Solar Cycle Variations of the Magnetosphere: Causes and Consequences I Posters
Presiding: D F Webb, Institute for Scientific Research, Boston College; T Onsager, NOAA Space Environment Center
SM41A-01 0830h
Angular Distribution of Neutral Atoms in the Solar Wind on October 24 & 31, 2003
In 2003, during intervals of magnetospheric compression on October 24 and 31, the IMAGE spacecraft was in the solar wind, upstream of the Earth's bow shock. While in the solar wind, the Low Energy Neutral Atom (LENA) instrument detected an unusually wide and intense angular distribution of energetic neutral hydrogen centered about the solar direction. These measurements resemble LENA's repeated observation of a narrower, less intense energetic neutral atom (ENA) distribution, thought to result from charge exchange interactions between magnetosheath ions and geocoronal hydrogen. The uniqueness of these excursions into the solar wind results from the changing IMAGE orbit; the line of apsides of the precessing orbit was only briefly near the Sun-Earth line, with an apogee of 8 RE toward the Sun, the most favorable orientation for entry into the solar wind. We investigate the ion populations present during the 2003 events, including those detected at IMAGE by the HENA instrument and upstream at ACE with the SWEPAM and ULEIS instruments. We consider solar wind and suprathermal ions that charge exchange with geocoronal hydrogen as potential ENA sources and model the resultant ENA distribution. We will report on the likely source of these ENAs in the solar wind, with particular attention to understanding their angular distribution.
SM41A-02 0830h
Comparing Deep Dropouts of Relativistic Electron Fluxes with Geomagnetic Storms and Coronal Mass Ejections
High fluxes of relativistic (> 1 MeV) electrons in the outer radiation belt are a recognized hazard to spacecraft in geosynchronous orbits through mechanisms such as deep dielectric charging. It is also known that the electron flux levels can be highly variable and do not always track geomagnetic activity, such as during large storms (e.g., Reeves et al., 2003). It has been noted that very deep dropouts or decreases down to low magnetic L shells of the population of electrons sometimes occur during intense storms driven by strong magnetic cloud/coronal mass ejections (CMEs). Two nice examples are during the late Oct. and late Nov. storms in 2003. We used daily-averaged flux data from the AFRL CEASE detector onboard the TSX5 satellite in LEO orbit to identify periods of deep dropouts from July 2000 to the present. We searched for uniform dropouts in the E > 1.2 MeV electron channel having fluxes < 0.1 electrons/cm**2 sec sr extending below L = 4. The dropout events were first identified visually on color plots and then by the quantitative criterion that the flux drop by a factor of 10 or more from one day to the next. About 40 events met these criteria and 75% of these occurred during geomagnetic storms with peak Dst < -50nT. Most of these stormtime dropout event-storms were driven by the strong southward solar wind magnetic fields associated with CMEs. We will discuss these results in terms of solar wind drivers of electron flux loss in the radiation belts.
SM41A-03 0830h
Substorm and High Speed Stream Observations During Solar Cyles 22 and 23
Magnetic measurements from the MIRACLE network are used to identify substorms during solar cycles 22 and 23, from 1993 to 2004. For the first time substorm activity is examined over a complete solar cycle. In this study more than 5000 substorms are identified and their interplanetary drivers are examined. A new parameter called substorm number Rsu is formed based on (monthly) averages of substorm peak amplitudes. The substorm number measures magnetic activity of the Earth's magnetosphere in a way analogous to how sunspot number Rz estimates the level of Sun's magnetic activity. Analysis of WIND, ACE and SOHO interplanetary measurements indicate that high speed streams (HSS, with Sun-to-Earth velocities over 700 km/s) are the main drivers of the terrestrial substorms. The substorm number peaked in 1994-1995 and in 2003-2004 (at 3-4 years after the sunspot maximum), which is when the high speed streams occurred repeatedly every 27 days. During the years of repeated HSSs, substorms occurred more frequently, were more intense, and carried more magnetic energy to the auroral ionosphere, compared to the substorms existing during non-HSS intervals.
