New Radiosonde Temperature Bias Adjustments for Potential NWP Applications Based on GPS RO Data

Transcription

1 Eighth FORMOSAT-3/COSMIC Data Users Workshop 30 September 2 October 2014 Boulder, Colorado, USA New Radiosonde Temperature Bias Adjustments for Potential NWP Applications Based on GPS RO Data Bomin Sun 1,4, Tony Reale 1, Bradley Ballish 2, Dian J. Seidel 3, and Andrew Collard 2,4 1 NOAA/NESDIS/STAR, College Park, Maryland 2 NOAA/NWS/NCEP, College Park, Maryland 3 NOAA/OAR/ARL, College Park, Maryland 4 IMSG, College Park, Maryland 1

2 Problems Radiosonde temperature observations have biases Errors due to solar and IR radiation Adjustments made at stations are not adequate, so biases remain NCEP radiation correction (RADCOR)method is outdated Based on RS80 as the reference Does not include modern sonde types 2

3 Biases in RAOB and GFS forecast relative to COSMIC Tdry (global average over all stations) hpa Sun et al. (2013, JGR) Solar Elevation Categories hpa

4 Outline Use GPS RO Tdry retrievals as a reference to quantify radiosonde T errors and develop new adjustments based on COSMIC-RAOB collocation data of from NPROVS Compare new adjustments with existing NCEP RADCOR Radiosonde observation (OB) minus the NCEP GDAS background (BG) with and without our corrections. Based on data of

5 NOAA Products Validation System (NPROVS) Global Collocations for one day Different products collocated at one site 5

6 Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) Occulting GPS Ionosphere From Bill Kuo 2003 Neutral atmosphere Occulting LEO All-weather sounding capability High vertical resolution No calibration issues Good spatial and temporal distribution N P 77.6 T 3.73x10 5 P T w 2 Earth Dry term wet term P: pressure T: temperature Pw: water vapor pressure 6

7 COSMIC dry T and wet T Dry temperature: derived by neglecting the water vapor term in refractivity (N) Wet temperature: 1DVar initialized with NWP forecast For This Study Dry T (at or above 150 hpa) + Wet T (below 150 hpa) serve as Reference to assess raob temperature biases Dry T Wet T 7

8 Sonde types flown in global operational network ( ) Operational raobs are used for the analysis. Data for most of the sonde types already experienced radiation corrections at the field sites using schemes 8 provided by vendors, etc.

9 Global sondes difference from COSMIC T Mean Diff. SD Diff. 186,000 profiles 9

10 Global sondes (older vs. newer) difference from COSMIC T Older sondes Mean Diff. Newer sondes Mean Diff. Older sondes: already flown prior to 2000 and are still in use Newer sondes: started being flown after ,000 profiles 152,000 profiles 10

11 Vaisala RS92 difference from COSMIC T Mean Diff. SD Diff. 72,300 profiles Warm forecast in the troposphere due to assimilation of warm aircraft data Ballish and Kumar (2008, BAMS) 11

12 Russian MRZ difference from COSMIC T Mean Diff. SD Diff. 40,000 profiles 12

13 Sippican B2 (no correction done) difference from COSMIC T Mean Diff. SD Diff profiles 13

14 Sonde T difference from COSMIC T NCEP Radcor

15 Tables of new RADCOR (varying with height and solar angle) are created for all individual sondes. 15

16 Evaluate the new RADCOR Statistics of radiosonde observation (OB) minus Background (BG) Unadjusted radiosonde (corrected at site using manufacturer RADCOR) Adjusted radiosonde by NCEP RADCOR Adjusted radiosonde by our new RADCOR The BG was from existing operations (i.e., assimilation of radiosonde data adjusted by NCEP RADCOR, NOT by our new RADCOR). 16

17 OB-minus-BG for Global New RADCOR Unadjusted RAOB-minus-Background Adjusted RAOB (NCEP RADCOR) -minus-background Adjusted RAOB (New RADCOR) -minus-background 17

18 Biases in RAOB and GFS forecast T diff. from COSMIC Tdry (global average over all stations) hpa Raob has a warm bias ECMWF-minus-raob NCEP-minus-raob It is anticipated that assimilation of new radcor-adjusted raobs move the NCEP GFS towards ECMWF. 18

19 Summary Radiation-induced biases in global operational radiosonde temperature data ( ) are examined by using collocated GPSRO COSMIC data The data on average show a nighttime cold bias and a daytime warm bias with daytime bias increasing with altitude and solar elevation angle New RADCOR varying with solar angle and height was developed for individual sonde types The stats of OB BG ( ) indicates that the corrected temperature using new RADCOR generally fits the model background better than using NCEP RADCOR or without adjustment. 19

20 Future work Test the potential operational value of the new RADCOR in the NCEP data assimilation and forecast system. Evaluate the sensitivity of choice to GPSRO products. 20

21 UCAR COSMIC & EUMETSAT GRAS 09/08/2014, temperature retrieval at 103 hpa COSMIC 1387 GRAS

22 COSMIC vs GRAS (within 0.5 hr & 250 km) GRAS (brown) COSMIC (black) Product uncertainty is desirable for application. 22

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24 UCAR COSMIC vs. EUMETSAT GRAS COSMIC and GRAS collocated at radiosonde sites 6hr & 250-km Tdry diff. from ECMWF for COSMIC and GRAS Aug , 2014 Sept. 2-12,

25 UCAR COSMIC vs. EUMETSAT GRAS COSMIC and GRAS collocated at radiosonde sites 3hr & 250-km Tdry diff. from ECMWF for COSMIC and GRAS Aug , 2014 Sept. 2-12,

26 UCAR COSMIC vs. EUMETSAT GRAS COSMIC and GRAS collocated at radiosonde sites 3hr & 250-km Tdry diff. from radiosonde for COSMIC and GRAS Aug , 2014 Sept. 2-12,