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Evaluations of AMDAR Observations using Co-Located Radiosonde and Inter-Aircraft Comparisons

Evaluations of AMDAR Observations using Co-Located Radiosonde and Inter-Aircraft Comparisons. Lee Cronce 1 , Ralph Petersen 1 , Erik Olson 1 , Wayne Feltz 1 , David Helms 2 and Randy Baker 3

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Evaluations of AMDAR Observations using Co-Located Radiosonde and Inter-Aircraft Comparisons

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  1. Evaluations of AMDAR Observationsusing Co-Located Radiosonde andInter-Aircraft Comparisons Lee Cronce1, Ralph Petersen1, Erik Olson1, Wayne Feltz1, David Helms2 and Randy Baker3 1 Cooperative Institute for Meteorological Satellite Studies (CIMSS), University of Wisconsin – Madison 2 NOAA, National Weather Service, Office of Science and Technology, Silver Spring, Maryland 3 United Parcel Service, Louisville, Kentucky

  2. AMDAR data have helped improve NWP for over 10 years 250 hPa 24-hr forecasts vector Wind Error (m/s) 10 m/s 1996 2001 2006 1982 1987 1992 most recent Measurements of Temperature, Wind, and Moisture

  3. Measuring Moisture from Commercial Aircraft • Efforts underway for over a decade • Research instruments not appropriate for “day-to-day”, “real world” application • Initial experiments were made using a “stand-alone” Temperature/Relative Humidity sensor called the Water Vapor Sensing System (WVSS-I) • Used humidity sensors “similar” to those used on radiosondes • Test results showed: • Substantial Biases and RMS values that exceeded WMO specification • Systems became contaminated by everyday airport “gunk”, e.g. de-icer, dirt on runways, etc.

  4. Measuring Moisture from Commercial Aircraft • Newer system was developed • Second-generation Water Vapor Sensing System (WVSS-II) measures Mixing Ratio(specific humidity) directly • Uses a laser-diode system to measure number of water molecules passing sensor • Instruments Tested on UPS 757s • Used by UPS for fog forecasting • Final tests in 2009-2010 • Re-engineered electronics • Improved mechanics • New installations for Southwest Airlines Evaluations of AMDAR Observations using Co-Located Radiosonde and Inter-Aircraft Comparisons provide the basis for most of the results shown here

  5. EXPERIMENTAL DESIGN • Most recent independent • ground-truth assessments • of the WVSS-II systems • have been conducted for • three periods: • - November 2009 • - May - June 2010 • - August 2010 • The WVSS-II humidity data (along with aircraft temperature) were compared with radiosonde and ground based remote sensing systems. • Between 15 and 20 different UPS B757 aircraft provided WVSS-II data • - Data available via GTS • Radiosonde observations were made at the UPS hub in Rockford, Illinois, where about 20-25% of the WVSS-II equipped planes land/take off daily (Monday - Thursday).

  6. WVSS-II Validation Experiment Ground-Based Instrumentation • Vaisala DigiCORA III RS-92 GPS Sounding System (Use of night-time only radiosondes eliminated issue of ~8% dry in RS-92 TPW during mid-day observations) • VAISALA Surface PTU Station • GPS Receiver • Atmospheric Emitted Radiance Interferometer (AERI) • VAISALA 25K Ceilometer http://cimss.ssec.wisc.edu/aeribago/

  7. Comparisons between Ascent/Descent WVSS-II/AMDAR Measurements with Co-Located Radiosonde Measurements

  8. 2009-2010 Validation Results Direct Sounding Inter-comparisons Direct Data Comparison: Aircraft data generally fell between bounding radiosonde reports

  9. 2009-2010 Validation Results Direct Sounding Inter-comparisons Direct Data Comparison: Aircraft data generally fell between bounding radiosonde reports Large variability within moist regimes led to large specific humidity differences

  10. 2009-2010 Validation Results Summary of Direct Specific Humidity Inter-comparisons All SH data All Levels Spring SH data All Levels Differences showed: Aircraft data and radiosonde reports agreed quite well Overall small positive WVSS-II bias Few moist outliers from one case in 10-12 g/kg range – good for moister data

  11. 2009-2010 Validation Results Direct Specific Humidity Inter-comparisons by Relative Humidity Bins All observations – All Levels Differences showed: Small positive bias across all RH ranges Random errors average ~0.5-0.7 g/kg Higher random errors near 20-25% RH and approaching saturation

