同化福衛三號全球定位系統無線電掩星觀測對西北太平洋地區颱風路徑預報之影響

摘要

本文就颱風預報作業的觀點，系統性評估全球定位系統無線電掩星（Global Positioning System Radio Occultation, GPSRO）觀測對西北太平洋地區颱風路徑預報的效益。實驗以中央氣象局作業之45公里解析度TWRF（typhoon WRF, The Weather Research & Forecasting Model)模式分析預報系統，對西北太平洋地區2008至2010年間11個颱風個案（總共有327個分析預報時窗）分別對有無同化福衛三號（FORMOSAT-3/COSMIC）GPSRO折射率觀測作比較。平均而言，在每12小時的部分循環（partial cycle）同化期間，約有100筆GPSRO觀測被納入同化。實驗結果顯示，同化GPSRO觀測能有效改善36小時之後的路徑預報，至72小時預報則能減少路徑預報誤差約12km（5%），此預報誤差之改善程度雖不大，但具有統計意義上的顯著性。路徑預報誤差有所改進的原因是同化GPSRO對於模式溫度、水氣及風場的分析與預報均能有所改善。更進一步的分析顯示，颱風路徑預報誤差因西太平洋副熱帶高壓及其環流預報藉由同化GPSRO而獲得改善，而使得對環境駛流能有更佳的掌握。
此外，本文基於同化GPSRO折射率觀測能改善颱風路徑預報的結論，利用偏折角局地波譜寬（local spectral width, LSW），測試更進一步提升GPSRO觀測效益之可行性。LSW是在掩星觀測發生多重路徑傳播（multipath propagation）與繞射現象，為決定掩星觀測偏折角時所衍生之觀測產品。偏折角的LSW可用來表示該筆RO觀測之不確定性，透過此特性，本研究將LSW運用在同化福衛三號GPSRO觀測折射率時的觀測品質檢定（quality control, QC）及四維動態觀測誤差。透過颱風個案實驗顯示，利用LSW之QC與動態觀測誤差技術，對於改善該個案颱風路徑預報均有正面影響，建議LSW應用技術的發展有其可行性。

The impacts of assimilation of FORMOSAT-3/COSMIC GPSRO data on the prediction of typhoons over the Northwestern Pacific

Abstract

In this research, we perform a systematic evaluation of the impact of Global Positioning System radio occultation (GPSRO) data on typhoon track prediction over the Northwestern Pacific with respect to the point of view of operational forecasts. Specifically, we perform data assimilation and forecast experiments using the Typhoon Weather Research and Forecasting (TWRF) system, the regional operational model, at 45-km resolution on eleven typhoons (with a total of 327 cases) in the period of 2008-2010 over the Northwestern Pacific, with or without the use of FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) GPSRO refractivity observations. On average, about 100 GPSRO soundings are assimilated over a 12-h partially cycling assimilation period. The results indicate that the assimilation of GPSRO data reduces the typhoons’ track forecast errors after the 36-hour forecast, especially the reduction of the 72-hour track forecast errors by approximately 12 km (5%). Although this is only a modest improvement, it is statistically significant. The improvement of track forecast errors is due to improvement of the analysis and the forecast of temperature, water vapor, and wind fields by assimilating of GPSRO data. Further analysis shows that the reduction in typhoon track forecast errors can be attributed to the improved prediction of Western Pacific Subtropical High (WPSH) and its associated circulation, which leads to better forecasting of the environmental steering flow.
On the other hand, based on the conclusion of positive impacts of GPSRO data on forecast of typhoon movements, local spectral width (LSW) of bending angle is applied to further increase this impact. The LSW is a derivative obtained while retrieving the bending angle under multipath propagation and diffraction and can be used to as a measure of the uncertainty of RO observation. Hence, taking the advantage of this feature, this study applied the LSW on the quality control procedure of assimilating the FORMOSAT-3/COSMIC GPSRO refractivity data and its 4-D dynamic observational errors in TWRF. By the results from experiments for typhoon events, applications of the LSW show neutral impact on both track and field forecasts but have positive impact for some cases. According to the analyses of these cases, The LSW have the potential to increase the value of GPSRO data.

