SA33A-1609
Effect of Solar Cycle on Geomagnetic Storms
Geomagnetic activities have been studied for the solar years of 1991 to 2007. It was found that the solar activity controls the intensity of geomagnetic storms. The intensities of these storms are found to be more severe in solar maximum years than in solar minimum years. The solar wind effect is dependent on the cycle, and invariably both are well correlated with geomagnetic storm intensity. The effects of disturbance ring current and large changes of interplanetary magnetic field Bz, both are responsible for the equatorial magnetic storm effects.
SA33A-1610 INVITED
Solar wind - high speed stream effects in the equatorial ionosphere/thermosphere system
The effects of solar wind- high speed streams in the equatorial ionosphere in the Brazilian longitudinal sector are studied. Focus is given to ionospheric responses in terms of its critical parameters, like the F layer critical frequency, peak height and the vertical plasma drift, and the total plasma content of the ionosphere resulting from both the short duration prompt penetration electric field as well as the longer lasting disturbance dynamo electric fields. The interplanetary data utilized in the study corresponds to geocentric distances of 20-50 earth radii in the sunward direction. The ionospheric data are obtained from a Digisondes operated at São Luis (44.6W, 2.33S dip angle 2.3S for epoch 2003), and total electron content data is from the GPS satellite receiving network.
SA33A-1611
A Study of Auroral Energy Behavior During HILDCAA Events
It is possible to identify geomagnetic storms and substorms with geomagnetic indices. By analysing Dst and AE, Tsurutani and Gonzalez (1987) defined a category of events called High-Intensity, Long-Duration, Continuous AE Activity, or HILDCAA. During these events, the AE index must reach, at least, 1000 nT, and never fall bellow 200 nT for more than 2 hours at a time. These conditions must last for at least 2 days, and must occur outside main phases of magnetic storms. In this paper, we focus our attention to this class of events. During the period 1998 to 2001, 14 HILDCAAs have been identified. Our main interest is to investigate how energy transfer occurs between solar wind and magnetosphere during HILDCAA events. One form of investigating this transfer energy is through the Hemispheric Power (HP), an estimate of the energy of all particles precipitating into a hemisphere. HP is obtained by comparing the energy flux observed along an orbital track of a NOAA/TIROS spacecraft. We analyze the time profile of the auroral particle precipitation energy in parallel with the time variation of geomagnetic indices for the 14 HILDCAA events. For each selected event we obtain correlation coefficients between the HP and the AE time series. The comparison was chosen since HP is a measurement of particles precipitation and AE index can be used as a proxy for the auroral energy deposition and Joule heating. Preliminary results indicate that HP and AE show similar behavior of the time evolution during HILDCAAs indicating the two are closely related. Similar analysis has also been carried out for magnetic storms to study how energy dissipation processes are different during these processes.
SA33A-1612
A model of the equatorial eastward electric field driven by ACE solar wind data.
Penetration of interplanetary electric fields (IEF) to the equatorial ionosphere is studied using solar wind data
from the ACE satellite and equatorial ionsopheric eastward electric field (EEF) data from the JULIA radar for
the time period 2000-2008. The study brings out the dependence of prompt penetration of IEF to the day
time equatorial ionosphere for all local times, seasons, IMF Bz conditions and f10.7 as a function of
frequency. We propose a transfer function based model to predict EEF from the IEF data. The use of this
transfer function decreases the misfit of a climatological model of the measured equatorial electric field by
30%. To improve the long period (> 3 hours) portion of the transfer function, we explore the use of EEF
data derived from the magnetic measurements by the CHAMP satellite. The model and coefficients are
available at http://geomag.us.
