The Experts below are selected from a list of 5349 Experts worldwide ranked by ideXlab platform
Ying-hwa Kuo - One of the best experts on this subject based on the ideXlab platform.
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a quality control procedure based on bending angle measurement uncertainty for Radio Occultation data assimilation in the tropical lower troposphere
Journal of Atmospheric and Oceanic Technology, 2018Co-Authors: Zhen Zeng, Ying-hwa Kuo, Hui Liu, Sergey Sokolovskiy, Xiaolei Zou, Lingfeng Hsiao, Benjamin RustonAbstract:AbstractThe fluctuation of Radio Occultation (RO) signals in the presence of refractivity irregularities in the moist lower troposphere results in uncertainties of retrieved bending angle and refra...
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characterizing gps Radio Occultation loss of lock due to ionospheric weather
Space Weather-the International Journal of Research and Applications, 2016Co-Authors: Xinan Yue, William Schreiner, N M Pedatella, Ying-hwa KuoAbstract:Transient loss of lock is one of the key space weather effects on the Global Navigation Satellite System (GNSS). Based on the Constellation Observing System for Meteorology, Ionosphere, and Climate Global Positioning System (GPS) Radio Occultation (RO) observations during 2007–2011, we have analyzed the signal cycle slip (CS) occurrence comprehensively and its correlation to the ionospheric weather phenomena such as sporadic E (Es), equatorial F region irregularity (EFI), and the ionospheric equatorial ionization anomaly (EIA). The high vertical resolution of RO observations enables us to distinguish the CS resulting from different ionospheric layers clearly on a global scale. In the E layer, the CS is dominated by the Es occurrence, while in the F layer, the CS is mainly related to the EIA and EFI at low and equatorial latitudes. In the polar region, the CS is primarily related to polar cap electron density gradients. The overall average CS (>6 cycles) occurrence is ~23% per Occultation, with the E (50–150 km) and F (150–600 km) layers contributing ~8.3% and ~14.7%, respectively. Awareness of the effect of the ionospheric weather on the CS of the low Earth orbit (LEO)-based GNSS signal could be beneficial to a variety of applications, including the LEO-based GNSS data processing and the corresponding hardware/firmware design.
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estimating atmospheric boundary layer depth using cosmic Radio Occultation data
Journal of the Atmospheric Sciences, 2011Co-Authors: P Guo, Ying-hwa Kuo, Sergey Sokolovskiy, Donald H LenschowAbstract:This study presents an algorithm for estimating atmospheric boundary layer (ABL) depth from Global Positioning System (GPS) Radio Occultation (RO) data. The algorithm is applied to the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO data and validated using highresolution Radiosonde data from the island of St. Helena (16.08S, 5.78W), tropical (308S‐308N) Radiosondes collocated with RO, and EuropeanCentre for Medium-Range WeatherForecasts (ECMWF) high-resolution global analyses. Spatial and temporal variations of the ABL depth obtained from COSMIC RO data for a 1-yr period over tropical and subtropical oceans are analyzed. The results demonstrate the capability of RO data to resolve geographical and seasonal variations of ABL height. The spatial patterns of the variations are consistent with those derived from ECMWF global analysis. However, the ABL heights derived from ECMWF global analysis, on average, are negatively biased against those estimated from COSMIC GPS RO data. These results indicate that GPS RO data can provide useful information on ABL height, which is an important parameter for weather and climate studies.
