Spatial dependence of diurnal temperature range trends on precipitation from 1950 to 2004

This paper analyzes the spatial dependence of annual diurnal temperature range (DTR) trends from 1950–2004 on the annual climatology of three variables: precipitation, cloud cover, and leaf area index (LAI), by classifying the global land into various climatic regions based on the climatological annual precipitation. The regional average trends for annual minimum temperature (T _min) and DTR exhibit significant spatial correlations with the climatological values of these three variables, while such correlation for annual maximum temperature (T _max) is very weak. In general, the magnitude of the downward trend of DTR and the warming trend of T _min decreases with increasing precipitation amount, cloud cover, and LAI, i.e., with stronger DTR decreasing trends over drier regions. Such spatial dependence of T _min and DTR trends on the climatological precipitation possibly reflects large-scale effects of increased global greenhouse gases and aerosols (and associated changes in cloudiness, soil moisture, and water vapor) during the later half of the twentieth century.     

阿勒泰地区气温日较差的气候变化特征

利用线性趋势法对1961-2008年阿勒泰地区7个气象站点气温日较差进行趋势研究,并根据各因子趋势值,应用相关统计法分析了影响气温日较差呈减小趋势的因子。结果表明：阿勒泰地区四季日较差呈现显著减小趋势,其中冬季最显著,秋季变化最弱。各季节最低气温上升趋势最明显,而最高气温上升趋势较弱。阿勒泰地区与月平均气温日较差相关性最强的因子是日照时数,呈正相关;其次分别为总云量、降水量和水汽压,都呈负相关。年气温日较差与降水量和水汽压相关性最大。     

Empirical estimation of the monthly-mean daily temperature range

Summary ?This is a sequel to a study of the empirical estimation of the annual mean temperature and its range, at any location on land, based on the historical surface climate record. Here the spatial patterns of the daily temperature range (DTR) and its seasonal variation are examined. The DTR is highest in the subtropical deserts and is less at high latitudes, as well as within 30–150 km from an ocean. It is generally higher in winter (summer) at low (high) latitudes. The coastal DTR reduction is explained by sea breezes, onshore advection, and low-level cloud cover. Even large bodies of water, such as Lake Michigan, affect the near-shore DTR. Elevation does not directly affect the DTR, but valleys tend to have a DTR that is 2–6 K larger than adjacent hills or ridges. The main factor affecting the DTR is the afternoon relative humidity, which is dynamically linked to low-level cloud cover. An empirical relationship between DTR and afternoon relative humidity has an uncertainty of about 1.4 K for monthly-mean values. Received March 6, 2002; revised September 20, 2002; accepted November 3, 2002     

Detection and attribution of anthropogenic forcing to diurnal temperature range changes from 1950 to 1999: comparing multi-model simulations with observations

Observations show that the surface diurnal temperature range (DTR) has decreased since 1950s over most global land areas due to a smaller warming in maximum temperatures (T _max) than in minimum temperatures (T _min). This paper analyzes the trends and variability in T _max, T _min, and DTR over land in observations and 48 simulations from 12 global coupled atmosphere-ocean general circulation models for the later half of the 20th century. It uses the modeled changes in surface downward solar and longwave radiation to interpret the modeled temperature changes. When anthropogenic and natural forcings are included, the models generally reproduce observed major features of the warming of T _max and T _min and the reduction of DTR. As expected the greenhouse gases enhanced surface downward longwave radiation (DLW) explains most of the warming of T _max and T _min while decreased surface downward shortwave radiation (DSW) due to increasing aerosols and water vapor contributes most to the decreases in DTR in the models. When only natural forcings are used, none of the observed trends are simulated. The simulated DTR decreases are much smaller than the observed (mainly due to the small simulated T _min trend) but still outside the range of natural internal variability estimated from the models. The much larger observed decrease in DTR suggests the possibility of additional regional effects of anthropogenic forcing that the models can not realistically simulate, likely connected to changes in cloud cover, precipitation, and soil moisture. The small magnitude of the simulated DTR trends may be attributed to the lack of an increasing trend in cloud cover and deficiencies in charactering aerosols and important surface and boundary-layer processes in the models.     

