Temporal variability of the Buenos Aires, Argentina, urban heat island

This paper describes the statistical characteristics and temporal variability of the urban heat island (UHI) intensity in Buenos Aires using 32-year surface meteorological data with 1-h time intervals. Seasonal analyses show that the UHI intensity is strongest during summer months and an “inverse” effect is found frequently during the afternoon hours of the same season. During winter, the UHI effect is in the minimal. The interannual trend and the seasonal variation of the UHI for the main synoptic hours for a longer record of 48?years are studied and associated to changes in meteorological factors as low-level circulation and cloud amount. Despite the population growth, it was found a negative trend in the nocturnal UHI intensity that could be explained by a decline of near clear-sky conditions, a negative trend in the calm frequencies and an increase in wind speed. Urban to rural temperature differences and rural temperatures are negatively correlated for diurnal and nocturnal hours both for annual and seasonal scales. This result is due to the lower interannual variability of urban temperatures in comparison to rural ones.     

Wind wave climate change: Impacts on the littoral processes at the Northern Buenos Aires Province Coast, Argentina

Several works reported wind-wave climate changes at Buenos Aires Province continental shelf. The aim of this work is to investigate the impact of these changes in the coastal processes of the region. This study is carried out by means of visual wave parameters gathered at the surf zone of Pinamar and by a conveniently implemented and validated numerical wave model (SWAN). Numerical results corresponding to a grid point located 30 km off Pinamar show a significant increase of wave heights from the S and SSE directions and in the frequency of occurrence of waves coming from the S, SSE and E. It is shown that these slight offshore appreciated trends would not have significant effects on the breaker heights observed at the surf zone at Pinamar. On the contrary, the slight positive trend observed offshore in the frequency of occurrence could be affecting the incidence of waves onshore, producing an increase in the number of cases of normal incidence at the surf zone and, consequently, a significant decrease in the alongshore wave energy flux assessed at Pinamar. This reduction in the alongshore wave energy flux could be responsible for some coastal changes detected in the region as, for instance, the remarkable shortening of Punta Rasa spit located 70 km northward Pinamar.     

Objective method for classifying air masses: an application to the analysis of Buenos Aires’ (Argentina) urban heat island intensity

Summary ?During recent years, numerous studies have examined the Buenos Aires urban climate, but the relationship between large-scale weather conditions and the Buenos Aires urban heat island (UHI) intensity has not been studied. The goal of this paper is to apply an objective synoptic climatological method to identify homogeneous air masses or weather types affecting Buenos Aires during winter, and to relate the results to the UHI intensity. A K-means clustering method was used to define six different air masses considering the 03:00, 09:00, 15:00 and 21:00 LT surface observations of dry bulb temperature, dew point, cloud cover, atmospheric pressure and wind direction and velocity at Ezeiza, the most rural meteorological station of the Buenos Aires metropolitan area (Fig. 1). Results show that the mean UHI intensity is at its maximum (2.8 °C) a few hours before sunrise when conditions are dominated by cold air masses associated with cold-core anticyclones, weak winds and low cloud cover. Inverse heat islands are found during the afternoon for all air masses indicating that surface processes are not dominant at that time. The relatively infrequent and warmest air mass is the only one that presents a mean negative urban-rural temperature difference (−0.1 °C) during the afternoon with the smallest diurnal cycle of the UHI intensity probably due to the prevailing high humidity and cloudy sky conditions. The paper provides an insight into the Buenos Aires urban–rural temperature difference under a variety of winter weather types and results could be useful to improve local daily temperature forecasts for the metropolitan area of Buenos Aires on the basis of the routine forecasts of weather types. Received October 24, 2001; revised June 12, 2002; accepted October 10, 2002     

义乌市降水变化特征分析

根据历史和实测资料的统计分析,得到义乌市的降水变化特征。结果表明：丰水期义乌市的涝年偏多,旱年偏少,而枯水期则旱年偏多,涝年偏少。厄尔尼诺事件的当年或翌年,义乌市的降水显著偏多,而拉尼娜事件的当年或翌年,义乌市的降水则显著偏少。丰水期平均入梅日偏早,平均出梅日偏晚,平均梅雨日数偏长,平均梅雨量偏多,而在枯水期则反之。义乌市6月6—15日入梅的可能性最大,出梅日期的时间分布相对比较分散,其集中期的发生规律不如入梅集中期明显。厄尔尼诺事件的当年或翌年,义乌市的出梅日偏晚,而拉尼娜事件的当年或翌年,义乌市的出梅日偏早。研究结果可为水库源区雨季的人工增雨作业提供科学依据。     

