Observations Of OI Research Articles

Far UV narrowband mirrors tuned at H Lyman α.

Imaging at H Ly-α (121.6 nm), among other spectral lines in the short far UV (FUV), is of high interest for astrophysics, solar, and atmosphere physics, since this spectral line is ubiquitously present in space observations. However, the lack of efficient narrowband coatings has mostly prevented such observations. Present and future space observatories like GLIDE and the IR/O/UV NASA concept, among other applications, can benefit from the development of efficient narrowband coatings at Ly-α. The current state of the art of narrowband FUV coatings lacks performance and stability for coatings that peak at wavelengths shorter than ∼135 nm. We report highly reflective AlF3/LaF3 narrowband mirrors at Ly-α prepared by thermal evaporation, with, to our knowledge, the highest reflectance (over 80%) of a narrowband multilayer at such a short wavelength obtained so far. We also report a remarkable reflectance after several months of storage in different environments, including relative humidity levels above 50%. For astrophysics targets in which Ly-α may mask a close spectral line, such as in the search for biomarkers, we present the first coating in the short FUV for imaging at the OI doublet (130.4 and 135.6 nm), with the additional requirement of rejecting the intense Ly-α, which might mask the OI observations. Additionally, we present coatings with the symmetric design, aimed to observe at Ly-α, and reject the strong OI geocoronal emission, that could be of interest for atmosphere observations.

Airglow imaging observations of some evolutionary aspects of equatorial plasma bubbles from Indian sector

The ground-based all sky imager (ASI) is an advanced optical technique, capable of measuring the strong F-region nightglow in OI 630.0 nm emission from atomic oxygen. This emission is used to study the large-scale F-region plasma irregularities; called as Equatorial Plasma Bubbles (EPBs) which often disturbs the communication and navigation systems over low latitudes. The observations of OI 630.0 nm nightglow emission have been carried out from low latitude station Kolhapur (16.8°N, 74.2°E, 10.6° dip. lat.) using ASI during moonless nights for the period of 2011 to 2015. We have analyzed images recorded by ASI during this period and found some interesting features of EPBs on few nights (08 cases). This paper reports the analysis and the dynamics of EPBs features such as bifurcation, merging and detachment. The bifurcation in EPBs occurs before mid-night and extends to couple of hours towards dawn. Also, the secondary structures are seen as evolving features on the eastern wall of EPBs. In one of the case, the EPBs are seen to merge with each other due to their opposite tilts. Also, some EPBs detach due to unequal drifts along the meridian indicating the presence of strong latitudinal gradient in zonal neutral winds or altitudinal shear in zonal plasma drift which might be responsible for this detachment. In some cases we note that the EPBs shrink. Some of these features support the previous findings and some are new which needs further detailed investigation.

On the Role of Thermospheric Winds and Sporadic E Layers in the Formation and Evolution of Electrified MSTIDs in Geomagnetic Conjugate Regions

AbstractThe electrified medium‐scale traveling ionospheric disturbances (EMSTIDs) occurring as geomagnetically conjugate features in the middle latitude F region ionosphere are studied using multi‐instrument observations. Airglow imaging of OI 630 nm emission over Sata, Japan, and Darwin, Australia, are used to identify the occurrence of EMSTIDs. Thermospheric wind measurements made with the Fabry‐Perot interferometer observations of OI 630 nm from Shigaraki, Japan, and Darwin, Australia, are used along with ionosonde observations over Yamagawa, Japan, and Darwin, Australia, to study the thermospheric and ionospheric characteristics. These are the first results from such multi‐instrument observations simultaneously made from geomagnetic conjugate locations. Our results show that the amplitudes of the EMSTIDs are often different between the hemispheres. Thermospheric meridional winds appear to control the EMSTID amplitudes in the respective hemisphere. However, EMSTIDs are generated only when there is significant sporadic E activity with foEs often reaching greater than 6 MHz and (foEs − fbEs) reaching above 5 MHz at least for a short duration occurred. Existence of strong sporadic E activity on one of the hemispheres is found to be sufficient enough for generation of EMSTIDs in the conjugate F regions. These results conclusively indicate the importance of sporadic E layers in the generation of EMSTIDs. Further, it shows the significance of interhemispheric coupling between the E and F region ionospheres in the formation of EMSTIDs while their amplitudes in the respective hemispheres appear to have control of thermospheric neutral winds in the same hemisphere.

