1. Global Change in the Mesosphere and USU’s Green Beam Vincent B. Wickwar Physics Department & Center for Atmospheric and Space Sciences www.usu.edu/alo January 18, 2005 Major Contributions by Joshua P. Herron & Troy A. Wynn

2. Outline Global Change Mesosphere — 45 to 90 km Physical processes that affect temperatures Rayleigh-scatter Lidar — Green Beam Temperature trends since 1993 NLC observations at 41.7° !! Conclusions

5. Radiative Equilibrium – Greenhouse Effect System: F s (1-A)/4 = (1-f)σT 0 4 + fσT 1 4 Layer: fσT 0 4 = 2fσT 1 4 Surface: F s (1-A)/4 + fσT 1 4 = σT 0 4 F s = 1370 W/m 2 A = 0.28 [Jacob, 1999]

6. Radiative Equilibrium – Greenhouse Effect No Atmospheric Layer T 0 = 257 K Atmospheric Layer with absorption f = 0.77 T 0 = 290 K T 1 = 244 K Atmospheric Layer with absorption f = 0.82 T 0 = 293 K T 1 = 246 K

7. Why Look High in the Atmosphere? Large Effects Predicted for 2 x (CO 2 & CH 4 ) 1-D Model 1 st above 60 km Cooling by enhanced CO 2 emissions Enhanced H 2 O NLCs may increase because of lower temperatures & more water vapor [Roble & Dickinson, 1989] 200% 50%

8. Mesospheric Energy Flow

9. Solar & Terrestrial Radiation [Jacob, 1999]

10. Maximum Solar Absorption Unity Optical Depth 121.6 nm Lyman α by O 2 and H 2 O 130-175 nm O 2 Schumann-Runge Continuum 175-200 O 2 Schumann-Runge Bands 200-240 O 2 Herzberg Continuum 203-305 nm O 3 Hartley Bands [Goody, 1995]

11. Terrestrial Radiation 8-12 μm. From the surface in the Sahara 9.6 μm. From where O 3 becomes relatively thin in the stratosphere 15 μm. From where CO 2 becomes relatively thin at ~the tropopause 7 & 20 μm. From where H 2 O becomes relatively thin in the mid troposphere [Jacob, 1999]

12. Heating and Cooling via Radiation Heating from solar MUV and FUV radiation Heating from solar MUV and FUV radiation Cooling from terrestrial IR radiation Cooling from terrestrial IR radiation [Brasseur & Solomon, 1984]

13. CO 2 Volume Mixing Ratios Enters the tropospheric atmosphere (~1.5–2.0 ppmv/year) Propagates to stratosphere in ~5 years Constant vmr from turbulent mixing in stratosphere and mesosphere (~360 ppmv) Above ~85–90 km vmr decreases rapidly because of diffusive separation and UV photolysis [Lopez-Puertas et al., 2000]

14. Mesospheric Heating Upper Mesosphere (70–90 km) Upper Mesosphere (70–90 km) Solar radiation (O 2, O 3, CO 2 ) Solar radiation (O 2, O 3, CO 2 ) Exothermic chemical reactions Exothermic chemical reactions Compressional heating (Winter) Compressional heating (Winter) Wave dissipation Wave dissipation Lower Mesosphere (50–70 km) Lower Mesosphere (50–70 km) Solar radiation (O 2, O 3, CO 2 ) Solar radiation (O 2, O 3, CO 2 ) Compressional heating (Winter) Compressional heating (Winter) Wave dissipation Wave dissipation

15. Mesospheric Cooling Upper Mesosphere (70–90 km) Upper Mesosphere (70–90 km) CO 2 radiation at 15 μm (Excited by collisions with O) CO 2 radiation at 15 μm (Excited by collisions with O) Airglow Airglow Adiabatic expansion (Summer) Adiabatic expansion (Summer) Lower Mesosphere (50–70 km) Lower Mesosphere (50–70 km) CO 2 radiation at 15 μm CO 2 radiation at 15 μm O 3 radiation at 9.6 µm O 3 radiation at 9.6 µm H 2 O radiation in the 6.3-µm vib-rot bands and far-IR rot bands H 2 O radiation in the 6.3-µm vib-rot bands and far-IR rot bands Airglow Airglow Adiabatic expansion (Summer) Adiabatic expansion (Summer)

16. Role of Dynamics Waves Gravity waves: orography, jet stream, storms Tides: Tropospheric H 2 O, Stratospheric O 3 Planetary waves: Largely from Troposphere Filtering by Zonal Winds Near Stratopause Transmit westward propagating waves in winter Transmit eastward propagating waves in summer Break in the Mesosphere Generate turbulence for mixing & energy Deposit momentum affecting global circulation

17. Topographic Source of Gravity Waves [Fritts, 1995]

18. Zonally Averaged Zonal Winds for January [m/s]

19. Schematic Diagram of the Meridional Circulation

20. Atmospheric Lidar Observatory (ALO) USU/CASS Co-axial design Nd:YAG @ 532 nm 44-cm Telescope 1.47 km above sea level Temperature & relative density between 45 and ~85 km 37.5-m altitude resolution 2-min integration time Narrowband interference filter Electron Tubes 9954B green sensitive PMT Electronic Gating & Mechanical Chopper

