Lidar Measurements of Atmospheric State Parameters in the Mesosphere and Lower Thermosphere
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12 April 2007
Lidar Measurements of Atmospheric State Parameters in the
Mesosphere and Lower ThermosphereJonathan Friedman
Arecibo Observatory Seminar
12 April 2007
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Outline• Atmospheric Structure• Lidar Technique
– Light Scattering– From photons to state parameters– Transmitter– Receiver (broadband/narrowband)
• Results– Ion-neutral interactions … sporadic layers
– Mesospheric chemistry– MLT temperature measurements & solar influence
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Atmospheric Structure
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Light Scattering
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€
N(z) = ηTA2( )PLτhc λ
⎛
⎝ ⎜
⎞
⎠ ⎟σ eff n z( )Δz( )
A R
4πz 2
⎛ ⎝ ⎜
⎞ ⎠ ⎟+ NBRτ( )
Total Receiver Efficiency No. of
transmitted photons
# of photons scattered from the atmosphere
Probability that a scattered photon will be collected by the telescope
Total Background photons
Lidar Equation
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BlockingDetector
RayleighScatter Resonance
Scatter
30 second average in 150 m bins
Example of lidar data
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Rayleigh Temperatures in the upper stratosphere and
mesosphere
AssumptionsThe atmosphere is an ideal gasIn hydrostatic equilibrium
Assuming a starting temperature, T(z1), integrate downward
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– Resonance Technique : Laser is tuned to the resonance wavelength of the atoms to be studied.
– There is no signal if the laser is not on resonance with the target atoms. This allows us to map out the Doppler structure of the mesospheric metal atoms, both in terms of width (temperature) and shift (wind).
– We know with fairly high accuracy, << 10 MHz in 400 THz, where in the spectrum the excitation laser is. 10 MHz is roughly equivalent to 7 m/s wind error and 1 K temperature error.
Resonance Technique
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Transmitter & Receiver
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Daytime Receiver
Typical filter 1/2 width~ 1 nm.
1 pm 10 pm 100 pm 1 nm
100%
75%
25%
50%
0%
Faraday Filter 1/2 width 1–10 pm
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Some Results1. Summary of some past results
• Sporadic layers• Metal layer seasonal structures• Metal layer and meteors• Temperatures, inversion layers, and Gravity
Wave events2. Recent scientific results on the seasonal
thermal structure of the mesopause over Arecibo and its place in the global picture.
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Sporadic layer event during the 1998 Coquí II sounding
rocket campaign
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Tepley et al., 2003
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Metal Layer Topside
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Temperatures and gravity waves
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Seasonal Climatology and how the mesopause above Arecibo fits into the
global picture
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78°N, SpitsbergenHöffner, 2006
Latitude Comparison
35°N, Albuquerque, NM (Starfire)Chu et al., 2005
18°N, Arecibo, PRFriedman and Chu, 2007
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21°N, Maui, HIFriedman and Chu, 2006
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Radiative vs. Dynamic Heating/Cooling
• Radiative balance & upper mesosphere temperatures:
- Coldest place on earth winter polar mesopause- Warmest mesopause summer pole- Tropical mesopause nearly isothermal
• In fact:- Coldest place on earth summer polar mesopause
Under constant sunlight!- Warmest mesopause equinox- Tropical mesopause structured and dynamic
• Does not explain the summer cold tropical lower thermosphere
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12-tidal oscillationsa work in progress
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January Analysis
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12-h tide at 95 km
Dusk
Dawn
Midnight
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Summary• Lidar allows us to make remote measurements of the “ignorosphere” with high time and range resolution.
• Takes advantage of a high-intensity coherent source and an inefficient but reliable tracer to probe atmospheric state parameters.
• Allows us to study a variety of phenomena in the middle atmosphere.