Utilization of GPS Radio Occultation Data for the Studies of Atmosphere Dynamics. Toshitaka Tsuda RISH, Kyoto University

Transcription

1 The First International Workshop on Prevention and Mitigation of Meteorological Disasters in Southeast Asia 3-5 March 2008, Kyoto Utilization of GPS Radio Occultation Data for the Studies of Atmosphere Dynamics Toshitaka Tsuda RISH, Kyoto University

2 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model Scientific applications Current and Future GPS RO missions

3 Occultation (solar eclipse, lunar eclipse) Radio occultation technique Application of the radio occultation to the Earth s atmosphere was studied in 1980 s in US and Russia. It was realized by the GPS/MET project in by using a stable GPS radio signal and accurate orbital elements of a satellite (position: 10cm, speed: 0.1mm/s) Exploration of planetary atmosphere and ionosphere by analyzing radio signals emitted from an interplanetary spacecraft. Mariner IV: Mars, 1965 Mariner V: Venus, 1967 Voyager: Saturn, Jupiter

4 Radio and optical ray path bends at an interface of two layers with different refractive index values. Snell s Low n 1 sin a = n 2 sin b n 1 a n 2 b

5 Typical Geometry for Precise Orbit Determination Modified from a PPT file by Dr. T.P. Yunck

6 Because of motion of LEO satellite, time variation of the bending angle is obtained. Onion Skin Model Partial bending angle in individual layer can be related to the refractive index gradient in the corresponding layer by a triangular matrix. (iteration method) Snell s law must be satisfied at the interface between the layers.

7 Basic Concept of GPS Occultation Measurement GPS Signals received on a low earth orbiting (LEO) satellite are used for an active limb sounding of the atmosphere and ionosphere. During a rising or setting of a GPS satellite (occultation), the radio rays between the GPS and LEO satellites successively scan the atmosphere (and the ionosphere) from the receiver height down to the surface. A refractive index profile can be retrieved from the time variations of the ray bending angles. Propagation Delay of GPS Signals Determination of LEO Orbit Bending of Radio Ray Path Refractive Index Profile near the Tangent Point LEO Satellite Bending Angle Humidity Temperature Electron Density Tangent Point Data Assimilation Into NWP models GPS Satellite

8 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model Scientific applications Current and Future GPS RO missions

9 GEOSS (Global Earth Observation System of Systems) in Japan Theme 2 : Water cycle and climate changes in the Asia-monsoon region Application of of GPS radio occultation (RO) data data to to the the studies of of temperature and and humidity variations in in the the tropical troposphere Project Leader: Prof. Prof. Toshitaka Tsuda Tsuda (RISH, (RISH, Kyoto Kyoto University) (1) Development of retrieval algorithm for GPS RO data Y. Murayama (NICT; National institute of information and Communications Technology), Y. Aoyama (NIPR: National Institute of Polar Research), H. Hayashi, J. Furumoto (RISH, Kyoto Univ.) (2) Assimilation of GPS RO data into a meso-scale numerical weather prediction model Y. Shoji, H. Seko, T. Kawabata, K. Aonashi, M. Kunii (MRI; Meteorological Research Institute) (3) Validation and scientific application of GPS RO data T. Tsuda, M. Shiotani, T. Nakamura, T. Horinouchi, H. Hayashi, J. Furumoto (RISH; Research Institute for Sustainable Humanosphere, Kyoto University), S. Yoden, N. Nishi (Dep. Earth and Planetary Sci., Kyoto University)

10 GPS Radio Occultation with CHAMP, SAC-C and COSMIC Fundamental data-sets: phase delay (φ), bending angle(α) (1)Development of data analysis system (2)Assimilation of GPS RO data to MSM (3)Validation of GPS RO data and application to scientific subjects NICT MRI Kyoto-U (1) Retrieval of refractive index (n) with a good height resolution (2) Development of 4D-Var assimilation system of MSM, and expansion of the MSM area toward the equatorial region Objective analysis, JMA Satellite data: AQUA-AIRS Initial value (1) 1D-Var analysis of temperature (T) and humidity (q) (2) Assimilation of φ and n into MSM for a better prediction of severe weather, including typhoon Initial value JMA: RSM, GSM (3) Ground-based observations at validation sites: balloon, lidar etc (3) Validation of n, T and q with groundbased and satellite data, and comparison with objective analysis (3) Time and spatial variations of n, T and q in the Asian monsoon region

11 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model Scientific applications Current and Future GPS RO missions

