Barnston, A. G., 1996: Time-scales
of the variability of the atmosphere. International Journal of Climatology,
16, 499-535.
In this study the time-scales of variability of several weather elements
are explored by season and location across the globe, emphasizing the Northem
Hemisphere and especially the USA. The resulting description is useful
because regions that exhibit low frequency variability (i.e. longer periods
than the 2-5 days synoptic-scale) are assumed to be related more directly
to changes in boundary conditions (e.g. anomalies of ENSO-related sea-surface
temperature [SST], snow cover, etc.). Therefore, this low frequency variability
may be predictable at greater ranges than those for which numerical weather
prediction is helpful. New as well as established measures of persistence
and frequency dependence are used and intercompared. In particular, the
standard deviation of the differences between adjacent period means, when
compared over a range of period lengths, reflects both autocorrelation
and (if applicable) cycle time. Frequency dependence is thereby summarized
with minimal computation. The geographical distribution of the amplitude
(amount of variability depends largely on latitude) and the upstream geographical
environment (i.e. higher latitude and continentality of upstream environment
tend to increase variability). At most locations, variability is greatest
(lowest) during the cold (warm) seasons of the year. The geographical distribution
of the dominant frequencies of variability are examined by season for Northern
Hemisphere sea-level pressure and 700 hPa geopotential height, and USA
surface temperature and precipitation. It is demonstrated that the dominant
frequencies tend to vary in parallel across all four fields. In general,
weather variables are found to vary at relatively low frequency (long periods)
at high latitudes and, to a lesser extent, at subtropical latitudes. At
mid-latitude, low frequency variability prevails most over the blocking
regions in the eastern and central North Pacific and North Atlantic oceans.
High frequency variability occurs in the synoptically active jet exit regions
over the western oceans and the eastern and central parts of the Northern
Hemisphere continents. Data from the Atmospheric Model Intercomparison
Project integration of the National Centers for Environmental Prediction
(formerly National Meteorological Center) medium-range-forecast general
circulation model, which reproduce the Northern Hemisphere frequency dependence
well at 700 hPa, indicate roughly analogous behaviour in the Southern Hemisphere.
However, the longitudinal variation of mid-latitude frequency dependence
is substantially less in the Southern Hemisphere, possibly because of the
comparative absence of large, topographically significant land masses with
favourable separation distance. KEY WORDS: USA; Northern Hemisphere; fast
Fourier transform; autocorrelation; temporal variability scales. empirical
modelling of variability; surface temperatures; 700 hPa height.