SA31B-01 INVITED
Magnetospheric Energetics Associated With High Speed Stream Arrival
Some aspects of energy transfer from the solar wind to the Earth´s magnetosphere during high speed stream arrivals are discussed in the context of a summation of short agnetopause reconnection events, associated with the quasi periodic behavior of the IMF Bz component within interplanetary Alfven wave trains. A global magnetospheric MHD simulation is used to illustrate the response of the near-Earth plasma sheet to the changing character of IMF Bz during idealized HILDCAA (High-ntensity, Long-Duration, Continuous AE activity) events, associated with some high speed streams. It is argued that HILDCAAs are a new type of geomagnetic activity, substantially different from substorms or storms.
SA31B-02 INVITED
A New Solar-Terrestrial Connection: Multi-Day Oscillations in Thermosphere and Ionosphere Properties
We report on a new solar-terrestrial connection where multi-day periodicities observed in solar wind high speed streams are manifested in the thermosphere and ionosphere response. We illustrate particularly strong periodicities at 9 and 7 days in 2005 and 2006 in solar wind speed, geomagnetic activity, thermosphere mass density, neutral temperature, columnar O/N2 ratio, carbon dioxide and nitric oxide IR emission, and global ionosphere total electron content, TEC. These periodic oscillations are not observed in the solar EUV flux. This allows for the geomagnetic effects to be separated from solar flux effects in describing the response of the thermosphere and ionosphere to solar wind high speed streams. We will present the thermosphere and ionosphere observations and discuss the implications of the varying response of these parameters to solar wind high speed streams. We expect these multiday periodicities to be observed in other thermosphere/ionosphere/magnetosphere data sets during the declining phase of this solar cycle, enabling a much more extensive analysis of the entire geospace response to solar wind high speed stream disturbances.
SA31B-03
The Geoeffectiveness of High Speed Solar Wind Streams: Ionospheric Effects
There are a number of different coupling mechanisms for getting solar wind energy into the magnetosphere during high speed solar wind intervals. These will be reviewed. Specifically recent time intervals have been empirically studied to quantify these effects and the effects of coordinate transformations of the interplanetary parameters. The results of this recent study will be presented together with possible interpretations.
SA31B-04 INVITED
GUVI observations of the ionosphere during the declining phase of the solar cycle
GUVI has established a remarkable record of observations of the ionosphere since its launch in December
2001. By and large, these observations were recorded in what we call "imaging" mode. In that a scan mirror
directs the instrument line of sight from horizon to horizon. On just about the sixth anniversary of the launch
of TIMED, the GUVI scan mechanism failed. This remarkable motor and gearbox made over 10 million cycles
over 140 degrees of rotation. Since that time GUVI has been operated in "spectrograph" mode. In
spectrograph mode the scan mirror is held fixed and the instrument records and downlinks the entire
spectrum. This mode is of interest to the community because it provides a new view of the ionosphere: we
now have the signal to noise ratio to make observations of the solar minimum ionosphere at high spatial
resolution on the disk; we have observed MSTIDs and we have observed the signature of nitric oxide (NO).
NO is an important constituent of the lower thermosphere.
One of the most interesting observations at solar minimum is that we have been able to observe NO as well
as O+ under a variety of conditions. One of the more interesting situations is that it appears that we are able
to see a change in the distribution of NO during Stratospheric Sudden Warmings.
In this talk we discuss these new observations and the future of GUVI: in short, as long as the TIMED
spacecraft works we should be able to continue to provide these observations as we continue to linger at
solar minimum and on into the next solar cycle. In addition, we will look at the impact of high speed streams
on the ionosphere as seen by GUVI.
http://guvi.jhuapl.edu
SA31B-05
No Two Ionospheric Storms Are the Same ..... Nonsense!
