Usefulness of vertical Usefulness of vertical velocity measurementsvelocity measurements

in clouds with a 1290 MHz in clouds with a 1290 MHz profilerprofiler

Henk Klein Baltink

Atmospheric Research Section

21 October 2002 Cloudnet Workshop KNMI 2

Quiet-air fall velocityspectral line

Spectral broadeningby turbulence2w

wi -w

wi +w

wi

Resulting spectrum

Mean vertical speed w

Problem: Velocity power spectrum <> DSD

21 October 2002 Cloudnet Workshop KNMI 3

DSD retrieval from single cloudradar spectrumGossard (et al) (1994,1997) Babb et al (1999), Klugmann (2001):

- use specific spectral shape in the small droplet range to estimate w

- cloud peak is at mean vertical speed

Babb et al (2000):

- double sided constrained inversion technique

21 October 2002 Cloudnet Workshop KNMI 4

1290 MHz Windprofiler vertical speed

Origin backscatter: Rayleigh vs. Bragg

• in rain: Rayleigh• scatter from higher levels (ice clouds): mainly Rayleigh• in drizzle/light rain: often both• in water clouds: (only?) Bragg• in clear-air: Bragg

21 October 2002 Cloudnet Workshop KNMI 5

Windprofiler operational acquisition cycle

• alternating low (100 m) and high mode (400 m)• per mode 1 vertical and 4 oblique beams• dwelltime per beam 25 sec.• spectral resolution 30 cm/s• not co-located with cloudradar• beam-width: 6°

quantative use of w and w limited?

21 October 2002 Cloudnet Workshop KNMI 6

Case: 27-July-2002

21 October 2002 Cloudnet Workshop KNMI 7

Backscatter profiler and CT75

21 October 2002 Cloudnet Workshop KNMI 8

Low mode vertical beam, CT75 Base

21 October 2002 Cloudnet Workshop KNMI 9

35 GHz Cloudradar Backscatter

21 October 2002 Cloudnet Workshop KNMI 10

Follow-up (?):

• assessment usefulness “w” on a case-by-case base • enhanced backscatter in water clouds: related to cloud geometry/top ?• use of co-planar oblique beams for estimation of w• optimize acquisition cycle (or use SA-technique ?)• discrimination between Rayleigh/Bragg scatter