Radar derived precipitation part 4
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Radar-Derived Precipitation Part 4. I.Radar Representation of Precipitation II.WSR-88D, PPS III.PPS Adjustment, Limitations IV.Effective Use. COMET Hydrometeorology 00-1 Matt Kelsch Tuesday, 19 October 1999 [email protected] V.Effective Use Stage I PPS Strengths.

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Radar-Derived Precipitation Part 4

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Radar derived precipitation part 4

Radar-Derived Precipitation Part 4

I.Radar Representation of Precipitation

II.WSR-88D, PPS

III.PPS Adjustment, Limitations

IV.Effective Use

COMET Hydrometeorology 00-1

Matt Kelsch

Tuesday, 19 October 1999

[email protected]


V effective use stage i pps strengths

V.Effective UseStage I PPSStrengths

  • Numerous quality control steps to minimize limitations both in the radar estimate of precipitation, and the rain gauge representation of precipitation.

  • Spatial and temporal resolution are excellent for the mesoscale detail of precipitation systems.

    • Spatial detail over a large area

    • Monitor evolution of events between gauge sites

    • Real time information


Stage 1 pps strengths cont

Stage 1 PPS:Strengths (cont.)

  • Opportunity for important rainfall information in remote, poorly instrumented areas.

  • Adaptation parameters provide some flexibility for different locations and climate regimes.

  • Has the versatility to evolve into a better algorithm that can effectively account for variability on a geographic, seasonal, and even hourly basis.

  • Offers important input for a comprehensive, multi-sensor system.


Radar derived precip when changing z r coefficients is not the real solution

Radar-Derived Precip:When changing Z-R coefficients is not the real solution:

  • Range degradation, overshooting low-levels

    • Problem associated with propagation of beam, not Z-R.

  • Snowfall

    • More complexity than liquid hydrometeors.

    • Phase changes and mixed phases exist over small space/time scales.

    • Range degradation often co-exists.

  • Phase change: hail, melting snow

    • Radical storm-scale changes in Z to R relationship.

    • Minimal proof that hail correction can be done with Z-R.

    • Inconsistent relationship between Z-R and hail occurrence.


Radar derived precip when changing z r may help

Radar-Derived Precip:When changing Z-R may help:

  • Consistently different average DSD (climate)

    • Tropical versus mid-latitude (warm vs. cold process)

    • Maritime versus continental

  • Consistently different average DSD (season)

    • Convective versus stratiform

  • Precip System character

    • Identify Convective versus Stratiform signature

    • Identify warm versus cold rain signature

    • Identify maritime versus continental


Why can t the adaptation parameters and bias adjustment procedure solve all the limitations

Why can’t the adaptation parameters and bias adjustment procedure solve all the limitations?

  • Radar bias adjustment is only one uniform adjustment. It depends on adequate representation of precip by the local gauge network.

  • Adaptation parameters can greatly help the algorithm performance for a given site and/or season. The parameters “tune” the algorithm for the typical scenario. Atypical events, such as unusually high rainfall rates, may not be diagnosed well.

  • The most effective use of PPS is to make it a function of meteorology, not the “normal” climatology.


Radar derived precipitation part 4

Can we account for the important atypical events without degrading the guidance for the more common typical events?

  • Meteorological information from soundings, profilers, and surface reports are a few examples of data sources that can assist with real-time adjustment of adaptation parameters.

  • Information from other NEXRAD algorithms, such as HAIL or VIL, may provide some guidance.

  • The most effective use of PPS is to make it a function of meteorology, not the “normal” climatology.


Data soundings and rainfall rates what are reasonable maximum rainfall rates expected

DATA: Soundings and Rainfall RatesWhat are reasonable maximum rainfall rates expected?


Radar derived precipitation a summary of major points

Radar-derived Precipitation:A Summary Of Major Points

  • Radar provides one of several useful methods for sampling precipitation

  • Quantitative reliability issues are related to the fact that radar is sampling some volume at some elevation to estimate precipitation at the ground

  • Radar-derived precipitation is most reliably modeled for liquid hydrometeors; hail and snow add complexity

  • The above two points are not effectively corrected by changing Z-R coefficients; Z-R changes should be related to Drop Size Distribution knowledge.

  • Radars and rain gauges do not measure equal samples

  • Rain gauges do not provide a good representation of precipitation distribution, especially convective precip.

  • Radar provides excellent information about the spatial and temporal evolution of precipitation systems.


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