An investigation of the solar cycle impact on the lower thermosphere O(S) nightglow emission as observed by WINDII/UARS

The yearly variation of the integrated emission rate of the O(¹S) nightglow in the lower thermosphere is studied and the solar cycle impact is examined from the observations of the Wind Imaging Interferometer (WINDII) operated on the Upper Atmosphere Research Satellite (UARS). More than 300,000 volume emission rate profiles of the O(¹S) nightglow observed by WINDII for 40°S–40°N latitudes during November 1991–August 1997 over half of a solar cycle are utilized. These profiles are vertically integrated for the altitude range of 80–100 km and the equivalent column integrated emission rates are then zonally averaged for bins with 10° latitude and 3 month intervals. It is found that for each latitude the O(¹S) nightglow emission rate appears to increase with increasing solar F10.7 cm flux, following a linear relationship. This characterizes the solar cycle impact on the O(¹S) nightglow, while the solar influence is modulated by a seasonal variation. Based on these variations, an empirical formula is derived for predicting the three-month averages of the O(¹S) nightglow integrated emission rate. The standard error of the estimated values from the formula is smaller than 30 Rayleigh.     

Variations of the O(D) and O(S) peak volume emission rates without direct solar effects

Airglow volume emission rates of the O(¹D) red line at 630.0 nm and the O(¹S) green line at 557.7 nm were measured by the Wind Imaging Interferometer (WINDII) on the Upper Atmospheric Research Satellite (UARS) during 1991–1997. Focus of this study is on the peak volume emission rates of the two airglows after removing the direct solar effect, which are referred to as the ‘dark’ peak emission rates. The main results are as follows. For the red line emission, at low and mid-latitudes the daytime variation does not have a clear pattern except an enhancement at dusk; during nighttime there is an enhancement in the equatorial region at 20–03 h, which has a semiannual variation with maxima at equinoxes; at solstices the daytime O(¹D) dark emission rate is stronger in winter than in summer. For both the green line E-and F-layers the distribution of the dark peak volume emission rate is symmetric about noon in all seasons, symmetric about the equator at equinoxes, and stronger in summer than in winter. The O(¹S) E-layer is profoundly affected by tides. For the first time the diurnal and semidiurnal amplitudes for the emission rates are derived using 24-h zero-sun data. The amplitude of the diurnal tide can be as large as 20% of the mean peak volume emission rate, and has maxima at the equator and about 40°N/S, and minima at about 20°N/S. The daily diurnal maximum is at noon at the equator but at midnight at 40°N/S. There is a clear semiannual variation of the diurnal amplitude in the equatorial region with maxima at equinoxes. The amplitude of the semidiurnal tide is mostly less than 10% of the mean peak volume emission rate with maximum amplitudes at noon and midnight. There is an annual variation of the semidiurnal amplitude at mid-latitudes peaking in summer. Aurorae appear in all three emission layers day and night. The green aurorae are brighter than the red aurorae, and the green E-layer aurorae are 2–3 times stronger than the F-layer aurorae. The green aurora has a clear midday gap in the F-layer and an afternoon gap in the E-layer. The red aurorae are particularly strong in the so-called cusp region at equinoxes.     

Multi-year high latitude mesospheric neutral wind observations using a Fabry–Perot interferometer

From 1995 to 1999, a Fabry–Perot Interferometer was stationed at Resolute Bay, Canada (75°N, 95°W) to measure the mesospheric neutral winds in the polar cap from the OH nightglow emission during winter seasons. A 12-h wave is the most prominent feature in the neutral winds. The wave amplitude has large day-to-day variations and inter-annual variability, whereas the phase of the wave appears to be largely consistent for year to year. Small phase shift from early winter to later winter was noticed during most of the seasons when early winter data were available. The 12-h wave showed stronger variability during the 1995/1996 winter season, which may be related to nonlinear interactions with planetary waves. Large negative zonal winds were observed during stratospheric sudden warming events.     

An updated model of atomic oxygen redline dayglow emission

A comprehensive model is developed using the updated rate coefficients and transition probabilities to study the redline dayglow emission of atomic oxygen. The solar EUV fluxes are obtained from the Solar Irradiance Platform (SIP), and incorporated into the model successfully. All possible production and loss mechanisms of O(¹D) are considered in the model. The neutral number densities and temperature are adopted from the NRLMSISE-00 model. The ion and electron densities, and electron temperature are adopted from the IRI-07 model. The model results are validated with the help of measurements as provided by the Wind Imaging Interferometer (WINDII) on board Upper Atmosphere Research Satellite (UARS). The present results are found in better agreement with the measurements in comparison with the earlier model. The measured volume emission rate profiles are reproduced quite well by the present model. The model results show that the updated rate coefficients and transition probabilities are quite consistent and may be used in the aeronomical studies.     

