QBO (Quasi-Biennial Oscillation) Part II
QBO (Quasi-biennial Oscillation)
Analysis and Reconstructed Codes by Sandro Lubis
Graduate Student of Leipzig Institute for Meteorology, University of Leipzig, Germany
Figure 1. Amplitude Spectrum and FFT Phase of QBO (Lubis, 2011)
Data: 1948-2011 NCEP Reanalysis I.
QBO or Quasi-Biennial Oscillation is indicated by zonally symmetric easterly and westerly wind regimes alternating regularly with periods varying from about 24-30 months in the equator. A simple analysis was conducted, zonal wind data from NCEP/NCAR Reanalysis [I] were directly used in order to identify the existence of QBO in the lower middle atmosphere during last decade (1948-2011). The chosen grid was located near the equator at 100 E and 2.5 N. The vertical average of zonal wind were computed due to an indication of the existence of QBO at 10-70 hPa. This result is consistent with previous studies (Dunkerton, 2003) show that alternating downward propagating westerly and easterly (E) regimes appear around the height of 10-70 hPa layer. Spectral analysis was applied to the average of zonal wind (10- 70hPa) from 1998-2010 giving the result that that the peak of spectral density is observed around 0.03-0.04 Hz month/cycle in other words the period of QBO cycle is obviously detected around 28 month/cycle. A 28 month/cycle is indicated by the max peak of amplitude as shown in figure. The maximum amplitude of QBO is 6.6 m/s and phase angle exceeds 160. The result of this spectral is realistic if it’s compared to the early study pointing out that QBO is associated to the alternating wind regimes repeating at intervals 22 to 34months, with an average period of slightly more than 28months (Baldwin et al., 2001, Holton and Matsuno 1984).
Figure 2. Zonal wind of QBO in period of 1948-2011 from NCEP/NCAR Reanalysis [I]
-Sandro Lubis, Graduate student in Department of Meteorology, University of Leipzig, Germany, Germany 2011-