A reappraisal of relationships between northern hemispheric surface air temperatures and Indian summer monsoon rainfall

Summary Zonally averaged surface air temperatures have been analysed to form time series of surface air temperature anomalies over the tropics (TTA), extratropics (ETA), the poles (PTA) and the whole northern hemisphere (NHTA) for the period 1901–1990. The temporal statistical relationships between these temperature time series and Indian monsoon rainfall over all India (AIR), northwest India (NWR) and peninsular India (PIR) have been examined for the above period.The northern hemispheric January–February (JF) temperature correlates significantly and positively with all the three monsoon rainfall series, the regional peninsular rainfall series (PIR) displaying the best correlation. The Strongest correlation is observed during 1951–1980 for both AIR and NWR but weakened in 1961–1990. For PIR, the highest correlation is observed during 1961–1990, remaining almost stable since 1951–1980. The JF series AIR monsoon relationship showed the highest correlation over the tropics during 1901–1940, over the polar region during 1941–1980 and over the northern hemisphere during 1951–1980. AIR and NWR moreover show a significant negative relationship with simultaneous, succeeding autumn and following year TTA series, while AIR and PIR monsoon rainfall series show significant positive association with the following year PTA series.The results also suggest that cooler January–February NHTA not only lead to a poor monsoon, but a poor monsoon also leads to warmer temperatures over the tropics and cooler temperatures over the polar region in the following year.With 1 Figure     

Spatial asymmetry of temperature trends over India and possible role of aerosols

Dissimilarities in temperature trends in space and time over the Indian region have been examined to look for signatures of aerosols’ influence. Separate temperature time series for North and South India were constructed for dry (November–May) and wet (June–October) seasons. Temperature trend for the entire period 1901–2007 and different subperiods of 1901–1950, 1951–1990, 1971–2007, and 1991–2007 have been examined to isolate the aerosol and other greenhouse gas influences on temperatures. Maximum (daytime) temperatures during dry season corresponding to North and South India show significant warming trend of 0.8 and 1.0?°C per hundred years during the period 1901–2007, while minimum temperature shows nebulous trend of 0.2 and 0.3?°C per hundred years over North and South India, respectively. During the wet season, maximum temperature shows nearly half of dry season maximum temperature warming trend. However, asymmetry is observed in dry season maximum temperature trend during post-industrial period 1951–1990 wherein the North/South India shows decreasing/increasing trends, while during the recent period 1991–2007 trends are uniformly positive for both the regions. Spatial and temporal asymmetry in observed trends clearly point to the role of aerosols in lowering temperature trends over northern India. Atmospheric aerosols could cause a negative climate forcing that can modulate the regional surface temperature trends in a significant way. As this forcing acts differentially on day and night temperatures, trends in diurnal temperature range (DTR) provide a direct assessment of impacts of aerosols on temperature trends. Time series of diurnal temperature range for dry and wet seasons have been examined separately for North and South India. Over North India, the DTR for dry season has increased gradually during the period 1901–1970 and thereafter showed decreasing trend, while trends in temperature range over Southern India were almost opposite in phase with North India. The aerosol and greenhouse gases seem to play an important role in the spatial and temporal variability of temperature range over India.     

Mathematical modelling of the annual temperature wave based on monthly mean temperatures,and comparisons between local climate trends at seven Norwegian stations