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data assimilation retrieval of electron density profiles from Radio Occultation measurements
Journal of Geophysical Research, 2011Co-Authors: Xinan Yue, Ying-hwa Kuo, William Schreiner, Christian Rocken, Yucheng Lin, Biqiang ZhaoAbstract:[1] In this paper, the Kalman filter is used to retrieve the electron density profile along the tangent points by assimilating the slant total electron content data observed during a Radio Occultation (RO) event into an empirical background model. The RO data observed by COSMIC satellites on day of year 266 in 2009 are selected to do both the simulation work and the real data retrieval test. The results show that the data assimilation technique can improve the electron density retrieval in comparison with the Abel inversion. It is less influenced by the ionospheric inhomogeneity than the Abel method. Some pseudo‐large‐scale features made by the Abel retrieval, such as the plasma cave underneath the equatorial ionization anomaly region and the three peaks along the latitude direction in the E layer, disappear in the data assimilation retrieval results. Independent validation by ground‐based ionosonde observations confirms the improvement of data assimilation retrieval below the F2 peak. In addition, some potential research on RO data assimilation is also discussed.
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error analysis of abel retrieved electron density profiles from Radio Occultation measurements
Annales Geophysicae, 2010Co-Authors: Xinan Yue, William Schreiner, Jiuhou Lei, Sergey Sokolovskiy, C Rocken, Douglas Hunt, Ying-hwa KuoAbstract:Abstract. This letter reports for the first time the simulated error distribution of Radio Occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC Occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.
S B Healy - One of the best experts on this subject based on the ideXlab platform.
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a modification to the standard ionospheric correction method used in gps Radio Occultation
Atmospheric Measurement Techniques, 2015Co-Authors: S B Healy, I D CulverwellAbstract:Abstract. A modification to the standard bending-angle correction used in GPS Radio Occultation (GPS-RO) is proposed. The modified approach should reduce systematic residual ionospheric errors in GPS Radio Occultation climatologies. A new second-order term is introduced in order to account for a known source of systematic error, which is generally neglected. The new term has the form κ(a) × (αL1(a)-αL2(a))2, where a is the impact parameter and (αL1, αL2) are the L1 and L2 bending angles, respectively. The variable κ is a weak function of the impact parameter, a, but it does depend on a priori ionospheric information. The theoretical basis of the new term is examined. The sensitivity of κ to the assumed ionospheric parameters is investigated in one-dimensional simulations, and it is shown that κ s 10–20 rad−1. We note that the current implicit assumption is κ=0, and this is probably adequate for numerical weather prediction applications. However, the uncertainty in κ should be included in the uncertainty estimates for the geophysical climatologies produced from GPS-RO measurements. The limitations of the new ionospheric correction when applied to CHAMP (Challenging Minisatellite Payload) measurements are noted. These arise because of the assumption that the refractive index is unity at the satellite, made when deriving bending angles from the Doppler shift values.
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impact of gps Radio Occultation measurements in the ecmwf system using adjoint based diagnostics
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Carla Cardinali, S B HealyAbstract:In this article, a comprehensive assessment of the impact of Radio Occultation (RO) observations in the operational ECMWF assimilation and forecast system is presented using different diagnostic tools. In particular, the observations' influence in the assimilation process and the related contribution to the short-range forecast error of Radio Occultation observations is evaluated with recently developed diagnostic tools based on the adjoint version of the assimilation and forecast model. The sensitivity with respect to observation error variances is also evaluated for the assimilated observations. GPS-RO is found to have the largest mean influence among satellite observations in the analysis. It is the fourth best satellite system for analysis information content and the second largest satellite contributor together with IASI and AIRS to decreasing the 24 h forecast error. For the whole observing system, with the exception of Radiosondes and polar atmospheric motion vectors, the forecast error sensitivity to the observation error variance indicates that a deflation of the assumed observation errors would improve the forecast skill. For RO observations at all vertical levels, but predominantly between 10 and 20 km, a deflation of the observation error variance is suggested. Interestingly, the sensitivity computation recommends reducing the assumed errors mostly in layers where the weight given to GPS-RO data is quite large.