WAMDII — A wide angle Michelson Doppler imaging interferometer for spacelab

A CCD imaging device has been designed which combines a spatial resolution of 0.1° with a spectral resolving power of 10⁵, sufficient to measure Doppler shifts and line widths of individual atmospheric emission lines. It will be flown aboard Spacelab and will be used to study neutral winds and temperatures as functions of height, latitude and time of day.     

IUE observations of cool stars

A summary of IUE results concerning late-type stars is presented. Observations show that high-temperature outer atmospheres, as indicated by N V, C IV emission at T ≈ 10⁵K, are generally present only in high-gravity (log g ? 2) stars. Objects with high-temperature emission tend not to exhibit cool circumstellar shells, and vice versa, although there are several transition objects, the hybrid atmosphere stars, which combine C IV emission with cool winds. Ultraviolet emission from stellar transition regions correlates well with chromospheric and X-ray emission. Transition-region line ratios indicate that many stars have differential emission measure distributions similar to the Sun's. Ultraviolet observations also give indications of important dynamical effects in low-gravity stars. Density diagnostics indicate extended chromospheres for some red giants and supergiants. In addition, the large widths of lines of high temperature ions in several luminous stars indicate supersonic motions.     

Observation of Mercury’s sodium tail using Fabry–Perot Interferometer

We observed sodium emission from Mercury’s atmosphere using a Fabry–Perot Interferometer at Haleakala Observatory on June 14, 2006. The Fabry–Perot Interferometer was used as a wavelength-tunable filter. The spectra of the surface reflection were subtracted from the observed spectra because sodium emission is contaminated by the surface reflection of Mercury. The image obtained in our observation shows the sodium exosphere extended to the anti-solar direction. The lifetime of a sodium atom was estimated to be 1.6 × 10⁴ to 1.9 × 10⁵ s with an error by a factor of 3–4.     

Large-scale circulation of atomic oxygen in the upper mesosphere and lower thermosphere

The variability of the atomic oxygen green line airglow at 557.7 nm, originating from the O(¹S) level, has a long history of observation. Only recently, global observations of the oxygen airglow, interpreted with the help of global circulation models have provided some understanding. Satellite observations of winds and temperatures clearly demonstrate the dynamical influence of tides on the daily variations. Both annual and semi-annual components of the variation have been identified as occurring over the course of the year. From the large-scale circulation of the atmosphere one expects downwelling in the winter at high latitudes, causing enhanced atomic oxygen and enhanced airglow while the opposite is expected in summer. In the present investigation a search is made for this large-scale signature using data from the WIND Imaging Interferometer on the Upper Atmosphere Research Satellite, model results from the Thermosphere–Ionosphere–Mesosphere-Electrodynamics-Global Circulation Model, and earlier published results. A well-defined semi-annual variation of emission rate is found in the tropics, apparently the result of the semi-annual variation of the diurnal tide. Annual and semi-annual patterns are found at mid-latitudes, in satellite and model data, while ground-based observations detect only an annual variation, with a maximum in the autumn. At still higher latitudes the fall peak persists, but with a deep depletion of atomic oxygen in the springtime; this appears to be the signature of the large-scale circulation.     

Validation of 9.6 μm ozone transmittances by spectral radiance satellite measurements

The accuracy of atmospheric transmittances is important in remote sensing applications. In this paper the atmospheric ozone transmittances in the 1042 cm^?1 ozone band were calculated for different temperatures and ozone profiles using line-by-line integration method. The absorption line parameters were taken from McClatchey's line parameter compilation. The transmittances were used to derive the main characteristics of the atmospheric ozone profile and the total ozone amount from radiance measurements of Meteor satellites.     

