Evolution of the sun''s near-surface asphericities over the activity cycle

Solar oscillations provide the most accurate measures of cycle dependent changes in the sun, and the Solar and Heliospheric Observatory/Michelson Doppler Imager (MDI) data are the most precise of all. They give us the opportunity to address the real challenge — connecting the MDI seismic measures to observed characteristics of the dynamic sun. From inversions of the evolving MDI data, one expects to determine the nature of the evolution, through the solar cycle, of the layers just beneath the sun's surface. Such inversions require one to guess the form of the causal perturbation — usually beginning with asking whether it is thermal or magnetic. Matters here are complicated because the inversion kernels for these two are quite similar, which means that we don't have much chance of disentangling them by inversion. However, since the perturbation lies very close to the solar surface, one can use synoptic data as an outer boundary condition to fix the choice. It turns out that magnetic and thermal synoptic signals are also quite similar. Thus, the most precise measure of the surface is required.

We argue that the most precise synoptic data come from the Big Bear Solar Observatory (BBSO) Solar Disk Photometer (SDP). A preliminary analysis of these data implies a magnetic origin of the cycle-dependent sub-surface perturbation. However, we still need to do a more careful removal of the facular signal to determine the true thermal signal.     

Local-area helioseismology as a diagnostic tool for solar variability

Dynamical and thermal variations of the internal structure of the Sun can affect the energy flow and result in variations in irradiance at the surface. Studying variations in the interior is crucial for understanding the mechanisms of the irradiance variations. “Global” helioseismology based on analysis of normal mode frequencies, has helped to reveal radial and latitudinal variations of the solar structure and dynamics associated with the solar cycle in the deep interior. A new technique, - “local-area” helioseismology or heliotomography, offers additional potentially important diagnostics by providing three-dimensional maps of the sound speed and flows in the upper convection zone. These diagnostics are based on inversion of travel times of acoustic waves which propagate between different points on the solar surface through the interior. The most significant variations in the thermodynamic structure found by this method are associated with sunspots and complexes of solar activity. The inversion results provide evidence for areas of higher sound speed beneath sunspot regions located at depths of 4–20 Mm, which may be due to accumulated heat or magnetic field concentrations. However, the physics of these structures is not yet understood. Heliotomography also provides information about large-scale stable longitudinal structures in the solar interior, which can be used in irradiance models. This new diagnostic tool for solar variability is currently under development. It will require both a substantial theoretical and modeling effort and high-resolution data to develop new capabilities for understanding mechanisms of solar variability.     

The SOHO CELIAS/SEM EUV database from SC23 minimum to the present

The SOHO Solar EUV Monitor has been in operation since December 1995 onboard the SOHO spacecraft. This instrument is a highly stable transmission grating solar extreme ultraviolet spectrometer. It has made nearly continuous full disk solar irradiance measurements both within an 8 nm bandpass centered at 30.4 nm and throughout the 0.1 to 50 nm solar flux region since launch. The 30.4 nm flux, the 0.1 to 50 nm flux and the extracted soft X-ray (0.1 to 5 nm) flux are presented and compared with the behavior of solar proxies.     

Mars Phobos and Deimos Survey (M-PADS) – A martian Moons orbiter and Phobos lander

We describe a Mars ‘Micro Mission’ for detailed study of the martian satellites Phobos and Deimos. The mission involves two ∼330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988–89) failed to realise its full potential. Many questions remain concerning the moons’ origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA’s Aurora programme.     

Nighttime cloud properties retrieval using MODIS and artificial neural networks

In this work a methodology for inferring water cloud macro and microphysical properties from nighttime MODIS imagery is developed. This method is based on the inversion of a theoretical radiative transfer model that simulates the radiances detected in each of the sensor infrared bands. To accomplish this inversion, an operational technique based on Artificial Neural Networks (ANNs) is proposed, whose main characteristic is the ability to retrieve cloud properties much faster than conventional methods. Furthermore, a detailed study of input data is performed to avoid different sources of errors that appear in several MODIS infrared channels. Finally, results of applying the proposed method are compared with in-situ measurements carried out during the DYCOMS-II field experiment.     

The solar cosmic ray ground-level enhancements on 20 January 2005 and 13 December 2006

Close to the current solar activity minimum, two large solar cosmic ray ground-level enhancements (GLE) were recorded by the worldwide network of neutron monitors (NM). The enormous GLE on 20 January 2005 is the largest increase observed since the famous GLE in 1956, and the solar cosmic-ray event recorded on 13 December 2006 is among the largest in solar cycle 23. From the recordings of the NMs during the two GLEs, we determined the characteristics of the solar particle flux near Earth.     