http://geomag.us
SA33A-1613
Statistical Dependence of the Large-Scale Birkeland Currents on Solar Wind Parameters
Since February 1999, distributions of the large-scale field-aligned Birkeland currents have been derived continuously from magnetic perturbations measured globally by the Iridium constellation of satellites. In a statistical study, over 1500 two-hour intervals (5% of the data) were identified for which the currents were stable to within at least 45% overlap between successive hours, corresponding to conditions in the solar wind were sufficiently stable to obtain reliable Birkeland currents. Organized by the interplanetary magnetic field (IMF) clock angle, the statistical current distributions show familiar Regrion-1 and Region-2 currents for southward IMF, NBZ currents for northward IMF, and a continuous distortion of the currents with IMF clock angle consistent with changes in the location of outflow from magnetopause reconnection (Anderson et al. 2008). Here we extend the statistical analysis to examine the dependence of the large-scale Birkeland currents on solar wind electric field in the plane normal to the Earth-Sun line, Eyz, to assess the sensitivity to the strength of the solar wind dynamo, Alfvén Mach number to assess the influence of dayside reconnection mass loading, and dynamic pressure to investigate the dependence on ram pressure. The current intensities are first corrected for variations in EUV-produced ionospheric conductance, normalizing the current densities to zero dipole tilt conditions. Findings include: (1) with increasing solar wind electric field the large-scale Birkeland currents shift duskward and expand equatorward, and the total current intensifies; (2) the total current intensifies with increasing solar wind dynamic pressure by 0.4 MA/nPa; (3) the total current intensifies with increasing Alfvén Mach number by 0.07 MA per unit Alfvén Mach number change. The analysis and implications are discussed.
SA33A-1614
Ionospheric Storms: Average Patterns for Seasonal, Solar Cycle and Local Time of Storm Onset at Sub-Auroral Sites in Both Hemispheres.
Near the east US coast (~70°W), ionospheric storms show an initial positive phase, which maximizes with a "dusk-effect" at sub-auroral latitudes, followed by nighttime depletion signatures of the trough, and then several days of daytime negative phase effects. Electrodynamical transport processes are responsible for the initial behavior of the storms, while thermospheric circulation and composition changes initiated by heating in the auroral zones determine the development of the negative phase. In the Australian sector (~130°E), however, the dipole tilt results in geophysically-comparable locations to those at ~70 W in the northern hemisphere. We have taken the 206 storm events during solar cycle #20 (1964-1976) and analyzed ionosonde data from Hobart, Tasmania (43 S, 147 E, geomagnetic lat = -52), as well as from Wallops Island (39 N, 76 W, geomagnetic latitude = 52). The disturbance patterns in NmF2 at Wallops Island and Hobart are broadly consistent, with some differences occurring for the initial positive phase. We have conducted a new analysis of the F-layer to investigate how the solar cycle phase, the local time of the storm commencement, and the season in which the storm occurs might affect the initial positive phase and the duration of an ionospheric storm.
SA33A-1615
Seasonal Comparisons of Storm/Quiet Ratios Using TIMED/SABER NO+(v) VER Measurements and ISR Electron Densities at E-Region Altitudes
The TIMED/SABER instrument is a multi-channel radiometer that measures limb emission in the MLTI region. At night, 4.3um emission is used to estimate NO+(v) Volume Emission Rates (VER) at E-region altitudes. NO+(v) VER can be derived by removing the background CO2(nu3)4.3 um radiance contribution using SABER-based non-LTE radiation transfer models, and by performing a standard Abel inversion on the residual radiance. SABER observations show that NO+(v) VER is significantly enhanced during magnetic storms in accordance with increased ionization of the neutral atmosphere by auroral electron precipitation, followed by vibrational excitation of NO+ (i.e., NO+(v)) from fast exothermic ion-neutral reactions, and prompt infrared emission at 4.3 um. Due to charge neutrality, the NO+(v) VER enhancements are highly correlated with electron density enhancements, as observed for example by Incoherent Scatter Radar (ISR). In order to characterize the response of the storm-time E-region from both TIMED/SABER and ISR measurements, a Storm/Quiet ratio (SQR) parameter is defined as a function of altitude. For TIMED/SABER, the SQR is the ratio of storm-to-quiet NO+(v) VER. Similarly, SQR is the storm- to-quiet ratio of electron densities for ISR. In this work, we compare TIMED/SABER and ISR SQR values for different magnetic storm events seasonally distributed. Preliminary results indicate a good correlation between TIMED/SABER and ISR SQR values particularly between 100 to 120 km. SQR values are intended to be used as a correction factor to be included in an empirical storm-time correction to the International Reference Ionosphere model at E-region altitudes.
