Evaluation of the IRI-2016 and NeQuick electron content specification by COSMIC GPS radio occultation, ground-based GPS and Jason-2 joint altimeter/GPS observations

Abstract. GPS radio occultation can estimate ionospheric electron density and total electron content (TEC) with high spatial resolution, e.g., China's recent Fengyun-3C GPS radio occultation. However, high-order ionospheric delays are normally ignored. In this paper, the high-order ionospheric effects on electron density estimation from the Fengyun-3C GPS radio occultation data are estimated and investigated using the NeQuick2 ionosphere model and the IGRF12 (International Geomagnetic Reference Field, 12th generation) geomagnetic model. Results show that the high-order ionospheric delays have large effects on electron density estimation with up to 800 el cm−3, which should be corrected in high-precision ionospheric density estimation and applications. The second-order ionospheric effects are more significant, particularly at 250–300 km, while third-order ionospheric effects are much smaller. Furthermore, the high-order ionospheric effects are related to the location, the local time, the radio occultation azimuth and the solar activity. The large high-order ionospheric effects are found in the low-latitude area and in the daytime as well as during strong solar activities. The second-order ionospheric effects have a maximum positive value when the radio occultation azimuth is around 0–20°, and a maximum negative value when the radio occultation azimuth is around −180 to −160°. Moreover, the geomagnetic storm also affects the high-order ionospheric delay, which should be carefully corrected.

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Optimum prediction of atmospheric temperature using GPS radio occultation measurements

Geodesy and Cartography ◽

10.22389/0016-7126-2017-919-1-48-51 ◽

2017 ◽

Vol 919 (1) ◽

pp. 48-51

Author(s):

N.H. Javadov ◽

R.A. Eminov ◽

N.Ya. Ismailov

Keyword(s):

Radio Occultation ◽

General Procedure ◽

Atmospheric Temperature ◽

Mean Value ◽

Optimization Criterion ◽

Temperature Measurements ◽

Gps Radio Occultation ◽

Applied Optimization ◽

Quadratic Deviation ◽

The Mean

The matters of optimum forecasting atmospheric temperature using GPS radio occultation measurements are considered. The analysis of the available data regarding to the comparison of temperature measurements using radio occultation method and radiosondes was made. As a result it was concluded that the mean value of those results’ difference and also the mean quadratic deviation of these difference increases in common by increase of the forecasting time. In order to prevent surplus loading of telemetry channels and broadcasting inaccurate forecast values via them the optimization of general procedure of radio occultation temperature measurements are carried out using fine functions method. For optimization the concurrent parameters, changing on antiphase order are determined. It is found out that utilization of fine function method taking into account the applied optimization criterion and some limitation conditions make it possible to optimize the whole procedure of forecasting atmospheric temperature using the GPS radio occultation measurements.

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

Remote Sensing ◽

10.3390/rs13010001 ◽

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.

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Comparison of seasonal and longitudinal variation of daytime MSTID activity using GPS observation and GAIA simulations

Earth Planets and Space ◽

10.1186/s40623-021-01369-5 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Mani Sivakandan ◽

Yuichi Otsuka ◽

Priyanka Ghosh ◽

Hiroyuki Shinagawa ◽

Atsuki Shinbori ◽

...

Keyword(s):

Standard Deviation ◽

Meridional Wind ◽

Lower Atmosphere ◽

Electron Content ◽

Longitudinal Variation ◽

Total Electron ◽

Winter Peak ◽

Density Perturbations ◽

Two Peaks ◽

Gps Observations

AbstractThe total electron content (TEC) data derived from the GAIA (Ground-to-topside model of Atmosphere Ionosphere for Aeronomy) is used to study the seasonal and longitudinal variation of occurrence of medium-scale traveling ionospheric disturbances (MSTIDs) during daytime (09:00–15:00 LT) for the year 2011 at eight locations in northern and southern hemispheres, and the results are compared with ground-based Global Positioning System (GPS)-TEC. To derive TEC variations caused by MSTIDs from the GAIA (GPS) data, we obtained detrended TEC by subtracting 2-h (1-h) running average from the TEC, and calculated standard deviation of the detrended TEC in 2 h (1 h). MSTID activity was defined as a ratio of the standard deviation to the averaged TEC. Both GAIA simulation and GPS observations data show that daytime MSTID activities in the northern and southern hemisphere (NH and SH) are higher in winter than in other seasons. From the GAIA simulation, the amplitude of the meridional wind variations, which could be representative of gravity waves (GWs), shows two peaks in winter and summer. The winter peak in the amplitude of the meridional wind variations coincides with the winter peak of the daytime MSTIDs, indicating that the high GW activity is responsible for the high MSTID activity. On the other hand, the MSTID activity does not increase in summer. This is because the GWs in the thermosphere propagate poleward in summer, and equatorward in winter, and the equatorward-propagating GWs cause large plasma density perturbations compared to the poleward-propagating GWs. Longitudinal variation of daytime MSTID activity in winter is seen in both hemispheres. The MSTID activity during winter in the NH is higher over Japan than USA, and the MSTID activity during winter in the SH is the highest in South America. In a nutshell, GAIA can successfully reproduce the seasonal and longitudinal variation of the daytime MSTIDs. This study confirms that GWs cause the daytime MSTIDs in GAIA and amplitude and propagation direction of the GWs control the noted seasonal variation. GW activities in the middle and lower atmosphere cause the longitudinal variation.

