1. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Dry Bias in the Beijing Radiosonde Soundings as Revealed by GPS and MWR Measurements Chu Yanli 1, Ying-Hwa Kuo 2, John Braun 2, Zhang Chaolin 1, Wang Yingchun 1, Zhang Jingjiang 1, Wang Jingli 1 1. Institute of Urban Meteorology (IUM), Beijing Meteorological Bureau (BMB), Beijing, China 2. COSMIC, University Corporation for Atmospheric Research (UCAR), Boulder, CO., USA

2. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Before 01-Aug-2006(15 GPS stations) After 01-Aug-2006(42 GPS stations) Introduction of the ground-based moisture observation network around Beijing ground-based GPS stations 54511 radiosonde (RS) station, ground-based GPS station, microwave water vapor radiometer (MWR) station 1

3. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Introduction of instruments RS at 54511: GTS-1 radiosonde system from ChangWang MeteoTech Co. Ltd, China MWR at 54511: TP/WVP-3000 from Radiometrics Corporation, US GPS antenna & receiver at 54511: TRM29659.00 & TRIMBLE 5700 from Trimble Company., US GPS antenna & receivers at Fang Shan district: TOPCR3_GGD & TPS LEGACY from Topcon Co., Japan 2

4. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Methodology GPS_PW: RS_PW: Mandatory levels: surface, 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100 Specific levels: about 10 levels 3

5. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 30 km Ground-based GPS network at Fang Shan district to the south of Beijing with 5 ~ 10 km station separation 4 ground-based GPS stations 54511 radiosonde (RS) station

6. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Temporal variation of GPS PW in the Fang Shan district of Beijing through the 12-month period of September 2003 - August 2004. 5

7. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Comparison of PW derived from GPS and RS over the 10-month period of January - October 2004. (a) scatter diagram of GPS PW versus RS PW, (b) scatter diagram of GPS-RS PW differences versus RS PW. Difference between GPS PW and RS PW over the 10-month period of January - October 2004. BIAS(mm)SD(mm) -2.992.72 6

8. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Monthly mean values of RS PW (white dots) and its bias differences (red squares) from the GPS PW over the period of January - October 2004. 7

9. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 PW retrieved from IGS ZTD reveals the obvious dry bias in the radiosonde soundings at Beijing 54511 station during August 2004. 8

10. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Investigate the systematic difference between GPS PW and RS PW. Is the systematic difference aroused by the climatic deviation? Or which one is more accurate? 9

11. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 (a)(b) (a) Mean bias and (b) SD difference between a GPS station and YSDD GPS station as a function of separation distance over the period of January - October 2004. SITE Height Difference to YSDD (m) Separation to YSDD (km) PW BIAS to YSDD (mm) PW SD to YSDD (mm) 54511 (RS)-1530-2.992.72 HCHD (GPS)13190.341.17 GDSS (GPS)138-0.260.77 DDSS (GPS)1512-0.140.81 YCSS (GPS)2514-0.250.96 Difference of station height, station separation, PW mean bias and PW standard deviation (SD) at the radiosonde station and a GPS station as compared against YSDD GPS station over the period of January - October 2004. The height of YSDD station is 38 m. 10

12. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Comparison of GPS ZTD between IUM and GFZ and CODE solutions at BJFS GPS station over the month of August 2004. BIAS(mm)SD (mm) IUM-COD2.10 (0.32)8.77 (1.35) IUM-GFZ1.97 (0.30)7.60 (1.17) COD-GFZ-0.13 (0.02)2.87 (0.44) Difference of GPS ZTD between IUM and GFZ and CODE solutions at BJFS GPS station over August 2004. ZTD difference (black) is scaled to PW (red) in II = 6.5. 11

13. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 12 Bias(mm) SD(mm) Samples GPS-MWR 0.2 0.98 583 RS-MWR -2.3 0.69 28 RS-GPS -1.9 1.30 32

14. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 13 Bias(mm) SD(mm) Samples GPS-MWR -0.9 2.4 1347 RS-MWR -2.7 2.7 44 RS-GPS -1.4 2.8 50

15. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Difference of the moisture observations in GTS-1 minus RS-80A at the Beijing 54511 station over 26 Nov – 3 Dec 2003 by Prof. ShuQing Ma, CMA 14

16. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 June Wang etc., NCAR, RS80 JingMia Liu etc., CMA, Naqu, Tibet, GTS1 Dry bias in the radiosonde soundings as revealed in the other experiments 15

17. 5 th ICMCS - Dry bias in the Beijing radiosonde soundings, 02-Nov-2006 Summary and discussion:. Nakamura (2004) compared GPS PW with measurements of the Vaisala RS- 80A radiosonde, and found similar dry bias in the RS-80A radiosonde soundings.. Furthermore, he showed that relative humidity as measured by the RS-80A was about 5 to 15% smaller than that of the dew-point hygrometer.. Our results showed that the Beijing radiosonde soundings (using a GTS-1 radiosonde system) has a 15% dry bias compared with the GPS PW over a ten-month period. GTS-1 is a radiosonde made by ChangWang MeteoTech Co. Ltd., which was known to have been calibrated against RS-80A.. We suggest additional comparison of humidity measurements by GTS-1 with a dew-point hygrometer to further evaluate the dry bias of the GTS-1 system.. We also suggest performing similar studies for other radiosonde stations in China. 16