Direct observations of blob deformation during a substorm

T Ishida,K Hosokawa,A Kadokura,Y Otsuka,Y Ogawa

doi:10.5194/angeo-33-525-2015

Abstract

Abstract. Ionospheric blobs are localized plasma density enhancements, which are mainly produced by the transportation process of plasma. To understand the deformation process of a blob, observations of plasma parameters with good spatial–temporal resolution are desirable. Thus, we conducted the European Incoherent Scatter radar observations with high-speed meridional scans (60–80 s) during October and December 2013, and observed the temporal evolution of a blob during a substorm on 4 December 2013. This paper is the first report of direct observations of blob deformation during a substorm. The blob deformation arose from an enhanced plasma flow shear during the substorm expansion phase, and then the blob split into two smaller-scale blobs, whose scale sizes were more than ~100 km in latitude. Our analysis indicates that the Kelvin–Helmholtz instability and dissociative recombination could have deformed the blob structure.

Highlights

Localized plasma density enhancements are often produced in the high-latitude ionosphere by the transportation process of plasma or particle precipitations
The TEC maps indicate that the European Incoherent Scatter (EISCAT) radar observed the plasma structuring in the pre-midnight to dusk subauroral region, and the structuring was shown in the trough region
If EISCAT observed the enhanced plasma flow shear accompanied by the substorm expansion phase, the blob deformation might have been caused by the enhanced flow shear through the Kelvin–Helmholtz instability (KHI)

Summary

Introduction

Localized plasma density enhancements are often produced in the high-latitude ionosphere by the transportation process of plasma or particle precipitations. Among such plasma density enhancements, structures enhanced by a factor of 2– 10 above the background density, and with horizontal dimensions ranging from ∼ 100 to 1000 km, are generally called patches in the polar cap, or blobs outside of the polar cap (e.g., Tsunoda, 1988; Crowley et al, 2000). The blobs are generally categorized into the following three types: (1) boundary blobs, (2) subauroral blobs, and (3) auroral blobs. Auroral blobs are observed in the auroral oval, and they appear to be localized in longitude when compared with boundary and subauroral blobs. New techniques that can follow variations of plasma parameters (e.g., density, velocity, and temperature) in detail are highly desirable

Results

Discussion

Conclusion