Camera calibration by an integrating sphere for the auroral tomography observation

Auroral tomography is a technique to reconstruct three-dimensional (3 D) luminous structure from multiple two-dimensional (2D) images of aurora. The reconstructed auroral luminous structure can provide useful information such as altitude profiles and vortex configuration. In order to obtain the absolute volume emission rate of the aurora distribution, it is essential to have the absolute sensitivity calibration of imaging by formulating the relation between pixel values and absolute brightness of corresponding direction of each pixel. The relation between pixel value and brightness is formulated and calculated from the absolute sensitivity calibration. We took the flat-field images of the integrating sphere calibration standard at National Institute of Polar Research using one camera system, which was installed at Merasjarvi (one of the ALIS observing site, ALIS is the acronym of Auroral Large Imaging System, which is a multi-station ground-based optical observing network). National Institute of Polar Research, Japan and Swedish Institute of Space Physics in Kiruna, Sweden have carried out collaborative observations for auroral tomography under ALIS. The sensitivity calibration result is applied to the reconstruction of volume emission rate distribution from the tomographic images observed by ALIS on March 1, 1998

3-D extent of the main ionospheric trough - a case study

The EISCAT radar system has been used for the first time in a four-beam meridional mode. The FAST satellite and ALIS imaging system is used in conjunction to support the radar data, which was used to identify a main ionospheric trough. With this large latitude coverage the trough was passed in 21/2hours period. Its 3-dimensional structure is investigated and discussed. It is found that the shape is curved along the auroral oval, and that the trough is wider closer to the midnight sector. The position of the trough coincide rather well with various statistical models and this trough is found to be a typical one

2001), Geomagnetic substorms as perturbed self-organized critical dynamics of the magnetosphere

Abstract The e ect of self-organized criticality (SOC), known from the theory of complex nonlinear systems, is considered as an internal mechanism of geomagnetic uctuations accompanying the development of magnetospheric substorms. It is suggested that spatially localized current sheet instabilities, followed by magnetic reconnection in the magnetotail, can be considered as SOC avalanches, the superposition of which leads naturally to the 1=f ÿ power spectra (f -frequency, ÿ -numerical parameter) of geomagnetic activity. A running 2D avalanche model with controlled dissipation rate is proposed for numerical investigation of the multi-scale plasma sheet behavior in stationary and nonstationary states of the magnetosphere. Two basic types of perturbations have been studied, the ÿrst induced by an increase in the solar wind energy input rate and the second induced by a decrease in critical current density in the magnetotail. The intensity of large-scale perturbations in the model depends on accumulated energy level and internal dissipation in a manner similar to the dependence characteristic of real magnetospheric substorms. A spectral structure of model dynamics exposed to variations of solar wind parameters reveals distinctive features similar to natural geomagnetic uctuations, including a spectral break at 5 h separating frequency bands with di erent spectral slopes

Auroral tomography analysis of a folded arc observed at the ALIS-Japan multi-station campaign on March 26, 1995

Auroral tomography is a state-of-the-art method to retrieve three dimensional (3D) structure of luminous aurora from images taken simultaneously at multiple observation points. Imaging is basically monochromatic and altitude structures as well as horizontal vortex structures at particular wavelength are reconstructed. These are crucial for quantitative understanding of auroral formation and dynamical processes. In March 1995,the first multi-point international campaign between Sweden and Japan was carried out using three unmanned Swedish ALIS stations (Kiruna, Merasjarvi, Tjautjas) and two Japanese sites (Abisko, Nikkaluokta), separated by about 50km in Kiruna region. ALIS stands for the Auroral Large Imaging System which aims at capturing large-scale composite auroral images as well as optical tomographic imaging by a computer-controlled networking. In this paper, a description is given on the analysis of auroral tomography on the reconstruction of folded auroral arc observed at 2340 : 30 UT on March 26,1995. The images are taken for 1-5s integration at a green line of 557.7nm. Cameras were pointed to one of the preset common field of view, viz., a core region which is just overhead of Kiruna. Optical tomography relying on inversion analysis by the algebraic reconstruction technique has been carried out. The result indicates a fold structure of auroral arc with inferred altitude profile of photo-emission peaking at around 120km

Brominated flame retardants and organochlorines in the European environment using great tit eggs as a biomonitoring tool

Large-scale studies are essential to assess the emission patterns and spatial distribution of organohalogenated pollutants (OHPs) in the environment. Bird eggs have several advantages compared to other environmental media which have previously been used to map the distribution of OHPs. In this study, large-scale geographical variation in the occurrence of OHPs, such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs), was investigated throughout Europe using eggs of a terrestrial residential passerine species, the great tit (Parus major). Great tit eggs from 22 sampling sites, involving urban, rural and remote areas, in 14 European countries were collected and analysed (5–8 eggs per sampling site). The environmentally most important congeners/compounds of the analysed pollutants were detectable in all sampling locations. For PCBs, PBDEs and OCPs, no clear geographical contamination pattern was found. Sum PCB levels ranged from 143 ng/g lipid weight (lw) to 3660 ng/g lw. As expected, PCB concentrations were significantly higher in the sampled urban compared to the remote locations. However, the urban locations did not show significantly higher concentrations compared to the rural locations. Sum PBDEs ranged from 4.0 ng/g lw to 136 ng/g lw. PBDEs were significantly higher in the urbanized sampling locations compared to the other locations. The significant, positive correlation between PCB and PBDE concentrations suggests similar spatial exposure and/or mechanisms of accumulation. Significantly higher levels of OCPs (sum OCPs ranging from 191 ng/g lw to 7830 ng/g lw) were detected in rural sampling locations. Contamination profiles of PCBs, PBDEs and OCPs differed also among the sampling locations, which may be due to local usage and contamination sources. The higher variance among sampling locations for the PCBs and OCPs, suggests that local contamination sources are more important for the PCBs and OCPs compared to the PBDEs. To our knowledge, this is the first study in which bird eggs were used as a monitoring tool for OHPs on such a large geographical scale.Peer reviewe