參考文獻
沈彥志、馮欽賜、陳雯美、曹伶伶、陳御群、楊明仁, 2010：以GSI同化GPS RO資料對中央氣象局全球預報系統之影響，九十九年天氣分析與預報研討會，台北市，2010年6月28日至30日，中央氣象局主辦，247-252。
沈彥志、陳御群、楊明仁、馮欽賜、陳雯美, 2011：GPSRO資料對中央氣象局全球模式之颱風路徑預報的影響，建國百年天氣分析預報與地震測報研討會，台北市，2011年9月20日至22日，中央氣象局主辦，90-93。
陳御群、楊明仁、張忍成、曾建翰, 2008：同化GPS無線電掩星觀測應用於中央氣象局全球預報系統之影響，九十七年天氣分析與預報研討會，台北市，2008年9月9日至11日，中央氣象局主辦，45-50。
Anisetty, S. K. A. V. P. R., C.-Y. Huang, and S.-Y. Chen, 2014: Impact of FORMOSAT-3/COSMIC radio occultation data on the prediction of super cyclone Gonu (2007): A case study. Nat. Hazards, 70, 1209–1230, doi:10.1007/s11069-013-0870-0.
Anthes, R. A. , D. Ector, D. C. Hunt, Y.-H. Kuo, C. Rocken, W. S. Schreiner, S. V. Sokolovskiy, S. Syndergaard, T.-K. Wee, Z. Zeng, P. A. Bernhardt, K. F. Dymond, Y. Chen, H. Liu, K. Manning, W. J. Randel, K. E. Trenberth, L. Cucurull, S. B. Healy, S.-P. Ho, C. McCormic, T. K. Meehan, D. C. Thompson, and N. L. Yen, 2008: The COSMIC/FORMOSAT-3 mission: Early results, B. Am. Meteorol. Soc., 89, 313–333.
Ao, C. O., T. K. Meehan, G. A. Hajj, A. J. Mannucci, and G. Beyerle, 2003: Lower troposphere refractivity bias in GPS occultation retrievals. J. Geophys. Res., 108, 4577, doi:10.1029/2002jD003216, D18.
Aparicio, J. M., Deblonde, G., Garand, L., and Laroche, S., 2009: The signature of the atmospheric compressibility factor in COSMIC, CHAMP and GRACE radio occultation data, J. Geophys. Res., 114, D16144, doi:10.1029/2008JD011156.
Buontempo, C., Jupp, A., and Rennie, M. P., 2008: Operational NWP assimilation of GPS radio occultation data, Atmos. Sci. Lett., 9, 129-133.
Chen, F., and Dudhia, J., 2001: Coupling an advanced land surface-hydrology model with the Penn State-NCAR MM5 modeling system . Part I: Model implementation and sensitivity, Mon. Weather Rev., 129, 569-585.
Chen, S.-Y., C.-Y. Huang, Y.-H. Kuo, Y.-R. Guo, and S. Sokilovskiy, 2009: Assimilation of GPS Refractivity from FOMOSAT-3/COSMIC Using a Nonlocal Operator with WRF 3DVAR and Its Impact on the Prediction of a Typhoon Event. Terr. Atmos. Ocean Sci., 20, 133-154, doi: 10.3319/TAO.2007.11.29.01(F3C).
Cucurull, L., 2010: Improvement in the Use of an Operational Constellation of GPS Radio Occultation Receivers in Weather Forecasting. Wea. Forecasting, 25, 749-767.
Cucurull, L., and J. C. Derber, 2008: Operational implementation of COSMIC observations into NCEP’s global data assimilation system, Weather Forecast., 23, 702-711.
Cucurull, L., J. C. Derber, R. Treadon, and R. J. Purser, 2007: Assimilation of Global Positioning System Radio Occultation Observations into NCEP’s Global Data Assimilation System, Mon. Weather Rev., 135, 3174-3193.