An investigation of the ionospheric F region near the EIA crest in India using OI 777.4 and 630.0 nm nightglow observations

Abstract. Simultaneous observations of OI 777.4 and OI 630.0 nm nightglow emissions were carried at a low-latitude station, Allahabad (25.5° N, 81.9° E; geomag. lat. ∼ 16.30° N), located near the crest of the Appleton anomaly in India during September–December 2009. This report attempts to study the F region of ionosphere using airglow-derived parameters. Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using Constellation Observing System for Meteorology, Ionosphere, and Climate/Formosa Satellite Mission 3 (COSMIC/FORMOSAT-3) electron density profiles. Next, the electron density maximum (Nm) and its height (hmF2) of the F layer have been derived from the information of two calibrated intensities. Nocturnal variation of Nm showed the signatures of the retreat of the equatorial ionization anomaly (EIA) and the midnight temperature maximum (MTM) phenomenon that are usually observed in the equatorial and low-latitude ionosphere. Signatures of gravity waves with time periods in the range of 0.7–3.0 h were also seen in Nm and hmF2 variations. Sample Nm and hmF2 maps have also been generated to show the usefulness of this technique in studying ionospheric processes.

Study of equatorial plasma bubbles using all sky imager and scintillation technique from Kolhapur station: a case study

The nightglow observations of OI 630.0 nm emission carried out from low latitude station Kolhapur using All Sky Imager (ASI) with $140^{\circ}$ field of view (FOV) for the month of April 2011 are used. The images were processed to study the field aligned irregularities often called as equatorial plasma bubbles (EPBs). The present study focuses on the occurrence of scintillation during the traversal of EPBs over ionospheric pierce point (IPP). Here we dealt with the depletion level (depth) of the EPB structures and its effect on VHF signals. We compared VHF scintillation data with airglow intensities at Ionospheric pierce point (IPP) from the same location and found that the largely depleted EPBs make stronger scintillation. From previous literature, it is believed that the small scale structures are present near the steeper walls of EPBs which often degrades the communication, the analysis presented in this paper confirms this belief.

Nature of shocks revealed by SOFIA OI observations in the Cepheus E protostellar outflow

Context.Protostellar jets and outflows are key features of the star-formation process, and primary processes of the feedback of young stars on the interstellar medium. Understanding the underlying shocks is necessary to explain how jet and outflow systems are launched, and to quantify their chemical and energetic impacts on the surrounding medium.Aims.We performed a high-spectral resolution study of the [OI]63μmemission in the outflow of the intermediate-mass Class 0 protostar Cep E-mm. The goal is to determine the structure of the outflow, to constrain the chemical conditions in the various components, and to understand the nature of the underlying shocks, thus probing the origin of the mass-loss phenomenon.Methods.We present observations of the O i3P1→3P2, OH between2Π1/2J= 3/2 andJ= 1/2 at 1837.8 GHz, and CO (16–15) lines with the GREAT receiver onboard SOFIA towards three positions in the Cep E protostellar outflow: Cep E-mm (the driving protostar), Cep E-BI (in the southern lobe), and Cep E-BII (the terminal position in the southern lobe).Results.The CO (16–15) line is detected at all three positions. The [OI]63μmline is detected in Cep E-BI and BII, whereas the OH line is not detected. In Cep E-BII, we identify three kinematical components in O iand CO. These were already detected in CO transitions and relate to spatial components: the jet, the HH377 terminal bow-shock, and the outflow cavity. We measure line temperature and line integrated intensity ratios for all components. The O icolumn density is higher in the outflow cavity than in the jet, which itself is higher than in the terminal shock. The terminal shock is the region where the abundance ratio of O ito CO is the lowest (about 0.2), whereas the jet component is atomic (N(O i)/N(CO) ~ 2.7). In the jet, we compare the [OI]63μmobservations with shock models that successfully fit the integrated intensity of 10 CO lines. We find that these models most likely do not fit the [OI]63μmdata.Conclusions.The high intensity of O iemission points towards the propagation of additional dissociative or alternative FUV-irradiated shocks, where the illumination comes from the shock itself. A picture emerges from the sample of low-to-high mass protostellar outflows, where similar observations have been performed, with the effects of illumination increasing with the mass of the protostar. These findings need confirmation with more observational constraints and a larger sample.

