During this event, both the storm and substorm subsided.įigure 1B shows auroral keograms at the dawn (01–07 MLT) and dusk (18–22 MLT) sectors from 16:30 to 2000 UT (the auroral region from ~08 to 16 MLT was outside of the field of view of the UVI). A small geomagnetic storm (minimal Dst ~ − 40 nT) commenced at ~12:00 UT, accompanied by a substorm ( AE ~1500 nT). The overall geomagnetic activity associated with this event was moderate ( Kp ~ 3). This northward turning was associated with a field rotation, possibly a rotational discontinuity, because the total magnetic field strength did not change significantly (see Figure 1Ah). We are interested in the northward turning at ~17:08 UT. The z component (red) of the interplanetary magnetic field (IMF) turned northward from ~ −7 nT to 7 nT at 1600 UT and then fluctuated between negative and positive thereafter, with a period of ~ 1 hr. It then increased (up to ~80 km/s) and became more variable. The y component of the flow speed was near zero from 17:07 to 17:30 UT. The x component of the solar wind velocity was slightly faster than usual (~550 km/s) and increasing. Both the solar wind density and dynamic pressure were small and relatively stable. The y-axis is the magnetic latitudes.įigure 1A shows solar wind plasma and magnetic field observations convected to the subsolar bow shock from NASA GSFC's OMNIWeb for the interval from 15:00 to 21:00 UT interval 6 January 2000. (B) Auroral keograms derived with the Polar UVI image data for a number of hourly sectors from 22 (top panel) to 01 MLT (bottom panel). ![]() ![]() (A) From top to bottom, the panels show: (a) solar wind density (N p), (b) the x- and (c) y-component of the solar wind velocity ( V x and V y), (d) dynamic pressure ( P d), (e) three components of magnetic field ( B x, B y, B z), (f) IMF latitude and longitude, (g) IMF clock angle ( θ cl = sin(B y) cos -1(B z/ 1/2) and defined for -180° < ( θ cl ≤ 180°) and cone angle (( θ cn = tan -1, blue dots), (h) and the total magnetic field (| B|).
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