Height and time variability of planetary wave activity

Abstract

The height-season and year-to-year regularities of parameters of first and second spatial harmonics determine the structure of the stratosphere and mesosphere circulation and its variability. In the period 1992-2002 at heights 0-55 km, the amplitudes and phases of the first and second spatial harmonics in the field of temperature, geopotential height, zonal and meridional wind were calculated by the method of harmonic decomposition. Dispersion (standard or mean square deviation) of their day-to-day and year-to-year variations was calculated by their wavelength constants. Height and season patterns of variability have been estimated. The difference in height-longitude variability for wave numbers m = 1 and 2 has been discovered. At the same time, the intensity of wave disturbances for m = 1 is less than for m = 2 excluding the polar areas, where a significant variability appears at the heights 0-55 km. There is also a tendency for the intensity of year-to-year variations to decrease in comparison with day-to-day variations. In cold and warm periods the amplitude of perturbation waves with m = 2 both for day-to-day and year-to-year variations is greater than for waves with m = 1. Transient height areas in the interval of 20-30 km are more distinct for day-to-day variations of polar area. The mean square deviation (RMS) of the first harmonic of the zonal and meridional winds is less than that of the second harmonic and its year-to-year variability is less than day-to-day one. The amplitude of the first harmonic of zonal and meridional wind is higher than the amplitude of the second harmonic, and the day-to-day variability is greater than the year-to-year variability for the Northern hemisphere. The heterogeneous height and latitude structure is a characteristic of the year-to-year variation of the phase of the second harmonic. It could be caused by a non-steady state of the second harmonic. Crown Copyright © 2008.