The Global Positioning System (GPS) Radio Occultation (OR) technique provides estimates of atmospheric density, temperature, and water vapour content with high vertical resolution, global coverage, and high accuracy. We have used data acquired using this technique in the period 1995–2009 to create a reference climatology of radio occultation bending angle and atmospheric temperature which are used for meteorological studies. The bending angle is interesting because it is a direct measurement and independent of models. It is given with one-degree spatial resolution and 50-meter vertical sampling. In addition, we give the temperature climatology with one-degree spatial resolution and 100-meter vertical sampling. This dataset can be used for several applications including weather forecast, physics of atmosphere, and climate changes. Since the GPS signal is not affected by clouds and the acquisitions are evenly distributed in the globe, the dataset is well suited for studying extreme events (such as convective systems and tropical cyclones) and remote areas. 1. Introduction The Global Positioning System (GPS) Radio Occultation (RO) technique [1] enables measurements of the global atmospheric density structure under any meteorological condition [2]. As illustrated in Figure 1, the RO technique involves a GPS satellite transmitting the signal and a Low Earth Orbit (LEO) satellite carrying a receiver. The signal transmitted by the GPS satellite is refracted in the atmosphere, and the associated propagation delay, refractive index, and bending angle are measured on the LEO satellite. From the measurements, it is possible to estimate profiles of atmospheric parameters such as temperature, water vapour, and pressure [3]. These parameters are secondary products, derived from the refractivity together with the European Centre for Medium-Range Weather Forecasts (ECMWF) model, and are given with high vertical resolution. The highest accuracy on the refractivity is achieved between 5 and 25？km altitude with average errors estimated in the range 0.3%–0.5% [4]. The RO technique has improved the weather forecast in regions of the globe that is poorly covered by standard measurements, such as the southern hemisphere which is dominated by oceans [5]. For instance, forecasting the track of tropical cyclones (energized over the oceans) has greatly improved [6]. Also the upper atmosphere is better forecasted as in the case of the ECMWF Upper Troposphere Lower Stratosphere (UTLS) model [7]. Figure 1: The GPS RO technique scheme (the proportions are not respected) [ 1]. Dashed
References
[1]
E. R. Kursinski, G. A. Hajj, J. T. Schofield, R. P. Linfield, and K. R. Hardy, “Observing Earth's atmosphere with radio occultation measurements using the global positioning system,” Journal of Geophysical Research D, vol. 102, no. 19, pp. 23429–23465, 1997.
[2]
Y. H. Kuo, W. Schreiner, J. Wang, D. L. Rossiter, and Y. Zhang, “Comparison og GPS radio occultation soundings with radiosondes,” Geophysical Research Letters, vol. 32, no. 5, Article ID L05817, 2005.
[3]
F. Pelliccia, P. Bonafoni, P. Basili, P. Ciotti, and N. Pierdicca, “Atmospheric profiling in the inter-tropical ocean area based on neural network approach using GPS radio occultations,” The Open Atmospheric Science Journal, vol. 4, pp. 202–209, 2010.
[4]
Y. H. Kuo, T. K. Wee, S. Sokolovskiy et al., “Inversion and error estimation of GPS radio occultation data,” Journal of the Meteorological Society of Japan, vol. 82, no. 1, pp. 507–531, 2004.
[5]
D. H. Bromwich and R. L. Fogt, “Strong trends in the skill of the ERA-40 and NCEP-NCAR reanalyses in the high and midlatitudes of the southern hemisphere, 1958–2001,” Journal of Climate, vol. 17, no. 23, pp. 4603–4619, 2004.
[6]
C. Y. Huang, Y. H. Kuo, S. H. Chen, and F. Vandenberghe, “Improvements in typhoon forecasts with assimilated GPS occultation refractivity,” Weather and Forecasting, vol. 20, no. 6, pp. 931–953, 2005.
[7]
C. Cardinali, “Monitoring the observation impact on the short-range forecast,” Quarterly Journal of the Royal Meteorological Society, vol. 135, no. 638, pp. 239–250, 2009.
