Spectral analysis of wind field in the Indian Ocean

摘要

To study the variability in wind fields over the Indian Ocean, we used ERA INTERIM daily winds for the period 1979-2012. In order to analyse the temporal variation of wind field, we partitioned the whole Indian Ocean into 6 zones based on spatial inhomogeneity in the analysed wind fields. Spectral analysis of the time series (extracted at the centre of each zone) was performed using the auto-regression analysis based on the Yule-Walker equations. and it confirms that universality of the spectral shaps Frequency spectra show distinct annual variations at all zones; semi-annual variations are observed in the Arabian Sea (Z1) and the Bay of Bengal (Z2) due to the seasonal changes and gradually it disappears from equatorial region (Z3) to southern Indian Ocean (Z6). Also, we observe local maxima at the scale of 1 and 0.5 days(-1). The characteristic shape of the spectrum was obtained at two different powers of the frequencies. Decay rate and variance at all zones are analysed. The decay rate varies almost linearly as a function of zones Z1 to Z6. Trend of the variance in low frequency range is linear whereas, in high frequency range is exponential. The variance is large in the storm track region. It is found that over the range of frequencies, wind field is independent and is increasing along the zones Z1 to Z6. Latitudinal dependency is clearly observed in both spectral slopes and variances.