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gnss Radio Occultation constellation observing system experiments
Monthly Weather Review, 2014Co-Authors: Peter Bauer, Gabor Radnoti, S B Healy, Carla CardinaliAbstract:AbstractObserving system experiments within the operational ECMWF data assimilation framework have been performed for summer 2008 when the largest recorded number of Global Navigation Satellite System (GNSS) Radio Occultation observations from both operational and experimental satellites were available. Constellations with 0%, 5%, 33%, 67%, and 100% data volume were assimilated to quantify the sensitivity of analysis and forecast quality to Radio Occultation data volume. These observations mostly constrain upper-tropospheric and stratospheric temperatures and correct an apparent model bias that changes sign across the upper-troposphere–lower-stratosphere boundary. This correction effect does not saturate with increasing data volume, even if more data are assimilated than available in today’s analyses. Another important function of Radio Occultation data, namely, the anchoring of variational radiance bias corrections, is demonstrated in this study. This effect also does not saturate with increasing data vo...
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scaling of gnss Radio Occultation impact with observation number using an ensemble of data assimilations
Monthly Weather Review, 2013Co-Authors: F Harnisch, Peter Bauer, S B Healy, Stephen EnglishAbstract:AbstractAn ensemble of data assimilations (EDA) approach is used to estimate how the impact of Global Navigation Satellite System (GNSS) Radio Occultation (RO) measurements scales as a function of observation number in the ECMWF numerical weather prediction system. The EDA provides an estimate of the theoretical analysis and short-range forecast error statistics, based on the ensemble “spread,” which is the standard deviation of the ensemble members about the ensemble mean. This study is based on computing how the ensemble spread of various parameters changes as a function of the number of simulated GNSS RO observations. The impact from 2000 up to 128 000 globally distributed simulated GNSS RO profiles per day is investigated. It is shown that 2000 simulated GNSS RO measurements have an impact similar to real measurements in the EDA and that the EDA-based impact of real data can be related to the impact in observing system experiments. The dependence of the ensemble statistics on observation error statist...
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gps Radio Occultation results from champ grace and formosat 3 cosmic
Terrestrial Atmospheric and Oceanic Sciences, 2009Co-Authors: Jens Wickert, S B Healy, G Beyerle, Torsten Schmidt, Norbert Jakowski, Stefan Heise, Cheng-yung Huang, Grzegorz Michalak, C Z Cheng, W KohlerAbstract:The Taiwan/US FORMOSAT-3/COS MIC (FORMOsa SATellite mission - 3/Constellation Observing System for Meteorology, Ionosphere and Climate) satellite constellation was success fully launched on 14 April 2006. It is expected to leverage the use of the GPS (Global Positioning System) Radio Occultation data for atmospheric and ionospheric research to improve global weather forecasts and aid climate change related studies. FORMOSAT-3/COSMIC, together with the European MetOp, German CHAMP and US/Ger man GRACE-A satellites, form a 9 satellite constellation for precise atmospheric sounding on a global scale. This satellite constellation is expected to provide about 3500 Occultation measurements daily. Recent results and the status of the CHAMP and GRACE-A orbit and Occultation data analysis are reviewed and complemented with a review of initial results from FORMOSAT-3/COSMIC at GFZ. The significantly in creased potential of the CHAMP, GRACE-A and FORMOSAT-3/COSMIC constellation for atmospheric studies, compared to single satellite missions, is demonstrated for selected applications such as global monitoring of water vapor distributions, tropopause parameters and ionospheric irregularities.
Sergey Sokolovskiy - One of the best experts on this subject based on the ideXlab platform.
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a quality control procedure based on bending angle measurement uncertainty for Radio Occultation data assimilation in the tropical lower troposphere
Journal of Atmospheric and Oceanic Technology, 2018Co-Authors: Zhen Zeng, Ying-hwa Kuo, Hui Liu, Sergey Sokolovskiy, Xiaolei Zou, Lingfeng Hsiao, Benjamin RustonAbstract:AbstractThe fluctuation of Radio Occultation (RO) signals in the presence of refractivity irregularities in the moist lower troposphere results in uncertainties of retrieved bending angle and refra...