  12. Spring 2010 Validation Results Direct Temperature and Specific Humidity Inter-comparisons All Spring Data Only Differences from radiosondes showed: Warm temperature bias at all levels Large temperature variability Random SH differences average ~ ± 0.5 g/kg

  13. 2009-2010 Validation Results Specific Humidity (Excludes cases with large time and vertical radiosonde differences) Systematic Differences: WVSS-II Biases at low levels of 0.1 to +0.4 g/kg from surface to 850 hPa. ±0.2 g/kg above Random Differences (Including Dry/Moist Environments): Differences between aircraft data and radiosonde reports generally showed variability of 0.3 to 0.7 g/kg from the surface to 600 hPa – decreases aloft. StdDev slightly larger than 1-hour variability between bounding radiosonde reports (gray shading). Note: Fewer inter-comparisons near 800 hPa and above 700 hPa. Greater time and space separation above 650 hPa.

  14. 2009-2010 Validation Results Specific Humidity (Excludes cases with large time and vertical radiosonde differences) -- Ascents Only -- Systematic Differences: WVSS-II Biases at low levels of 0.1 to +0.5 g/kg from surface to 850 hPa. 0.0-0.3 g/kg above Random Differences (Including Dry/Moist Environments): Differences between aircraft data and radiosonde reports generally showed variability of 0.3 to 0.7 g/kg from the surface to 800 hPa – >0.6 g/kg between 800 and 600 hPa - decreases aloft. StdDev slightly larger than 1-hour variability between bounding radiosonde reports except between 800-600 hPa (gray shading).

  15. 2009-2010 Validation Results Specific Humidity (Excludes cases with large time and vertical radiosonde differences) -- Descents Only -- Systematic Differences: WVSS-II Biases at low levels of 0.0 to +0.3 g/kg from surface to 700 hPa -0.2 g/kg above Random Differences (Including Dry/Moist Environments): Differences between aircraft data and radiosonde reports generally showed variability of 0.4 to 0.7 g/kg from the surface to 750 hPa – 0.4-0.6 g/kg aloft. StdDev slightly larger than 1-hour variability between bounding radiosonde reports except above 750 hPa (gray shading).

  16. 2009-2010 Validation Results AMDAR Temperature Systematic Differences: Aircraft Temperature Biases at low levels of 0.2 to +0.7°C. from surface to 700 hPa. Net neutral above that level Random Differences : Differences between aircraft data and radiosonde reports generally showed variability of 0.8 to +1.5°C from the surface to 850 hPa. Above 850 hPa, SdtDev stabilizes to about 1.0°C Differences larger than 1-hour variability between bounding radiosonde reports (gray shading).

  17. 2009-2010 Validation Results Relative Humidity (From WVSS-II Humidity & AMDAR Aircraft Temperature) Systematic Differences: WVSS-II RH Biases were very small positive (0 – ±3%) from surface to 650 hPa. Random Differences (Including Dry/Moist Environments): Differences between aircraft data and radiosonde reports generally showed variability of 5 to 8% from the surface to 750 hPa. Above 750 hPa, RH StdDev increases as number of matches decreases and space/time distance increases. Differences slightly larger than 1-hour variability between bounding radiosonde reports (gray shading).

  18. Comparisons between WVSS-II/AMDAR Measurements from Different Aircraft

  19. AMDAR Measurement Inter-Comparison Specific Humidity Variability amongst WVSS-II Observations RMS calculated for: Time ranges of 0-15, 0-30 and 0-60 minutes Distance ranges of 0-20, 0-40 and 0-60 km RMS Differences show (ALL reports, Including Dry/Moist Environments): 0-15 minute / 0-20 km variability of <0.20 g/kg Variability nearly doubled for 0-60 time window Variability increased for larger distance separations: 30% increase for short time windows 10% increase for longer time windows

  20. AMDAR Measurement Inter-Comparison Specific Humidity Variability amongst WVSS-II Observations RMS calculated for: Time ranges of 0-15, 0-30 and 0-60 minutes Distance ranges of 0-20, 0-40 and 0-60 km RMS Differences show (ALL reports,Including Dry/Moist Environments): WVSS-II observations from different aircraft and instruments agree extremely well with one another Atmospheric Variability: - Smaller increases over distance, but larger for time spacing