Some new insights of the characteristics of equatorial plasma bubbles obtained from Indian region

All-sky imaging observations of OI 630.0nm airglow were carried out in campaign mode from Panhala (16.8°N, 74.1°E geographic; 11.1°N dip latitude), India, during January to March 2008. On 14 of 37 nights, equatorial plasma bubbles were observed. The drift speeds were observed to decrease with time in concurrence with the previous results. The tilts were mostly westward while on rare occasions the plasma bubbles tilted eastwards. The drifts were found to be relatively lesser on disturbed nights while the tilts appear to be marginally larger. The interdepletion distances (or bubble spacings) also showed a decreasing trend with time till midnight indicating that the bubbles approach each other with the passage of time. Such a behavior is not reported earlier and it seems to have important implications for understanding the time evolution of plasma bubbles. On occasions, the bubbles occurred in groups. An ionosonde operating over Indian dip equatorial site Tirunelveli (1.1°N dip latitude) was used to study the variations in the base height of the ionosphere during the plasma bubble observations. The ionosonde measurements indicate lack of significant pre-reversal enhancement (PRE) during geomagnetic quiet days in which the bubbles were observed.

Shrinking equatorial plasma bubbles

AbstractThe formation of equatorial plasma bubbles (EPBs) associated with spread F irregularities are fairly common phenomenon in the postsunset equatorial ionosphere. These bubbles grow as a result of eastward polarization electric field resulting in upward E × B drift over the dip equator. As they grow they are also mapped to low latitudes along magnetic field lines. The EPBs are often observed as airglow depletions in the images of OI 630 nm emission. On occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all‐sky images obtained from low latitudes. Herein, we present interesting observations of decrease in the latitudinal extent of the EPBs corresponding to a reduction in their apex altitudes over the dip equator. Such observations indicate that these bubbles not only grow but also shrink on occasions. These are the first observations of shrinking EPBs. The observations discussed in this work are based on all‐sky airglow imaging observations of OI 630.0 nm emission made from Panhala (11.1°N dip latitude). In addition, ionosonde observations made from dip equatorial site Tirunelveli (1.1°N dip latitude) are used to understand the phenomenon better. The analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts. When the EPBs shrink, they might decay before sunrise hours.

Occurrence of equatorial plasma bubbles over Kolhapur

This paper reports the nightglow observations of OI 630.0nm emissions, made by using all sky imager operating at low latitude station Kolhapur (16.8°N, 74.2°E and dip lat. 10.6°N) during high sunspot number years of 24th solar cycle. The images are analyzed to study the nocturnal, seasonal and solar activity dependence occurrence of plasma bubbles. We observed EPBs in images regularly during a limited period 19:30 to 02:30LT and reach maximum probability of occurrence at 22:30LT. The observation pattern of EPBs shows nearly no occurrence during the month of May and it maximizes during the period October–April. The equinox and solstice seasonal variations in the occurrence of plasma bubbles show nearly equal and large differences, respectively, between years of 2010–11 and 2011–12.

A study on the night time equatorward movement of ionization anomaly using thermospheric airglow imaging technique

In the night time low latitude ionosphere, the equatorial ionization anomaly (EIA) crest move towards the equator as a result of change in the direction of the zonal electric field from eastward to westward. This is referred to as reverse plasma fountain. On some nights, imaging observations of OI 630.0nm thermospheric nightglow taken from low latitude Indian station Panhala (16.8°N, 74.1°E; 11.1°N dip latitude) during deep solar minimum period revealed southward movement of a broad enhanced airglow intensity region that is aligned along east–west direction. This could be seen in the meridional keograms and is interpreted as the equatorward passage of the EIA crest. The studies that concentrate on the night time evolution of EIA with the help of airglow observations are sparse. In addition to the equatorward motion, the thickness of the crest region decreased as a result of recombination. This reduction in thickness is pronounced in the earlier part of the night and brings about an apparent drift that is added to the true equatorward drift of the EIA crest. In this work, we describe a method to measure the equatorward drift speed of the EIA crest from airglow imaging observations. The method includes the estimation and correction for the apparent drift caused by recombination. The results show that drift speed varies widely between 28m/s and 89m/s (~100km/h to ~315km/h) with an average speed of 52m/s (188km/h). A part of the variability might be due to variations in thermospheric meridional wind. The drifts observed during magnetically disturbed days were found to be relatively smaller than that on quiet days.

