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1.
Changes in snowfall in northern Europe (55–71°N, 5–35°E) are analysed from 12 regional model simulations of twenty-first century climate under the Special Report on Emissions Scenarios A1B scenario. As an ensemble mean, the models suggest a decrease in the winter total snowfall in nearly all of northern Europe. In the middle of the winter, however, snowfall generally increases in the coldest areas. The borderline between increasing and decreasing snowfall broadly coincides with the ?11 °C isotherm in baseline (1980–2010) monthly mean temperature, although with variation between models and grid boxes. High extremes of daily snowfall remain nearly unchanged, except for decreases in the mildest areas, where snowfall as a whole becomes much less common. A smaller fraction of the snow in the simulated late twenty-first century climate falls on severely cold days and a larger fraction on days with near-zero temperatures. Not only do days with low temperatures become less common, but they also typically have more positive anomalies of sea level pressure and less snowfall for the same temperature than in the present-day climate.  相似文献   

2.
Based on the daily sea level pressure (SLP) circulation catalogue obtained by Esteban, Martin-Vide and Mases, Int J Climatol 26:1501–1515, (2006) for Western Europe, high-resolution maps of daily maximum and minimum temperature, mean daily precipitation and daily precipitation probability have been obtained for Andorra (Pyrenees). The 20 daily-circulation patterns cover the period 1960–2001 and were generated using new approaches based on the rotated principal component analysis (PCA) and clustering technique. The final maps of Andorra associated with each circulation pattern have been constructed using altitude, latitude, continentality and solar radiation as multiple regression predictors (Ninyerola, Pons and Roure, Int J Climatol 20:1823–1841, 2000). The daily temperature and rainfall series used from Andorran, French and Catalan/Spanish weather stations have been checked for data quality. The results confirm the complexity of the spatial distribution of meteorological phenomena over mountainous areas such as in Andorra, and show the importance of the Mediterranean and Atlantic influence upon the climate of this country of the Pyrenees. On the other hand, different tests have been made showing that the classification results could improve the resulting interpolated climate maps by the use of the circulation-pattern frequencies.  相似文献   

3.
Recent studies have shown that the Madden–Julian Oscillation (MJO) impacts the leading modes of intraseasonal variability in the northern hemisphere extratropics, providing a possible source of predictive skill over North America at intraseasonal timescales. We find that a k-means cluster analysis of mid-level geopotential height anomalies over the North American region identifies several wintertime cluster patterns whose probabilities are strongly modulated during and after MJO events, particularly during certain phases of the El Niño-Southern Oscillation (ENSO). We use a simple new optimization method for determining the number of clusters, k, and show that it results in a set of clusters which are robust to changes in the domain or time period examined. Several of the resulting cluster patterns resemble linear combinations of the Arctic Oscillation (AO) and the Pacific/North American (PNA) teleconnection pattern, but show even stronger responses to the MJO and ENSO than clusters based on the AO and PNA alone. A cluster resembling the positive (negative) PNA has elevated probabilities approximately 8–14 days following phase 6 (phase 3) of the MJO, while a negative AO-like cluster has elevated probabilities 10–20 days following phase 7 of the MJO. The observed relationships are relatively well reproduced in the 11-year daily reforecast dataset from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). This study statistically links MJO activity in the tropics to common intraseasonal circulation anomalies over the North American sector, establishing a framework that may be useful for improving extended range forecasts over this region.  相似文献   