The study of ionospheric disturbances was initiated in the paper "Note on Kennelly-Heaviside Layer Observations During a Magnetic Storm" by Hafstad and Tuve in 1929. A remarkable degree of progress followed, first from the discovery of morphologies during individual case studies, and then from the statistical treatment of large numbers of ionospheric storms at many sites. By the end of 1950s (as the first space probes were being launched), the pioneers of aeronomy (e.g., Martyn, Sato, Matsushita) had analyzed many hundreds of ionospheric storms, reported on their effects, and offered theoretical explanations for the patterns observed. Data from satellites dominated the field during the 1960s to 1980s, producing a coherent picture of morphologies, physical mechanisms and models at most latitudes. With the advent of Space Weather in the 1990s, the field reverted to case study methods only, and new diagnostics (e.g., GPS and IMAGE) gave the impression that new patterns were being discovered and that new ideas were needed to explain them. Indeed, new names (for individual storm events, storm patterns and causative processes) now dominate the field. In many ways, this is a giant step backwards in that the potential for applications to technological systems is offered as sufficient reason to re-cast knowledge gained via the traditional methods of science. A self-perpetuating series of case studies now propels solar- terrestrial-physics via the theme that only one storm at a time can be understood. In this paper, evidence is offered to show that 80 years of study of ionospheric storms has been productive, and that the onset of a new solar cycle in 2009 should not be sufficient to warrant yet another period of re-discovery of solar- terrestrial physics. Rather, new diagnostics from the ground, and crucially needed satellite observations within the ionosphere-thermosphere system, can add to our knowledge if efforts are made to build upon past results, not just re-describe them with better observing systems. As an example, the analysis of 206 ionospheric storms from solar cycle 20 are used to demonstrate the existence of "geophysically comparable sites" --- locations where theory would suggest coherence of storm-time effects in both hemispheres. Long- term ionosonde data show that well understood fundamental processes yield statistical agreement at such locations. Moreover, small departures from coherence then point to subtle differences in mechanisms that add to our overall understanding of the geospace system.
SA31B-06
A statistical study of AE response to solar wind structures
We present in this work a statistical study of the Auroral Eletroject (AE) index response to solar wind magnetic interplanetary structures over the entire observational period (1964-2003). The structures studied were magnetic clouds (MCs, 170 events), corotating interaction regions (CIRs, 727 events) and interplanetary shocks (830 events). The geoeffectiveness of these structures was assessed in terms of the geomagnetic AE peak value within 2 days after the interplanetary structure had passed near Earth's orbit. We have found that the probability to have moderate or intense AE activity after MCs, shocks and CIRs is 94.8%, 82.6% and 85.3%, respectively. Finally, from empirical frequency distributions, a theoretical probability function for AE peak values for each one of the main interplanetary structure were obtained. This gives the probability of every interplanetary structure being followed by intense, moderate, weak, or quiet (none) magnetic activity levels. The knowledge of probability distribution is important in schemes to forecast space weather conditions after the detection, by in situ solar wind observations, of an interplanetary structure approaching Earth.
SA31B-07
Strong post-midnight Equatorial Ionospheric Anomaly and Equatorial spread F Observations during magnetically quiet period
Post sunset equatorial ionospheric irregularities, especially during magnetically active periods, have been a subject of many studies. The most prominent irregularities often observed right after sunset are the resurgence of the equatorial ionospheric anomaly (EIA) and equatorial spread F (ESF). It is well understood and documented that pre-reversal enhancement, due to the ionospheric conductivity gradient at the dusk, is one of the prime triggering mechanisms for the post-sunset irregularities in the equatorial region. However, less attention has been given to the equatorial irregularities (EIA and ESF) that often occur in post-midnight, especially during magnetically quiet periods. It has been suggested that the primary process responsible for the dramatic post-midnight ESF during magnetically active periods is the change in magnitude and direction of the usual equatorial electric field. Earlier studies speculated that during magnetically active post-midnight periods the change in electric field direction from westward to eastward for a short intervals cause an upward E × B drift, resulting in increased h'F and decreased electron densities at the magnetic equator. Individual scans of Jicamarca vertical drift also often observe significant upward drift during post-midnight periods. We present a case of post-midnight strong equatorial ionospheric anomaly during a magnetically quiet (Kp < 3) period using TOPEX altimeter TEC data. Simultaneously, the ionosonde station at S.J. Campos (23.2°S, 45.9°W; dip lat. 17.6°S) observed strong ESF and unusual h'F height rise during post-midnight period, where TOPEX detected strong EIA. At the same time ROCSAT-1 and DMSP satellites also clearly show existence of EIA during post-midnight period at their orbiting altitude. The former satellite also detected post-midnight in situ density irregularities (such as bubbles) at the same time as strong EIA and ESF. The questions here are what triggers these post-midnight equatorial ionospheric irregularities? Are these post-midnight EIAs related to dusk side pre-reversal EIA? If so, what causes the post-midnight ESF and bubble formation? If, as suggested before, the electric field shifted direction from westward to eastward during post-midnight period, how does this happen and what is the physics behind this direction shift?
