Nighttime ionosphere–thermosphere coupling observed during an intense geomagnetic storm

The electrodynamics of the ionosphere in the tropical region presents various scientific aspects, which remain subject of intensive investigations and debates by the scientific community. During the year 2002, in a joint project between the Universidade do Vale do Paraíba (UNIVAP) and Universidade Luterana do Brasil (ULBRA), a chain of three Canadian Advanced Digital Ionosondes (CADIs) was established nearly along the geomagnetic meridian direction, for tropical ionospheric studies, such as, changes and response due to geomagnetic disturbances and thermosphere–ionosphere coupling and the generation and dynamics of ionospheric irregularities, in the Brazilian sector. The locations of the three ionosondes stations are São José dos Campos (23.2°S, 45.9°W, dip latitude 17.6°S – under the southern crest of equatorial ionospheric anomaly), Palmas (10.2°S, 48.2°W, dip latitude 5.5°S – near the magnetic equator) and Manaus (2.9°S, 60.0°W, dip latitude 6.4°N – between the geographic and geomagnetic dip equators). It should be pointed out that Palmas and Manaus are located on the opposite sides of the magnetic equator but both are south of the geographic equator. The three CADIs work in time-synchronized mode and obtain ionograms every 5 min. This configuration of the ionospheric sounding stations allowed us to study the F-region dynamics during geomagnetically disturbed period in the meridional direction. Just after the installation and testing of the three CADIs, on September 05, 2002 a coronal mass ejection (CME) left the Sun and about 2 days after the CME left the Sun, it reached the Earth’s magnetosphere and complex and multi step events took place during the period September 07–09. In the study we note that the equatorial stations located north (Manaus, dip latitude 6.4°N) and south (Palmas, dip latitude 5.5°S) of the dip equator presented significant F-layer height asymmetries during the storm main phase. In addition, the low-latitude station SJC (dip latitude 17.6°S) presented decrease in the F-layer densities (negative phase), whereas Palmas presented increase in the F-layer densities (positive phase) during the main phase. This was followed by positive phase at both the stations. During the first night of the recovery phase a strong formation and evolution of large-scale ionospheric irregularities (equatorial spread-F (ESF)) was observed, but on the second night of the recovery phase, there was strong and almost simultaneous sporadic E (Es) formation at all three stations. During the presence of Es, spread-F formation is not observed, indicating the suppression of spread-F, possibly by sporadic E.     

The Structure and Dynamics of the Corona—Heliosphere Connection

Determining how the heliospheric magnetic field and plasma connect to the Sun’s corona and photosphere is, perhaps, the central problem in solar and heliospheric physics. For much of the heliosphere, this connection appears to be well understood. It is now generally accepted that so-called coronal holes, which appear dark in X-rays and are predominantly unipolar at the photosphere, are the sources of quasi-steady wind that is generally fast, >500?km/s, but can sometimes be slow. However, the connection to the Sun of the slow, non-steady wind is far from understood and remains a major mystery. We review the existing theories for the sources of the non-steady wind and demonstrate that they have difficulty accounting for both the observed composition of the wind and its large angular extent. A?new theory is described in which this wind originates from the continuous opening and closing of narrow open field corridors in the corona, which give rise to a web of separatrices (the S-Web) in the heliosphere. Note that in this theory the corona—heliosphere connection is intrinsically dynamic, at least for this type of wind. Support for the S-Web model is derived from MHD solutions for the corona and wind during the time of the August 1, 2008 eclipse. Additionally, we perform fully dynamic numerical simulations of the corona and heliosphere in order to test the S-Web model as well as the interchange model proposed by Fisk and co-workers. We discuss the implications of our simulations for the competing theories and for understanding the corona—heliosphere connection, in general.     

On the Radial Evolution of Alfvénic Turbulence in the Solar Wind

The observations at different solar distances and latitudes, collected in the past three decades, and the results obtained from more and more sophisticated numerical simulations allowed us to reach a good understanding on many aspects of the complex phenomenon of solar wind turbulence. Moreover, new interesting insights in the theory of turbulence have been obtained, in the past decade, from the point of view that considers a turbulent flow as a complex system, where chaotic behavior and well-established scaling laws coexist. This review aims to provide a quick overview on the state of art in this research field with particular focus on local generation mechanisms.     

Partially Ionized Plasmas in Astrophysics

Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress.     