Summary Based on observed monthly mean temperatures, it is possible to construct a simple mathematical model of the annual variation of daily mean temperature, the annual temperature wave. For periods of 15 years, the model gives a good correlation with the observed monthly values. The model may be used as a tool for the generation of daily mean temperatures for the corresponding period. It is continuous, differentiable and strictly monotonous between the unique maximum and the minimum of the curve. Consequently, climate quantities of interest for each period can be calculated by the means of simple mathematical analyses. The model was tested by reproducing values for quantities such as annual mean temperature, winter mean temperature, summer mean temperature and temperature sums. Model calculated values, fit values calculated directly from observed data well. The model was also tested by comparing results from two different but neighbouring stations. There was a good correlation between the results from the two stations. Long homogenised time series with 130 years of monthly mean temperature from seven Norwegian stations were analysed by means of the model. It was found that the Frost Free Season Length and the Growth Season Length had increased for all stations by 10–20 days/100 years in the period 1871–1990. The Summer Half-year Length, even if it was defined relative to the annual mean temperature, also increased for all stations by 4–9 days/100 years. The Hot Season Length showed positive trends as well, and for the five stations in Southern Norway, the trends were as high as 18–29 days/100 years. The Heat Sum had increased by 6–11% for southern stations and 20–22% for the northern stations. The results indicate that the level as well as the shape of the annual temperature wave changed in the period from 1871 to 1990. Some of the results for the period 1990–1999 diverge substantially from the trends, possibly indicating significant changes in the shape of the annual temperature wave in this last period.     

1951～2002年中国平均最高、最低气温及日较差变化

利用1951～2002年全国733个台站的月平均最高、最低气温资料,对我国年、季平均最高、最低气温变化趋势的空间分布状况和时间变化特征进行了分析.结果表明:近52年来,我国平均最高气温的变化特征呈现北方增暖明显、南方变化不明显或呈弱降温趋势;年平均最低气温全国各地基本一致,呈明显的变暖趋势;无论是年还是季,平均最低气温的增暖幅度明显大于平均最高气温的增幅;我国年平均日较差多呈下降趋势,并在我国北方地区尤为明显,各季平均日较差亦均呈下降趋势,并以冬季的下降幅度为最大;年平均最高气温和最低气温的变化在年代际变化上基本呈现较为一致的步伐,即52年来主要的变暖均是从20世纪80年代中期开始,均在90年代后期达到了近52年来的历史新高,近年来又略有回落.     

Variability and trends in daily minimum and maximum temperatures and in the diurnal temperature range in Lithuania,Latvia and Estonia in 1951–2010

Spatial distribution and trends in mean and absolute maximum and minimum temperatures and in the diurnal temperature range were analysed at 47 stations in the eastern Baltic region (Lithuania, Latvia and Estonia) during 1951–2010. Dependence of the studied variables on geographical factors (latitude, the Baltic Sea, land elevation) is discussed. Statistically significant increasing trends in maximum and minimum temperatures were detected for March, April, July, August and annual values. At the majority of stations, the increase was detected also in February and May in case of maximum temperature and in January and May in case of minimum temperature. Warming was slightly higher in the northern part of the study area, i.e. in Estonia. Trends in the diurnal temperature range differ seasonally. The highest increasing trend revealed in April and, at some stations, also in May, July and August. Negative and mostly insignificant changes have occurred in January, February, March and June. The annual temperature range has not changed.     

1960～2010年四川最高、最低气温的非对称性变化特征

本文利用四川138个气象站点1960~2010年的气温资料,分析了四川地区年均最高、最低气温及日较差的时空变化特征。结果表明:1960~2010年四川年均最高、最低气温在时间变化上呈非对称性升温,年均最高气温和最低气温的气候倾向率分别为0.131℃/10a和0.185℃/10a,后者增温幅度约为前者的1.4倍。年均最高、最低气温气候倾向率在空间分布上多数地区也呈非对称现象,年均最高、最低气温在西部高原地区升温较快,但最低气温的升温速率明显高于最高气温,这导致气温日较差在高原西部地区下降幅度较大。年均最高气温在1980年代最低,2000年代达到最高;年均最低气温在1960年代最低,2000年代最高;年均气温日较差在1960年代最大,1980年代最小。年均最高、最低气温分别在1996年和1993年发生转变,年均气温日较差分别在1973年和2005年发生了转变,年均最高、最低气温气候倾向率的不同及转变年的不一致导致气温日较差在转变年上的不一致。      