VARIABILITY OF DIURNAL TEMPERATURE RANGE IN EAST AFRICA DURING 1921–2010

This study investigates the long-term spatiotemporal variability of diurnal temperature range(DTR) in East Africa(EA). The study carries out non-parametric trend analysis of gridded DTR monthly data sourced from Climatic Research Unit(CRU). The DTR exhibits mixed signals in space and time over EA. The DTR correlates negatively with rainfall over EA. Reduction in DTR coincides with the summer season in the northern and southern hemispheres respectively, suggesting the influence of cloud cover on it. There was a non-uniform pattern of DTR changes across the region with time. Lake Victoria basin recorded the highest warming rates. The Indian Ocean coast recorded the least spatiotemporal variability in DTR. A reduction in DTR is evident in the two seasons: hot and cold. The start of the study period; 1921—1930, was the coolest decade in the study period. Most parts of EA recorded negative DTR anomalies in 1961—1970. The overall reduction in DTR throughout the study period highlights the ongoing warming which is a global phenomenon. There remains need for investigating the causation of the observed DTR variability for effective monitoring of the variability in future.     

Long-term trend analysis for temperature in the Jinsha River Basin in China

On the basis of the mean annual and seasonal temperatures from 30 meteorological stations in the Jinsha River Basin (JRB) from 1961 to 2008, the temperature trends are analyzed by using Mann–Kendall test and linear trend analysis. There is an increasing trend in mean annual and seasonal temperatures during this period, and the increasing trends in winter seem more significant than those in the other three seasons. The mean annual temperature has increased by 0.0158°C/year during the last 48 years. There are more than 70% of stations exhibiting increasing trends for annual and seasonal temperatures. The increasing trends in the headwater and upper reaches are more dominant than those in the middle and lower reaches. The largest increase magnitude occurred in the low temperature area, while the largest decrease magnitude occurred in the high temperature area. The decreasing trends are mainly characterized for the maximum temperature time series, and summer is the only season showing a slight and insignificant increasing trend. All the time series showed a statistically significant increasing trend at the level of α?=?0.05 for the minimum temperature time series. As a whole, the increasing magnitude of the minimum temperature is significantly greater than the decreasing magnitude of the maximum temperature.     

西南地区云量变化特征

利用西南地区(云南、贵州、四川、重庆)记录较为完整的73个测站1956~2005年月平均云量资料,采用经验正交函数分析和Mann-Kendall突变检验方法,研究分析了西南地区云量的时空分布特征。结果表明:就全年而言,整个西南地区总云量的变化趋势一致,且存在着明显的年际变化特征,1990年代以后全年总云量表现出减少趋势;此外,总云量的分布在一定程度上受地形和区域气候的影响。从季节来看,夏、秋、冬季的总云量在西南地区为空间一致的变化趋势,而春季四川盆地北部总云量的变化趋势与其余地区相反;四季总云量也有明显的年际变化特征。低云量,全年和四季的时空变化特征相似,由于受地形起伏及区域气候差异的影响,川西高原东部和重庆地区的变化趋势与四川盆地的相反,且同样存在着明显的年际变化特征。另外,突变分析结果显示,西南地区的低云量近50a来呈持续减少趋势,而总云量在1990年发生突变,突变前在0线附近震荡,突变后总云量持续减少。     

Biases in the diurnal temperature range in Central Europe in an ensemble of regional climate models and their possible causes

The study examines how regional climate models (RCMs) reproduce the diurnal temperature range (DTR) in their control simulations over Central Europe. We evaluate 30-year runs driven by perfect boundary conditions (the ERA40 reanalysis, 1961–1990) and a global climate model (ECHAM5) of an ensemble of RCMs with 25-km resolution from the ENSEMBLES project. The RCMs’ performance is compared against the dataset gridded from a high-density stations network. We find that all RCMs underestimate DTR in all seasons, notwithstanding whether driven by ERA40 or ECHAM5. Underestimation is largest in summer and smallest in winter in most RCMs. The relationship of the models’ errors to indices of atmospheric circulation and cloud cover is discussed to reveal possible causes of the biases. In all seasons and all simulations driven by ERA40 and ECHAM5, underestimation of DTR is larger under anticyclonic circulation and becomes smaller or negligible for cyclonic circulation. In summer and transition seasons, underestimation tends to be largest for the southeast to south flow associated with warm advection, while in winter it does not depend on flow direction. We show that the biases in DTR, which seem common to all examined RCMs, are also related to cloud cover simulation. However, there is no general tendency to overestimate total cloud amount under anticyclonic conditions in the RCMs, which suggests the large negative bias in DTR for anticyclonic circulation cannot be explained by a bias in cloudiness. Errors in simulating heat and moisture fluxes between land surface and atmosphere probably contribute to the biases in DTR as well.     