[8]
R. Biondi, T. Neubert, S. Syndergaard, and J. Nielsen, “Measurements of the upper troposphere and lower stratosphere during tropical cyclones using the GPS radio occultation technique,” Advances in Space Research, vol. 47, no. 2, pp. 348–355, 2011.
[9]
R. Biondi, J. W. Randel, S. P. Ho, T. Neubert, and S. Syndergaard, “Thermal structure of intense convective clouds derived from GPS radio occultations,” Atmospheric Chemistry and Physics, vol. 12, no. 1, pp. 1–87, 2012.
[10]
R. A. Anthes, P. A. Bernhardt, Y. Chen et al., “The COSMIC/Formosat-3 mission: early results,” Bulletin of the American Meteorological Society, vol. 89, no. 3, pp. 313–333, 2008.
[11]
G. Beyerle, T. Schmidt, G. Michalak, S. Heise, J. Wickert, and C. Reigber, “GPS radio occultation with GRACE: atmospheric profiling utilizing the zero difference technique,” Geophysical Research Letters, vol. 32, no. 13, Article ID L13806, 2005.
[12]
M. Bonnedal, J. Christensen, A. Carlstr？m, and A. Berg, “Metop-GRAS in-orbit instrument performance,” GPS Solutions, vol. 14, no. 1, pp. 109–120, 2010.
[13]
G. Perona, R. Notarpietro, and M. Gabella, “GPS radio occultation on-board the OCEANSAT-2 mission: an Indian (ISRO)—Italian (ASI) collaboration,” Indian Journal of Radio and Space Physics, vol. 36, pp. 386–393, 2007.
[14]
J. P. Aguttes, J. Schrive, C. Goldstein, M. Rouze, and G. Raju, “MEGHA-TROPIQUES, a satellite for studying the water cycle and energy exchanges in the tropiques,” in Proceedings of the International Geoscience and Remote Sensing Symposium (IGARSS '00), vol. 7, pp. 3042–3044, July 2000.
[15]
A. Sen, K. Yunjin, D. Caruso et al., “Aquarius/SAC-D mission overview,” in 10th Sensors, Systems, and Next-Generation Satellites, vol. 6361 of Proceedings of SPIE, Stockholm, Sweden, September 2006.
[16]
R. Biondi, T. Neubert, S. Syndergaard, and J. Nielsen, “Radio occultation bending angle anomalies during tropical cyclones,” Atmospheric Measurement Techniques Discussions, vol. 4, no. 1, pp. 1371–1395, 2011.
[17]
University Corporation for Atmospheric Research (UCAR), UCAR-COSMIC Data Analysis and Archive Center (CDAAC), 2012, http://cdaac-www.cosmic.ucar.edu/cdaac/.
[18]
C. Rocken, R. Anthes, M. Exner et al., “Analysis and validation of GPS/MET data in the neutral atmosphere,” Journal of Geophysical Research D, vol. 102, no. 25, pp. 29849–29866, 1997.
[19]
G. A. Hajj, C. O. Ao, B. A. Iijima et al., “CHAMP and SAC-C atmospheric occultation results and intercomparisons,” Journal of Geophysical Research D, vol. 109, no. 6, Article ID D06109, 24 pages, 2004.
[20]
R. Biondi, Upper troposphere lower stratosphere structure during convective systems using GPS radio occultations [Ph.D. thesis], 2012.
[21]
R. Biondi, S. P. Ho, J. W. Randel, S. Syndergaard, and T. Neubert, “Tropical cyclone cloud top height and vertical temperature structure detection using GPS radio occultation measurements,” Journal of Geophysical Research. In press.
[22]
A. K. Steiner, B. C. Lackner, F. Ladst？dter, B. Scherllin-Pirscher, U. Foelsche, and G. Kirchengast, “GPS radio occultation for climate monitoring and change detection,” Radio Science, vol. 46, no. 6, Article ID RS0D24, 2011.
