# Presentation: 077657

## Intercomparison of CHARM Data

- and WSR-88D Storm Integrated Rainfall
- Gary Jedlovec (NASA), Paul Meyer (NASA), Anthony Guillory (NASA), Ashutosh Limaye (USRA), Global Hydrology and Climate Center,Huntsville, Alabama and Keith Stellman (NOAA/NWS), LMRFC, Slidell, Louisiana

- Goal:  Produce a fine scale hourly rainfall product by combining radar and special rain gauge measurements.
-    Outline:
-  CHARM rain gauge network
-  NWS WSR-88D HDP products
-  Case study intercomparison
-  Data combination
-  Discussion

## COOPERATIVE HUNTSVILLE-AREA RAINFALL MEASUREMENT NETWORK (CHARM)

**Local precipitation network ( est. 1/2001)**
- 110 sites in Huntsville & Madison County, AL
- NASA, Army, USGS, and NWS sites and weather enthusiasts
- Daily rainfall totals (1200UTC reports)
- 3600 km2 coverage (1 gauge per 6x6 km)
- Primarily 4” manual gauges (70%) with  remaining (30%) manual or automated tipping bucket (6” and 8”)
- Plans to expand to 200 stations by 2003
-          4x4 km average spacing
- 	    twice daily manual observations
- 	    1 minute data from 40 automated sites

**Supports local weather and climate research at the GHCC**
-    validate weather radar and lightning data from satellites
-    monitor spatial distributions of precipitation for modeling activities
-    various satellite remote sensing studies of soil moisture and energy fluxes

***big picture***

***http://wwwghcc.msfc.nasa.gov/charm***

## TYPES OF RAIN GAUGES USED IN CHARM

## Details:

***big picture***

- _Details_:
-  Strong north-south gradient on
-     either side of the storm track.
-  Width of heavy rainfall area is
-     about 10 km
- Maximum of 2.96” on east of
-     region, secondary max (2.73”) in
-     the western half of network

## Hourly Digital Precipitation Product

**Hourly Digital Precipitation Product**

- NWS offices produce their own precipitation estimates*** ***from their local WSR-88D radar.  The Nashville and Hytop (northeast of Huntsville) radars captured this storm event.
- Figures present storm totals (sum of hourly product over storm lifetime ~ 4-6 hours).  *** ***
* **Same general structure*
* **Nashville radar depicts more intense and *
*    **widespread rainfall *
*Radar calibration, elevation, scan patterns and *
*    **distance from storm may all contribute to the  *
*    **difference.*

**4-5”**

**~3”**

## NWS HDP Products

**Rainfall (cm)**

*Note the dual rainfall maximum in the stage III radar product corresponds nicely both in position and magnitude to the CHARM data. *

- _Stage I_  - integrated precipitation from local radar using standard or tropical Z-R relationships on
- 4 km grid – dependent on Z-R relationship used
- _Stage II_  - adjusted stage I product for bias using local (hourly) rain gauges
- _Stage III_  - combination of stage II HDP from individual radars to produce a regional precipitation estimate
-  minimal bias due to mis-calibration and different Z-R, local and seasonal adjustments
-  regional continuity and consistency

- Example of stage III radar product for
- June 4, 2001 over Northern Alabama.
- Hourly stage III product summed from 2100 – 0300 UTC.

- CHARM

*Stellman et al. 2001 (Wea. Fore.)*

## Stage III versus  CHARM

- _Resolution issues will affect comparison_
- Radar:
-  radar volume – varies with distance
-  4km grid cells – arbitrary selection
- Rain gauge:
-  point measurement – microscale variability of rainfall greatest in convective situations
-  multiple rain gauges for each grid cell (a single best comparison used in analysis below)

- Comparison shows little or no bias (0.19”) between CHARM measurements and radar estimates.  Scatter is considerable especially for amounts > 1.00”.

- ALL POINTS
- MD = 0.19”
- SD = 0.50”

-          <1”        > 1”
- MD = 0.21”   0.17”
- SD = 0.15”    0.60”

## Combined Stage III and CHARM Data

*Can time-continuous stage III data products be used to improve on 24h precipitation estimates from spatially dense CHARM rain gauge network?*

- Adjust hourly stage III data using CHARM 24h data
- Assume rain gauge (24h total) is correct and assume (radar – rain gauge) bias is constant with time
- Calculate bias between stage III data and CHARM 24h amount on a gauge-to-radar (4km data cell) basis
- Use point-to-point bias to scale (or “adjust”) stage III data

- For NSSTC site, bias factor was 1.36  (radar under-estimate).
-  Rainfall duration is spread over wider span
- Adjustment produces radar under-estimate

- Actual gauge values

## Combined Radar – Rain Gauge Product - Summary

- Individual radar estimates of precipitation vary greatly from radar-to-radar without some bias adjustment.
- The NWS stage III HDP product which uses (a few) regional rain gauges to adjust radar estimates of precipitation for calibration and Z-R inaccuracies  shows considerable improvement in precipitation estimation.
- Hourly radar rainfall estimates can be used to increase the utility of daily precipitation measurements (24h totals) from gauges by applying local bias corrections and radar time estimates.  However, as a result
- the duration of the rain event is often over estimated by up to 2t
- 	(2 hours for this study),
- 2)   the duration over estimate will lead to an storm intensity underestimate
- Despite these minor shortcomings, the combined radar and gauge rainfall product has a variety of uses for meso/microscale studies.

## GAUGE OWNERSHIP MAP

- JANUARY 2002

**GAUGE OWNERSHIP MAP**

- 80km

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