Observations of OI 557.7 nm nightglow at Kolhapur (17° N), India

Abstract. Ground-based nightglow observations of the atomic oxygen green line at 557.7 nm have been carried out at a low latitude station Kolhapur (17° N), India, during November 2003–April 2004 and December 2004–May 2005. The nocturnal behaviour of OI 557.7 nm intensity and a comparative study with simultaneous OH Meinel band temperature measurements has been presented. OI 557.7 nm intensity and OH temperature variations covary on many occasions. It was found that an 8 h tide characterizes the variation of intensity and temperature on most nights, and especially during the month of January. This is the first report of prolonged measurements of OI 557.7 nm emission from India.

Unusual optical observations of OI greenline during a geospace event on 1 February 2008

[1] We herein report the first observations of an unusual phenomenon recorded by an all-sky airglow imager from the low-latitude site Panhala (16.8°N, 74.1°E, geographic; 8.2°N geomagnetic), on the night of 1 February 2008, during the main phase of a moderate geomagnetic storm. The observations of OI 557.7 nm emission reveal discrete, transient, filamentary structures referred to as “streaks.” No such features were seen in the OI 630.0 nm emission and the mesospheric sodium and hydroxyl emissions. Here we speculate on possible mechanisms for generation of such structures, though we cannot conclude firmly that any one of them was responsible for the observed features. This is a puzzling observation made from very low geomagnetic latitude during the main phase of a moderate recurrent geomagnetic storm in the declining phase of solar cycle. In spite of the limitations in identifying the mechanism or mechanisms responsible for this striking observation, it is felt that understanding of processes driving such unusual and rare events will substantiate our knowledge on the mysterious coupling processes occurring in the equatorial upper atmosphere.

Evidence for OI 630.0 nm dayglow variations over low latitudes during onset of a substorm

Observations of OI 630.0 nm dayglow intensity from Mt. Abu (magnetic latitude (MLAT): 16.2°N; magnetic longitude (MLONG): 148°E) at two different directions corresponding to two different magnetic latitudes (MLATZenith: 16.2°N and MLAT20°Elevation: 22.2°N) revealed nearly simultaneous intensity enhancements on 2 February 2002 (Ap = 19) during 0554–0635 universal time (UT) (1124–1205 Indian Standard Time (IST); IST = UT + 5.5 h). This feature is found to be absent on a typical control day (3 February 2002; Ap = 4). The dayglow enhancements were concomitant with enhancements in the E‐region zonal electric field inferred from deviations of the northward component of magnetic field (ΔH) obtained from a meridional chain of magnetometers encompassing the dip equatorial and low‐latitude regions. Simultaneous positive bay signatures in ΔH were also recorded at all stations along the 210° magnetic meridian (MM) in the afternoon sector (∼1454–1535 magnetic local time). The changes in the solar wind parameters including the dawn‐to‐dusk component of IEF and ram pressure are found negligible during 0554–0635 UT. However, the variations in the auroral electrojet and ring current indices indicate the presence of a substorm during 0554–0635 UT. Sudden enhancements in the energetic particle fluxes measured by the Los Alamos National Laboratory (LANL) 1991–080 satellite at geosynchronous altitude provide evidence for the onset of the expansion phase of a magnetospheric substorm. Therefore, the present investigation adduces the response of 630.0 nm dayglow intensities over low latitudes corresponding to the onset of the expansion phase of an auroral/magnetospheric substorm.

