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This study explores the relaxation and sustainability of density irregularities and plasma flows in the Earth's ionosphere. To do this, we use a modified model of drift‐wave turbulence known as the Hasegawa‐Wakatani model. Similar to turbulent processes in laboratory plasmas, we explore a powerful mechanism that can reduce the turbulent plasma transport. This mechanism is associated with the creation of "zonal flows," cutting across the gradients of particle density and magnetic fields. They work effectively to minimize particles' random movement and reduce the turbulence causing this movement. The zonal flows create transport barriers in areas where the density gradient is steepest and where drift waves grow most vigorously. The transport barriers significantly delay the refill of low‐density regions with surrounding plasma. They also lead to changes in the electric potential of the plasma and influence the movement of ions in the direction of the magnetic field. Our research investigates how these zonal flows are generated and how effectively they sustain density irregularities. We also examine the spectral characteristics of turbulence in and around these barriers. Key Points: Density troughs formed in the Earth's ionosphere are likely to develop fast gradient instabilities but typically live longer than expectedWe argue that while driving turbulent plasma transport along the density gradient, the drift‐wave instability also generates macroscopic (zonal) flows across the gradient and magnetic fieldZonal flows efficiently self‐regulate the instability‐transport relation, essentially suppressing both [ABSTRACT FROM AUTHOR]

This paper describes the dynamic characteristics of ionospheric plasma turbulences excited by high‐power high‐frequency radio waves during ionospheric modification experiments at the High‐frequency Active Auroral Research Program heating facility, Gakona, Alaska. The data come from measurements of high‐frequency‐induced stimulated electromagnetic emission (SEE) and anomalous absorption of test radiowaves. In addition to quasi‐continuous pump (QCP) waves that excite the "standard" SEE, short pulses of diagnostic waves at frequencies shifted from the QCP frequency have been injected to generate diagnostic SEE. This experimental setup allowed us to study the spectra and damping rates of the plasma waves related to both diagnostic and QCP waves, as well as the QCP‐related small‐scale magnetic field‐aligned irregularities at different altitudes, ±25 km around the center of the heated volume. The results of numerical simulations of the upper hybrid‐related SEE and diagnostic SEE under a "double‐transformation" scheme with the use of an empirical model of the irregularities' spatial spectrum and its dynamics are in good agreement with the observations. Key Points: Artificial ionospheric turbulence dynamics is studied at the High‐frequency Active Auroral Research Program facilityAltitude size of the region occupied by pump‐induced small‐scale striations and their scales across the geomagnetic field are estimatedDamping rates of pump‐induced Langmuir and upper hybrid waves are determined [ABSTRACT FROM AUTHOR]

Abstract: Subauroral polarization streams (SAPS) often show large, rapid enhancements above their slowly varying component. We present simultaneous observations from ground‐based all‐sky imagers and flows from the Super Dual Auroral Radar Network radars to investigate the relationship between auroral phenomena and flow enhancement. We first identified auroral streamers approaching the equatorward boundary of the auroral oval to examine how often the subauroral flow increased. We also performed the reverse query starting with subauroral flow enhancements and then evaluated the auroral conditions. In the forward study, 98% of the streamers approaching the equatorward boundary were associated with SAPS flow enhancements reaching ~700 m/s and typically hundreds of m/s above background speeds. The reverse study reveals that flow enhancements associated with streamers (60%) and enhanced larger‐scale convection (37%) contribute to SAPS flow enhancements. The strong correlation of auroral streamers with rapid evolution (approximately minutes) of SAPS flows suggests that transient fast earthward plasma sheet flows can often lead to westward SAPS flow enhancements in the subauroral region and that such enhancements are far more common than only during substorms because of the much more frequent occurrences of streamers under various geomagnetic conditions. We also found a strong correlation between flow duration and streamer duration and a weak correlation between SAPS flow velocity and streamer intensity. This result suggests that intense flow bursts in the plasma sheet (which correlate with intense streamers) are associated with intense SAPS ionospheric flows perhaps by enhancing the ring current pressure and localized pressure gradients when they are able to penetrate close enough to Earth. [ABSTRACT FROM AUTHOR]

Active ionospheric experiments using high-power, high-frequency transmitters, "heaters", to study plasma processes in the ionosphere and magnetosphere continue to provide new insights into understanding plasma and geophysical proceses. This review describes the heating facilities, past and present, and discusses scientific results from these facilities and associated space missions. Phenomena that have been observed with these facilities are reviewed along with theoretical explanations that have been proposed or are commonly accepted. Gaps or uncertainties in understanding of heating-initiated phenomena are discussed together with proposed science questions to be addressed in the future. Suggestions for improvements and additions to existing facilities are presented including important satellite missions which are necessary to answer the outstanding questions in this field. [ABSTRACT FROM AUTHOR]

We have numerically investigated the development of strong Langmuir turbulence (SLT) and associated electron acceleration at different angles of incidence of ordinary (O) mode pump waves. For angles of incidence within the Spitze cone, the turbulence initially develops within the first maximum of the Airy pattern near the plasma resonance altitude. After a few milliseconds, the turbulent layer shifts downwards by about 1 km. For injections outside the Spitze region, the turning point of the pump wave is at lower altitudes. Yet, an Airy-like pattern forms here, and the turbulence development is quite similar to that for injections within the Spitze. SLT leads to the acceleration of 10–20 eV electrons that ionize the neutral gas thereby creating artificial ionospheric layers. Our numerical modeling shows that most efficient electron acceleration and ionization occur at angles between the magnetic and geographic zenith, where SLT dominates over weak turbulence. Possible effects of the focusing of the electromagnetic beam on magnetic field-aligned density irregularities and the finite heating beam width at the magnetic zenith are also discussed. The results have relevance to ionospheric heating experiments using ground-based, high-power radio transmitters to heat the overhead plasma, where recent observations of artificial ionization layers have been made. [ABSTRACT FROM PUBLISHER]