Spatial variability and mechanisms underlying El Niño-induced droughts in Mexico     

Tripti Bhattacharya  John C. H. Chiang 《Climate Dynamics》2014,43(12):3309-3326

The El Niño Southern Oscillation plays a key role in modulating interannual rainfall variability in Mexico. While El Niño events are linked to drought in Mexico, uncertainty exists about the spatial pattern and causal mechanisms behind El Niño-induced drought. We use lead/lag correlation analysis of rainfall station data to identify the spatial pattern of drought associated with the summer before, and the spring following, the peak of warm SST anomalies in the eastern equatorial Pacific. We also use atmospheric fields from the North American Regional Reanalysis to calculate the anomalous moisture budget and diagnose the mechanisms associated with El Niño-induced drought in Mexico. We find that reduced rainfall occurs in Mexico in both the summer before and the spring after a peak El Niño event, especially in regions of climatologically strong convection. The teleconnection in the developing phase of El Niño is primarily driven by changes in subsidence resulting from anomalous convection in the equatorial Pacific. The causes of drought during the decaying phase of El Niño events are varied: in some years, descent anomalies dominate other moisture budget terms, while in other years, drying of the boundary layer on the Mexican plateau is important. We suggest that the latter may result from the interaction of weakened southeasterly winds in the Intra-Americas Sea with high topography along the Atlantic coast of Mexico. Weakened winds are likely driven by a reduced sea level pressure gradient between the Atlantic and the Pacific. Changes in easterly wave activity may contribute to drought in the developing phase of El Niño, but may be less important in the decaying phase of El Niño.  相似文献   

A new coarse-time GPS positioning algorithm using combined Doppler and code-phase measurements   总被引：2，自引：2，他引：0  

Hung-Wei Chen  He-Sheng Wang  Yi-Te Chiang  Fan-Ren Chang 《GPS Solutions》2014,18(4):541-551

A new coarse-time Global Positioning System (GPS) positioning algorithm based on the use of Doppler and code-phase measurements is proposed and described. The proposed method was demonstrated to be essential for reducing the time to first fix and the power consumption in a GPS receiver. Only 1 ms of data is required to obtain a positioning fix with accuracy comparable to that of the traditional GPS navigation algorithm. The algorithm is divided into two parts. In the first part, the Doppler measurement of the GPS signal is used to determine the coarse user position. With proper constraints, the required time accuracy for the Doppler measurements can be relaxed to be as long as 12 h. In the second part of the algorithm, the accurate user position is calculated by means of the 1 ms code-phase data. The traditional tracking process is no longer necessary in the proposed algorithm. Using the acquired 1-ms code-phase measurement, the positioning accuracy was determined to be approximately a few tens of meters in our experimental results. However, if the data length is extended to 10 ms, the positioning accuracy can be improved to within 10–20 m, which is similar to that of the traditional GPS positioning method. Various experiments were conducted to verify the usefulness of the proposed algorithm.  相似文献   

Global energy budget changes to high latitude North Atlantic cooling and the tropical ITCZ response     

