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Precipitation Validation & Data sets

Precipitation Validation & Data sets. Dr Chris Kidd NASA/Goddard Space Flight Center & University of Maryland/Earth System Science Interdisciplinary Center c hris.kidd@nasa.gov. Goddard Space Flight Center. IPWG Training Course, Seoul, Korea. 5-9 November 2018. Validation Overview.

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Precipitation Validation & Data sets

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  1. Precipitation Validation& Data sets Dr Chris Kidd NASA/Goddard Space Flight Center& University of Maryland/Earth System Science Interdisciplinary Center chris.kidd@nasa.gov

  2. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Validation Overview • What is the purpose/goal of validating precipitation products? • What sources of data are available to you – both satellite product and surface data? • What are the characteristics of these data? • What is the quality of the input data sets? • Which statistics are required? • What are the meteorological conditions? • Are there requirements of the algorithm/product providers and/or the user community? • How do you make the best use of your own limited resources?

  3. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Validation considerations I • What do the instruments (satellite or surface) sense or measure? • Be aware of auto-correlation: - lengths in time and space: small for instantaneous, longer for monthly; time ≡space - allgauge data is auto-correlated with the GPCC gauge data set. • Data timing – GEO scanning pattern, start/end times, accumulation (end times), none-UTC (Z) times, daylight savings time (!). • Which statistics are appropriate – both for the data and for interpretation by the user?

  4. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Validation considerations II • Data sets should be of the highest quality – both satellite, model and surface. • Care is needed with mapping/interpolation of any data (note extrapolation should not even be considered). • Always generate plots/maps of the data sets – this provides a check on the integrity of the data! • Statistics should be used thoughtfully; choose ones that address the goals of the validation, and ones that can be understood! Critically, get to know the data, products and situation

  5. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Validation data sources Direct: • Gauges • Weather radar (International and national networks) • Field campaigns – aircraft, distrometers, etc. Indirect: • Stream flow • Soil moisture • Vegetation BUT: be aware of cross-contamination: • models use satellite and gauge data; • many satellite products use gauge data; • radars are calibrated with gauges; etc.

  6. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Mapping Precipitation

  7. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Precipitation Observing Systems Surface Satellite

  8. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Surface & Satellite Observing Systems Passive Microwave Imagers Passive Microwave Sounders Active Microwave (Radar) Rain/ Snow gauge Surface- Based radar Micro rain radar Visible Infrared Atmosphere 20 minutes Different systems observe things differently – spatially, temporally and physically

  9. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Surface Observations of Precipitation Rain/snow gauges • point-based spatial sampling • temporal (accumulation) or quantified sampling - accumulation gauges, tipping bucket (many sizes/designs) Weather radar • spatial/volume sampling • instantaneous observations - scanning, vertically-pointing, etc Microwave links ‘line of sight’ observations, ~15 minute samples Precipitation is highly variable both temporally and spatially: measurements need to be representative

  10. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Gauge measurements Rain gauges are critical for providing long-term measurements of precipitation worldwide and the calibration/validation of other precipitation measurements (e.g. satellite, radar, models…) But, density is generally poor and very variable except for a few well-instrumented regions – virtually no gaugesover the world’s oceans. Number of gauges vary due to availability (latency, politics, etc.) and temporal sampling (instantaneous, hourly, monthly, etc.) Estimates of the number of gauges worldwide vary from less than 10,000 (WMO/GTS) to maybe >250,000 (Strangeways, 2007)

  11. Syphon gauge tipping bucket gauge manual gauge tipping bucket gauges pit gauge Sevruk & Klaman identified 50 types of daily, manually-read gauges worldwide

  12. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 What is truth?Co-located 8 gauges / 4 MRRs

  13. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 1st gauge…

  14. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 2nd gauge…

  15. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 2 more gauges

  16. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 All gauges

  17. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 plus the MRR…

  18. 20,000 Rain gauges Radarduplicates rain-gauge coverage Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Conventional Observations Precipitation is highly variable both temporally and spatially. Measurements need to be representative

