Coronal Mass Ejections Observed at the Total Solar Eclipse on 13 November 2012     

Yoichiro Hanaoka  Jun Nakazawa  Osamu Ohgoe  Yoshiaki Sakai  Kazuo Shiota 《Solar physics》2014,289(7):2587-2599

White-light observations of the total solar eclipse on 13 November 2012 were made at two sites, where the totality occurred 35 min apart. The structure of the corona from the solar limb to a couple of solar radii was observed with a wide dynamic range and a high signal-to-noise ratio. An ongoing coronal mass ejection (CME) and a pre-CME loop structure just before the eruption were observed in the height range between 1?–?2 R_⊙. The source region of CMEs was revealed to be in this height range, where the material and the magnetic field of CMEs were located before the eruption. This height range includes the gap between the extreme ultraviolet observations of the low corona and the spaceborne white-light observations of the high corona, but the eclipse observation shows that this height range is essential for the study of CME initiation. The eclipse observation is basically just a snapshot of CMEs, but it indicates the importance of a continuous coverage of CME observations in this height range in the future.  相似文献   

Hydrometeorological behaviour of pine and larch forests in eastern Siberia     

Shuko Hamada  Takeshi Ohta  Tetsuya Hiyama  Takashi Kuwada  Atsuhiro Takahashi  Trofim C. Maximov 《水文研究》2004,18(1):23-39

Seasonal changes in the water and energy exchanges over a pine forest in eastern Siberia were investigated and compared with published data from a nearby larch forest. Continuous observations (April to August 2000) were made of the eddy‐correlation sensible heat flux and latent heat flux above the canopy. The energy balance was almost closed, although the sum of the turbulent fluxes sometimes exceeded the available energy flux (R_n ? G) when the latent heat flux was large; this was related to the wind direction. We examined the seasonal variation in energy balance components at this site. The seasonal variation and magnitude of the sensible heat flux (H) was similar to that of the latent heat flux (λE), with maximum values occurring in mid‐June. Consequently, the Bowen ratio was around 1·0 on many days during the study period. On some clear days just after rainfall, λE was very large and the sum of H and λE exceeded R_n ? G. The evapotranspiration rate above the dry canopy from May to August was 2·2 mm day^?1. The contributions of understory evapotranspiration (E_u) and overstory transpiration (E_o) to the evapotranspiration of the entire ecosystem (E_t) were both from 25 to 50% throughout the period analysed. These results suggest that E_u plays a very important role in the water cycle at this site. From snowmelt through the tree growth season (23 April to 19 August 2000), the total incoming water, comprised of the sum of precipitation and the water equivalent of the snow at the beginning of the melt season, was 228 mm. Total evapotranspiration from the forest, including interception loss and evaporation from the soil when the canopy was wet, was 208–254 mm. The difference between the incoming and outgoing amounts in the water balance was from +20 to ?26 mm. The water and energy exchanges of the pine and larch forest differed in that λE and H increased slowly in the pine forest, whereas λE increased rapidly in the larch forest and H decreased sharply after the melting season. Consequently, the shape of the Bowen ratio curves at the two sites differed over the period analysed, as a result of the differences in the species in each forest and in soil thawing. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A theory of filament eruptions before the impulsive phase of solar flares     

Jun-Ichi Sakai  Shinji Koide 《Solar physics》1992,137(2):293-306

We present a theory of filament eruption before the impulsive phase of solar flares. We show that the upward motion of the magnetic X-point tracing the filament eruption begins several minutes before the impulsive phase of the flare, where the explosive magnetic reconnection starts at the X-point magnetic field configuration located under the filament. No change occurs in the character of the motion of the X-point during the onset of the explosive magnetic reconnection. The upward speed of the X-point is about 110 km s^-1 at the onset of the impulsive phase. We give an important condition leading to filament eruptions, which relate to the state of the current sheet under the filament, where the magnetic energy can be released.  相似文献   

