的天氣型態。就綜觀天氣的觀點而言，大氣環境是相當穩定的。此外，從分析場的大氣折射效應診斷中，臺灣地區確實有超折射層的存在。因此，大氣折射效應對雷達波偏折到海表面且造成異常回波扮演了生成機制。

During the night of July 3, 2003, a lone echo was detected in the Northern Taiwan Strait by weather radar at Wufensan showing the size of 100 km in width, 300 km length, and the maximum reflectivity intensity of 45 dBZ. Also, it stays there longer than 12 hours. The vertical column structures of radar image are similar to that f convective system, but it’s reflectivity intensity is not continuous vertically. In addition, the uniform radar spectrum width shows the stable environment over the Taiwan Strait without any significant turbulence. In this period, the infrared satellite cloud image with 5 km horizontal resolution does not observe such long-lived and organized cloud system. such phenomenon are also the same as those observed from the precipitation radar (PR) of tropical rainfall measuring mission (TRMM) and the moderate-resolution imaging spectroradiometer (MODIS), in which their horizontal resolutions are 10 and 1 km, respectively. Their retrieval data demonstrate the clear sky and no precipitation over Taiwan area. According to every six hour diagnostic analysis from National Center for Environment Prediction/Final Analysis (NCEP/FNL), the convective available potential energy (CAPE) is rather weak and the environment is under subsidence around Taiwan area. From the synoptic point of view, the atmosphere is stable. Besides, with the calculation of atmosphere refractivity index, it does show the super refraction layer around Taiwan. Therefore, the effect of atmospheric refraction plays the formation mechanism to force the radar wave bending to the sea surface and to cause such abnormal echoes.