scholarly journals Improvements to a GPS radio occultation ray-tracing model and their impacts on assimilation of bending angle

2003 ◽  
Vol 108 (D17) ◽  
Author(s):  
H. Liu
Keyword(s):  
Ray Tracing ◽  
Radio Occultation ◽  
Bending Angle ◽  
Gps Radio Occultation ◽  
Ray Tracing Model

scholarly journals Global 3D Features of Error Variances of GPS Radio Occultation and Radiosonde Observations

2020 ◽  
Vol 13 (1) ◽  
pp. 1
Author(s):  
Xu Xu ◽  
Xiaolei Zou
Keyword(s):  
Radio Occultation ◽  
Weather Prediction ◽  
Lower Troposphere ◽  
Error Variance ◽  
Specific Humidity ◽  
Temperature Error ◽  
Observation Error ◽  
Bending Angle ◽  
Gps Radio Occultation ◽  
Low Latitudes

Global Positioning System (GPS) radio occultation (RO) and radiosonde (RS) observations are two major types of observations assimilated in numerical weather prediction (NWP) systems. Observation error variances are required input that determines the weightings given to observations in data assimilation. This study estimates the error variances of global GPS RO refractivity and bending angle and RS temperature and humidity observations at 521 selected RS stations using the three-cornered hat method with additional ERA-Interim reanalysis and Global Forecast System forecast data available from 1 January 2016 to 31 August 2019. The global distributions, of both RO and RS observation error variances, are analyzed in terms of vertical and latitudinal variations. Error variances of RO refractivity and bending angle and RS specific humidity in the lower troposphere, such as at 850 hPa (3.5 km impact height for the bending angle), all increase with decreasing latitude. The error variances of RO refractivity and bending angle and RS specific humidity can reach about 30 N-unit2, 3 × 10−6 rad2, and 2 (g kg−1)2, respectively. There is also a good symmetry of the error variances of both RO refractivity and bending angle with respect to the equator between the Northern and Southern Hemispheres at all vertical levels. In this study, we provide the mean error variances of refractivity and bending angle in every 5°-latitude band between the equator and 60°N, as well as every interval of 10 hPa pressure or 0.2 km impact height. The RS temperature error variance distribution differs from those of refractivity, bending angle, and humidity, which, at low latitudes, are smaller (less than 1 K2) than those in the midlatitudes (more than 3 K2). In the midlatitudes, the RS temperature error variances in North America are larger than those in East Asia and Europe, which may arise from different radiosonde types among the above three regions.

scholarly journals An Impact Study of GPS Radio Occultation Observations on Frontal Rainfall Prediction with a Local Bending Angle Operator

2016 ◽  
Vol 31 (1) ◽  
pp. 129-150 ◽  
Author(s):  
Ching-Yuang Huang ◽  
Shu-Ya Chen ◽  
S. K. A. V. Prasad Rao Anisetty ◽  
Shu-Chih Yang ◽  
Ling-Feng Hsiao
Keyword(s):  
Radio Occultation ◽  
Positive Impact ◽  
Three Dimensional ◽  
Wrf Model ◽  
Satellite Mission ◽  
Bending Angle ◽  
Nonlocal Operators ◽  
Gps Radio Occultation ◽  
Rainfall Prediction ◽  
The Impact

Abstract The impact of global positioning system (GPS) radio occultation (RO) soundings on the prediction of severe mei-yu frontal rainfall near Taiwan in June 2012 was investigated in this study using a developed local bending angle (LBA) operator. Two operators for local refractivity (REF) and nonlocal refractivity [excess phase (EPH)] were also used for comparisons. The devised LBA simplifies the calculation of the Abel transform in inverting model local refractivity without a loss of accuracy. These operators have been implemented into the three-dimensional variational data assimilation system of the Weather Research and Forecasting (WRF) Model to assimilate GPS RO soundings available from the Formosa Satellite Mission 3/Constellation Observing Systems for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC). The RO data are found to be beneficial to the WRF forecast of local severe rainfall in Taiwan. Characteristics of assimilation performance and innovation for the three operators are discussed. Both of the local operators performing assimilation at observation levels appear to produce mostly larger positive moisture increments than do the current nonlocal operators performing assimilation on the mean height of each model vertical level. As the information of the initial increments has propagated farther south with the frontal flow, the simulation for LBA shows better prediction of rainfall peaks in Taiwan on the second day than both REF and EPH, with a maximum improvement of about 25%. The positive impact of the RO data results partially from several RO observations near Mongolia and north China. This study provides an intercomparison among the three RO operators, and shows the feasibility of regional assimilation with LBA.