Ivana Cvijanovic  John C. H. Chiang 《Climate Dynamics》2013,40(5-6):1435-1452

The intertropical convergence zone (ITCZ) in atmospheric general circulation models (coupled to slab ocean) shift southwards in response to northern extratropical cooling. Previous studies have demonstrated the utility of diagnosing the atmospheric energy fluxes in interpreting this teleconnection. This study investigates the nature of global energy flux changes in response to North Atlantic high latitude cooling applied to the Community Atmosphere Model version 3 coupled to a slab ocean, focusing on key local and remote feedbacks that collectively act to alter the energy budget and atmospheric energy transport. We also investigate the relative roles of tropical sea surface temperature (SST) and energy flux changes in the ITCZ response to North Atlantic cooling. Using a radiative kernel technique, we quantify the effects of key feedbacks—temperature, cloud and water vapor, to the top-of-the-atmosphere radiative flux changes. The results show only partial local energy flux compensation to the initial perturbation in the high latitudes, originating from the negative temperature feedback and opposed by positive shortwave albedo and longwave water vapor feedbacks. Thus, an increase in the atmospheric energy transport to the Northern extratropics is required to close the energy budget. The additional energy flux providing this increase comes from top-of-the-atmosphere radiative flux increase over the southern tropics, primarily from cloud, temperature and longwave water vapor feedbacks, and largely as a consequence of increased deep convection. It has been previously argued that the role of tropical SST changes was secondary to the role played by the atmospheric energy flux requirements in controlling the ITCZ shifts, proposing that the SST response is a result of the surface energy budget and not a driver of the precipitation response. Using a set of idealized simulations with the fixed tropical SSTs, we demonstrate that the ITCZ shifts are not possible without the tropical SST changes and suggest that the tropical SSTs are a more suitable driver of tropical precipitation shifts compared to the atmospheric energy fluxes. In our simulations, the ITCZ shifts are influenced mainly by the local (tropical) SST forcing, apparently independent of the actual high latitude energy demand.  相似文献   

A probabilistic approach for earthquake risk assessment based on an engineering insurance portfolio     

Wen-Ko Hsu  Wei-Ling Chiang  Qiang Xue  Dung-Mou Hung  Pei-Chun Huang  Cheng-Wu Chen  Chung-Hung Tsai 《Natural Hazards》2013,65(3):1559-1571

This paper presents the construction classification of the existing engineering covers in Taiwan. The exposure profile and variable vulnerability during different construction phases are established for some kinds of classes of construction. Finally, we present a method and framework to estimate the probable maximum loss of engineering insurance portfolio during an earthquake with consideration of the dynamic nature of structural changes and exposure values during a construction project.  相似文献   

Simultaneous measurement of humidity and temperature in the lower troposphere over Chung-Li,Taiwan     

Chih-Wei Chiang  Subrata Kumar Das  Jan-Bai Nee  Shun-xing Hu  Huan-ling Hu 《Journal of Atmospheric and Solar》2009,71(12):1389-1396

A combined Raman–Rayleigh lidar has been designed at Chung-Li, Taiwan for the simultaneous measurement of water-vapor mixing ratio, temperature and extinction-to-backscatter ratio of aerosol in the lower troposphere. The technique of Raman–Rayleigh lidar can retrieve correct temperature profile in the lower troposphere where the measurements are underestimated due to the aerosol loading. Two typical cases are discussed under different humidity (dry/wet) conditions. The water vapor and temperature profile have shown a good agreement with radiosonde. Simultaneous measurement of Raman–Rayleigh lidar also illustrates the physical nature of the aerosol and is useful in understanding the effects of humidity on aerosol swelling.  相似文献   

Equivalent series system to model a multiple friction pendulum system with numerous sliding interfaces for seismic analyses     

C. S. Tsai  H. C. Su  T. C. Chiang 《地震工程与工程振动(英文版)》2014,13(1):85-99

Current structural analysis software programs offer few if any applicable device-specifi c hysteresis rules or nonlinear elements to simulate the precise mechanical behavior of a multiple friction pendulum system(MFPS) with numerous sliding interfaces.Based on the concept of subsystems,an equivalent series system that adopts existing nonlinear elements with parameters systematically calculated and mathematically proven through rigorous derivations is proposed.The aim is to simulate the characteristics of sliding motions for an MFPS isolation system with numerous concave sliding interfaces without prior knowledge of detailed information on the mobilized forces at various sliding stages.An MFPS with numerous concave sliding interfaces and one articulated or rigid slider located between these interfaces is divided into two subsystems: the fi rst represents the concave sliding interfaces above the slider,and the second represents those below the slider.The equivalent series system for the entire system is then obtained by connecting those for each subsystem in series.The equivalent series system is validated by comparing numerical results for an MFPS with four sliding interfaces obtained from the proposed method with those from a previous study by Fenz and Constantinou.Furthermore,these numerical results demonstrate that an MFPS isolator with numerous concave sliding interfaces,which may have any number of sliding interfaces,is a good isolation device to protect structures from earthquake damage through appropriate designs with controllable mechanisms.  相似文献   

