Use of mixed bivariate distributions for deriving inter‐station correlation coefficients of rain rate

Even though rain rate is notorious for its spatial and temporal intermittency, its effect on the second‐order statistics of rain rate, especially the inter‐station correlation coefficients, has not been intensively evaluated before. This study has derived and compared the inter‐station correlation coefficient of rain rate for three cases of data: (1) only the positive measurements at both locations; (2) the positive measurements at either one or both locations; (3) all the measurements including zero measurement at both locations. For these three cases, the inter‐station correlation coefficients are analytically derived by applying the mixed bivariate log‐normal distribution. As an application example, the model parameters are estimated using the rain rate data collected at the Geum River basin, Korea, and the resulting inter‐station correlation coefficients are evaluated and compared with those estimated by applying the Gaussian distribution. We could find that highly biased inter‐station correlation coefficients are unavoidable when simply estimating them under the assumption of Gaussian distribution, or even when using the log‐transformed rain rate data. Copyright © 2007 John Wiley & Sons, Ltd.     

Novel integrated approaches for predicting the compressibility of clay using cascade forward neural networks optimized by swarm- and evolution-based algorithms

Acta Geotechnica - Soft soils are considered as disadvantages in construction, especially in clay layers. It requires many advanced techniques to treat the soft soils before construction, aiming to...     

Under-ice measurements of suspended particulate matters using ADCP and LISST-Holo

Ocean Science Journal - Using a mooring package comprising an acoustic Doppler current profiler (ADCP) and holographic imaging system, a 1-day ice camp study was performed under the Arctic sea ice...     

Simulation of snowstorm over the Yellow Sea using a mesoscale coupled model

This study aims to examine the favorable conditions for an ocean effect snowstorm across the Yellow Sea over the southwestern coast of Korea on 21 December 2005, using a coupled model with a Coupled Ocean/Atmosphere Mesoscale Prediction System as the atmospheric component and the Regional Ocean Modeling System as the oceanic component. Simulation of heavy snowfall event, which was 44.3 cm of snow accumulated in 24-hour, was performed to investigate the mesoscale structure, dynamics and development mechanisms in the snowstorm. As a result from 48-hour integration, the results of simulation showed that barotropic instability and turbulent heat fluxes played important roles in the formation of snowstorm. The enhanced surface diabatic heating was dominant in the latent heat flux, and eventually induced convective instability. An additional factor was the favorable condition of synoptic environment, accessing the cold air transport by the approach of the upper-level cold vortex over the warm ocean. Besides these factors, conditional symmetric instability (CSI) is a mechanism which can result in a heavy snowfall with sufficient moisture and upward vertical motion. A slantwise convection from the release of CSI could support a complex snowfall event with heavier than expected amounts. The result comparison between a coupled model and an uncoupled model supports that airsea coupling has an impact of decreasing of about 10% in a snowfall amount on the snowstorm.     

Interdecadal shift in the relationship between the East Asian summer monsoon and the tropical Indian Ocean

In this work, the authors investigate changes in the interannual relationship between the East Asian summer monsoon (EASM) and the tropical Indian Ocean (IO) in the late 1970s. By contrasting the correlations of the EASM index (EASMI) with the summer IO sea surface temperature anomaly (SSTA) between 1953–1975 and 1978–2000, a pronounced different correlation pattern is found in the tropical IO. The SSTA pattern similar to the positive Indian Ocean Dipole (IOD) shows a strongly positive correlation with the EASMI in 1953–1975. But in 1978–2000, significant negative correlation appears in the northern IO and the IOD-like correlation pattern disappears. It is indicated that the summer strong IOD events in 1953–1975 can cause a weaker-than-normal western North Pacific (WNP) subtropical high, which tends to favor a strong EASM. In 1978–2000, the connection between the summer IOD and the WNP circulation is disrupted by the climate shift. Instead, the northern IO shows a close connection with the WNP circulation in 1978–2000. The warming over the northern IO is associated with the significant enhanced 500 hPa geopotential height and an anomalous anticyclone over the WNP. The change in the IO–EASM relationship is attributed to the interdecadal change of the background state of the ocean–atmosphere system and the interaction between the ENSO and IO. In recent decades, the tropical IO and tropical Pacific have a warmer mean SST, which has likely strengthened (weakened) the influence of the northern IO (IOD) on the EASM. In addition, due to the increase in the ENSO variability along with the higher mean equatorial eastern Pacific SST in 1978–2000, the influence of ENSO on the East Asian summer circulation experiences a significant strengthening after the late 1970s. Because the warming over the northern IO is associated with the significant warming in the equatorial eastern Pacific, the strengthened ENSO–EASM relationship has likely also contributed to the strengthened relationship between the northern IO and the EASM in 1978–2000.     

The worldwide character of the 1969–1970 impulse of the secular acceleration rate

This paper continues earlier studies to ascertain whether the distribution of the 1969–1970 jump of the secular variation rate has a worldwide character. The geometry of the jump presents some similarities with the geometry of the secular variation itself. We give a new estimation of the westward drift rate and information about spatial and temporal variations of the secular variation field.     

Electromagnetic fields in a steel-cased borehole

The development of an electromagnetic numerical modelling scheme for a magnetic dipole in an arbitrary casing segment in an inhomogeneous conductivity background has been difficult, due to the very high electrical conductivity and magnetic permeability contrasts between the steel casing and the background medium. To investigate the effect of steel casing efficiently, we have developed an accurate but simple finite‐element modelling scheme to simulate electromagnetic fields in a medium of cylindrically symmetric conductivity structures. In order to preserve the cylindrical symmetry in the resulting electromagnetic fields, a horizontal loop current source is used throughout. One of the main advantages of the approach is that the problem is scalar when formulated using the azimuthal electric field, even if the casing is both electrically conductive and magnetically permeable. Field calculations have been made inside the cased borehole as well as in another borehole which is not cased. Careful analyses of the numerical modelling results indicate that the anomaly observed in a cross‐borehole configuration is sensitive enough to be used for tomographic imaging.