GFDL - Geophysical Fluid Dynamics Laboratory

An Observational Study of Intramonthly Quasi-Periodicities in the Northern Hemisphere, Extratropical Geopotential Height Field


Intramonthly quasi-periodicities (IQP’s) in the extratropical, cold season (November-March) tropospheric geopotential height data of the Northern Hemisphere were studied through the use of rotated complex principal components (RCPC’s). Heights at the 700 mb level, which span 36 years, were preprocessed using a 10-30 day bandpass filter prior to the RCPC analysis. Tests of rotation sensitivity and robustness (to the deletion of part of the sample) insured the stability of the RCPC analysis. A Monte Carlo procedure was used to objectively identify episodes of occurrence.

Composite maps which depict the evolution of the IQP’s over a typical lifecycle were found useful in interpreting their behavior. Three classes of IQP’s were found. The first class contains several modes which each involve a high latitude transient disturbance (zonal wavenumber 1 or 2) and a quasi-periodically oscillating standing wave. The distinction between the modes is mostly in the location of the standing wave pattern. The wavenumber 1 transient is probably the “16-day wave” or (1,3) Rossby normal mode which has been identified in the atmosphere by others. The second class consists of only one mode, an oscillating di-pole concentrated in the Atlantic sector, which is speculated to be the result of a regional, baroclinic zonal index cycle. The third class contains several distinct regional mid-latitude wave trains which to a large extent are progressive; the two most important are located over Eurasia and North America.

It is interesting that all of the modes have periods of about 16-18 days with a range of 13-22 days. Also, the vertical structures were found to be generally consistent with those of other studies of large-scale atmospheric motions. Vertical tilt was found to be large over the continents (especially central and eastern portions) while over the oceans the IQP’s were found to be nearly equivalent barotropic. Finally, about a third of the IQP’s were found to be associated with a particular low frequency state; these states are configured in the form of two well known atmospheric teleconnections patterns.

Lanzante, John Robert

Publication Date:

Record Format:
Theses/Dissertations Book

xii, 194 leaves : ill. ; 29 cm.

UMCP McKeldin Library
UMCP HBK Maryland Room

Call number:
LD3231.M70d Lanzante, J. R.

Dissertation note:
Thesis (Ph. D.)–University of Maryland, College Park, 1988.

Includes bibliographical references (leaves 188-194).

Atmospheric circulation — Northern Hemisphere.
Tropospheric circulation — Northern Hemisphere.