ken cook – soo nws wichita, ks (ict) an assessment of using the mean field bias correction to...
DESCRIPTION
What is the Mean Field Bias? A statistical analysis between the gauge observations and the radar bin that matches that gauge (NPair) Performed hourly Uses a minimum of 10 NPairs –If 10 cannot be ascertained during the current hour, then looks back in time until 10 is reached –User adaptable parameter Applies this statistical analysis (one number) to the entire coverage area Software part of Multi-sensor Precipitation Estimator (MPE)TRANSCRIPT
Ken Cook – SOO NWS Wichita, KS (ICT)
An Assessment of Using the Mean Field Bias Correction to Improve
Precipitation EstimatesKen Cook and Maggie Schoonover
NOAA/National Weather Service Office2142 South Tyler Road
Wichita, KS 67209Phone: (316) 942-8483 Fax: (316) 945-9553
Email: [email protected]
Ken Cook – SOO NWS Wichita, KS (ICT)
Outline• Introduction• Prompted Use• Methodology of Analysis• Assessment
– Examination Results – Case Studies– Challenges– Advantages
Ken Cook – SOO NWS Wichita, KS (ICT)
Ken Cook – SOO NWS Wichita, KS (ICT)
What is the Mean Field Bias?• A statistical analysis between the gauge observations
and the radar bin that matches that gauge (NPair)• Performed hourly• Uses a minimum of 10 NPairs
– If 10 cannot be ascertained during the current hour, then looks back in time until 10 is reached
– User adaptable parameter• Applies this statistical analysis (one number) to the entire
coverage area• Software part of Multi-sensor Precipitation Estimator
(MPE)
Ken Cook – SOO NWS Wichita, KS (ICT)
Why Use It?• June 8th, 2005 case• 2-3X observed
precipitation• Latest in a number of
cases where precipitation estimates were less than desirable
• Saw media partners using this bad data
• Needed to improve forecasters confidence in radar estimated precipitation
• Improve service/warning meteorology
Ken Cook – SOO NWS Wichita, KS (ICT)
Once Implemented• Results were instantly improved• Noticed some underestimation during
various events• How much have we improved?• How can we make the system better?
– Local training/learning– National science sharing/improve
development
Ken Cook – SOO NWS Wichita, KS (ICT)
Methodology• Radar Data (ICT)
– 12Z STP level III data from NCDC– Nexrad Exporter (create shapefiles)– ArcGIS 9, create rasters
• Observation Data– Gathered 12Z Rain Gauge (Tipping Buckets/COOP)
reports– Imported into Microsoft Access– Loaded then added XY Data in ArcGIS 9
• Compared Datasets for the period March through June 2006
• Resulted in ~ 400 G-R Observation Cases• Gauge data assigned a “bin” value
– .45 gauge value assigned to the .3 to .6 radar “bin”
Ken Cook – SOO NWS Wichita, KS (ICT)
Results
• Slight underestimation evident
Ken Cook – SOO NWS Wichita, KS (ICT)
Results
Ken Cook – SOO NWS Wichita, KS (ICT)
Results
Ken Cook – SOO NWS Wichita, KS (ICT)
Results• There seems to be a clear signal of slight
underestimation• More noticeable as
– Event grows in size– Amount of precipitation increases
Ken Cook – SOO NWS Wichita, KS (ICT)
Case Studies• 32 Gauge
Observations• Light Rain
Event• Average Gauge
Observation .14 inches
• Highest Gauge Observation .22 inches
• Estimates were outstanding
• Hourly MFB Calculations Very Consistent
Ken Cook – SOO NWS Wichita, KS (ICT)
Case Studies• 43 Gauge
Observations• Moderate Rain Event• Average Gauge
Observation 1.10 inches
• Highest Gauge Observation 2.85 inches
• Poorest estimation of the cases
• Largest number of observations for one case (largest coverage)
• Highest average precipitation
• Hourly MFB Calculations somewhat less stable
Ken Cook – SOO NWS Wichita, KS (ICT)
Challenges - How to Improve the MFB
• Use proper overlays in MPE to inspect suspect gauges
• Inspect gauge table in MPE
• Take out bad gauges from MPE ingest filter
• Inspect MPE Local Bias for areas that may be over/underestimating as compared to Mean Field Bias
Ken Cook – SOO NWS Wichita, KS (ICT)
Advantages - Using the MFB• Better Precipitation
Estimations• No change to Z/R
relationship necessary
• Updated hourly• Reacts to a warm
rain process with no interaction
• Improved credibility & customer service
Ken Cook – SOO NWS Wichita, KS (ICT)
Future• Continued assessment
– Alter adaptable parameters?– Alter npairs?
• Science sharing with developers other users– Incorporate differences from second/third runs of
bias?– Assume 1:1 bias after no precipitation?
• Goal: Improve performance
• Thank you – Questions??
Ken Cook – SOO NWS Wichita, KS (ICT)
Resources• Cook, Kenneth (SOO – ICT), 2006: WFO Wichita Science and Training Intranet Page (
http://204.194.227.45/soo/soopage.htm)– Training Materials Also Available
• Hunter, S. M., 1996: WSR-88D rainfall estimation: Capabilities, limitations, and potential improvements. National Weather Digest 20 (4), 26-38
• WHFS Field Support Group Web Site (http://www.nws.noaa.gov/om/whfs)