实验室模拟海水结冰装置与试验

研究海冰的声学探测技术需要实际海冰和低温环境。介绍了设计制造模拟海水结冰的试验装置的方法。采用人工制冷技术在实验室环境下实现了封闭容器里海水表面冻结一定厚度的海冰。试验结果表明，将容器中接近冰点的海水持续冻结32h后，海冰的厚度达到20cm。对容器里的海冰进行了声波信号探测冰水界面的试验，为测冰声呐技术研究和测冰试验创造了有利条件。     

Nonlinear response of runoff to atmospheric freezing level height variation based on hybrid prediction models

ABSTRACT

We use data on the freezing level height (FLH) and summer runoff in the Hotan River, China, from 1960 to 2013, to analyse the nonlinear relationships of atmospheric and hydrological factors at different time scales, by employing three nonlinear decomposition methods. Six hybrid prediction models are established by combining linear regression and back-propagation artificial neural network (BPANN) models. The decomposition results by three nonlinear methods are compared, indicating that the extreme-point symmetric mode decomposition (ESMD) method ensures the best prediction capacity. The runoff and FLH have periods of 3 and 6 years, respectively, at the inter-annual scale, which pass the significance test of 0.05 (P < 0.05) by using the Monte Carlo method, although there were slight differences in the periods at the inter-decadal scale. Among the six models, ESMD-BPANN exhibits the highest accuracy, with good reliability and resolution, according to several performance indicators. The ESMD-BPANN model is thus selected for the simulation and prediction of runoff.     

A three‐phase thermo‐hydro‐mechanical finite element model for freezing soils

Artificial ground freezing (AGF) is a commonly used technique in geotechnical engineering for ground improvement such as ground water control and temporary excavation support during tunnel construction in soft soils. The main potential problem connected with this technique is that it may produce heave and settlement at the ground surface, which may cause damage to the surface infrastructure. Additionally, the freezing process and the energy needed to obtain a stable frozen ground may be significantly influenced by seepage flow. Evidently, safe design and execution of AGF require a reliable prediction of the coupled thermo‐hydro‐mechanical behavior of freezing soils. With the theory of poromechanics, a three‐phase finite element soil model is proposed, considering solid particles, liquid water, and crystal ice as separate phases and mixture temperature, liquid pressure, and solid displacement as the primary field variables. In addition to the volume expansion of water transforming into ice, the contribution of the micro‐cryo‐suction mechanism to the frost heave phenomenon is described in the model using the theory of premelting dynamics. Through fundamental physical laws and corresponding state relations, the model captures various couplings among the phase transition, the liquid transport within the pore space, and the accompanying mechanical deformation. The verification and validation of the model are accomplished by means of selected analyses. An application example is related to AGF during tunnel excavation, investigating the influence of seepage flow on the freezing process and the time required to establish a closed supporting frozen arch. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of agricultural drought in Iiuni,Eastern Kenya: application of a Markov model

In semi‐arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop performance and yield. The objective of this study was to stochastically simulate the behaviour of dry and wet spells and rainfall amounts in Iiuni watershed, Kenya. The stochastic behaviour of the longest dry and wet spells (runs) and largest rainfall amounts were simulated using a Markov (order 1) model. There were eight raingauge stations within the watershed. The entire analysis was carried out using probability parameters, i.e. mean, variance, simple and conditional probabilities of dry and rain days. An analysis of variance test (ANOVA ) was used to establish significant differences in rainfall characteristics between the eight stations. An analysis of the number of rain days and rainfall amount per rain day was done on a monthly basis to establish the distribution and reliability of seasonal rainfall. The graphic comparison of simulated cumulative distribution functions (Cdfs) of the longest spells and largest rainfall amounts showed Markovian dependence or persistence. The longest dry spells could extend to 24 days in the long rainy season and 12 in the short rainy season. At 50% (median) probability level, the largest rainfall amounts were 91 mm for the long rainy season and 136 mm for the short rainy season. The short rains were more reliable for crop production than the long rains. The Markov model performed well and gave adequate simulations of the spells and rainfall amounts under semi‐arid conditions. Copyright © 2004 John Wiley & Sons, Ltd.     