12 Main Ground-Based Validation Sites in in the Asia Monsoon Region in in our Project Ground-based validation sites (4) (4) MST Radar Observatory Gadanki, India (13.5N, 9.2E) ISRO-NARL (1) The MU Radar Obs., Shigaraki, Japan (34.8N, 136.1E) RISH (3) (3) Equatorial Atmosphere Radar (EAR), Koto Tabang, Indonesia (0.2S, 100.3E), RISH and and LAPAN (2) Okinawa Obs., Ogimi, Japan (26.7N, 128.1E9) NICT

13 (1) (1) The Middle and Upper (MU) Atmosphere Radar, RISH, Kyoto Univ (34.8N, 136.1E) LIDAR (Raman, Rayleigh) 46.5 MHz, 1MW, 103mφ 475 Yagi antenna array

14 (3) (3) Equatorial Atmosphere Radar (EAR), West Sumatra, Indonesia (0.2S, 100.3E) VHF (47MHz) wind profiler Antenna array (110 m in diameter): 560 sets of 3-elements Yagi antennas. Peak transmitting power: 100 kw. Radiosonde Lidars RASS X-band radar Micro rain radar Optical rain gauge Ceilometer Radiometer Disdrometer GPS receiver

15 (4) (4) Gadanki MST radar facility (13.5N, 79.2E) National Atmosphere Research Laboratory (NARL), Indian Space Research Organization (ISRO) VHF wind profiler 53 MHz, 1MW, 100mx100 m, Yagi antenna array Raman and Rayleigh lidars Intensive radiosode soundings VAISALA: RS80, RS92 daily at 12 GMT from Apr 10 - Sep profiles

16 High resolution radiosonde data by routine and campaign soundings Ground-based validation sites Kyoto-U, Shigaraki MU obs. India, Gadanki MST radar obs. We obtain original records of routine radiosonde soundings at meteorological agencies (twice daily at 0 and 12 GMT) with sampling interval of 2-5 seconds (10-30 meter height resolution) Japan (JMA): 18 sites Malaysia: 7 sites Singapore: 1 site Vietnam: 3 sites Kyoto-U/LAPAN Equatorial Atmosphere Radar (EAR), Indonesia Japan Meteorol. Agency (JMA) 18 stations, 2/day NICT, Okinawa obs. Malaysia (7 sites), Vietnam (3 sites), Singapore Met. Offices

17 Derivation of atmospheric temperature and humidity from a refractive index profile observed with GPS occultation Refractive index: n (n-1)x10 6 =77.6p/T x10 5 q/t 2 atmospheric temperature: T (K) pressure: p (hpa) partial pressure of water vapor: q (hpa) For a dry atmosphere, the second term of n can be neglected. Assuming ideal gas law, p = ρrt (n-1)x10 6 =77.6ρR i.e., n is uniquely related to the atmospheric density, ρ(kg/m3)). By using hydrostatic equilibrium (dp/dz=-gρ), pressure (p) can be integrated. Then, by employing equation of state, a T profile is derived. In a moist atmosphere, T and q are separated from n by applying 1D- Var analysis with NWPM values as the initial value.

18 Comparison of temperature profiles between the COSMIC GPS RO result (#49 and #50) and radiosonde at Kuching, Malaysia. Profiles are shifted by 5K each. Kuching #50 #49 Temperature profiles with GPS RO have a height resolution comparable to a radiosonde, which is useful for the studies of the detailed structure of the tropopause, perturbations with atmospheric waves, etc.

19 Kuching #49 #50 Comparison of temperature profiles between the COSMIC GPS RO result (#49; Blue and Green) and radiosonde (Orange). Profiles are shifted by 5K each. Retrieval at UCAR (Blue): Geometric Optics and FSI above/below 10.6 km Retrieved at RISH (Green): FSI below 30.5 km (We will open the RISH database to public. Coming soon!)

20 Comparison of temperature profiles between the COSMIC GPS RO result (Green) and other satellites. Limb sounding: HIRDLS (Blue, solid) SABER (Blue, dotted). Nadir: AIRS (Red). A nearby radiosonde profile (Orange)

21 Comparison between 1D-Var analysis of T (left) and q (right) from COSMIC GPS RO data with a nearby radiosonde sounding at the JMA Yonago station on 17 November 2006 Good agreement between GPS RO(1D-Var) and radiosonde Black dashed: GSM forecast, Black solid: our 1D-Var analysis Blue dashed: NCEP-AVN, Blue solid: UCAR s 1D-Var analysis Orange: NCEP/NCAR reanalysis Red: radiosonde result at Yonago, Japan.