4.
ABSTRACT

Trends in indices based on daily temperature and precipitation are examined for two periods: 1948–2016 for all stations in Canada and 1900–2016 for stations in the south of Canada. These indices, a number of which reflect extreme events, are considered to be impact relevant. The results show changes consistent with warming, with larger trends associated with cold temperatures. The number of summer days (when daily maximum temperature >25°C) has increased at most locations south of 65°N, and the number of hot days (daily maximum temperature >30°C) and hot nights (daily minimum temperature >22°C) have increased at a few stations in the most southerly regions. Very warm temperatures in both summer and winter (represented by the 95th percentile of their daily maximum and minimum temperatures, respectively) have increased across the country, with stronger trends in winter. Warming is more pronounced for cold temperatures. The frost-free season has become longer with fewer frost days, consecutive frost days, and ice days. Very cold temperatures in both winter and summer (represented by the 5th percentile of their daily maximum and minimum temperatures, respectively) have increased substantially across the country, again with stronger trends in the winter. Changes in other temperature indices are consistent with warming. The growing season is now longer, and the number of growing degree-days has increased. The number of heating degree-days has decreased across the country, while the number of cooling degree-days has increased at many stations south of 55°N. The frequency of annual and spring freeze–thaw days shows an increase in the interior provinces and a decrease in the remainder of the country. Changes in precipitation indices are less spatially coherent. An increase in the number of days with rainfall and heavy rainfall is found at several locations in the south. A decrease in the number of days with snowfall and heavy snowfall is observed in the western provinces, while an increase is found in the north. There is no evidence of significant changes in the annual highest 1-day rainfall and 1-day snowfall. The maximum number of consecutive dry days has decreased, mainly in the south.  相似文献   

5.
A weather pattern clustering method is applied and calibrated to Argentinean daily weather stations in order to predict daily precipitation data. The clustering technique is based on k-means and is applied to a set of 17 atmospheric variables from the ERA-40 reanalysis covering the period 1979–1999. The set of atmospheric variables represent the different components of the atmosphere (dynamical, thermal and moisture). Different sensitivity tests are applied to optimize (1) the number of observations (weather patterns) per cluster, (2) the spatial domain size of the weather pattern around the station and (3) the number of members of the ensembles. All the sensitivity tests are compared using the ROC (Relative Operating Characteristic) Skill Score (RSS) derived from the ROC curve used to assess the performance of a predictive system. First, we found the number of observations per cluster to be optimum for values larger than 39. Second, the spatial domain size (~4° × 4°) was found to be closer to a local scale than to a synoptic scale, certainly due to a dominant role of the moisture components in the optimization of the transfer function. Indeed, when reducing the set of variables to the subset of dynamical variables, the predictive skill of the method is significantly reduced, but at the same time the domain size must be increased. A potential improvement of the method may therefore be to consider different domains for dynamical and non-dynamical variables. Third, the number of members per ensembles of simulations was estimated to be always two to three times larger than the mean number of observations per cluster (meaning that at least all the observed weather patterns are selected by one member). The skill of the statistical method to predict daily precipitation is found to be relatively homogeneous all over the country for different thresholds of precipitation.  相似文献   

6.
根据有关研究成果,分别取日平均气温5.87℃和15.17℃为钉螺和日本血吸虫生长的下限温度,取3846.28 d·℃和842.95 d·℃为其有效积温指标。以1986年为分界点,利用1950-2003年气象台站日平均气温资料,计算了80%保证率下,5 d滑动平均气温稳定通过5.87℃和15.17℃的起始日和结束日以及历年有效积温,借助ArcGIS8.3模块分析了钉螺和血吸虫生长发育季节气候条件的变化。结果表明：气候变化使大部分地区钉螺和血吸虫生长发育季节延长,生长发育速度加快。气候变化可能使钉螺感染季节延长,感染率增高。  相似文献   

