Download The Green Beam* Lidar investigations of the Mesosphere

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