I. Naito et al., Three-dimensional atmospheric angular momentum simulated by the Japan Meteorological Agency model for the period of 1955-1994, J METEO JPN, 78(2), 2000, pp. 111-122
Axial and equatorial atmospheric angular momentum (AAM) functions for the r
otational dynamics of the Earth are calculated monthly from ensemble mean d
ata of three independent 40-year simulations during 1955-1994 by the global
model of the Japan Meteorological Agency (JMA) forced by observed near-glo
bal sea surface temperature (SST) conditions. The model results are compare
d with those from the reanalysis data of the National Centers for Environme
ntal Prediction (NCEP) and the operational objective analysis data of JMA a
nd with the functions inferred from the observed length of day (LOD) and po
lar motion. The annual term of the simulated axial wind AAM function (dimen
sionless relative angular momentum of atmosphere due to zonal wind) during
1984-1994 agrees well with those from the two analysis data sets and roughl
y with the inferred function from LOD, while the semi-annual term is consid
erably over-estimated, suggesting an incompleteness in the simulated subtro
pical zonal winds. The annual term of the simulated equatorial pressure AAM
function (dimensionless atmospheric inertia products due to atmospheric ma
ss redistribution) is considerably over-estimated with respect to those fro
m the two analysis data sets, presumably due to the large simulated redistr
ibution of atmospheric mass between the Eurasian continent and the North Pa
cific Ocean. For interannual Variations during 1955-1994, only the axial wi
nd AAM function is reasonably simulated and shows good agreement with that
from NCEP data as well as the Southern Oscillation Index. The above results
lead to an understanding that the SST-forced AGCM simulates reasonably the
atmospheric axial modes exciting LOD change but not the equatorial (non-ax
ial) modes exciting the polar motion.