SA33B-1633
Photometric observations of 630.0-nm OI and 427.8-nm N2+ emission from South Pole and McMurdo Stations during winter: Analysis of temporal variations spanning minutes to yearly timescales
Time series analysis of wide field-of-view photometer measurements of OI 630.0-nm (originating from a wide O layer in the thermosphere between 200 km and ~300 km and peaking at 250 km) and N2+ 427.8-nm (originating from the mesopause at 95 km) emissions taken simultaneously from South Pole station and from McMurdo (78 S geographic) during winter periods of 2003-2005 are presented. The high sampling rate and extended duration of measurements at both locations allow for the analysis of phenomena with periods spanning order of minutes to seasonal variations. It is shown that 1) 24-, 12-, 8-, and 6-, 4.8-, and 4-hour tidal influences dominate the spectrum from McMurdo at both altitudes and are substantially weaker at South Pole station, 2) higher frequency variations (i.e., with periods of 90-, 24-,15-, 9-, 6-, and 3.3 minute) are occasionally observed which may be related to periodic injection of plasma associated with Pc magnetospheric resonances, and 3) the 630.0-nm emission at South Pole station steadily decreases throughout the winter period, whereas the emission level remains relatively constant at McMurdo, indicating a general reduction in the horizontal transport of plasma poleward of McMurdo. These results lend insight into the role of tides and meridional transport in the high latitude neutral atmosphere as well as to plasma-neutral coupling (e.g., plasma injection) at high geomagnetic latitudes.
SA33B-1634
A new High-level Gridded Madrigal Data Product for IPY Incoherent Scatter Radar Data and Model Output.
The World's high-latitude incoherent scatter radars are contributing to the International Polar Year (IPY) through an unprecedented set of long-duration runs. From March, 2007 through February, 2008 he EISCAT Svalbard Radar and the Poker Flat Incoherent Scatter Radar operated almost continuously and the Sondrestromfjord and Millstone Hill Radars ran on a regular biweekly schedule. These extensive data sets present a major data handling challenge as do the physics-based model runs covering this period. The radar data are all available through the distributed Madrigal Database. However, the radars employ different, sometimes complex, operating modes which can present a significant challenge to modelers and other users who are not experts in the incoherent scatter radar technique. We have addressed this problem by developing a higher level data product which casts the data from all the radars into an identical gridded form. Several modelers are also providing model output through Madrigal in the same format. For the radar data, tensor product cubic spline fits to the measured electron density, ion temperature and electron temperature are computed and output in Madrigal format at 15 minute intervals and a standard set of altitudes from 100 to 548 km. In addition, hmF2, integrated electron content and the neutral temperature are computed and included in the output Madrigal file. As an aid to studying day-to-day variability, files have been produced both for individual days of the year and monthly averages.
SA33B-1635
In-situ Ion Temperature Measurements in the Joule Heating Region
Measuring the temperature of ionospheric ions in situ is challenging because the temperatures involved (often < 0.1 eV) are comparable to or less than typical fluctuations in spacecraft potential and other sources of measurement noise. We demonstrate a new technique to determine Ti that is relatively immune to changes in spacecraft potential. Specifically, we construct two-dimensional maps of core ion distribution functions provided by Suprathermal Ion Imagers (SII) flown on the JOULE and JOULE-II sounding rockets. Ram flow in the plane of these images produces anisotropy that can be quantified and related through modeling to Mach number and therefore to thermal velocity and ion temperature. We provide examples from the ionospheric E region showing ion temperature enhancements that are a direct result of Joule heating at altitudes between 105-135 km.
SA33B-1636
Statistical Signature of NEIALs in International Polar Year PFISR Data
Naturally Enhanced Ion Acoustic Lines (NEIALs) in Incoherent Scatter Radar (ISR) spectral data are characterized by strong enhancements in either or both ion acoustic lines above thermal level over an extended altitude region. The occurrence of NEIALs is associated with plasma turbulence, particle precipitation and strong shears, and typically occurs at the edges of auroral arcs and in the polar cusp. The Poker Flat ISR (PFISR) is located under the auroral oval at about 67-degree invariant latitude, and since the beginning of the International Polar Year (IPY) in March of 2007 the radar has been running continuously, producing a unique dataset very well suited for the study of trends. In this paper we present a statistical study of the occurrence of NEIALs in the IPY dataset from PFISR. The study includes seasonal, and diurnal occurrence frequency of NEIALs, duration of NEIAL events, altitude extent and correlation to geophysical activity and optical aurora occurrence.
