C. Robert Clauer

Autonomous low-power magnetic data collection platform to enable remote high latitude array deployment.

A major driver in the advancement of geophysical sciences is improvement in the quality and resolution of data for use in scientific analysis, discovery, and for assimilation into or validation of empirical and physical models. The need for more and better measurements together with improvements in technical capabilities is driving the ambition to deploy arrays of autonomous geophysical instrument platforms in remote regions. This is particularly true in the southern polar regions where measurements are presently sparse due to the remoteness, lack of infrastructure, and harshness of the environment. The need for the acquisition of continuous long-term data from remote polar locations exists across geophysical disciplines and is a generic infrastructure problem. The infrastructure, however, to support autonomous instrument platforms in polar environments is still in the early stages of development. We report here the development of an autonomous low-power magnetic variation data collection system. Following 2 years of field testing at the south pole station, the system is being reproduced to establish a dense chain of stations on the Antarctic plateau along the 40 degrees magnetic meridian. The system is designed to operate for at least 5 years unattended and to provide data access via satellite communication. The system will store 1 s measurements of the magnetic field variation (<0.2 nT resolution) in three vector components plus a variety of engineering status and environment parameters. We believe that the data collection platform can be utilized by a variety of low-power instruments designed for low-temperature operation. The design, technical characteristics, and operation results are presented here.

Investigation of a rare event where the polar ionospheric reverse convection potential does not saturate during a period of extreme northward IMF solar wind driving

A variety of statistical studies have shown that the ionospheric polar potential produced by solar wind-magnetosphere-ionosphere coupling is linear for weak to moderate solar wind driving but becomes nonlinear during periods of very strong driving. It has been shown that this applies to the two-cell convection potential that develops during southward interplanetary magnetic field (IMF) and also to the reverse convection cells that develop during northward IMF. This has been described as polar potential saturation, and it appears to begin when the driving solar wind electric field becomes greater than 3 mV/m. Utilizing measurements from the Resolute Incoherent Scatter Radar (RISR-N), we examine ionospheric data near local noon within the reverse convection cells that developed during a period of very strong northward interplanetary magnetic field (IMF) on 12 September 2014. During this period we measure the electric field within the throat of the reverse convection cells to be near 150 mV/m at a time when the IMF is nearly 28 nT northward. This is far in excess of the 30–40 mV/m expected for polar potential saturation of the reverse convection cells. In fact, the development of the electric field responds linearly to the IMF Bz component throughout this period of extreme driving. The conditions in the solar wind show the solar wind velocity near 600 km/s, number density near 20 ions/cm3, and the Alfvén velocity about 75 km/s giving an Alfvén Mach number of 8. A search of several years of solar wind data shows that these values occur together 0.035% of the time. These conditions imply a high plasma β in the magnetosheath. We believe that condition of high β along with high mass density and a strong merging electric field in the magnetosheath are the significant parameters that produce the linear driving of the ionospheric electric field during this unusual period of extreme solar wind conditions. A discussion of current theories to account for cross-polar cap potential saturation is given with the conclusion that theories that utilize magnetosheath parameters as they affect the reconnection rate appear to be the most relevant to the cross-polar cap potential saturation solution.

Conjugate observations of electromagnetic ion cyclotron waves associated with traveling convection vortex events

We report on simultaneous observations of electromagnetic ion cyclotron (EMIC) waves associated with traveling convection vortex (TCV) events caused by transient solar wind dynamic pressure (Pd) impulse events. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft located near the magnetopause observed radial fluctuations of the magnetopause, and the GOES spacecraft measured sudden compressions of the magnetosphere in response to sudden increases in Pd. During the transient events, EMIC waves were observed by interhemispheric conjugate ground-based magnetometer arrays as well as the GOES spacecraft. The spectral structures of the waves appear to be well correlated with the fluctuating motion of the magnetopause, showing compression-associated wave generation. In addition, the wave features are remarkably similar in conjugate hemispheres in terms of bandwidth, quasiperiodic wave power modulation, and polarization. Proton precipitation was also observed by the DMSP spacecraft during the wave events, from which the wave source region is estimated to be 72°–74° in magnetic latitude, consistent with the TCV center. The confluence of space-borne and ground instruments including the interhemispheric, high-latitude, fluxgate/induction coil magnetometer array allows us to constrain the EMIC source region while also confirming the relationship between EMIC waves and the TCV current system.

The Role of Solar Wind Density in Cross Polar Cap Potential Saturation Under Northward Interplanetary Magnetic Field: ROLE OF SW DENSITY IN CPCP SATURATION

The role of solar wind density in the cross polar cap potential (CPCP) response under northward interplanetary magnetic field is investigated with observation-based global simulations. A rare event was reported by Clauer et al. (2016) during which the ionospheric electric field EISP does not saturate under extreme interplanetary electric field (IEF) of ∼15 mV/m. While commonly utilized coupling functions based on IEF fail to provide an unambiguous explanation for the linear response, the Lyon-Fedder-Mobarry-Magnetosphere-Ionosphere Coupler/Solver model is used to explore the mechanisms in this study. The model first reproduces the observed linear features of the EISP. The simulated CPCP also responds linearly to IEF variations. A controlled simulation is designed with solar wind density artificially reduced to 10% of the observed value while all other parameters such as the IEF are kept the same. The controlled simulation shows saturation of the EISP as well as the CPCP. Further analysis shows the difference in the magnetosheath plasma β , implying the distinct dominant forces between the two simulations. The Lopez magnetosheath force balance theory is used to explain the CPCP responses under different solar wind densities. This comparison study highlights the role of solar wind density in determining the magnetosphere-ionosphere response to extreme interplanetary drivings. Plain Language Summary The cross polar cap potential is the electrical potential imposed on the Earth by solar wind driver. It measures the electrodynamic coupling between the Earth and the solar wind. Typically, this potential is thought to depend mostly on the electric field in the solar wind and would saturate when the solar wind electric field exceeds certain threshold. Recently, a rare case was found when the potential did not saturate under very large solar wind electric field. We use global magnetosphere-ionosphere model to investigate this event and found the solar wind density plays a critical role in affecting the potential response under the extreme driving conditions.