Observed Mid-To-High Latitude Interchange of Atmospheric Angular Momentum and Some Implications

Details Observed Mid-To-High Latitude Interchange of Atmospheric Angular Momentum and Some Implications Observed Mid-To-High Latitude Interchange of Atmospheric Angular Momentum and Some Implications

Jun 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990em%26p...49..221t&link_type=abstract

Earth, Moon and Planets, Volume 49, Issue 3, pp.221-238

Computer Science

Scientific paper

The global distribution of atmospheric angular momentum (M) during 1977 1978 and 1982 1983 is examined to identify evidence of prominent short term interchanges of relative atmospheric momentum between mid and high latitude zones, in both hemispheres. Thirty day detrended angular momentum time series, prepared from the NMC gridded zonal wind data are examined in latitude bands. These data exhibit obvious quasi-coherent oscillations with periods near 30 days plus variations with shorter periods. An examination of latitude/altitude cross sections of zonal winds reveals that the oscillations are present almost simultaneously at all altitude levels between 1000 and 50 mb. Cross latitude teleconnections, evident as strong anticorrelated signatures between adjacent latitude bands are observed in the midlatitudes of both hemispheres. Comparison of these signatures with the time integrated flux of angular momentum across the nodal interface confirms that direct eddy transport of momentum is occurring. Transport of momentum from the mid latitude bands results in an increase in the momentum of the higher latitude bands and vice versa. Transport of planetary angular momentum by a Hadley/Ferrel type meridional circulation is specifically ruled out although that process may contribute to seasonal and longer term modulations. The short term oscillations in M can reach magnitudes which dominate the global variation in momentum, as noted in the recent 1982 83 El Niño episode in which the January 1983 momentum peaked at a decadal high. Similar “El-Niño like” changes in the trans-latitude momentum redistribution are observed in the Southern Hemisphere winters, following the Northern Hemisphere episode. Overall, our results confirm and describe in more detail the long recognized fact that momentum can be selectively redistributed between tropical, temperate, and high latitudes, in patterns indicative of the development and dissipation of interacting regions, described variously in studies of the ‘index cycle’, ‘seesaws’ and ‘teleconnections’. In emphasizing the large scale coordination of these interchanges, and moreover their occasional very short time scales, these results will hopefully stimulate studies relating atmospheric behavior in distant regions thereby contributing to improvements in forecasting the circulation process.

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