Surface and upper air temperatures over India in relation to monsoon rainfall

Summary The relationship between the all-India summer monsoon rainfall and surface/upper air (850, 700, 500 and 200 mb levels) temperatures over the Indian region and its spatial and temporal characteristics have been examined to obtain a useful predictor for the monsoon rainfall. The data series of all-India and subdivisional summer monsoon rainfall and various seasonal air temperatures at 73 surface observatories and 9 radiosonde stations (1951–1980) have been used in the analysis. The Correlation Coefficients (CCs) between all-India monsoon rainfall and seasonal surface air temperatures with different lags relative to the monsoon season indicate a systematic relationship.The CCs between the monsoon rainfall and surface-air temperature of the preceding MAM (pre-monsoon spring) season are positive over many parts of India and highly significant over central and northwestern regions. The average surface air temperature of six stations i.e., Jodhpur, Ahmedabad, Bombay, Indore, Sagar and Akola in this region (Western Central India, WCI) showed a highly significant CC of 0.60 during the period 1951–1980. This relationship is also found to be consistently significant for the period from 1950 to present, though decreasing in magnitude after 1975. WCI MAM surface air temperature has shown significant CCs with the monsoon rainfall over eleven sub-divisions mainly in northwestern India, i.e., north of 15 °N and west of 80 °E.Upper air temperatures of the MAM season at almost all the stations and all levels considered show positive CCs with the subsequent monsoon rainfall. These correlations are significant at some central and north Indian stations for the lower and middle tropospheric temperatures.The simple regression equation developed for the period 1951–1980 isy = – 183.20 + 8.83x, wherey is the all-India monsoon rainfall in cm andx is the WCI average surface air temperature of MAM season in °C. This equation is significant at 0.1% level. The suitability of this parameter for inclusion in a predictive regression model along with five other global and regional parameters has been discussed. Multiple regression analysis for the long-range prediction of monsoon rainfall, using several combinations of these parameters indicates that the improvement of predictive skill considerably depends upon the selection of the predictors.With 9 Figures     

Variations and trends in annual and seasonal air temperatures in Greece determined from ground and satellite measurements

Summary The variations and trends in annual and seasonal air temperatures in Greece were examined on the basis of ground measurements for 25 stations during the period 1951–1993, and satellite measurements for the south eastern Mediterranean during the period 1979–1991. Data were smoothed using a 5-year running mean and were thereafter examined by regression analysis to define trends in the long duration time series. Data were also examined to detect abrupt changes and trends in the long duration annual, winter and summer series of mean maximum, mean minimum and mean temperatures. An overall cooling trend was detected for the majority of stations in winter over the entire period; the same cooling trend was also recognised for the annual and summer mean values, although a reverse warming trend was detected around the mid-70s at several stations. Satellite measurements indicate a slight warming trend, although this is not statistically significant. Considering the results of the regression analysis and the statistical tests applied to the 25 stations, it may be concluded that annual mean temperatures are dominated by an overall cooling trend, with the exception of stations in urban areas where urbanisation effects may have resulted in a warming trend. Summer temperatures, however, exhibit a warming trend roughly after 1975 at most stations.With 5 Figures     

Fractal analysis of climatic data: Mean annual temperature records in Hungary

Summary Rescaled range analysis of the annual mean surface air temperatures at 7 meteorological stations in Hungary for the period of 1901–1991 indicates that the considered temperatures are fractals with a mean fractal dimension of 1.23 ± 0.01. This value compares favourably with the fractal dimensions of other climatic records, both on small time scale of 10–100 years and for time spans 10³–10⁶ years. Possibly such fractal dimensions are characteristic of climate change over the whole spectral range of 10 to 10⁶ years. If this assumption becomes confirmed through analysis of a wider set of climatic records, long-range climatic prediction (in statistical sense) on different time scales will appear feasible.With 4 Figures     

Climatic change in Britain: Is SO2 more significant than CO2?