7.
To carry out this research, interpolated data of daily rainfall from Iran’s Asfazari data base during 1/1/1979–31/12/2013 is used. The day along with pervasive rainfall considered a day that at least 50% of Iran’s territory has received more than 1 mm for at least two consecutive days. Based on mentioned thresholds, 224 days selected for statistical analysis. The sea level pressure data, zonal and meridional wind components and specific humidity with spatial resolution of 0.25*0.25 Gaussian degree in spatial domain of 10 °N to 60 °N and 15 °E to 75 °E obtained from the European Center for Medium range Weather Forecasting (ECMWF) ERA-Interim for selected days. Then on the data matrix of sea level pressure, the cluster analysis by Ward linkage method done and 4 sea level pressure patterns with different configuration of synoptic systems were identified. The findings showed that in the sea level, the interaction between southern thermal low pressure systems (Arabia low pressure) with Europe and Siberia cold immigrant high pressure both by individual and integration and anticyclone circulation of Arab sea from the low level of 1000–500 hPa of troposphere have the most role on occurrence of durable and pervasive rainfall of Iran. The most Vertically Integrated Moisture Flux Convergence in the first layer of troposphere (1000–850 hPa) observed in low height regions, in the second layer of troposphere (775–700 hPa) on Zagros Mountains and in third layer of troposphere (600–500 hPa) is seen in mountains leeward of Iran. Also the results showed that the maximum rainfall cores has the most coordination with Vertically Integrated Moisture Flux Convergence (VIMFC) in the second layer of troposphere (775–700 hPa) on the Zagros heights in the southwest of Iran.  相似文献   

8.
This study describes a two-step analogue statistical downscaling method for daily temperature and precipitation. The first step is an analogue approach: the “n” days most similar to the day to be downscaled are selected. In the second step, a multiple regression analysis using the “n” most analogous days is performed for temperature, whereas for precipitation, the probability distribution of the “n” analogous days is used to define the amount of precipitation. Verification of this method has been carried out for the Spanish Iberian Peninsula and the Balearic Islands. Results show good performance for temperature (BIAS close to 0.1 °C and mean absolute errors around 1.9 °C) and an acceptable skill for precipitation (reasonably low BIAS except in autumn with a mean of ?18 %, mean absolute error lower than for a reference simulation, i.e. persistence and a well-simulated probability distribution according to two non-parametric tests of similarity).  相似文献   

9.
This study is motivated by an interest in obtaining a new automated classification scheme of daily circulation types suitable for use throughout Europe. The classification scheme is performed on 500 hPa geopotential height anomalies (NCEP Reanalysis data, 2.5°×2.5°). Nine grid points represent the study area. Five anticyclonic types (Anw, Ane, A, Asw and Ase) and seven cyclonic types (C, Cnnw, Cwnw, Cwsw, Cssw, Cse, Cne) are defined. Each of the circulation types has a distinct underlying synoptic pattern that produces the expected type and direction of flow over the study area. The classification scheme is applied to three different case studies in the Mediterranean Basin: Greece, Cyprus and central Italy. The precipitation percentage of the cyclonic type and the mean seasonal correlation coefficients for all circulation types are the two criteria used to evaluate the performance of the classification scheme. The ability of the HadAM3P general circulation model to reproduce the mean pattern and frequency of circulation types at the 500 hPa level in comparison to the NCEP dataset for the period 1960–1990 is also evaluated. The percentage of rainfall that corresponds to the cyclonic circulation types is greater than 85% for the three study regions. Furthermore, the correlation coefficients for the three classifications are very encouraging, for nearly all days of the study period. Compared to observations, the GCM is able to capture the mean patterns but not able to replicate exactly the observed variability of the circulation types over the three study regions.  相似文献   

10.
Summer mean daily temperature extremes in Svalbard Lufthavn (Central Spitsbergen) in the period 1975–2010 and daily pressure patterns and directions of air circulation conducive to their occurrence were analyzed. Positive (negative) extremes of daily mean temperatures in the summer were determined as higher (lower) than or equal to the value of the 90th (10th) percentile. The annual number of selected days shows a great year-to-year variability, although the annual number of extremely low mean daily temperature (≤1.3 °C) was decreasing in the 1976–2010 period, with a rate of about 4 days per decade. At the same time, the number of days with extremely high mean daily temperatures (≤8.2 °C) was increasing with a rate of about 2 days per decade. The summer pressure patterns and the air circulation conditions have an impact on the occurrence of the air mean daily temperature extremes. Namely, anticyclones spreading east to the Svalbard Archipelago, accompanied by the Icelandic Low, cause the air inflow from the southerly direction and positive mean daily temperature extremes. A cyclonal system spreading east or southeast towards the archipelago, together with a high-pressure ridge over the North Atlantic, indicates the northern air flow and negative mean daily temperature extremes in summer. The results obtained in this study prove that the summer air temperature in the Atlantic region of the Arctic is partly controlled by air circulation, and despite the intensity and stability of the summer cyclones and anticyclones being weaker than in the winter, their position strongly determines the occurrence of mean daily temperature extremes in the summer.  相似文献   

