ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-903-2012 Advances and limitations of atmospheric boundary layer observations with GPS occultation over southeast Pacific Ocean Xie F. 1 2 Wu D. L. 2 4 Ao C. O. 2 Mannucci A. J. 2 Kursinski E. R. 3 5 Joint Institute for Regional Earth System Science and Engineering (JIFRESSE), University of California, Los Angeles, California, USA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA Department of Atmospheric Sciences, University of Arizona, Tucson, Arizona, USA now at: NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA now at: Broad Reach Engineering, Golden, Colorado, USA 19 01 2012 12 2 903 918 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/903/2012/acp-12-903-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/903/2012/acp-12-903-2012.pdf

The typical atmospheric boundary layer (ABL) over the southeast (SE) Pacific Ocean is featured with a strong temperature inversion and a sharp moisture gradient across the ABL top. The strong moisture and temperature gradients result in a sharp refractivity gradient that can be precisely detected by the Global Positioning System (GPS) radio occultation (RO) measurements. In this paper, the Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) GPS RO soundings, radiosondes and the high-resolution ECMWF analysis over the SE Pacific are analyzed. COSMIC RO is able to detect a wide range of ABL height variations (1–2 km) as observed from the radiosondes. However, the ECMWF analysis systematically underestimates the ABL heights. The sharp refractivity gradient at the ABL top frequently exceeds the critical refraction (e.g., −157 N-unit km<sup>−1</sup>) and becomes the so-called ducting condition, which results in a systematic RO refractivity bias (or called <i>N</i>-bias) inside the ABL. Simulation study based on radiosonde profiles reveals the magnitudes of the <i>N</i>-biases are vertical resolution dependent. The $N$-bias is also the primary cause of the systematically smaller refractivity gradient (rarely exceeding −110 N-unit km<sup>−1</sup>) at the ABL top from RO measurement. However, the <i>N</i>-bias seems not affect the ABL height detection. Instead, the very large RO bending angle and the sharp refractivity gradient due to ducting allow reliable detection of the ABL height from GPS RO. The seasonal mean climatology of ABL heights derived from a nine-month composite of COSMIC RO soundings over the SE Pacific reveals significant differences from the ECMWF analysis. Both show an increase of ABL height from the shallow stratocumulus near the coast to a much higher trade wind inversion further off the coast. However, COSMIC RO shows an overall deeper ABL and reveals different locations of the minimum and maximum ABL heights as compared to the ECMWF analysis. At low latitudes, despite the decreasing number of COSMIC RO soundings and the lower percentage of soundings that penetrate into the lowest 500-m above the mean-sea-level, there are small sampling errors in the mean ABL height climatology. The difference of ABL height climatology between COSMIC RO and ECMWF analysis over SE Pacific is significant and requires further studies.

