Lidar Measurements of Atmospheric State Parameters in the Mesosphere and Lower Thermosphere

1. Lidar Measurements of Atmospheric State Parameters in the Mesosphere and Lower Thermosphere Jonathan Friedman Arecibo Observatory Seminar 12 April 2007

2. 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

3. Atmospheric Structure

4. Light Scattering

5. Lidar Equation Total Background photons Total Receiver Efficiency Probability that a scattered photon will be collected by the telescope # of photons scattered from the atmosphere No. of transmitted photons

6. Example of lidar data 30 second average in 150 m bins Blocking Detector Rayleigh Scatter Resonance Scatter

7. Rayleigh Temperatures in the upper stratosphere and mesosphere Assumptions The atmosphere is an ideal gas In hydrostatic equilibrium Assuming a starting temperature, T(z1), integrate downward

8. Resonance Technique • 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.

9. Transmitter & Receiver

10. Daytime Receiver 100% 75% 50% Faraday Filter 1/2 width 1–10 pm 25% 0% 1 pm 10 pm 100 pm 1 nm Typical filter 1/2 width ~ 1 nm.

11. Some Results • Summary of some past results • Sporadic layers • Metal layer seasonal structures • Metal layer and meteors • Temperatures, inversion layers, and Gravity Wave events • Recent scientific results on the seasonal thermal structure of the mesopause over Arecibo and its place in the global picture.

12. Sporadic layer event during the 1998 Coquí II sounding rocket campaign

13. Tepley et al., 2003

14. Metal Layer Topside

15. Temperatures and gravity waves

16. Seasonal Climatology and how the mesopause above Arecibo fits into the global picture

17. Latitude Comparison 78°N, Spitsbergen Höffner, 2006 35°N, Albuquerque, NM (Starfire) Chu et al., 2005 21°N, Maui, HI Friedman and Chu, 2006 18°N, Arecibo, PR Friedman and Chu, 2007

18. 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

19. 12-tidal oscillationsa work in progress

20. January Analysis

21. 12-h tide at 95 km Dawn Midnight Dusk

22. 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.