scholarly journals COSMIC Radio Occultation Processing: Cross-Center Comparison and Validation

2011 ◽  
Vol 28 (6) ◽  
pp. 737-751 ◽  
Author(s):  
Michael E. Gorbunov ◽  
A. V. Shmakov ◽  
Stephen S. Leroy ◽  
Kent B. Lauritsen
Keyword(s):  
Data Processing ◽  
Radio Occultation ◽  
Weather Prediction ◽  
Processing System ◽  
Fourier Integral ◽  
Small Scale ◽  
Cosmic Radio ◽  
Structural Uncertainty ◽  
Height Range ◽  
The Tropics

Abstract A radio occultation data processing system (OCC) was developed for numerical weather prediction and climate benchmarking. The data processing algorithms use the well-established Fourier integral operator–based methods, which ensure a high accuracy of retrievals. The system as a whole, or in its parts, is currently used at the Global Navigation Satellite System Receiver for Atmospheric Sounding (GRAS) Satellite Application Facility at the Danish Meteorological Institute, German Weather Service, and Wegener Center for Climate and Global Change. A statistical comparison of the inversions of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) data by the system herein, University Corporation for Atmospheric Research (UCAR) data products, and ECMWF analyses is presented. Forty days of 2007 and 2008 were processed (from 5 days in the middle of each season) for the comparison of OCC and ECMWF, and 20 days of April 2009 were processed for the comparison of OCC, UCAR, and ECMWF. The OCC and UCAR inversions are consistent. For the tropics, the systematic difference between OCC and UCAR in the retrieved refractivity in the 2–30-km height interval does not exceed 0.1%; in particular, in the 9–25-km interval it does not exceed 0.03%. Below 1 km in the tropics the OCC – UCAR bias reaches 0.2%, which is explained by different cutoff and filtering schemes implemented in the two systems. The structure of the systematic OCC – ECMWF difference below 4 km changes in 2007, 2008, and 2009, which is explained by changes in the ECMWF analyses and assimilation schemes. It is estimated that in the 4–30-km height range the OCC occultation processing system obtains refractivities with a bias not exceeding 0.2%. The random error ranges from 0.3%–0.5% in the upper troposphere–lower stratosphere to about 2% below 4 km. The estimate of the bias below 4 km can currently be done with an accuracy of 0.5%–1% resulting from the structural uncertainty of the radio occultation (RO) data reflecting the insufficient knowledge of the atmospheric small-scale structures and instrumental errors. The OCC – UCAR bias is below the level of the structural uncertainty.

scholarly journals Estimation and evaluation of COSMIC radio occultation excess phase using undifferenced measurements

2017 ◽  
Vol 10 (5) ◽  
pp. 1813-1821
Author(s):  
Pengfei Xia ◽  
Shirong Ye ◽  
Kecai Jiang ◽  
Dezhong Chen
Keyword(s):  
Radio Occultation ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Double Difference ◽  
Cosmic Radio ◽  
Processing Strategy ◽  
Single Difference ◽  
Excess Phase ◽  
Mean Square Errors ◽  
Better Than

Abstract. In the GPS radio occultation technique, the atmospheric excess phase (AEP) can be used to derive the refractivity, which is an important quantity in numerical weather prediction. The AEP is conventionally estimated based on GPS double-difference or single-difference techniques. These two techniques, however, rely on the reference data in the data processing, increasing the complexity of computation. In this study, an undifferenced (ND) processing strategy is proposed to estimate the AEP. To begin with, we use PANDA (Positioning and Navigation Data Analyst) software to perform the precise orbit determination (POD) for the purpose of acquiring the position and velocity of the mass centre of the COSMIC (The Constellation Observing System for Meteorology, Ionosphere and Climate) satellites and the corresponding receiver clock offset. The bending angles, refractivity and dry temperature profiles are derived from the estimated AEP using Radio Occultation Processing Package (ROPP) software. The ND method is validated by the COSMIC products in typical rising and setting occultation events. Results indicate that rms (root mean square) errors of relative refractivity differences between undifferenced and atmospheric profiles (atmPrf) provided by UCAR/CDAAC (University Corporation for Atmospheric Research/COSMIC Data Analysis and Archive Centre) are better than 4 and 3 % in rising and setting occultation events respectively. In addition, we also compare the relative refractivity bias between ND-derived methods and atmPrf profiles of globally distributed 200 COSMIC occultation events on 12 December 2013. The statistical results indicate that the average rms relative refractivity deviation between ND-derived and COSMIC profiles is better than 2 % in the rising occultation event and better than 1.7 % in the setting occultation event. Moreover, the observed COSMIC refractivity profiles from ND processing strategy are further validated using European Centre for Medium-Range Weather Forecasts (ECMWF) analysis data, and the results indicate that the undifferenced method reduces the noise level on the excess phase paths in the lower troposphere compared to the single-difference processing strategy.

