Observational evidence of quasi-27-day oscillation propagating from the lower atmosphere to the mesosphere over 20° N

• Published in: Annales geophysicae (1988) 2015-10, Vol.33 (10), p.1321-1330
• Main Authors: Huang, K. M., Liu, A. Z., Zhang, S. D., Yi, F., Huang, C. M., Gan, Q., Gong, Y., Zhang, Y. H., Wang, R.
• Format: Article
• Language: English
• Subjects: Amplitude; Amplitudes; Analysis; Antennas; Atmosphere; Computer centers; Convective activity; Decay; Fourier transforms; Gravitational waves; Humidity; Investigations; Long wave radiation; Lower atmosphere; Meridional wind; Mesosphere; Meteors & meteorites; NCEP/NCAR reanalysis; Observational studies; Outgoing long-wave radiation; Periodicity; Phase velocity; Planetary waves; Radar; Radiation; Radiosondes; Rossby waves; Satellite observation; Specific humidity; Spectral analysis; Spectrum analysis; Stratosphere; Tropical climate; Tropical environment; Tropical environments; Troposphere; Wavelengths; Wind; Wind shear; Zonal winds
• ISSN: 1432-0576; 0992-7689; 1432-0576
• DOI: 10.5194/angeo-33-1321-2015

By using meteor radar, radiosonde and satellite observations over 20° N and NCEP/NCAR reanalysis data during 81 days from 22 December 2004 to 12 March 2005, a quasi-27-day oscillation propagating from the troposphere to the mesosphere is reported. A pronounced 27-day periodicity is observed in the raw zonal wind from meteor radar. Spectral analysis shows that the oscillation also occurs in the meridional wind and temperature and propagates westward with wavenumber s = 1; thus the oscillation is of Rossby wave type. The oscillation attains a large amplitude of about 12 m s−1 in the eastward wind shear region of the troposphere. When the wind shear reverses, its amplitude rapidly decays, and the background wind gradually evolves to be westward. However, the oscillation can penetrate through the weak westward wind field due to its relatively large phase speed. After this, the oscillation restrengthens with its upward propagation and reaches about 20 m s−1 in the mesosphere. Reanalysis data show that the oscillation can propagate to the mid and high latitudes from the low latitudes and has large amplitudes over there. There is another interesting phenomenon that a quasi-46-day oscillation appears simultaneously in the troposphere, but it cannot penetrate through the westward wind field because of its smaller phase speed. In the observational interval, a quasi-27-day periodicity in outgoing long-wave radiation (OLR) and specific humidity is found in a latitudinal zone of 5–20° N. Thus the quasi-27-day oscillation may be an atmospheric response to forcing due to the convective activity with a period of about 27 days in the tropical region.