22 In a moist atmosphere, temperature (T) and humidity (q) are separated from n by applying 1D-Var analysis with NWPM values as the initial value. Profiles of q with COSMIC GPS RO are compared with radiosonde results September UT Radio Sonde : Latitude 2.73 N, Longitude E Cosmic Radio Sonde Airs Kuala Lumpur International Airport (2.73N, 101.7E), Malaysia Height (km) Water vapor (g/kg) 28 September UT Radio Sonde : Latitude 2.73 N, Longitude E Cosmic Radio Sonde Airs Height (km) Statistical Comparison between COSMIC and Radio sonde at Klia Latitude 2.73 o N, Longitude o E 10 No. of Occultations = No. of Occultations =5 (>2.0 km) 4 - ( km) 3 - ( km) 2 - ( km) Height (km) Water vapor (g/kg) Mean (WV COSMIC -WV Rad ) (g/kg)

23 Advantages and Application of GPS Radio Occultation (RO) Data Advantages = Good vertical resolution superior to conventional satellite radiometer measurements: km with geometrical optics, and 0.1 km with advanced algorithm = Accurate profiles comparable to balloon soundings over both land and oceans Application (6.9S,107.6E) Radiosonde Comparison of a temperature profile between GPS occultation (GPS/MET) and a nearby radiosonde in Indonesia GPS occultation = Data assimilation in to both global and meso-scale numerical weather prediction models to improve prediction accuracy = Studies of detailed temperature and humidity variations by taking advantages of good height resolution and accuracy In a dry atmosphere (>10km) temperature can be determined with a good height resolution. Detailed thermal structure around the tropopause is seen. In a moist atmosphere humidity can be delineated with 1D-Var analysis by referring to model results and/or satellite data.

24 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model 16:30 16:50 Masaru KUNII (MRI); Meso-Scale Data Assimilation Experiment in Low Latitudes Scientific applications Current and Future GPS RO missions

25 Courtesy by E. Ozawa

26 Various methods for data assimilation Courtesy by E. Ozawa (JMA) Retrieval Procedure of GPS RO Data Delay length by the atmosphere operational use at JMA Bending angle Refractivity Assimilation concept Forward Temperature First guess Tangent Linear Adjoint No operator Analysis Forecast experiments 3 or 4D-Var data assimilation using GPS data Improvement of the initial field Improvement of the forecast

27 4D-Var assimilation of LEO-GPS RO data into a global numerical prediction model at JMA (Japan Meteorological Agency) Courtesy by E. Ozawa

28 4D-Var assimilation of of CHAMP-GPS RO RO data data in in to to a meso-scale numerical weather prediction model, H. H. Seko Seko (MRI) レーダアメダス 時 通常のデータ (CNTL) CNTL+CHAMP 7/ 時 (FT=3) CHAMP-GPS RO data 7/ 時 (FT=3) 7/ 時 (FT=3) Radar observations of precipitation during LT on July 16, Prediction without GPS RO data. Prediction with GPS RO data.

29 Prediction on development of a typhoon is greatly improved by assimilating GPS RO data with COSMIC into a meso-scale weather prediction model at MRI. 16:30-16:50 Masaru KUNII (MRI); Meso-Scale Data Assimilation Experiment in Low Latitudes G A MA-RO GA MA FT=7 2 FT=7 2 ベストトラック MA-RO FT=9 6 FT=9 6 図 年 7 月 27 日 9 時の全球解析値 (GA) 通常観測データを同化したメソ解析値 (MA) MA に加え GPS 掩蔽データを同化したメソ解析値 (MA-RO) を初期値とする台風予報実験のうち GA と MA-RO についての 時間後の気圧および降水分布 図 年 7 月 27 日 9 時の全球解析値 (GA) 通常観測データを同化したメソ解析値 (MA) MA に加え GPS 掩蔽データを同化したメソ解析値 (MA- RO) を初期値とする台風予報実験のそれぞれについて 台風 0705 号の中心気圧の時系列を示したもの

30 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model Scientific applications Current and Future GPS RO missions

31 Active cloud convection in the tropics generates various atmospheric waves which propagate upward carrying wave energy and momentum.

32 COSMIC: 140E, Dec 2006 Red: NCEP 7-day averaged u, with solid eastward, dashed westward Wave mean flow interactions Geostrophic adjustment of jet stream, planetary waves Meteorological disturbances Tropopause Orographic sources too Topography Cloud convection Wind shear in the tropics around jet More PE equatorward of jet at ~10km may be due to wider range of generation frequencies. Low PE at jet core. Interaction between waves and background mean flow (NH). Large PE extends upward and poleward toward the polar night jet.