Oxygen lines in solar granulation

Context: There is a lively debate about the solar oxygen abundance and the role of 3D models in its recent downward revision. The models have been tested using high resolution solar atlases. Further testing can be done using centre-to-limb variations. Aims: Using high quality observations of oxygen lines across the solar surface we seek to test if the 3D and 1D models reproduce their observed centre-to-limb variation (CLV). In particular we seek to assess whether the 3D model is appropriate to derive the solar oxygen abundance. Methods: We use our recent observations of OI 777 nm, OI 615.81 nm, [OI] 630.03 nm and nine lines of other elements for five viewing angles 0.2<mu<1 of the quiet solar disk. We compare them with the predicted line profiles from the 3D and 1D models computed using the most up-to-date line formation codes, line data and allowing for departures of LTE. The CLV of the OI 777 nm lines is also used to obtain an empirical correction for the poorly known efficiency of the inelastic collisions with H. Results: The 3D model generally reproduces the CLV observations of the lines very well, particularly the oxygen lines. From the OI 777 nm lines we find that the classical Drawin recipe slightly overestimates H collisions. The limb observations of the OI 615.82 nm line allow us to identify a previously unknown contribution of molecules for this line, prevalent at the solar limb. A detailed treatment of the [OI] 630.03 nm line shows that the 3D modeling provides an excellent agreement with the observations. The derived oxygen abundances with the 3D model are 8.68 (OI 777 nm), 8.66 ([OI] 630.03 nm) and 8.62 (OI 615.82 nm). Conclusions: These additional tests have reinforced the trustworthiness of the 3D model and line formation for abundance analyses.

Not a search in vein: novel stimulus for vascular dysfunction after simulated microgravity

cardiovascular adjustments to real or simulated microgravity appear to be appropriate adaptations as long as the microgravity environment is maintained. It is when the subject returns to 1 G that problems with these adjustments arise. Rat models simulating microgravity use head-down tilt (HDT),

Observations of Atmospheric Gravity Waves in Airglow Over Adelaide

利用澳大利亚Adelaide(34.5°S,138.5°E)地区7年(1995-2001年)的OH和OI气辉观测数据,以及同地区中频雷达所测背景风场数据,通过最大熵谱分析方法,统计分析了该地区大尺度重力波的传播特性.结果表明,(1)在中层顶气辉观测区,利用OH气辉探测到48个重力波事件,利用OI气辉探测到29个重力波事件,这些重力波的周期和水平相速度分别集中在68 min和36 m/s左右,具有东南向的优势传播方向,平均仰角为8°～10°,接近水平方向传播;(2)通过OH气辉和OI气辉观测到了同一个重力波事件,并根据两个高度上观测到的扰动相位差判断该重力波为上行波.

First Ground Observations of OI5577 Green Line Emission over the Taiwan Area

ABSTRACT 1 Institute of Space Science, National Central University, Chung-Li, Taiwan, ROC 2 Department of Physics, National Central University, Chung-Li, Taiwan, ROC * Corresponding author address: Prof. Lin-Ni Hau, Institute of Space Science, National CentralUniversity, Chung-Li, Taiwan, ROC; E-mail: lnhau@jupiter.ss.ncu.edu.tw doi: 10.3319/TAO.2007.18.4.843(AA) Worldwide ground observations of upper atmospheric airglow withparticular emphasis on the OI 557.7 and 630 nm emissions have been con-ducted since 1960s. This study reports the first ground observations ofOI 557.7 nm green line emission over the Taiwan area. For comparison, thebackground continuum at 530 nm was also measured by the same system.The experiments were conducted during the period of Aug - Dec, 2004 atvarious locations in Taiwan using a self-developed photometer instrument.Daily height integrated intensity of the night-time green line emission mayvary in the range of 80 - 210 Rayleighs and twilight enhancement is alsoidentified. The observational results may serve as a useful reference forfollow-up sounding rocket measurements of OI 557.7 nm airglow emissionover the Taiwan area.(Key words: Airglow, OI 5577, Taiwan area, Ground observation)1. INTRODUCTION

