SA43A-01 INVITED
PFISR Observations of Gravity Waves in the Thermosphere
The tracers of atmospheric gravity waves (AGWs) are observed frequently at high latitudes by examining fluctuations in ionospheric parameters measured by incoherent scatter radars, ionosondes, or HF radars (e.g., SuperDARN), and have been studied for decades. These waves are in general thought to be associated with auroral electrojet activity, which impart momentum and energy into the neutral gas through Lorentz forcing and Joule heating. Tropospheric sources may also be a major source of a certain subset of AGWs that reach ionospheric altitudes. The Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) is a unique tool allowing for the study of the propagation characteristics and source region identification of AGWs. Multi-position measurements with PFISR allow for the direct and nearly unambiguous extraction of AGW parameters, including period, horizontal and vertical wavelengths, and propagation direction and speed [Nicolls and Heinselman, 2007]. This allows for the explicit evaluation of a recently derived AGW dispersion relation [Vadas and Fritts, 2005] that includes the role of kinematic viscosity and thermal diffusivity, important effects in the upper atmosphere, without assumption about horizontal wavelengths. Because this dispersion relation is formulated in the intrinsic frame of reference, PFISR observations of the vertical wavelength of the propagating waves as a function of altitude can be used to obtain altitude profiles of the neutral winds in the direction of the waves [Vadas and Nicolls, 2007]. This technique may allow for the extraction of altitude profiles of F-region winds (including the zonal component) on a regular basis, especially during the daytime when background densities are sufficiently high. In addition, PFISR studies will allow for source region identification using observed AGW amplitudes and wavelengths, which could shed light on the major sources of AGWs at high latitudes. We will show some case studies where PFISR data have been used to extract AGW properties and discuss how PFISR can be used, in combination with other instruments, to better understand AGW generation, propagation, and interaction with the ionosphere.
SA43A-02
PFISR and Lidar Observations of the Summer Mesopause Region in August 2007
In August of 2007, 19 consecutive days of PFISR radar coverage were obtained in a mode designed for the study of Polar Mesospheric Summer Echoes. This mode consisted of four beams within 10 degrees of vertical and one beam pointed vertically. Several of the days had simultaneous iron resonance and Raleigh lidar observations and all occurred during operation of the AIM (Aeronomy of Ice in the Mesosphere) satellite. PMSE was detected with the UHF PFISR system as early as May 24, 2007 [ Varney et al., 2007] and has also been studied using a 26-position imaging mode [ Nicolls et al., 2007]. Many examples of UHF PMSE were detected in all of these modes, the implication being that irregularities with scales of only .33 m are a common occurrence in PMSE. This is two orders of magnitude smaller than the inner scale of neutral turbulence. Since there seems to be little evidence in the data for aspect sensitivity of the echoes, turbulence must be rather isotropic at this scale. PMSE is generally a daytime phenomenon due to the need for ambient electrons to charge the ice particles and provide electrons for scattering targets. In this data set we find a number of nighttime events in the presence of aurorally enhanced D and E regions. The mode is suitable for spectral analysis, and the spectral widths will be presented in this talk.
SA43A-03
D-Region studies with PFISR
We present observations of the polar D-region performed with the new Poker Flat Incoherent Scatter Radar (PFISR). The observations were performed during a 24-hr period near summer solstice covering the 40 to 140 km altitude range and were designed to measure the radar return from 4 pointing directions, ~10 degrees east, south, north and west from zenith. We utilized a 13-baud, 130 us Barker code (1.5 km resolution) and a 2 ms IPP in order to obtain precise spectral information from this region of the ionosphere. The results indicate that PFISR will be a powerful tool to study the high latitude D region. We will show and discuss results that include meridional and zonal wind profiles extending from 65 to 95 km as well as estimates of the vertical flux of both the zonal and meridional momentum, measurements that are facilitated by PFISR's ability to steer on a pulse-to- pulse basis. We will also show characteristics of the spectra before, during and after the occurrence of polar mesospheric summer echoes (PMSE). In particular, we find that clear and narrow D-region spectra seem to be measured only around the times when PMSE are present. We investigate and discuss possible reasons for this correlation.
SA43A-04 INVITED
Using PFISR to Enable High-Latitude Modeling to Separate Climate and Weather in Ionospheric Variability Studies
An outstanding challenge in modeling the high-latitude ionosphere using physics-based models revolves about validating the models ionospheric climatology and weather when both occur simultaneously. One effective way to separate these two phenomena is based on their distinctively different timescales. Climatology variations occur on scales of weeks to years while weather is characterized by impulsive phases of minutes to hours and recovery lasting days. The recently commissioned Poker Flat Incoherent Scatter Radar (PFISR), in a revolutionary way, is amassing a data set for climate-weather separation by being able to operate continuously. PFISR has been operating continuously and will continue to do so throughout the International Polar Year (IPY) that began in March 2007. PFISR has already collected six months of observations, which contain equinox and summer climate information and the corresponding seasonal transitions. The expected PFISR progress through the Fall AGU Meeting will extend the data set by an equinox through winter seasonal transition. This then establishes a continuous ionospheric climate record at Poker Flat with superimposed weather episodes. The record is extensive: altitude profiles through the ionosphere of electron density; field-aligned ion drift; and ion and electron temperatures. It is this complement of state parameters that makes the ISR technique unique from a ground-based observation perspective. The Utah State University (USU) first principles Time Dependent Ionospheric Model (TDIM) is used in this study to investigate how its modeled seasonal climatology can be validated. The validation will be of the model's plasma flux tubes continuity, momentum, and energy equation solutions and both the inputs and boundary conditions of the numerical solutions of these equations. At the same time, a method then becomes available to separate the weather from the climate in the observations which leads to a significantly improved set of measurements of the impact of space weather on the ionosphere. The investigation will focus on the entire PFISR data set rather than focus on a "best case subset." A second continuous ISR data base from the Svalbard EISCAT ISR will be referenced to show the generalization of the PFISR-TDIM analysis to the whole high-latitude region.