Coronal fast wave trains of the decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare

The 22 min long decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare simultaneously by the Brazilian Solar Spectroscope (BSS) and the Ond?ejov radiospectrograph in frequency range 1200–4500 MHz has been analyzed. We have found that the characteristic periods of about 60 s belong to the long-period spectral component of the fast wave trains with a tadpole pattern in their wavelet power spectra. We have detected these trains in the whole frequency range 1200–4500 MHz. The behavior of individual wave trains at lower frequencies is different from that at higher frequencies. These individual wave trains have some common as well as different properties. In this paper, we focus on two examples of wave trains in a loop segment and the main statistical parameters in their wavelet power and global spectra are studied and discussed.     

Substorms in the inner plasma sheet

Thin Current Sheets (TCS) are regularly formed prior to substorm breakup, even in the near-Earth plasma sheet, as close as the geostationary orbit. A self-consistent kinetic theory describing the response of the plasma sheet to an electromagnetic perturbation is given. This perturbation corresponds to an external forcing, for instance caused by the solar wind (not an internal instability). The equilibrium of the configuration of this TCS in the presence of a time varying perturbation is shown to produce a strong parallel thermal anisotropy (T T) of energetic electrons and ions (E>50keV) as well as an enhanced diamagnetic current carried by low energy ions (E<50keV). Both currents tend to enhance the confinement of this current sheet near the magnetic equator. These results are compared with data gathered by GEOS-2 at the geostationary orbit, where the magnetic signatures of TCS, and parallel anisotropics are regularly observed prior to breakup. By ensuring quasi-neutrality everywhere we find, when low frequency electromagnetic perturbations are applied, that although the magnetic field line remains an equipotential to the lowest order in T_e/T_i, a field-aligned potential drop exists to the next order in (T_e/T_i). Thus the development of a TCS implies the formation of a field-aligned potential drop ( few hundred volts) to ensure the quasi-neutrality everywhere. For an earthward directed pressure gradient, a field-aligned electric field, directed towards the ionosphere, is obtained, on the western edge of the perturbation (i.e. western edge of the current sheet). Thus field aligned beams of electrons are expected to flow towards the equatorial region on the western edge of the current sheet. We study the stability of these electron beams and show that they are unstable to “High Frequency” (HF) waves. These “HF” waves are regularly observed at frequencies of the order of the proton gyrofrequency (f_H+) just before, or at breakup. The amplitude of these HF waves is so large that they can produce a strong pitch-angle diffusion of energetic ions and a spatial diffusion that leads to a reduction of the diamagnetic current. The signature of a fast ion diffusion is indeed regularly observed during the early breakup; it coincides with the sudden development of large amplitude transient fluctuations, ballooning modes, observed at much lower frequencies (fH+). These results suggest that the HF waves, generated by field-aligned electron beams, provide the dissipation which is necessary to destabilize low frequency (ballooning) modes.     

Collision Risk Mitigation in Geostationary Orbit

The short- and long-term effects of spacecraft explosions, as a function of the end-of-life re-orbit altitude above the geostationary orbit (GEO), were analyzed in terms of their additional contribution to the debris flux in the GEO ring. The simulated debris clouds were propagated for 72yrs, taking into account all the relevant orbital perturbations.The results obtained show that 6–7 additional explosions in GEO would be sufficient, in the long term, to double the current collision risk with sizable objects in GEO. Unfortunately, even if spacecraft were to re-orbit between 300 and 500km above GEO, this would not significantly improve the situation. In fact, an altitude increase of at least 2000km would have to be adopted to reduce by one order of magnitude the long-term risk of collision among geostationary satellites and explosion fragments. The optimal debris mitigation strategy should be a compromise between the reliability and effectiveness of spacecraft end-of-life passivation, the re-orbit altitude and the acceptable debris background in the GEO ring. However, for as long as the re-orbit altitudes currently used are less than 500km above GEO, new spacecraft explosions must be avoided in order to preserve the geostationary environment over the long term.     

Short-term variation of cosmic ray diurnal anisotropy and solar activity

A correlative analysis has been made between cosmic ray intensity and solar activity (sunspot numbers) during high amplitude days for the period 1991–1995. The high amplitude days with the time of maximum in the corotational/azimuthal direction do not indicate any significant correlation with solar activity. The diurnal amplitude significantly remains constant and high (0.5%) during the entire period. Our observations suggest that the direction of the anisotropy of high amplitude anisotropic wave train events contribute significantly to the short-term behavior of the cosmic ray diurnal anisotropy. The correlation coefficient is found to remain positive during solar activity maximum for all the high amplitude anisotropic wave train events.