Spatial and Temporal Changes of Groundwater Level Induced by Thrust Faulting     

Yeeping Chia  Jessie J. Chiu  Yi-Hsuan Chiang  Tsai-Ping Lee  Chen-Wuing Liu 《Pure and Applied Geophysics》2008,165(1):5-16

Changes of groundwater level, ranging from a fall of 11.10 m to a rise of 7.42 m, induced by thrust faulting during the 1999 M_w 7.6, Chi-Chi earthquake have been recorded in 276 monitoring wells in Taiwan. Most coseismic falls appeared near the seismogenic fault as well as other active faults, while coseismic rises prevailed away from the fault. Coseismic groundwater level rises and falls correlated fairly well with hypocentral distance in the vicinity of the thrust fault. We found a major difference of coseismic changes in wells of different depths at most multiple-well stations. The recovery process of coseismic groundwater level changes is associated with the confining condition of the aquifer. Cross-formational flow is likely to play an important role in groundwater level changes after the earthquake. In the hanging wall of the thrust fault, an abnormal decline of groundwater level was observed immediately before the earthquake. The underlying mechanism of the unique preseismic change warrants further investigation.  相似文献   

Non-local scaling in two-dimensional gravitational clustering     

Dipak Munshi  Lung-Yih Chiang  Peter Coles  & Adrian L. Melott 《Monthly notices of the Royal Astronomical Society》1998,293(3):L68-L72

Using an ensemble of high-resolution 2D numerical simulations, we explore the scaling properties of cosmological density fluctuations in the non-linear regime. We study the scaling behaviour of the usual N -point volume-averaged correlations, but also examine the scaling of the entire probability density function (PDF) of the fluctuations. We focus on two important issues: (i) whether the scaling behaviour of 2D clustering is consistent with what one infers from radial collapse arguments; and (ii) whether there is any evidence from these high-resolution simulations that a regime of stable clustering is ever entered. We find that the answers are (i) yes and (ii) no. We further find that the behaviour of the highly non-linear regime in these simulations suggests the existence of a regime in which the correlation function is independent of the initial power spectrum.  相似文献   

The influence of faculae on sunspot heat blocking     

Wei-Hwan Chiang  Peter Foukal 《Solar physics》1985,97(1):9-20

We study the influence of faculae on sunspot heat blockage using a thermal model based on eddy heat diffusion through the convection zone. The facula is represented as a localized area of excess emission surrounding the sunspot, which is represented as a thermal plug. Our computations using a range of reasonable combinations of spot and facular depths show no significant influence of the facula on the long storage times of heat blocked by sunspots. However, the local cooling of surface layers produced by excess facular emission in this model propagates globally within the convection zone in a similar way to the heating produced by a spot. The net effect of spots and faculae on L over time scales longer than an active region lifetime should thus be determined by the global sum of sunspot flux deficits and facular excesses.  相似文献   

Note on sediment sorting in a sandy bed under standing water waves     

Blake J. Landry  Matthew J. Hancock  Chiang C. Mei 《Coastal Engineering》2007

We present new quantitative data on the sorting of sediments on a sandy seabed under standing waves. Starting from a flat bed composed of a homogeneous mixture of a coarse and a fine sand with mean diameters 0.11 and 0.21 mm, we observed simultaneous ripple and sand bar formation and sand sorting on the seabed. Over days of wave action, sand bars formed with crests beneath the surface wave nodes and flat plateaus flanked by mounds beneath the antinodes. Bar crests were composed of sand coarser on average than 0.21 mm, while the flat plateaus were covered by sand finer on average than 0.11 mm. Comparison with two experiments involving sand beds of more homogeneous size distributions shows that the mounds are characteristic of the motion of fine suspensions.  相似文献