基于Fabry-Perot干涉仪气辉观测数据反演中性风速方法比较

利用半径法、完整傅里叶级数描述法和非线性回归法分别对安装在河北省境内国家天文台兴隆园区（40.2°N,117.4°E）的Fabry-Perot干涉仪（FPI）获得的地基中高层大气气辉观测数据进行风速反演.反演结果表明,半径法、完整傅里叶级数描述法和非线性回归法均能很好地反演风速,在误差范围内反演结果存在很好的一致性.相对于半径法和完整傅里叶级数描述法,非线性回归方法更完整地利用了观测数据信息,反演结果可信度较高.      

红外窗口材料的热辐射特性测量方法

飞行器在大气层内高超声速飞行时,高温窗口迅速成为气动热辐射效应的主要因素,气动热辐射效应会降低甚至破坏红外(IR)探测系统的性能.通过分析红外探测窗口热辐射传输特性,提出一种红外窗口材料的热辐射特性测量方法,并测量了应用于中波红外(MWIR)探测系统的某蓝宝石红外窗口材料在高温状态下的透过率和自身辐射等热辐射数据.结果表明:在100~350℃范围内,0.1mm厚蓝宝石材料薄层在中波红外3.7~4.8μm波段的热辐射特性与温度近似呈3次方关系,温度越高,蓝宝石透过率越小,自身辐射越大.强烈的自身辐射极易导致红外探测器局部饱和现象,对探测系统造成的影响比透过率引起的信噪比(SNR)下降要大得多.      

The oriented scintillation spectrometer experiment for the gamma-ray observatory

The Oriented Scintillation Spectrometer Experiment (OSSE) for the Gamma Ray Observatory is described. OSSE uses four identical NaI(T1)-CsI(Na) phoswich detectors to provide gamma-ray line and continuum detection capability in the 0.05–10 MeV energy range. Additional gamma-ray and neutron detection capability is achieved above 10 MeV. Each detector has a CsI annular shield and a tungsten alloy collimator which define a 5° × 11° (FWHM) field-of-view. The detectors have independent, single-axis orientation systems which permit offset pointing to provide source-background subtraction. The sensitivity for line gamma rays in the 0.05–10 MeV region will be 2–3 × 10^?5 photons/cm²-s for a 10⁶-second observation period. The several modes of data acquisition and the emphases for the planned observational program are discussed.     

Measurement of stratospheric trace constituent distributions from balloon-borne far infrared observations

Far infrared limb thermal emission spectra obtained from balloon borne measurements made as a part of the Balloon Intercomparison Campaign (BIC) have been analyzed for retrieval of stratospheric trace constituent distributions. The measurements were made with a high resolution Michelson Interferometer and covered the 15–180 cm⁻¹ spectral range with an unapodized spectral resolution of 0.0033 cm⁻¹. The retrieved vertical profiles of O₃, H₂O, HDO, HCN, CO and isotopes of O₃ are presented. The results are compared with the BIC measurements for O₃ and H₂O made from the same balloon gondola and with other published data. A comparison of the simultaneously retrieved profiles for several gases with the published data shows good agreement and indicates the validity of the far infrared data, the retrieval techniques and the accuracy of the inferred profiles.     

Oxygen line mapping of SN 1006 with Suzaku

SN 1006 is one of the supernova remnants (SNRs) with relatively low-temperature electrons, considering the young age of just 1000 years. We carried out SN 1006 mapping observations with the X-ray Imaging Spectrometers (XIS) and the Hard X-ray Detector (HXD) onboard Suzaku, the fifth Japanese X-ray satellite. Thanks to the excellent spectral resolution of XIS in the soft X-ray band, H-like and He-like oxygen emission lines were clearly detected, and we could make a map of the line intensity, and as well as a flux and the photon index of nonthermal component. We found that these parameters have spatial dependences from region to region in the SNR; the north region is bright in nonthermal, while dim in thermal; the east region is bright in both nonthermal and thermal; the inner region shows dim nonthermal and bright thermal emission. The photon index is the smallest in the north region.     

