[1] In this paper, we describe an approach for computing vector electric fields in the F region and neutral winds in the E region from incoherent scatter radar (ISR) measurements, applicable especially for Advanced Modular Incoherent Scatter Radar (AMISR) systems, namely, the Poker Flat Incoherent Scatter Radar (PFISR). PFISR is a 128-panel (upgraded from 96 panels in September 2007) AMISR system installed at the Poker Flat Research Range near Fairbanks, Alaska. The pulse-to-pulse steering capabilities of AMISR support the measurement of line-of-sight velocities in multiple look directions essentially simultaneously. This capability in turn allows electric fields and neutral winds to be resolved with minimal assumptions regarding time stationarity of the medium. The multibeamforming capability also allows additional flexibility in the estimation of those parameters, for which experiment planning can become very important. The approach described herein is ideally suited for such planning, is appropriate for the overdetermined problem characteristic of AMISR measurements, and allows in a simple way for the inclusion of appropriate a priori information such as the assumption of negligible parallel electric fields and negligible vertical neutral winds. We present some case studies from the PFISR that demonstrate some of the new capabilities.Citation: Heinselman, C. J., and M. J. Nicolls (2008), A Bayesian approach to electric field and E-region neutral wind estimation with the Poker Flat Advanced Modular Incoherent Scatter Radar, Radio Sci., 43, RS5013,
[1] We report initial results of an effort to model the diurnal and seasonal variability of the meteor rate detected by high power and large aperture (HPLA) radars. The model uses Monte Carlo simulation techniques and at present assumes that most of the detected particles originate from three radiant distributions with the most dominant concentrated around the Earth's apex. The other two sources are centered 80°in ecliptic longitude to each side of the apex and are commonly known as helion and antihelion. To reproduce the measurements, the apex source flux was set to provide $70% of the total number of particles while the other $30% is provided by the combined contribution of the two remaining sources. The results of the model are in excellent agreement with observed diurnal curves obtained at different seasons and locations using the 430 MHz Arecibo radar in Puerto Rico, the 50 MHz Jicamarca radar in Perú, and the 1.29 GHz Sondrestrom radar in Greenland. To obtain agreement with the observed diurnal and seasonal variability of the meteor rate, an empirical atmospheric filtering effect was introduced in the simulation which prevents meteors with low-elevation radiants ( 20°) from being detected by the radars at mesospheric altitudes. The filtering effect is probably produced by a combination of factors related to the interaction of the meteor with the air molecules such as electron production and/or the ablation at higher altitudes. On the basis of these results we calculate the micrometeor global, diurnal, and seasonal input in the upper atmosphere.Citation: Janches, D., C. J. Heinselman, J. L. Chau, A. Chandran, and R. Woodman (2006), Modeling the global micrometeor input function in the upper atmosphere observed by high power and large aperture radars,
[1] In the companion paper, we identified a repeatable sequence of events leading to substorm onset in THEMIS all-sky imager observations: enhanced flows bring new plasma into the plasma sheet. The new plasma then moves earthward as a flow channel, bringing it to the near-Earth plasma sheet and where it produces onset instability. New plasma entering the dusk (dawn) convection cell drifts equatorward and eastward and then around the Harang reversal, leading to pre-midnight (near-and post-midnight) onset. Here we present evidence supporting this sequence using incoherent scatter radar (ISR) ionospheric observations. Using the Sondrestrom ISR, we find that enhanced flows of new plasma commonly enter the plasma sheet from the polar cap ∼8 min prior to onset. These flows are related to poleward boundary intensification signatures, consistent with the inferences from the imagers. Using the Poker Flat ISR (PFISR), we find that shortly before onset, enhanced westward flows reach the subauroral polarization streams (SAPS) region equatorward of the Harang reversal (dusk-cell onsets) or enhanced eastward flows enter the onset region from the poleward direction (dawn-cell onset). PFISR proton precipitation signatures are consistent with the possibility that the enhanced flows consist of reduced-entropy plasma sheet plasma, and that onset occurs poleward of much of the enhanced SAPS flow (dusk-cell onsets) or equatorward of the enhanced eastward flows (dawn-cell onsets). Consistency with reduced entropy plasma is seen only within the enhanced flows, leading us to suggest that intrusion of low-entropy plasma may alter the radial gradient of entropy toward onset instability.
In this paper, we present results from the Advanced Modular Incoherent Scatter Radar (AMISR) installed at the Poker Flat Research Range near Fairbanks, Alaska, the Poker Flat Incoherent Scatter Radar (PFISR), that focus on the ability of the system to make three‐dimensional, simultaneous measurements of ionospheric parameters. We present observations from PFISR where we were able to resolve the three components of the k vector of a traveling ionospheric disturbance (TID), as well as the period. These measurements give insight into the atmospheric gravity wave (AGW)‐TID relationship, allowing us to apply a recently developed dispersion relation for AGWs that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumptions about horizontal wavelengths. The analysis indicates that for this particular case, the wave must have been propagating against a background wind of ∼125 m/s. PFISR will be a powerful tool for studying the sources and propagation of waves in the upper atmosphere.
[1] Observations from the newly available Poker Flat Incoherent Scatter Radar have been used to study the ionospheric electrodynamics during the substorm expansion phase. Substorm events selected have been divided into three categories based on onset location relative to the radar, and repeatable features have been identified. West of onset, westward flows increased in response to the passage of the westward traveling surge (WTS) poleward of them. The enhanced flows occurred within the Sub-Auroral Polarization Streams region of downward Region 2 currents, which extend equatorward from near the equatorward boundary of electron precipitation. Strong E region ionization increase associated with the WTS occurred poleward of the enhanced westward flows, suggesting that poleward Pedersen currents fed by the downward Region 2 field-aligned current (FAC) further equatorward contribute at least partially to closure of the upward FAC of the WTS. An enhanced eastward flow channel developed east of onset. E region ionization decreased poleward of this flow peak, implying formation of downward FAC, and further increased equatorward of the flow peak, suggesting strengthening of preexisting Region 2 upward FAC. These observations indicate that the downward FAC formed at onset at least partially closes via the upward Region 2 currents. The enhanced eastward flows decreased after passage of the auroral bulge, and the reduced E region ionization increased again. When onset occurred within the radar fov, the thin breakup arc of onset occurred at the center of the Harang reversal, while if the optical onset was poleward of the radar fov, the Harang reversal was observed after the onset. A 2-D picture of the evolution of ionospheric electrodynamics was generated by synthesizing observations from the three categories, which provides a schematic description of the relationship between Region 2 and substorm expansion electrodynamics.
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