Summary Many climate scientists have suggested that anthropogenic emissions of greenhouse gases may create severe climate problems for Britain; however, the potential cooling effects of sulphur dioxide are widely acknowledged. In this investigation, we analyze British mean annual temperature, mean annual precipitation, and mean diurnal air temperature range over the period 1929–1988. Our analyses of these records reveal (a) a shift in the early 1950s away from warming and toward cooling, (b) a relative decline in maximum air temperatures when compared to minimum air temperatures, (c) a strong decline in the diurnal air temperature range and (d) a significant linkage between diurnal temperature range and precipitation. Given these signals in the observed climate record, it would appear that SO₂ rather than CO₂ has been the major anthropogenic climate influence in Britain over the past four decades.With 6 Figures     

Changes in temperature and temperature gradients in the French Northern Alps during the last century

In mountain environments, local factors such as topography or exposure to the sun influence the spatial distribution of temperatures. It is therefore difficult to characterise the global evolution of temperatures over several decades. Such local effects can either accentuate or attenuate thermal contrasts between neighbouring areas. The present study uses two regional thermal indicators—thermal gradients and temperatures reduced to sea level—to monitor the monthly evolution of minimum and maximum temperatures in the French Northern Alps. Measures were calculated for the period extending from 1960 to 2007 based on data from 92 measuring stations. Temperature gradients were computed and further used to monitor the altitudinal evolution of temperatures. A characteristic regional temperature was determined for the whole of the French Northern Alps based on temperatures reduced to sea level, and changes in temperatures since 1960 were assessed. Multiple linear regression models made it possible to extend measurements over a longer period and to make enhanced calculations of temperature changes in the mountains since 1885. This is the first study to examine temperature changes in the French Northern Alps over such an extended period. Gradient data suggest that over the last 50 years, temperatures have changed at all altitudes. In addition, the evaluation of the temperature rise over 100 years reveals that minimal and maximal monthly temperatures trends are only significant a few months of the year.     

中国最高、最低温度及日较差在海拔高度上变化的初步分析

本文利用中国740个气象台站1963~2012年均一化逐日最高温度和最低温度资料,分析了中国地区最高、最低气温和日较差变化趋势的区域特征及其与海拔高度的关系。结果表明:近50年气温的变化趋势无论是年或季节变化,最低温度的增温幅度都高于最高温度,且其增温显著区域都对应我国高海拔地区。除了春季,其他季节最高、最低温度及日较差的升温幅度随着海拔高度的升高而增大,其中最高温度的变化趋势与海拔高度的相关性最好。同一海拔高度上,最高、最低温度在不同年代的增幅具有不一致性:20世纪80年代,二者变化幅度最小;20世纪90年代,二者增幅最大,尤以低海拔地区最为明显。2000 m以上高海拔地区:最高温度和最低温度的变化趋势在20世纪90年代以前变化较小,而在近十年增幅十分明显;日较差季节变化大:夏季减小,冬季增加。20世纪90年代以前,最高、最低温度随海拔高度变化不大,而近20年随海拔高度升高,最高、最低温度的变化趋势几乎都是先减小后增加。高海拔地区比低海拔地区对全球变化反应更明显。     

Changes in temperature extremes and their possible causes at the SE boundary of the Alps

Summary A trend analysis is performed on the years 1954 to 1995 annual and seasonal mean maximum and minimum temperature, diurnal temperature range, air pressure, and occurrence of different weather types, grouped according to the related diurnal temperature ranges for two mountain stations in Croatia. During the last 42 years an increase in annual mean maximum and mean minimum temperature has occurred. At both stations the increase in mean maximum was faster than in the mean minimum, resulting in an increase in mean diurnal temperature range. At the same time mean annual air pressure shows a significant increase both at Zavian and at Puntijarka. An increase in occurrence of weather types with high diurnal temperature range appears at both locations, but is significant only at the inland station of Puntijarka.With 5 Figures     

