| 1. |
|
|
| 2. |
- Lomidze, Levan, et al.
(författare)
-
Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground-Based Radars and Satellite Radio Occultation Measurements
- 2018
-
Ingår i: Radio Science. - 0048-6604 .- 1944-799X. ; 53:1, s. 15-36
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we calibrate and validate in situ ionospheric electron density (N-e) and temperature (T-e) measured with Langmuir probes (LPs) on the three Swarm satellites orbiting the Earth in circular, nearly polar orbits at similar to 500km altitude. We assess the accuracy and reliability of the LP data (December 2013 to June 2016) by using nearly coincident measurements from low- and middle-latitude incoherent scatter radars (ISRs), low-latitude ionosondes, and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites, covering all latitudes. The comparison results for plasma frequency (f alpha root Ne) for each Swarm satellite are consistent across these three, principally different measurement techniques. It shows that the Swarm LPs systematically underestimate plasma frequency by about 10% (0.5-0.6MHz). The correlation coefficients are high (0.97), indicating accurate relative variation in the Swarm LP densities. The comparison of T-e from high-gain LPs and those from ISRs reveals that all three satellites overestimate it by 300-400K but exhibit high correlations (0.92-0.97) against the validation data. The low-gain LP T-e data show larger overestimation (similar to 700K) and lower correlation (0.86-0.90). The adjustment of the Swarm LP data based on Swarm-ISR comparison results removes the systematic biases in the Swarm data and gives plasma frequencies and high- and low-gain electron temperatures that are precise within about 0.4MHz (8%), 150-230K, and 260-360K, respectively. We demonstrate that the applied correction significantly improves the agreement between (1) the plasma densities from Swarm, and from ionosondes and COSMIC, and (2) the T-e from Swarm LPs and International Reference Ionosphere 2016.
|
|
| 3. |
- Zou, Ying, et al.
(författare)
-
Localized field-aligned currents in the polar cap associated with airglow patches
- 2016
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:10, s. 10172-10189
-
Tidskriftsartikel (refereegranskat)abstract
- Airglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field-aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all-sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1-0.2 mu A/m(-2) and have a distribution of width peaking at similar to 75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn-dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere-ionosphere coupling embedded in large-scale convection.
|
|