SM41A-04 0830h
Solar Cycle Effects on Geosynchronous Satellite Surface Charging
Spacecraft in geosynchronous Earth orbit (GEO) frequently undergo surface charging following injection of energetic (E ~ 10 keV) electrons into the environment, especially within the post-midnight sector. Charging data from the GEO spacecraft Defense Satellite Communication System (DSCS-III) B-7 have been recorded over one half solar cycle. The Charge Control Experiment (CCE) aboard DSCS-III B-7 recorded incident fluxes of energetic electrons, ion spectra for determining frame-to-plasma potentials, and dielectric surface-to-frame (differential) charging levels; additionally, it incorporated a Xe plasma contactor for neutralization of charged components. Previous studies have shown 1) a general correlation between geomagnetic activity indices and the severity of frame charging, and 2) a general correlation between the intensity of energetic electron fluxes and differential charging severity. However, it was also shown that the event-specific correlations contain enough variance to cast doubt on the utility of these correlations for a predictive system. With this study, we present both a principle components analysis and a multiple linear regression of the data which incorporate a combination of factors leading to both frame and differential charging, including the geomagnetic activity indices and intensities of the energetic electron fluxes.
SM41A-05 0830h
Nonlinearity in Magnetospheric Activity and the Solar Cycle
Nonlinearities inherent to the historical data stream of the Kp index from 1932 to present are examined using mutual information and cumulant based cost as discriminating statistics. The discriminating statistics are compared with surrogate data streams that share the same linear properties as the historical data set. Differences are regularly seen in the discriminating statistics a few years prior to solar minima, while no differences are apparent at the time of solar maximum. The result suggests that the dynamics of the magnetosphere tend to be more linear at solar maximum than at solar minimum. The strong nonlinear dependencies tend to peak on a timescale around 40-50 hours and are statistically significant up to one week. Because the solar wind driver variables, VBs and dynamical pressure exhibit a much shorter decorrelation time for nonlinearities the results seem to indicate that the nonlinearity is related to internal magnetospheric dynamics. Moreover, the timescales for the nonlinearity seem to be on the same order as that for storm/ring current relaxation. We suggest that the strong solar wind driving that occurs around solar maximum dominates the magnetospheric dynamics suppressing the internal magnetospheric nonlinearity. On the other hand, in the descending phase of the solar cycle just prior to solar minimum, when magnetospheric activity is weaker, the dynamics exhibit a significant nonlinear internal magnetospheric response that may be related to increased solar wind speed.
http://w3.pppl.gov/~jrj/cumulant.html
SM41A-06 0830h
Studying Radiation Belt Electrons with Adaptive Linear State-Space Models
Linear state-space models offer a compact and flexible data-derived dynamical modeling framework for describing the coupled multi-output linear response of geophysical systems like the Earth's electron radiation belts. Unlike more traditional finite impulse response (FIR) linear filters, they effectively separate external perturbations from internal dynamics. In addition, when recent observations of the modeled system are available for comparison, prediction residuals, or innovations, can be filtered through an optimal gain matrix to further refine model output. This stochastic addition to the state-space model can reproduce persistent correlated structure in radiation belt observations that is unrelated to the external solar wind drivers. We use this so-called innovations form state-space model to more closely study both the temporal and spatial evolution of the deterministic radiation belt response to multiple solar wind inputs. A variant of the well-known Extended Kalman Filter (EKF) is used to determine time-varying linear coefficients for this model, thus providing additional flexibility that accounts for some portion of the nonlinear radiation belt response that cannot be modeled with time-stationary linear state-space models alone.
