An analysis of the structure and forcing semiannual oscillation in zonal wind

The low-frequency variability in the equatorial middle atmosphere is dominated by the semiannual oscillation (SAO) and quasi-biennial (QBO) oscillation. Although the general characteristics and forcing mechanisms of these oscillations are thought to be known, these oscillations are still not well reproduced in modeling experiments of the middle atmosphere. The relatively long period (1992-1996) of Upper Atmosphere Research Satellite (UARS) measurements and U.K. Meteorological Office (UKMO) assimilated model data have been used to examine the zonal wind SAO in the upper stratosphere. The SAO in zonal wind is found to be latitudinally asymmetric about the equator with strongest amplitudes in the southern hemisphere subtropics. The latitudinal asymmetry is diagnosed by using the TEM momentum equation and UKMO data. The asymmetry is mostly due to the different phasing of the peak advective forcing by the mean meridional circulation in each hemisphere. The contribution of gravity waves to the zonal wind SAO are also explored by using the forcing from a linear gravity wave model. Gravity waves are found to be the primary source of westerly momentum in each hemisphere during fall and contribute to the latitudinal asymmetry of the SAO by having more easterly forcing in the southern hemisphere during surmner compared to in the northern hemisphere during summer.

[1]  M. Alexander,et al.  Interpretations of observed climatological patterns in stratospheric gravity wave variance , 1998 .

[2]  Donald P. Delisi,et al.  Interaction of the quasi-biennial oscillation and stratopause , 1997 .

[3]  R. Garcia,et al.  The Role of Equatorial Waves Forced by Convection in the Tropical Semiannual Oscillation , 1997 .

[4]  K. Rosenlof,et al.  Nonstationary gravity wave forcing of the stratospheric zonal mean wind , 1996 .

[5]  Paul B. Hays,et al.  Measurements of stratospheric winds by the high resolution Doppler imager , 1996 .

[6]  L. Froidevaux,et al.  Residual Circulation in the Stratosphere and Lower Mesosphere as Diagnosed from Microwave Limb Sounder Data , 1996 .

[7]  L. Froidevaux,et al.  Equatorial Kelvin wave variability during 1992 and 1993 , 1995 .

[8]  K. Rosenlof.  Seasonal cycle of the residual mean meridional circulation in the stratosphere , 1995 .

[9]  L. Gray,et al.  Simulation of the semi‐annual oscillation of the equatorial middle atmosphere using the Extended UGAMP General Circulation Model , 1994 .

[10]  Paul B. Hays,et al.  High-Resolution Doppler Imager on the Upper Atmosphere Research Satellite , 1994, Optics & Photonics.

[11]  Richard Swinbank,et al.  Quasi-biennial and semi-annual oscillations in equatorial wind fields constructed by data assimilation , 1994 .

[12]  Richard Swinbank,et al.  A Stratosphere-Troposphere Data Assimilation System , 1994 .

[13]  R. Garcia,et al.  The stratopause semiannual oscillation in the NCAR Community Climate Model , 1993 .

[14]  T. Dunkerton.  Inertial Instability of Nonparallel Flow on an Equatorial , 1993 .

[15]  Paul B. Hays,et al.  The high-resolution Doppler imager on the Upper Atmosphere Research Satellite , 1993 .

[16]  J. Gille,et al.  Kelvin wave variability in the upper stratosphere observed in SBUV ozone data. [SBUV (solar backscatter ultraviolet)] , 1991 .

[17]  Kevin Hamilton,et al.  General Circulation Model Simulation of the Semiannual Oscillation of the Tropical Middle Atmosphere , 1988 .

[18]  C. Leovy,et al.  Estimation of the Kelvin Wave Contribution to the Semiannual oscillation. , 1988 .

[19]  G. Russell,et al.  The GISS Global Climate-Middle Atmosphere Model. Part I: Model Structure and Climatology , 1988 .

[20]  J. Gille,et al.  Quasi-Stationary Zonally Asymmetric Circulations in the Equatorial Lower Mesosphere , 1987 .

[21]  H. Kida.  A numerical experiment on the general circulation of the middle atmosphere with a three-dimensional model explicitly representing internal gravity waves and their breaking , 1984 .

[22]  J. Mahlman,et al.  Stratospheric and Mesospheric Kelvin Waves Simulated by the GFDL “SKYHI” General Circulation Model , 1984 .

[23]  J. Gille,et al.  Evidence for Equatorial Kelvin Modes in Nimbus-7 LIMS , 1984 .

[24]  J. Gregory.  Middle atmosphere dynamics , 1981, Nature.

[25]  T. Dunkerton.  On the Inertial Stability f the Equatorial Middle Atmosphere , 1981 .

[26]  Isamu Hirota,et al.  Equatorial Waves in the Upper Stratosphere and Mesosphere in Relation to the Semiannual Oscillation of the Zonal Wind , 1978 .

[27]  G. D. Nastrom,et al.  Periodic Variations in Stratospheric-Mesospheric Temperature from 20–65 km at 80°N to 30°S , 1975 .

[28]  R. H. Hopkins.  Evidence of Polar-Tropical Coupling in Upper Stratospheric Zonal Wind Anomalies , 1975 .

[29]  G. D. Nastrom,et al.  Periodic variations in stratospheric zonal wind from 20 to 65 km, at 80° N to 70° S , 1974 .

[30]  D. G. Dartt.  Semiannual Variation in Zonal Wind from 20 to 65 Kilometers , 1973 .

[31]  W. Meyer.  A Diagnostic Numerical Study of the Semiannual Variation of the Zonal Wind in the Tropical Stratosphere and Mesosphere , 1970 .

[32]  J. Angell,et al.  Quasi-biennial, annual, and semiannual zonal wind and temperature harmonic amplitudes and phases in the stratosphere and low mesosphere of the Northern Hemisphere , 1970 .

[33]  A. J. Miller,et al.  Note on the semi-annual wind variation in the equatorial stratosphere. , 1967 .

[34]  R. J. Reed.  Zonal wind behavior in the equatorial stratosphere and lower mesosphere , 1966 .

[35]  R. J. Reed.  The Quasi-Biennial Oscillation of the Atmosphere Between 30 and 50 km Over Ascension Island , 1965 .

[36]  J. Holton,et al.  A numerical model of the zonal mean circulation of the middle atmosphere , 1980 .

[37]  J. Holton.  The dynamic meteorology of the stratosphere and mesosphere , 1975 .

[38]  W. L. Webb.  Structure of the Stratosphere and Mesosphere , 1966 .