Characterization of GPS Scintillations in the Polar Ionosphere
AbstractThe climatology map of the GPS phase scintillation at high latitudes identifies two regions of high scintillation occurrences: around magnetic noon and magnetic midnight. The scintillation occurrence rate is higher around noon, while the scintillation level is strongest around magnetic midnight. Paper 1 focuses on the dayside scintillation region. In order to resolve the role of the cusp auroral processes in the production of irregularities, we put the GPS phase scintillation in the context of the observed auroral morphology. Results show that the occurrence rate of the GPS phase scintillation is highest inside the auroral cusp, regardless of the scintillation strength and the interplanetary magnetic field (IMF). On average, the scintillation occurrence rate in the cusp region is about 5 times as high as in the region immediately poleward of it. The scintillation occurrence rate is higher when the IMF Bz is negative. When partitioning the scintillation data by the IMF By, the distribution of the scintillation occurrence rate around magnetic noon is similar to that of the poleward moving auroral form (PMAF): there is a shift in the occurrence rate towards prenoon (postnoon) when the IMF By is positive (negative). This indicates that the irregularities which give rise to scintillations follow the IMF By controlled east-west motion of the cusp auroral forms and the flow of solar EUV ionized plasma into the polar cap. Furthermore, the scintillation occurrence rate is higher when IMF By is positive which can be explained as follows: during positive IMF By, the cusp is shifted toward the postnoon sector where it may access to the higher density plasma. This suggests that the combination of the auroral activities (e.g., PMAF) and the intake of the high density solar EUV ionized plasma are crucial for the production of scintillations. In Papers 2 and 3, we directly compare the relative GPS phase scintillation levels associated with three phenomena: regions of enhanced plasma irregularities called auroral arcs, polar cap patches, and auroral blobs which frequently occur in the polar ionosphere. We define two types of auroral blobs: blob type 1 (BT-1) which is formed when islands of high-density F region plasma (polar cap patches) enter the nightside auroral oval, and blob type 2 (BT-2) which are generated locally in the auroral oval by intense particle precipitation alone. In a case study (Paper 1) based on observations from Ny-Ålesund on January 13, 2013, we detected several polar cap patches exiting the polar cap into the auroral oval (then termed BT- 1 blobs). The BT-1 blobs were associated with the strongest phase scintillation, followed by patches and BT-2 blobs (produced by pure auroral arcs). In the statistical study (Paper 3), we show that BT-1 blobs are associated with significantly higher scintillation level than the corresponding polar cap patches in general; however, there is no clear relationship between the scintillation level inside the polar cap patch and the resulting BT-1 blob. For BT-2 blobs we find that they are associated with much weaker scintillations than BT-1 blobs. Compared to polar cap patches and BT-2 blobs, the significantly higher scintillation level for BT-1 blobs implies that the auroral dynamics plays an important role in the structuring of BT-1 blobs. Since BT-1 blobs are formed after patches merged into the auroral region, it will be important to enable predictions of patches exiting the polar cap in space weather predictions of GPS scintillations.
List of papers
|Paper 1 - Jin, Y., J. I. Moen, and W. J. Miloch (2015), On the collocation of the cusp aurora and the GPS phase scintillation: A statistical study, J. Geophys. Res. Space Physics, 120, doi:10.1002/2015JA021449. The paper is available in DUO: http://urn.nb.no/URN:NBN:no-55912|
|Paper 2 - Jin, Y., J. I. Moen, and W. J. Miloch (2014), GPS scintillation effects associated with polar cap patches and substorm auroral activity: Direct comparison, J. Space Weather Space Clim., 4, A23, doi:10.1051/swsc/2014019. The paper is available in DUO: http://urn.nb.no/URN:NBN:no-55911|
|Paper 3 - Jin, Y., J. I. Moen, W. J. Miloch, L. B. N. Clausen, and K. Oksavik (2016), Statistical study of the GNSS phase scintillation associated with two types of auroral blobs, J. Geophys. Res. Space Physics, 121, doi:10.1002/2016JA022613. The paper is available in DUO: http://urn.nb.no/URN:NBN:no-55914|