Observations of non-migrating tides and ionospheric perturbations of O(D) airglow by ISUAL instrument

In this paper, we present the spatial variations of O(¹D) airglow observed by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) instrument on board the FORMOSAT-2 satellite. With a CCD camera and a 630 nm filter, ISUAL can measure global atmospheric emissions lying between the heights of 80 and 300 km. In days of 3–6 September 2008 and 25–27 February 2009, ISUAL has measured the emissions of O(¹D) airglow with results showing strong longitudinal peak-3 and peak-4 structures. The Lomb-Scargle analyses for these two cases show periods of longitudes of 120° and 90° supporting the DE2 and DE3 non-migrating tides. The 630 nm emissions are enhanced in equatorial regions and are lying along the equator. Over Africa its intensity can sometimes increase up to 80% relative to other longitudes. The perturbation is so strong that non-migrating tides are erased. A case of bimodal distribution with strong emissions at latitudes in equator and mid-latitude in geographic coordinates was observed.     

Initial phase of mid-latitude aurora during strong geomagnetic storms

Analysing the initial mid-latitude aurora phase during strong geomagnetic storms we found that the initial phase of the mid-latitude aurorae observed at 630 nm emission during the strong geomagnetic storms on March 24, 1991, April 6, 2000, October 30 and November 20, 2003 is characterized by a short (∼1 h) wave-like disturbance. This disturbance corresponds to the beginning of main phase of the magnetic storms. The marked effect of the mid-latitude aurorae is analyzed using data on magnetosphere and ionosphere conditions in observation periods. The features of the dynamics of the 630 nm emission intensity and its connection with the dynamics of magnetospheric–ionospheric structures are considered. Possible excitation mechanisms of the atomic oxygen emission (630 nm) during these disturbances are discussed.     

Possible evidence for small-scale wave seeding of equatorial plasma bubbles

The small-scale wave-like structure (SSWS) of F region bottomside plasma density was proposed to be an important seeding for equatorial plasma bubble (EPB) generation, and employed in theoretical simulations of EPBs in recent years. The seeding role of SSWS, however, is waiting to be demonstrated by observation. Here we present two cases of SSWS and EPB observed by the Fuke all-sky airglow imager (19.3°N, 109.1°E; dip latitude 14.3°N). For each case, the results show that two large-scale wave-like structures (LSWSs) initially appeared around sunset in the longitude regions separated by 3–4°, but EPB irregularities were only generated in one of the LSWSs where SSWSs were seen riding on LSWS. For the other LSWS, no SSWS and EPB irregularities were seen. Considering that the two LSWSs were situated closely in longitude where the amplitude of pre-reversal enhancement of background eastward electric field should be similar, the observation that EPB was only generated in the longitude with simultaneous LSWS and SSWS could provide supporting evidence for SSWS seeding of EPB.     

Development and verification of an innovative photomultiplier calibration system with a 10-fold increase in photometer resolution

In this study, we construct a photomultiplier calibration system. This calibration system can help scientists measuring and establishing the characteristic curve of the photon count versus light intensity. The system uses an innovative 10-fold optical attenuator to enable an optical power meter to calibrate photomultiplier tubes which have the resolution being much greater than that of the optical power meter. A simulation is firstly conducted to validate the feasibility of the system, and then the system construction, including optical design, circuit design, and software algorithm, is realized. The simulation generally agrees with measurement data of the constructed system, which are further used to establish the characteristic curve of the photon count versus light intensity.     

Effect of severe geomagnetic storm conditions on atomic oxygen greenline dayglow emission in mesosphere

Severe geomagnetic storms and their effects on the 557.7 nm dayglow emission are studied in mesosphere. This study is primarily based on photochemical model with the necessary input obtained from a combination of experimental observations and empirical models. The model results are presented for a low latitude station Tirunelveli (8.7°N, 77.8°E). The volume emission rates are calculated using MSISE-90 and NRLMSISE-00 neutral atmospheric models. A comparison is made between the results obtained from these two models. A positive correlation amongst volume emission rate (VER), O, O₂ number densities and Dst index has been found. The present results indicate that the variation in emission rate is more for MSISE-90 than in NRLMSISE-00 model. The maximum depletion in the VER of greenline dayglow emission is found to be about 30% at 96 km during the main phase of the one of the geomagnetic storms investigated in the case of MSISE-90 (which is strongest with Dst index −216 nT). The O₂ density decreases about 22% at 96 km during the main phase of the same geomagnetic storm.The NRLSMSISE-00 model does not show any appreciable change in the number density of O during any of the two events. The present study also shows that the altitude of peak emission rate is unaffected by the geomagnetic storms. The effect of geomagnetic storm on the greenline nightglow emission has also been studied. It is found that almost no correlation can be established between the Dst index and variations in the volume emission rates using the NRLMSISE-00 neutral model atmosphere. However, a positive correlation is found in the case of MSISE-90 and the maximum depletion in the case of nightglow is about 40% for one of the storms. The present study shows that there are significant differences between the results obtained using MSISE-90 and NRLMSISE-00.     

Adelaide地区大气重力波的气辉观测

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.