SA33A-1616
Storm-Time Mid-Latitude Dayside TEC Enhancements: Longitudinal Dependence
Large-scale storm-time electron density enhancements have often been observed at Millstone Hill and other locations in the US, and have been less frequently reported from other stations around the globe. This has raised the question as to whether the formation of such enhancements may have a longitudinal dependence, and whether the US might occupy a favored longitude sector for such effects. To answer this question, we work from the premise that the driver for creating the enhancements is an electric field penetrating to mid-latitudes. Previous modeling studies carried out at Utah State University have shown that such an electric field may cause the dayside TEC to be increased by as much as 300 units during a large storm. We incorporate an expanded Volland-type electric field model into the Utah State University Time Dependent Ionospheric Model [TDIM] to simulate the effects of geomagnetic storms at locations throughout the mid-latitude northern hemisphere. We perform simulations at longitudes around the globe, covering a 24 hr range of storm onset times at each longitude. We find that a longitudinal dependence does indeed exist. Any given longitude sector has its own optimal storm onset time, whereby the storm-time density enhancements are maximized. However, by no means are the maximum possible enhancements equal in different longitude sectors. In fact, there are ranges of longitude, particularly in the Asian sector, where a penetrating electric field has very little effectiveness in creating density enhancements; while in other regions, such as the US sector, the same electric field will produce greatly elevated levels of TEC.
SA33A-1617
Multiple Magnetic Storm Study of the High-Altitude Redistribution of Equatorial Plasma
During geomagnetic storms, particularly when prompt penetration electric fields (PPE) occur, the equatorial plasma can be lifted to very high altitudes and then diffuse along magnetic field lines to higher than normal latitudes. During these cases very high plasma density (total electron content (TEC) greater than 200 TECU) can be found at these higher latitudes. Shortly after the PPE lifts the equatorial plasma to higher altitudes, at least in the US sector, phenomena known as storm-enhanced density (SED) can occur. SEDs occur in the post-noon time frame and consist of a very high density bulge that seems to occur in the southern USA and Caribbean region, followed by a narrow plume of high density plasma that flows into the high-latitude throat near local noon, and across the polar cap. An outstanding research question is: Exactly how is the high density SED plasma, particularly in the bulge related to the PPE and lifting of the equatorial plasma? Ionospheric imaging of electron density and TEC seem to show a gap in density between the poleward extent of the equatorial plasma and the equatorial extent of the SED plasma. Further, there are magnetic storm events where SEDs do not form (November 2004 as a good example). This paper will investigate the relationship between the equatorial high altitude plasma distribution during magnetic storms, and the initiation and evolution of the SED feature. We will examine eight separate storms from 2003-2006 using the ionospheric data assimilation algorithm IDA4D. In particular we will focus on time periods when LEO satellite GPS TEC data is available from CHAMP, SACC, GRACE and the COSMIC constellation (2006 and beyond). These data sets directly measure the TEC above the satellites, and therefore are good tracers of the high altitude plasma distribution. IDA4D ingests these data sets and uses them to get an improved image of the plasma density for the topside ionosphere and plasmasphere. The resulting 4D images of high altitude densities will be cross compared for the various storms and the similarities and differences will be studied and correlated with various geophysical parameters such as the interplanetary magnetic field (Bz), Dst, hemispheric power, cross cap potential, PPE, equatorial vertical drifts, and the interplanetary electric field. The overall objective is to elucidate the physical relationships that govern the redistribution of equatorial plasma during storms, and the generation and evolution of SEDs.
SA33A-1618
Numerical modeling of the ionospheric effects of substorms
The investigations of the substorm are carried out already many years. In spite of that, the single-valued answers on many questions which arise at the researchers of the substorm till now are not given. To such questions it is possible to concern the questions about the mechanism of occurrence of the substorm and on the influence of the substorm on the Earth's ionosphere. At modeling of the ionospheric effects of substorms it is important to know the following. How does the potential drop through polar caps change at initial stages of the substorm development – stepwise or smoothly? What is the duration of these changes? What and how does occur with the potential drop in the further during development of the substorm down to its termination? How does the time course of intensity of the field aligned currents of the first zone change before the substorm beginning, during substorm and after its termination? Is there a time delay of changes of the field aligned currents of the second zone relative to changes of the field aligned currents of the first zone or potential drop through polar caps? If the delay exists, what is it? How does the high-energy particle precipitation in the auroral zones and polar caps change during the substorm? Is it necessary to set at the modeling of the substorm effects the Substorm Current Wedge? If it is necessary, how make it correctly? On these questions we do not have the single-valued answers. But we shall like very strongly for them to have. We have carried out the modeling researches of the substorm influence on the ionosphere in various statements of the problem. The investigations were spent on the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere, added by the new block of calculation of electric fields in the Earth's ionosphere. In our investigations we have given the particular attention: to electrodynamics of the ionosphere; to changes of the global distributions of foF2, TEC and ion composition of the external ionosphere; to the penetration of magnetospheric convection electric field to the middle and low latitudes; to the effects in the equatorial ionosphere. This work was done under support of the Russian Foundation of Basic Research (Grant N08-05-00274).