Dynamical model of prominence formation and oscillation,I     

J. Sakai  A. Colin  E. Priest 《Solar physics》1987,114(2):253-271

We investigate a dynamical model of prominence formation in a current sheet at the boundary between two regions of opposite magnetic polarity. Coupled nonlinear equations describing the temporal compression and condensation of plasma in the current sheet are set up as a natural extension of the usual equations for current sheet collapse (Imshennik and Syrovatskii, 1967). It is shown that under certain conditions the current sheet undergoes a nonlinear oscillation during the compression. The thermal instability with cooling is driven by a density enhancement produced during the current sheet formation stage.  相似文献   

Radiative Heat Transfer and Hydrostatic Stability in Nocturnal Fog   总被引：1，自引：0，他引：1  

Toru Nishikawa  Shigenao Maruyama  Seigo Sakai 《Boundary-Layer Meteorology》2004,113(2):273-286

We have performed a one-dimensional and transient radiative heat transfer analysis in order to investigate interaction between atmospheric radiation and convective instability within a nocturnal fog. The radiation element method using the Ray Emission Model (REM²), which is a generalized numerical method, in conjunction with a line-by-line (LBL) method, is employed to attain high spectral resolution calculations for anisotropically scattering fog. The results show that the convective instability has a strong dependence on radiative properties of the fog. For the condition of a 20-m droplet diameter and liquid water content of 0.1 × 10^–3 kg m^–3;, the temperature profile within the fog becomes S shaped, and a convective instability layer forms in the middle or lower level of the fog. However, for the same water content and a 40-m diameter droplet, no strong convective instability layer forms, whereas for a 10-m diameter droplet a strong convective instability is observed.  相似文献   

Effects of riverbed incision on the hydrology of the Vietnamese Mekong Delta     

Doan Van Binh  Sameh A. Kantoush  Tetsuya Sumi  Nguyen Phuong Mai  Trieu Anh Ngoc  La Vinh Trung  Tran Dang An 《水文研究》2021,35(2):e14030

The hydrogeomorphology of the Vietnamese Mekong Delta (VMD) has been significantly altered by natural and anthropogenic drivers. In this study, the spatiotemporal changes of the flow regime were examined by analysing the long-term daily, monthly, annual and extreme discharges and water levels from 1980 to 2018, supported by further investigation of the long-term annual sediment load (from the 1960s to 2015), river bathymetric data (in 1998, 2014 and 2017) and daily salinity concentration (from the 1990s to 2015) using various statistical methods and a coupled numerical model. Then, the effects of riverbed incision on the hydrology were investigated. The results show that the dry season discharge (i.e., in March–June) of the Tien River increased by up to 23% from the predam period (1980–1992) to the postdam period (1993–2018) but that the dry season water level at My Thuan decreased by up to −46%. The annual mean and monthly water levels in June at Tan Chau and in January and June–October at My Thuan in the Tien River decreased statistically, even though the respective discharges increased significantly. These decreased water levels instead of the increased discharges were attributed to the accelerated riverbed incision upstream from My Thuan, which increased by more than three times, from a mean rate of −0.16 m/year (−16.7 Mm³/year) in 1998–2014 to −0.5 m/year (−52.5 Mm³/year) in 2014–2017. This accelerated riverbed incision was likely caused by the reduction in the sediment load of the VMD (from 166.7 Mt/year in the predam period to 57.6 Mt/year in the postdam period) and increase in sand mining (from 3.9 Mm³ in 2012 to 13.43 Mm³ in 2018). Collectively, the decreased dry season water level in the Tien River is likely one of the main causes of the enhanced salinity intrusion.  相似文献   

