12 April 2007

Lidar Measurements of Atmospheric State Parameters in the

Mesosphere and Lower ThermosphereJonathan Friedman

Arecibo Observatory Seminar

12 April 2007

12 April 2007

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

12 April 2007

Atmospheric Structure

12 April 2007

Light Scattering

12 April 2007

€

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

12 April 2007

BlockingDetector

RayleighScatter Resonance

Scatter

30 second average in 150 m bins

Example of lidar data

12 April 2007

Rayleigh Temperatures in the upper stratosphere and

mesosphere

AssumptionsThe atmosphere is an ideal gasIn hydrostatic equilibrium

Assuming a starting temperature, T(z1), integrate downward

12 April 2007

– 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

12 April 2007

Transmitter & Receiver

12 April 2007

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

12 April 2007

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.

12 April 2007

Sporadic layer event during the 1998 Coquí II sounding

rocket campaign

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

12 April 2007

Tepley et al., 2003

12 April 2007

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Metal Layer Topside

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

12 April 2007

Temperatures and gravity waves

12 April 2007

Seasonal Climatology and how the mesopause above Arecibo fits into the

global picture

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

12 April 2007

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

78°N, SpitsbergenHöffner, 2006

Latitude Comparison

35°N, Albuquerque, NM (Starfire)Chu et al., 2005

18°N, Arecibo, PRFriedman and Chu, 2007

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

21°N, Maui, HIFriedman and Chu, 2006

12 April 2007

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

12 April 2007

12-tidal oscillationsa work in progress

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

12 April 2007

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

January Analysis

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

12 April 2007

12-h tide at 95 km

Dusk

Dawn

Midnight

12 April 2007

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.