SA33A-1619
Seasonal and solar activity variations of the Weddell Sea Anomaly observed in the TOPEX TEC measurements
The Weddell Sea Anomaly (WSA) in the ionosphere is characterized by higher plasma density at night than during the day in the region near the Weddell Sea. According to previous studies on the WSA, it is known to occur mostly in southern summer and has not been reported in other seasons. We have utilized more than 13-year TOPEX TEC measurements in order to study how the WSA varies with seasons and how it changes with solar activity. The TOPEX TEC data have been extensively utilized for the climatological study of the ionosphere due to its excellent spatial and temporal coverage. We investigate the seasonal and solar activity variations of the WSA using four seasonal cases (Mar. equinox, Jun. solstice, Sep, equinox, and Dec. solstice) and two solar activity conditions (F10.7<120 for solar minimum and F10.7>120 for solar maximum conditions) for geomagnetically quiet periods. Our analysis shows that the WSA occurs only in the southern summer hemisphere for low F10.7, as in previous studies, but the WSA occurs all of seasons except for winter when F10.7 is high: it is most prominent during the December solstice (southern summer) and still strong during both equinoxes. The WSA appears to be an extreme case of global longitudinal variations at mid-and high-latitudes.
SA33A-1620
Three-Dimensional Ionospheric Electron Density Structure of the Weddell Sea Anomaly
This paper provides the first three-dimensional description of the ionospheric density structure of the Weddell Sea Anomaly (WSA). The WSA is characterized by a night-time ionospheric density greater than that in daytime in the Weddell Sea region during the southern hemisphere summer. It was first observed by ground-based ionosondes located in the Antarctica back in the 1950s. Recently, the WSA was further investigated by two-dimensional maps over the oceans using TEC measurements collected by the TOPEX/Poseidon. Although these TEC maps have provided two-dimensional views for tracking the time- evolution and spatial coverage of the WSA, the vertical distribution of this peculiar feature is still unavailable. With the vertical ionospheric density profiles observed by the FORMOSAT-3/COSMIC, three-dimensional density structure of the WSA is presented here for the first time. The altitudinal structure of the WSA suggests that the southward offset of the magnetic equator with respect to the geographic equator plays an important role for the formation of WSA.
SA33A-1621
Low Latitude Ionosphere Measurements by the Global-scale Observations of the Limb and Disk (GOLD) Mission
The GOLD Mission of Opportunity will provide answers to key elements of an overarching question for Heliophysics science: what is the global-scale response of the thermosphere and ionosphere to forcing in the integrated Sun-Earth system? GOLD will perform remote-sensing measurements of the Earth's thermosphere and ionosphere, using an ultraviolet imager on board a commercial, geosynchronous satellite. The resulting measurements of the electron densities in the nighttime ionosphere as well as the neutral composition and temperature in the thermosphere, when combined with current modeling capabilities, will advance our understanding of Thermosphere-Ionosphere (T-I) forcing. GOLD will provide the first global- scale "snapshot" of temperature that can be compared with the coincident "snapshot" of composition changes to understand how these two major parameters simultaneously react to the various forcing mechanisms. GOLD will continue observing the same longitudes from the daytime into the night allowing the relationship between presunset conditions in the T-I system and the longitudinal dependence of variations in the ionosphere to be separated. One question that GOLD will address is: do vertical ion drifts, as manifested in the structure of the equatorial anomaly, affect the occurrence of ionospheric irregularities? Solar and geomagnetic forcing produces variations in the structure of the equatorial ionosphere at night (equatorial anomaly) and the occurrence of irregularities within the ionosphere. These ionospheric density variations, with scale sizes ranging from hundreds to tens of km, have profound effects on systems using radio frequencies. Irregularities at low latitudes are produced in the post-sunset ionosphere by the Rayleigh-Taylor (R-T) instability. The growth of these R-T instabilities into large-scale plasma bubbles has an optical signature and is the greatest source of ionospheric irregularities at low latitudes. Simulations of GOLD observations indicate that bubbles on the order of 25 km will be observable. At low latitudes, our understanding is currently based on relatively limited geographic coverage, and even that understanding is not well connected to the global-scale variations/changes. In particular, the longitude dependence of the pre-reversal enhancement in upward E×B drift velocity, which initiates the R-T instability mechanism, is poorly known. The relationships between these vertical E×B drifts, as manifested in the structure of the equatorial anomaly, and the occurrence of ionospheric irregularities will be established using observations from GOLD.