 References Anthes, R. A., Bernhardt, P. A., Chen, Y., Cucurull, L., Dymond, K. F., Ector, D., Healy, S. B., Ho, S.-P., Hunt, D. C., Kuo, Y.-H., Liu, H., Manning, K., McCormick, C., Meehan, T. K., Randel, W. J., Rocken, C., Schreiner, W. S., Sokolovskiy, S. V., Syndergaard, S., Thompson, D. C., Trenberth, K. E., Wee, T.-K., Yen, N. L., and Zeng, Z.: The COSMIC/FORMOSAT-3 mission: Early results, B. Am. Meteorol. Soc., 89, 313–333, 2008. Ao, C. O.: Effect of ducting on radio occultation measurements: An assessment based on high-resolution radiosonde soundings, Radio Sci., 42, RS2008, http://dx.doi.org/10.1029/2006RS003485doi:10.1029/2006RS003485, 2007. Ao, C. O., Meehan, T. K., Hajj, G. A., Mannucci, A. J., and Beyerle, G.: Lower-troposphere refractivity bias in GPS occultation retrievals, J. Geophys. Res., 108, 4577, http://dx.doi.org/10.1029/2002JD003216doi:10.1029/2002JD003216, 2003. Ao, C. O., Chan, T. K., Iijima, B. A., Li, J.-L., Mannucci, A. J., Teixeira, T., Tian, B., and Waliser, D. E.: Planetary boundary layer information from GPS radio occultation measurements, ECMWF GRAS SAF Workshop on Applications of GPS Radio Occultation Measurements (16–18 June 2008), Reading, UK, 123–131, 2008. Ao, C. O., Hajj, G. A., Meehan, T. K., Dong, D., Iijima, B. A., Mannucci, A. J., and Kursinski, E. R.: Rising and setting GPS occultations by use of open-loop tracking, J. Geophys. Res., 114, D04101, http://dx.doi.org/10.1029/2008JD010483doi:10.1029/2008JD010483, 2009. Ao, C. O., Waliser, D. E., Li, J.-L., Chan, T. K., Tian, B., and Xie, F.: Planetary boundary layer depths from GPS radio occultation profiles, J. Geophys. Res., submitted, 2012. Basha, G., and Ratnam, M. V.: Identification of atmospheric boundary layer height over a tropical station using high resolution radiosonde refractivity profiles: Comparison with GPS radio occultation measurements, J. Geophys. Res., 114, D16101, http://dx.doi.org/10.1029/2008JD011692doi:10.1029/2008JD011692, 2009. Bauer, P., Lopez, P., Benedetti, A., Salmond, D., and Moreau, E.: Implementation of 1D+4D-Var assimilation of precipitation affected microwave radiances at ECMWF, Part I: 1D-Var, Q. J. Roy. Meteorol. Soc., 132, 2277–2306, 2006. Beyerle, G., Schmidt, T., Wickert, J., Heise, S., Rothacher, M., König-Langlo, G., and Lauritsen, K. B.: Observations and simulations of receiver-induced refractivity biases in GPS radio occultation, J. Geophys. Res., 111, D12101, http://dx.doi.org/10.1029/2005JD006673doi:10.1029/2005JD006673, 2006. Bony, S., and Dufresne J.-L.: Marine boundary layer clouds at the heart of tropical cloud feedback uncertainties in climate models, Geophys. Res. Lett., 32, L20806, http://dx.doi.org/10.1029/2005GL023851doi:10.1029/2005GL023851, 2005. Bretherton, C. S., Uttal, T., Fairall, C.W., Yuter, S. E.,Weller, R. A., Baumgardner, D., Comstock, K., Wood, R., and Raga, G. B.: The EPIC 2001 stratocumulus study, B. Am. Meteorol. Soc., 85, 967–977, http://dx.doi.org/10.1175/BAMS-85-7-967doi:10.1175/BAMS-85-7-967, 2004. Bretherton, C. S., Wood, R., George, R. C., Leon, D., Allen, G. and Zheng X.: Southeast Pacific stratocumulus clouds, precipitation and boundary layer structure sampled along 20S during VOCALS-Rex, Atmos. Chem. Phys., 10, 10639–10654, http://dx.doi.org/10.5194/acp-10-10639-2010doi:10.5194/acp-10-10639-2010, 2010. Cao, G., Giambelluca, T. W., Stevens, D. E. and Schroeder, T. A.: Inversion Variability in the Hawaiian Trade Wind Regime, J. Climate, 20, 1145–1160, 2007. Clement, A. C., Burgman R., and Norris J. R.: Observational and model evidence for positive low-level cloud feedback, Science, 325, 460–464, http://dx.doi.org/10.1126/science.1171255doi:10.1126/science.1171255, 2009. Cucurull, L., Kuo, Y. H., Barker, D., and Rizvi, S. R. H.: Assessing the impact of simulated COSMIC GPS radio occultation data on weather analysis over the Antarctic: A case study, Mon. Wea. Rev., 134, 3283–3296, 2006. Cucurull, L., Derber, J. C., Treadon, R., and Purser, R. J.: Assimilation of Global Positioning