Different Evolution Patterns of Subauroral Polarization Streams (SAPS) During Intense Storms and Quiet Time Substorms

Abstract

In this letter, we present multisatellite observations of the evolution of subauroral polarization streams (SAPS) during intense storms (ISs) and quiet time substorms (QSs). SAPS occurred during 37 ISs and 30 QSs were analyzed. Generally, SAPS occur after the southward turning of the interplanetary magnetic field (IMF) with time lags of 0-1.5 h for ISs and 0-2.5 h for QSs. SAPS usually occurred 0-3 h after the beginning of storm main phases and 0-2 h after the substorm expansion onsets. The lifetimes of SAPS are generally longer than the durations of southward IMF and storm main phases. During QSs, the lifetimes of SAPS are shorter than the duration of the ISs. Superposed epoch analysis shows different evolution patterns of SAPS during ISs and QSs. The results of this study provide both physical insight and constrains to modeling the magnetosphere-ionosphere-thermosphere coupling.

Evolution of the Subauroral Polarization Stream Oscillations During the Severe Geomagnetic Storm on 20 November 2003

“…During their lifetime, the evolution of the SAPS channels clearly exhibited distinct four stages. The first two stages were consistent with those in previous studies (He et al, , ). An interesting SAPSO phenomenon occurred in the third stage when the IMF B Y component had a large magnitude and turned rapidly from positive to negative.…”

“…The SAPS channels were observed by DMSP satellites during the period from ~06:30 UT on 20 November 2003 to ~01:30 UT on 21 November 2003 as shown in Figure 2. A SAPS channel was determined when the westward ion drift velocity (abnormal subauroral ion drift was not observed during this storm) was larger than 250 m/s and the location of the drifts was equatorward of the auroral precipitating electrons in the dusk to midnight sector (e.g., Foster & Burke, ; He et al, ). The westward ion drift peaks of the SAPS channels were marked by the downward arrows with the scale shown at the lower left corner of each panel in Figure 2.…”

“…The perturbations in the latitudinal profiles of the westward drift velocities in Figure 2h (e.g., 16:37:48N13) were similar to the electromagnetic wave structures reported in Mishin et al (). Since there were no SAPS observations between 17:20 and 18:00 UT at MLTs later than 19 hr, we could just infer that the SAPS channels should keep moving toward lower latitudes according to the statistical relationship between the latitude of SAPS and the Dst index (He et al, ; Huang & Foster, ). The observations between 17:50 and 18:30 UT in Figure 2i demonstrated this trend, and the SAPS channels moved to MLATs of less than 40° (e.g., 17:52:45S13 and 18:03:26S14).…”

A New Empirical Model of the Subauroral Polarization Stream

“…A majority of previous studies find that SAPS exhibit a strong dependence on MLT (Erickson et al, ;Foster & Vo, ; He et al, , ). Recent results presented in He et al () suggest that SAPS occurrence maximized around 18 MLT during severe geomagnetic storms and near 21 MLT during quiet time substorms.…”

Large‐Scale Structure of Subauroral Polarization Streams During the Main Phase of a Severe Geomagnetic Storm

“…It is noted here that Figure is just a schematic demonstration of the global‐scale evolution of the SAPS channel at a specific temporal resolution during the MP of a severe storm. Different evolution patterns of SAPS might appear in different storms/substorms (e.g., He et al, ), and this requires a detailed investigation in the future. Besides, instabilities in the magnetosphere‐ionosphere‐thermosphere (M‐I‐T) coupling lead to large localized changes in the position and intensity of SAPS on the order of minutes (e.g., Foster et al, ).…”