SA33B-1637
Automated Identification of Field-Aligned Electron Bursts from GEODESIC Sounding Rocket Data
An effective peak finding algorithm for automated identification and display of field-aligned suprathermal electron bursts peak points has been created. The logic of the algorithm and how it streamlines the process for analyzing the coincidence of these bursts with Alfvén wave activity is described. The algorithm was used to investigate the occurrence of suprathermal electron bursts and their timing with respect to auroral breakups within the electron flux measurements made during the GEODESIC flight. The bursts are observed in the data near the edges of auroral arcs and demonstrated energy-time dispersion, with higher energy electrons appearing earlier in time. Analysis of these signatures allows inference of the source location(s) and characteristics. The algorithm has been developed and tested on measurements made by the GEODESIC sounding rocket with a goal of applying it to larger satellite datasets, such as from Freja and FAST.
SA33B-1638
Electrodynamics of an Omega-Band and Comparison of Ground- and Space-Based Conductance Estimates
We investigate an Omega-band event that took place above northern Scandinavia around 02:00 - 02:30 UT on 9.3.1999. The Omega-band event occured in the recovery phase of a moderate substorm. In the first part of the study we compare ground- and space-based estimates of the ionospheric Hall and Pedersen conductances during the Omega-band event. Ground-based measurements offer good spatial and temporal resolution, but their spatial extent is often limited. Space based observation are complementary, offering good coverage but limited resolution. The ground-based conductance estimates are derived with two different methods: (i) from measurements of cosmic radio noise absorption with the method developed by Senior et al. (2007) and (ii) by combining riometer data with 557.7 nm ASC data with the method by Kosch et al. (2001). The absorption measurements are done with the Kilpisjärvi IRIS imaging riometer. The space- based conductance estimates are derived from ultraviolet images taken by the UVI instrument on board the POLAR satellite. The process of estimating ionospheric conductances from the intensity of the auroral ultraviolet emission is descibed by Lummerzheim et al. (1991). We compare these three conductance estimates for the Omega-band event by taking temporal and spatial averages of the higher resolution ground-based data. Our data set of 12 time frames (with 10 grid points each) shows the tendency of space- based conductances to be 15-40% smaller than ground-based conductance estimates. In the second part of the study we examine the electrodynamic structure of the Omega-band. The ionospheric electric field of Omega-bands has mostly been studied with coherent scatter radars, which may have trouble in resolving small electric fields, such as those that are present in the highly conductive luminous "tongues" of the Omega-band. We calculate the ionospheric electric field from the conductance estimates and ground magnetic measurements with the method developed by Vanhamäki and Amm (2007). Both the riometer- and UVI-based conductance estimates should have their best accuracy in the luminous "tongues", where electron precipitation is intense and conductances are high. High resolution riometer and magnetometer measurements allow us to asses the electric field structure of the whole Omega-band, including the luminous tongues, thus completing the previous studies.
SA33B-1639
EISCAT observations and TRANSCAR simulation of the solar eclipse of August 1, 2008
On 1 August 2008, the footprint of the solar eclipse passed north east of the Svalbard archipelago, where the EISCAT Svalbard Radars (ESR) are installed. The radars measured a depletion in electron density in the low F-region of a factor ~10 and a decrease in temperature of about 1000K. Also, the VHF dish of the mainland EISCAT system measured a decrease in the same parameters, showing the influence of the penumbra and of a partial eclipse. We have modelled the response of the high-latitude ionosphere to a solar eclipse with the TRANSCAR code and used its new capability to model the response of the conjugated ionosphere in the southern hemisphere.
SA33B-1640
Solar Wind and Global Electron Hemispheric Power in Solar Minimum Intervals
We assess the periodicities of the hourly and daily solar wind velocity (Vsw) and average global electron auroral hemispheric power (Hpeg) with Lomb-Scargle (L-S) and Fast Fourier Transforms (FFTs) using three Carrington Rotations (CRs) to a year or more of data in two different solar minimum periods. The first Whole Sun Month (WSM) interval (96223-96252) was during the last solar minimum where the solar magnetic field relaxed into a dipole. A strong 'semiannual' periodicity in Vsw maximizing in equinoxes was found, which enhanced the equinoctial maxima found in Hpeg (and Kp) due to the preferred solar wind and magnetospheric reconnection during equinoxes. In the present solar minimum, the solar magnetic field has considerable quadrupole components during the Whole Heliospheric Interval (WHI, 08080-08107). Hpeg exhibits solar rotational periodicities similar to those for Vsw using both L-S and FFT analyses, where the 9- day periodicity is particularly strong in the present solar minimum period. The 9-day periodicity in the WHI CR was caused by three periods of slow-speed solar wind from near the ecliptic plane as seen in the sign of IMF Bx. Periodicities are examined in Vsw since 1972, and in Hpeg since 1978 to assess solar cycle variations. Periodicities longer than 100 days are not as strong or as well correlated between Vsw and Hpeg compared to the shorter solar rotational periodicities.