CII] emission and star formation in the spiral arms of M 31

The CII 158 microns line is the most important coolant of the interstellar medium in galaxies but substantial variations are seen from object to object. The main source of the emission at a galactic scale is still poorly understood. Previous studies of the CII emission in galaxies have a resolution of several kpc or more so the observed emission is an average of different ISM components. The aim of this work is to study, for the first time, the CII emission at the scale of a spiral arm. We want to investigate the origin of this line and its use as a tracer of star formation. We present CII and OI observations of a segment of a spiral arm of M~31 using the Infrared Space Observatory. The CII emission is compared with tracers of neutral gas (CO, HI) and star formation (H\alpha, Spitzer 24 mu.) The similarity of the CII emission with the Ha and 24 mu images is striking when smoothed to the same resolution, whereas the correlation with the neutral gas is much weaker. The CII cooling rate per H atom increases dramatically from ~2.7e-26 ergs/s/atom in the border of the map to ~ 1.4e-25 ergs/s/atom in the regions of star formation. The CII/FIR(42-122) ratio is almost constant at 2%, a factor 3 higher than typically quoted. However, we do not believe that M~31 is unusual. Rather, the whole-galaxy fluxes used for the comparisons include the central regions where the CII/FIR ratio is known to be lower and the resolved observations neither isolate a spiral arm nor include data as far out in the galactic disk as the observations presented here. A fit to published PDR models yields a plausible average solution of G_0~100 and n~3000 for the PDR emission in the regions of star formation in the arm of M31.

Thermospheric gravity wave modes over low and equatorial latitudes during daytime

The small‐scale intensity fluctuations obtained from 56 days of observations of OI 630.0 nm dayglow emission intensities from Mount Abu (24.6°N, 73.7°E, dip latitude 19.09°N), a station under the crest of equatorial ionization anomaly (EIA), have been subjected to harmonic analysis to unravel different modes of atmospheric gravity waves (AGW). Similar analysis is carried out for 26 days of dayglow intensity data recorded from Waltair (17.7°N, 83.3°E, dip latitude 10.09°N), a low‐latitude station, and for 8 days of available data from Thumba (8.68°N, 77.0°E, dip latitude 0.45°N), an equatorial station with the same objective. The analysis reveals the relative dominance (“preferred mode”) of 0.5–1.0 hour periodic component over Mount Abu, 2.0–2.5 hour periodic component over Waltair, and 1.0–1.5 hour component over Thumba during geomagnetically quiet periods. Qualitative arguments have been propounded to explain the differences in the preferred modes over these places, and it is suggested that the source responsible for the preferred modes may lie in the lower atmosphere. Further, the analysis also indicates the presence of additional preferred modes over low latitudes during geomagnetically disturbed periods.

Occurrence characteristics of medium‐scale gravity waves observed in OH and OI nightglow over Adelaide (34.5°S, 138.5°E)

This paper presents a 7 year climatology describing medium‐scale gravity waves observed in the menopause region covering the years from 1995 to 2001. The data comes from the OI and OH airglow observations of the three‐field photometer employed at the University of Adelaide's Buckland Park, Australia (34.5°S, 138.5°E). About 1300 gravity wave events (AGW) are identified during the years 1995–2001. These AGW events usually persist for between 40 min and 4 hours. The magnitudes range from 1% to 14% of the background intensities and peak at 2% for OI observations and at 3% for OH observations. The observed periods range from 10 to 30 min, and the horizontal phase speeds range from 20 to 250 m s−1, with dominant wave scales of 17 min, 70 m s−1 for OI observations and 20 min, 40 m s−1 for OH observations. The intrinsic parameters are obtained by using medium‐frequency (MF) wind data observed at the same place. The occurrence frequency of AGW events peaks at 13 min, 40 m s−1 for both OI and OH observations. The occurrence rate of gravity waves has a major peak in summer and a minor peak in winter. There is an obvious dominating southeastward direction for gravity waves, with azimuths of 160° in summer and 130° in winter. Studies for gravity waves observed in various locations show a similar tendency of propagating meridionally toward the summer pole. This implies that the tendency of propagating toward the summer pole may be a global trend for medium‐scale gravity waves observed in the mesopause region. During summer, gravity waves propagate against winds measured by MF radar in their dominating direction. Using the ray tracing method, we found that the seasonal variation of winds limits the access of gravity waves to the observation height through reflection and critical coupling, which is one of the causes leading to the seasonal behavior of gravity waves observed over Adelaide.