System radio occultation observations into NCEP's Global Data Assimilation System, Mon. Wea. Rev., 135, 3174–3193, 2007. de Szoeke, S. P., Fairall, C. W., Wolfe, D. E., Bariteau, L., and Zuidema, P.: Surface Flux Observations on the Southeastern Tropical Pacific Ocean and Attribution of SST Errors in Coupled Ocean–Atmosphere Models, J. Climate, 23, 4152–4174, 2010. Deardorff J. W.: On the entrainment rate of a stratocumulus-topped mixed layer, Q. J. Roy. Meteorol. Soc., 102, 563–582, 1976. Fjeldbo, G., Kliore, A. J., and Eshleman, V. R.: The neutral atmosphere of Venus as studied with the Mariner V radio occultation experiment, Astron. J., 76, 123–140, 1971. Garay, M. J., de Szoeke, S. P., and Moroney, C. M.: Comparison of marine stratocumulus cloud top heights in the southeastern Pacific retrieved from satellites with coincident ship-based observations, J. Geophys. Res., 113, D18204, http://dx.doi.org/10.1029/2008JD009975doi:10.1029/2008JD009975, 2008. Gorbunov, M. E., Benzon, H.-H., Jensen, A. S., Lohmann, M. S., and Nielsen, A. S.: Comparative analysis of radio occultation processing approaches based on Fourier integral operators, Radio Sci., 39, RS6004, http://dx.doi.org/10.1029/2003RS002916doi:10.1029/2003RS002916, 2004. Guo, P., Kuo, Y.-H., Sokolovskiy, S. V., and Lenschow, D. H.: Estimating atmospheric boundary layer depth using COSMIC radio occultation data, J. Atmos. Sci., 68, 1703–1713, 2011. Hajj, G. A., Kursinski, E. R., Romans, L. J., Bertiger, W. I., and Leroy, S. S.: A technical description of atmospheric sounding by GPS occultation, J. Atmos. Solar Terr. Phys., 64, 451–469, 2002. Harshvardhan, Zhao, G., Girolamo, Di, L., and Green, R. N.: Satellite-observed location of stratocumulus cloud-top heights in the presence of strong inversions, IEEE Trans. Geosci. Remote Sens., 47, 1421–1428, http://dx.doi.org/10.1109/TGRS.2008.2005406doi:10.1109/TGRS.2008.2005406, 2009. Healy, S. and Thépaut, J.-N.: Assimilation experiments with CHAMP GPS radio occultation measurements, Q. J. Roy. Meteorol. Soc., 132, 605–623, 2006. Healy, S. B.: Assimilation of GPS radio occultation measurements at ECMWF, Proceedings of the GRAS SAF Workshop on Applications of GPSRO measurements, ECMWF, Reading, UK, 16–18 June 2008, 99–109, 2008. Ho, S.-P., Kirchengast, G., Leroy, S., Wickert, J.; Mannucci, A. J., Stiner, A. K., Hunt, D., Schreiner, W., Sokolovskiy, S., Ao, C. O., Borsche, M., von Engeln, A., Foelsche, U., Heise, S., Iijima, B., Kuo, Y.-H., Kursinski, R., Pirscher, B., Ringer, M., Rocken, C., and Schmidt, T.: 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, http://dx.doi.org/10.1029/2009JD011969doi:10.1029/2009JD011969, 2009. Jordan, N. S., Hoff, R. M., and Bacmeister, J. T.: Validation of Goddard Earth Observing System-version 5 MERRA planetary boundary layer heights using CALIPSO, J. Geophys. Res., 115, D24218, http://dx.doi.org/10.1029/2009JD013777doi:10.1029/2009JD013777, 2010. Klein, S. A. and Hartmann, D. L.: The seasonal cycle of low stratiform clouds, J. Climate, 6, 1587–1606, 1993. Kursinski, E. R., Hajj, G. A., Schofield, J. T., Linfield, R. P., and Hardy, K. R.: Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System, J. Geophys. Res., 102, 23429–23465, 1997. Lilly, D. K.: Models of cloud topped mixed layers under a strong inversion, Q. J. Roy. Meteorol. Soc., 94, 292–309, 1968. Lopez, P.: A 5-yr 40-km-Resolution Global Climatology of Superrefraction for Ground-Based Weather Radars, J. Appl. Meteorol. Clim., 48, 89–110, 2009. Ma, C.