Cucurull, L., J. C. Derber, and R. J. Purser, 2013: A bending angle forward operator for global positioningsystem radio occultation measurements, J. Geophys. Res. Atmos., 118, 14–28, doi:10.1029/2012JD017782.
Galarneau, T. J. and C. A. Davis, 2013: Diagnosing forecast errors in tropical cyclone motion, Mon. Weather Rev., 141, 405–430.
Gorbunov, M. E., 2002: Canonical Transform Method for Processing GPS Radio Occultation Data in Lower Troposphere, Radio Sci., 37, 9-1–9-10; doi: 10.1029/2000RS002592.
Gorbunov, M. E., K. B. Lauritsen, A. Rodin, M. Tomassini, and L. Kornblueh, 2005: Analysis of the CHAMP Experimental Data on Radio-Occultation Sounding of the Earth’s Atmosphere, Atmos. Ocean. Phys., 41, 726-740.
Gorbunov, M. E., K. B. Lauritsen, A. Rhodin, M. Tomassini, and L. Kornblueh, 2006: Radio Holographic Filtering, Error Estimation, and Quality Control of Radio Occultation Data, J. Geophys. Res., 111, D10 105, doi:10.1029/2005JD006427.
Hajj, G. A., C. O. Ao, B. A. Iijima, D. Kuang, E. R. Kursinski, A. J. Mannucci, T. K. Meehan, L. J. Romans, M. de la Torre Juarez, and T. P. Yunck, 2004: CHAMP and SAC-C atmospheric occultation results and intercomparisons, J. Geophys. Res., 109, doi:10.1029/2003JD003909 (D06109).
Healy, S. B., and J.-N. Thépaut, 2006: Assimilation experiments with CHAMP GPS radio occultation measurements. Q. J. Roy. Meteor. Soc., 132, 605-623, DOI: 10.1256/qj.04.182.
Healy, S. B., 2008: Forecast impact experiment with a constellation of GPS radio occultation receivers, Atmos. Sci. Lett., 9, 111-118.
Hong, S.-Y., Y. Noh, and J. Dudhia, 2006: A new vertical diffusion package with an explicit treatment of entrainment processes. Mon. Wea. Rev., 134, 2318-2341.
Ho, S.-P., G. Kerchengast, S. Leroy, J. Wickert, A. J. Mannucci, A. Steiner, D. Hunt, W. Schreiner, S. Sokolovskiy, C. Ao, M. Borsche, A. von Engeln, U. Foelsche, S. Heise, B. Iijima, Y.-H. Kuo, R. Kursinski, B. Pirscher, M. Ringer, C. Rocken, and T. Schmidt, 2009: Estimating the uncertainty of using GPS radio occultation data for climate monitoring: Intercomparison of CHAMP refractivity climate records from 2002 to 2006 from different data centers, J. Geophys. Res., 114, D23107, doi: 10.1029/2009JD011969.
Hollingsworth, A. and P. Lönnberg, 1986: The statistical structure of short-range forecast errors as determined from radiosonde data. Part I: The wind field. Tellus, 38A, 111–136.
Hong, S.-Y., Y. Noh, and J. Dudhia, 2006: A new vertical diffusion package with an explicit treatment of entrainment processes, Mon. Weather Rev., 134, 2318-2341.
Hsiao, L.-F., D.-S. Chen, Y.-H. Kuo, Y.-R. Guo, T.-C. Yeh, J.-S. Hong, C.-T. Fong, and C.-S. Lee, 2012: Application of WRF 3DVAR to operational typhoon prediction in Taiwan: impact of outer loop and partial cycling approaches. Wea. Forecasting, 27, 1249-1263.
Huang, C.-Y., Y.-H. Kuo, and S.-H. Chen, 2005: Improvements on Typhoon Forecast with Assimilated GPS Occultation Refractivity. Wea. Forecasting, 20, 931–953.
Huang, C.-Y., Y.-H. Kuo, S.-Y. Chen, C.-T. Terng, F.-C. Chien, P.-L. Lin, M.-T. Kueh, S.-H. Chen, M.-J. Yang, C.-J. Wang, and S. K. A. V. P. R. Anisetty, 2010: Impact of GPS radio occultation data assimilation on regional weather predictions. GPS Solut., 14, 35-49, DOI 10.1007/s 1029 1-009-0144-1.
