Cloud liquid water path and Cloud liquid water path and drizzle from attenuation of drizzle from attenuation of CloudSat ocean return (CloudSat ocean return (00))

Lee SmithLee SmithAnthony IllingworthAnthony Illingworth

Surface echo attenuation methodSurface echo attenuation method

• Oxygen: 0.35-0.4 dB• Water:

• Ice particles: negligble• Liquid water: ~ 1dB per 120 gm-2 • Water vapour: ~ 1dB per 10 000 gm-2

• Factor of ~100 greater attenuation for liquid water liquid water drops dominate attenuation in cloudy conditions

• Use of CALIPSO lidar allows discrimination between clear sky and cloudy areas

Two - way attenuation at 94 GHz:Two - way attenuation at 94 GHz:

Corrections to surface echoCorrections to surface echo

(2) Correct for poor vertical sampling of surface echo

(1) Temperature dependent vapour attenuation, using AMSR-E vapour path, model temperatures and Liebe attenuation model

Surface echo well characterized

(3) Derive combined Wind/SST correction table for variability in surface echo derived from clear sky data

Statistics of corrected clear sky Statistics of corrected clear sky oo::

Standard deviation of 0 generally < 0.5 dB 50 gm-2 even over 200 km

Case study: Measure attenuationCase study: Measure attenuation• Identify clear sky using LIDAR and set reference 0 (blue line)

20 km

Case study: Liquid water path:Case study: Liquid water path:• Multiply attenuation by temperature dependent coefficient LWP• Compare with MODIS, AMSR-E and Z-R relationship

Case study: DrizzleCase study: Drizzle• Simulate adiabatic LWC from LWP and LIDAR cloud top

0.16

0.033

0.007

0.0012

Driz

zle

rate

mm

hr-1

Advantages:Advantages:• LWP at 1km resolution coincident with cloud

profiles during both local day and night• Possibility that lack of shadowing effects may

give advantage over MODIS in horizontally small cumulus

• Simple discrimination between drizzling and non-drizzling clouds by comparison of simulated Z from cloud water content and observed Z (dominated by drizzle)

• Method can be applied to boundary layer clouds beneath ice cloud

Next steps:Next steps:• Currently refining quality flags• Statistics of LWP and drizzle occurrence• Model comparisons