Interannual signals in length of day and atmospheric angular momentum
Atmospheric angular momentum (AAM) and length of day (LOD) series are investigated for their characteristics on interannual time scales during the half-century period 1949 to 1998. During this epoch, the interannual variability in LOD can be separated naturally into three bands: a quasi-biennial...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2000-03-01
|
| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/18/347/2000/angeo-18-347-2000.pdf |
| Summary: | Atmospheric angular momentum (AAM) and length
of day (LOD) series are investigated for their characteristics on interannual
time scales during the half-century period 1949 to 1998. During this epoch, the
interannual variability in LOD can be separated naturally into three bands: a
quasi-biennial, a triennial-quadrennial and one at six-seven years. The
atmosphere appears to excite the first two bands, while it does not contribute
to the last. Considering the quasi-biennial (QB) band alone, the atmosphere
appears to excite most of its signal in LOD, but it arises from separate
fluctuations with stratospheric and tropospheric origin. Thus, although close in
frequency, stratospheric and tropospheric processes differ in their amplitude
and phase variability. The time shift can be noted especially during the strong
El Niño events of 1982-83 and 1997-98 when both processes have positive phase
and thus combine to help produce particularly strong peak in AAM and LOD. In
addition, we have reconfirmed the downward propagation in the stratosphere and
upward propagation in the troposphere of AAM observed in earlier studies for
other variables. In the triennial-quadrennial (TQ) band, time-variable spectral
analyses reveal that LOD and AAM contain strong variability, with periods
shorter than four years before 1975 and longer thereafter. This signal
originates mainly within the troposphere and propagates upwards from the lower
to the higher layers of the troposphere. According to a zonal analysis, an
equatorial poleward mode, strongly linked to the SOI, explains more than 60% of
the total variability at these ranges. In addition, this study also indicates
that an equatorward mode, originating within polar latitudes, explains, on
average, more than 15% of the triennial-quadrennial oscillation (TQO)
variability in AAM, and up to 30% at certain epochs. Finally, a six year period
in LOD noted in earlier studies, as well as in lengthier series covering much of
the century, is found to be absent in atmospheric excitations, and it is thus
likely to arise from mantle/core interactions.<br><br><b>Key words: </b>Meteorology and atmospheric dynamics
(general circulation) - Solar physics, astrophysics and astronomy (celestial
mechanics) |
|---|---|
| ISSN: | 0992-7689 1432-0576 |