Type: Journal Article
Venue: Journal of Geophysical Research
Gutzler, D.S., and R.M. Ponte, 1990. Exchange of momentum exchange among atmosphere, ocean, and solid earth associated with the Madden-Julian oscillation. Journal of Geophysical Research, 95, 18679-18686.
We investigate coherences among time series of tropical zonal winds, total atmospheric angular momentum (M), the length of day of Earth rotation (LOD), and near‐equatorial sea level, all of which exhibit a broad intraseasonal spectral density peak. We seek to ascertain how the wavy, eastward propagating “40–50 day” or “Madden‐Julian” oscillation (MJO) in near‐equatorial zonal winds is related to intraseasonal fluctuations of the zonally averaged zonal wind in the tropics [u] and global momentum M. It is found that 40–50 day upper tropospheric zonal wind fluctuations at western Pacific stations (where the MJO signal is pronounced) are mostly incoherent with fluctuations of M and [u] in the tropics, but lower tropospheric fluctuations at the same stations are significantly coherent. The observed phase lags between variations of near‐surface wind and M are consistent with the hypothesis that fluctuations of surface stress on the Pacific Ocean associated with the MJO are the primary agent for deposition and removal of momentum into and out of the atmosphere. We then examine whether equatorial sea level variability at the South American coast represents a continental torque coupling the ocean and solid Earth on the 40–50 day time scale, thereby accounting for the high coherence observed between M and LOD. Coherence between sea level and LOD is not significant, however, suggesting that oceanic baroclinic wave activity, which is the primary cause of 40–50 day sea level fluctuations, does not contribute significantly to the exchange of momentum between the ocean and solid Earth. On the other hand, the results support the conjecture that barotropic ocean waves provide the required transport and exchange of momentum, and the potential importance of such waves is briefly discussed.