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estimating atmospheric boundary layer depth using cosmic Radio Occultation data
Journal of the Atmospheric Sciences, 2011Co-Authors: P Guo, Ying-hwa Kuo, Sergey Sokolovskiy, Donald H LenschowAbstract:This study presents an algorithm for estimating atmospheric boundary layer (ABL) depth from Global Positioning System (GPS) Radio Occultation (RO) data. The algorithm is applied to the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO data and validated using highresolution Radiosonde data from the island of St. Helena (16.08S, 5.78W), tropical (308S‐308N) Radiosondes collocated with RO, and EuropeanCentre for Medium-Range WeatherForecasts (ECMWF) high-resolution global analyses. Spatial and temporal variations of the ABL depth obtained from COSMIC RO data for a 1-yr period over tropical and subtropical oceans are analyzed. The results demonstrate the capability of RO data to resolve geographical and seasonal variations of ABL height. The spatial patterns of the variations are consistent with those derived from ECMWF global analysis. However, the ABL heights derived from ECMWF global analysis, on average, are negatively biased against those estimated from COSMIC GPS RO data. These results indicate that GPS RO data can provide useful information on ABL height, which is an important parameter for weather and climate studies.
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error analysis of abel retrieved electron density profiles from Radio Occultation measurements
Annales Geophysicae, 2010Co-Authors: Xinan Yue, William Schreiner, Jiuhou Lei, Sergey Sokolovskiy, C Rocken, Douglas Hunt, Ying-hwa KuoAbstract:Abstract. This letter reports for the first time the simulated error distribution of Radio Occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC Occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.
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postprocessing of l1 gps Radio Occultation signals recorded in open loop mode
Radio Science, 2009Co-Authors: Sergey Sokolovskiy, William Schreiner, C Rocken, Douglas Hunt, James JohnsonAbstract:[1] GPS Radio Occultation (RO) profiling from low-Earth orbiting satellites is operationally used for numerical weather forecasting and is starting to be used for climate studies. Obtaining high-quality observations near the surface requires recording of RO signals in model-aided open loop (OL) mode by the GPS receiver. Postprocessing of the OL RO signals is different from that of the signals recorded in traditional phase-locked loop (PLL) mode. It requires modeling of the signal frequency for connection of the phase between samples and removal of the GPS navigation data modulation (NDM). It is important that the postprocessing does not introduce errors (biases) in the connected phase. This paper describes the postprocessing of the OL RO signals which does not depend on the receiver model. The postprocessing includes: modeling of the RO signal frequency from refractivity climatology and the subsequent adjustment of this model by use of feedback which makes the postprocessing model-independent; internal (as in PLL) removal of NDM and the use of externally recorded NDM bit sequence. Statistical comparison of the refractivity inversion results demonstrates that external demodulation of RO signals reduces the inversion bias in the tropical lower troposphere by about 0.5%.
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monitoring the atmospheric boundary layer by gps Radio Occultation signals recorded in the open loop mode
Geophysical Research Letters, 2006Co-Authors: Sergey Sokolovskiy, Ying-hwa Kuo, William Schreiner, Douglas Hunt, Chris Rocken, Richard A AnthesAbstract:[1] A new type of Radio Occultation (RO) data, recorded in open-loop (OL) mode from the SAC-C satellite, has been tested for monitoring refractivity in the Atmospheric Boundary Layer (ABL). Previously available RO signals, recorded in phase-locked loop mode were often unusable for sensing the lower troposphere (LT) or resulted in significant inversion errors, especially in the tropics. The OL RO signals allow sensing of the LT and accurate monitoring of the ABL and, especially, its depth. Comparison of RO-inverted refractivity profiles to ECMWF analysis and available Radiosondes generally shows good agreement in the depth of the ABL. However, in a number of cases, ECMWF fails to reproduce the top of ABL. Future OL RO signals will provide information about the ABL depth which is an important parameter for weather prediction and climate monitoring.
Douglas Hunt - One of the best experts on this subject based on the ideXlab platform.