SA33A-1622
Ionosphere tomography derived by FORMOSAT-3/COSMIC TIP and GOX data
The tiny ionospheric photometer (TIP) and GPS occultation experiment (GOX) onboard FORMOSAT- 3/COSMIC record the OI 135.6 nm airglow intensities and the occultation total electron content (TEC) for the nighttime ionosphere, respectively. Due to its very high sensitivity ~600 counts/Rayleigh and rather narrow nadir pointing 3.8° circular field-of-view, the TIP provides accurate characterization of ionospheric electron density gradients in the horizontal direction. Meanwhile, the GOX data gives the information in the vertical direction. Here, we combine the two observations to carry out the GOX-TIP tomographic inversions.
SA33A-1623
A Medium-Scale Traveling Ionospheric Disturbance Observed from the Ground and from Space
We report the first optical observations from space of a Medium-scale Traveling Ionospheric Disturbance (MSTID) of the Traveling Wave Packet type. The observations were made during the Combined Radio Interferometry and COSMIC Experiment in Tomography Campaign (CRICKET) held on September 15, 2007 at ~0830 UT. The experiment used a Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC also known as FORMOSAT-3) satellite in conjunction with the Very Large Array (VLA) radio telescope, located near Socorro, NM, to study the ionosphere from the global scale down to the regional scale while the TIDs propagated through it. The COSMIC/FORMOSAT-3 satellite measured the ionosphere both horizontally and with altitude while the VLA measured the directions and speed of the TIDs. Our observations provide new information on this poorly understood class of TID
SA33A-1624
Short-Term TEC Perturbations Associated With Planetary Waves Occurrence in the Ionosphere
Analysis of TEC response to storm showed short-term perturbations which were observed after initial phase of geomagnetic storms. The perturbations demonstrated very well expressed latitudinal structure and were recognized on diurnal variations as surges of TEC enhancement of TEC. Ordinary such storm-time positive effect was associated with TAD. Duration of the perturbations was about 2-4 hours and their amplitude increased toward low latitudes. Such TEC perturbations have the longitudinal dependence. It is important that time location of surges have week dependence on latitude. The observed structure appeared to arrive from high latitudes, but at middle latitudes it was represented as a standing wave. It is assumed that such TEC perturbations can be produced due to superposition of the eastward and westward propagating planetary Poincare waves. The periods of these waves are usually several hours. Poincare waves can be excited at the atmosphere in storm time. At middle latitudes their superposition is as standing wave that forms observing TEC perturbations. In the report, the possibilities of application Poincare waves to the ionosphere dynamics studies are discussed and an explanation of the observed ionospheric effects is given.
SA33A-1625
Ionospheric and Geomagnetic Activity Investigated Using Oblique Sounding Comparisons With an HF Radio Propagation Model
Oblique HF sounder paths over ~2000km have been operating between New Zealand and Australia for a
number of years. The maximum observed frequencies (MOF) are compared with predictions from the
climatological HF radio skywave propagation model used by IPS. Variations from predicted median
(MUF),lower (OWF) and upper decile frequencies may be interpreted in terms of ionospheric and
geomagnetic activity and the effectiveness of parameterisation of
ionospheric support for HF by the T-index examined. Closely spaced multiple paths provide opportunities to
investigate small scale F2 layer structures.