Trends in extreme temperature indices in Huang-Huai-Hai River Basin of China during 1961–2014

Spatial and temporal characteristics of temperature extremes have been investigated in Huang-Huai-Hai (HHH) region based on the daily series of temperature observations from 162 meteorological stations. A total of 11 indices were used to assess the changes of temperature pattern. Linear trend analyses revealed that the daily maximum temperature (TXx) increased at α = 0.05 level with a magnitude of 0.15 °C per decade on the regional scale during the period of 1961–2014. More pronounced warming trend of the daily minimum temperature (TNn) was detected at a rate of 0.49 °C per decade (α = 0.01 level). Consequently, a decreasing trend of the temperature range of TXx and TNn (extreme temperature range) was observed. The frequency of hot days (TXf90) and annual average of warm events (warm spell duration indicator, WSDI) showed significant increasing trends, while that of cold nights (TNf10) and cold events (cold spell duration indicator, CSDI) showed opposite behaviors. Both warm winter (W-W) and hot summer (H-S) series displayed significant increasing trends at α = 0.01 confidence level. The cold winter (C-W) series showed a decreasing trend at α = 0.01 confidence level, while the cool summer (C-S) series showed a nonsignificant decreasing trend that is not passing the 90% confidence level (α = 0.1). Abrupt increments of warm­related extremes (TXx, TXf90, WSDI) have been detected since 1990s, and a steadily decreasing trend of cold related extremes (TNf10, CSDI) was found since 1970s. Ten hot summers out of 11 and nine warm winters out of 10 occurred after 1990s. Altitude has a large impact on spatial pattern of extreme temperature indices, and the urban heat island effect also has an impact on amplitude of variation in extreme temperature. Trend magnitudes are significantly larger at sites with high altitudes for warm­related indices (TXx, TXf90, WSDI), while those involving cold-related indices (TNn, TNf10) are remarkably larger for stations with low altitudes.     

Interannual and Decadal Variations of Surface Solar Radiation over East China in the First Half of the 20th Century

Variability and long-term trends of sunshine duration(SSD) and total cloud cover(TCC) were studied based on surface observations from 10 meteorological stations over East China in the first half of the 20 th century. The correlation coefficients between SSD and diurnal temperature range(DTR), as well as TCC, were analyzed. SSD experienced a significant increasing trend(0.16 h d-1 per decade) from 1908 to 1936, and the maximum brightening was in autumn(0.33 h d-1 per decade). The good agreement between the variability of SSD and DTR, supported by the correlation coefficient between them of 0.72, implies that the SSD measurements were reliable. TCC showed a decreasing trend(-0.93% per decade) and was significantly inversely related to SSD(-0.74), indicating the variation of SSD was attributable to changes in cloud cover. The result was obviously different to that since the 1960 s, when clouds could not account for the decadal trend of surface solar radiation in China.     

Watershed-wide trend analysis of temperature characteristics in Karun-Dez watershed, southwestern Iran

Trend estimation of climatic characteristics for a watershed is required to determine developing compatible strategies related to design, development, and management of water resources. In this study, the trends of the annual maximum (T _max), minimum (T _min), and mean (T _mean) air temperature; temperature anomaly (T _anomaly); and diurnal temperature range (DTR) time series at 13 meteorological stations located in the Karun-Dez watershed were analyzed using the Mann–Kendall and linear regression trend tests. The pre-whitening method was used to eliminate the influence of serial correlation on the Mann–Kendall test. The result showed increasing trends in the T _min, T _mean, and T _anomaly series at the majority of stations and decreasing trend in the T _max and DTR series. A geographical analysis of the trends revealed a broad warming trend in most of the watershed, and the cooling trends were observed only in the southern parts. Furthermore, the geographical pattern of the trends in the T _mean and T _anomaly series was similar, and the T _max data did not show any dominant trend for the whole watershed. This study provides temperature change scenarios that may be used for the design of future water resource projects in the watershed.     

Analysis of recent trends in mean maximum and minimum temperatures in a region of the NW of Spain (Castilla y León)

Summary The present paper is an analysis of mean maximum and minimum temperatures carried out on monthly, seasonal and annual time-scales examining the data collected at 171 meteorological stations over a region in the North West of Spain (Castilla y León) for the period 1961–1997. Various statistical tools were used to detect and describe significant trends in these data. The magnitude of the trends was derived from the slopes of the regression lines using the least squares method, and the statistical significance was determined by means of the non-parametric Mann-Kendall test. The pattern obtained is quite similar for mean maximum and minimum temperatures with increases in all months of the year, and in the annual series. The seasonal series corresponding to winter and summer also followed this same pattern. Spring and autumn were found to be more irregular. Because maximum temperature increased at a higher rate than minimum temperature in this period, an increase in the annual diurnal temperature range (DTR) was observed. The correlation between the North Atlantic Oscillation (NAO) and the regional maximum and minimum temperatures and DTR series for the period 1961–1997 have also be studied in this paper.     

