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Nonmigrating diurnal tides in the thermosphere

Nonmigrating diurnal tides in the thermosphere. R. S. Lieberman, Colorado Research Associates Division, Northwest Research Associates J. Oberheide, Clemson University E. R. Talaat, Johns Hopkins University. Many thermospheric and ionospheric parameters exhibit longitudinal variability.

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Nonmigrating diurnal tides in the thermosphere

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  1. Nonmigrating diurnal tides in the thermosphere R. S. Lieberman, Colorado Research Associates Division, Northwest Research Associates J. Oberheide, Clemson University E. R. Talaat, Johns Hopkins University

  2. Many thermospheric and ionospheric parameters exhibit longitudinal variability. • Equatorial ionization anomaly: Sagawa et al., 2005. • Equatorial electrojet: Luhr et al., 2008. • O+ airglow: England et al., 2006. • Electron density: Lin et al., 2007. • Total electron content: Scherliess et al., 2008.

  3. These observations have fueled interest in nonmigrating tides in the F-region. Immel et al. (2006) and Hagan et al. (2009) have examined modulation of electric fields by nonmigrating diurnal tides in the LT. Several studies have examined direct propagation of tides into F-region using numerical models (Hagan et al., 2007)…. …and “Hough mode extensions” that in effect extrapolate MLT tidal determinations to higher altitudes (Svoboda, 2005; Hausler et al., 2009; Oberheide et al., 2009).

  4. Thermospheric nonmigrating tides have been identified in CHAMP accelerometer winds near 400 km (Hausler and Luhr, 2009). However, very few direct measurements of nonmigrating diurnal tides between 120-400 km have been presented. The purpose of this study is to infer nonmigrating diurnal tides between 120-250 km from UARS WINDII global wind measurements (1992-1997).

  5. Upper Atmosphere Research Satellite Wind imaging interferometer (WINDII) measured daytime V between 90-270 km from the phase shifts of O emissions near 557.7 nm (“green line”), and 630.0 nm (“red line”). Nighttime emissions occur between 90-110 km, and above 200 km (Shepherd et al., 1993; Gault et al., 1996). This study uses wind data between 1992-1997, binned in longitude, latitude, altitude, local time and season. We also show retrievals from UARS high resolution Doppler imager (HRDI) as a reality check (Hays et al., 1993).

  6. Sampling and Analysis Most WINDII altitudes are sampled only during daytime (nighttime winds between 90-110 km and above 200 km). Space-time spectral analysis is therefore not feasible for tidal studies (due to undersampling in local time). Instead, we infer tides from the longitudinal variations. Diurnal m observed by UARS as m-1if westward-propagating and m+1if eastward-propagating. Ex: Eastward diurnal wave 3 viewed as ks = 4. Westward diurnal wave 0 viewed as ks = 1.

  7. WINDII daytime wind Talaat and Lieberman (2010) identified 4-peaked structures in longitude at the equator that alternated sign over 12 hours. These were interpreted as DE3. Longitude Longitude Talaat and Lieberman (2010)

  8. 12-hour differences in eq. U emphasize diurnal tides Longitude Longitude 17-7 LT U difference (SON) Wave 4 component

  9. Wave 1 also present at the eq. Longitude Longitude 17-7 LT U difference SON (zonal mean removed). Wave 1 component

  10. Lat-ht wave 1 Symmetry in wave-1 U about the equator is accompanied by a strong and largely antisymmetric pattern in V.

  11. Deconvolution Diurnal m observed by satellites as m-1if westward-propagating and m+1if eastward-propagating. Working backward: Observed zonal wave 1 corresponds to diurnal westward 2 and/or s = 0 (zonal mean). Observed zonal wave 4 corresponds to diurnal westward 5 and/or eastwards = 3. Deconvolution methods of Oberheide et al. (2002) are applied to vertical structures in order to partition signal among the aliased components.

  12. DE3 dominates the satellite-viewed wave 4 pattern 17-7 LT U difference U wave 3 at 17 LT

  13. Consistency with HRDI 17-7 LT U difference U wave 3 at 17 LT

  14. Wave-1 pattern in thermosphere represents aliased DS0. 17-7 LT U difference U wave 0 at 17 LT

  15. Lat-ht wave 0 V 17-7 V difference V wave 0 at 17 LT

  16. DW2 and S0 are consistent with HRDI in DJF 17-7 LT V difference V wave 0 at 17 LT V wave 2 at 17 LT

  17. Summary Nonmigrating diurnal tides appear in daytime and nighttime WINDII winds, and are emphasized in 10-hour difference patterns. Deconvolution analysis indicates that DE3 and DS0 are prominent in the thermosphere, up to ~200 km. For the leading diurnal waves, WINDII is generally consistent with HRDI data at, as evidenced by continuity at 100 km.

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