Deep and Shallow Solid-Earth Structures Reconstructed with Sequential Integrated Inversion (SII) of Seismic and Gravity Data

In this paper, the possibility of using simultaneously seismic and gravity data, for the reconstruction of solid-Earth structures, has been investigated through the use of an algorithm which allows joint efficient and reliable optimisation of compressional velocity and mass density parameters. We view the measured data as a realisation of a stochastic process generated by the physical parameters to be sought and we construct a “probability density function” which includes three kinds of information: information derived from gravity measurements; information derived from seismic travel time inversion and information on the physical correlation among density and velocity parameters. We show that combining data has a beneficial effect on the inversion since: it makes the problem more stable and as a consequence, providing that the quality of data is sufficiently high, enables more accurate and reliable reconstruction of the unknown parameters. In this context, we look forward the GOCE mission, which promises high spatial resolution (100–200 km) and accurate (1–2 mGals) gravity data. We show results obtained from data sets calculated for a lateral inhomogeneous earth synthetic model and from seismic and gravity field data analysed: — in the framework of TOMOVES (TOMOgraphy of Mt. VESuvius) experiment, an European project aiming at reconstructing the 3-D image of Mt. Vesuvius volcano and the crust underneath. using high resolution seismic tomography techniques and other geophysical methods; — for a profile inserted in a project aiming at reconstructing the crustal structure between Corsica and the Northern Appennines which crosses the Ligurian Sea and cuts the Ligurian Appennines W of La Spezia, extending up to Parma. This revised version was published online in August 2006 with corrections to the Cover Date.     

JIRAM, the image spectrometer in the near infrared on board the Juno mission to Jupiter

The Jovian InfraRed Auroral Mapper (JIRAM) has been accepted by NASA for inclusion in the New Frontiers mission "Juno," which will launch in August 2011. JIRAM will explore the dynamics and the chemistry of Jupiter's auroral regions by high-contrast imaging and spectroscopy. It will also analyze jovian hot spots to determine their vertical structure and infer possible mechanisms for their formation. JIRAM will sound the jovian meteorological layer to map moist convection and determine water abundance and other constituents at depths that correspond to several bars pressure. JIRAM is equipped with a single telescope that accommodates both an infrared camera and a spectrometer to facilitate a large observational flexibility in obtaining simultaneous images in the L and M bands with the spectral radiance over the central zone of the images. Moreover, JIRAM will be able to perform spectral imaging of the planet in the 2.0-5.0 microm interval of wavelengths with a spectral resolution better than 10 nm. Instrument design, modes, and observation strategy will be optimized for operations onboard a spinning satellite in polar orbit around Jupiter. The JIRAM heritage comes from Italian-made, visual-infrared imaging spectrometers dedicated to planetary exploration, such as VIMS-V on Cassini, VIRTIS on Rosetta and Venus Express, and VIR-MS on the Dawn mission.     

Reasoning about Depth and Motion from an Observer's Viewpoint

ABSTRACT

The goal of this paper is to present a logic-based formalism for representing knowledge about objects in space and their movements, and show how this knowledge could be built up from the viewpoint of an observer immersed in a dynamic world. In this paper space is represented using functions that extract attributes of depth, size and distance from snapshots of the world. These attributes compose a novel spatial reasoning system named Depth Profile Calculus (DPC). Transitions between qualitative relations involving these attributes are represented by an extension of this calculus called Dynamic Depth Profile Calculus (DDPC). We argue that knowledge about objects in the world could be built up via a process of abduction on DDPC relations.     

Unusual nighttime impulsive foF2 enhancements at low latitudes: Phenomenology and possible explanations

This paper is focused on unusual nighttime impulsive electron density enhancements that are rarely observed at low latitudes on a wide region of South America, under quiet and medium/high geomagnetic conditions. The phenomenon under investigation is very peculiar because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. The phenomenon was studied and analyzed using both the F2 layer critical frequency (foF2) and the virtual height of the base of the F region (h′F) values recorded at five ionospheric stations widely distributed in space, namely: Jicamarca (−12.0°, −76.8°, magnetic latitude −2.0°), Peru; Sao Luis (−2.6°, −44.2°, magnetic latitude +6.2°), Cachoeira Paulista (−22.4°, −44.6°, magnetic latitude −13.4°), and São José dos Campos (−23.2°, −45.9°, magnetic latitude −14.1°), Brazil; Tucumán (−26.9°, −65.4°, magnetic latitude −16.8°), Argentina. In a more restricted region over Tucumán, the phenomenon was also investigated by the total electron content (TEC) maps computed by using measurements from 12 GPS receivers. A detailed analysis of isoheight ionosonde plots suggests that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could play a significant role in causing the phenomenon both for quiet and for medium/high geomagnetic activity; in the latter case however a recharging of the fountain effect, due to electric fields penetrating from the magnetosphere, joins the TID propagation and plays an as much significant role in causing impulsive electron density enhancements.     

An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005

In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15–16 May 2005. The geomagnetic storm reached a minimum Dst of −263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Belém, Brasília, Presidente Prudente, and Porto Alegre, Brazil, during the period 14–17 May 2005. Also, we present ionospheric parameters h’F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas and São José dos Campos, Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14–15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.     

Radar Signal Propagation and Detection Through Ice

In this paper we describe the existing and planned radar measurements of the planetary bodies. The dielectric properties of water ice and other potential surface and subsurface materials are discussed, as well as their dependency on temperature and structure. We then evaluate the performance of subsurface sounding radars using these parameters. Finally we describe some laboratory technique to help interpret the radar data, presenting some results obtained using dielectric spectroscopy methods.