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781.
E. Hilsenrath M. R. Schoeberl A. R. Douglass P. K. Bhartia J. Barnett R. Beer J. Waters M. Gunson L. Froidevaux J. Gille P. F. Levelt 《Space Science Reviews》2006,125(1-4):417-430
Aura, the last of the large EOS observatories, was launched on July~15, 2004. Aura is designed to make comprehensive stratospheric
and tropospheric composition measurements from its four instruments, HIRDLS, MLS, OMI and TES. These four instruments work
in synergy to provide data on ozone trends, air quality and climate change. The instruments observe in the nadir and limb
and provide the best horizontal and vertical resolution ever achieved from space. After over one year in orbit the instruments
are nearly operational and providing data to the scientific community. We summarize the mission, instruments, and initial
results and give examples of how Aura will provide continuity to earlier chemistry missions. 相似文献
782.
T. G. Forbes J. A. Linker J. Chen C. Cid J. Kóta M. A. Lee G. Mann Z. Mikić M. S. Potgieter J. M. Schmidt G. L. Siscoe R. Vainio S. K. Antiochos P. Riley 《Space Science Reviews》2006,123(1-3):251-302
This chapter provides an overview of current efforts in the theory and modeling of CMEs. Five key areas are discussed: (1) CME initiation; (2) CME evolution and propagation; (3) the structure of interplanetary CMEs derived from flux rope modeling; (4) CME shock formation in the inner corona; and (5) particle acceleration and transport at CME driven shocks. In the section on CME initiation three contemporary models are highlighted. Two of these focus on how energy stored in the coronal magnetic field can be released violently to drive CMEs. The third model assumes that CMEs can be directly driven by currents from below the photosphere. CMEs evolve considerably as they expand from the magnetically dominated lower corona into the advectively dominated solar wind. The section on evolution and propagation presents two approaches to the problem. One is primarily analytical and focuses on the key physical processes involved. The other is primarily numerical and illustrates the complexity of possible interactions between the CME and the ambient medium. The section on flux rope fitting reviews the accuracy and reliability of various methods. The section on shock formation considers the effect of the rapid decrease in the magnetic field and plasma density with height. Finally, in the section on particle acceleration and transport, some recent developments in the theory of diffusive particle acceleration at CME shocks are discussed. These include efforts to combine self-consistently the process of particle acceleration in the vicinity of the shock with the subsequent escape and transport of particles to distant regions. 相似文献
783.
A unique kinetic isotope effect has been found in the formation process of ozone molecules. Isotope enrichments of about 10%
above statistically expected values were first discovered in atmospheric isotopomers 49O3 and 50O3 and later in many other molecular combinations. Most recently the source of this effect was identified through measurement
of isotope-specific ozone formation rate coefficients which show a large variability of over 50%. Ozone molecule formation
is a complex process since different reaction channels contribute to a specific isotopomer. In addition, fast oxygen isotope
exchange reactions determine the abundance of atomic oxygen participating in ozone formation. The isotope enrichments observed
are both pressure and temperature-dependent and they decrease at pressures above 100 mbar and toward lower temperatures. Ozone
possesses not only one of the most unusual isotope anomalies, it also serves as a mediator by transferring heavy oxygen from
the O2 reservoir to other species. Stratospheric isotope composition of CO2 has been recently measured with high accuracy and a pronounced isotopic signature was found which shows that 17O is preferentially transferred from O3 into CO2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
784.
