基于交叉小波分析方法的西太平洋副热带高压年际变率与热带海温及大气环流异常的相关性研究

西太平洋副热带高压的年际变率受热带多个关键海区的海-气相互作用过程调控,但彼此间的因果关联和影响机制尚不清楚。为揭示西太平洋副热带高压的年际变率与热带海温及大气环流异常之间的内在关联特性,定义了三个关键海区以及赤道纬向西风区的特征指数,并分别与西太平洋副热带高压强度、脊线指数进行了交叉小波和相干小波分析。研究发现:西太平洋副热带高压指数存在显著的2～3年和准5年的周期振荡,20世纪八九十年代后,由于暖池区海温及赤道纬向西风区的Hadley环流强迫加强,致使副热带高压特征指数的2～3年周期振荡加强;从位相关系看,先是西太平洋副热带高压减弱南撤导致纬向西风加强,其后影响赤道东太平洋海温升高,同时暖水向东传,使赤道中太平洋以及暖池区海温逐渐升高,在Hadley环流作用下使副高加强北抬。基于上述西太平洋副热带高压的年际变率与热带海温及大气环流异常变化相关性诊断研究,进一步探讨了造成这种相关性的影响机理和因果关联,为揭示西太平洋副热带高压年际变率与热带海温及大气环流异常的相关性做探索研究。     

南大洋气旋气候与变化特征

A new climatology of cyclones in the Southern Ocean is generated by applying an automated cyclone detection and tracking algorithm(developed by Hodges at the Reading University) for an improved and relatively highresolution European Centre for Medium-Range Weather Forecasts atmospheric reanalysis during 1979–2013.A validation shows that identified cyclone tracks are in good agreement with a available analyzed cyclone product.The climatological characteristics of the Southern Ocean cyclones are then analyzed,including track,number,density,intensity,deepening rate and explosive events.An analysis shows that the number of cyclones in the Southern Ocean has increased for 1979–2013,but only statistically significant in summer.Coincident with the circumpolar trough,a single high-density band of cyclones is observed in 55°–67°S,and cyclone density has generally increased in north of this band for 1979–2013,except summer.The intensity of up to 70% cyclones in the Southern Ocean is less than 980 h Pa,and only a few cyclones with pressure less than 920 h Pa are detected for1979–2013.Further analysis shows that a high frequency of explosive cyclones is located in the band of 45°–55°S,and the Atlantic Ocean sector has much higher frequent occurrence of the explosive cyclones than that in the Pacific Ocean sector.Additionally,the relationship between cyclone activities in the Southern Ocean and the Southern Annular Mode is discussed.     

Low-Level Westerly Winds,Topography, and Tropical Cyclogenesis of Arlene (2005): Observations and Model Simulations

The evolution process of the low-level westerly winds over the eastern North Pacific is investigated to understand the tropical cyclogenesis (TCG) of Tropical Storm Arlene (2005) over the Intra-Americas Sea (IAS). Also considered are the influences of the topography of the Central American mountain region interacting with the low-level westerly winds on Arlene's TCG by comparing results from a modified-topography simulation of Arlene's TCG with those from a simulation with the original topography in the Weather Research and Forecast (WRF) model. Interactions among large-scale circulations associated with subtropical highs in both hemispheres and an anticyclone over the warm eastern North Pacific produced low-level westerly winds into the IAS. WRF model experiments with a virtually elevated terrain filling in mountain passes in Central America resulted in the delayed and suppressed development of the incipient storm. The model experiments suggest that the low-level winds and moisture fluxes from the eastern North Pacific passing through the low-level mountain passes in Central America could play a critical role in the TCG process and perhaps also sustenance of storms over the western Caribbean.     