丽江干河坝冰-岩碎屑流地貌、沉积特征与成因机制分析

2004年3月12日,云南省丽江市玉龙雪山南坡发生了较大规模的冰-岩碎屑流型高速远程滑坡。位于斜坡顶部（高程为4 337~5 350 m）的岩体和冰川块体沿着高陡岩壁向下滑动,在峡谷地形控制下于干河坝内形成体积约11.2×10⁶ m³的滑坡堆积体。本文通过遥感影像分析和现场调查,对干河坝冰-岩碎屑流的地貌与堆积特征进行了详细研究,初步阐释了干河坝冰-岩碎屑流发生的成因机制和运动过程。研究结果表明,节理裂隙发育、源区冻融作用加剧和历史地震效应是此次地震的诱发因素。地形的坡度变化特征、滑体表面“乘船石”结构及内部岩屑的定向排列表明滑坡的运动过程可分为碰撞破碎阶段和扩散堆积阶段。滑坡堆积区广泛分布的“冰川乳坑”和冰水沉积物暗示堆积体底部松散沉积物减阻或是干河坝冰-岩碎屑流具有远程效应的有利因素。深入理解干河坝冰-岩碎屑流的地貌特征及运动学过程,对揭示高速远程滑坡的超强运动机理具有重要的理论意义,同时对我国西部高寒山区大型滑坡灾害的预测预警亦具有现实意义。     

A PREDICTION SCHEME FOR THE PRECIPITATION OF SPR BASED ON THE DATA MINING ALGORITHM AND CIRCULATION ANALYSIS

Based on the 74 circulation indexes provided by National Climate Center of China (hereinafter referred to as NCC) and the 24 indexes compiled by NOAA, the study used the C4.5 algorithm in data mining to establish a decision tree prediction model to predict whether the Spring Persistent Rains (hereinafter referred to as SPR) of 55 years (from 1961 to 2015) is more than the normal, and obtained 5 rules to determine whether the SPR is more than the normal. The accuracy rate of the test set, namely “whether the SPR is more than the normal”, is 98.18%. After evaluating the model by conducting ten 10-fold cross validations to take the average value, the test accuracy rate gained is 84%. There are differences between the three types of years with a SPR more than the normal when it comes to intensity and distribution. In spring, they have respective anomalous 850hPa monthly mean wind fields and water-vapor flux distribution, and 700hPa forms the zone where the vertical speed is anomalously negative. As indicated by the results, the SPR prediction model based on the C4.5 algorithm has a high prediction accuracy rate, the model is reasonably and effectively constructed, and the decision rules take comprehensive factors into consideration. The anomalous rainfall and circulation distribution characteristics obtained based on the decision classification results provide new ideas and methods for the climatic prediction of SPR.     

黑龙江省土壤冻融期气象要素变化特征

黑龙江省春季土壤冻融剧烈,土壤湿度和温度受土壤冻融影响较大,利用黑龙江省64个气象观测站1961—2018年的逐日最高气温、最低气温、平均气温、降水量、地温资料及34个农气观测站人工观测的1981—2018年的土壤湿度资料,分析土壤冻结期间的气象要素变化,研究春季土壤冻融过程中湿度和温度的变化。结果表明：土壤冻结期从北向南缩短,且逐年缩短,冻结期平均气温从北向南升高,逐年上升,降水量西部少、东部和北部多,逐年增加;春季冻融次数平原少、山区多,逐年减少。春季融雪开始日期由北向南提前,并且呈现逐年提前的趋势,融雪期升温速率北部、东部低,中部、南部高;在春季冻融过程中,土壤湿度随着土壤深度的增加而增多,东部土壤湿度受土壤融冻影响最大;在整个冬季土壤冻结期间,北部、中部及东部土壤湿度是增加的,且随着土壤深度的增加,土壤湿度增加的越多,而西部土壤湿度是减少的,且随着土壤深度的增加,土壤湿度减少的越少;春季土壤冻融期间,0 cm平均地温全省平均在-17.3~22.1 ℃之间,南部与全省变化趋势基本一致,升温趋势明显,而北部升温速度明显慢于南部。     

Correlation of icing events with meteorological variables, and two statistical models to discriminate freezing days