J. H. Waite Jr. W. S. Lewis W. T. Kasprzak V. G. Anicich B. P. Block T. E. Cravens G. G. Fletcher W.-H. Ip J. G. Luhmann R. L. Mcnutt H. B. Niemann J. K. Parejko J. E. Richards R. L. Thorpe E. M. Walter R. V. Yelle 《Space Science Reviews》2004,114(1-4):113-231
The Cassini Ion and Neutral Mass Spectrometer (INMS) investigation will determine the mass composition and number densities of neutral species and low-energy ions in key regions of the Saturn system. The primary focus of the INMS investigation is on the composition and structure of Titan’s upper atmosphere and its interaction with Saturn’s magnetospheric plasma. Of particular interest is the high-altitude region, between 900 and 1000 km, where the methane and nitrogen photochemistry is initiated that leads to the creation of complex hydrocarbons and nitriles that may eventually precipitate onto the moon’s surface to form hydrocarbon–nitrile lakes or oceans. The investigation is also focused on the neutral and plasma environments of Saturn’s ring system and icy moons and on the identification of positive ions and neutral species in Saturn’s inner magnetosphere. Measurement of material sputtered from the satellites and the rings by magnetospheric charged particle and micrometeorite bombardment is expected to provide information about the formation of the giant neutral cloud of water molecules and water products that surrounds Saturn out to a distance of ∼12 planetary radii and about the genesis and evolution of the rings.The INMS instrument consists of a closed ion source and an open ion source, various focusing lenses, an electrostatic quadrupole switching lens, a radio frequency quadrupole mass analyzer, two secondary electron multiplier detectors, and the associated supporting electronics and power supply systems. The INMS will be operated in three different modes: a closed source neutral mode, for the measurement of non-reactive neutrals such as N2 and CH4; an open source neutral mode, for reactive neutrals such as atomic nitrogen; and an open source ion mode, for positive ions with energies less than 100 eV. Instrument sensitivity is greatest in the first mode, because the ram pressure of the inflowing gas can be used to enhance the density of the sampled non-reactive neutrals in the closed source antechamber. In this mode, neutral species with concentrations on the order of ≥104 cm−3 will be detected (compared with ≥105 cm−3 in the open source neutral mode). For ions the detection threshold is on the order of 10−2 cm−3 at Titan relative velocity (6 km sec−1). The INMS instrument has a mass range of 1–99 Daltons and a mass resolutionM/ΔM of 100 at 10% of the mass peak height, which will allow detection of heavier hydrocarbon species and of possible cyclic hydrocarbons such as C6H6.The INMS instrument was built by a team of engineers and scientists working at NASA’s Goddard Space Flight Center (Planetary Atmospheres Laboratory) and the University of Michigan (Space Physics Research Laboratory). INMS development and fabrication were directed by Dr. Hasso B. Niemann (Goddard Space Flight Center). The instrument is operated by a Science Team, which is also responsible for data analysis and distribution. The INMS Science Team is led by Dr. J. Hunter Waite, Jr. (University of Michigan).This revised version was published online in July 2005 with a corrected cover date. 相似文献
785.
Radar: The Cassini Titan Radar Mapper 总被引:1,自引:0,他引:1
C. Elachi M. D. Allison L. Borgarelli P. Encrenaz E. Im M. A. Janssen W. T. K. Johnson R. L. Kirk R. D. Lorenz J. I. Lunine D. O. Muhleman S. J. Ostro G. Picardi F. Posa C. G. Rapley L. E. Roth R. Seu L. A. Soderblom S. Vetrella S. D. Wall C. A. Wood H. A. Zebker 《Space Science Reviews》2004,115(1-4):71-110
The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.RADAR Team LeaderThis revised version was published online in July 2005 with a corrected cover date. 相似文献
786.
787.
H. Nilsson R. Lundin K. Lundin S. Barabash H. Borg O. Norberg A. Fedorov J.-A Sauvaud H. Koskinen E. Kallio P. Riihelä J. L. Burch 《Space Science Reviews》2007,128(1-4):671-695
The Ion Composition Analyzer (ICA) is part of the Rosetta Plasma Consortium (RPC). ICA is designed to measure the three-dimensional
distribution function of positive ions in order to study the interaction between the solar wind and cometary particles. The
instrument has a mass resolution high enough to resolve the major species such as protons, helium, oxygen, molecular ions,
and heavy ions characteristic of dusty plasma regions. ICA consists of an electrostatic acceptance angle filter, an electrostatic
energy filter, and a magnetic momentum filter. Particles are detected using large diameter (100 mm) microchannel plates and
a two-dimensional anode system. ICA has its own processor for data reduction/compression and formatting. The energy range
of the instrument is from 25 eV to 40 keV and an angular field-of-view of 360° × 90° is achieved through electrostatic deflection
of incoming particles. 相似文献
788.