33 Dec 2003 / Jan-Feb 2004 Cloud top height /OLR(K) Atmospheric wave energy Ep (J/kg) at km Convective rain rate (mm) / TRMM-PR In the northern winter months (Dec/Jan/Feb), intense cloud convections are located over Indonesia and western Pacific, which actively generates atmospheric gravity waves as well as Kelvin wave-like disturbances in the equatorial region.

34 Gravity wave potential energy (Ep) at km altitude in winter 2006/07 (Dec-Feb) by using the COSMIC GPS RO temperature data. Red contour: the winter mean NCEP u at hpa in units of ms 1. Black contour: winter mean GPCP precipitation in mm day 1 Ep is low over Pacific Canadian Rockies have large Ep Himalayas & Tibet have large Ep some orographic effects but also jet stream Japan separate large Ep: strong jet & orography Large Eastern USA Ep associated with jet

35 Outline Basic concept of GPS radio occultation (RO) technique A project of GEOSS on utilization of GPS RO data Validation of GPS RO profiles with ground-based observations Data assimilation into a meso-scale weather prediction model Scientific applications Current and Future GPS RO missions

36 Bull. Amer. Met. Soc., 77, 19-40, GPS/MET (GPS Meteorology) Experiment First GPS Occultation Experiment was conducted by UCAR from April 1995 to February 1997 by using a small satellite (MicroLab-1). A total of 10,853 profiles were obtained, though the observation periods were limited to the period without anti-spoofing (A/S) encryption.

37 GPS radio occultation (RO) missions GPS/MET CHAMP GFZ, July 2000 UCAR, Apr 95-Feb 97 SAC-C Argentine + JPL, Nov 2000 GRACE FORMOSAT-3/COSMIC METOP Ocean Sat/Mega Tropiques CHINOOK(SWIFT+ARGO) UCAR + Taiwan-NSPO, Apr 2006 EUMETSAT, 2006 India-ISRO, (low inclination) Canada-CSA, 2011 (polar orbit) COSMIC-follow on (US), CIERTO (commercial), GEMSS (India),. Data rate 5,000/yr /day/Satellite 2,500/day 5,000/day

38 Number of GPS RO data with CHAMP (top) and FORMOSAT-3/COSMIC (bottom) CHAMP One GPS RO antenna 4,500/month =150/day COSMIC: 6 LEO satellites 2 GPS RO antennas (It is expected to obtain 12 times larger data than CHAMP) 2,000/day

39 CHAMP / COSMIC Occultations Climatological study study (monthly mean) mean) with with CHAMP GPS GPS RO RO data data from from May May Dec Distribution of the CHAMP GPS RO data in October 2002 Preliminary case case studies with with COSMIC data data after after September 2006, 2006, with with a better better time time and and spatial spatial resolution COSMIC GPS RO data in 5 days on September 2006 line: number of GPS data in each 10 deg, red dot: data rate normalized by the area

40 Comparison of data (temperature profiles) points between (LEFT) GPS RO with FORMOSAT-3/COSMIC and (RIGHT) Routine radiosonde stations. GPS RO data on 4 June 2007, 2081 points Routine radiosonde atations (850 sites, 1-2 launches/day)

41 India, Tirupati MST radar obs. Intensive ground validation sites Distribution of GPS occultation data Malyasia, Vietnam, Singapore, Indonesia Met. Office Kyoto-U, Shigaraki MU obs. NICT, Okinawa obs.

42 SUMMARY 1. We developed a retrieval software for GPS RO data (refractive index; n) with a good height resolution (about 100 m) comparable to a radiosonde. 2. In the lower troposphere n is separated into temperature(t ) and humidity (q) by applying 1D-Var analysis with GCM results as the initial value. 3. Through close international collaboration, we operate four validation sites for GPS RO (Shigaraki and Okinawa, Japan; EAR, Indonesia, Gadanki, India), where observations with a wind profiler, lidar, etc are continued. We also use campaign and routine radiosonde results for comparison. 4. We found a very good consistency between GPS RO and radiosonde results in the refractive index (n), temperature (T ) and humidity (q). 5. We have created a data-base of COSMIC GPS RO data for practical and scientific utilization. The data-base is very useful especially in the Asia monsoon region where routine balloon soundings are sparse. 6. Prediction accuracy of severe weather phenomena, such as a typhoon, a meso-scale weather prediction model as greatly been improved by assimilating GPS RO data. 7. GPS RO data (T and q) are useful for the studies of structure and perturbations of temperature and humidity at 0-40 km, such as stratospheric wave energy, details of the tropopause structures, thin layers in T and q profiles.

43 Thank you