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quantification of structural uncertainty in climate data records from gps Radio Occultation
Atmospheric Chemistry and Physics, 2013Co-Authors: Douglas Hunt, Anthony J Mannucci, Gottfried Kirchengast, Andrea K Steiner, Barbara Scherllinpirscher, Hans Gleisner, A Von Engeln, Torsten SchmidtAbstract:Abstract. Global Positioning System (GPS) Radio Occultation (RO) has provided continuous observations of the Earth's atmosphere since 2001 with global coverage, all-weather capability, and high accuracy and vertical resolution in the upper troposphere and lower stratosphere (UTLS). Precise time measurements enable long-term stability but careful processing is needed. Here we provide climate-oriented atmospheric scientists with multicenter-based results on the long-term stability of RO climatological fields for trend studies. We quantify the structural uncertainty of atmospheric trends estimated from the RO record, which arises from current processing schemes of six international RO processing centers, DMI Copenhagen, EUM Darmstadt, GFZ Potsdam, JPL Pasadena, UCAR Boulder, and WEGC Graz. Monthly-mean zonal-mean fields of bending angle, refractivity, dry pressure, dry geopotential height, and dry temperature from the CHAMP mission are compared for September 2001 to September 2008. We find that structural uncertainty is lowest in the tropics and mid-latitudes (50° S to 50° N) from 8 km to 25 km for all inspected RO variables. In this region, the structural uncertainty in trends over 7 yr is
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error analysis of abel retrieved electron density profiles from Radio Occultation measurements
Annales Geophysicae, 2010Co-Authors: Xinan Yue, William Schreiner, Jiuhou Lei, Sergey Sokolovskiy, C Rocken, Douglas Hunt, Ying-hwa KuoAbstract:Abstract. This letter reports for the first time the simulated error distribution of Radio Occultation (RO) electron density profiles (EDPs) from the Abel inversion in a systematic way. Occultation events observed by the COSMIC satellites are simulated during the spring equinox of 2008 by calculating the integrated total electron content (TEC) along the COSMIC Occultation paths with the "true" electron density from an empirical model. The retrieval errors are computed by comparing the retrieved EDPs with the "true" EDPs. The results show that the retrieved NmF2 and hmF2 are generally in good agreement with the true values, but the reliability of the retrieved electron density degrades in low latitude regions and at low altitudes. Specifically, the Abel retrieval method overestimates electron density to the north and south of the crests of the equatorial ionization anomaly (EIA), and introduces artificial plasma caves underneath the EIA crests. At lower altitudes (E- and F1-regions), it results in three pseudo peaks in daytime electron densities along the magnetic latitude and a pseudo trough in nighttime equatorial electron densities.
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assessment of Radiosonde temperature measurements in the upper troposphere and lower stratosphere using cosmic Radio Occultation data
Geophysical Research Letters, 2009Co-Authors: Hongbin Chen, Douglas Hunt, Xinjia Zhou, Ying-hwa KuoAbstract:[1] Temperature profiles derived from Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission are compared with those from four types of Radiosonde systems from 12 to 25 km to assess the performance of these Radiosonde systems in the upper troposphere and lower stratosphere. Results show that temperature measurements from the Vaisala-RS92 and Shanghai Radiosonde systems agree well with those of COSMIC with a close-to-zero mean difference. Large temperature biases are shown for the MRZ and VIZ-B2 Radiosonde systems relative to COSMIC, which are probably caused by diurnal radiative effects. In addition, we show that the temperature measurements from a new Chinese Radiosonde system are improved compared to those of an older system through a comparison with COSMIC measurements.
