The retrieval of the LWC in water clouds

O. A. Krasnov and H. W. J. Russchenberg

International Research Centre for Telecommunications-transmission and Radar,

Faculty of Information Technology and Systems, Delft University of Technology,

Mekelweg 4, 2628 CD Delft, The Netherlands.

Ph. +31 15 2787544, Fax: +31 15 2784046

E-mail: o.krasnov@irctr.tudelft.nl, : h.w.j.russchenberg@irctr.tudelft.nl

Are power laws useful?

bLWCaZ

Radar reflectivity Liquid water content

Dropsize distributionVery sensitive to tail of dsd

A million droplets of 10 microngive the same radar reflection as one droplet of 100 micron!

A million droplets of 10 micron containa thousand times as much water as one one droplet of 100 micron...

And so: one drizzle droplet changes the reflectivity significantly without changing the liquid water content

drizzle “transition” drizzle

non-drizzling

Common opinion: No, there is too much scatter due to drizzle

unless

we can identify the drizzle droplets somehow...

Techniques for identification

• Radar reflectionSeparation based on differences in reflectivity of drizzleand non-drizzling clouds

• High resolution Doppler radarSeparation based on differences in fall speeds

• Radar – lidar combinationSeparation based on differences in sensitivity of reflection on droplet size

Radar reflection

Non-drizzling

Drizzling

Coarse classification

Radar and lidar observables in relation to microphysical water cloud.

Radar and lidar observables in relation to microphysical water cloud.

Radar reflectivity vs liquid water content Radar-lidar ratio vs effective radius

The Radar, Lidar, and Radiometer datasetfrom the Baltex Bridge Cloud (BBC) campaign

August 1- September 30, 2001, Cabauw, NL

• Radar Reflectivity from the 95 GHz Radar MIRACLE (GKSS)

• Lidar Backscattering Coefficient from the CT75K Lidar Ceilometer (KNMI)

• Liquid Water Path from the 22 channel MICCY (UBonn)

All data were presented in equal time-height grid with time interval 30 sec and height interval 30 m.

Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 The profiles of measured variables

Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 The profiles of Optical Extinction and Radar-Lidar Ratio

Z1 = -20 dBZ, Z2 = -10 dBZ; thresholds for radar only

+ 0 dB

+ 5 dB

+ 10 dB

+ 5 dB

+ 10 dB

0 dB

Frisch’s algorithmFrisch’s algorithm

2

log0, LWCNaZ

effr

• log-normal drop size distribution

• concentration and distribution width are equal to constant values

max

0

2/1

2/1

)(

)()(

h

h

RMMW

hZ

hZ

h

LWPhLWC

From radiometer’s LWP and radar reflectivity profile:

Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Retrieval Results for Frisch’s algorithm

Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Histogram of Differences in Retrieval Results for

the Frisch’s and the Radar-Lidar algorithm

Difference between LWC that retrieved using Frisch method and retrieved from radar-to-lidar ratio

Frisch’s fittings

Log-Normal DSDN=1000 - 2000 cm-3, = 0.8N=1000 - 2000 cm-3, = 0.1

Case study: August 28, 2001, Cabauw, NL, 10.12-11.20 Representation results on the Z-LWC plane

Case: cloud without drizzle

Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The profiles of measured variables

Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The Resulting Classification Map (radar and lidar data)

Atlas Z-LWC relationshipAtlas Z-LWC relationship

Frisch’s fittings

Case study: September 23, 2001, Cabauw, NL, 8.00-10.00 The results of Frisch’s algorithm application

Log-Normal DSDN=1000 - 2000 cm-3, = 0.8N=1000 - 2000 cm-3, = 0.1

Z-LWC relationship based on aircraft data

Comparison aircraft – radar data

September 23, 2001, Z+13 dBZ

Merlin flight

Frisch Z-LWC relations after adding 13 dB to Z

September 23, 2001, Z+13 dBZ

Atlas equation

September 23, 2001, Z+13 dBZ

Frisch retrievals

September 23, 2001, Z+13 dBZ

Atlas - Baedi - Drizzle equations

Frisch retrievals –

Z/ retrieval

Radar intercomparison; Miracle - KNMI

In ice cloudsalso agreement with Tara

Possible explanations for radar – aircraft difference

Cloud inhomogeneity: temporal and spatial sampling?Clipping of Doppler spectrum?

Conclusions

Given a proper calibration of the instruments,

• Radar-lidar

• Radar-microwave radiometer

• Radar alone

produce similar LWC profiles of non-drizzling clouds.

What’s going on with the radar data?