-C., Mechoso, C. R., Robertson, A. W., and Arakawa, A.: Peruvian stratus clouds and the tropical Pacific circulation: A coupled ocean–atmosphere GCM study, J. Climate, 9, 1635–1645, 1996. Palm, S. P., Benedetti, A., and Spinhirne, J.: Validation of ECMWF global forecast model parameters using GLAS atmospheric channel measurements, Geophys. Res. Lett., 32, L22S09, http://dx.doi.org/10.1029/2005GL023535doi:10.1029/2005GL023535, 2005. Pirscher, B., Foelsche, U., Borsche, M., Kirchengast, G., and Kuo, Y.-H.: Analysis of migrating diurnal tides detected in FORMOSAT-3/COSMIC temperature data, J. Geophys. Res., 115, D14108, http://dx.doi.org/10.1029/2009JD013008doi:10.1029/2009JD013008, 2010. Poli, P., Healy, S. B., and Dee, D. P.: Assimilation of global positioning system ratio occultation data in the ECMWF ERA-Interim reanalysis, Q. J. Roy. Meteorol. Soc. 136, 1972–1990, http://dx.doi.org/10.1002/qj.722doi:10.1002/qj.722, 2010. Rahn,~D A. and Garreaud,~R.: Marine boundary layer over the subtropical southeast Pacific during VOCALS-REx – Part 1: Mean structure and diurnal cycle, Atmos. Chem. Phys., 10, 4491–4506, http://dx.doi.org/10.5194/acp-10-4491-2010doi:10.5194/acp-10-4491-2010, 2010. Randall, D. A., Coakley, J. A., Lenschow, D. H., Fairall, C. W., and Kropfli, R. A.: Outlook for Research on Subtropical Marine Stratification Clouds, B. Am. Meteorol. Soc., 65, 1290–1301, 1984. Randall, D., Curry, J., Battisti, D., Flato, G., Grumbine, R., Hakkinen, S., Martinson, D., Preller, R., Walsh, J., and Weatherly, J.,: Status and outlook for large scale modeling of atmosphere-ice-ocean interactions in the Arctic, B. Am. Meteorol. Soc., 79, 197–219, 1998. Seidel D., Ao, C. O., and Li, K.: Estimating climatological planetary boundary layer heights from radiosonde observations: Comparison of methods and uncertainty analysis, J. Geophys. Res., 115, D16113, http://dx.doi.org/10.1029/2009JD013680doi:10.1029/2009JD013680, 2010. Slingo, A.: Sensitivity of the earth's radiation budget to changes in the low clouds, Nature, 343, 49–51, 1990. Smith, E. K. and Weintraub, S.: The constants in the equation for atmospheric refractive index at radio frequencies, Proc. Inst. Radio Engrs., 41, 1035–1037, 1953. Sokolovskiy, S. V.: Tracking tropospheric radio occultation signals from low Earth orbit, Radio Sci., 36, 483–498, 2001. Sokolovskiy, S. V.: Effect of superrefraction on inversions of radio occultation signals in the lower troposphere,Radio Sci., 38, 1058, http://dx.doi.org/10.1029/2002RS002728doi:10.1029/2002RS002728, 2003. Sokolovskiy, S., Kuo, Y.-H., Rocken, C., Schreiner, W. S., Hunt, D., and Anthes, R. A.: Monitoring the atmospheric boundary layer by GPS radio occultation signals recorded in the open-loop mode, Geophys. Res. Lett., 33, L12813, http://dx.doi.org/10.1029/2006GL025955doi:10.1029/2006GL025955, 2006. Sokolovskiy, S. V., Rocken, C., Lenschow, D. H., Kuo, Y.-H., Anthes, R. A., Schreiner, W. S. and Hunt, D. C.: Observing the moist troposphere with radio occultation signals from COSMIC, Geophys. Res. Lett., 34, L18802, http://dx.doi.org/10.1029/2007GL030458doi:10.1029/2007GL030458, 2007. Toniazzo,~T., Abel,~S J., Wood,~R., Mechoso,~C R., Allen,~G., and Shaffrey,~L C.: Large-scale and synoptic meteorology in the south-east Pacific during the observations campaign VOCALS-REx in austral Spring 2008, Atmos. Chem. Phys., 11, 4977–5009, http://dx.doi.org/10.5194/acp-11-4977-2011doi:10.5194/acp-11-4977-2011, 2011. von Engeln, A. and Teixeira, J.: A ducting climatology derived from the European Centre for Medium-Range Weather Forecasts global analysis fields, J. Geophys. Res., 109, D18104, http://dx.doi.org/10.1029/2003JD004380doi:10.1029/2003JD004380, 