SM41A-07 0830h
Variatons of Geomagnetic Responses and Low-Altitude Radiation Belt Enviroment During Extreme Storm Events
The October-November 2003 Sun-Earth connection events produced huge geomagnetic storms (Dst as low as -400 nT) and enhancements of the Earth's radiation belt. Using the newly developed Magnetospheric State Quer System (MSQS, http://radbelts.gsfc.nasa.gov), we have identified several additional storm events (July, 1982; September, 1982; March, 1989; October, 1989; March, 1991; November, 1991; July, 2000, March, 2001 and November, 2001) which reached similar magnitude in Dst, i.e. consecutive Dst < -250 nT for more than 5 hours. Using the low-altitude radiation environment data obtained continuously by NOAA POES satellites for more than 20 years, we can study the behaviors of the low-altitude electron and proton belts during these extreme storm events, and contrast them with their quiet-time behaviors. Some events, e.g. March, 1989 and March, 1991, show formation of new proton belts. The formation and enhancement of new proton belts (L less than 2.5) in NOAA POES/MEPED enery channels (0.25 MeV to 80 MeV) will be shown and the decay-time (over years) of the proton belt inferred from these past events will be discussed. Transient evolution of electron belt at energy channels (100 keV and 300 keV) during these extreme condition events will be shown with regard to the variations of the Dst index and other magnetospheric state parameters. Common features and distiguished characteristics in the radiation belt behavior during these extreme storm events will be discussed. In addition, we will apply the recently developed magnetospheric state-based model [Fung and Shao, 2005] to prescribe the geomagnetic responses (AL, Kp, Dst) during the October-November 2003 event using the data from past extreme condition events and assess the model performance. Fung, Shing F., and Xi Shao, Magnetospheric State Specification, submitted to J. Geophys. Res., 2005.
SM41A-08 0830h
A Statistical Study of IMF Bz Generation in the Solar Wind
It is well known that the interplanetary magnetic field (IMF) Bz component plays an important role in the generation of geomagnetic activity. The origin of IMF Bz is yet not completely understood but some simple cases of coronal mass ejections when the ambient IMF is draping the CME plasma clouds. However, IMF Bz is observed not only during CMEs but practically continuously. For this study we used correlation analysis of solar wind data near the Earth in the solar-ecliptic coordinate system. First we studied the IMF Bz generation during two minima of geomagnetic activity related to negative and positive Sun's magnetic field polarity, respectively. We found that both sign and magnitude of IMF Bz have a regular character and clearly correlate with other solar wind parameters: the IMF Bx component, IMF orientation, and Sun's magnetic field. Then we analyzed events related to all levels of solar activity for ten years from 1995 through 2004 when almost continuous series of solar wind data is available. The most interesting result is a strong dependence of IMF Bz on IMF orientation in the horizontal plane: IMF Bz tends to zero when IMF vector in the horizontal plane is along the Parker spiral and increases with the deflection of the IMF vector from Parker spiral orientation. The correlation between IMF Bz and the IMF Bn component orthogonal to the Parker spiral increases with time of averaging. Correlation coefficient for daily mean data is about 0.63. The correlation increases if we account also for IMF magnitude, B, in the horizontal plane. Correlation between IMF Bz and a combination of IMF Bn and B leads to correlation coefficient for daily mean data of about 0.71. We did not find any evident dependence of IMF Bz on solar wind speed but a strong increase in correlation with increasing solar wind speed. Thus, we have found that the "false" (non-Parker spiral) IMF orientation in the horizontal plane is an important factor for IMF Bz generation. We discuss the obtained results in terms of MHD waves and quasi-steady-state inhomogeneities moving with the solar wind.
SM41A-09 0830h
Global Auroral Energy Deposition Observed from UVI: 1996-2003
Energy deposition in the northern auroral zone is examined from 1996 to 2003 using image parameters from the UVI Online Search Tool (OST). OST uses a database of image-derived search criteria such as auroral boundaries, integrated power, polar cap area, and auroral morphology. The database spans the entire Polar UVI mission lifetime with a 10 minute resolution. This database of image information represents a useful collection of auroral activity that can be used to perform extended (multi-year) studies of auroral variations. This represents the first time that continuous, high-resolution (10 minutes) energy deposition observations have been presented for such an extended period. Seasonal variations will be examined and correlation studies with standard activity indices will be presented. A discussion of methodological difficulties will also be given.
http://csds.uah.edu/uvi-ost/