Mesospheric doppler wind measurements from Aura Microwave Limb Sounder (MLS)

This paper describes a microwave limb technique for measuring Doppler wind in the Earth’s mesosphere. The research algorithm has been applied to Aura Microwave Limb Sounder (MLS) 118.75 GHz measurements where the O₂ Zeeman lines are resolved by a digital autocorrelation spectrometer. A precision of ∼17 m/s for the line-of-sight (LOS) wind is achieved at 80–92 km, which corresponds to radiometric noise during 1/6 s integration time. The LOS winds from Aura MLS are mostly in the meridional direction at low- and mid-latitudes with vertical resolution of ∼8 km. This microwave Doppler technique has potential to obtain useful winds down to ∼40 km of the Earth’s atmosphere if measurements from other MLS frequencies (near H₂O, O₃, and CO lines) are used. Initial analyses show that the MLS winds from the 118.75 GHz measurements agree well with the TIDI (Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer) winds for the perturbations induced by a strong quasi 2-day wave (QTDW) in January 2005. Time series of MLS winds reveal many interesting climatological and planetary wave features, including the diurnal, semidiurnal tides, and the QTDW. Interactions between the tides and the QTDW are clearly evident, indicating possible large tidal structural changes after the QTDW events dissipate.     

星载FPI探测低热层温度的研究

80～350km高度区域的大气温度与风场探测研究对于认识全球性空间动力学和日地耦合机制具有重要科学意义.法布里-珀罗干涉仪(FPI)能够通过分析接收光的干涉环反演计算出一定高度大气层的风场和温度.近年来,中国利用多种地基探测设备对中高层大气进行了观测研究,对于温度反演和星载探测技术的研究开始起步.本文基于系统传输函数和发射谱线函数的卷积,讨论了利用FPI探测高空大气温度反演计算的原理;分析了星载FPI探测的方法,根据星载FPI探测与地基探测的不同点,仿真了星载探测干涉图;结合中国观测技术现况及空间探测需要,讨论了发展星载空间环境探测仪的可行性.      

Simultaneous dual wavelength observations of an impulsive microwave burst using the V.L.A.

Simultaneous observations of a microwave burst at 2 and 6 cm wavelengths were carried out with the Very Large Array (VLA). The 6 cm burst source is located close to a magnetic neutral line, presumably near the top of a flaring loop, while the 2 cm emission originates from the footpoints of the loop. It is concluded that the 6 cm emission is dominated by gyrosynchrotron radiation of the thermal electrons in the bulk heated plasma at a temperature of ～ 4 × 10⁷ K, while the 2 cm emission is due to nonthermal particles released and accelerated during the flare process. From the observed low degree of polarization and the lack of the 2 cm source cospatiality with the 6 cm source a magnetic field of 200–350 G and δ ? 4 are estimated in the flare energy release site. A DC electric field flare model is invoked to explain the long delay between the peaks at the two wavelengths. From the delay, the strength of the electric field is estimated to be 0.2–4 μ statvolt cm^?1 in the flaring region.     

The compatability of cloud tracked winds from the United States,European, and Japanese geostationary satellites

Overlap of coverage of the five geostationary satellites has allowed an intercomparison of the FGGE cloud tracked winds. No attempt was made during FGGE to standardize the cloud tracking techniques. In spite of this potential for differences between data sets, the compatability of the various cloud wind data sets was generally quite good. The vector magnitude differences between nearly co-located vectors showed similar cumulative frequency statistics for all data producers. A study of systematic biases which could affect a global wind analysis of any given synoptic period showed that image alignment errors caused less than 2 m s^?1 bias for all data producers except the NESS high level winds which had an average bias of slightly greater than 3 m s^?1. This appears to be caused by the manual alignment of images in the movie loops. Height bias studies showed the Japanese winds to be higher than other data producers by as much as 100 mb for both the high and low levels winds. Height biases appear to be caused by the differences in cloud wind height assignment procedures.     

Wolf–Rayet optically thick winds with Alfvén waves

The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.     

Relation between solar wind velocity and properties of its source region

Different kinds of coronal holes are sources of different kind of solar winds. A successful solar wind acceleration model should be able to explain all those solar winds. For the modeling it is important to find a universal relation between the solar wind physical parameters, such as velocity, and coronal physical parameters such as magnetic field energy. To clarify the physical parameters which control the solar wind velocity, we have studied the relation between solar wind velocity and properties of its source region such as photospheric/coronal magnetic field and the size of each coronal hole during the solar minimum. The solar wind velocity structures were derived by using interplanetary scintillation tomography obtained at Solar-Terrestrial Environment Laboratory, Japan. Potential magnetic fields were calculated to identify the source region of the solar wind. HeI 1083 nm absorption line maps obtained at Kitt Peak National Solar Observatory were used to identify coronal holes. As a result, we found a relation during solar minimum between the solar wind velocity and the coronal magnetic condition which is applicable to different kind of solar winds from different kind of coronal holes.