scholarly journals Ionospheric correction of GPS radio occultation data in the troposphere

2016 ◽  
Vol 9 (2) ◽  
pp. 335-346 ◽  
Author(s):  
Z. Zeng ◽  
S. Sokolovskiy ◽  
W. Schreiner ◽  
D. Hunt ◽  
J. Lin ◽  
...  
Keyword(s):  
Radio Occultation ◽  
Neutral Atmosphere ◽  
Ionospheric Correction ◽  
Bending Angle ◽  
Gps Radio Occultation ◽  
Strong Inversion ◽  
Occultation Data ◽  
Horizontal Inhomogeneity ◽  
L1 And L2 ◽  
Bending Angles

Abstract. For inversions of the GPS radio occultation (RO) data in the neutral atmosphere, this study investigates an optimal transition height for replacing the standard ionospheric correction using the linear combination of the L1 and L2 bending angles with the correction of the L1 bending angle by the L1–L2 bending angle extrapolated from above. The optimal transition height depends on the RO mission (i.e., the receiver and firmware) and is different between rising and setting occultations and between L2P and L2C GPS signals. This height is within the range of approximately 10–20 km. One fixed transition height, which can be used for the processing of currently available GPS RO data, can be set to 20 km. Analysis of the L1CA and the L2C bending angles shows that in some occultations the errors of standard ionospheric correction substantially increase around the strong inversion layers (such as the top of the boundary layer). This error increase is modeled and explained by the horizontal inhomogeneity of the ionosphere.

scholarly journals The Impact of Vertical Resolution in the Assimilation of GPS Radio Occultation Data

2018 ◽  
Vol 33 (4) ◽  
pp. 1033-1044 ◽  
Author(s):  
Ji-Hyun Ha ◽  
Jeon-Ho Kang ◽  
Suk-Jin Choi
Keyword(s):  
Geopotential Height ◽  
Radio Occultation ◽  
Three Dimensional ◽  
Vertical Resolution ◽  
Bending Angle ◽  
Gps Radio Occultation ◽  
Angle Data ◽  
Upper Level ◽  
Occultation Data ◽  
The Impact

Abstract The sensitivity of GPS radio occultation (GPSRO) bending angle assimilation to vertical resolution was studied within a global three-dimensional variational data assimilation (3DVAR) system. The sensitivity experiments were performed using different vertical resolutions of GPSRO data at 2 km, 1 km, 500 m, and 200 m. The assimilation of the higher vertical resolution GPSRO data showed better consistency in the analysis–forecast cycle in terms of the differences between GPSRO bending angle data and 6-h forecasts (O-F). This resulted in an improved analysis of the temperature, geopotential height, and wind in the mid-/upper-level troposphere by the hydrostatic response and the related model dynamics. It should be noted that the highest vertical resolution of the GPSRO data (200 m in this study) improved the forecasting skill level in terms of the root-mean-square error (against the European Centre for Medium-Range Weather Forecasts analysis) and the anomaly correlation of the geopotential height forecasting at 500 and 200 hPa in both the Northern and Southern Hemispheres. The benefits of assimilating higher vertical resolution GPSRO data were more pronounced in the upper-level troposphere, which was in agreement with previous studies using real GPSRO observations.

