QBO 与南海夏季风爆发的关系

利用1979—2001 年ECMWF 再分析资料和NOAA 海温资料,通过相关分析和合成分析等统计方法,分析了平流层准两年周期振荡(QBO)与南海夏季风建立时间的关系。结果表明,QBO 位相与南海夏季风爆发时间有显著的相关关系:超前南海夏季风爆发约18 个月的QBO 西(东)风位相对应着季风爆发时间偏早(晚)。QBO 与南海夏季风爆发的联系要比ENSO 与南海夏季风爆发的联系更密切。      

Meteorological causes of Harmattan dust in West Africa

We investigated the temporal dynamics of dust entrainment in the Bodélé Depression, Central Sahara, to better understand the intra-annual variability of aerosol emission in the world's largest dust source. The linkages between dust entrainment and large-scale meteorological factors were examined by correlating several meteorological variables in the Mediterranean and Africa north of the equator with the aerosol concentrations in the Bodélé Depression separately for winter and summer. The methodological tools applied are NCEP/NCAR reanalysis data and the aerosol index of the Total Ozone Mapping Spectrometer (TOMS-AI), available for 15 years from 1978 to 1993. We found that dust mobilisation during the Harmattan season is highly dependent on air pressure variability in the Mediterranean area. High pressure to the north of the Bodélé intensifies the NE trade winds, leading to an increased entrainment of dust in the Bodélé Depression. In summer, dust mobilization cannot be explained by the large scale meteorological conditions. This highlights the importance of local to regional wind systems linked to the northernmost position of the intertropical convection zone (ITCZ) during this time.     

URBAN TRANSPORTATION PLANNING IN CALIFORNIA: AN EVALUATION

California's excellent road system has provided unmatched mobility for most of the state's residents. Recently, however, constraints on construction of high-capacity roads have threatened the future of unrestricted auto use. California's transportation planners have therefore shifted emphasis from expanding the transportation system to increasing its efficiency. No concomitant change has occurred, however, in state legislation or resource allocation. As a result, rather than being an integrated process, transportation planning and implementation are fragmented. This paper examines the origins and implications of this situation and possible remedies for it.     

TEMPORAL SENSITIVITY OF REGIONAL CLIMATE TO LAND-SURFACE HETEROGENEITY

Increased interest in climate change at local and regional scales has prompted climate simulations for regional areas, but tests of climate models have not specifically examined the impacts of regional heterogeneity, and they have largely overlooked possible temporal sensitivity. In this study I used a coupled surface-atmosphere mesoscale model to evaluate the effects of regional heterogeneity in five land-surface parameters that have the strongest impacts on the surface energy balance: albedo, roughness, canopy resistance, rooting profile, and soil water content. I included temporal variability in climate sensitivity by completing a series of mid-month simulations representative of the June-September growing season. I modeled land surfaces of maize contrasted with bare soil, grass, or coniferous trees. Roughness discontinuities were important factors in determining regional energy balance and surface temperature for all three surface contrasts. The effects varied over the growing season as a function of maize height. Canopy resistance was equally important, especially during the middle of the season when the maize canopy was at its fullest extent. Albedo effects appeared to be secondary, but often were more important in September. Changes in soil water content had little impact because vegetation in these simulations was not stressed by low soil moisture. The importance of roots in these simulations was primarily a function of their presence or absence, rather than of the specific profile assigned to each vegetation type. Roughness and canopy resistance discontinuities appeared to play the largest role in determining the regional average energy balance and surface temperature for growing season dates. [Key words: land-surface heterogeneity, energy balance, climatology.]     

STRATIFIED MARINE LAKES OF PALAU (WESTERN CAROLINE ISLANDS)

The physical geography of the limestone islands of Palau permits permanent water-column stratification in 13 tropical sea-level marine lakes, each with unique water-column physics, chemistry, and biology. Embayments and lagoons amid the coral became isolated as marine lakes after Miocene uplifting. Surface mixing of lake water by wind is reduced by jungle-covered karst ridges. Surface tidal exchange through fissures in fenestrated karst is slow while midwater exchange through submarine tunnels is fast, but both produce damped, delayed tides with modest seawater exchange from the barrier-reef lagoon. Topographic protection from wind, heavy regular rain throughout the year, with precipitation exceeding evaporation, and modest tidal exchange produce stratified water columns with brackish waters above permanently anoxic saline hypolimnia. Permanent lake stratification is documented for 18 years; sediment cores (by others) show stratification for >100 years, and recent constant sea level implies ecosystem stability for thousands of years. Therefore, the marine lakes in Palau are small, closed, simple ecosystems that do not change over time–steady-state chemostats permitting replicate field measurements of biological and physical attributes from day to day, month to month, or decade to decade. [Key words: Palau, meromictic, marine lake, karst, lake stratification, tides, model ecosystem.]     