http://www.ips.gov.au
SA33A-1626
Radio and optical observation of polar cap tongue of ionization during the geomagnetic storm on December 15, 2006
During intervals of the southward IMF conditions, enhanced anti-sunward convection at the high-latitude carries solar-produced daytime plasma into the polar cap ionosphere. This feature is known as a tongue of ionization (TOI) and presents a significant space weather problem because the plasma density irregularities within and/or surrounding the structure produce a disturbed scintillation environment for communications links crossing the polar ionosphere. TOI is generally broken into discrete polar cap patches by the transient bursts of magnetopause reconnection or reorientation of the dayside convection pattern associated with changes in IMF orientation before it penetrates deep into the dark hemisphere. During geomagnetic storms, however, TOI is sometimes seen to penetrate into the nightside auroral latitudes through the central polar cap as an elongated plume of enhanced ionization. In this paper, we present first simultaneous radio and optical observations of TOI structure extending from the dayside to the nightside polar cap. Optical manifestation of the elongated TOI plume was detected with an all-sky airglow imager of OMTIs (Optical Mesosphere Thermosphere Imagers) at Resolute Bay (74.73N, 265.07E; AACGM latitude 82.9N) during a geomagnetic storm on December 15, 2006. Optical data demonstrate that the TOI plume changed its shape very dynamically in close association with the polar cap convection streamlines as determined independently from the Super Dual Auroral Radar Network (SuperDARN). The absolute optical intensity of the TOI feature is approximately 1000 Rayleigh, which is much brighter than that of non-stormtime polar cap patches. This suggests that the source of plasmas within the TOI plume is far from the polar cap, that is in the mid-latitudes. In reality, mid-latitude SuperDARN radar in Hokkaido, Japan observed enhanced anti-sunward plasma flow at 65° magnetic latitude during this interval, which indicates that unusual equatorward expansion of the high-latitude two-cell convection boundary played an important role in entraining lower-latitude solar- produced plasma as a source population for the TOI plume. The IMF clock angle was stable throughout the interval of the TOI plume, which implies that the dayside convection pattern did not change its spatial distribution with time. This suggests that the fragmentation of TOI into discrete polar patches was not likely to occur and then TOI could penetrate deep into the polar cap without being chopped. We will discuss, through this case example, differences of continuous TOI plume and discrete polar cap patches in terms of stormtime expansion of the high-latitude convection pattern and variability of IMF orientation.
SA33A-1627
On the Generation of Ionospheric Irregularities in the Dayside Polar Cap
In this paper we review recent work on the formation of ionospheric irregularities in the dayside polar cap. The last 6-7 years we have carried out several observational campaigns at the EISCAT Svalbard Radar to study polar cap patches and the local plasma flow in the F-region. A key discovery is the existence of Reversed Flow Events (RFEs), which are 100-200 km wide channels of intense flow that opposes the background convection. Here we discuss the role that these events have for the growth of ionospheric plasma irregularities. The cusp ionosphere is known to be a very efficient backscatter target for HF radars like SuperDARN. It has long been thought that the Gradient Drift Instability (GDI) is the primary mechanism behind the decameter size irregularities that these radars obtain their echoes from. But the newly discovered RFE channels open up the possibility that other mechanisms like the Kelvin Helmholtz Instability (KHI) can operate in conjunction with the GDI too. The effect is a more rapid and more efficient structuring of the F- region plasma as it enters the dayside polar cap. In this paper we present ground-based observations from both optical and radar techniques that support this new idea.
SA33A-1628
Storm-time E-region radar backscatter observed by the SuperDARN HF radars
Storm-time coherent echoes observed by the SuperDARN HF radars in the short ranges corresponding to the E-region backscatter are investigated. Analysis of the spatial distribution of the echoes shows that during storms most of the echoes are detected at locations that are close to the expected locations calculated using a straight-line propagation model (i.e. assuming no radar wave refraction). Analysis of the E layer critical frequency, foE, from one subauroral ionosonde station confirmed that during storms foE typically decreases to lower values as compared with normal conditions. This result suggests that the electron density in the E region is often depleted during storms. The progression of depletion with storm-time and MLT is analysed using several SuperDARN radars separated in longitude. The types of short-range echoes detected during storms are also examined. A new storm-time population of echoes is identified; the echoes exhibit small negative Doppler velocities for a large range of spectral widths. Local ionospheric plasma convection velocity measurements are then used to study the conditions favorable for the generation of these echoes.
