Impacts of Ice Clouds on GPS Radio Occultation Measurements

X. Zou Department of Earth, Ocean and Atmospheric Sciences, The Florida State University, Tallahassee, Florida, and Center of Data Assimilation for Research and Application, Nanjing University of Information Science and Technology, Nanjing, China

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S. Yang Center of Data Assimilation for Research and Application, Nanjing University of Information Science and Technology, Nanjing, China

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P. S. Ray Department of Earth, Ocean and Atmospheric Sciences, The Florida State University, Tallahassee, Florida

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Abstract

Mathematical solutions accounting for the effects of liquid and ice clouds on the propagation of the GPS radio signals are first derived. The percentage contribution of ice water content (IWC) to the total refractivity increases linearly with the amount of IWC at a rate of 0.6 (g m−3)−1. Measurements of coincident profiles of IWC from CloudSat in deep convection during 2007–10 are then used for estimating the ice-scattering effects on GPS radio occultation (RO) measurements from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). The percentage contribution of IWC to the total refractivity from CloudSat measurements is consistent with the theoretical model, reaching about 0.6% at 1 g m−3 IWC.

The GPS RO refractivity observations in deep convective clouds are found to be systematically greater than the refractivity calculated from the ECMWF analysis. The fractional N bias (GPS minus ECMWF) can be as high as 1.8% within deep convective clouds. Compared with ECMWF analysis, the GPS RO retrievals have a negative temperature bias and a positive water vapor bias, which is consistent with a positive bias in refractivity. The relative humidity calculated from GPS retrievals is usually as high as 80%–90% right above the 0°C temperature level in deep convection and is about 15%–30% higher than the ECMWF analysis. The majority of the data points in deep convection are located on the negative side of temperature differences and the positive side of relative humidity differences between GPS RO retrievals and ECMWF analysis.

Corresponding author address: Dr. X. Zou, Department of Earth, Ocean and Atmospheric Science, The Florida State University, Tallahassee, FL 32306-4520. E-mail: xzou@fsu.edu

Abstract

Mathematical solutions accounting for the effects of liquid and ice clouds on the propagation of the GPS radio signals are first derived. The percentage contribution of ice water content (IWC) to the total refractivity increases linearly with the amount of IWC at a rate of 0.6 (g m−3)−1. Measurements of coincident profiles of IWC from CloudSat in deep convection during 2007–10 are then used for estimating the ice-scattering effects on GPS radio occultation (RO) measurements from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC). The percentage contribution of IWC to the total refractivity from CloudSat measurements is consistent with the theoretical model, reaching about 0.6% at 1 g m−3 IWC.

The GPS RO refractivity observations in deep convective clouds are found to be systematically greater than the refractivity calculated from the ECMWF analysis. The fractional N bias (GPS minus ECMWF) can be as high as 1.8% within deep convective clouds. Compared with ECMWF analysis, the GPS RO retrievals have a negative temperature bias and a positive water vapor bias, which is consistent with a positive bias in refractivity. The relative humidity calculated from GPS retrievals is usually as high as 80%–90% right above the 0°C temperature level in deep convection and is about 15%–30% higher than the ECMWF analysis. The majority of the data points in deep convection are located on the negative side of temperature differences and the positive side of relative humidity differences between GPS RO retrievals and ECMWF analysis.

Corresponding author address: Dr. X. Zou, Department of Earth, Ocean and Atmospheric Science, The Florida State University, Tallahassee, FL 32306-4520. E-mail: xzou@fsu.edu
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  • Anthes, R., and Coauthors, 2008: The COSMIC/Formosat-3 mission. Bull. Amer. Meteor. Soc., 89, 313333.

  • Atlas, D., 1964: Advances in radar meteorology. Advances in Geophysics, Vol. 10, Academic Press, 317–478.

  • Bennartz, R., and G. W. Petty, 2001: The sensitivity of microwave remote sensing observations of precipitation to ice particle size distributions. J. Appl. Meteor., 40, 345364.

    • Search Google Scholar
    • Export Citation
  • Bennartz, R., and P. Bauer, 2003: Sensitivity of microwave radiances at 85-183 GHz to precipitating ice particles. Radio Sci., 38, 8075, doi:10.1029/2002RS002626.

    • Search Google Scholar
    • Export Citation
  • Bohren, C. F., and D. R. Huffman, 1983: Absorption and Scattering of Light by Small Particles. Wiley-Interscience, 544 pp.

  • Foelsche, U., B. Pirscher, M. Borsche, G. Kirchengast, and J. Wickert, 2009: Assessing the climate monitoring utility of radio occultation data: From CHAMP to FORMOSAT-3/COSMIC. Terr. Atmos. Ocean. Sci., 20, 155170, doi:10.3319/TAO.2008.01.14.01(F3C).

    • Search Google Scholar
    • Export Citation
  • Foelsche, U., B. Scherllin-Pirscher, F. Ladstädter, A. K. Steiner, and G. Kirchengast, 2011: Refractivity and temperature climate records from multiple radio occultation satellites consistent within 0.05%. Atmos. Meas. Tech. Discuss., 4, 15931615, doi:10.5194/amtd-4-1593-2011.