Huang, C.-Y., S.-Y. Chen, S. K. A. V. P. R. Anisetty, S.-C. Yang, and L.-F. Hsiao, 2016: An Impact Study of GPS Radio Occultations on Frontal Rainfall Prediction with a Local Bending Angle Operator. Wea. Forecasting, 31, 129-150, DOI: 10.1175/WAF-D-15-0085.1.
Kain, J. S., and J. M. Fritsch, 1990: A one-dimensional entraining/detraining plume model and its application in convective parameterization. J. Atmos. Sci., 47, 2784-2802.
Kueh, M.-T., C.-Y. Huang, S.-Y. Chen, S.-H. Chen, and C.-J. Wang, 2009: Impact of GPS radio occultation soundings on prediction of Typhoon Bilis (2006) landfalling Taiwan. Terr. Atmos. Ocean Sci., 20, 115-131, doi: 10.3319/TAO.2008.01.21.03(F3C).
Kuo, Y.-H., X. Zou, and W. Huang, 1997: The impact of GPS data on the prediction of an extratropical cyclone: An observing system simulation experiment. J. Dyn. Atmos. Ocean., 27, 439-470.
Kuo, Y.-H., T.-K. Wee, S. Sokolovskiy, C. Rocken, W. Schreiner, D. Hunt, and R. A. Anthes, 2004: Inversion and error estimation of GPS radio occultation data, J. Meteor. Soc. Japan., 82, 507-531.
Kuo, Y.-H., H. Liu, Y.-R. Guo (more) , 2009: Impact for FORMOSAT-3/COSMIC data on typhoon and Mei-yu prediction. Recent Progress in Atmospheric Sciences: Applications to the Asia-Pacific Region, World Scientific, 458-483.
Kursinski, E. R., G. A. Hajj, K. R. Hardy, J. T. Schofield, and R. Linfield, 1997: Observing Earth’s atmosphere with radio occultation measurements. J. Geophys. Res., 102, 23429–23465.
Landsea, C. W., and J. L. Franklin, 2013: Atlantic Hurricane Database Uncertainty and Presentation of a New Dataset Format, Mon. Weather Rev., 141, 3576-3592.
Larsen, G. B., K. B. Lauritsen, F. Rubek and M. B. Borensen, 2004: GRAS-SAF Radio Occultation Data from EPS/Metop. Occultation for Probing Atmosphere and Climate. Kirchengast, G., U. Foelsche and A. Steiner, Springer, 111-118.
Liu, H., X. Zou, H. Shao, R. A. Anthes, J. C. Chang, J.-H. Tseng, and B. Wang, 2001: Impact of 837 GPS/MET bending angle profiles on assimilation and forecasts for the period June 20-30, 1995, J. Geophys. Res., 106, 31771-31786.
Liu, H., J. Anderson, and Y.-H. Kuo, 2012: Improved Analyses and Forecasts of Hurricane Ernesto’s Genesis Using Radio Occultation Data in an Ensemble Filter Assimilation System, Mon. Weather Rev., 140, 151-166.
Ma, Z., Y.-H. Kuo, B. Wang, W.-S. Wu, and S. Sokolovskiy, 2009: Comparison of local and nonlocal observation operators for the assimilation of GPS radio occultation refractivity data in the NCEP GSI system: An observing system simulation experiment. Mon. Wea. Rev., 137, 3575–3587, doi:10.1175/2009MWR2809.1.
Ma, Z., Y.-H. Kuo, F. M. Ralph, P. J. Neiman, G. A. Wick, E. Sukovich, and B. Wang: Assimilation of GPS Radio Occultation Data for an Intense Atmospheric River with the NCEP Regional GSI System. Mon. Wea. Rev., 139, 2170-2183, DOI: 10.1175/2011MWR3342.1.
Mlawer, E. J., Taubman, S. J., Brown, P. D., Iacono, M. J., and Clough, S. A. , 1997: Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave, J. Geophys. Res., 102, 16663-16682.
