Transient convection in the Earth's magnetosphere and the generation of Pi2 pulsations

We present the results of studies exploring the generation of Pi2 pulsations by transient magnetotail flow bursts. After a brief introduction, we present in situ and ground observations from seven events. The relative timing of substorm onset phenomena is an important constraint on theories of substorm onset, and we show that high-speed ion flow begins 1–3 min prior to the detection of nightside Pi2 onset, auroral arc brightening and the formation of the substorm current wedge. Flank and dayside Pi2 are delayed an additional ∼30 s. We find that waveforms of low-latitude Pi2 match the variations in flow velocity measured in the middle magnetotail with a 1–3 minute delay. This correlation had not been previously reported and identifies the intrinsic periodicity in flow bursts as the source of low-latitude Pi2. We also find a precursor in the high-latitude, nightside ionosphere prior to auroral are brightening and Pi2 onset. We relate this precursor to the earthward propagation of magnetotail flow bursts. Pi2 generation is related to the types of impulses generated when a flow reaches the transition region between stretched tail and dipolar field lines. The field-aligned, Alfvénic component partially reflects at the ionosphere and leads to the generation of what we refer to as transient response (TR) Pi2. The periods of these Pi2 is intrinsic to the local flux tubes and is unrelated to the periodicity of flow enhancements. Transient currents caused by flow deceleration are also generated and we term the pulsations that result inertial current (IC) Pi2. An impulsive, cross-field, compressional wave is also produced by the braking of the flow. How this signal generates low-latitude Pi2 was unknown prior to this dissertation. We offer compelling evidence that the impulsive signal travels sunward and perturbs field lines launching Alfvén waves towards the ionosphere. The Pi2 perturbations observed on the ground are directly-driven, and the waveforms of these waves match the flow variations. Finally, we examine the relative timing of Pi2 pulsations and auroral are brightening, critique previous work on this topic, and offer suggestions for quantifying each onset.