Dune-forming winds on Titan and the influence of topography   总被引：1，自引：0，他引：1  

Tetsuya Tokano 《Icarus》2008,194(1):243-262

Numerous extended dunes on Saturn's moon Titan detected by the Cassini RADAR constrain the long-term pattern of surface winds. We analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model (GCM) in order to constrain surface wind predictions of this GCM by dune observations. The model shows that modern winds are sufficient for saltation and dune formation at low latitudes, in agreement with the presence of dunes there. The best condition for the dune-forming wind occurs with a threshold friction speed of 0.02 m s⁻¹ or slightly less. The equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the Hadley circulation. The cross-equatorial wind is steady, and is characterised by a high Weibull shape parameter (k∼4). The wind pattern at higher latitudes is more complex and gusty, and neither longitudinal nor transversal dunes would be able to form. Putative large-scale topography is found to have a profound influence on the near-surface wind pattern. Generally mountains cause a convergence and speeding up on the flank, while basins weaken the wind and cause a divergent flow. Longitudinal dunes can be deflected on the foot of mountains by up to 90°. If Xanadu is a hypothetical large mountain, a wind pattern converging in Xanadu that entirely disagrees with the dune observations is predicted. If instead Xanadu is a large basin, the wind arcs clockwise north of Xanadu and anti-clockwise west and southwest of Xanadu, in agreement with the dune orientations in the vicinity of Xanadu. The albedo pattern has comparatively little influence on the wind field. Isolated mountain chains cause only local-scale change in the wind pattern. However, the persistent surface easterlies in Belet, which are in conflict with the dune orientations, do not disappear by any combination of large-scale topography.  相似文献   

Detection of high-energy solar neutrons and protons by ground level detectors on April 15, 2001     

Y. Muraki  Y. Matsubara  S. Masuda  S. Sakakibara  T. Sako  K. Watanabe  R. Bütikofer  E.O. Flückiger  A. Chilingarian  G. Hovsepyan  F. Kakimoto  T. Terasawa  Y. Tsunesada  H. Tokuno  A. Velarde  P. Evenson  J. Poirier  T. Sakai 《Astroparticle Physics》2008,29(4):229-242

In association with the large solar flare of April 15, 2001, the Chacaltaya neutron monitor observed a 3.6σ enhancement of the counting rate between 13:51 and 14:15 UT. Since the enhancement was observed beginning 11 min before the GLE, solar neutrons must be involved in this enhancement. The integral energy spectrum of solar neutrons can be expressed by a simple power law in energy with the index γ=-3.0±1.0. On the other hand, an integral energy spectrum of solar protons has been obtained in the energy range between 650 MeV and 12 GeV. The spectrum can also be expressed by a power law with the power index γ=-2.75±0.15. The flux of solar protons observed at Chacaltaya (at 12 GeV) was already one order less than the flux of the galactic cosmic rays. It may be the first simultaneous observation of the energy spectra of both high-energy protons and neutrons. Comparing the Yohkoh soft X-ray telescope images with the observed particle time profiles, an interesting picture of the particle acceleration mechanism has been deduced.  相似文献   

Development of partial factor design method on bending strength of piles for Japanese Specifications for Highway Bridges     

Toshiaki Nanazawa  Tetsuya Kouno  Gaku Sakashita  Takashi Nakaura 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2019,13(3):176-184

ABSTRACT

This paper describes the development of a partial factor design method on the bending strength of piles for the Japanese Specifications for Highway Bridges. First, uncertainties in mobilised bending moments and yield bending moments were evaluated by Monte Carlo simulations. Second, the reliability of piles designed by the previous specifications were evaluated on the basis of reliability analysis considering uncertainties in the mobilised bending moments, yield bending moments, and other factors. Finally, a partial factor design method utilising a survey subsurface investigation method and ground type was developed to reach target reliability levels determined by the Standards.  相似文献   

Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay,Hokkaido, Japan     

Yusaku Shimizu  Atsushi Ooki  Hiroji Onishi  Tetsuya Takatsu  Seiji Tanaka  Yuta Inagaki  Kota Suzuki  Naoto Kobayashi  Yoshihiko Kamei  Kenshi Kuma 《Journal of Atmospheric Chemistry》2017,74(2):205-225

Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH₂I₂, CH₂ClI, CH₃I, and C₂H₅I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C₂H₅I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO₄ ^3? variation profile. Correlation between C₂H₅I and PO₄ ^3? concentrations (r = 0.93) suggests that C₂H₅I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH₂I₂ and CH₂ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).  相似文献