On the kinematic evolution of flare-associated cmes

We report a common tendency of the kinematic evolution of three flare-associated coronal mass ejections (CMEs). Their kinematic evolutions are examined using well-observed data (eruptive filaments, X-ray structures, and prominences) very close to the solar surface as well as SOHO/LASCO C2-C3 data. Their height–time data are fitted using three analytical models (exponential, power-law, and linear) to examine their kinematic behaviors. The speed and acceleration of the CMEs are then obtained from the analytical expressions of height–time data. From this analysis, it is found that the kinematic patterns of these three CMEs have a typical tendency; that is, the speed of the CMEs very close to the surface (lower corona) is approximately exponential in form, but it is nearly constant in the upper corona. The peak of the acceleration is found to occur within 2–3 solar radii and during the eruptive phase of the associated flare. It is also noted that the observed kinematic patterns are quite similar to those predicted by two flux rope emergence models: (i) a theoretical, electrodynamic model (Chen, 1996); and (ii) a numerical simulation, self-consistent, 2 ;D MHD model (Wu, Guo, and Dryer, 1997).     

A New Method for Resolving the 180° Ambiguity in Solar Vector Magnetograms

We present a new method to resolve the 180° ambiguity for solar vector magnetogram measurements. The basic assumption is that the magnetic shear angle (), which is defined as the difference between the azimuth components of observed and potential fields, approximately follows a normal distribution. The new method is composed of three steps. First, we apply the potential field method to determine the azimuthal components of the observed magnetic fields. Second, we resolve the ambiguity with a new criterion: –90°+_mp lele90°+_mp, where _mp is the most probable value of magnetic shear angle from its number distribution. Finally, to remove some localized field discontinuities, we use the criterion B _tB _mt ge0, where B _t and B _mt are an observed transverse field and its mean value for a small surrounding region, respectively. For an illustration, we have applied the new ambiguity removal method (Uniform Shear Method) to a vector magnetogram which covers a highly sheared region near the polarity inversion line of NOAA AR 0039. As a result, we have found that the new ambiguity solution was successful and removed spatial discontinuities in the transverse vector fields produced in the magnetogram by the potential field method. It is also found that our solution to the ambiguity gives nearly the same results, for highly sheared vector magnetograms and vertical current density distributions, of NOAA AR 5747 and AR 6233 as those of other methods. The validity of the basic assumption for an approximate normal distribution is demonstrated by the number distributions of magnetic shear angle for the three active regions under consideration.     

Teleconnections：Summer Monsoon over Korea and India

This study investigates the relationship between the summer monsoon rainfall over Korea and India,by using correlation analysis and Singular Value Decomposition(SVD).Results reveal that summer monsoon rainfall over Korea is negatively(significant at the 99% level) correlated with the rainfall over the northwest and central parts of India.In addition,coupled spatial modes between the rainfall over Korea and India have been identified by the SVD analysis.The squared covariance fraction explained by the first mode is 70% and the correlation coefficient between the time coefficients of the two fields is significant at the 99% level,indicating that the coupled mode reflects a large part of the interaction between the summer monsoon rainfall over Korea and India.The first mode clearly demonstrates the existence of a significant negative correlation between the rainfall over the northwest and central parts of India and the rainfall over Korea.Possible mechanisms of this correlation are investigated by analyzing the variation of upper-level atmospheric circulation associated with the Tibetan high using NCEP/NCAR Reanalysis data.     

Causes of the Unusual Coastal Flooding Generated by Typhoon Winnie on the West Coast of Korea

On 19 August 1997 Typhoon Winnie brought unusually strong and extensive coastal flooding from storm surges to the west coast of Korea, which was farenough from the typhoon's center to lack significant local wind and pressure forcing.Sea levels at some tidal stations broke 36-year records and resulted in property damages of $18,000,000. This study investigated the causes of the unusual high sea levels by using an Astronomical-Meteorological Index (AMI) and a coupled ocean wave-circulation model developed by the present authors. The AMI analysis and the numerical simulation of the surge event showed that the major cause of the high sea levels was not the standard inverse barometric effect supplemented by water piling up along the coast by the wind field of the typhoon as is usual for a typical storm surge, but rather an enhanced tidal forcing from the perigean spring tide and water transported into the Yellow Sea by the currents generated by the typhoon. The numerical results also indicated that the transported water accounted for about 50% of the increased sea levels. Another cause for the coastal flooding was the resonance coupling of the Yellow Sea (with a natural normal mode period of 37.8 h) and the predominant period of the surge (36.5 h).     