SA33A-1629
Intriguing observations of elevated temperatures around double-layer Sporadic- E
As part of the of the EQUIS II sounding rocket campaign, two separate rockets were launched into thin radar scattering layers that were observed as precursors to nighttime Equatorial Spread-F. The payloads carried an RF Plasma Impedance Probe, an internally heated sweeping Langmuir probe, and four booms for double- probe type E-field measurement. We present the in-situ density and temperature measurements of the two flights. The ion saturation region analysis of the Langmuir Probe I-V curve produces absolute ion density that matches within 5% of the absolute electron density derived from the impedance probe. The electron retardation region analysis of the I-V curve gives electron temperatures with magnitudes that are in general agreement with averaged models such as the IRI but also show unusual structure in the F-region as well as elevated temperatures around a double-layer sporadic-E that was observed on one of the flights. While the F-region structure still remains unexplained, this work presents possible mechanisms for the temperature enhancement around the sporadic-E double-layer.
SA33A-1630
On the Effect of Medium Energy Electron Precipitation on the Earth's Middle and Low Atmosphere
Precipitating medium energy (>30 keV) electrons represent an important energy source for the Earth's high-latitude ionosphere and atmosphere. Recent satellite data analyses suggest that up to 40% of the NOx in the stratospheric polar region on an annual basis can be attributed to the descent of NOx produced by energetic particle precipitation at high altitudes. In this work, the processes of NOx production by medium energy electrons and subsequent descent will be investigated by using the Whole Atmosphere Community Climate Model (WACCM) from the National Center for Atmospheric Research. We will first introduce our recently developed parameterization scheme for the electron impact ionization rate calculation, which is applicable for 100 eV to 1 MeV electrons in a Maxwellian energy distribution. The new parameterization method is derived by following Roble and Ridley (1987) but taking into account further functional dependence on the incident electron energy. With highly improved accuracy, the new parameterization method provides a more reliable approach to include medium energy electron precipitation in WACCM. While there is a perception that bremsstrahlung X rays generated by energetic particles dominate the ionization in the stratosphere, little is known about their significance with regard to atmospheric composition on global and long-term scales. In this study, the ionization rates from direct electron impact and associated bremsstrahlung X rays will be investigated using WACCM. The importance of medium energy electron precipitation in producing NOx and modifying stratospheric ozone will then be assessed.
SA33A-1631
On the estimation of particle energies and fluxes incident over Boston during a daytime auroral event
The earth's upper atmosphere gets affected by the influence of particles of solar wind origin, especially during space weather events. Estimating the energy inputs into the upper atmosphere is very essential to be able to eventually quantify the energy budget into the upper atmosphere and also to understand the coupling between atmospheric regions. During space weather events the incidence of energy flux shows significant spatial and temporal variation. Particle energies have predominantly been measured from instruments onboard satellites. Estimation of energies using radar-based inversion techniques are quiet involved and even when possible, particle energies at only higher energy range (around keV and beyond) can be inferred. In the present paper, we present the results on particle fluxes and energies that we obtained from combined investigations of optical, radar and modeling techniques. The storm of October 30, 2003 was considered for analysis. On that day we had carried out one of the first daytime auroral observations of the OI red emission line from Boston using the BU-built High Resolution Echelle spectrograph. We had measured the peak brightness of aurora to be 38 kR, which is not predicted by the GLOW model. However, the match between the measured brightness and the model prediction during non-storm period of that day is very good. Therefore, assuming the discrepancy in the measured and the model emissions during the storm time to be only due to the particle inputs, we inferred the particle energy fluxes for given characteristic energies as obtained from the peak ionospheric heights observed by the Millstone Hill Incoherent Scatter radar. The energy fluxes vary between 2 to 12 mWm-2. Results such as these add to the credence of the capability of the daytime measurement technique in understanding the upper atmospheric dynamics.
SA33A-1632
Electron Precipitation Parameters and Ionospheric Conductances Inferred From Auroral Images Acquired by the Visible Imaging System (VIS)on the Polar Spacecraft
The Visible Imaging System (VIS) on the polar spacecraft provided time sequences of auroral images at multiple wavelengths that yield information of auroral dynamics on a global scale with a spatial resolution of ~ 20 km and temporal resolution of ~ 1 minute. Time sequences of VIS images in which the aurora was highly dynamic are used to infer global maps for the electron precipitation parameters, energy flux and characteristic energies, and ionospheric conductances. The maps are inferred from the corresponding VIS images using an auroral model (Lumerzheim et al., 1987). The temporal and spatial resolution of the VIS inferred patterns are unprecedented. The inferred patterns are highly structured and vary significantly on a time scale of less than 5 minutes. These patterns can be very beneficial for global physics-based numerical models for the high-latitude ionosphere which previously had to rely on statistical models for the electron precipitation and ionospheric conductance.