high-latitudes to low-latitudes. The significant coincidence between the structures of 630 nm band airglow and total electron content indicates that the perturbations take place in the bottomside of the ionospheric F region. Coherent echoes from the field-aligned irregularities were observed by the MU radar in the nights when the TID activity was high.

The nighttime traveling ionospheric disturbances (TIDs) and the F-region 3-m scale field-aligned irregularities were simultaneously observed with the MU radar and GEONET, a GPS network, during the FRONT (F-region Radio and Optical measurement of the Nighttime TID) campaign periods in May 1998 and August 1999. The vertical profile of electron density detected by the incoherent scatter observation of the MU radar clarified that ionized atmosphere on the bottomside of the ionospheric F-region was deeply modulated by TIDs, which would cause the variations of the 630 nm band airglow luminosity. The coherent echoes from the 3-m scale fieldaligned irregularities were detected also on the bottomside of the F-region in the nights when TIDs were intense in amplitude and the ionosphere was uplifted. Two-dimensional structures of the field-aligned irregularities detected by the multi-beam observation of the MU radar revealed that the 3-m scale irregularities formed band-like structures and traveled to the southwest in several nights. Their wave vector and traveling velocity were coincident with those of the nighttime TIDs that were simultaneously detected by the TEC observation of GEONET. The intense Doppler velocities of the coherent echoes indicate that the polarization electric field is generated inside the TIDs. We consider that the horizontal gradient of the electric conductivity associated by TIDs and the vertical gradient of the conductivity on the bottomside of the F-region ionosphere generates the 3-m scale irregularities through the gradient-drift instability process. The anti-correlation of the occurrence rate of the F-region field-aligned irregularities to the solar activity would be caused by the anti-correlation of the amplitude of TIDs and of the vertical gradient of the Pedersen conductivity.

This study investigates scaling behavior of quotation activities in the foreign exchange market. The power-law relationship between a mean of quotation activities and their standard deviation for each currency pair is found, and the dependence of the scaling exponent α on the time window ∆t is calculated. It is found that the scaling exponent fluctuates temporally in a range from 0.8 to 0.9 at ∆t = 1 [min], depending on observation days. The extraction between specific fluctuations and a common fluctuation from quotation activities is conducted. It is concluded that quotation activities in the foreign exchange market are not independently Poissonian, and that temporally or mutually correlated activities of quotations happen. We propose a stochastic model for the foreign exchange market based on a bipartite graph representation. The components' centrality on a bipartite graph is estimated from multiple time series and visualized on a currency pair network. Consequently, the scaling exponents can be used to quantify market participants' states based on information flows in the foreign exchange market. We found that as increasing the window length market participants are affected by exogenous field.

This article proposes mathematical methods to quantify states of market participants in the foreign exchange market (FX market) and conduct comprehensive analysis on behavior of market participants by means of high-frequency financial data. Based on econophysics tools and perspectives we study similarity measures for both rate movements and quotation activities among various currency pairs. We perform also clustering analysis on market states for observation days, and find scaling relationship between mean values of quotation activities and their standard deviations. Using these mathematical methods we can visualize states of the FX market comprehensively. Finally we conclude that states of market participants temporally vary due to both external and internal factors.Recent development of ICT will provide us with computational environment comparable to super-computers in 1990s on our desktop. Therefore we would be able to handle massive financial data for a purpose of personal use. In the near future both computational technology and successive supply of massive data about at University Library on March 20, 2015 http://ptps.oxfordjournals.org/ Downloaded from