义乌市降水变化特征分析

根据历史和实测资料的统计分析,得到义乌市的降水变化特征。结果表明:丰水期义乌市的涝年偏多,旱年偏少,而枯水期则旱年偏多,涝年偏少。厄尔尼诺事件的当年或翌年,义乌市的降水显著偏多,而拉尼娜事件的当年或翌年,义乌市的降水则显著偏少。丰水期平均入梅日偏早,平均出梅日偏晚,平均梅雨日数偏长,平均梅雨量偏多,而在枯水期则反之。义乌市6月6—15日入梅的可能性最大,出梅日期的时间分布相对比较分散,其集中期的发生规律不如入梅集中期明显。厄尔尼诺事件的当年或翌年,义乌市的出梅日偏晚,而拉尼娜事件的当年或翌年,义乌市的出梅日偏早。研究结果可为水库源区雨季的人工增雨作业提供科学依据。     

半干旱榆中地区最小有效降水量及降水转化率的研究

有效降水对于土壤水分的补充和农作物的生长来说是一个很重要的概念。通常认为大于5 mm的降水即为有效降水。但是有效降水的影响因素很多,在不同的地理环境和气候背景条件下,最小有效降水量也会有所不同。利用2006年6月—2011年3月兰州大学半干旱气候与环境观测站资料,从土壤湿度变化的角度出发,根据有效降水的定义,对甘肃榆中地区的最小有效降水量做了初步研究。通过分析该地区不同季节、温度和植被条件下不同土壤深度最小有效降水量,发现5、10、20 cm土壤层的最小有效降水量分别为4、5、8 mm。季节分布上,各层土壤最小有效降水量均为夏季最高,春季和秋季值较为接近。高温年的最小有效降水量高于低温年的值,生长季高于非生长季。在降水超过最小有效降水量并且量级较小时,随着降水量的增大,土壤湿度增量呈指数形式增大,这时降水的转化率也较高;而当降水达到一定量级时,超过了土壤的入渗率,水分以径流的形式损失,土壤湿度增量的变化率减小,降水的转化率也趋于一定值。0—20 cm土壤层降水转化率达到70%。     

陕西黄土高原诱发地质灾害降雨临界值研究

利用陕西黄土高原47 a地质灾害和相对应的降雨资料,在陕西黄土高原地质灾害易发区划分基础上,采用面平均雨量确定各易发区的诱发地质灾害的临界降雨量,各易发区的临界雨量有明显的地域性差别;滑坡和崩塌的临界雨量明显不同,一般滑坡临界雨量均高于崩塌;高易发区的临界雨量并不一定低于中易发区和易发区。利用相关统计分析和日综合雨量方法,确定诱发地质灾害的降雨临界值,诱发滑坡的降雨启动值、加速值、临灾值分别为25、35、65 mm,诱发崩塌降雨启动值、加速值、临灾值分别为15、30、50 mm。     

江西省土壤体积含水量对降水的响应特征

利用2017—2020年江西省36站壤土质地土壤水分观测站土壤体积含水量资料和降水资料,研究了江西省土壤体积含水量对降水过程的响应特征.结果表明:1)土壤体积含水量对不同类型降水过程的响应差异大,对于小于10 mm的降水过程几乎无响应,对10—25 mm的降水过程响应深度为0—10 cm,对25—50 mm的降水过程响应深度为0—20 cm,对大于50 mm的降水过程响应深度为0—60 cm.2)土壤体积含水量对降水的响应分为快速增长和平稳减弱两个阶段,在快速增长阶段土壤体积含水量先快速增长到最大值,然后缓慢下降,且增长阶段的持续时间小于减弱阶段的持续时间,增长过程和减弱过程不对称.3)响应过程的持续时间主要集中在1—9 h,其中3—6 h占比高达49％.     