SA31B-08
Spectacular low and mid-latitude electrical fields and neutral inds during a superstorm
In November 2004, a major magnetic storm occurred and a lengthy portion of which was recorded by the Upper Atmospheric Radar Chain. On the 9th and 10th of November, the Jicamarca radar detected the highest magnitude penetrating electric fields and vertical drifts ever seen. These large and variable drifts were highly correlated with the interplanetary magnetic and electric fields and created a double F layer on the dayside equatrorial ionosphere and unusual TEC behavior throughout the low latitude zone. These solar wind induced drifts, both suppressed and generated irregularities at the magnetic equator at different times. Large scale thermospheric disturbances were generated by high latitude heating and tracked through the middle to low latitude zones, where both parallel and perpendicular plasma drifts created major ionospheric changes. The auroral oval was located at a magnetic L shell of about three for many hours.
SA31B-09
Variations of Auroral Electron Precipitation Measured by TIMED/GUVI
This work investigates changes of high-latitude auroral precipitation energy with geophysical conditions using measurements by the Global Ultraviolet Imager (GUVI) on the TIMED satellite from 2002 to 2007. GUVI images can obtain emissions from a significant potion of the auroral oval, and thus have much better coverage than in-situ particle measurements along satellite tracks. Six years of GUVI observations make it possible to study solar cycle, seasonal, hemispheric and geomagnetic variations of auroral electron precipitation. In this study, we use energy flux and mean energy retrieved from GUVI images to obtain hemispheric power and composite auroral maps. The change of hemispheric power and auroral maps with solar wind, solar activity, season and geomagnetic activity are then investigated. We also compare hemispheric power and auroral maps from the two hemispheres under same geophysical conditions to investigate whether there are significant hemispheric asymmetries in auroral precipitation.
SA31B-10
Convection and overshielding electric fields in the global ionosphere as observed with magnetometers and SuperDARN during the geomagnetic storm on 14-15 December 2006
The convection electric field penetrates to the equatorial ionosphere with no significant shielding effects during the DP2 fluctuation event of period of 30 - 60 min (Nishida, 1968) and during the storm main phase continuing over several hours (Huang et al., 2007). On the other hand, shielding becomes effective during the substorm growth phase (Somajajulu et al., 1987; Kikuchi et al., 2000) and even during storm main phase (Kikuchi et al., 2008). The well-developed shielding electric field results in an overshielding at the beginning of the recovery phase of storm/substorms (Kikuchi et al., 2003, 2008). Thus, the electric field manifests complex features at mid-equatorial latitudes, which is not determined only by the solar wind electric field but strongly controlled by magnetospheric processes such as the ring current. To reveal comparative roles of the convection and overshielding electric fields and in what condition the overshielding occurs at mid-equatorial latitudes, we analyzed the geomagnetic storm on 14-15 December, 2006, characterized by the quasi-periodic DP2 fluctuation of 30 min period at the beginning of the storm. We used magnetometer data from mid- equatorial latitudes to detect magnetic signatures due to the electric field originating in the magnetosphere, and used the SuperDARN data to identify electric fields associated with the solar wind dynamo (Region-1 FAC) and the ring current (R2 FAC). We further calculated an electric potential pattern caused by the R1 and R2 FACs with the comprehensive ring current model (CRCM) to better understand the SuperDARN convection pattern. First we show that the DP2 fluctuation was caused by alternating eastward (e-EJ) and westward currents (w-EJ) in the equatorial ionosphere, which were caused by the southward and northward IMF, respectively. We further show that the e-EJ was associated with the large-scale two-cell convection vortices, while the w-EJ accompanied a reverse flow equatorward of the two-cell vortices. With the aid of the CRCM ring current simulation, we show that the R2 FAC develops immediately after the growth of the R1 FAC, and produces a reversed electric potential at mid latitude when the R1 FAC decreases its intensity. Thus, the reversed convection on the SuperDARN convection map must be caused by an electric potential associated with the R2 FAC. As a conclusion, both the convection and overshielding electric fields appear at mid-equatorial latitudes, and the overshielding electric field could become predominant irrespective of the period of the disturbances, when the R1 FAC decreases its intensity. This scenario well explains both the continuous penetration over several hours during storm main phase and the overshielding at the beginning of storm recovery phase.