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postprocessing of l1 gps Radio Occultation signals recorded in open loop mode
Radio Science, 2009Co-Authors: Sergey Sokolovskiy, William Schreiner, C Rocken, Douglas Hunt, James JohnsonAbstract:[1] GPS Radio Occultation (RO) profiling from low-Earth orbiting satellites is operationally used for numerical weather forecasting and is starting to be used for climate studies. Obtaining high-quality observations near the surface requires recording of RO signals in model-aided open loop (OL) mode by the GPS receiver. Postprocessing of the OL RO signals is different from that of the signals recorded in traditional phase-locked loop (PLL) mode. It requires modeling of the signal frequency for connection of the phase between samples and removal of the GPS navigation data modulation (NDM). It is important that the postprocessing does not introduce errors (biases) in the connected phase. This paper describes the postprocessing of the OL RO signals which does not depend on the receiver model. The postprocessing includes: modeling of the RO signal frequency from refractivity climatology and the subsequent adjustment of this model by use of feedback which makes the postprocessing model-independent; internal (as in PLL) removal of NDM and the use of externally recorded NDM bit sequence. Statistical comparison of the refractivity inversion results demonstrates that external demodulation of RO signals reduces the inversion bias in the tropical lower troposphere by about 0.5%.
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monitoring the atmospheric boundary layer by gps Radio Occultation signals recorded in the open loop mode
Geophysical Research Letters, 2006Co-Authors: Sergey Sokolovskiy, Ying-hwa Kuo, William Schreiner, Douglas Hunt, Chris Rocken, Richard A AnthesAbstract:[1] A new type of Radio Occultation (RO) data, recorded in open-loop (OL) mode from the SAC-C satellite, has been tested for monitoring refractivity in the Atmospheric Boundary Layer (ABL). Previously available RO signals, recorded in phase-locked loop mode were often unusable for sensing the lower troposphere (LT) or resulted in significant inversion errors, especially in the tropics. The OL RO signals allow sensing of the LT and accurate monitoring of the ABL and, especially, its depth. Comparison of RO-inverted refractivity profiles to ECMWF analysis and available Radiosondes generally shows good agreement in the depth of the ABL. However, in a number of cases, ECMWF fails to reproduce the top of ABL. Future OL RO signals will provide information about the ABL depth which is an important parameter for weather prediction and climate monitoring.
Jens Wickert - One of the best experts on this subject based on the ideXlab platform.
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geros iss gnss reflectometry Radio Occultation and scatterometry onboard the international space station
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2016Co-Authors: Jens Wickert, Estel Cardellach, Manuel Martinneira, Jorge Bandeiras, Laurent Bertino, Ole Baltazar Andersen, Adriano Camps, Nuno Catarino, Bertrand Chapron, Fran FabraAbstract:GEROS-ISS stands for GNSS REflectometry, Radio Occultation, and scatterometry onboard the International Space Station (ISS). It is a scientific experiment, successfully proposed to the European Space Agency in 2011. The experiment as the name indicates will be conducted on the ISS. The main focus of GEROS-ISS is the dedicated use of signals from the currently available Global Navigation Satellite Systems (GNSS) in L-band for remote sensing of the Earth with a focus to study climate change. Prime mission objectives are the determination of the altimetric sea surface height of the oceans and of the ocean surface mean square slope, which is related to sea roughness and wind speed. These geophysical parameters are derived using reflected GNSS signals (GNSS reflectometry, GNSS-R). Secondary mission goals include atmosphere/ionosphere sounding using refracted GNSS signals (Radio Occultation, GNSS-RO) and remote sensing of land surfaces using GNSS-R. The GEROS-ISS mission objectives and its design, the current status, and ongoing activities are reviewed and selected scientific and technical results of the GEROS-ISS preparation phase are described.
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semidiurnal tidal signature in sporadic e occurrence rates derived from gps Radio Occultation measurements at higher midlatitudes
Annales Geophysicae, 2009Co-Authors: Christina Arras, Christoph Jacobi, Jens WickertAbstract:Abstract. GPS (Global Positioning System) Radio Occultation (RO) measurements from CHAMP, GRACE and FORMOSAT-3/COSMIC satellites at Northern Hemisphere midlatitides (50°–55° N) are analysed to obtain the diurnal variation of sporadic E layer occurrence frequency in 2006 and 2007. Interconnections with zonal wind shears measured by meteor radar at Collm (51.3° N, 13° E), Germany, are investigated. According to theory, maximum Es occurrence is expected when the zonal wind shear, which is mainly produced by the semidiurnal tide in midlatitudes, is negative. This is confirmed by the present measurements and analysis.