scholarly journals Implementation of a GPS-RO data processing system for the KIAPS-LETKF data assimilation system

2014 ◽  
Vol 7 (11) ◽  
pp. 11927-11956 ◽  
Author(s):  
H. Kwon ◽  
J.-S. Kang ◽  
Y. Jo ◽  
J. H. Kang
Keyword(s):  
Quality Control ◽  
Data Assimilation ◽  
Data Processing ◽  
Weather Prediction ◽  
Processing System ◽  
Data Processing System ◽  
Bending Angle ◽  
Quality Control Process ◽  
Data Assimilation System ◽  
Assimilation System

Abstract. The Korea Institute of Atmospheric Prediction Systems (KIAPS) has been developing a new global numerical weather prediction model and an advanced data assimilation system. As part of the KIAPS Package for Observation Processing (KPOP) system for data assimilation, preprocessing and quality control modules for bending angle measurements of global positioning system radio occultation (GPS-RO) data have been implemented and examined. GPS-RO data processing system is composed of several steps for checking observation locations, missing values, physical values for Earth radius of curvature, and geoid undulation. An observation-minus-background check is implemented by use of a one-dimensional observational bending angle operator and tangent point drift is also considered in the quality control process. We have tested GPS-RO observations utilized by the Korean Meteorological Administration (KMA) within KPOP, based on both the KMA global model and the National Center for Atmospheric Research (NCAR) Community Atmosphere Model-Spectral Element (CAM-SE) as a model background. Background fields from the CAM-SE model are incorporated for the preparation of assimilation experiments with the KIAPS-LETKF data assimilation system, which has been successfully implemented to a cubed-sphere model with fully unstructured quadrilateral meshes. As a result of data processing, the bending angle departure statistics between observation and background shows significant improvement. Also, the first experiment in assimilating GPS-RO bending angle resulting from KPOP within KIAPS-LETKF shows encouraging results.

scholarly journals Estimation and Evaluation of COSMIC Radio Occultation Excess Phase Using Non-differenced Measurements

2016 ◽  
Author(s):  
Pengfei Xia ◽  
Shirong Ye ◽  
Kecai Jiang ◽  
Dezhong Chen
Keyword(s):  
Radio Occultation ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Precise Orbit Determination ◽  
Cosmic Radio ◽  
Processing Strategy ◽  
Comparison Results ◽  
Excess Phase ◽  
Mean Square Errors ◽  
Better Than

Abstract. In the GPS radio occultation technique, the atmospheric excess phase (AEP) can be used to derive the refractivity which is an important quantity in numerical weather prediction. The AEP is conventionally estimated based on GPS double-differenced or single-differenced techniques. These two techniques, however, require the reference link data in the data processing increasing the complexity of computation. In this study, a non-differenced (ND) processing strategy is proposed to estimate the AEP. To begin with, we used PANDA (Positioning and Navigation Data Analyst) software to perform the precise orbit determination (POD) for the COSIMC (The Constellation Observing System for Meteorology, Ionosphere and Climate) satellite to acquire the position and velocity of the center of mass of the satellite and the corresponded receive clock offset. The bending angles, refractivity and dry temperature profiles are derived from the estimated AEP by the ROPP (Radio Occultation Processing Package) software. The ND method is validated by the COSMIC products in typical rising and setting occultation events. Comparison results indicate that RMS (root mean square) errors of relative refractivity differences between ND-derived and "atmPrf" profiles are better than 4 % and 3 % in rising and setting occultation events, respectively. In addition, we also compared the relative refractivity bias between ND-derived and "atmPrf" profiles of globally distributed 200 COSMIC occultation events on December 12, 2013. The statistic results show that the average RMS relative refractivity deviation between ND-derived and COSMIC profile is better than 2 % in the rising occultation event, and it is better than 1.7 % in setting occultation event. Moreover, the observed COSMIC refractivity profiles from ND processing strategy are further validated using European Centre for Medium-Range Weather Forecasts (ECMWF) analyses data, and the results indicate that non-differencing reduces the noise level on the excess phase paths in the lower troposphere compared to single difference processing strategy.