    • Search Google Scholar
    • Export Citation
  • Gresh, D. L., 1990: Voyager radio occultation by the Uranian rings: Structure, dynamics, and particle sizes. Ph.D. dissertation, Stanford University, 202 pp.

  • King, M. D., and Coauthors, 2003: Cloud and aerosol properties, precipitable water, and profiles of temperature and humidity from MODIS. IEEE Trans. Geosci. Remote Sens., 41, 442458.

    • Search Google Scholar
    • Export Citation
  • King, M. D., S. Platnick, P. Yang, G. T. Arnold, M. A. Gray, J. C. Riedi, S. A. Ackerman, and K. N. Liou, 2004: Remote sensing of liquid water and ice cloud optical thickness and effective radius in the arctic: Application of airborne multispectral MAS data. J. Atmos. Oceanic Technol., 21, 857875.

    • Search Google Scholar
    • Export Citation
  • Kuo, C., and Coauthors, 2004: High-resolution observations of the cosmic microwave background power spectrum with ACBAR. Astrophys. J., 600, 3251.

    • Search Google Scholar
    • Export Citation
  • Kursinski, E. R., 1997: The GPS radio occultation concept: Theoretical performance and initial results. Ph.D. dissertation, California Institute of Technology, 289 pp.

  • Kursinski, E. R., and Coauthors, 1996: Initial results of radio occultation observations of Earth’s atmosphere using the Global Positioning System. Science, 271, 11071100.

    • Search Google Scholar
    • Export Citation
  • Lin, L., X. Zou, R. Anthes, and Y.-H. Kuo, 2010: COSMIC GPS cloudy profiles. Mon. Wea. Rev., 138, 11041118.

  • Luntama, J.-P., and Coauthors, 2008: Prospects of the EPS GRAS mission for operational atmospheric applications. Bull. Amer. Meteor. Soc., 89, 18631875.

    • Search Google Scholar
    • Export Citation
  • Mie, G., 1908: Considerations on the optics of turbid media, especially colloidal metal sols. Ann. Phys., 25, 377442.

  • Ohring, G., B. Wielicki, R. Spencer, B. Emery, and R. Atlas, 2005: Satellite instrument calibration for measuring global climate change – Report of a workshop. Bull. Amer. Meteor. Soc., 86, 13031313.

    • Search Google Scholar
    • Export Citation
  • Platnick, S., J. Y. Li, M. D. King, H. Gerber, and P. V. Hobbs, 2001: A solar reflectance method for retrieving the optical thickness and droplet size of liquid water clouds over snow and ice surfaces. J. Geophys. Res., 106 (D14), 15 18515 199.

    • Search Google Scholar
    • Export Citation
  • Ray, P. S., 1972: Broadband complex refractive indices of ice and water. Appl. Opt., 11, 18361844.

  • Solheim, F. S., J. Vivkanandan, R. H. Ware, and C. Rocken, 1999: Propagation delays induced in GPS signals by dry air, water vapor, hydrometeors, and other particulates. J. Geophys. Res., 104, 96639670.

    • Search Google Scholar
    • Export Citation
  • Sokolovskiy, S., Y.-H. Kuo, and W. Wang, 2005: Assessing the accuracy of a linearized observation operator for assimilation of radio occulation data: Case simulations with a high-resolution weather model. Mon. Wea. Rev., 133, 22002212.

    • Search Google Scholar
    • Export Citation
  • Steiner, A. K., G. Kirchengast, B. C. Lackner, B. Pirscher, M. Borsche, and U. Foelsche, 2009: Atmospheric temperature change detection with GPS radio occultation 1995 to 2008. Geophys. Res. Lett., 36, L18702, doi:10.1029/2009GL039777.

    • Search Google Scholar
    • Export Citation
  • Stephens, G. L., and Coauthors, 2002: The CloudSat mission and the A train. Bull. Amer. Meteor. Soc., 83, 17711790.

  • Weng, F., and N. C. Grody, 2000: Retrieval of ice cloud parameters using a microwave imaging radiometer. J. Atmos. Sci., 57, 10691081.

    • Search Google Scholar
    • Export Citation
  • Wickert, J., and Coauthors, 2009: GPS radio occultation: Results from CHAMP, GRACE and FORMOSAT-3/COSMIC. Terr. Atmos. Ocean. Sci., 20, 3550, doi:10.3319/TAO.2007.12.26.01(F3C).

    • Search Google Scholar
    • Export Citation
  • Yang, S., and X. Zou, 2012: Assessments of cloud liquid water contributions to GPS RO refractivity using measurements from COSMIC and CloudSat. J. Geophys. Res., 117, D06219, doi:10.1029/2011JD016452.

    • Search Google Scholar
    • Export Citation
  • Zhao, L., and F. Weng, 2002: Retrieval of ice cloud parameters using the advanced microwave sounding unit (AMSU). J. Appl. Meteor., 41, 384395.

    • Search Google Scholar
    • Export Citation
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