Global GNSS-RO Electron Density in the Lower Ionosphere
Lack of instrument sensitivity to low electron density (<i>N<sub>e</sub></i>) concentration makes it difficult to measure sharp <i>N<sub>e</sub></i> vertical gradients (four orders of magnitude over 30 km) in the <i>D/E</i>-region. A robust...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-03-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/14/7/1577 |
| _version_ | 1797437925578768384 |
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| author | Dong L. Wu Daniel J. Emmons Nimalan Swarnalingam |
| author_facet | Dong L. Wu Daniel J. Emmons Nimalan Swarnalingam |
| author_sort | Dong L. Wu |
| collection | DOAJ |
| description | Lack of instrument sensitivity to low electron density (<i>N<sub>e</sub></i>) concentration makes it difficult to measure sharp <i>N<sub>e</sub></i> vertical gradients (four orders of magnitude over 30 km) in the <i>D/E</i>-region. A robust algorithm is developed to retrieve global <i>D/E</i>-region <i>N<sub>e</sub></i> from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes <i>F</i>-region contributions in the RO excess phase profile by fitting a linear function to the data below the <i>D</i>-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the <i>N<sub>e</sub></i> morphology. While the <i>D/E</i>-region <i>N<sub>e</sub></i> is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude <i>N<sub>e</sub></i> and sporadic <i>E</i> (<i>E<sub>s</sub></i>) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new <i>TEC</i> retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the <i>E</i>- to <i>F</i>-transition in <i>N<sub>e</sub></i> and more accurate <i>TEC</i> retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km. |
| first_indexed | 2024-03-09T11:28:34Z |
| format | Article |
| id | doaj.art-80406c16e0ec4397839016cee542da6f |
| institution | Directory Open Access Journal |
| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-09T11:28:34Z |
| publishDate | 2022-03-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Remote Sensing |
| spelling | doaj.art-80406c16e0ec4397839016cee542da6f2023-11-30T23:55:58ZengMDPI AGRemote Sensing2072-42922022-03-01147157710.3390/rs14071577Global GNSS-RO Electron Density in the Lower IonosphereDong L. Wu0Daniel J. Emmons1Nimalan Swarnalingam2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USAThe Air Force Institute of Technology, Wright-Patterson Air Force Base, Dayton, OH 45433, USANASA Goddard Space Flight Center, Greenbelt, MD 20771, USALack of instrument sensitivity to low electron density (<i>N<sub>e</sub></i>) concentration makes it difficult to measure sharp <i>N<sub>e</sub></i> vertical gradients (four orders of magnitude over 30 km) in the <i>D/E</i>-region. A robust algorithm is developed to retrieve global <i>D/E</i>-region <i>N<sub>e</sub></i> from the high-rate GNSS radio occultation (RO) data, to improve spatiotemporal coverage using recent SmallSat/CubeSat constellations. The new algorithm removes <i>F</i>-region contributions in the RO excess phase profile by fitting a linear function to the data below the <i>D</i>-region. The new GNSS-RO observations reveal many interesting features in the diurnal, seasonal, solar-cycle, and magnetic-field-dependent variations in the <i>N<sub>e</sub></i> morphology. While the <i>D/E</i>-region <i>N<sub>e</sub></i> is a function of solar zenith angle (χ), it exhibits strong latitudinal variations for the same χ with a distribution asymmetric about noon. In addition, large longitudinal variations are observed along the same magnetic field pitch angle. The summer midlatitude <i>N<sub>e</sub></i> and sporadic <i>E</i> (<i>E<sub>s</sub></i>) show a distribution similar to each other. The distribution of auroral electron precipitation correlates better with the pitch angle from the magnetosphere than from one at 100 km. Finally, a new <i>TEC</i> retrieval technique is developed for the high-rate RO data with a top reaching at least 120 km. For better characterization of the <i>E</i>- to <i>F</i>-transition in <i>N<sub>e</sub></i> and more accurate <i>TEC</i> retrievals, it is recommended to have all GNSS-RO acquisition routinely up to 220 km.https://www.mdpi.com/2072-4292/14/7/1577GNSS radio occultation<i>D/E</i>-region ionosphereelectron densitytotal electron contentsporadic-Esatellite constellation |
| spellingShingle | Dong L. Wu Daniel J. Emmons Nimalan Swarnalingam Global GNSS-RO Electron Density in the Lower Ionosphere Remote Sensing GNSS radio occultation <i>D/E</i>-region ionosphere electron density total electron content sporadic-E satellite constellation |
| title | Global GNSS-RO Electron Density in the Lower Ionosphere |
| title_full | Global GNSS-RO Electron Density in the Lower Ionosphere |
| title_fullStr | Global GNSS-RO Electron Density in the Lower Ionosphere |
| title_full_unstemmed | Global GNSS-RO Electron Density in the Lower Ionosphere |
| title_short | Global GNSS-RO Electron Density in the Lower Ionosphere |
| title_sort | global gnss ro electron density in the lower ionosphere |
| topic | GNSS radio occultation <i>D/E</i>-region ionosphere electron density total electron content sporadic-E satellite constellation |
| url | https://www.mdpi.com/2072-4292/14/7/1577 |
| work_keys_str_mv | AT donglwu globalgnssroelectrondensityinthelowerionosphere AT danieljemmons globalgnssroelectrondensityinthelowerionosphere AT nimalanswarnalingam globalgnssroelectrondensityinthelowerionosphere |