On the Contrasting Decadal Changes of Diurnal Surface Temperature Range between the Tibetan Plateau and Southeastern China during the 1980s–2000s

The diurnal surface temperature range(DTR) has become significantly smaller over the Tibetan Plateau(TP) but larger in southeastern China, despite the daily mean surface temperature having increased steadily in both areas during recent decades.Based on ERA-Interim reanalysis data covering 1979–2012, this study shows that the weakened DTR over TP is caused by stronger warming of daily minimum surface temperature(Tmin) and a weak cooling of the daily maximum surface temperature(Tmax); meanwhile, the enhanced DTR over southeastern China is mainly associated with a relatively stronger/weaker warming of Tmax/Tmin. A further quantitative analysis of DTR changes through a process-based decomposition method—the Coupled Surface–Atmosphere Climate Feedback Response Analysis Method(CFRAM)—indicates that changes in radiative processes are mainly responsible for the decreased DTR over the TP. In particular, the increased low-level cloud cover tends to induce the radiative cooling/warming during daytime/nighttime, and the increased water vapor helps to decrease the DTR through the stronger radiative warming during nighttime than daytime. Contributions from the changes in all radiative processes(over-2?C) are compensated for by those from the stronger decreased surface sensible heat flux during daytime than during nighttime(approximately 2.5?C), but are co-contributed by the changes in atmospheric dynamics(approximately-0.4?C) and the stronger increased latent heat flux during daytime(approximately-0.8?C). In contrast, the increased DTR over southeastern China is mainly contributed by the changes in cloud, water vapor and atmospheric dynamics. The changes in surface heat fluxes have resulted in a decrease in DTR over southeastern China.     

1960～2005年新疆气候变化的基本特征

采用新疆地区最完善的94个气象站的观测资料,系统地分析了新疆地区1960～2005年近地表主要气候要素(包括降水、气温、风速、日照时数、总云量、低云量、蒸发皿蒸发、气温日较差等)演变的时间和空间特征,并结合几个站点的太阳总辐射资料分析了日照、总云量、低云量、蒸发皿蒸发和太阳总辐射之间的关系,揭示了近50年来新疆气候变化的一些新特点。对导致这些变化的原因进行了初步分析,得到的结果包括:1)新疆区域年降水在1987年发生转折性变化,而冬季降水在1986年就开始发生转折性变化,是4个季节中最早的。新疆区域降水与比湿和低云量之间具有极高的相关性,尤其是低云量的增加可能是导致降水增加的主要原因。2)气温显著升高的同时,气温日较差是明显下降的。气温的升高可能是空气中水汽增多的结果,但也可能是气温长期自然振荡过程中的一个上升阶段。3)日照时数在总云量减小的前提下减少,这可能是降水和低云量增多导致的结果。4)蒸发皿蒸发的减小可能是风速、气温日较差、降水以及云量共同作用的结果,单站分析表明太阳辐射的下降也可能是导致蒸发皿蒸发下降的一个重要原因。     

ENSO对南沙海域气候状况的影响

对１９６１—１９９０年（部分资料到１９９４年）期间在南沙海域的观测资料，进行了统计分析，其结果表明：在ＥＮＳＯ发生的当年，南沙海域的海平面气压呈正距平，年降水量明显偏少，热带气旋活动的日数一般偏少；在历次ＥＮＳＯ过程中，南沙海域的总云量与ＳＯＩ的变化趋势基本一致。该项工作有助于了解ＥＮＳＯ对南沙海域天气气候的综合影响和提高天气预报的质量     

1951~2010年云贵高原大理和丽江气温、降水的气候特征分析

利用大理和丽江气象站1951~2010年的逐日气象资料,分析了横断山脉东部气温、降水的气候特征。结果表明,1991年以后,大理和丽江地区均存在显著增温的趋势（0.58和0.55℃/10 a）,明显高于同时期中国平均气温的增加幅度;而在1991年之前,大理和丽江的年平均气温呈现下降或微弱上升的趋势（-0.14和0.07℃/10 a）。与夏季平均气温的增温幅度相比,冬季平均气温的增温更显著,且其变化趋势与年均气温的气候特征是一致的。大理和丽江年总降水及各季节降水量在1951~2010年并没有明显增加或减少的趋势。大理和丽江雨季开始的时间分别为第28候和第30候,持续时间分别约为5.5和4.5个月。20世纪80年代以后,丽江年平均风速的减小强度明显大于大理,这是因为丽江站地处城区,城市化剧烈,地表粗糙度增加显著。日照时数与云量呈反相的季节变化,降水量的多年平均的逐候变化与日照时数、总云量、尤其是低云云量相关,随风速增大而减小。     

