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Solar Semidiurnal Tide in the Atmosphere

Solar Semidiurnal Tide in the Atmosphere. Jeff Forbes Department of Aerospace Engineering Sciences University of Colorado, Boulder, CO 80309-0429. Forcing of the Semidiurnal Tide Vertical Propagation of the Semidiurnal Tide and its Interactions with the Overlying Atmosphere

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Solar Semidiurnal Tide in the Atmosphere

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  1. Solar Semidiurnal Tide in the Atmosphere Jeff Forbes Department of Aerospace Engineering Sciences University of Colorado, Boulder, CO 80309-0429 • Forcing of the Semidiurnal Tide • Vertical Propagation of the Semidiurnal Tide and its Interactions with the Overlying Atmosphere • Distortion by Zonal Mean Winds • Modulation by Longitude Variations in Mean Winds (Stationary Planetary Waves) • Modulation by Traveling Planetary Waves (e.g., 2-day wave) • Solar Semidiurnal Tide in Mars’ Dusty Atmosphere NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  2. The ITM System H Escape Magnetospheric Coupling B E B Energetic Particles Ion Outflow E Wind Dynamo Mass Transport Polar/Auroral Dynamics Joule Heating Wave Generation Solar Heating CO2 Cooling Turbulence Topographic Generation of Gravity Waves O3 Convective Generation of Gravity Waves & Tides CO2 CH4 solar-driven tides Planetary Waves H2O 400 km ITM System 60 km 0 km Pole Equator NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  3. The semidiurnal tide is just one example from a whole spectrum of waves that couple different atmospheric regions and produce observable phenomena. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  4. EUV Absorption by O, O2, N2 diurnal mean heating rate semidiurnal 0 12 local time 24 heating rate UV Absorption by O3 +90 0 latitude -90 Near-IR Absorption by H2O, latent heating Thermal Excitation of the Semidiurnal Tide 150 100 Height (km) 50 0 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  5. heating rate, Q Converting to universal timetLT = t + l/W, we have an expression of the form 0 12 local time 24 Implying a zonal phase speed In the local time frame, the heating may be represented as Q NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  6. : Migrating Solar Thermal Tides Solar Heating Distribution from a Space-Based Perspective To an observer in space, it looks like the heating bulge (and the tides it generates) are fixed with respect to the Sun, and the planet is rotating beneath. To an observer on the ground, the heating bulge, and the tides it generates, are moving westward or “migrating” at the apparent motion of the Sun. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  7. Meridional wind field at 103 km (April) associated with the semidiurnal tide propagating upward from the lower atmosphere, mainly excited by UV absorption by O3 in the stratosphere-mesosphere Courtesy M. Hagan The tide propagates westward with respect to the surface once per day, and is locally seen as the same semidiurnal tide at all longitudes. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  8. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  9. 150 Coupling into higher-order shorter-wavelength modes 100 TIMED/SABER Semidiurnal Tide at 100 km Distortion by zonal mean zonal winds Height (km) 50 Propagation to surface 0 Semidiurnal variation in surface pressure 6oS UV Absorption by O3 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  10. Tidal Variability Eastward Winds over Saskatoon, Canada, 65-100 km Note the transition from easterlies (westerlies) below ~80-85 km to westerlies (easterlies) above during summer (winter), due to GW filtering and momentum deposition. Note the predominance of the semidiurnal tide at upper levels, with downward phase progression. Courtesy of C. Meek and A. Manson NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  11. : Non-Migrating Solar Thermal Tides Longitude variations are taken into account with zonal wavenumbers s  n. A spectrum of tides thus exists, to first order representable as a linear superposition of waves of various frequencies (n) and zonal wavenumbers (s): The waves with s ≠ n are referred to as non-migrating tides because they do not migrate with respect to the Sun to a planetary-fixed observer. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  12. SW1 Observed over South Pole, 92 km SW4 SW0 EQ 116 km 5-year mean Semidiurnal Amplitude Temperatures, TIMED/SABER Interaction with (modulation by) longitude variation in background wind field (s = 1 only) s = 1,3 (SW1,3) Coupling into sum and difference secondary waves SW1 SW3 s = 1 (SW1) Interaction with (modulation by) longitude variation in background wind field (s = 1 only) SW2 migrating semidiurnal tide SW3 “sum” SW1 “difference” EQ 116 km s = 2 (SW2) 200 150 100 Height (km) 50 UV Absorption by O3 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  13. Zonal Mean Winds due to Dissipation of Semidiurnal Tides SW2 + SW1 + SW3 SW2 only SW1 + SW3 Angelats i Coll and Forbes, 2002 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  14. The total atmospheric response to solar forcing is the result of constructive and destructive interference between migrating and nonmigrating tidal components, giving rise to a different tidal response at each longitude. TIMED/SABER Semidiurnal Temperatures 110 km April 2004 Zhang et al., 2006 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  15. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  16. 400 NCAR TIME-GCM: QTDW Modulation of Semidiurnal Tide Generates Sideband Waves that Propagate Above 100 km. Interaction with (modulation by) Quasi-Two-Day Wave (QTDW) with s = 3 • QTDW reflected in Critical Plasma Frequency s = -1 16 h Coupling into sum and difference secondary waves SW2 migrating semidiurnal tide Westward s = 5 9.6 h “sum” Eastward s = 1 16.0 h “difference” s = 5 9.6 h • QTDW Modulation of Semidiurnal Meridional Wind Amplitude • In the E-Region, EISCAT (Huskonen et al., 1995). Interaction with (modulation by) Quasi-Two-Day Wave (QTDW) with s = 3 Are the above results due to modulation of the equatorial fountain by dynamo electric fields? Is the dynamo driven directly by the 2-day wave, or by a 2-day modulated semidiurnal tide? Palo, Roble & Hagan, Earth Planets Space, 51, 629-647, 1999 s = 2 (SW2) Do these waves beat with the semidiurnal tide generated in-situ in the thermosphere? Penetration into upper thermosphere & ionosphere 350 300 Height (km) 50 UV Absorption by O3 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  17. Solar Semidiurnal Tide in the Dusty Mars Atmosphere NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  18. The Model • Time-dependent global model of the mutually-interactive semidiurnal tide and zonal mean circulation; • Parameterization employed to handle convective instability -- eddy diffusivity introduced to keep wave amplitude at stable limit. • Heating rates used based on • observed dust distributions; • validated against surface pressure • perturbations measured by • Viking-1and Viking-2 landers. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  19. 200 To what degree does the solar semidiurnal tide contribute to the observed density changes at aerobraking altitudes in connection with dust storms? ~80 K 150 Height (km) 100 ‘whole atmosphere response’ 50 s = 2 (SW2) s = 2 (SW2) UV Absorption by O3 Solar radiation absorption by dust ~60% density perturbations at 122 km in aerobraking regime 0 Solar Semidiurnal Tide in Mars’ Atmosphere, Ls = 270, High Dust (t ~ 2.3) Solar Semidiurnal Tide in Earth’s Atmosphere, Ozone Heating Solar Semidiurnal Tide in Mars’ Atmosphere, Dust Heating NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  20. Semidiurnal Temperature Perturbation NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  21. Eddy diffusion Coefficient due to Breaking Semidiurnal Tide NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  22. Zonal Mean Acceleration of the Atmosphere due to the Dissipating Semidurnal Tide Zonal Mean Zonal Wind, Low Dust Zonal Mean Zonal Wind Difference,  = 2.3 NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

  23. Solar Semidiurnal Tide in the Atmosphere CONCLUDING REMARKS • The semidiurnal tide and its effects are pervasive and ubiquitous in Earth’s atmosphere • There are new things to be learned, and probably, to be discovered • The semidiurnal tide is just one example from a whole spectrum of waves that couple different atmospheric regions and produce observable phenomena. • The solar semidiurnal tide is important in vertically-coupling Mars’ atmosphere, with potential importance to aerobraking. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008

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