In this paper, the characteristics of meteorological variables are statistically correlated with icing events (i.e., glaze and rime) in China, using daily observations of air temperature, relative humidity, wind speed, and weather phenomena from 700 stations in China from 1954 to 2008. The weather conditions most favorable for icing events are investigated and two statistical models are developed to discriminate potential freezing days. Low air temperature, high relative humidity, and low wind speed are shown to be important conditions for occurrence of icing events; also, the favorable daily mean air temperature is shown to have a decreasing trend from north to south in China, while the favorable relative humidity and wind speed varies little across the country. The statistical model developed with the daily mean temperature combined with precipitation, fog, and mist weather phenomena proved to be well able to determine the possible occurrence of freezing days. The accuracy of model outputs is well above 60% for northwestern Yunnan, Guizhou, northern Guangxi, southern Hunan, and southern Jiangxi, among other regions where icing events are more frequent, and the average false alarms are few. Using observations or forecast products of conventional meteorological variables, this model has high performance and is practical and applicable for early warning and monitoring of icing events.     

Temporal Variations of the Spring Persistent Rains and South China Sea Sub-high and Their Correlations to the Circulation and Precipitation of the East Asian Summer Monsoon

National Meteorological Information Center （NMIC） rainfall data and NCEP/NCAR daily circulation reanalysis data are employed to establish the onset-pentad time index of the spring persistent rains （SPR） and the decay-pentad time index of the South China Sea （SCS） sub-high. These indexes are used to study the relationship between the factors in SPR period and their relations to the circulation and precipitation of the East Asian summer monsoon （EASM）. Results show that, the summer rainfall over southeastern China decreases when SPR onset is late. For then EASM strengthens and the cyclonic circulation around the Tibetan Plateau （TP） strengthens, which makes abnormal anti-cyclonic circulation （cyclonic convergent circulation weakens） appear over southeastern China. When the decay of SCS sub-high delays, abnormal flood prevails over the middle and lower reaches of the Yangtze River （MLYR） and to the south. That is mainly caused by EASM weakening while SCS sub-high strengthening, then the abnormal southwesterly over South China and the abnormal northerlies of anti-cyclonic circulation around the TP converge over the Yangtze Valley. The two indexes have high correlations with multivariate ENSO index （MEI） in March, indicating that the climate abnormity in East Asia is related to global climate abnormity tightly. The two time indexes are independent of each other, which is favorable for the prediction of the anomalies of the circulation and precipitation of EASM. From this point of view, we must take the global climate background into account when we analyze and predict the East Asian summer circulation and precipitation.     

The Unprecedented Freezing Disaster in January 2008 in Southern China and Its Possible Association with the Global Warming

The unprecedented disaster of low temperature and persistent rain, snow, and ice storms, causing widespread freezing in the Yangtze River Basin and southern China in January 2008, is not a local or regional event, but a part of the chain events of large-scale low temperature and snow storms in the same period in Asia. The severity and impacts of the southern China 2008 freezing disaster were the most significant among others. This disastrous event was characterized by three major features： （1） snowfall, freezing rain, and rainfall, the three forms of precipitation, coexisted with freezing rain being the dominant producer responsible for the disaster; （2） low temperature, rain and snow, and freezing rain exhibited extremely great intensity, with record-breaking measurements observed for eight meteorological variables based on the statistics made by China National Climate Center and the provincial meteorological services in the Yangtze River Basin and southern China; （3） the disastrous weathers persisted for an exceptionally long time period, unrecorded before in the meteorological observation history of China.
The southern China 2008 freezing disaster may be resulted from multiple different factors that superimpose on and interlink with one another at the right time and place. Among them, the La Nina situation is a climate background that provided conducive conditions for the intrusions of cold air into southern China; the persistent anomaly of the atmospheric circulation in Eurasia is the direct cause for a succession of cold air incursions into southern China; and the northward transport of warm and moist airflows from the Bay of Bengal and South China Sea finally warranted the formation of the freezing rain and snow storms and their prolonged dominance in the southern areas of China.
A preliminary discussion of a possible association of this disastrous event with the global warming is presented. This event may be viewed as a short-term regional perturbation to the global warming. There is no