  21. AMDAR Measurement Inter-Comparison Approximating WVSS-II Observational Error RMS calculated for: Time (and distance) ranges of 0-15, 15-30, 30-45, and 45-60 minutes (km) ~0.16 g/kg • RMS Differences show (ALL reports,All Seasons): • Moisture Variability more than doubles from 0-15 to 30-45 minute intervals • Because the Total Variability is made up of two parts: • 1) Instrument Error and 2) Atmospheric Variability • We can project nearby results to exact co-locations ( @ΔT~0 and ΔX~0, Δq~0.16 g/kg).

  22. AMDAR Measurement Inter-Comparison Approximating AMDAR Temperature Observational Error RMS calculated for: Time (and distance) ranges of 0-15, 15-30, 30-45, and 45-60 minutes (km) Variability by Distance ~0.5oC Linear(Variability by Distance) RMS Differences show ( ALL reports, ALL Seasons ): Variability can more than double over 60 minutes and 60 kms VariableObserved Variability @ 45-60 km and 45-60 minutesDerived Variability for perfect co-locations Specific Humidity ~0.45 g/kg (both) > ~0.16 g/kg Temperature ~1.0oC (both) > ~0.5oC

  23. AMDAR Measurement Inter-Comparison Approximating AMDAR Derived Relative Humidity Error RMS calculated for: Time (and distance) ranges of 0-15, 15-30, 30-45, and 45-60 minutes (km) ~4% RMS Differences show ( ALL reports, ALL Seasons ): Variability can more than double from 0-15 to 30-45 minute intervals VariableObserved Variability @ 45-60 km and 45-60 minutesDerived Variability for perfect co-locations Specific Humidity ~0.45 g/kg (both) > ~0.16 g/kg Temperature ~1.0oC (both) > ~0.5oC Derived Relative Humidity ~11% and ~6% (respectively) > ~4%

  24. Earlier Observation Accuracy Studies • Temperature comparisons showed similar results • Wind Assessments more Complicated (Vectors) Comparison of AMDAR and time/space co-located GPS radiosonde shows better Wind performance over US – Vector RMS <3.0 m/s

  25. AMDAR Measurement Inter-Comparison Approximating AMDAR Wind Observational Error RMS calculated for: Time (and distance) ranges of 0-15, 15-30, 30-45, and 45-60 minutes (km) ~2.5 m/s RMS Differences show (ALL reports,All Seasons): Variability increases from 0-15 to 30-45 minute intervals VariableObserved Variability @ 45-60 km and 45-60 minutesDerived Variability for perfect co-locations Specific Humidity ~0.45 g/kg (both) > ~0.16 g/kg Temperature ~1.0oC (both) > ~0.5oC Derived Relative Humidity ~11% and ~6% (respectively) > ~4% Vector Wind RMS ~3.5 m/s (both) > ~2.5 m/s

  26. Summary • Tests made against raobs over wide range of moisture conditions show: •  Sensors agreed extremely closely with each other • - Overall Specific Humidity (SH) RMS ~0.5 g/kg •  Sensors agreed well with co-located radiosonde observations • - Overall SH Bias ~0.2 g/kg, SH StDev ~0.5 g/kg •  Temperature differences between raob/aircraft were small • - Overall T Bias ~0.3°C, T StDev ~0.8°C, T RMS ~0.9°C •  Relative Humidity differences due to WVSS-II were small • - Overall RH Bias ~1%, RH StDev ~8%, RH RMS ~8% •  Ascent or Descent Data (separately) show similar results • Comparison between aircraft for all variables show: • Atmospheric Variability can more than double from 0-15 to 30-45 minute intervals • For precise co-locations: • VariableObserved Variability @ 45-60 km and 45-60 minutesDerived Variability for perfect co-locations • Specific Humidity ~0.45 g/kg (both) ~0.16 g/kg • Temperature ~1.0oC (both) ~0.5oC • Derived Relative Humidity ~11% and ~6% (respectively) ~4% • Vector Wind RMS ~3.5 m/s (both) ~2.5 m/s • ALL AMDAR data Meet WMO requirements for mesoscale observations

  27. The FutureWVSS-II Installations increasing on Southwest Airlines B-373

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