SA43A-05
High Latitude Electron Density Distribution determined by GPS TEC and Incoherent Scatter Radar measurements
The March 1-6, 2007 incoherent scatter radar (ISR) world day experiments coincided with the start of the International Polar Year. The primary objective of the March 1-6 campaign was to examine the distribution of the topside electron density by comparing GPS and high latitude ISR total electron content (TEC) measurements. A detailed comparison between TEC measurements from multiple GPS receivers either collocated or in close proximity to the Poker Flat, Alaska ISR (PFISR) facility will be presented. Similar observations from the Sondrestrom and EISCAT ISRs will also be discussed. Although the geomagnetic conditions during the March 1- 6 time period were primarily quiet (Kp = 1,2), there were a few periods of mild to moderate activity. The quiet time periods were used to determine the background conditions. At the beginning of the geomagnetically disturbed time period, the PFISR TEC observations revealed an increase of 1.5 TEC units approximately an hour after local noon (1:30 UT). This TEC enhancement also corresponded to an increase in the height of the F layer by tens of kilometers. Later that day, at approximately 12 UT, an enhanced E-region electron density distribution was observed for 2-3 hours. During these time periods, elevated TEC measurements were detected by several of the surrounding GPS receivers. Using the network of GPS receivers in Alaska and the directional capability of the PFISR radar, we will analyze the location and size of these enhancements and discuss possible source mechanisms.
SA43A-06
Naturally Enhanced Ion Acoustic Lines with the Poker Flat AMISR radar.
The study of Naturally Enhanced Ion Acoustic Lines (NEIALs) have become one of the key studies for EISCAT both in the polar cusp using the EISCAT Svalbard Radar (ESR), and in the auroral zone, using the EISCAT UHF and VHF systems. Still many questions regarding the temporal and spatial extent of the NEIAL events remain unanswered. The new Advanced Modular Incoherent Scatter Radar (AMISR) in Poker Flat, Alaska is the first phased array Incoherent Scatter Radar at high latitudes, and by taking advantage of its possibility of (almost) simultaneous looking directions, we can resolve some of the space time ambiguity associated with NEIALs. During the night of the 23. March 2007, a period of NEIALs occurred. The radar ran in a 10 position mode with 9 beams in a narrow quadratic grid spaced by 3 degrees, plus a 10th position up B - slightly offset from the grid. Raw voltage data were sampled to allow for very high time resolution ACFs and spectra. Combining high time resolution data from multiple positions, we have the opportunity for the first time to look at the space-time ambiguity in the development of NEIALs. During the campaign a narrow field of view imager from university of Boston were operational at the Davis science center close by the AMISR array. The night of the 23. March, the imager was pointed field aligned, and at around 11:20 UT - at the time of the radar NEIALs - a field of dynamic rays occurred at and near the zenith. High time resolution multi position data from AMISR will be shown to follow the space and time development of the NEIAL event. This will also be correlated with high time resolution data from the imager.
SA43A-07 INVITED
Fundamental Features of Solar Wind-Magnetosphere-Ionosphere Coupling Revealed by High-Latitude Incoherent-Scatter Radars
Important features of solar wind-magnetosphere-ionosphere coupling can be observed within the ionosphere, where accessibility to ground-based observation allows decoupling of space-time ambiguities that are inherent to spacecraft observations. Incoherent-scatter radars (ISRs) make an important contribution to these ground- based observations by being able to reliably measure plasma flows and electron densities over areas of the ionosphere. These radars have provided critical measurements of the strength and changes of dayside convection imparted to the magnetosphere-ionosphere system by the interplanetary plasma and its changes, as well as of the transfer of polar cap flows to closed field lines that is associated with nightside reconnection. ISR measurement of the nightside flow transfer, complemented by SuperDARN radar observations, provided the first evidence of localized bursts of strongly enhanced nightside convection that lead to auroral poleward boundary intensifications, which are now known to be a major and frequently occurring disturbance of the magnetosphere- ionosphere system. With the recent addition of the ISR at Poker Flat, Alaska, we now have the capability of observing the detailed evolution of electric fields and auroral induced ionization within the nightside auroral oval, which is the ionospheric mapping of the tail plasma sheet. The energy-dependent magnetic drift of plasma sheet ions leads to a divergence of particles, and thus also of cross-tail current. This current divergence leads to the Region 2 field-aligned system and to major changes in magnetosphere-ionosphere convection, which are associated with shielding, formation of the Harang reversal, and are critical to the development of substorms and the stormtime ring current. By combining Poker Flat observations with higher latitude ISR observations, we have implemented a program to observe the Region 2 evolution in response to changes in polar cap convection and initial results show the promise of yielding much new understanding of the evolution of the Region 2 system and its effects on convection