淮海地区降水周期及突变特征分析

利用淮海地区1955—2004年23个气象站点的逐日降水资料,分析了淮海地区降水的主要周期振荡以及突变点,结果表明:该地区降水均有多个时间尺度的周期变化特征,降水周期变化显著,干湿交替现象明显;降水的年代际以及年际尺度的主要周期:年降水为12a、9a、5a,春季降水为14a、6a、3a,夏季为10a、4a,秋季为21a、10a、7a,冬季为18a、5a。年降水减少趋势明显,在1967年发生了突变,由相对多雨期转入相对少雨期;春季、夏季、秋季降水都有不同程度的减少趋势,而冬季降水则表现为增加的趋势。     

Seasonal relationship between temperature,precipitation and snow cover in a mountainous region

Summary An analysis of correlation coefficients for climatological data covering the period 1901–1994 or 1931–1994 for six locations in Switzerland has been made in order to highlight the relationships between temperature, precipitation (rain and snow) and snow in summer and in winter. The results show that colder summers tend to be associated with more precipitation, mainly in terms of the frequency of occurrence of precipitation, but also in terms of its abundancy. In winter, sites located at lower altitudes behave differently from those at higher elevations. At lower altitudes, warmer winters tend to be rainier and to have less snow (only a small part of winter precipitation falls in the form of snow). Above 1000–1500 m, correlations between temperature on the one hand, and precipitation or snow on the other, tend to be weaker than at lower elevations; warmer winters are associated with less snow but also with less precipitation in general, while the relationship between precipitation and snow is stronger.These results confirm that during cold periods of the past, such as Löbben Phase (1400 BC — 1230 BC) cold summers were probably linked to frequent and abundant precipitation. These conditions led to increased mortality as well as to population migrations. In terms of potential future global warming, if the current temperature/precipitation relationships remain unchanged, then warmer summers will likely be linked to a decrease in precipitation. Higher winter temperatures can be expected to lead to a general decrease of snow and to a decrease in precipitation, but only at higher elevations; warmer winters would conversely be associated with an increase in precipitation at lower altitudes.With 4 Figures     

分类型最优法在江苏沿江地区降水估测中的应用与讨论

为提高现有天气雷达产品生成模块中处理系统算法精度、并为其他短时临近预报系统或数值预报模式提供合适的Z-I关系为目的,选择江苏沿江地区作为试验区域,采用分类型最优法建立相应的Z-I关系,并比较分类型最优法与单一Z-I关系对过程雨量和分段雨量的估测能力.结果表明:分类型最优法比单一Z-I关系法明显提高过程雨量估测的精度,梅汛期降水估测精度提高近2.5倍,夏季台风降水估测由低估72％降低至低估45％.对不同雨量段进行估测比较后发现,分类型最优法对强降水雨量段改善较为明显,对雨强＞ 10 mm/h的梅汛期对流云降水和台风降水所有雨量段的雨量估测改善明显.最后在气候统计的基础上,通过改进雷达估测降水产品色标数值等级,以达到优化雷达估测降水产品图像的显示能力.     

Climatic change and quasi-oscillations in central-west Argentina summer precipitation: main features and coherent behaviour with southern African region

Summer rainfall variability (October to March) shows inter-annual to multi-decadal fluctuations over a vast area of subtropical Argentina between 28°S–38°S and 65°W–70°W. Statistically significant oscillations of quasi-period in the bands of 18–21, 6, 4 and 2 years can be found throughout the region and intra-regionally, though the latter are variable. The lower frequency variation produces alternating episodes of above and below normal rainfall each lasting roughly 9 years. This quasi-fluctuation appears to be shared with the summer rainfall region of South Africa and were in-phase related one another until mid-1970s. The teleconnection between both subtropical regions could be generated by an atmospheric-oceanic bridge through the global sea surface temperatures (SSTs), particularly those of the equatorial-tropical South Atlantic. From mid-1970s, the alternating wet and dry pattern has been interrupted in the Argentine region producing the longest, as yet unfinished, wet spell of the century. Thus, a significant change of the long-term variation was observed around 1977 toward lower frequencies. Since then the statistical model that explains more than 89% of the variance of the series until 1977, diverges from the observed values in the 1980s and 1990s. In addition the Yamamoto statistical index, employed to detect a climatic jump, reaches its major value in 1973 at the beginning of the current long wet spell. Therefore the change could be located between 1973 and 1977. Application of the t-student's test gives significant differences of mean values for pre-1977 and post-1977 sub-samples from both individual time series and the regional index series. The spectral analysis also shows changes in energy bands in concordance with the features of the change that occurred from mid-1970s. The change gives rise to a significant increment of more than 20% in average of normal rainfall over the region. Conversely, a drought between mid-1980s and the 1990s has been observed in the South African counterpart with severe characteristics, thereby continuing the quasi-18-year oscillation. Consequently, the low-frequency coherent behaviour between both the Argentine and South African regions is lost from the mid-1970s. The analysis of association of wet/dry spells and warm/cold, El Niño/La Niña episodes appears to be not significant at scales of year-to-year variability although at decadal to multi-decadal scales the association could be relevant. More than one process of multi-decadal variability of global SSTs could influence the Argentine summer rainfall region and the former bi-decadal teleconnection. Finally, potential hypothetical factors of change are discussed, such as the strengthening of direct and indirect mechanisms of moisture flux transport associated with global warming, low-level atmospheric circulation changes and/or to SSTs mean condition long-term variations over tropical and subtropical South Atlantic and South Pacific oceans.     