Combined forecast impact of GRACE-A and CHAMP GPS radio occultation bending angle profiles

2007 ◽  
Vol 8 (2) ◽  
pp. 43-50 ◽  
Author(s):  
S. B. Healy ◽  
J. Wickert ◽  
G. Michalak ◽  
T. Schmidt ◽  
G. Beyerle
Keyword(s):  
Radio Occultation ◽  
Bending Angle ◽  
Gps Radio Occultation

scholarly journals Empirical analysis and modeling of errors of atmospheric profiles from GPS radio occultation

2011 ◽  
Vol 4 (3) ◽  
pp. 2599-2633 ◽  
Author(s):  
B. Scherllin-Pirscher ◽  
A. K. Steiner ◽  
G. Kirchengast ◽  
Y.-H. Kuo ◽  
U. Foelsche
Keyword(s):  
Geopotential Height ◽  
Radio Occultation ◽  
Error Model ◽  
Atmospheric Parameters ◽  
Observational Error ◽  
Bending Angle ◽  
Gps Radio Occultation ◽  
Error Characteristics ◽  
Precise Knowledge ◽  
Observational Errors

Abstract. The utilization of radio occultation (RO) data in atmospheric studies requires precise knowledge of error characteristics. We present results of an empirical error analysis of GPS radio occultation (RO) bending angle, refractivity, dry pressure, dry geopotential height, and dry temperature. We find very good agreement between data characteristics of different missions (CHAMP, GRACE-A, and Formosat-3/COSMIC (F3C)). In the global mean, observational errors (standard deviation from "true" profiles at mean tangent point location) agree within 0.3 % in bending angle, 0.1 % in refractivity, and 0.2 K in dry temperature at all altitude levels between 4 km and 35 km. Above ≈20 km, the observational errors show a strong seasonal dependence at high latitudes. Larger errors occur in hemispheric wintertime and are associated mainly with background data used in the retrieval process. The comparison between UCAR and WEGC results (both data centers have independent inversion processing chains) reveals different magnitudes of observational errors in atmospheric parameters, which are attributable to different background fields used. Based on the empirical error estimates, we provide a simple analytical error model for GPS RO atmospheric parameters and account for vertical, latitudinal, and seasonal variations. In the model, which spans the altitude range from 4 km to 35 km, a constant error is adopted around the tropopause region amounting to 0.8 % for bending angle, 0.35 % for refractivity, 0.15 % for dry pressure, 10 m for dry geopotential height, and 0.7 K for dry temperature. Below this region the observational error increases following an inverse height power-law and above it increases exponentially. The observational error model is the same for UCAR and WEGC data but due to somewhat different error characteristics below about 10 km and above about 20 km some parameters have to be adjusted. Overall, the observational error model is easily applicable and adjustable to individual error characteristics.

scholarly journals Radio occultation bending angle anomalies during tropical cyclones

2011 ◽  
Vol 4 (6) ◽  
pp. 1053-1060 ◽  
Author(s):  
R. Biondi ◽  
T. Neubert ◽  
S. Syndergaard ◽  
J. K. Nielsen
Keyword(s):  
Radio Occultation ◽  
Lower Stratosphere ◽  
Time Window ◽  
Deep Convection ◽  
Atomic Clock ◽  
Space Station ◽  
Radiation Balance ◽  
Bending Angle ◽  
Upper Troposphere ◽  
Gps Radio Occultation

Abstract. The tropical deep convection affects the radiation balance of the atmosphere changing the water vapor mixing ratio and the temperature of the upper troposphere lower stratosphere. The aim of this work is to better understand these processes and to investigate if severe storms leave a significant signature in radio occultation profiles in the tropical tropopause layer. Using tropical cyclone best track database and data from different GPS radio occultation missions (COSMIC, GRACE, CHAMP, SACC and GPSMET), we selected 1194 profiles in a time window of 3 h and a space window of 300 km from the eye of the cyclone. We show that the bending angle anomaly of a GPS radio occultation signal is typically larger than the climatology in the upper troposphere and lower stratosphere and that a double tropopause during deep convection can easily be detected using this technique. Comparisons with co-located radiosondes, climatology of tropopause altitudes and GOES analyses are also shown to support the hypothesis that the bending angle anomaly can be used as an indicator of convective towers. The results are discussed in connection to the GPS radio occultation receiver which will be part of the Atomic Clock Ensemble in Space (ACES) payload on the International Space Station.

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