Abstract
Abstract. We investigate a series of six TCRs (traveling compression regions), appearing in the course of a small substorm on 19 September 2001. Except for two of these TCRs, all Cluster spacecraft were located in the lobe and detected the typical signatures of TCRs, i.e., compressions in |B| and bipolar Bz variations. We use these perturbations in Bz for calculations on the magnetic energy inside the TCR and compare the amount of magnetic field energy with the kinetic energy inside the underlying plasma bulge. According to results obtained from theory, the amount of magnetic energy inside TCRs is about two times higher than the kinetic plasma energy inside the accompanied plasma bulge. We verify this theoretical result by first investigations of the magnetic field energy inside TCRs. The calculations lead to a magnetic energy in the order of 1010 Joule per RE for each of the TCRs.
Highlights
Within the Near-Earth Neutral Line (NENL) model of substorms (Baker et al, 1996), substorm-associated magnetotail reconnection evolves and leads to several transient and localized mesoscale phenomena with typical temporal scales of several minutes and spatial scales of a few Earth radii (Sharma et al, 2008)
Since the disturbance in Bz enters this equation as boundary condition, we can determine the amount of magnetic energy inside the compression region from Eqs. (4) and (5), as long as the spacecraft is sufficiently close to the outflow region in z-direction
We used a series of TCRs during a substorm on 19 September 2001 to estimate the kinetic energy inside the plasma flow regions and the magnetic field energy inside the compression regions above the flow
Summary
Within the Near-Earth Neutral Line (NENL) model of substorms (Baker et al, 1996), substorm-associated magnetotail reconnection evolves and leads to several transient and localized mesoscale phenomena with typical temporal scales of several minutes and spatial scales of a few Earth radii (Sharma et al, 2008) One of these phenomena are traveling compression regions (TCRs, Slavin et al, 1984). It was suggested that TCRs are the lobe signatures of plasmoids/flux tubes, which locally increase the plasma sheet thickness and compress the surrounding lobe regions, i.e., the lobe’s magnetic field These plasmoids were described as large magnetic islands, resulting from magnetotail reconnection, and travel rapidly down the tail during substorms (e.g., Hones Jr. et al, 1984). Slavin et al (2003c) proposed to distinguish between mainly earthward propagating brief TCRs in the near tail and tailward propagating long lasting TCRs by different types of underlying flux ropes, i.e., “BBF-type” and “plasmoid-type” flux ropes, respectively
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