广东阳江一次强降水过程的成因分析

2011年6月28—30日广东南部沿海及珠江三角洲地区发生连续强降水过程, 其中29日强降水发生在季风涌背景下。采用常规气象资料、 区域自动站资料以及NCEP/NCAR分辨率1°×1°再分析资料, 着重分析29日受季风涌影响的强降水成因。结果表明, 此次过程发生在季风槽偏强的背景下, 季风涌的爆发和加强主要表现在低空急流的增强上; 无论时间上和空间上, 低空急流与强降水均有很好的对应关系, 其左侧的强辐合与高层的强辐散相配合, 是强降水发生发展的原因之一; 季风涌爆发后, 不稳定能量得到再次积累, 大气维持高温高湿的条件不稳定状态, 有利于降水增大和维持。     

Precipitation extremes in a karst region: a case study in the Guizhou province, southwest China

The topography of hilly landscapes modifies crop environment changing the fluxes of water and energy, increasing risk in these vulnerable agriculture systems, which could become more accentuated under climate change (drought, increased variability of rainfall). In order to quantify how wheat production in hilly terrain will be affected by future climate, a newly developed and calibrated micro-meteorological model for hilly terrain was linked to a crop growth simulation model to analyse impact scenarios for different European regions. Distributions of yield and growing length of rainfed winter wheat and durum wheat were generated as probabilistic indices from baseline and low (B2) and high (A2) emission climate scenarios provided from the Hadley Centre Regional Climate Model (HadRM3). We used site-specific terrain parameters for two sample catchments in Europe, ranging from humid temperate (southeast UK) to semi-arid Mediterranean (southern Italy). Results for baseline scenario show that UK winter wheat is mainly affected by annual differences in precipitation and yield distributions do not change with terrain, whilst in the southern Mediterranean climate yield variability is significantly related to a slope × elevation index. For future climate, our simulations confirm earlier predictions of yield increase in the UK, even under the high emission scenario. In the southern Mediterranean, yield reduction is significantly related to slope × elevation index increasing crop failure in drier elevated spots but not in wet years under baseline weather. In scenarios for the future, the likelihood of crop failure rises sharply to more than 60%, and even in wet years, yields are likely to decrease in elevated spots.     

2009年7月17日唐山地区强降水成因分析

利用常规天气资料和NCEP/NCAR再分析资料,对2009年7月17日唐山地区暴雨天气过程进行分析。结果表明：强降水是暖湿空气向北输送与低层冷空气交汇引起的。降水前期,唐山地区中低层水汽强辐合为强降水提供了水汽条件。冷空气从底层侵入,抬升暖湿气流,低层暖锋锋生使对流不稳定性增大,上升运动加强,降水量增大。强降水区存在低层辐合、高层辐散和斜升运动机制。850 hPa湿位涡正压项MPV1〉0区域较好地反映出冷空气活动特征,强降水出现在MPV1零线附近偏冷空气一侧。     