An Investigation into Effect of Randomly Distributed Small Scale

Previous studies concerning the interaction of dual vortices have been made generally in the deterministic framework. In this paper, by using an advection equation model, eight numerical experiments whose integration times are 30 h are performed in order to analyze the interaction of dual vortices and the vortex self-organization in a coexisting system of deterministic and stochastic components. The stochastic components are introduced into the model by the way that the Iwayama scheme is used to produce the randomly distributed small-scale vortices which are then added into the initial field. The different intensity of the small-scale vortices is described by parameter K being 0.0, 0.4, 0.6, 0.8, and 1.0, respectively. When there is no small-scale vortex （K=0.0）, two initially separated meso-beta vortices rotate counterclockwise mutually, and their quasi-final flow pattern is still two separated vortices; after initially incorporating small-scale vortices （K=0.8, 1.0）, the two separated meso-beta vortices of initially same intensity gradually evolve into a major and a secondary vortex in time integration. The major vortex pulls the secondary one, which gradually evolves into the spiral band of the major vortex. The quasi-final flow pattern is a self-organized vortex with typhoon-like circulation, and the relative vorticity at its center increases with increasing in K value, suggesting that small-scale vortices feed the self-organized vortex with vorticity. This may be a possible mechanism responsible for changes in the strength of the self-organized vortex. Results also show that the quasi-final pattern not only relates with the initial intensity of the small-scale vortices, but also with their initial distribution. In addition, three experiments are also performed in the case of various boundary conditions. Firstly, the periodic condition is used on the E-W boundary, but the fixed condition on the S-N boundary; secondly, the fixed condition is set on all the boundaries; and thirdly, the periodic conditio     

The Upper Ocean Thermal Structure and the Genesis Locations of Tropical Cyclones in the South China Sea

The relationship between the upper ocean thermal structure and the genesis locations of tropical cyclones （TCs） in the South China Sea （SCS） is investigated by using the Joint Typhoon Warning Center （JTWC） best-track archives and high resolution （1/4 degree） temperature analyses of the world＇s oceans in this paper In the monthly mean genesis positions of TCs from 1945 to 2005 in the SCS, the mean sea surface temperature （SST） was 28.8℃ and the mean depth of 26℃ water was 53.1 m. From the monthly distribution maps of genesis positions of TCs, SST and the depth of 26℃ water in the SCS, we discovered that there existed regions with SST exceeding 26℃ and 26℃ water depth exceeding 50m where no tropical cyclones formed from 1945 to 2005 in the SCS, which suggests that there were other factors unfavorable for TC formation in these regions.     

A historical review and assessment of urban heat island research in Singapore

This historical review of 20 studies since the 1960s examines the influence of urban development on the thermal environment in Singapore, a fast growing tropical island city‐state. Past observations are critically assessed with regard to experimental controls and station metadata. Given the availability of historical climate and developmental data spanning almost 50 years, changes in urban heat island (UHI) intensity and spatial coverage can be traced temporally. Rapid urban expansion in Singapore is clearly reflected in spatially and temporally changing air and surface temperature patterns. The nocturnal canopy‐layer UHI intensity – measured as the difference between the commercial urban core and undeveloped areas close to primary or secondary rainforests for example – doubled in magnitude between 1965 and 2004. At the same time, the spatial extent of the nocturnal UHI has also expanded with the development of new housing and industrial districts. The influence of the growing city is also reflected in surface temperature. Two satellite images dated 13 years apart demonstrate the encroachment of areas with high surface temperatures into previously cooler areas during daytime corresponding with new public housing estates and low‐rise residential areas or facilities being built. The results from our study contribute to the growing body of tropical heat island research. They provide baseline data for future research and urban development in the Singapore context and, more generally, offer important cues for urban planners to make tropical cities more sustainable.     

