Causes and effects of spatial and temporal variations of cold period in Chinese oases between 1960 and 2014

Based on daily average temperatures and observation data from 74 meteorological stations in Chinese oases, we calculate five-day (pentad) average temperature ≤0°C for the start and end pentad as well as pentads of cold period using linear regression analysis, nonparametric Mann-Kendall tests, the Morlet wavelet power spectrum, and correlation analysis. We also analyze spatial and temporal variations and their effects on the start and end pentad as well as pentads of cold period in Chinese oases. Results show that over the last 55 years, the start pentad of cold period has been postponed while the end pentad has been advanced. Overall, the pentads have gradually shortened over time at trend rates that are 0.3 p/10a,–0.27 p/10a, and–0.58 p/10a, respectively. Spatial differences are significant, especially for the Qaidam Basin oasis where the start pentad is the earliest, the end pentad is the latest, and the trend of change is most obvious. Mutation points for the start and end pentad as well as pentads of cold period were observed in 1990, 1998, and 1994, respectively. Of these, the start pentad and pentads of cold period show a periodic cycle, related to atmospheric circulation and El Nino events, while the end pentad exhibits a periodic cycle, related to solar activity. The Tibetan Plateau index (TPI), the Asian polar vortex area index (APVAI), and carbon dioxide emissions (CDE) are the main factors affecting cold period in the study area, whereas the South Asian summer monsoon (SASM) index exerts the greatest effect on the Qaidam Basin oasis. The start and end pentad as well as pentads of cold period increase in concert with latitude, longitude, and altitude; in response to these changes, the start pentad is advanced, the end pentad is postponed, and pentads of cold period are gradually extended. Results show that change in latitude is most significant. Overall, the start and end pentad as well as pentads of cold period show clear responses to regional warming, but there are different effects on each.     

A Hierarchy of Spatial Marginality Through Spatial Filtering

Abstract

Taking a clue from classic time-series decomposition, this article demonstrates a spatial filtering and search technique that permits the partitioning of a measure of marginality, here measured as the percent of the population living at less than 50 percent of the poverty level, into macro, meso, and micro components. This approach supports theory that has argued for scale-specific explanations of spatial marginality. The technique also offers promise for many other types of investigations such as disease incidence, microclimate dynamics, and consumer preferences.     

Hydro-climatic variability and forest fires in Mexico’s northern temperate forests

Global warming is likely modifying the hydrological cycle of forested watersheds. This report set as objectives to: a) assess the hydrological variables interception loss, I, potential and actual evapo-transpiration, E, Et, runoff, Q, and soil moisture content, θ; b) evaluate whether these variables are presenting consistent trends or oscillations that can be associated to global warming or climate variability; and c) relate θ to the number of wildfires and the burned area in Durango, Mexico. A mass balance approach estimated daily variables of the water cycle using sub-models for I and Et to calculate Q and θ for a time series from 1945 to 2007. Regression and auto-regressive and moving averaging (ARIMA) techniques evaluated the statistical significance of trends. The cumulative standardized z value magnified and ARIMA models projected statistically similar monthly and annual time series data of all variables of the water cycle. Regression analysis and ARIMA models showed monthly and annual P, I, E, and Et, Q, and θ do not follow consistent up or downward linear tendencies over time with statistical significance; they rather follow oscillations that could be adequately predicted by ARIMA models (r² ≥ 0.70). There was a consistent statistical association (p ≤ 0.05) of θ with the number of wildfires and the area burned regardless of the different spatial scales used in evaluating these variables. The analysis shows seasonal variability is increasing over time as magnifying pulses of dryness and wetness, which may be the response of the hydrological cycle to climate change. Further research must center on using longer time series data, testing seasonal variability with additional statistical analysis, and incorporating new variables in the analysis.     

改进的修正预测法预报电离层

利用自回归移动平均ARMA模型的线性最小方差预测法预报电离层存在的主要问题是极值点处预测误差较大。通过对模型阶数上限及定阶准则的选取进行实验分析,确定了合适的模型阶数并建立了相应模型。修正预测法可利用新信息对线性最小方差预测法的预测结果进行修正。这是一种短期预报方法,每次向前预测一步即2 h,但结果并不理想。考虑到电离层变化的周期性,为了进一步减小极值点处预测误差,提出了改进的修正预测法。实验表明,改进的修正预测法预测结果与原始值符合较好。     

高速铁路建设对我国省际可达性空间格局的影响

以省会城市为网络中的节点,采用加权平均旅行时间指标对我国"四纵四横"高速铁路网及长三角、珠三角和环渤海地区城际客运系统建成前后省际可达性及演变态势进行分析。研究表明,高速铁路建设使东中西地带内、地带间及省区的总体可达性均获得了大幅度提升,可达性中心区的范围沿骨干客运专线向华南、西南和西北地区拓展,圈层状空间格局依然很突出,两极分化趋势在加剧,高速铁路网建设对各地区的空间经济效应还存在很大差异。经过对高速铁路建成前后各省区的地带内、地带间及总体可达性空间格局的对比分析,从客观上论证了高速铁路建设的必要性及加强省际经济联系的重要性。     

