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

2. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 2 ITM System 0 km 60 km 400 km PoleEquator Mass Transport Wave Generation Planetary Waves Convective Generation of Gravity Waves & Tides Turbulence CO 2 CH 4 CO 2 Cooling Ion Outflow Solar Heating The ITM System The ITM System H Escape Wind Dynamo B E Energetic Particles B Polar/Auroral Dynamics E Magnetospheric Coupling Joule Heating H2O solar-driven tides O3 Topographic Generation of Gravity Waves

3. 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.

4. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 4 0 50 100 150 Height (km) UV Absorption by O 3 12 local time 024 heating rate 0 latitude +90-90 heating rate Near-IR Absorption by H 2 O, latent heating EUV Absorption by O, O 2, N 2 Thermal Excitation of the Semidiurnal Tide mean diurnal semidiurnal

5. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 5 12 local time 024 heating rate, Q In the local time frame, the heating may be represented as Q Implying a zonal phase speed Converting to universal time t LT = t + / , we have an expression of the form

6. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 6 Solar Heating Distribution from a Space-Based Perspective : Migrating Solar Thermal Tides 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.

7. 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 O 3 in the stratosphere-mesosphere The tide propagates westward with respect to the surface once per day, and is locally seen as the same semidiurnal tide at all longitudes. Courtesy M. Hagan

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

9. 9 0 50 100 150 Height (km) Coupling into higher-order shorter-wavelength modes Semidiurnal variation in surface pressure 6 o S Propagation to surface Distortion by zonal mean zonal winds UV Absorption by O3 TIMED/SABER Semidiurnal Tide at 100 km

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

11. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 11 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): : Non-Migrating Solar Thermal Tides 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.

12. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 12 EQ 116 km 50 100 150 Height (km) Interaction with (modulation by) longitude variation in background wind field (s = 1 only) UV Absorption by O3 s = 2 (SW2) Coupling into sum and difference secondary waves s = 1 (SW1) s = 1,3 (SW1,3) Interaction with (modulation by) longitude variation in background wind field (s = 1 only) SW2 migrating semidiurnal tide SW1 “difference” SW3 “sum” SW1 Observed over South Pole, 92 km 200 EQ 116 km 5-year mean Semidiurnal Amplitude Temperatures, TIMED/SABER SW1SW3 SW0 SW4

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

14. 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

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

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

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

18. 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.

19. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 19 0 50 100 150 200 Height (km) UV Absorption by O3 s = 2 (SW2) Solar radiation absorption by dust s = 2 (SW2) Solar Semidiurnal Tide in Mars’ Atmosphere, Ls = 270, High Dust (  ~ 2.3) ~60% density perturbations at 122 km in aerobraking regime ~80 K ‘whole atmosphere response’ Solar Semidiurnal Tide in Earth’s Atmosphere, Ozone Heating Solar Semidiurnal Tide in Mars’ Atmosphere, Dust Heating To what degree does the solar semidiurnal tide contribute to the observed density changes at aerobraking altitudes in connection with dust storms?

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

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

22. 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

23. NCAR Advanced Study Program (ASP) Seminar, February 13, 2008 23 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. CONCLUDING REMARKS Solar Semidiurnal Tide in the Atmosphere