  19. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Gauge Area Representation At best – all gauges, largest orifice (% global/land surface): • 250,000 gauges@1 km = 785,368 km2 (0.15%-0.53%) At worst – (all) GTS gauges, smallest orifice: • 10,000 gauges@1 km = 31,416 km2 (0.006%-0.021%) The area that each gauge represents varies greatly: • gauge measurements are generally a true value of what falls into the gauge (less evaporation/wetting losses) • the representativeness of a gauge diminishes with distance from the gauge location – dependent upon: - Gauge location (representative of actual site) - Precipitation system (meteorology) - Topography (climatological precipitation maps)

  20. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Precipitation Correlation lengths Toronto (King Radar) winter & summer (Paul Joe, Environment Canada, 2014) Iowa summer precipitation, gauges (Habib & Krajewski, 2001) For instantaneous precipitation, correlation lengths are very small

  21. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Precipitation variance - monthly Variance explained by nearest station (%) Jürgen Grieser shorter periods = less variance explained

  22. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Weather radar systems and networks University of Helsinki C-band Clee-Hill ATCRadar and C-band ChilboltonC-Band

  23. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Weather radar Weather radars provide: • useful information on the location, intensity and movement of precipitation • vertical distribution of precipitation • spatial information (as opposed to gauge ‘points’) However, radars are: • limited globally, often to more developed countries • provide less direct measurements • suffer from under- and over-estimation due to ‘missing’ precipitation or false-echoes Radars provide good instantaneous, BUT poor long-term results

  24. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Real-time Weather radar http://rain-alarm.com/ (not all weather radar locations available)

  25. Blockage Anaprop Wind Farms Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Radar artefacts IR vs NMQ Thresholded IR data as a proxy for rain: radar over/under-estimation

  26. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Global precipitation data sets Many different products at different spatial/ temporal resolutions … and formats!

  27. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Organised Ground Validation Both approaches are complementary Kidd et al. 2019

  28. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 IPWG validation Exploit available surface reference data sets • national and international gauge and radar data • regional to national scales • 0.25 x 0.25 degree resolution • daily • Several regional validation sites across the world, using both gauge, radar or gauge&radar. • Standard set of statistics, and presentation

  29. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 IPWG Inter-comparison regions Near real-time inter-comparison of model & satellite estimates vs radar/gauge IPWG – International Precipitation Working Group (WMO/CGMS)

  30. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Accessing IPWG intercomparisons http://www.isac.cnr.it/~ipwg/

  31. Main IPWG Inter-comparison Web sites

  32. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Regional Web pages - Japan Daily images and statistics and summary plots CHECK Web-Link!

  33. Regional Web pages - US

  34. Regional Web pages – South America

  35. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 South Africa Validation of products (including radar!) against gauge data

  36. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018

  37. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018

  38. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018

  39. Validation data Precipitation product Occurrence comparison Accumulation comparison Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 “Standard” Layout Contingency tables PoD/FAR/ HSS Scatter-plot Descriptive Statistics Cumulative distribution

  40. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 PMIR results: Australia 2008-12-25

  41. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Monthly and seasonal validation Monthly and seasonal diagnostic validation summaries

  42. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 NEW! IPWG inter-comparisons over India SEE POSTER - TUESDAY SEE POSTER - TUESDAY

  43. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 European Instantaneous Inter-comparisons

  44. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018

  45. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Field Campaigns Concerted validation efforts through organised field campaigns, as exemplified by the GPM-GV with a multi-tier approach. Surface data sets: • Gauge network (usually TBRs, and 2 per location) • Distrometers – measuring particle size • Radar(s) – polarmetric, Doppler. Aircraft: • Microphysics sensors (particles, met. measurements) • Earth observation instruments – radiometers and radars Satellites: • Coordination with satellite overpasses

  46. GPM includes ground validation – to check the satellite measurements with surface measurements • Validation sites over the US, and worldwide to capture different weather systems and precipitation types. Goddard Space Flight Center IPWG Training Course, Seoul, Korea. 5-9 November 2018 Ground Validation Activities Wallops

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