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gps Radio Occultation results from champ grace and formosat 3 cosmic
Terrestrial Atmospheric and Oceanic Sciences, 2009Co-Authors: Jens Wickert, S B Healy, G Beyerle, Torsten Schmidt, Norbert Jakowski, Stefan Heise, Cheng-yung Huang, Grzegorz Michalak, C Z Cheng, W KohlerAbstract:The Taiwan/US FORMOSAT-3/COS MIC (FORMOsa SATellite mission - 3/Constellation Observing System for Meteorology, Ionosphere and Climate) satellite constellation was success fully launched on 14 April 2006. It is expected to leverage the use of the GPS (Global Positioning System) Radio Occultation data for atmospheric and ionospheric research to improve global weather forecasts and aid climate change related studies. FORMOSAT-3/COSMIC, together with the European MetOp, German CHAMP and US/Ger man GRACE-A satellites, form a 9 satellite constellation for precise atmospheric sounding on a global scale. This satellite constellation is expected to provide about 3500 Occultation measurements daily. Recent results and the status of the CHAMP and GRACE-A orbit and Occultation data analysis are reviewed and complemented with a review of initial results from FORMOSAT-3/COSMIC at GFZ. The significantly in creased potential of the CHAMP, GRACE-A and FORMOSAT-3/COSMIC constellation for atmospheric studies, compared to single satellite missions, is demonstrated for selected applications such as global monitoring of water vapor distributions, tropopause parameters and ionospheric irregularities.
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a global climatology of ionospheric irregularities derived from gps Radio Occultation
Geophysical Research Letters, 2008Co-Authors: Christina Arras, Jens Wickert, G Beyerle, S Heise, Torsten Schmidt, Christoph JacobiAbstract:[1] GPS Radio Occultation measurements from CHAMP, GRACE-A and FORMOSAT-3/COSMIC are used to derive global information on small-scale ionospheric irregularities such as sporadic E layers between January 2002 and December 2007. The investigations are based on the analysis of amplitude variations of the GPS Radio Occultation signals. The global distribution of ionospheric irregularities shows strong seasonal variations with highest occurrence rates during summer in the middle latitudes. The long-term data set of CHAMP allows for first climatological studies, while the data coverage increases significantly with the combination of CHAMP, GRACE and FORMOSAT-3/COSMIC measurements. This allows for global maps of sporadic E occurrence rates of very high spatial resolution where the influence of the Earth's magnetic field becomes visible in global sporadic E maps for the first time.
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using champ Radio Occultation data to determine the top altitude of the planetary boundary layer
Geophysical Research Letters, 2005Co-Authors: Jens Wickert, Axel Von Engeln, Jo Ao Teixeira, Stefan BuehlerAbstract:[1] A simple approach to derive the Planetary Boundary Layer (PBL) top altitude from CHAMP (CHAllenging Minisatellite Payload) Radio Occultation (RO) data is presented. Our RO processing cuts off at an altitude, typically ≤4 km, below which the GPS signals are affected by tracking errors. This lowest processed altitude (LPA) is assumed to coincide with the PBL top. We average LPAs for the years 2001 to 2004 over 5 Degree latitude longitude boxes and compare them to ECMWF analysis data. The ECMWF PBL top was calculated from the relative humidity gradient with respect to altitude. Agreement between the data sets is good in terms of mean PBL height, especially over sea. The CHAMP data shows the major features of PBL height with a realistic transition from stratocumulus regions to shallow and deep cumulus areas. CHAMP also shows a substantial amount of PBL height variability that may prove useful to study PBL dynamics.