Remediation of TCE-contaminated groundwater using zero valent iron and direct current: experimental results and electron competition model

The objectives of this study are to design an optimal electro-enhanced permeable reactive barrier (E2PRB) system for the remediation of trichloroethylene (TCE)-contaminated water using zero valent iron (ZVI) and direct current (DC) and to investigate the mechanisms responsible for TCE degradation in different ZVI-DC configurations. A series of column experiments was conducted to evaluate the effect of different arrangements of electrodes and ZVI barriers in the column on the TCE removal capacity (RC). In twelve different combinations of ZVI and/or DC application in the test columns, the rate of reductive dechlorination of TCE was improved up to six times with simultaneous application of ZVI and DC compared to that using ZVI only. The most effective arrangement of electrode and ZVI for TCE removal was the column set with ZVI and a cathode installed at the down gradient. Based on the electrokinetic study for the column systems with only DC input, single acid front movement could explain different RCs. An enhanced dechlorination rate of TCE using E2PRB systems, compared to a conventional PRB system, was observed, and is considered to be attributed to more electron sources: (1) external DC, (2) electrolysis of water, (3) oxidation of ZVI, (4) oxidation of dissolved Fe²⁺, (5) oxidation of molecular hydrogen at the cathode, and (6) oxidation of Fe²⁺ in mineral precipitates. Each of these electron sources was evaluated for their potential influencing the TCE RC through the electron competition model and energy consumption. A strong correlation between the quantity of electrons generated, RC, and the energy-effectiveness was found.     

Estimating long-term cliff recession rates from shore platform widths

Coastal cliff erosion is a problem in many coastal areas. However, often only very limited data are available to quantify the rates of recession for the development of coastal management strategies. In the soft flysch deposits of the Waitemata Group, Auckland, New Zealand, coastal cliffs are associated with shore platforms. Two models exist for the profile evolution of shore platforms and associated cliffs: the first suggests that an equilibrium profile develops in response to erosive processes, and this profile subsequently migrates landward; the second model suggests that the seaward margin of the shore platform is relatively static, and the profile extends landward through a combination of cliff recession and platform lowering. Physical simulations and field measurements for mudstone and limestone lithologies indicate that the second model is more likely for soft flysch deposits. A eustatic sea-level curve for the Weiti Estuary, Auckland, suggests that up to 7120 ± 70 years have been available for shore platform development since sea level reached the present seaward margins of shore platforms. Shore platform widths were measured using GPS at two sites in Waitemata Group rocks: the North Shore of Auckland; and the southern side of the Tawharanui Peninsula, North Auckland. The long-term cliff recession rates estimated from shore platform widths (1.4 ± 0.1 to 14.3 ± 0.1 mm y^− 1) are consistent with the lower end of the average range of cliff top and face recession rates published for Waitemata Group rocks using different methods (11–75 mm y^− 1), and in agreement with cliff base recession estimates (3.5 mm y^− 1). Shore platform widths were qualitatively related to the rock mass characteristics of the associated cliffs, and therefore platform widths could provide a method of identifying regions of potential hazard.     

Fe-Mg order-disorder in orthopyroxenes

Published data on the distribution of Fe and Mg between the two distinct octahedral sites (M1 and M2) in orthopyroxenes show that the equilibrium Fe-Mg distribution coefficient (K_D) is roughly constant at intermediate ferrosilite content (X_Fs of 0.2 to 0.6) but at low X_Fs (<0.2) is either anomalously high (Mössbauer data) or low (XRD data) compared to K_D at intermediate X_Fs. We report an experimental study on the equilibrium K_D values for two natural single crystals of orthopyroxene (with X_Fs of 0.011 and 0.160) using a high-sensitivity Mössbauer spectrometer. The K_D values were determined at 1 bar and temperatures between 600 and 1000°C, and reversed at 600 to 900°C. The values are found to be independent of orthopyroxene composition at a given temperature within analytical uncertainties, and in agreement with K_D values at intermediate X_Fs. A least-squares fit to the K_D data yields: lnK_D = 0.391(±0.131) − 2205(±141)/T, where T is temperature in K, and uncertainties are at the 2σ level. This equation is valid for X_Fs values up to at least 0.6. We suggest that previous Mössbauer and XRD data at low X_Fs were compromised by analytical difficulties. The new result that K_D is roughly independent of X_Fs greatly simplifies treatment of equilibrium and speedometry based on Fe-Mg order-disorder in orthopyroxene.     

The frictional resistance characteristics of a bedrock‐influenced river channel

Much of the published literature relating to reach‐scale total ?ow resistance concentrates on alluvial rivers and little mention is made of the more extreme resistance found in bedrock‐in?uenced river systems. This paper presents the results of a detailed investigation of total ?ow resistance variation for ?ve channel types on the Sabie River, South Africa (cohesive mixed anastomosed, uncohesive mixed anastomosed, mixed pool–rapid, alluvial braided and alluvial single thread) over a range of discharges. Manning's ‘n’ and Darcy‐Weisbach f resistance coef?cients are calculated using Barnes' methodology (H. H. Barnes, US Geological Survey Water Supply Paper 1849, 1967). These data are analysed at the scales of channel type and morphologic unit and the resultant resistance values are compared with the literature. Generally the low‐?ow friction values estimated for the bedrock‐in?uenced channel types are higher than any reported. Flow resistance quanti?cation of the alluvial channel type study sites on the Sabie River produced values slightly higher than earlier studies of similar morphologies. In situations where signi?cant areas of irregular bedrock are exposed (cohesive mixed anastomosed and mixed pool–rapid channel types) the high ?ow resistance coef?cients at low discharges probably re?ect energy dissipation due to hydraulic jumps and internal distortions; however, these values fall as discharge increases to values comparable to those recorded for step–pool rivers. It is suggested that the slightly elevated resistance coef?cients recorded in the alluvial channel types are the result of the vegetation roughness component, operating when the macro‐channel bar features are inundated. Copyright © 2004 John Wiley & Sons, Ltd.