GFDL - Geophysical Fluid Dynamics Laboratory

Publication 8502

Lanzante, J., 1985: Further studies of singularities associated with the
semiannual cycle of 700 mb heights.
Mon. Wea. Rev., 113, 1372-1378.


An investigation of singularities associated with the semiannual cycle
of Northern Hemisphere (25-90oN) 700 mb heights was conducted
using 33 years of data. Extension of the harmonic analyses of Lanzante (1983)
to a larger domain revealed the considerable importance of the semiannual
cycle to the seasonal progression of heights over subtropical Asia; this is
undoubtedly a reflection of the Asiatic monsoon. From a global perspective,
the semiannual cycle varies in such a fashion that this Asiatic region is
out of phase with a region stretching from northeastern Siberia to the Gulf
of Alaska, as well as the subtropical Atlantic and eastern Pacific.
Furthermore, it is suggested that the semiannual cycle is reflected
regionally in the persistence of height anomalies as reported by van den Dool
and Livezey (1984).

Indices for nine regions of relatively large explained variance and uniform
phase angle of the second harmonic of heights were derived in order to
quantify interannual variations in the semiannual cycle. Frequency
distributions of parameters, based on 25-day and seasonal aggregates of the
daily indices were found to be largely Gaussian. It is concluded that (for
the time averages considered) there is no indication that the indices come
from two populations representing either the occurrence or nonoccurrence of
an amplified semiannual cycle. Finally, interannual relationships among the
nine indices were investigated through auto- and cross-correlation analyses;
the results were largely negative.