Monthly air temperature trends in Switzerland 1901–2000 and 1975–2004

Summary We analysed long-term temperature trends based on 12 homogenised series of monthly temperature data in Switzerland at elevations between 316 m.a.s.l. and 2490 m.a.s.l for the 20^th century (1901–2000) and for the last thirty years (1975–2004). Comparisons were made between these two periods, with changes standardised to decadal trends. Our results show mean decadal trends of +0.135 °C during the 20^th century and +0.57 °C based on the last three decades only. These trends are more than twice as high as the averaged temperature trends in the Northern Hemisphere. Most stations behave quite similarly, indicating that the increasing trends are linked to large-scale rather than local processes. Seasonal analyses show that the greatest temperature increase in the 1975–2004 period occurred during spring and summer whereas they were particularly weak in spring during the 20^th century. Recent temperature increases are as much related to increases in maximum temperatures as to increases in minimum temperature, a trend that was not apparent in the 1901–2000 period. The different seasonal warming rates may have important consequences for vegetation, natural disasters, human health, and energy consumption, amongst others. The strong increase in summer temperatures helps to explain the accelerated glacier retreat in the Alps since 1980. Authors’ addresses: Martine Rebetez, WSL Swiss Federal Research Institute, 1015 Lausanne, Switzerland; Michael Reinhard, Laboratory of Ecological Systems (ECOS), EPFL Swiss Federal Institute of Technology, 1015 Lausanne, Switzerland.     

Comparison of Lower-Tropospheric Temperature Climatologies and Trends at Low and High Elevation Radiosonde Sites

Observations of rapid retreat of tropical mountain glaciers over the past two decades seem superficially at odds with observations of little or no warming of the tropical lower troposphere during this period. To better understand the nature of temperature and atmospheric freezing level variability in mountain regions, on seasonal to multidecadal time scales, this paper examines long-term surface and upper-air temperature observations from a global network of 26 pairs of radiosonde stations. Temperature data from high and low elevation stations are compared at four levels: the surface, the elevation of the mountain station surface, 1 km above the mountain station, and 2 km above the mountain station. Climatological temperature differences between mountain and low elevation sites show diurnal and seasonal structure, as well as latitudinal and elevational differences. Atmospheric freezing-level heights tend to decrease with increasing latitude, although maximum heights are found well north of the equator, over the Tibetan Plateau. Correlations of interannual anomalies of temperature between paired high and low elevation sites are relatively high at 1 or 2 km above the mountain station. But at the elevation of the station, or at the two surface elevations, correlations are lower, indicating decoupling of the boundary layer air from the free troposphere.Trends in temperature and freezing-level height are generally upward, both during 1979–2000 and during longer periods extending back to the late 1950s. However, some negative trends were found at extratropical locations. In many cases, statistically significant differences were found in trends at paired high and low elevation stations, with tropical pairs revealing more warming (and greater increases in freezing-level height) at mountain stations than at low elevations. This result is consistent with both the observed retreat of tropical glaciers and the minimal change in tropics-wide tropospheric temperatures over the past two decades.Overall, the analysis suggests that, on diurnal, seasonal, interannual, and multidecadal time scales, temperature variations at mountain locations differ significantly from those at relatively nearby (a few hundred kilometers) low elevation stations. These differences are greatest at the two surface levels, but can persist up to 2 km above the mountain site. Therefore, to determine the nature of climate variability at high elevation sites requires local observations, since large-scale patterns derived from low elevation observations may not be representative of the mountain regions. Conversely, temperature change in mountain regions should not be viewed as necessarily representative of global surface or tropospheric trends.     

ON CHANGES OF CHINA’S MAXIMUM AND MINIMUM TEMPERATURES IN 1951-1990

Based on China's observational data in 1951-1990,after minimizing the possible biases caused by station relocation and urban heat island,the spatial and temporal distributions of trends for maximum and minimum temperatures are studied.The results show that increasing trends of maximum temperatures are in the areas west to 95°E,and north to the Huanghe (Yellow) River,while decreasing trends exist in eastern China south to the Yellow River.Minimum temperatures are generally increasing throughout China,with dominant warming trends at the higher latitudes.This resulted in very obvious decreasing trends in diurnal temperature ranges.The periodic cycles are consistent between the maximum and minimum temperatures,but asymmetric trends are very obvious.The significant increase of minimum(nighttime) temperatures reflects the evidence of enhancement of greenhouse effect.Further analysis shows that the changes of maximum and minimum temperatures are mainly related to sunshine duration and atmospheric water vapor content.     

