Ambient noise variation in the South Pole

Ambient noises are generated due to the interaction of atmosphere with the solid Earth and the noises which occur within the time period of 2-20s are known as microseisms. As the noise generation mechanism is not very well understood in the extreme climatic condition of Antarctic continent, in this study we target to understand the microseism generation in the South Pole station situated in the Antarctic continent. We have carried out our analysis using continuous data from IRIS data management center. Our main focus is to characterize the source direction of noise and their seasonal amplitude variations. We have employed the frequency dependent polarization analysis through the Eigen decomposition of the 3×3 spectral covariance matrix.

 The source of the noise have been analyzed using the backazimuth and time period for all the three bands of microseism, SPDF (short period double frequency), LPDF (long period double frequency), and PM (primary microseism). We observed that the noise is mainly due to the strong winds of Southern Ocean and some amounts of noise are also from the Ross Sea. In southern hemisphere, winter starts from May and it ends in August and also the number of polarized signals is lower in the winter season, and it is comparatively higher in the summer season. Additionally, when we plot Power spectral density against time period we see the splitting of the double frequency microseism into SPDF and LPDF which is only observed in the summer months and not in the winter months (only one single peak is observed).  Because, in the winter month’s sea ice concentration is extremely high in the South Pole; therefore, there is no significant wind interaction with sea waves of the coastal part which generates the SPDF. In winter, the continent is completely frozen; however, the amplitude of noise is high due to the strong winds. In summer, the noise is generated due to the low pressure systems develops in Southern Ocean which leads to cyclones in the Ross Sea. Antarctic circumpolar current also plays a significant role in the generation of noise. Therefore, we can conclude that the source of noise is from the Southern Ocean and Ross Sea. Also, we noticed the seasonal variation in the splitting of the double frequency microseism due to variation in the sea ice concentration.