Directional Characteristics of Potentially Damaging Wind Gusts in the Southeast United States

Annual estimated storm damage in the United States is seven billion dollars. Much of that damage is caused by tree blowover that is induced by high wind gusts. The prevailing directions of these wind gusts dictate the zones around structures in which trees may potentially fall and cause damage. To gain a better understanding of hazardous wind gusts, this research examines the directional component of wind gusts in the Southeast United States. Regional patterns of wind gusts are identified and tied to atmospheric and terrestrial patterns. Results indicate the following: (1) gusts along the northeast coast of the study area are bidirectional, being from the northeast and southwest; (2) the southeast coast has a predominantly westerly component to the gusts with little impact from the east; (3) the Piedmont is strongly influenced by westerly gusts, but an easterly component increases gradually to the northeast; and (4) high gusts in the mountains demonstrate a strong relationship with the regional and local topographic characteristics.     

An analysis of intra-event precipitation variability for the United States (1980–2010)

Hourly precipitation data were collected from 143 first-order US weather stations during the period from 1980 to 2009 to assess the internal distribution of precipitation events lasting at least three hours. A total of 46,595 individual precipitation events were identified and evaluated using the mean, standard deviation, skewness, kurtosis, and the number of peaks occurring within an event. Mean event duration is longest along the West and Northwest coasts, the Mid-South, the Mid-Atlantic, and the Northeast; while shorter-duration events are more frequent in the Rocky Mountains, the Southwest, and the Great Plains. Mean event precipitation and standard deviation are greatest along the Gulf Coast and decrease inland. Precipitation events are positively skewed, indicating that more precipitation tends to occur earlier in the event. The most positively-skewed events are also located in regions flanking the Gulf of Mexico, while less-skewed events are common in the Northwest and Rocky Mountain regions. Event kurtosis is negative throughout the entire USA, with the highest negative values generally west of the Front Range, where cyclonic development and transition produce more evenly distributed precipitation within storms. Intra-event precipitation maxima were also evaluated, with western Florida and the desert Southwest having the greatest number per event.     

A Climatology of Northwest Missouri Snowfall Events: Long-Term Trends and Interannual Variability

The goal of this study was to develop a 50-yr. statistical climatology of snowfall occurrences using data from a dense network of cooperative station observations covering northwest and central Missouri, and these records were provided by the Missouri Climate Center. This included a study of the long-term trends and interannual variability in snowfall occurrence as related to sea surface temperature variations in the Pacific Ocean basin associated with the El Niño and Southern Oscillation (ENSO) and the North Pacific Oscillation (NPO). These trends and variations were then related to four synoptic-scale flow regimes that produce these snowfalls in the Midwest. The results demonstrate that during the snowfall season (Oct-April) the northwest Missouri region can expect about eight snowfall events which produce ≥3 in. (>7.5 cm) of accumulation. While no significant long-term trend in overall snowfall occurrence was found, a decrease in the number of extreme events (≥10 in., >25 cm) was noted. Also, fewer snowfall events were found during El Niño years, while more heavy snowfall events occurred during "neutral" years, and these results could be related to synoptic-scale variability. A closer examination of the results demonstrated that El Niño/La Niña related variability in snowfall occurrence was superimposed on longer-term NPO-related variability.     

Analyses of the warm season rainfall climatology of the northeastern US using regional climate model simulations and radar rainfall fields

We examine the warm season (April-September) rainfall climatology of the northeastern US through analyses of high-resolution radar rainfall fields from the Hydro-NEXRAD system and regional climate model simulations using the weather research and forecasting (WRF) model. Analyses center on the 5-year period from 2003 to 2007 and the study area includes the New York-New Jersey metropolitan region covered by radar rainfall fields from the Fort Dix, NJ WSR-88D. The objective of this study is to develop and test tools for examining rainfall climatology, with a special focus on heavy rainfall. An additional emphasis is on rainfall climatology in regions of complex terrain, like the northeastern US, which is characterized by land-water boundaries, large heterogeneity in land use and cover, and mountainous terrain in the western portion of the region. We develop a 5-year record of warm season radar rainfall fields for the study region using the Hydro-NEXRAD system. We perform regional downscaling simulations for the 5-year study period using the WRF model. Radar rainfall fields are used to characterize the interannual, seasonal and diurnal variation of rainfall over the study region and to examine spatial heterogeneity of rainfall. Regional climate model simulations are characterized by a wet bias in the rainfall fields, with the largest bias in the high-elevation regions of the model domain. We show that model simulations capture broad features of the interannual, seasonal, and diurnal variation of rainfall. Model simulations do not capture spatial gradients in radar rainfall fields around the New York metropolitan region and land-water boundaries to the east. The model climatology of convective available potential energy (CAPE) is used to interpret the regional distribution of warm season rainfall and the seasonal and diurnal variability of rainfall. We use hydrologic and meteorological observations from July 2007 to examine the interactions of land surface processes and rainfall from a regional perspective.     

亚印太交汇区海表温度的分布和变化特征及其对中国降水的影响

利用1967-2009年的逐月海表温度(Sea Surface Temperature,SST)资料和降水资料,以及经验正交函数(Empirical Orthogonal Function,EOF)和相关分析方法,探讨了亚印太交汇区(Joining Area of Asia and Indian-Pacific Oce...