Initial results of Syowa MF radar observations in Antarctica

Observations of the neutral atmosphere from the mesosphere to the lower thermosphere were performed using the MF radar system that was installed at Syowa Station (69°S, 39°E), Antarctica in April 1999. The radar is equipped with four antennas and independent receivers and is able to conduct interferometric observations, such as meteor echo observations, in addition to observations based on conventional spaced antenna techniques. Observational parameters are carefully designed so that the same raw data can be processed using various analysis techniques, including correlation analyses, meteor echo analysis and electron density analysis. The radar equipment specifications and preliminary results of wind observations are presented

Quantitative ring current model: Overview and comparison with observations

This paper describes a new quantitative ring current model that solves temporal evolution of the ion distribution in the magnetosphere by tracing the ion drift motion. The plasma sheet density as a boundary condition of our model depends on the solar wind density. The tracing is performed under a dipole magnetic field and a time-dependent convection electric field depending on the solar wind parameters. The ions are lost by two processes; the charge exchange with neutral hydrogen and the convection outflow due to encounter with the dayside magnetopause. Magnetic disturbance is directly derived from the calculated current density with the three- dimensional Biot-Savart integral; this is a new simulation method. Using this model, we have examined the physical mechanism of the storm-time ring current responding to the interplanetary parameters. We simulated three successive storms which occurred in April 1997 as a case study. The following subjects concerned with dynamics of the ring current were examined; (1) the causes of the ring current development, (2) the electric current distribution, (3) the effects of the charge exchange loss, (4) the energy composition of the plasma pressure, (5) the response time lag of the plasma sheet density variation to the solar wind density and (6) the diamagnetic effect

A new all-sky optics for aurora and airglow imaging

This report reviews the initial performance of a new all-sky imager (ASI-2) that utilizes commercial lenses and a high-sensitivity cooled CCD camera. The use of a commercial fish-eye lens as an optical front end and a standard camera lens as a final imaging lens makes the ASI-2 optics smaller, lighter and less expensive than the original ASI optics, with minimal degradation of optical performance. Despite the lower production cost, the speed of the ASI-2 lens system is not markedly slower than the ASI optics, with speed slightly faster than half the speed of ASI. Although the motors driving bandpass filter switching and focusing have been removed to reduce weight, the narrow bandpass filter can be exchanged manually to select specific emission lines, and focusing can be performed manually using a micrometer. The optical performance of the ASI-2 optics is measured and shown to be sufficient for auroral and airglow imaging. The ASI-2 optics is currently installed at Syowa Station, Antarctica, and is involved in observations during the 2004 polar night season

A new meridian imaging spectrogarph for the auroral spectroscopy

Spectroscopic and monochromatic imaging observations of emissions in the upper atmosphere are mutually complementary. A meridian imaging auroral spectrograph (ASG) that can measure a spectrum in the visible region along a meridian has been developed for research on the auroral physics and the polar upper-atmosphere dynamics. Combination of a fast optical system inherited from a monochromatic all-sky imager, a grism as a dispersive element, and a cooled CCD camera has enabled a wide field-of-view of 180° along a meridian, spectral coverage of 420-730 nm, spectral resolution of 1.5-2.0 nm, and high sensitivity to be obtained. The absolute sensitivity over a full-image field was calibrated using a National Institute of Standards and Technology (NIST) traceable integrating sphere and determined to be 0.06 cts/s/R at a wavelength of 560 nm at the zenith. The ASG was installed at Longyearbyen in March 2000, and routine operation was started in the 2000/2001 winter season. An example of an auroral spectral image is presented in this report to demonstrate the performance of the ASG

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

Calibration of CRL all-sky imagers using an integrating sphere

As part of an international collaboration with the Geophysical Institute of the University of Alaska, we have developed two all-sky imagers (CRL-ASIs). A sensitivity calibration of the CRL-ASIs was performed using an integrating sphere belonging to the National Institute of Polar Research (NIPR). The two-dimensional sensitivities of the CRL-ASIs produced symmetrical distributions. Using this sensitivity data, we converted airglow/aurora images into two-dimensional distributions of absolute intensity. The sensitivity of the CRL-ASIs was measured for 13 wavelengths between 427.8 nm and 866.5 nm, and the relationship between the sensitivity and the wavelength was investigated for both imagers. The peak sensitivity occurred at about 550 nm

Evolution of the ring current energy during May 2-4, 1998 magnetic storm

We study the evolution of the ring current energy density during May 2-4, 1998 storm event as measured by Polar CAMMICE/MICS instrument and modelled by proton tracing in the guiding center approximation. Particle data from Polar shows that during the storm main phase protons with medium energies (20-80 keV) contribute more to the total ring current energy than the high energy protons (80-200 keV) whereas during the recovery phase high energies dominate. We trace protons with arbitrary pitch angles numerically in the guiding center approximation taking into account charge-exchange losses. Tracing is performed in the large-scale and smaller-scale time-dependent magnetic and electric field models. We model the substorm activity by several electric field pulses at times of the substorm onsets. It is shown that impulsive electric fields associated with substorms are effective in the proton transport and energization to higher energies more than 100 keV in the storm time ring current

Event-oriented modelling of magnetic fields and currents during storms

We model the magnetospheric magnetic field during two storms, moderate and intense, using the event-oriented modelling technique which includes the representations of the magnetic field arising from the various magnetospheric current systems. The model free parameters are specified for each time step separately using observations from GOES 8, 9, and 10, Polar, Interball and Geotail satellites and Dst measurements. It is shown that the ring current is most important during intense storms, whereas the near Earth tail currents contribute more to the Dst index than the ring current during moderate storms