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Measurements of the upper troposphere and lower stratosphere during tropical cyclones using the GPS radio occultation technique

Advances in Space Research ◽

10.1016/j.asr.2010.05.031 ◽

2011 ◽

Vol 47 (2) ◽

pp. 348-355 ◽

Cited By ~ 7

Author(s):

Riccardo Biondi ◽

Torsten Neubert ◽

Stig Syndergaard ◽

Johannes Nielsen

Keyword(s):

Tropical Cyclones ◽

Radio Occultation ◽

Lower Stratosphere ◽

Upper Troposphere ◽

Gps Radio Occultation

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Parallelization Strategies for the GPS Radio Occultation Data Assimilation with a Nonlocal Operator in the Weather Research and Forecasting Model

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-13-00195.1 ◽

2014 ◽

Vol 31 (9) ◽

pp. 2008-2014 ◽

Cited By ~ 2

Author(s):

Xin Zhang ◽

Ying-Hwa Kuo ◽

Shu-Ya Chen ◽

Xiang-Yu Huang ◽

Ling-Feng Hsiao

Keyword(s):

Data Assimilation ◽

Radio Occultation ◽

Weather Prediction ◽

Weather Research And Forecasting ◽

Forecasting Model ◽

Observation Operator ◽

Gps Radio Occultation ◽

Phase Observation ◽

Excess Phase ◽

Weather Research

Abstract The nonlocal excess phase observation operator for assimilating the global positioning system (GPS) radio occultation (RO) sounding data has been proven by some research papers to produce significantly better analyses for numerical weather prediction (NWP) compared to the local refractivity observation operator. However, the high computational cost and the difficulties in parallelization associated with the nonlocal GPS RO operator deter its application in research and operational NWP practices. In this article, two strategies are designed and implemented in the data assimilation system for the Weather Research and Forecasting Model to demonstrate the capability of parallel assimilation of GPS RO profiles with the nonlocal excess phase observation operator. In particular, to solve the parallel load imbalance problem due to the uneven geographic distribution of the GPS RO observations, round-robin scheduling is adopted to distribute GPS RO observations among the processing cores to balance the workload. The wall clock time required to complete a five-iteration minimization on a demonstration Antarctic case with 106 GPS RO observations is reduced from more than 3.5 h with a single processing core to 2.5 min with 106 processing cores. These strategies present the possibility of application of the nonlocal GPS RO excess phase observation operator in operational data assimilation systems with a cutoff time limit.

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Impact of GPS Radio Occultation Refractivity Soundings on a Simulation of Typhoon Bilis (2006) upon Landfall

Terrestrial Atmospheric and Oceanic Sciences ◽

10.3319/tao.2008.01.21.03(f3c) ◽

2009 ◽

Vol 20 (1) ◽

pp. 115 ◽

Cited By ~ 7

Author(s):

Mien-Tze Kueh ◽

Ching-Yuang Huang ◽

Shu-Ya Chen ◽

Shu-Hua Chen ◽

Chien-Ju Wang

Keyword(s):

Radio Occultation ◽

Gps Radio Occultation

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GPS radio occultation with TerraSAR-X and TanDEM-X: sensitivity of lower troposphere sounding to the Open-Loop Doppler model

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-7-12719-2014 ◽

2014 ◽

Vol 7 (12) ◽

pp. 12719-12733 ◽

Cited By ~ 1

Author(s):

F. Zus ◽

G. Beyerle ◽

S. Heise ◽

T. Schmidt ◽

J. Wickert

Keyword(s):

Radio Occultation ◽

Weather Prediction ◽

Lower Troposphere ◽

Systematic Difference ◽

Open Loop ◽

Negative Bias ◽

Upper Troposphere ◽

Gps Radio Occultation ◽

Global Positioning ◽

Data Source

Abstract. The Global Positioning System (GPS) radio occultation (RO) technique provides valuable input for numerical weather prediction and is considered as a data source for climate related research. Numerous studies outline the high precision and accuracy of RO atmospheric soundings in the upper troposphere and lower stratosphere. In this altitude region (8–25 km) RO atmospheric soundings are considered to be free of any systematic error. In the tropical (30° S–30° N) Lower (<8 km) Troposphere (LT), this is not the case; systematic differences with respect to independent data sources exist and are still not completely understood. To date only little attention has been paid to the Open Loop (OL) Doppler model. Here we report on a RO experiment carried out on-board of the twin satellite configuration TerraSAR-X and TanDEM-X which possibly explains to some extent biases in the tropical LT. In two sessions we altered the OL Doppler model aboard TanDEM-X by not more than ±5 Hz with respect to TerraSAR-X and compare collocated atmospheric refractivity profiles. We find a systematic difference in the retrieved refractivity. The bias mainly stems from the tropical LT; there the bias reaches up to ±1%. Hence, we conclude that the negative bias (several Hz) of the OL Doppler model aboard TerraSAR-X introduces a negative bias (in addition to the negative bias which is primarily caused by critical refraction) in our retrieved refractivity in the tropical LT.

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