The 20th century cooling trend over the southeastern United States

Portions of the southern and southeastern United States, primarily Mississippi, Alabama, and Georgia, have experienced century-long (1895–2007) downward air temperature trends that occur in all seasons. Superimposed on them are shifts in mean temperatures on decadal scales characterized by alternating warm (1930s–1940s, 1990s) and cold (1900s; 1960s–1970s) regimes. Regional atmospheric circulation and SST teleconnection indices, station-based cloud cover and soil moisture (Palmer drought severity index) data are used in stepwise multiple linear regression models. These models identify predictors linked to observed winter, summer, and annual Southeastern air temperature variability, the observed variance (r²) they explain, and the resulting prediction and residual time series. Long-term variations and trends in tropical Pacific sea temperatures, cloud cover, soil moisture and the North Atlantic and Arctic oscillations account for much of the air temperature downtrends. Soil moisture and cloud cover are the primary predictors of 59.6 % of the observed summer temperature variance. While the teleconnections, cloud cover and moisture data account for some of the annual and summer Southeastern cooling trend, large significant downward trending residuals remain in winter and summer. Comparison is made to the northeastern United States where large twentieth century upward air temperature trends are driven by cloud cover increases and Atlantic Multidecadal Oscillation (AMO) variability. Differences between the Northeastern warming and the Southeastern cooling trends in summer are attributable in part to the differing roles of cloud cover, soil moisture, the Arctic Oscillation and the AMO on air temperatures of the 2 regions.     

近50年陕西黄土高原云量和气温年际变化

利用陕西黄土高原24个气象站1957年以来的气温、总云量和低云量观测资料,分析了它们的年际及年代际演变趋势及相关关系。结果表明:近50年区域年平均气温波动升高,尤其是1987年以后;北部风沙区气温的年际变化较大,增温幅度由北向南递减;1957年以来区域年平均总云量呈逐渐减少趋势,低云量下降趋势较总云量更为明显,2000年以后总云量有所增加。相关分析表明:陕西黄土高原年平均气温与年均总云量及低云量呈明显的负相关,均通过了0.001显著性水平检验,且低云量的相关更为显著;总云量和低云量与降水量呈显著正相关;不同区域和不同季节总云量和低云量与气温的相关系数有明显差异,但与降水量的相关非常显著。     

Planetary albedo in strongly forced climate, as simulated by the CMIP3 models

In an ensemble of general circulation models, the global mean albedo significantly decreases in response to strong CO₂ forcing. In some of the models, the magnitude of this positive feedback is as large as the CO₂ forcing itself. The models agree well on the surface contribution to the trend, due to retreating snow and ice cover, but display large differences when it comes to the contribution from shortwave radiative effects of clouds. The ??cloud contribution?? defined as the difference between clear-sky and all-sky albedo anomalies and denoted as ??CC is correlated with equilibrium climate sensitivity in the models (correlation coefficient 0.76), indicating that in high sensitivity models the clouds to a greater extent act to enhance the negative clear-sky albedo trend, whereas in low sensitivity models the clouds rather counteract this trend. As a consequence, the total albedo trend is more negative in more sensitive models (correlation coefficient 0.73). This illustrates in a new way the importance of cloud response to global warming in determining climate sensitivity in models. The cloud contribution to the albedo trend can primarily be ascribed to changes in total cloud fraction, but changes in cloud albedo may also be of importance.     

天津地区近40年日照时数变化特征及其影响因素

对天津市区、西青、蓟县、塘沽4个站1961~2003年日照时数以及对日照有影响的云量、水汽压和地面能见度等资料的进行了统计分析。结果表明:天津地区日照时数呈明显的下降趋势,1961~2003年4站气候变化率分别是为每10年-177.3-、165.2-、174.1-、145.6 h。与60年代相比,90年代4站的年日照时数分别减少了425.1、403.4、486.03、77.5 h,相当于市区每日的日照时数减少了1.2 h、西青1.1 h、蓟县1.3 h、塘沽1.0 h。40年来云量和水汽压的变化不大,而地面能见度呈下降趋势。能见度下降可能主要是对流层大气气溶胶含量上升的结果,这是造成天津地区日照时数减少的主要原因。