scholarly journals Evaluating the lower-tropospheric COSMIC GPS radio occultation sounding quality over the Arctic

2018 ◽  
Vol 11 (4) ◽  
pp. 2051-2066 ◽  
Author(s):  
Xiao Yu ◽  
Feiqin Xie ◽  
Chi O. Ao
Keyword(s):  
Data Processing ◽  
Radio Occultation ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Parametric Uncertainty ◽  
Ocean Surface ◽  
Specific Humidity ◽  
The Arctic ◽  
Near Surface ◽  
Active Research

Abstract. Lower-tropospheric moisture and temperature measurements are crucial for understanding weather prediction and climate change. Global Positioning System radio occultation (GPS RO) has been demonstrated as a high-quality observation technique with high vertical resolution and sub-kelvin temperature precision from the upper troposphere to the stratosphere. In the tropical lower troposphere, particularly the lowest 2 km, the quality of RO retrievals is known to be degraded and is a topic of active research. However, it is not clear whether similar problems exist at high latitudes, particularly over the Arctic, which is characterized by smooth ocean surface and often negligible moisture in the atmosphere. In this study, 3-year (2008–2010) GPS RO soundings from COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) over the Arctic (65–90° N) show uniform spatial sampling with average penetration depth within 300 m above the ocean surface. Over 70 % of RO soundings penetrate deep into the lowest 300 m of the troposphere in all non-summer seasons. However, the fraction of such deeply penetrating profiles reduces to only about 50–60 % in summer, when near-surface moisture and its variation increase. Both structural and parametric uncertainties of GPS RO soundings were also analyzed. The structural uncertainty (due to different data processing approaches) is estimated to be within  ∼  0.07 % in refractivity,  ∼  0.72 K in temperature, and  ∼  0.05 g kg−1 in specific humidity below 10 km, which is derived by comparing RO retrievals from two independent data processing centers. The parametric uncertainty (internal uncertainty of RO sounding) is quantified by comparing GPS RO with near-coincident radiosonde and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim profiles. A systematic negative bias up to  ∼  1 % in refractivity below 2 km is only seen in the summer, which confirms the moisture impact on GPS RO quality.

scholarly journals On the Relationship between Gravity Waves and Tropopause Height and Temperature over the Globe Revealed by COSMIC Radio Occultation Measurements

Atmosphere ◽  
2019 ◽  
Vol 10 (2) ◽  
pp. 75 ◽  
Author(s):  
Daocheng Yu ◽  
Xiaohua Xu ◽  
Jia Luo ◽  
Juan Li
Keyword(s):  
Radio Occultation ◽  
Correlation Coefficients ◽  
Lapse Rate ◽  
Cosmic Radio ◽  
Monthly Means ◽  
High Latitudes ◽  
Tropopause Height ◽  
The Tropics ◽  
The Relationship ◽  
Peak Correlation

