Clouds of vaporized samarium (Sm) were released during sounding rocket flights from the Reagan Test Site, Kwajalein Atoll in May 2013 as part of the Metal Oxide Space Cloud (MOSC) experiment. A network of ground‐based sensors observed the resulting clouds from five locations in the Republic of the Marshall Islands. Of primary interest was an examination of the extent to which a tailored radio frequency (RF) propagation environment could be generated through artificial ionospheric modification. The MOSC experiment consisted of launches near dusk on two separate evenings each releasing ~6 kg of Sm vapor at altitudes near 170 km and 180 km. Localized plasma clouds were generated through a combination of photoionization and chemi‐ionization (Sm + O → SmO+ + e–) processes producing signatures visible in optical sensors, incoherent scatter radar, and in high‐frequency (HF) diagnostics. Here we present an overview of the experiment payloads, document the flight characteristics, and describe the experimental measurements conducted throughout the 2 week launch window. Multi‐instrument analysis including incoherent scatter observations, HF soundings, RF beacon measurements, and optical data provided the opportunity for a comprehensive characterization of the physical, spectral, and plasma density composition of the artificial plasma clouds as a function of space and time. A series of companion papers submitted along with this experimental overview provide more detail on the individual elements for interested readers.

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Discrete high-density plasma structures in the Earth's ionosphere that convect across the polar cap from the dayside to nightside are known as polar cap patches. This high-latitude phenomenon can interfere and disrupt satellite and high-frequency (HF) communications when the associated sharp electron density gradients are encountered, and therefore, accurate modeling and forecasting of such events would be greatly beneficial. In this study, we have utilized the assimilative Global Positioning System Ionospheric Inversion (GPSII) method to reconstruct the high-latitude ionosphere utilizing data from Global Navigation Satellite System (GNSS) receivers, vertical ionosondes, the Resolute Bay Incoherent Scatter Radar (RISR-N), in situ satellite data, and Super Dual Auroral Radar Network (SuperDARN) radars. The novel method of assimilating RISR-N and SuperDARN ground scatter measurements helps to increase the limited number of observations at high latitudes. The reconstructed polar cap patches are shown to correspond with ground-and spaced-based observations, illustrating the ability of utilizing GPSII to study the complex high-latitude region.