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The Green Beam— Lidar Investigations of the Mesosphere Vincent B. Wickwar Center for Atmospheric & Space Sciences Department of Physics Utah State University [email protected] www.usu.edu/alo InTech Collegiate High School North Logan, Utah March 2, 2007 Laser Beam(s) above USU Jobs in Physics – Sources of Info. • American Institute of Physics – www.aip.org • American Geophysical Union – www.agu.org • American Association for the Advancement of Science – www.aaas.org – sciencecareers.sciencemag.org • National Science Foundation – www.nsf.gov • National Academy of Science – www.nationalacademies.org Physics Jobs – Exist, Well Paid, Fun • Where – – – – Private Sector 55% Education 25% Government 15% Other 5% • Starting Salaries – BS $23,000 – $54,000 – MS $33,000 – $70,000 – PhD $35,000 – $97,000 • 10 Years Later – PhD $45,000 – $125,000 My Background • Education – Bachelor’s at Harvard College • Reseach on airglow – MS & PhD at Rice University • Satellite instruments • Incoherent-scatter radar at Arecibo • Employment – Post Doc at Yale University • Incoherent-scatter radar at Arecibo and Chatanika, AK – Researcher at Stanford Research Institute • Incoherent-scatter radar at Chatanika and in Greenland – Program Manager at the National Science Foundation – Professor at USU • 50% teaching and 50% research on lidar Outline • Lidar (LIght Detection And Ranging) – Radar based on light instead of radio waves – Types of scattering: Mie, Rayleigh, Raman, Resonance • Atmospheric Regions – Troposphere, Stratosphere, Mesosphere, Thermosphere • Scientific Results – Temperatures – Temperature Variability – Noctilucent Cloud at 41.7° N latitude (instead of >50°) • Lidar Upgrade – Large & Steerable Telescope – Second Nd:Yag Laser Participation in ALO Project • Atmospheric Lidar Observatory (ALO) is in the same building as Physics & CASS — considerable student participation – 30 undergraduates have operated the lidar – 10 undergraduates have done research projects – 5 MS and PhD students • One student, Josh Herron, will defend his PhD research and dissertation in 3 weeks Rayleigh-Scatter Lidar Interference Filter Lenses Photomultiplier Folding Mirror 532 nm Dielectric Mirrors Beam Stops Nd:YAG 1064 nm Photomultiplier Tube Photocathode Dynodes 106 Gain Focusing Elements Photocathode d2 d1 d3 Mesh Anode Transit Time 41 ns d4 d5 d6 d7 d8 d9 d11 d12 d10 fwhm 3 ns Anode R14 R1 R2 R16 R15 R3 R4 R5 R6 R7 C7 C1 High Voltage (-1800 Volts) C2 R8 C8 R9 R10 C9 C5 Gate (300 Volts) C10 R11 C11 R12 C12 R13 Light Scattering • Scattering from particles – Mie scatter – Dust, cigarette smoke, snow flakes – Dust gives bright spots in green beam • Scattering from molecules – Rayleigh scatter – Green beam – most is much weaker than Mie scatter – Varies as 1/λ4 – scatters more blue than red light – Familiar with this • Orange sun at sunset & sunrise • Blue sky • Scattering from specific molecules at different wavelengths – Raman scatter • Scattering from Na, K, Ca+, Fe – Resonance Scatter – From break up of meteors and meteorites from 80 –100 km – Special wavelengths & strong scattering – Densities, Temperatures, and Velocities Signal versus Altitude Cirrus Optical Clouds Shutter High Gain Rayleigh Returns Background Photocounts Atmospheric Regions 75 50 25 0 Altitude [miles] 32° F Lidar Observations – Green Beam • Mie Scatter–Big Particles (H2O, ice, dust) – Cirrus Clouds (10–12 km) – Stratospheric Aerosols (h<30 km) – Noctilucent Clouds at (~83 km) • Rayleigh Scatter–Molecules (N2 & O2) – Relative Density Profiles (45–95 km) – Absolute Temperature Profiles (45–90 km) ALO Temperature Climatology 1993−2004 900 Nights 5,000 Hours 150,000 Profiles 540,000,000 Laser Shots Averaging Δh = 3 km Δt = 31 days [Herron & Wickwar, 2007] Mesospheric Temperatures Upper Mesosphere Winter Summer Transition Region Lower Mesosphere Winter Summer Dynamical Heating & Cooling July January Cooling by Expansion Compressional Heating Mesosphere Stratosphere Troposphere [Schematic diagram adapted from World Meteorological Organization, 1985] Temperature Variability Winter-Summer Comparison Nightly Temperature Profiles January July Mesospheric Inversion Layers Temperatures for 23 Feb. 1995 Positive Temperature Gradients Averaging Δh = 3 km Δt = 1 hour [Nelson & Wickwar, 2007] 2:30 UT 19:30 MST 12:30 UT 5:30 MST 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] Lidar Observation of NLC(1995) 22 June 1995 at 8:13 UT (2:13 MDT) Averaging Δh = 150 m Δt = 12 min [Herron, Wickwar, Espy & Meriwether, 2007] Lidar Observations of NLC(1995) [Herron, Wickwar, Espy & Meriwether, 2007] Unusual Temperatures for NLC(1995) Very Cold Very Hot [Adapted from Herron, Wickwar, Espy & Meriwether, 2007] Large Temperature Wave [Herron, Wickwar, Espy & Meriwether, 2007] Summary • Rayleigh Lidar – Mesospheric Exploration • Mesospheric Temperatures – Temperature climatology – Dynamical effects – Noctilucent clouds • Need for better observations – – – – Greater altitude—overlap with resonance and airglow Better precision Greater time resolution Initial temperatures Upgraded Lidar System • Bigger Telescope (30 times the area) – 2.5-meter equivalent vs 44-cm • Second Laser for Rayleigh Scatter – 40 W vs 20 W • Steerable Telescope – Structure and Winds • Three Detector Systems – 25–110 km vs 41–85 km • Resonance Lidar (Potassium at 770 nm) – Independent temperatures for 80–110 km – Winds Observatory, Yoke, & Cage Telescope – One Mirror, Pointing Off Zenith What is Involved? • Put it together & Make it work • Funds—Proposals – Maintenance Costs – Students to Operate – Graduate Student Stipends – Data Analysis The End