By Dustin Morris

Introduction General Overview Physics Behind Scattering Why We Care Our Results So Far Plans For Rest of Summer By Fir Own work, GFDL 1.2,

General Overview Aerosols seed cloud formation Lidars can detect aerosols by backscatter We are comparing data of ceilometers, a type of Lidar VS. Visalia CL51CHM 15k-Nimbus By Luft - en/products/optical- sensors/ceilometer- chm-15k-nimbus / By Visalia Users Guide 5 ft λ = 910 nm λ = 1064 nm

Physics Behind Scattering Rayleigh Scattering Requires: wavelength >> particle size For atmosphere below 100 km, molecular Rayleigh backscattering cross section is: o o Collis and Russell (1976, p. 89)

Physics Behind Scattering Then for degree of backscattering, at sea level and STP have N ≈ 2.55 * Atmospheric volume backscattering coefficient: By The original uploader was Dragons flight CC BY-SA 3.0, nm

Physics Behind Scattering Mie Scattering, similar general mechanics Requires wavelength comparable to particle size o Both used by ceilometers for aerosol detection, though Mie is dominant o

Why Should We Care? Clouds impacts Earth’s climate, overall net cooling effect By NASA -

Cloud Scattering High etage (cirrus): large ice crystals Low etage (stratus): very small water droplets By Taken byfir0002 | flagstaffotos.com.auCanon 20D + Canon 17-40mm f/4 L - Own work, GFDL 1.2, x.php?curid= By PiccoloNamek - Own work, CC BY-SA 3.0, g/w/index.php?curid= Earth

Low Clouds Scattering reflects short wavelength sunlight Long wavelength Earth emission can escape Net cooling

High Clouds Larger ice crystals are less effective at Rayleigh and Mie scattering of short wavelength sunlight Earth emitted long wavelength inferred closer to crystal size, thus scatters, causing some to return to Earth Net warming

Cloud Impact Earth’s climate incredibly complex Feedback with modern climate change unknown, clouds are largest uncertainty in global models (NASA 2005) If change increases cloud height acceleration of warming If change decreases cloud height clouds may offset and slow warming Thus cloud heights from ceilometers are important

Our Work So Far Constructed backscatter plots and profiles 0

Hour 19 Profile Hour 18 Profile 0

Cloud Base Heights Three layers of cloud bases Brown – First layer Cyan – Second layer Red – Third layer Precipitation Cloud base

First Cloud Layer Comparisons Nimbus – Cyan Visalia - Red

Hourly Average Nimbus – Cyan Visalia - Red May 31 st

Differences in Average Absolute Difference (Nimbus – Visalia)

First Cloud Layer: May 21 – June 15 Nimbus – Cyan Visalia - Red Time (days) Range (m)

24 Hour Overlap Nimbus – Cyan Visalia - Red

Daily Averages Nimbus – Cyan Visalia - Red May 21 st – June 15

Differences in Average Absolute Difference (Nimbus – Visalia) Take-home: sometimes ceilometers quite similar, sometimes very different Nimbus generally detects more high altitude clouds

What Next? More statistically robust comparisons Compare both ceilometers with Raman Lidar us/20-years-of-worldwide-research/

What Next? Long term trends with Visalia back to 2006 Compare ceilometers with satellite data?

Works Cited Lufft. (2014). Manual Ceilometer CHM 15k NIMBUS. Fellbach, Germany: Regeltechnik. NASA. (2005). The Importance of Understanding Clouds. Retrieved June 20, 2016, from NASA. (2016, March). Aerosol Optical Depth : Global Maps. Retrieved June 20, 2016, from Visalia. (2010). USER'S GUIDE Vaisala Ceilometer CL51. Helsinki, Finland: Vaisala Oyj. Cloud. (n.d.). Retrieved June 20, 2016, from