21. GREEN BEAM (532 nm) Rayleigh Scatter — Molecules Relative Density Profiles (45–95 km) Absolute Temperature Profiles Hydrostatic Equilibrium Ideal Gas Law Mie Scatter — Big Particles Cirrus Clouds (10–12 km) Stratospheric Aerosols (h<30 km) Noctilucent Clouds at (~83 km)

22. ALO Temperature Climatology: 1993–2003

23. Examples of Temperature Profiles

24. Monthly Temperature Comparisons

25. Nightly Temperatures — Winter-Summer Comparison — Waves June Ja nua ry

26. Analysis for Cycles & Trends Linear regression on ALO monthly averages Linear regression on ALO monthly averages T(t,z) = T 0 (z) + A(z)t + B(z)MgII(t) + C(z) cos2  t/12 + D(z) sin2  t/12 + E(z) cos2  t/6 + F(z) sin2  t/6+ Residual(t,z) T(t,z) = T 0 (z) + A(z)t + B(z)MgII(t) + C(z) cos2  t/12 + D(z) sin2  t/12 + E(z) cos2  t/6 + F(z) sin2  t/6+ Residual(t,z) Where Where T 0 = Mean temperature A = Coefficient for the linear trend B = Solar cycle response for the MgII proxy C & D = Give amplitude and phase of the Annual Variation E & F = Give amplitude and phase of the Semiannual Variation

27. ALO — Data & Fits

28. ALO –Annual & Semiannual Variations

29. Solar Cycle Variations (121-300 μm) Largest variation in Lyman α at 121.6 nm Much variation in the regions that affects the MLT & upper mesosphere Small variation in the region that affects the stratosphere [Brasseur et al., 2000]

30. Solar Cycle Response Proxies for solar UV F10.7 flux MgII Index Expect more heating at solar-cycle maximum Photolysis of O 2 and downward diffusion Photolysis of O 3 Model predictions [e.g., Brasseur et al., 2000; Khosravi et al., 2002] 1–6 K heating in upper mesosphere ~1 K heating near the stratopause

31. Solar Cycle Effects on Stratopause Temperatures US Rocket shots ~30° Latitude [Dunkerton et al., 1998]

32. ALO – Solar Cycle Variations Solar cycle proxy — MgII Found a solar cycle variation, but not very significant Max – Min Changes: Stratopause heating of 2 K Mid-Mesosphere cooling of 5 K Upper Mesosphere heating of 4 K

33. ALO – Temperature Trends

34. Significance of NLCs at 41.7°N Not previously seen below 50° latitude Not previously seen below 50° latitude Implications for global change [Thomas, 1996] — Miner’s Canary Implications for global change [Thomas, 1996] — Miner’s Canary See more often See more often See to lower latitudes See to lower latitudes Ice crystals at 83 km Ice crystals at 83 km Atmosphere becoming colder? Atmosphere becoming colder? Greater proportion of water vapor? Greater proportion of water vapor? Dynamical effects Dynamical effects Meridional circulation Meridional circulation Waves Waves

35. Solar Cycle Dependence of H 2 O Maximum at Solar Cycle minimum Minimum at Solar Cycle maximum Photolysized by Lyman α [Randel et al., 2000]

36. Noctilucent Cloud Seen from 41.7° N 10:30 PM on 22 June 1999 MDT [Wickwar et al., 2002; Photo by M. J. Taylor] Looking north over the Utah State University campus and the NE part of Logan

37. 1995 NLC Observation Enhancement due to MIE scattering Equivalent to the Rayleigh backscatter at 70 km. Backscatter Ratio S M : Mie Scattered Signal S R : Rayleigh Scattered Signal Maximum Backscatter Ratio ~8.1

38. local midnight NLC Comparison 1995 1999 2 a.m. local time Backscatter Ratio Maximum Backscatter Ratio 8.1 Altitude Range 83 – 85 km App. Descent Rate ~ 2 km/hr Maximum Backscatter Ratio 4.67 Altitude Range 81.5 – 83 km App. Descent Rate ~ 0.9 km/hr

39. Temperature Profiles Temperatures centered on the hour Temperatures centered on the hour Minimum at NLC altitude Minimum at NLC altitude Maximum at ~70 km Maximum at ~70 km NLC possibly due to dynamics NLC possibly due to dynamics

40. Temperature Differences ΔT = observation – June average Large Oscillation 15 to 20 K colder @ NLC altitudes 10 to 15 K warmer @ ~ 72 km

41. Conclusions Searching for small variations in a realm with periodic & episodic variations of equal or greater magnitude Searching for small variations in a realm with periodic & episodic variations of equal or greater magnitude Complex region Complex region Radiation Chemistry Global circulation Small-scale dynamics ALO 11-year temperature database ALO 11-year temperature database Good agreement on annual and semiannual variations Small solar cycle (MgII) signature Linear trends Rapid cooling in upper mesosphere Small Response in lower mesosphere Mid-latitude NLC appearances Mid-latitude NLC appearances Seen twice at our latitude But, only at our longitude Not general cooling or increase in H 2 O

42. Conclusions Large vertical oscillation associated with NLC – Unusual Minimum temperature of ~150 K Amplitude ~35 K Altitude of minimum ~ 84 km Vertical wavelength ~ 22 km Resolution Dynamical factors may be more important than thought Our location in extended mountainous area may have significant dynamical forcings (Orographic GWs, Standing PWs) Observational Implications Importance of knowing the context in which NLCs occur Multiple instruments Frequent observations Continued need for more complete models