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COMET Hydrometeorology 00-1Matt Kelsch

Tuesday, 19 October 1999kelsch@comet.ucar.edu

Radar-Derived PrecipitationPart 1

I. Radar Representation of Precipitation

II. WSR-88D, PPS

III. PPS Adjustment, Limitations

IV. Effective Use

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II. Radar Representation of Precipitation

1. Sampling Issues• Vertical Inconsistency • Range Degradation• Precip Phase (bright band, hail, snow)• Ground Clutter/Terrain Blocking

2. The reflectivity to rainfall rate (Z-R) conversion

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1. Sampling Issues Radar domain cannot be sampled at consistent

elevations, with consistent bin volumes, or for precipitation with similar stage of development or phase.

• Beam elevation increases with distance--low-level precip not represented well

• Bin size increases with distance--incomplete beam filling, smearing of small-scale structure

• Ground clutter and terrain features may block low level information• Changes in precip phase have inconsistent effects--bright band,

hail contamination

Radar Representation of Rainfall

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16 sep99: Storm Total Radar-derived Accumulationfrom KRAX (Raleigh NC)

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16 sep99: Storm Total Radar-derived Accumulationfrom KAKQ (Wakefield VA)

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Bright Band

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Radar Representation of Rainfall

2. Deriving rainfall (the Z-R conversion) Power returned to the radar is related to the

rainfall intensity, but not in a consistent, easily-modeled way.

– Offers a good quantitative approximation– Preserves important qualitative precip structure– Varies with drop size distribution and precip phase

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Historical Background

• Marshall, J. S. and W. McKay Palmer, 1948: The distribution of raindrops with size, J. Meteor., 5, 165-166.

• Spilhaus, A. F., 1948: Drop size, intensity, and radar echo, J. Meteor., 5, 161-164.

• Chapman, G., 1948: Size of raindrops and their striking force at the soil surface in a red pine plantation, Trans. Amer. Geophys. Union, 29, 664-670.

• Horton, R. E., 1948: Statistical distribution of drop sizes and the occurrence of dominate drop sizes in rain, Trans. Amer. Geophys. Union, 29, 624-637.

• Atlas, D., 1990: Radar in Meteorology, pp. 577-618.• Austin, P., 1987: Relation between measured radar reflectivity

and surface rainfall, Mon. Wea. Rev., 115, 1053-1070.

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Z-R RelationshipsWSR-88D, Marshall-Palmer (general), and

TropicalZ- 300 R1.4 200 R1.6 250 R1.2

20 dBZ 0.5 mm/h (0.02 in/h) 0.7 mm/h (0.03 in/h) 0.5 mm/h (0.02 in/h)25 1.0 (0.04) 1.3 (0.05) 1.2 (0.05)30 2.4 (0.09) 2.7 (0.11) 3.2 (0.12)35 5.4 (0.21) 5.6 (0.22) 8.3 (0.33)40 12.3 (0.48) 11.5 (0.45) 21.6 (0.85)45 27.9 (1.10) 23.7 (0.93) 56.5 (2.22)50 63.4 (2.50) 48.6 (1.91) 147.2 (5.80)51 74.7 (2.94) 56.1 (2.21) 178.6 (7.03)52 88.1 (3.47) 64.6 (2.55) 216.3 (8.52)53 103.8 (4.09) 74.8 (2.94) 261.8 (10.31)54 122.4 (4.82) 86.5 (3.41) 317.7 (12.51)55 144.2 (5.68) 99.8 (3.93) 384.6 (15.14)56 170.1 (6.70) 114.8 (4.52) 465.6 (18.33)57 200.5 (7.89) 133.0 (5.24) 564.9 (22.24)58 236.4 (9.31) 153.8 (6.05) 683.9 (26.92)59 278.6 (10.97) 177.4 (6.98) 827.9 (32.59)60 328.4 (12.92) 205.1 (8.07) 1004.6 (39.55)65 748.2 (29.46) 420.7 (16.56) 2618.2 (103.07)70 1702.2 (67.01) 865.0 (34.05) 6839.1 (269.26)

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