Parrish, D.F. and J.C. Derber, 1992: The National Meteorological Center’s Spectral Statistical Interpolation analysis system. Mon. Wea. Rev., 120, 1747–1763.
Poli, P., 2004: Effects of horizontal gradients on GPS radio occultation observation operators: II: A Fast Atmospheric Refractivity Gradient Operator (FARGO), Q. J. Roy. Meteor. Soc., 130, 2807-2825, DOI: 10.1256/qj.03.229
Poli, P., S. B. Healy, and D. P. Dee, 2010: Assimilation of Global Positioning System radio occultation data in the ECMWF ERA-Interim reanalysis, Q. J. Roy. Meteor. Soc., 136, 1972–1990, doi: 10.1002/qj.722.
Rennie, M. P., 2010: The impact of GPS radio occultation assimilation at the Met Office. Q. J. Roy. Meteor. Soc., 136, 116–131, doi:10.1002/qj.521.
Smith, E. K., and S. Weintraub, 1953: The constants in the equation for atmospheric refractive index at radio frequencies. Proceedings of the Institute of Radio Engineers (I.R.E.), 41, 1035–1037
Sokolovskiy, S., Y-H. Kuo, and W. Wang, 2005: Assessing the accuracy of a linearized observation operator for assimilation of radio occultation data: Case simulations with a high-resolution weather model. Mon. Wea. Rev., 133, 2200–2212.
Tao, W. -K., J. Simpson, D. Baker, S. Braun, M. -D. Chou, B. Ferrier, D. Johnson, A. Khain, S. Lang, B. Lynn, C. -L. Shie, D. Starr, C. -H. Sui, Y. Wang, and P. Wetzel, 2003: Microphysics, radiation and surface processes in the Goddard Cumulus Ensemble (GCE) model. Meteor. Atmos. Phys., 82, 97-137.
Vorob’ev, V.V. and T.G. Krasil’nikova, 1994: Estimation of the accuracy of the atmospheric refractive index recovery from Doppler shift measurements at frequencies used in the NAVSTAR system. Izv. Acad. Sci. USSR, Atmos. Oceanic Phys., Engl. Transl., 29, 602–609.
Ware, R., and Coauthors, 1996: GPS soundings of the atmosphere from low earth orbit: Preliminary results. Bull. Amer. Meteor. Soc., 77, 19–40.
Wickert, J., and Coauthors, 2001: Atmosphere sounding by GPS radio occultation: First results from CHAMP. Geophys. Res. Lett., 28, 3263–3266.
Wickert, J., C. Arras, C.O. Ao, G. Beyerle, C. Falck, L. Grunwaldt, S.B. Healy, S. Heise, A. Helm, C.Y. Huang, N. Jakowski, R. Konig, T. Mannucci, C. Mayer, G. Michalak, P. Poli, M. Rothacher, T. Schmidt, R. Stosius, and B. Tapley, 2008: CHAMP, GRACE, SAC-C, TerraSAR-X/TanDEM-X: Science results, status and future prospects. GRAS SAF Workshop on Applications of GPSRO Measurements, 16-18 June 2008.
Yang, M.-J., J. J.-C. Chang, X. Zou, Y.-C. Chen, C.-H. Tseng, and M.-D. Cheng, 2008: Assimilation of global positioning system radio occultation observations into the CWB’s global forecast system. Preprints, The 5th AOGS Annual General Meeting, Busan, Korea, 16-20 June 2008, Asian Oceania Geoscience Society （AOGS）.
Zou, X., and Coauthors, 1999: A ray-tracing operator and its adjoint for the use of GPS/MET refraction angle measurements. J. Geophys. Res., 104, 22 301–22 318, doi:10.1029/1999JD900450.
Zou, X., B.Wang, H. Liu, R. A. Anthes, T. Matsumura, and Y. J. Zhu, 2000: Use of GPS/MET refraction angles in 3D variational analysis. Quart. J. Roy. Meteor. Soc., 126, 3013–3040, doi:10.1002/qj.49712657003.