10/18/2011

Youngsun JungCAPS/OU

Applications of polarimetric radar data in NWP

Hydrometeor classification

Quantitative rain estimation

Radar data quality control

Verification of numerical weather forecast

Improvement in microphysical parameterization

Data assimilation

Capability of polarimetric radar data (PRD)

Hydrometeor classification

Quantitative rain estimation

Radar data quality control

Verification of numerical weather forecast

Improvement in microphysical parameterization

Data assimilation

Capability of polarimetric radar data (PRD)

PRD contains information on size, shape, orientation, and phase composition of particles.

If the model microphysics scheme is unable to properly handle these kinds of information, information carried by PRD can easily mislead users.– Particle shape: not (explicitly) assumed– Orientation: not assumed– Size distribution: Gamma DSD– Phase: each phase is independent of others

(exceptions: Ferrier and Ziegler schemes?)

Understanding PRD

PRD simulator should take account of DSD, shape, orientation and phase of particles.

Non-meteorological effects that cannot be simulated by the model can significantly influence polarimetric signatures.

PR variables has their own weaknesses.– KDP field is often very noisy in weak rain regions

and is vulnerable to errors.

– Polarimetric signatures are very weak at high altitudes where the hydrometeors are mostly ice particles.

Understanding PRD

Polarimetric signature

Verification using PRD

KTLX KVNX

Verification using PRD

KOUN

Drop size distribution:

Size

Num

ber o

f dro

ps

Jung, Xue, Zhang, 2010: Simulations of polarimetric signatures of a supercell storm using a two-moment bulk microphysics scheme. J. Appl. Meteorol. Clim., 49, 146-163

Size

Num

ber o

f dro

ps

SM DM

• Drop growth (shrinking) during accretion or diffusion (evaporation) while keeping the number concentration constant• Number concentration changes during aggregation or breakup while

the total mass remains constant• Size sorting due to differential sedimentation

KOUN observations and simulated polarimetric variables at .5° tilt at 0200 UTC

OBS

Obs

Z(dBZ)

ZDR(dB)

ρhv

KDP(° km-1)

By Bryan Putnam

SM DM

ice

Well-calibrated and QC-ed observations

Accurate forward observation operator

Two- or higher-moment microphysics scheme

Improved formulations of microphysical processes in the bulk microphysics scheme

What do we need to use PRD?