石家庄不同等级降水日数的时空分布特征

利用1972—2007年石家庄市17个观测站的逐日降水资料,采用线性趋势法和Mann-Kendall突变检验法,分析了近36 a石家庄市不同等级降水日数时空分布特征和变化规律。结果表明：石家庄市年总雨日数和不同等级降水日数均呈减少趋势,暴雨日数减少趋势最不明显;年总雨日数发生了突变,突变年份为1992年;20世纪90年代后,降水有向极端化发展的趋势。在空间分布上,石家庄市年总雨日数及不同等级降水日数自西北、东南向中部地区逐渐减少,西北部山区和东南部平原存在两个多雨日中心和多暴雨中心;各站年总雨日数和小雨日均呈显著减少趋势,北部、西北部和东南部地区减少趋势相对更显著,其它等级降水事件日数大多数观测站也呈减少趋势,但减少速率相对较小。     

石家庄市不同等级降水日数的时空分布特征

利用1972—2007年石家庄市17个测站逐日降水资料,采用线性趋势法和Mann-Kendall突变检验法,分析了近36 a石家庄市不同等级降水日数时空分布特征和变化规律。结果表明：石家庄市年总雨日数和不同等级降水日数均呈减少趋势,暴雨日数减少趋势最不明显;年总雨日数发生了突变,突变年份为1992年;20世纪90年代后,降水有向极端化发展的趋势。在空间分布上,石家庄市年总雨日数和不同等级降水日数自西北、东南向中部地区逐渐减少,西北部山区和东南部平原存在两个多雨日中心和多暴雨中心;各站年总雨日数和小雨日均呈显著减少趋势,北部、西北部和东南部地区减少趋势相对更显著,其他等级降水事件日数大多数观测站也呈减少趋势,但减少速率相对较小。     

2009年7月17日唐山地区强降水成因分析

利用常规天气资料和NCEP/NCAR再分析资料,对2009年7月17日唐山地区暴雨天气过程进行分析。结果表明：强降水是暖湿空气向北输送与低层冷空气交汇引起的。降水前期,唐山地区中低层水汽强辐合为强降水准备了条件。冷空气从底层侵入,抬升暖湿气流,低层暖锋锋生使对流不稳定性增大,上升运动加强,降水量增大。强降水区存在低层辐合、高层辐散和斜升运动机制。850hPa湿位涡正压项MPV1＞0区域能较好地反映出冷空气活动特征,强降水出现在MPV1零线附近偏冷空气一侧。     

辽宁降水分区变化特征及夏季降水影响因子分析

根据1961—2000年辽宁地区降水资料,将辽宁地区降水划分为4个区,分析各分区降水的年际、年代际、季节变化以及周期特征。结果表明:辽宁南部和东南部地区降水明显减少;自20世纪90年代开始,东南部和南部地区降水显著减少,而中部地区降水增加;东南部地区的夏冬季和南部地区的冬季降水减少,西部地区春季降水增多。周期特征为春季和冬季周期为2 a或4 a,夏季和秋季为10 a。各分区夏季降水的影响因子不同,辽南地区多雨年东亚槽明显加深,东南区多雨年东亚槽略有加深并且偏东;南部和东南部夏季降水与副热带高压系统相关显著;各区夏季降水与太阳黑子负相关较好,其中8月相关显著,南部和中部相关性均好于东南部和西部地区。     

1109号“梅花”台风对辽宁降水的影响分析

利用逐日NCEP再分析、常规观测、加密自动站、卫星云图及多普勒雷达等资料,分析了1109号台风“梅花”路径、结构和降水变化的原因,并对“梅花”的物理量特征进行了诊断分析.结果表明:副热带高压外围引导气流较强时,台风沿引导气流方向行进,引导气流较弱时,台风受高空槽的吸引,移动路径产生向西的分量;中低层冷空气的侵入,破坏了台风自上而下的暖心、不对称结构,呈现上暖下冷的稳定结构,趋于向温带气旋变性.“梅花”影响辽宁前期,主要受台风外围气流影响,水汽厚度浅薄,但维持时间长,产生的累计雨量较大.后期台风残余云系,在冷空气的作用下,冷暖空气交界处激发出整层上升运动,同时在台风外围水汽、偏南季风水汽共同作用下水汽厚度增加,更充沛的水汽来源为更强降水提供了有利的水汽条件,在辽宁中南部产生暴雨大暴雨天气.此外,雷达、自动站反映的中尺度切变、涡旋,为对流系统发展起到了触发作用.