Madden – Julian oscillations over a tropical Indian station using radar and ERA data of winds

Abstract

The Madden – Julian oscillation (MJO) activity over Gadanki (13.5°N, 79.2°E), a low latitude station is examined using four years MST radar data of winds (4 – 20 km) between January 2006 and December 2009. Wind data obtained from European Centre for Medium Range Weather Forecasting (ECWMF) Re-Analysis (ERA) for the same latitude – longitude and for the same period have also been used to study the wave activity in the same altitude region. MJO in two period bands, 4-7 weeks and 10-13 weeks, could be clearly identified with amplitudes of ~ 4 ms^-1 in zonal wind. Meridional winds also showed similar oscillations but with lesser amplitudes (~ 2.5 ms^-1). Fast Fourier Transform (FFT) analyses were performed on yearly data sets and very clear inter-annual variability of the oscillations is found. Wavelet analyses were carried out to find the temporal variation of the oscillations. The results obtained using radar and ERA data are found to be in good agreement. Outgoing longwave radiation (OLR) data is also used to study the relation between convection and MJO activity. A significant correlation is not observed between convection and MJO activity.