In this study, the relationship between gravity wave (GW) potential energy (Ep) and the tropopause height and temperature over the globe was investigated using COSMIC radio occultation (RO) dry temperature profiles during September 2006 to May 2013. The monthly means of GW Ep with a vertical resolution of 1 km and tropopause parameters were calculated for each 5° × 5° longitude-latitude grid. The correlation coefficients between Ep values at different altitudes and the tropopause height and temperature were calculated accordingly in each grid. It was found that at middle and high latitudes, GW Ep over the altitude range from lapse rate tropopause (LRT) to several km above had a significantly positive/negative correlation with LRT height (LRT-H)/ LRT temperature (LRT-T) and the peak correlation coefficients were determined over the altitudes of 10–14 km with distinct zonal distribution characteristics. While in the tropics, the distributions of the statistically significant correlation coefficients between GW Ep and LRT/cold point tropopause (CPT) parameters were dispersive and the peak correlation were are calculated over the altitudes of 14–38 km. At middle and high latitudes, the temporal variations of the monthly means and the monthly anomalies of the LRT parameters and GW Ep over the altitude of 13 km showed that LRT-H/LRT-T increases/decreases with the increase of Ep, which indicates that LRT was lifted and became cooler when GWs propagated from the troposphere to the stratosphere. In the tropical regions, statistically significant positive/negative correlations exist between GW Ep over the altitude of 17–19 km and LRT-H/LRT-T where deep convections occur and on the other hand, strong correlations exist between convections and the tropopause parameters in most seasons, which indicates that low and cold tropopause appears in deep convection regions. Thus, in the tropics, both deep convections and GWs excited accordingly have impacts on the tropopause structure.

scholarly journals Model inter-comparison for short-range forecasts over the southern African domain

2021 ◽  
Vol 117 (9/10) ◽  
Author(s):  
Patience T. Mulovhedzi ◽  
Gift T. Rambuwani ◽  
Mary-Jane Bopape ◽  
Robert Maisha ◽  
Nkwe Monama
Keyword(s):  
Wind Speed ◽  
South African ◽  
Weather Prediction ◽  
Weather Research And Forecasting ◽  
Small Scale ◽  
Spatial Coverage ◽  
Critical Issues ◽  
Scale Modelling ◽  
The Tropics ◽  
Horizontal Grid

Numerical weather prediction (NWP) models have been increasing in skill and their capability to simulate weather systems and provide valuable information at convective scales has improved in recent years. Much effort has been put into developing NWP models across the globe. Representation of physical processes is one of the critical issues in NWP, and it differs from one model to another. We investigated the performance of three regional NWP models used by the South African Weather Service over southern Africa, to identify the model that produces the best deterministic forecasts for the study domain. The three models – Unified Model (UM), Consortium for Small-scale Modelling (COSMO) and Weather Research and Forecasting (WRF) – were run at a horizontal grid spacing of about 4.4 km. Model forecasts for precipitation, 2-m temperature, and wind speed were verified against different observations. Snow was evaluated against reported snow records. Both the temporal and spatial verification of the model forecasts showed that the three models are comparable, with slight variations. Temperature and wind speed forecasts were similar for the three different models. Accumulated precipitation was mostly similar, except where WRF captured small rainfall amounts from a coastal low, while it over-estimated rainfall over the ocean. The UM showed a bubble-like shape towards the tropics, while COSMO cut-off part of the rainfall band that extended from the tropics to the sub-tropics. The COSMO and WRF models simulated a larger spatial coverage of precipitation than UM and snow-report records.

scholarly journals An Observing System Simulation Experiment with a Constellation of Radio Occultation Satellites

2018 ◽  
Vol 146 (12) ◽  
pp. 4247-4259 ◽  
Author(s):  
L. Cucurull ◽  
R. Atlas ◽  
R. Li ◽  
M. J. Mueller ◽  
R. N. Hoffman
Keyword(s):  
Radio Occultation ◽  
Simulation Experiment ◽  
System Simulation ◽  
Weather Prediction ◽  
Satellite System ◽  
Prediction Systems ◽  
Global Navigation Satellite ◽  
The Tropics ◽  
Observing System Simulation Experiment ◽  
The Impact

Abstract Experiments with a global observing system simulation experiment (OSSE) system based on the recent 7-km-resolution NASA nature run (G5NR) were conducted to determine the potential value of proposed Global Navigation Satellite System (GNSS) radio occultation (RO) constellations in current operational numerical weather prediction systems. The RO observations were simulated with the geographic sampling expected from the original planned Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) system, with six equatorial (total of ~6000 soundings per day) and six polar (total of ~6000 soundings per day) receiver satellites. The experiments also accounted for the expected improved vertical coverage provided by the Jet Propulsion Laboratory RO receivers on board COSMIC-2. Except that RO observations were simulated and assimilated as refractivities, the 2015 version of the NCEP’s operational data assimilation system was used to run the OSSEs. The OSSEs quantified the impact of RO observations on global weather analyses and forecasts and the impact of adding explicit errors to the simulation of perfect RO profiles. The inclusion or exclusion of explicit errors had small, statistically insignificant impacts on results. The impact of RO observations was found to increase the length of the useful forecasts. In experiments with explicit errors, these increases were found to be 0.6 h in the Northern Hemisphere extratropics (a 0.4% improvement), 5.9 h in the Southern Hemisphere extratropics (a significant 4.0% improvement), and 12.1 h in the tropics (a very substantial 28.4% improvement).

