Mikko T. Syrjasuo

Plasma sheet ion injections into the auroral bulge: Correlative study of spacecraft and ground observations

Multiple and sporadic time-of-flight velocity dispersed ion structures (TDIS) are systematically observed above the ionosphere at ∼3 Re altitude by Interball/Auroral spacecraft near the poleward edge of the auroral bulge. These events represent direct snapshots of the impulsive ion acceleration process in the equatorial plasma sheet which allow us to study the details of the connection between ionospheric and plasma sheet manifestations of the magnetospheric substorm. Two events are analyzed during which the spacecraft footpoints passed over the Scandinavian ground network. We found that the TDIS correlate with the intensifications of westward current and auroral activations at the poleward edge of the bulge, which confirms the association of these dispersed ion beams with the temporal evolution of impulsive reconnection in the tail. Furthermore, we present direct evidence of an active neutral line in the magnetotail during one of the events using plasma sheet measurements made concurrently by the Interball/Tail and Geotail spacecraft. The 2–3 min repetition period of these ∼1 min long activations indicates a fundamental time constant of the substorm instability. On the other hand, the estimated injection distances of the energy-dispersed ions were inferred to be smaller than the estimated position of the reconnection region in the tail. We also found that the TDIS ion beams are released within the closed plasma flux tubes deep inside the plasma sheet, and yet they are synchronized with auroral activations at the poleward boundary. These facts imply that the ion beams are formed in a spatially extended region of the plasma sheet rather than in the close vicinity of the neutral line. We argue that braking of the reconnection-induced fast flow bursts when they interact with the closed plasma flux tubes and the earthward propagating fast wave electric field generated in the braking region may be important in forming the observed multiple, sporadic, energy-dispersed ion beams.

Low-cost multi-band ground-based imaging of the aurora

Modern auroral research uses a variety of optical instruments ranging from photometers to spectral imagers. We report our results in developing an inexpensive auroral imager, which captures true-colour images using four wide-band channels. While not replacing dedicated highly sensitive cameras with filter wheels and narrow bandpass filters, the advantages of capturing the colour should not be underestimated. The colour not only provides more information about the physical processes in the ionosphere but also enhances both manual and automated image processing due to the discriminating power of colour information. We have operated our auroral imager RAINBOW in Athabasca, Alberta, Canada for over a year. RAINBOW can acquire images every ten seconds and operate even in moonlit conditions. A clever design using inexpensive optical components provides a field-of-view of approximately 150 degrees, and an external shutter provides protection from direct sunlight. We discuss the issues related to imager hardware and colour calibration. Future applications are also highlighted.

Using attribute trees to analyse auroral appearance over Canada

Modern space research uses both satellite-born and ground-based instruments to measure the near-Earth space environment. Studying the auroral display provides information of the electric currents in the ionosphere, which is why automated imaging stations capture millions of auroral all-sky images every year. However, due to the nature of the aurora, these images are difficult to analyse automatically: photon-limited images are noisy, and objects are irregular and difficult to identify. We used hierarchical attribute trees in a large scale experiment with over 350,000 auroral all-sky images. Tree-to-tree distances were utilised in classifying images and in locating similar images in content-based image retrieval fashion.