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Nonmigrating diurnal tides in the thermosphere

Nonmigrating diurnal tides in the thermosphere. R. S. Lieberman 1 E. R. Talaat 2 J. Oberheide 3 D. Riggin 1. 1 Northwest Research Associates, Inc., Colorado Research Associates 2 Johns Hopkins University, Applied Physics Lab 3 University of Wuppertal.

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Nonmigrating diurnal tides in the thermosphere

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  1. Nonmigrating diurnal tides in the thermosphere R. S. Lieberman1E. R. Talaat2J. Oberheide3D. Riggin1 1Northwest Research Associates, Inc., Colorado Research Associates2Johns Hopkins University, Applied Physics Lab3University of Wuppertal

  2. Many thermospheric and ionospheric parameters exhibit a 4-peaked structure in longitude. 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. Modulation of electric fields by upward-propagating nonmigrating diurnal tides has been suggested as an explanation (Immel et al., 2006, Hagan et al., 2009).

  3. Nonmigrating diurnal tides have been observed in many mesospheric and lower thermospheric datasets. UARS/HRDI V and T: Talaat and Lieberman (1999), Forbes et al. (2003). TIMED/SABER T: Zhang et al. (2006). TIMED/TIDI V: Oberheide et al. (2006), Wu et al. (2008). SNOE NO: Oberheide and Forbes (2008). In the thermosphere, diurnal tides have been identified in CHAMP accelerometer measurements near 400 km (Hausler and Luhr, 2009).

  4. Although the interaction between neutral wind tides and electrodynamics is unclear, many studies argue for a direct connection between tropospheric tidal sources, MLT tides, and F-region perturbations.These arguments have been based upon modeling studies of tidal generation and vertical propagation (Hagan et al., 2007; Hausler et al., 2009; Oberheide et al., 2009), and application of “extended Hough modes” (Svoboda, 2007) that in effect extrapolate MLT tidal determinations to higher altitudes. However, no direct global measurements of nonmigrating diurnal tides between 120-400 km have been presented.

  5. The purpose of this study is to infer nonmigrating diurnal tides between 60-250 km from global wind measurements. Nonmigrating tidal sources Data Sampling issues and data analysis DE2, DE3, DS0 and DW2. Comparisons with other missions, and HME predictions.

  6. Tidal Sources • H2Ov absorption of solar radiance (Groves, 1982, Lieberman et al., 2003). • Latent heat release, deep convection (Hamilton, 1981, Forbes et al., 1997). • Wave-tide interactions (Hagan and Roble, 2001).

  7. ISCCP-based diurnal convective heating, 1992-1996

  8. NVAP-based diurnal radiative heating, 1992-1996

  9. Upper Atmosphere Research Satellite: 1991-2005 High resolution Doppler imager (HRDI) measured V between 50-110 km from the positions of daytime O2 emission lines in the near-IR. Nighttime emission confined to ~95 km (Hays et al., 1993). 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 emission between 90-110 km, and above 200 km (Shepherd et al., 1993; Gault et al., 1996). This study uses HRDI and WINDII wind data between 1992-1996, binned in longitude, latitude, altitude, local time and season.

  10. Sampling and Analysis UARS stabilized in a precessing orbit; 36 day yaw period. Most altitudes measured daytime winds (nighttime winds between 90-110 km and above 200 km). Space-time spectral analysis is therefore not feasible for tidal studies throughout the 60-270 km range. Instead, we infer tides from the longitudinal variations. At a fixed local time, (m,) is viewed at an aliased “wavenumber” ks given by ks = m   / |c0| (c0 ~ -6.33 rad day-1 )

  11. ks = m   / |c0| Stationary, slow waves (> 7 days) observed at “true” m… …However, diurnal wavenumbermobserved by UARS asm-1 if westward-propagating andm+1ifeastward-propagating. Examples: Migrating diurnal tide (1,) viewed as ks = 0. Nonmigrating diurnal tide (2, ) viewed as ks = 1. Nonmigrating diurnal tide (3,-) viewed as ks = 4. Semidiurnal wavenumbermobserved by UARS asm-2 if westward-propagating andm+2ifeastward-propagating.

  12. WINDII daytime wind Mask

  13. WINDII nighttime wind Mask

  14. WINDII daytime wave 4

  15. Longitudinal wave 4 at fixed local times could be stationary, DE3, DW5, SE2, SW6, etc. Previous work with HRDI winds (Talaat and Lieberman 1999) convincingly argued that m = 4 corresponds uniquely to DE3 in MLT. In the thermosphere, nonmigrating semidiurnal tides have the same source as diurnal tides (convection), evolve in amplitude, and share some of the characteristics (e. g., deep vertical wavelength)… ...So, some of the longitudinal variability in the thermosphere could be semidiurnal as well as diurnal. Diurnal tides isolated by forming differences between morning and late afternoon measurements (17 and 7 LT ). HRDI data examined identically, as a reality check.

  16. 12-hour differences: DJF 25°N

  17. 12-hour differences: DJF 30°S

  18. 12-hour differences: JJA EQ

  19. 12-hour differences JJA EQ m = 4

  20. 12-hour differences JJA eq m = 3

  21. 10-hour difference highlights diurnal variations, mitigates semidiurnal tide… …but aliasing among eastward m-1 and westward m+1 still not resolved. Oberheide et al. (2002) outlined a method to deconvolve the interference patterns of eastward m=1 and westward m-1. Exact spectra are obtained at antinodes of the interference pattern (blue dots) and in between maxima and minima (red diamonds). Solutions interpolated to interim levels. Deconvolution

  22. UARS Deconvolution products DE3 and DW5 contributions to observed wavenumber 4. DW2 and DS0 contributions to observed wavenumber 1.

  23. DE3 JJA

  24. DE3 comparisons HME’s are solutions to linear tidal equations in a windless atmosphere, computed from GSWM (Svoboda et al., 2005).

  25. DW2 DJF

  26. DW2 comparisons

  27. DS0 DJF

  28. DS0 comparisons

  29. DS0 line HME

  30. Summary Nonmigrating diurnal tides appear in daytime and nighttime WINDII winds, and are emphasized in 10-hour difference patterns. Deconvolution analysis indicates that most prominent modes are DE3, DW2, DS0. Strong DE2 presence also suggested. DE3 has long wavelength, propagates above 200 km, observed wavelength shorter than predicted by linear theory (HME). DS0 has long vertical wavelength, propagates at least to 180 km in winter hemisphere. Observed wavelength shorter than HME. Strong asymmetry in winter hemisphere may have in-situ (nontropospheric) source.

  31. Additional slides

  32. 12-hour differences: DJF EQ

  33. 12-hour differences m = 1 25N

  34. 12-hour differences m = 1 30S

  35. Deconvolved DE 3 pattern exhibits eastward tilt with altitude, and a deep (~40 km) vertical wavelength. Independent HRDI and WINDII retrievals are highly consistent. Deconvolved DE3 eq

  36. m = 1 12-hour difference pattern is the combination of DW2 and DS0. Deconvolved DW 2 pattern exhibits westward tilt with altitude, and a vertical wavelength of ~22 km. Independent HRDI and WINDII retrievals highlight stronger amplitudes in HRDI, and a phase shift. Deconvolved DW2 lon-ht

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