Transcript telescope mount

Lidar Investigations of the Middle Atmosphere
or
What is the Middle Atmosphere,
What is the Green Beam, and
What is the Red Beam?
Vincent B. Wickwar
Utah State University
Center for Atmospheric and Space Sciences
[email protected]
Physics Colloquium
21 January 2003
Overview
• Middle Atmosphere
• Rayleigh & Mie Scatter Lidar
– Green Beam
• Lidar Upgrades
– Red Beam and Other Things
• Concluding Remarks
Region Defined by
Temperature Structure
Up From the Ground:
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
Very Hard to Observe
from the Ground
Considerable
Interesting Physics
Radiation Budget in the Earth-Atmosphere System
[Brasseur and Solomon,1984]
Zonally Averaged Zonal Winds for January [m/s]
Schematic Diagram of the Meridional Circulation
Gravity Wave Filtering by the Zonal Wind
[Adapted from Lindzen, 1981]
Topographic Source of Gravity Waves
[Fritts, 1995]
Wind Speed — Knots
Jet Stream often Close to Northern Utah in Winter
Aviation Model
20 January 2003
at 00 UT
300-mb Level
~9 km Altitude
100 knots Equals
115 mph
182 km/h
51 m/s
Gravity Waves Seen in Cirrus Clouds
h = 112.5 m t = 2 minutes
Altitude [km]
13 February 1999
Time [Min]
[Wickwar et al., 2001]
WHY ALO AT USU/CASS?
[41.7° North 111.8° West 1.5-km Altitude]
• Good Seeing Conditions
– Greater Return Signal
• Clear Weather
– Extensive Synoptic Observations
• Gravity Wave Sources
– Middle of Rocky Mountains
– Proximity to Jet Stream in Winter
• Correlative Observations at USU’s Bear Lake Observatory
– Passive Optical
– Radar and Radio
• Student Involvement
– Undergraduates
– Graduates
GREEN BEAM (532 nm)
• Rayleigh Scatter — Molecules
– Relative Density Profiles
– Absolute Temperature Profiles
• Mie Scatter — Aerosols
– Cirrus Clouds
– Noctilucent Clouds
SCIENCE PROJECTS
• Mesospheric Temperature Climatology
• Temperature Comparisons —
Observation & Model
• Tidal Variability
• Mesospheric Inversion Layers
• Secular Change (Global Warming)
• Density Variability (Wave Energy)
• Noctilucent Clouds
Contributions to the Backscattered Lidar Signal
Monthly Temperature Comparisons
Summer: May–July
Winter: Dec–Feb
ALO Data
1994 – 1999
[Wickwar et al., 2001]
Temperature Comparison — Observation & Model
Observations 1994—1999
MSISe90
[Wickwar et al., 2001]
Temperature Differences —
Stratopause & Upper Mesosphere
[ K. Nelson, 2001]
Temperature Analysis Depends on g(h)
[J. Herron, 2003]
Nightly Temperatures —
Winter-Summer Comparison
50–90 km and 150–300 K
[Wickwar et al., 2001]
Winter-Summer Nighttime Temperatures
Observations
Error Bars
Geophysical Variability
January
1994–2001
June
1994–2001
[Herron, 2003]
Mesospheric Inversion Layers at ALO
Amplitude of Mesospheric Inversion Layers at 44°
N
[Leblanc & Hauchecorne, 1997]
Altitude of Mesospheric Inversion Layers at 44° N
(Altitude where dT/dh becomes positive)
(Toronto, Canada)
[Whiteway et al., 1995]
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]
Noctilucent Cloud above USU at 41.7° N
Noctilucent Cloud — Change in Alt. & BSR
Installing ALO Telescope Mount — 9 May 1999
Telescope — One Mirror, Pointing Off Zenith
[January 2003]
RED BEAM (770 nm)
[Under Development]
• Resonance Scatter — Potassium (K)
– K Density Profiles
– Neutral Temperature Profiles
– Neutral Wind Profiles
Potassium Densities at 54° N — Seasonal Variations
Layer is Lower & Thicker in Winter
Solid Lines: Observations
Peak Density is Constant
Other Lines: Model Calculations
[Eska et al., 1999]
Backscatter Cross Section — 10-16 m-2
Potassium: D1 Line at 770 nm (39K & 41K)
Wavelength Offset — pm
[T. Wong, 1999]
Concluding Remarks
• Middle Atmosphere
• Rayleigh & Mie Scatter Lidar
– Green Beam
• Lidar Upgrades
– Red Beam and Other Things
ALO Capabilities — Present
• Existing
– Rayleigh & Mie Lidar
– The “Makings” of a Resonance Lidar
– The “Makings” of a Large Telescope
• Tremendous Mesospheric Data Set
– Many Science Opportunities — As
Touched Upon Earlier
– Correlative Observations with BLO
ALO Capabilities — Under Development
• Laser Systems — Simultaneous KResonance Capability
• 4-Barrel Telescope — Equivalent to a
2.5-m Telescope
• Detector System — Full Altitude
Coverage from Mid Stratosphere to
Lower Thermosphere
COMPARISON OF
RAYLEIGH-SCATTER LIDARS
Parameter
ALO
(Now)
Energy/Pulse (mJ)
600
600
600
400
Pulses/sec (Hz)
30
30
20
30
Power (W)
18
18
12
12
Aperture Diameter (m)
0.44
2.5
2.6
1.8
Scaling Factor
1.0
1.0
1.0
0.5a
Figure of Merit (W-m2)
2.7
84
66
15
aHalf
ALO
(Soon)
PCL
the light is for power and half is for spectral observations.
ALOMAR
COMPARISON OF
RESONANCE-SCATTER LIDARS
Parameter
ALO
(Soon)
IAP
Ft.
Urbana
Collins
Emission (nm)
K (770)
K (770)
Na (589) Na (589)
Energy/Pulse (mJ)
150
100
30
30
Pulses/sec (Hz)
30
25
50
20
Power (W)
4.5
2.5
1.5
0.6
Aperture Diameter (m)
2.5
0.8
0.36
1.0
Scaling Factor
0.011a
0.011a
0.5b
1.0
Figure of Merit (W-m2)
0.23
0.014
0.074
0.47
aBased
on the ratios of peak number densities and scatter cross sections:
[Nmax(K) / Nmax(Na)] x [s(K) / s(Na)] = [5.0x107 / 4.0x109] x [1.34x10-15 / 1.52x10-15]
bThe emission is split between two telescopes.
ALO Capabilities — Future
• Winds
– Resonance-Scatter Winds
• Refinement on Resonance Temperatures
– Rayleigh-scatter winds
• Appropriate Fabry-Perot System
• Daytime Observations
– Rayleigh observations
• Appropriate Fabry-Perot System
– Resonance observations
• Appropriate Fabry-Perot System