Tatsuo Shirakawa

The Effect of Impurities on the Surface Melt of a Glacier in the Suntar-Khayata Mountain Range, Russian Siberia

We investigated characteristics of impurities and their impact on the ablation of Glacier No.31 in the Suntar-Khayata Mountain Range in Russian Siberia during summer 2014. Positive degree-day factors (PDDFs) obtained from 20 stake measurements distributed across the glacier’s ablation area varied from 3.00 to 8.55 mm w.e. K-1 day-1. The surface reflectivity measured with a spectrometer as a proxy for albedo, ranged from 0.09 to 0.62, and was negatively correlated with the PDDF, suggesting that glacier ablation is controlled by surface albedo on the studied glacier. Mass of total insoluble impurities on the ice surface varied from 0.1 to 45.2 g m-2 and was not correlated with surface reflectivity, suggesting that albedo is not directly conditioned by the mass of the impurities. Microscopy of impurities revealed that they comprised mineral particles, cryoconite granules, and ice algal cells filled with dark-reddish pigments (Ancylonema nordenskioldii). There was a significant negative correlation between surface reflectivity and algal biomass or organic matter, suggesting that the ice algae and their products are the most effective constituents in defining glacier surface albedo. Our results suggest that the melting of ice surface was enhanced by the growth of ice algae, which increased the melting rate 1.6 - 2.6 times greater than that of the impurity free bare-ice.

Online Estimation of Friction Coefficients of Winter Road Surfaces Using the Unscented Kalman Filter

An innovation to a previously proposed method for estimating friction coefficients of winter road surfaces was achieved through the introduction of a relatively new algorithm, the unscented Kalman filter. Its use, instead of a generic algorithm, made estimating friction coefficients in real time possible while keeping the core vehicular motion model unchanged. The problem of estimating such coefficients was too complicated to apply conventional feedback techniques, such as an extended Kalman filter, because of the presence of not only a nonlinear algebra equation but also a set of multiple differential equations. The unscented Kalman filter did not require any explicit function of state and observation equations in deriving Kalman gain. This paper describes the usefulness of this new filter in solving the problem and describes numerical experiments that validated the effectiveness of the proposed new method in terms of computational efficiencies. The friction coefficients estimated with the new technique were in fairly good accordance with those measured in the field.

Inverse Estimation of Friction Coefficients of Winter Road Surfaces: New Considerations of Lateral Movements and Angular Movements

This study is an extension of a method developed in a previous paper. The major concern remains one of how to estimate the friction coefficient of a winter road surface indirectly with the use of vehicular motion data. Similarly, in this paper, there is no change in the central structure of the argument; the friction coefficient is estimated as the solution to an optimization problem in which a tire model describing the interaction between tire and road surface is integrated into a genetic algorithm. The tire model differs from the previous method. The one-degree-of-freedom (1-DOF) model that formulated only longitudinal motion is replaced by a 3-DOF model, in which lateral and angular motions have also been taken into account. This revised method was applied to data measured at three sites: at intersections on a test track, on curved sections of the same test track, and at intersections on arterials in Sapporo, Japan. The friction coefficients estimated by the method were in relatively good agreement with those actually measured. Lateral and angular motions have contributed to the improvement.

Surface mass balance on Glacier No. 31 in the Suntar–Khayata Range, eastern Siberia, from 1951 to 2014

This study presents a 64-year (1951–2014) reconstruction of the surface mass balance of Glacier No. 31, located in the Suntar-Khayata Range of the eastern Siberia, where the ablation zone is characterized by the extensive dark ice surface. We use a temperature index-based glacier mass-balance model, which computes all major components of glacier mass budget and is forced by daily air temperature and precipitation from a nearby meteorological station. The glacier shows a mean annual mass balance of–0.35 m w.e.a–1 during the past 64 years, with an acceleration of–0.50 m w.e. a–1 during the recent years. A cumulative mass loss of the glacier is ~22.3 m w.e. over the study period, about 56% of which is observed during 1991–2014. In addition to the contribution of temperature rise and precipitation decrease to recent mass loss of the glacier, an experimental analysis, in which the clean and dark ice surfaces are respectively assumed to cover the entire ablation zone, indicates that dark ice surface, caused by insoluble impurities consisting of mineral dusts, cryoconite granules, and ice algae, plays a crucial role in the changing mass balance through enhancing melt rates in the ablation zone of the glacier.