Global Change in the Mesosphere and USUs Green

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

Outline l l l l 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

Radiative Equilibrium – Greenhouse Effect Fs = 1370 W/m 2 A = 0. 28 l System: Fs(1 -A)/4 = (1 -f)σT 04 + fσT 14 l Layer: fσT 04 = 2 fσT 14 l Surface: Fs(1 -A)/4 + fσT 14 = σT 04 [Jacob, 1999]

Radiative Equilibrium – Greenhouse Effect l No Atmospheric Layer l l T 0 = 257 K Atmospheric Layer with absorption f = 0. 77 T 0 = 290 K l T 1 = 244 K l l Atmospheric Layer with absorption f = 0. 82 T 0 = 293 K l T 1 = 246 K l

Why Look High in the Atmosphere? Large Effects Predicted for 2 x (CO 2 & CH 4) l l l 200% 50% l l [Roble & Dickinson, 1989] 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

Mesospheric Energy Flow

Solar & Terrestrial Radiation [Jacob, 1999]

Maximum Solar Absorption Unity Optical Depth l l l [Goody, 1995] 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

Terrestrial Radiation l l [Jacob, 1999] 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

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

CO 2 Volume Mixing Ratios Enters the tropospheric atmosphere (~1. 5– 2. 0 ppmv/year) l Propagates to stratosphere in ~5 years l Constant vmr from turbulent mixing in stratosphere and mesosphere (~360 ppmv) l Above ~85– 90 km vmr decreases rapidly because of diffusive separation and UV photolysis l [Lopez-Puertas et al. , 2000]

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

Mesospheric Cooling l Upper Mesosphere (70– 90 km) l l CO 2 radiation at 15 μm (Excited by collisions with O) Airglow Adiabatic expansion (Summer) Lower Mesosphere (50– 70 km) l l l CO 2 radiation at 15 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 Airglow Adiabatic expansion (Summer)

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

Topographic Source of Gravity Waves [Fritts, 1995]

Zonally Averaged Zonal Winds for January [m/s]

Schematic Diagram of the Meridional Circulation

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 9954 B green sensitive PMT • Electronic Gating & Mechanical Chopper

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

ALO Temperature Climatology: 1993– 2003

Examples of Temperature Profiles

Monthly Temperature Comparisons

Nightly Temperatures — Winter-Summer Comparison — Waves January June

Analysis for Cycles & Trends l Linear regression on ALO monthly averages T(t, z) = T 0(z) + A(z)t + B(z)Mg. II(t) + C(z) cos 2 pt/12 + D(z) sin 2 pt/12 + E(z) cos 2 pt/6 + F(z) sin 2 pt/6+ Residual(t, z) l Where T 0 = Mean temperature A = Coefficient for the linear trend B = Solar cycle response for the Mg. II proxy C & D = Give amplitude and phase of the Annual Variation E & F = Give amplitude and phase of the Semiannual Variation

ALO — Data & Fits

ALO –Annual & Semiannual Variations

Solar Cycle Variations (121 -300 μm) l l l [Brasseur et al. , 2000] 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

Solar Cycle Response l Proxies for solar UV l l l Expect more heating at solar-cycle maximum l l l F 10. 7 flux Mg. II Index Photolysis of O 2 and downward diffusion Photolysis of O 3 Model predictions [e. g. , Brasseur et al. , 2000; Khosravi et al. , 2002] l l 1– 6 K heating in upper mesosphere ~1 K heating near the stratopause

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

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

ALO – Temperature Trends

Significance of NLCs at 41. 7°N l l Not previously seen below 50° latitude Implications for global change [Thomas, 1996] — Miner’s Canary l l l Ice crystals at 83 km l l l See more often See to lower latitudes Atmosphere becoming colder? Greater proportion of water vapor? Dynamical effects l l Meridional circulation Waves

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

Noctilucent Cloud Seen from 41. 7° N 10: 30 PM on 22 June 1999 MDT Looking north over the Utah State University campus and the NE part of Logan [Wickwar et al. , 2002; Photo by M. J. Taylor]

1995 NLC Observation • Enhancement due to MIE scattering • Equivalent to the Rayleigh backscatter at 70 km. • Backscatter Ratio SM: Mie Scattered Signal SR: Rayleigh Scattered Signal • Maximum Backscatter Ratio ~8. 1

NLC Comparison 1995 2 a. m. local time Maximum Backscatter Ratio 8. 1 Altitude Range 83 – 85 km App. Descent Rate ~ 2 km/hr Backscatter Ratio 1999 local midnight Maximum Backscatter Ratio 4. 67 Altitude Range 81. 5 – 83 km App. Descent Rate ~ 0. 9 km/hr

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

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

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

Conclusions l Large vertical oscillation associated with NLC – Unusual l l Resolution l l l 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 l l Minimum temperature of ~150 K Amplitude ~35 K Altitude of minimum ~ 84 km Vertical wavelength ~ 22 km Importance of knowing the context in which NLCs occur Multiple instruments Frequent observations Continued need for more complete models