D. McComas F. Allegrini F. Bagenal P. Casey P. Delamere D. Demkee G. Dunn H. Elliott J. Hanley K. Johnson J. Langle G. Miller S. Pope M. Reno B. Rodriguez N. Schwadron P. Valek S. Weidner 《Space Science Reviews》2008,140(1-4):261-313
The Solar Wind Around Pluto (SWAP) instrument on New Horizons will measure the interaction between the solar wind and ions created by atmospheric loss from Pluto. These measurements provide a characterization of the total loss rate and allow us to examine the complex plasma interactions at Pluto for the first time. Constrained to fit within minimal resources, SWAP is optimized to make plasma-ion measurements at all rotation angles as the New Horizons spacecraft scans to image Pluto and Charon during the flyby. To meet these unique requirements, we combined a cylindrically symmetric retarding potential analyzer with small deflectors, a top-hat analyzer, and a redundant/coincidence detection scheme. This configuration allows for highly sensitive measurements and a controllable energy passband at all scan angles of the spacecraft. 相似文献
789.
The THEMIS Fluxgate Magnetometer 总被引:2,自引:0,他引:2
H. U. Auster K. H. Glassmeier W. Magnes O. Aydogar W. Baumjohann D. Constantinescu D. Fischer K. H. Fornacon E. Georgescu P. Harvey O. Hillenmaier R. Kroth M. Ludlam Y. Narita R. Nakamura K. Okrafka F. Plaschke I. Richter H. Schwarzl B. Stoll A. Valavanoglou M. Wiedemann 《Space Science Reviews》2008,141(1-4):235-264
790.
R. P. Lepping M. H. Acũna L. F. Burlaga W. M. Farrell J. A. Slavin K. H. Schatten F. Mariani N. F. Ness F. M. Neubauer Y. C. Whang J. B. Byrnes R. S. Kennon P. V. Panetta J. Scheifele E. M. Worley 《Space Science Reviews》1995,71(1-4):207-229
The magnetic field experiment on WIND will provide data for studies of a broad range of scales of structures and fluctuation characteristics of the interplanetary magnetic field throughout the mission, and, where appropriate, relate them to the statics and dynamics of the magnetosphere. The basic instrument of the Magnetic Field Investigation (MFI) is a boom-mounted dual triaxial fluxgate magnetometer and associated electronics. The dual configuration provides redundancy and also permits accurate removal of the dipolar portion of the spacecraft magnetic field. The instrument provides (1) near real-time data at nominally one vector per 92 s as key parameter data for broad dissemination, (2) rapid data at 10.9 vectors s–1 for standard analysis, and (3) occasionally, snapshot (SS) memory data and Fast Fourier Transform data (FFT), both based on 44 vectors s–1. These measurements will be precise (0.025%), accurate, ultra-sensitive (0.008 nT/step quantization), and where the sensor noise level is <0.006 nT r.m.s. for 0–10 Hz. The digital processing unit utilizes a 12-bit microprocessor controlled analogue-to-digital converter. The instrument features a very wide dynamic range of measurement capability, from ±4 nT up to ±65 536 nT per axis in eight discrete ranges. (The upper range permits complete testing in the Earth's field.) In the FTT mode power spectral density elements are transmitted to the ground as fast as once every 23 s (high rate), and 2.7 min of SS memory time series data, triggered automatically by pre-set command, requires typically about 5.1 hours for transmission. Standard data products are expected to be the following vector field averages: 0.0227-s (detail data from SS), 0.092 s (detail in standard mode), 3 s, 1 min, and 1 hour, in both GSE and GSM coordinates, as well as the FFT spectral elements. As has been our team's tradition, high instrument reliability is obtained by the use of fully redundant systems and extremely conservative designs. We plan studies of the solar wind: (1) as a collisionless plasma laboratory, at all time scales, macro, meso and micro, but concentrating on the kinetic scale, the highest time resolution of the instrument (=0.022 s), (2) as a consequence of solar energy and mass output, (3) as an external source of plasma that can couple mass, momentum, and energy to the Earth's magnetosphere, and (4) as it is modified as a consequence of its imbedded field interacting with the moon. Since the GEOTAIL Inboard Magnetometer (GIM), which is similar to the MFI instrument, was developed by members of our team, we provide a brief discussion of GIM related science objectives, along with MFI related science goals. 相似文献