Cometary Deuterium

Deuterium fractionations in cometary ices provide important clues to the origin and evolution of comets. Mass spectrometers aboard spaceprobe Giotto revealed the first accurate D/H ratios in the water of Comet 1P/Halley. Ground-based observations of HDO in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp), the detection of DCN in Comet Hale-Bopp, and upper limits for several other D-bearing molecules complement our limited sample of D/H measurements. On the basis of this data set all Oort cloud comets seem to exhibit a similar ratio in H₂O, enriched by about a factor of two relative to terrestrial water and approximately one order of magnitude relative to the protosolar value. Oort cloud comets, and by inference also classical short-period comets derived from the Kuiper Belt cannot be the only source for the Earth's oceans. The cometary O/C ratio and dynamical reasons make it difficult to defend an early influx of icy planetesimals from the Jupiter zone to the early Earth. D/H measurements of OH groups in phyllosilicate rich meteorites suggest a mixture of cometary water and water adsorbed from the nebula by the rocky grains that formed the bulk of the Earth may be responsible for the terrestrial D/H. The D/H ratio in cometary HCN is 7 times higher than the value in cometary H₂O. Species-dependent D-fractionations occur at low temperatures and low gas densities via ion-molecule or grain-surface reactions and cannot be explained by a pure solar nebula chemistry. It is plausible that cometary volatiles preserved the interstellar D fractionation. The observed D abundances set a lower limit to the formation temperature of (30 ± 10) K. Similar numbers can be derived from the ortho-to-para ratio in cometary water, from the absence of neon in cometary ices and the presence of S₂. Noble gases on Earth and Mars, and the relative abundance of cometary hydrocarbons place the comet formation temperature near 50 K. So far all cometary D/H measurements refer to bulk compositions, and it is conceivable that significant departures from the mean value could occur at the grain-size level. Strong isotope effects as a result of coma chemistry can be excluded for molecules H₂O and HCN. A comparison of the cometary ratio with values found in the atmospheres of the outer planets is consistent with the long-held idea that the gas planets formed around icy cores with a high cometary D/H ratio and subsequently accumulated significant amounts of H₂ from the solar nebula with a low protosolar D/H. This revised version was published online in June 2006 with corrections to the Cover Date.     

二元进气道非均匀超音来流试验研究

介绍一种二元进气道模型在非均匀超音来流中的初步研究结果。试验在DLR小型超音风洞上进行。为造成非均匀来流条件,试验中将部分或全部试验段顶壁附面层引入进气道模型。结果表明,进气斜板产生的头激波与来流附面层相互作用的性状在不同的附面层隔道下变化极大。随隔道高度增加,激波附面层相互作用距离L起初亦增加,当全部附面层被排移后,L大幅度下降。与均匀来流试验结果相比较,当来流顶壁附面层全部被进气道吞入时,该进气道总压恢复σ及质量流率m分别降低18％及15％(M_∞=2.19),同时出口面总压畸变大幅度增加。文章分析了原因及对进气道性能影响的强度。     

Measurements of the radiation quality factor Q at aviation altitudes during solar minimum (2006–2008)

In radiation protection, the Q-factor has been defined to describe the biological effectiveness of the energy deposition or absorbed dose to humans in the mixed radiation fields at aviation altitudes. This particular radiation field is generated by the interactions of primary cosmic particles with the atoms of the constituents of the Earth’s atmosphere. Thus the intensity, characterized by the ambient dose equivalent rate H∗(10), depends on the flight altitude and the energy spectra of the particles, mainly protons and alpha particles, impinging on the atmosphere. These charged cosmic projectiles are deflected both by the interplanetary and the Earth’s magnetic field such that the corresponding energy spectra are modulated by these fields. The solar minimum is a time period of particular interest since the interplanetary magnetic field is weakest within the 11-year solar cycle and the dose rates at aviation altitudes reach their maximum due to the reduced shielding of galactic cosmic radiation. For this reason, the German Aerospace Center (DLR) performed repeated dosimetric on-board measurements in cooperation with several German airlines during the past solar minimum from March 2006 to August 2008. The Q-factors measured with a TEPC range from 1.98 at the equator to 2.60 in the polar region.     