Paleoclimatic inferences from glacial fluctuations on Svalbard during the last 20 000 years

The climate history of western Spitsbergen, Svalbard is deduced from variations of glaciers during the last 20 000 years. A major depression of the regional equilibrium line altitude (ELA) occurred during the Late Weichselian glacial maximum (18000–13000y ago) when low summer temperatures may have caused year-round snow accumulation on the ground. This rapid expansion of the glaciers also indicates nearby moisture sources, suggesting partly open conditions in the Norwegian Sea during the summers. A rapid glacial retreat around 13 000–12 500 y BP was caused by a sudden warming. During the Younger Dryas the ELA along the extreme western coast of Spitsbergen was not significantly lower than at present. In contrast to Fennoscandia, the British Isles and the Alps, there is no evidence for readvance of local glaciers during Younger Dryas on western Spitsbergen. This difference is attributed to a much dryer climate on Spitsbergen and probably only slight changes in sea surface temperatures. In addition, summer melting in this high arctic area is more sensitive to orbitally increased insolation. Around 10 000 y BP another rapid warming occurred and during early and mid Holocene the summer temperatures were significantly higher than at present. A temperature decline during the late Holocene caused regrowth of the glaciers which reached their maximum Holocene position during the last century.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

中国近四十年最高最低温度变化

利用中国１９５１－１９９０年的实测资料，在剔除测站迁移和城市化热岛效应对气候变化趋势的可能影响之后，研究了中国最高温度、最低温度的时空变化趋势特点。结果表明，最高温度在９５°Ｅ以西及黄河以北地区普遍呈增温趋势，而在东部黄河以南却呈降温趋势；最低温度在全国普遍呈增温趋势，在高纬度地区增暖最明显。这种变化使得日较差表现出明显的减少趋势。虽然最高、最低温度变化的准周期性规律是一致的，但它们的线性变化趋势却呈现出明显的不对称性。最低温度的显著升高反映了近４０ａ中温室效应持续加强的迹象。进一步的分析表明，最高最低温度变化是与日照条件及大气水分条件相关联的     

The Early 19th Century Climate of the Bahamas and a Comparison with 20th Century Averages

Two weather records kept at Nassau, Bahamas, from 1811 to 1837, and from 1838 to 1845, respectively, are analyzed and compared to 20th century reference periods. The average annual temperature of the period is 24.2°C (±0.65°C), which is 0.4°C lower than 1961–1990 and 0.1°C lower than 1901–1920, the coolest period in the 20th century. Cold periods occurred from 1812–1819 and 1835–1839. A warmer phase prevailed between these two episodes and another warm episode occurred in 1840–1842. Temperature fell after the volcanic eruptions of Tambora (April, 1815) and Coseguina (January, 1835). The maximum cooling after Tambora is estimated at 1.0°C (±0.56°) and after Coseguina is estimated at 0.4°C (±0.56°). The post-Tambora cooling is in line with previous estimates (Robock, personal communication). The 1810s were a period of extreme drought at Nassau and are unequalled in later years. Rainfall frequency was below contemporary (1812–1837) averages from 1812–1820 and 1836–1837 but was above average from 1821–1835. Moist (dry) periods occurred almost simultaneously with warm (cool) periods. The months of October, November, and April show the greatest (negative) deviations in precipitation frequency. Gale force winds were 85% more frequent than from 1901–1960. Much of this increase took place in the months of September through November and represents an increase in tropical cyclone frequency in the Nassau area above that of 1901–1960. Resultant winds show a tendency towards greater northerly components than in the 20th century, especially during the winter months. The increase in northerly wind components, temperatures below the 20th-century average, and reduction in rainfall frequency in the winter half of the year indicates a synoptic situation in which high pressure was more frequent over the southeast North American continent.     

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.