The Dayside Open/Closed Field line Boundary -Ground-based optical determination and examination

Abstract

The Open/Closed eld line Boundary (OCB) is the most important boundary in the magnetospheric system. On the dayside, the equatorward edge of the 6300 Å[OI] cusp aurora can be used as a proxy for the OCB. This work, which is a dissertation for the degree of philosophiæ Doctor consists of three scienti c papers focusing on the latitude of the optical cusp OCB and one paper focusing on polar cap patch generation mechanisms in the vicinity of the OCB. In Paper I we use modeling to demonstrate the variability of the cusp aurora with respect to vertical volume emission rate pro les and horizontal modulation owing to neutral wind. A meridian scanning photometer (MSP) simulator has been developed in order to study the manifestation of the cusp aurora in the MSP data from Svalbard. A method for obtaining the OCB location and nding the correct mapping altitude in order to transform the OCB location from MSP scan angle to magnetic latitude is found by simulating the horizontal movement of a reference cusp aurora. The reference cusp aurora, which is based on expected ionospheric and atmospheric conditions and electron precipitation characteristics, is de ned from the modeling results. Uncertainties in the scan angle to magnetic latitude transformation are found by simulating a wide range of realistic cusp auroras deviating from the reference cusp aurora. In Paper II the method of Paper I for finding the OCB is tested on real MSP data and compared with the OCB as obtained by satellite energetic particle measurements with very successful results. In Paper III the method of Paper I is used on 15 years of MSP data from Svalbard in order to study the statistical behavior of the cusp OCB. A possible relationship between the OCB latitude in the cusp and the solar cycle is revealed, and a possible expansion is brie y discussed. By comparing the OCB latitude with solar wind parameters, solar wind-magnetosphere coupling functions and geomagnetic indices, good correlations are found, which are in concurrence with previous satellite based, statistical studies. We nd a relationship between the OCB latitude and the ring current density (SYM/H), demonstrating great complexity in the physics behind the OCB location. We argue that the balance between reconnection dynamics on the dayside and nightside as well as the history or integral of previous events in the magnetospheric system are important factors for governing the cusp OCB latitude. Paper IV gives an overview of the solar wind and ionospheric conditions as measured during the Investigation of Cusp Irregularities 2 sounding rocket campaign. The rocket was launched through a newly produced polar cap patch. Based on the measurements performed in-situ by the rocket instrumentation and with groundbased optics and radars, a new creation mechanism, which partly involves ionization by both particle precipitation and solar irradiation and upwelling from sub F-layer altitudes, is suggested.