关键词: 南极;甚低频波;准TE_1模

Abstract:

When the VLF signals from the stations located in the area of middle or low latitudes are travelling across the equator along the direction from northeast to southwest or from southeast to northwest,the TE wave is present by the coupling effect of the geomagnetic field Basing on the VLF phase observation in Antarctica, it is found that the TE, mode becomes the dominant mode during night time in the propagation direction from northeast to southwest at a long distance, and that for GBR signal(16 kHz)tho mode conversion interference produces a cycle slip during the sunrise transition at a distance of 13660.7 km far away from the transmitter. In this case, the mode conversion coefficient from the TM, mode into the TE, mode during the sunrise transition is estimated to be 0.28. The average depths of the diurnal phase variation trapezium of the 10.2 kHz signals from the stations B, C and D of the Omega navigation system are 135 μs, 138μs and 140 μs respectively. If only TM, mode was present during both day and night times, the calcu- lated values of the depths of the phase trapezium should be 97.4μs, 135μs and 137.6μs respectively. For the 10.2 kHz signal from the station B in the direction from northeast to southwest. If the TE, mode is dominant during nighttime at the receiver site, the calcula ted values of the depth of the phase trapezoid should be about 141.7Us, which is agreed basi cally with the measured value. Because the receiver is located in the polar region, the measured value is slightly less than the calculated value. For the diurnal phase variations of the 10.2 kHz signals from the stations G and E observed at the Xinxiang, It is found that the situation is similar. For the 10.2 kHz signals from the station G travelling across the equator along the direction from southeast to northwest, the TE, mode becomes dominant during the night time at the receiver site, Xinxiang. The calculated value of the depth of the phase trapezoid is about 147.6 us, which is agreed well with the measured value of 151 us. When the 16kHz signals from the station GBR was observed at the Great Wall Station Antarctica, the diurnal phase variation curves exhibits a notable interference pattern during the sunrise transition, sometimes the interference even could be so serious that a whole cycle slip was caused. For the reason of which we can explain from the following five aspects: (1) The period of mode conversion interference △t. (2) The distance from the sunrise line to the site where the first amplitude interference minimum occured. (3) The composition of the phase vector. (4) The calculation of the condition |E2|>|E1|. (5) The calculated values of the interference phase deviation θ and the amplitude ratio of the TEi and TMt modes |E2| / |E1|, resulted from the observed curves during 6 days successively. To sum up, the diurnal phase variation curves exhibit a notable mode conversion inter-ferencer pattern due to the interference between the quasi-TE1 mode and the quasi-TM1 mode during the sunrise transition, occasionally the interference causes a whole cycle slip. Under the condition, the mode conversion coefficient from the TM1 mode into theTE, mode during the sunrise transition is estimated to be 0.28.