Temporally weighted average curve number method for daily runoff simulation

The modified Soil Conservation Service curve number (CN) method is widely used in long‐term continuous models to predict daily surface runoff. However, it has been shown that this method gives poor results in reproducing peak flows in high rainfall periods. This is because there is an inaccuracy stemming from the model algorithm as it adjusts the daily runoff curve number as a function of soil moisture content at the end of the previous day. This paper proposes an alternative daily based curve number technique that can provide better prediction of daily runoff during the high flow season. The proposed method uses the temporally weighted average curve number (TWA‐CN) to estimate daily surface runoff, while considering the effect of rainfall during a given day as well as the antecedent soil moisture condition. To test the applicability of the TWA‐CN method, it was incorporated with the long‐term, continuous simulation watershed models SWAT and SWAT‐G. Simulations were conducted for the Miho River watershed located in the middle of South Korea. The graphical displays and statistics of the determination coefficient (R²) and the Nash–Sutcliffe model efficiency (NSE) of the observed and simulated daily runoff indicated that the modified SWAT with the TWA‐CN method may provide better runoff prediction (R² = 0·837, NSE = 0·833) than the original SWAT (R² = 0·815, NSE = 0·824). Likewise, the determination coefficient (R² = 0·816) and the Nash–Sutcliffe efficiency (NSE = 0·834) for the modified SWAT‐G are also higher than the original version (R² = 0·782, NSE = 0·825). It is expected that the improved capability in predicting surface runoff using the suggested CN estimate method will provide a sound contribution to the accurate simulations of water yield. Copyright © 2008 John Wiley & Sons, Ltd.     

Analysis of earthquake ground motions using an improved Hilbert–Huang transform

Some limitations of the Hilbert–Huang transform (HHT) for nonlinear and nonstationary signal processing are remarked. As an enhancement to the HHT, a time varying vector autoregressive moving average (VARMA) model based method is proposed to calculate the instantaneous frequencies of the intrinsic mode functions (IMFs) obtained from the empirical mode decomposition (EMD) of a signal. By representing the IMFs as time varying VARMA model and using the Kalman filter to estimate the time varying model parameters, the instantaneous frequencies are calculated according to the time varying parameters, then the instantaneous frequencies and the envelopes derived from the cubic spline interpolation of the maxima of IMFs are used to yield the Hilbert spectrum. The analysis of the length of day dataset and the ground motion record El Centro (1940, N–S) shows that the proposed method offers advantages in frequency resolution, and produces more physically meaningful and readable Hilbert spectrum than the original HHT method, short-time Fourier transform (STFT) and wavelet transform (WT). The analysis of the seismic response of a building during the 1994 Northridge earthquake shows that the proposed method is a powerful tool for structural damage detection, which is expected as the promising area for future research.     

三维地震勘探中叠加速度成图

速度参数和成图方法和选取对于提高三维地震反射层构造图的精度是很重要的,文章提出了由地震资料的叠加速度来获得界面平均速度,并利用钻井资料对界面平均速度校正,得出了符合地质规律的平均速度,提高了作图精度。该方法成功地应用于华北某煤田勘探区的三维资料解释中,弥补了传统时深转换方法的不足,收到了很好的效果,所绘制的构造图深度同巷道资料吻合。     

靖边气田北部上古生界储层微观孔隙结构及其对生产动态影响

靖边气田北部盒8、山1段砂岩气藏气井投产存在井筒积液、稳产时间短等问题.通过扫描电镜、铸体薄片、常规压汞等技术对储层岩样进行了测试分析,研究了岩石学特征和孔隙类型.将其微观孔隙结构分为4类并研究了微观孔隙结构特征和气井生产动态的关系.研究表明,盒8、山1段储层的孔隙类型主要为溶孔、晶间微孔,孔隙组合类型主要为晶间微孔、...     

Average Annual Temperature Changes in the Holocene in China

In 1876 Blytt proposed a post-glacial climatic classification, maintaining that the then temperature fluctuated 1- 2℃ higher or lower than that today. Lamb (1969) held that in Europe " the axis of the subtropical high pressure belt was generally displaced north by about 10° latitudes" during the Hypsithermal and that the temperature was three to six times higher than that in the postglacial period.In China, there appear relict beachrocks (living fossils) in tropical tidal zones from the Bohai Bay (40° N) to coastal areas in South China. Many relict tropical marine fossils were discovered, such as Ostrea gigas in Tianjin (which is larger than that found today in Hainan), Placuna placenta in Zhejiang and Spondylus sp. in Fujian. In Hebei, Henan and Zhejiang provinces and Guilin of Guangxi, such tropical fossil animals as Elephas maximus and Rhinoceros sp, were discovered, and in Hebei and Jiangsu provinces such fresh water fossils as Unio douglasiae were found. Their living species are still seen in So