Multi-Radar Observations of an Isolated Substorm Development in the Early Evening to Midnight Sector
USPENSKY, M. (1,5), P. EGLITIS (2,1), N. PARTAMIES (1), G. STARKOV (3), A.FABIROVSKY (4), H. OPGENOORTH (2,1), T. PULKKINEN (1), R. PELLINEN (1)
(1) Finnish Meteorological Institute, Finland
(2) Institute of Space Physics, Sweden
(3) Polar Geophysical Institute, Russia
(4) Murmansk State Technical University, Russia
(5) On leave from Murmansk State Technical University, Russia
We continue to study a case when the Finland CUTLASS radar in a prolonged time monitored so-called SEEL echoes (SEEL: Subvisual Equatorward Edge of the diffuse Luminosity belt) [1] and the low-latitude edge of the quit-time auroral oval. In the framework of present study we pay attention to the initiation and details of an isolated double auroral substorm including the observed luminosity-echoes relationship. In our analysis we use data from the Finland and Iceland CUTLASS radars as well as from the Iceland West SuperDARN radar covering more than 5 hours of local time. The UHF EISCAT radar was run with antenna pointing along B in the area of the Finland radar observations. Due to the quiet geophysical background we can see a radar reaction on the WIND IMF Bz turn to negative values at about of 1557 UT. The effect is seen in the polar cap F-layer auroral echoes and also in low-latitude E-layer echoes by the two Iceland radars slightly after 1600 UT. The echoes move equatorward with velocities close to the auroral oval diurnal movement. A rise of the Finland radar F-layer echoes at 18 UT looks also like as a consequence of a growth of the solar wind particle density and dynamic pressure, which start at ~1753 UT during a positive IMF Bz. The growth phase initiation can be seen in the whole HF radar data at 1845-1850 UT as a start of the F-layer echo increased equatorward motion after the new gradual negative WIND IMF Bz turn at 1834-1842 UT. This is about 20-25 min earlier than the other ground-based instruments detect the growth phase development. Around midnight the F-layer blob-like core of the growth phase initiation located in a vicinity of the poleward arc inside of the quiet-time auroral oval. In contrast, earlier in the evening the F-layer growth phase core originated and traveled into the oval from increased polar cap distances. During the breakup and recovery phase the E-layer echoes cover an area, where could be a region of weak or sub-visual diffuse auroral luminosity. No echoes are detected in the increased diffuse luminosity that is probably due to the ray’s overrefraction. A-few-minute enhancement of the electric field up to more than 100 mV/m in the EISCAT data was not supported by the HF-backscatter. It occurred in an area, which was favorable for seeing echoes from a media with decreased ionisation. However the echoes were seen there before and after the time.
1. Uspensky, M., P. Eglitis, H. Opgenoorth, G. Starkov, T. Pulkkinen, R. Pellinen, Magnetospheric and solar wind signatures in HF radar data, Proceedings of the SuperDARN Annual meeting, Reykjavik, 1999, 57.1-57.4.
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