1 / 13

Radar/lidar observations of boundary layer clouds

Radar/lidar observations of boundary layer clouds. Ewan O’Connor, Robin Hogan, Anthony Illingworth, Nicolas Gaussiat. Overview. Radar and lidar can measure boundary layer clouds at high resolution: Cloud boundaries - radar and lidar LWP – microwave radiometer

michellegutierrez
Download Presentation

Radar/lidar observations of boundary layer clouds

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Radar/lidar observations of boundary layer clouds Ewan O’Connor, Robin Hogan, Anthony Illingworth, Nicolas Gaussiat

  2. Overview • Radar and lidar can measure boundary layer clouds at high resolution: • Cloud boundaries - radar and lidar • LWP – microwave radiometer • LWC – cloud boundaries and LWP • Cloudnet – compare forecast models and observations • 4 European remote-sensing sites (currently), 7 models (currently) • Cloud fraction, liquid water content statistics • Microphysical profiles: • LWC - dual-wavelength radar • Drizzle properties - Doppler radar and lidar • Drop concentration and size – radar and lidar

  3. Statistics - liquid water clouds • 2 year database • Use lidar to detect liquid cloud base • Low liquid water clouds present 23% of the time (above 400 m) • Summer: 25% • Winter: 20% • Use radar to determine presence of “drizzle” • 46% of clouds detected by lidar contain occasional large droplets • Summer: 42% • Winter: 52 %

  4. LWC - Scaled adiabatic method • Use lidar/radar to determine cloud boundaries • Use model to estimate adiabatic gradient of lwc • Scale adiabatic lwc profile to match lwp from radiometers http://www.met.rdg.ac.uk/radar/cloudnet/quicklooks/

  5. Compare measured lwp to adiabatic lwp • obtain ‘dilution coefficient’ Dilution coefficient versus depth of cloud

  6. Stratocumulus liquid water content • Problem of using radar to infer liquid water content: • Very different moments of a bimodal size distribution: • LWC dominated by ~10 m cloud droplets • Radar reflectivity often dominated by drizzle drops ~200 mm • An alternative is to use dual-frequency radar • Radar attenuation proportional to LWC, increases with frequency • Therefore rate of change with height of the difference in 35-GHz and 94-GHz yields LWC with no size assumptions necessary • Each 1 dB difference corresponds to an LWP of ~120 g m-2 • Can be difficult to implement in practice • Need very precise Z measurements • Typically several minutes of averaging is required • Need linear response throughout dynamic range of both radars

  7. Drizzle below cloud Doppler radar and lidar - 4 observables(O’Connor et al. 2005) • Radar/lidar ratio provides information on particle size

  8. Drizzle below cloud • Retrieve three components of drizzle DSD (N, D, μ). • Can then calculate LWC, LWF and vertical air velocity, w.

  9. Drizzle below cloud • Typical cell size is about 2-3 km • Updrafts correlate well with liquid water flux

  10. Profiles of lwc – no drizzle Examine radar/lidar profiles - retrieve LWC, N, D

  11. Profiles of lwc – no drizzle Consistency shown between LWP estimates. 260 cm-3 90 cm-3 80 cm-3

  12. Profiles of lwc – no drizzle Cloud droplet sizes <12μm • no drizzle present Cloud droplet sizes 18 μm • drizzle present Agrees with Tripoli & Cotton (1980) critical size threshold

More Related