2004. von Engeln, A. and Teixeira J.: A planetary boundary layer height climatology derived from ECMWF Re-analysis data, J. Appl. Meteorol. Clim., submitted, 2011. Wang, J., Rossow, W. B., Uttal, T., and Rozendaal, M.: Variability of cloud vertical structure during ASTEX observed from a combination of rawinsonde, radar, ceilometer and satellite, Mon. Weather Rev. 127, 2484–2502, 1999. Wang,~S., O'Neill,~L W., Jiang,~Q., de~Szoeke,~S P., Hong,~X., Jin,~H., Thompson,~W T., and Zheng,~X.: A regional real-time forecast of marine boundary layers during VOCALS-REx, Atmos. Chem. Phys., 11, 421–437, http://dx.doi.org/10.5194/acp-11-421-2011doi:10.5194/acp-11-421-2011, 2011. Wood, R. and Bretherton, C. S.: Boundary layer depth, entrainment and decoupling in the cloud-capped subtropical and tropical marine boundary layer, J. Clim., 17, 3576–3588, 2004. Wood, R., Bretherton, C. S., Mechoso, C. R., Weller, R. A., Huebert, B., Straneo, F., Albrecht, B. A., Coe, H., Allen, G., Vaughan, G., Daum, P., Fairall, C., Chand, D., Gallardo Klenner, L., Garreaud, R., Grados Quispe, C., Covert, D. S., Bates, T. S., Krejci, R., Russell, L. M., de Szoeke, S., Brewer, A., Yuter, S. E., Springston, S. R., Chaigneau, A., Toniazzo, T., Minnis, P., Palikonda, R., Abel, S. J., Brown, W. O. J., Williams, S., Fochesatto, J., and Brioude, J.: The VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) : goals, platforms, and field operations, Atmos. Chem. Phys., 11, 627–654, http://dx.doi.org/10.5194/acp-11-627-2011doi:10.5194/acp-11-627-2011, 2011. Wu, D., Hu, Y., McCormick, M., Xu, K., Liu, Z., Smith, B., Omar, A., and Chang, F.: Deriving marine-boundary-layer lapse rate from collocated CALIPSO, MODIS, and AMSR-E data to study global low-cloud height statistics, Geosci. Remote Sens. Lett., 5, 649–652, 2008. Wyant,~M C., Wood,~R., Bretherton,~C S., Mechoso,~C R., Bacmeister,~J., Balmaseda,~M A., Barrett,~B., Codron,~F., Earnshaw,~P., Fast,~J., Hannay,~C., Kaiser,~J W., Kitagawa,~H., Klein,~S A., Köhler,~M., Manganello,~J., Pan,~H.-L., Sun,~F., Wang,~S., and Wang,~Y.: The PreVOCA experiment: modeling the lower troposphere in the Southeast Pacific, Atmos. Chem. Phys., 10, 4757–4774, http://dx.doi.org/10.5194/acp-10-4757-2010doi:10.5194/acp-10-4757-2010, 2010. Xie, F.: Development of a GPS occultation retrieval method for characterizing the marine boundary layer in the presence of super-refraction, Dissertation, University of Arizona, USA, 134 pp., 2006. Xie, F., Syndergaard, S., Kursinski, E. R., and Herman, B. M.: An Approach for Retrieving Marine Boundary Layer Refractivity from GPS Occultation Data in the Presence of Super-refraction, J. Atmos. Ocean Tech, 23, 1629-1644, 2006. Xie, F., Wu, D. L., Ao, C. O., Kursinski, E. R., Mannucci, A. and Syndergaard, S.: Super-refraction effects on GPS radio occultation refractivity in marine boundary layers, Geophys. Res. Lett., 37, L11805, http://dx.doi.org/10.1029/2010GL043299doi:10.1029/2010GL043299, 2010a. Xie,~F., Wu,~D L., Ao,~C O., and Mannucci,~A J.: Atmospheric diurnal variations observed with GPS radio occultation soundings, Atmos. Chem. Phys., 10, 6889-6899, http://dx.doi.org/10.5194/acp-10-6889-2010doi:10.5194/acp-10-6889-2010, 2010b. Zeng, X., Brunke, M. A., Zhou, M., Fairall, C., Bond, N. A., and Lenschow, D. H.: Marine atmospheric boundary layer height over the eastern Pacific: data analysis and model evaluation. J. Climate, 17, 4159–4170, 2004. Zuidema, P., Painemal, D., de Szoeke, S., and Fairall, C.: Stratocumulus cloud-top height estimates and their climatic implications, J. Climate, 22, 4652–4666, 2009.