Climatic patterns in a tropical rainforest in Brunei

Meteorological parameters were monitored on an hourly basis over ten months during 1991–2, from altitudes of 45 and 913 metres in an undisturbed tropical rainforest in Brunei, near the north-west coast of Borneo. In general, the observed characteristics of the climate accorded with the regional meteorological systems and with published results from other studies in northern Borneo, although a greater degree of temporal variability was apparent. The seasonal variability was probably enhanced by the El Niño Southern Oscillation event of early 1992. Rainfall events were typically highly variable in nature, although storm intensity profiles were broadly similar. High magnitude and high intensity events are common among the large total number of events. More rain, of generally higher intensity, fell on the mountain. The total daily solar energy receipt was similar at both altitudes owing to greater cloud cover on the mountain. Temperatures varied significantly with season at both altitudes and the mean lapse rate was 4.5°C/km. Relative humidity at 913 metres tended to be significantly higher during the day and significantly lower at night than at 45 metres. Wind directions were dominantly controlled by local mountain and valley wind systems. Wind speeds were significantly higher during the dry seasons and at the higher altitude. Previous studies have shown that small but significant variations in meteorological parameters can have distinct ecological responses, and rainfall characteristics are important controls on geomorphological processes.     

末次冰期盛期中国热带的变迁

参照约６０个实例,探讨末次冰期盛期中国热带位置的纬度地带性和经度地带性变迁。当时,热带中部、热带北部、亚热带南部３个地带的北界分别南移５个、２个、６个纬距。经度地带性差异可分为５个区。其年均温下降幅度,台湾岛最大（５￣９℃）,两广及海南岛其次（３￣４℃）,闽南粤东较小（２￣３℃）,滇南最小（１￣２℃）。南海冬季水温降幅较大（２．４￣５．７℃）。除闽南、粤东、南海趋于冷干外,大部分地区环境趋于冷湿。     

An engineering geological approach to road cutting slope design in Ghana

Summary Road cutting slope design in tropical terrains often tends to be conservative when based on the methods of classical slope stability analysis. This could be attributed to the difficulties encountered in the accurate characterization of tropically weathered rocks and soils, and the time-dependent improvement in soil properties resulting from haematite-hardening of the slope faces. A field-orientated approach, based on a slope performance survey of both natural and existing cutting slopes in similar geo-environmental settings, often tends to provide a more reliable alternative for the design of cutting slopes along new roads. This paper presents the results of slope performance studies carried out at selected locations in Ghana as a guide to designing cutting slopes along two proposed road projects in the southwestern sector of the country. It is recommended that slopes in competent lithologies along the proposed roads should be cut at steep inclinations of 72° and 80° while slopes in the less competent lithologies should be cut at flatter inclinations of 45°.     

Coupled rainfall and water vapour stable isotope time series reveal tropical atmospheric processes on multiple timescales

High-frequency stable isotope data are useful for validating atmospheric moisture circulation models and provide improved understanding of the mechanisms controlling isotopic compositions in tropical rainfall. Here, we present a near-continuous 6-month record of O- and H-isotope compositions in both water vapour and daily rainfall from Northeast Australia measured by laser spectroscopy. The data set spans both wet and dry seasons to help address a significant data and knowledge gap in the southern hemisphere tropics. We interpret the isotopic records for water vapour and rainfall in the context of contemporaneous meteorological observations. Surface air moisture provided near-continuous tracking of the links between isotopic variations and meteorological events on local to regional spatial scales. Power spectrum analysis of the isotopic variation showed a range of significant periodicities, from hourly to monthly scales, and cross-wavelet analysis identified significant regions of common power for hourly averaged water vapour isotopic composition and relative humidity, wind direction, and solar radiation. Relative humidity had the greatest subdiurnal influence on isotopic composition. On longer timescales (weeks to months), isotope variability was strongly correlated with both wind direction and relative humidity. The high-frequency records showed diurnal isotopic variations in O- and H-isotope compositions due to local dew formation and, for deuterium excess, as a result of evapotranspiration. Several significant negative isotope anomalies on a daily scale were associated with the activity of regional mesoscale convective systems and the occurrence of two tropical cyclones. Calculated air parcel back trajectories identified the predominant moisture transport paths from the Southwest Pacific Ocean, whereas moisture transport from northerly directions occurred mainly during the wet season monsoonal airflow. Water vapour isotope compositions reflected the same meteorological events as recorded in rainfall isotopes but provided much more detailed and continuous information on atmospheric moisture cycling than the intermittent isotopic record provided by rainfall. Improved global coverage of stable isotope data for atmospheric water vapour is likely to improve simulations of future changes to climate drivers of the hydrological cycle.