Inferring Nighttime Ionospheric Parameters with the Far Ultraviolet Imager Onboard the Ionospheric Connection Explorer

The Ionospheric Connection Explorer (ICON) Far Ultraviolet (FUV) imager, ICON FUV, will measure altitude profiles of OI 135.6 nm emissions to infer nighttime ionospheric parameters. Accurate estimation of the ionospheric state requires the development of a comprehensive radiative transfer model from first principles to quantify the effects of physical processes on the production and transport of the 135.6 nm photons in the ionosphere including the mutual neutralization contribution as well as the effect of resonant scattering by atomic oxygen and pure absorption by oxygen molecules. This forward model is then used in conjunction with a constrained optimization algorithm to invert the anticipated ICON FUV line-of-sight integrated measurements. In this paper, we describe the connection between ICON FUV measurements and the nighttime ionosphere, along with the approach to inverting the measured emission profiles to derive the associated O⁺ profiles from 150–450 km in the nighttime ionosphere that directly reflect the electron density in the F-region of the ionosphere.     

Ultraviolet spectroscopy and remote sensing of the upper atmosphere

The Earth's ultraviolet airglow contains fundamental diagnostic information about the state of its upper atmosphere and ionosphere. Our understanding of the excitation and emission processes which are responsible for the airglow has undergone dramatic evolution from the earliest days of space research through the past several years during which a wealth of new information has been published from high-resolution spectroscopy and imaging experiments. This review of the field begins with an overview of the phenomenology: how the Earth looks in the ultraviolet. Next the basic processes leading to excitation of atomic and molecular energy states are discussed. These concepts are developed from first principles and applied to selected examples of day and night airglow; a detailed review of radiation transport theory is included. This is followed by a comprehensive examination of the current status of knowledge of individual emission features seen in the airglow, in which atomic physics issues as well as relevant atmospheric observations of major and minor neutral and ionic constituents are addressed. The use of airglow features as remote sensing observables is then examined for the purpose of selecting those species most useful as diagnostics of the state of the thermosphere and ionosphere. Imaging of the plasmasphere and magnetosphere is also briefly considered. A summary of upcoming UV remote sensing missions is provided.     

二维反向涡与翼型的相互作用及压力波形成的试验研究

在Ｍ＝０．８～０．８５，Ｒ＿ｅ＝１．４ｘｌ０￣５条件下，研究了环量为６～２４ｍ￣２／ｓ的二维反向旋转单涡与翼剖面为矩形、ＮＡＣＡ００１２、１１．４２°尖楔的二维翼型在下半平面的相互作用。风洞试验发现，当这样的单涡与尖楔作用时，观察到有强度为３０００Ｐａ的压力波形成并逆流前传。波的形成与反向涡诱导速度的变化有关，它引起楔前缘上表面气流的突然分离及分离区的突然消失，局部的瞬时高压区产生了前传压力波。在目前的试验条件下，能观察到压力波时翼型上表面压力源区的升压速率ｄＣ＿ｐ／ｄｔ约为４０００（１／ｓ），ΔＣ＿ｐ约为１．４。同样试验条件下，反向单涡与矩形、ＮＡＣＡ００１２互作用，未观察到有明显的压力波形成。     

Daytime O/N<Subscript>2</Subscript> Retrieval Algorithm for the Ionospheric Connection Explorer (ICON)

The NASA Ionospheric Connection Explorer Far-Ultraviolet spectrometer, ICON FUV, will measure altitude profiles of the daytime far-ultraviolet (FUV) OI 135.6 nm and N₂ Lyman-Birge-Hopfield (LBH) band emissions that are used to determine thermospheric density profiles and state parameters related to thermospheric composition; specifically the thermospheric column O/N₂ ratio (symbolized as \(\Sigma\)O/N₂). This paper describes the algorithm concept that has been adapted and updated from one previously applied with success to limb data from the Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission. We also describe the requirements that are imposed on the ICON FUV to measure \(\Sigma\)O/N₂ over any 500-km sample in daytime with a precision of better than 8.7%. We present results from orbit-simulation testing that demonstrates that the ICON FUV and our thermospheric composition retrieval algorithm can meet these requirements and provide the measurements necessary to address ICON science objectives.