scholarly journals Comparative Assessment of COSMIC Radio Occultation Data and TIMED/SABER Satellite Data over China

2015 ◽  
Vol 54 (9) ◽  
pp. 1931-1943 ◽  
Author(s):  
Z. Q. Fan ◽  
Z. Sheng ◽  
H. Q. Shi ◽  
X. Yi ◽  
Y. Jiang ◽  
...  
Keyword(s):  
Radio Occultation ◽  
Satellite Observation ◽  
Comparative Assessment ◽  
Observation Data ◽  
Cosmic Radio ◽  
Temperature Deviation ◽  
Height Range ◽  
Broadband Emission ◽  
Occultation Data ◽  
Good Agreement

AbstractThe accuracy of temperature data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) radio occultation and Thermosphere, Ionosphere, Mesosphere Energetics, and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) observation over China is analyzed. High-resolution sounding data are used to assess the accuracy of these two kinds of satellite observation data at corresponding heights, and the two sets of data are compared in the height range 15–40 km. Very good agreement between radiosondes and COSMIC is observed in the stratosphere. In the troposphere COSMIC temperatures are about 2 K higher than the radiosonde observations. SABER detection at 15–32 km agrees well with a maximum warm bias of ~2 K around 25-km altitude. The comparison between SABER and COSMIC for altitudes 15–40 km also indicates higher temperatures of SABER in the lower stratosphere. The standard deviations are all greater than 2.5 K and are larger near 15 km and smallest at 20 km. The temperature deviation and in particular the standard deviation comparing SABER and COSMIC changes with altitude, season, and latitude. The results of this comparative assessment can offer a basis for research into the application of COSMIC and TIMED/SABER over China.

Impact of Loss of U.S. Microwave and Radio Occultation Observations in Operational Numerical Weather Prediction in Support of the U.S. Data Gap Mitigation Activities

2015 ◽  
Vol 30 (2) ◽  
pp. 255-269 ◽  
Author(s):  
Lidia Cucurull ◽  
Richard A. Anthes
Keyword(s):  
Southern Hemisphere ◽  
Numerical Weather Prediction ◽  
Radio Occultation ◽  
Weather Prediction ◽  
Advanced Technology ◽  
Forecast System ◽  
Aqua Satellite ◽  
Data Gap ◽  
The Tropics ◽  
The U.S

Abstract As the U.S. polar-orbiting satellites NOAA-15, -18, and -19 and NASA’s Aqua satellite reach the ends of their lives, there may be a loss in redundancy between their microwave (MW) soundings, and the Advanced Technology Microwave Sounder (ATMS) on the Suomi–National Polar-Orbiting Partnership (NPP) satellite. With the expected delay in the launch of the next generation of U.S. polar-orbiting satellites, there may be a loss in at least some of the U.S. MW data. There may also be a significant decrease in the number of radio occultation (RO) observations. The mainstay of the global RO system, the COSMIC constellation of six satellites is already past the end of its nominal lifetime. A replacement of RO soundings in the tropics is planned with the launch of COSMIC-2 satellites in 2016. However, the polar constellation of COSMIC-2 will not be launched until 2018 or 2019, and complete funding for this constellation is not assured. Using the NCEP operational forecast system, forecasts for March–April 2013 are carried out in which various combinations of the U.S. MW and all RO soundings are removed. The main results are that the forecasts are only slightly degraded in the Northern Hemisphere, even with all of these observations removed. The decrease in accuracy is considerably greater in the Southern Hemisphere, where the greatest forecast degradation occurs when the RO observations are removed. Overall, these results indicate that the possible gap in RO observations is potentially more significant than the possible gap in the U.S. MW data.

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