SA33B-1641
Modeling the ionosphere in the IPY with the FLIP model
This paper presents results of comparisons of the Field Line Interhemispheric Plasma (FLIP) model with ionospheric data collected during the International Physical Year from the Poker Flat Incoherent Scatter Radar (PFISR) in Alaska. With regard to peak electron density (NmF2), the FLIP model is in good agreement in the spring but consistently underestimates the measured NmF2 in summer by a factor of 2. The data show frequent G conditions where the daytime peak electron density occurs below 200 km. This paper will discuss possible causes of the observed behavior as well as temperature and neutral wind variations.
SA33B-1642
Traveling Ionospheric Disturbances at northern mid-latitudes
Three low power coded transmitters have been used for measurement of gravity waves at London, Canada (43 geog. lat., 54 mag. lat). The transmitters are at apexes of an approximately equilateral triangle with 72 km sides. The signals reflected from the ionosphere are received at our university campus which is located within the triangle. TID measurements on 4 MHz have been recorded for more than 1 year. In all months daytime TIDs have closely the same behaviour. Motion is towards the east around dawn, and then slowly rotates clockwise to approximately southward around dusk. The directions are consistent with selective filtering by background tidal winds. The TIDs appear to be just the saturated spectrum of mesospheric gravity waves propagated to F-region heights. Since 2008 was very quiet magnetically we did not observe any obvious TIDs that might be from auroral zone disturbances.
SA33B-1643
Ionospheric Yearly Variations from Polar Cusp through Mid-latitude: IPY ISR Observations
The first year's IPY observations by incoherent scatter radars (ISRs) provided an excellent opportunity to investigate yearly variations of the upper atmosphere for a period with very low solar activity and quiet magnetic activities. Observations have been conducted by ISRs at Svalbard, Porker Flat, Sondrestrom and Millstone Hill. This array of radars spanning from polar cusp, auroral zone, to mid-latitudes enables us to address some fundamental concerns about the upper atmosphere climatology, such as the yearly changes of the ionosphere from high- to middle- latitudes, in particular the altitude dependency of such changes. In this work we use a full year's worth of data from all 4 radars to discuss annual and semiannual changes in electron density and plasma temperatures. Some interesting features will be presented, such as the pronounced semiannual variation in Ne at the polar cusp and its absence at auroral zone. Very different from known variation patterns typical for midlatitudes, the electron density variation at Millstone Hill is characterized with totally asymmetric inter-annual changes with the maximum in winter and a secondary one in spring. There is also clear phase changes of the maxima with height. We will also show a comparison was for Millstone Hill between this current IPY observations and those from previous solar cycles, in order to examine solar cycle to solar cycle variability as well as possible long-term trends.
SA33B-1644
Comparisons of Total Electron Content with GPS and Incoherent Scatter Radar during IPY
Since the early 1990's, comparisons of the measured total electron content (TEC) have been made between GPS and incoherent scatter radar (ISR). This was first done in 1990 using data collected at the Millstone Hill ISR site in Westford, MA. The Millstone Hill ISR can measure electron density up to approximately 800 km, depending on the amount of signal integration and/or the total amount background ionization. The initial ISR and GPS TEC comparisons were somewhat surprising in that the differences between these measurements varied significantly depending on the geomagnetic conditions. Prior to a geomagnetic storm, there were indications that as much as 20 percent of the background TEC was observed to be above 800 km. Directly after the geomagnetic storm, the average difference between the ISR and GPS TEC measurements was almost zero. This has been recently explained by the IMAGE satellite observations of the plasmaspheric drainage plumes which effectively drain plasma from the plasmasphere out into space during geomagnetically active conditions. Here, we will report on comparisons of the GPS and ISR estimates of the TEC in the high latitudes from the first year of the IPY, March 1, 2007 through March 1, 2008. Our analysis will focus on data from the ISRs associated with the high latitudes: the Poker Flat radar in Alaska, the EISCAT radar in Svalbard, the Sondrestrom radar in Greenland, and the Millstone Hill radar in Massachusetts. During this time period, the Poker Flat (PFISR) and EISCAT Svalbard (ESR) radars ran continuously. The Millstone Hill and Sondrestrom ISRs ran bi-weekly throughout the year. These comparisons will utilize TEC data from the Madrigal database that was estimated from the global network of GPS receivers. In addition, TEC data collected from individual GPS receivers located near the ISRs will be examined. The GPS versus ISR TEC comparisons will be used to study the variation of the high altitude electron content as a function of latitude, geomagnetic conditions, and season.