11.
This study aims to evaluate soil climate quantitatively under present and projected climatic conditions across Central Europe (12.1°–18.9° E and 46.8°–51.1° N) and the U.S. Central Plains (90°–104° W and 37°–49° N), with a special focus on soil temperature, hydric regime, drought risk and potential productivity (assessed as a period suitable for crop growth). The analysis was completed for the baselines (1961–1990 for Europe and 1985–2005 for the U.S.) and time horizons of 2025, 2050 and 2100 based on the outputs of three global circulation models using two levels of climate sensitivity. The results indicate that the soil climate (soil temperature and hydric soil regimes) will change dramatically in both regions, with significant consequences for soil genesis. However, the predicted changes of the pathways are very uncertain because of the range of future climate systems predicted by climate models. Nevertheless, our findings suggest that the risk of unfavourable dry years will increase, resulting in greater risk of soil erosion and lower productivity. The projected increase in the variability of dry and wet events combined with the uncertainty (particularly in the U.S.) poses a challenge for selecting the most appropriate adaptation strategies and for setting adequate policies. The results also suggest that the soil resources are likely be under increased pressure from changes in climate.  相似文献   

12.
Predicted increases in atmospheric CO2 concentration are expected to cause increases in air temperatures in many regions around the world, and this will likely lead to increases in the surface water temperatures of aquatic ecosystems in these regions. Using daily air and littoral water temperature data collected from Lake Tahoe, a large sub-alpine lake located in the Sierra Nevada mountains (USA), we developed and tested an empirical approach for constructing models designed to estimate site-specific daily surface water temperatures from daily air temperature projections generated from a regional climate model. We used cluster analysis to identify thermally distinct groups among sampled sites within the lake and then developed and independently validated a set of linked regression models designed to estimate daily water temperatures for each spatially distinct thermal group using daily air temperature data. When daily air temperatures projections, generated for 2080–2099 by a regional climate model, were used as input to these group models, projected increases in summer surface water temperatures of as much as 3 °C were projected. This study demonstrates an empirical approach for generating models capable of using daily air temperature projections from established climate models to project site specific impacts on littoral surface waters within large limnetic ecosystems.  相似文献   

13.
Fuzzy logic was applied as a methodology to create an objective calendar of daily atmospheric circulation based on an existing atmospheric circulation classification system for Poland called the Osuchowska-Klein method, which includes 13 circulation patterns. In this study, circulation patterns given by Osuchowska-Klein were expressed as normalized values of sea level pressure in a regular 5°?×?5° grid over the area of interest. Cases of daily atmospheric circulation (i.e., normalized values for the same domain) observed from January 1948 to December 2007 were defined in the same manner. The pattern-matching procedure employed in the study was made objective with the application of fuzzy logic sets in a few steps as follows: (1) discrimination and grouping of grid points as well as their classification in order to clearly define each Osuchowska-Klein circulation pattern, (2) calculation of the similarity between observed normalized pressure and that of the pattern at each selected grid point using a membership function, (3) determination of the degree of fulfillment for every class of grid points, (4) determination of the degree of a case and pattern, (5) selection of the circulation type for a particular day based on the degree of fulfillment for each pattern. The largest value of the degree of fulfillment indicates the type of circulation pattern on any given day. Finally, a validation of the obtained results is discussed. This was accomplished using the chi-square test and a comparison of consistency between the traditional and objective approach types. The results do show some differences between the subjective and objective methods, however, they are not major differences, especially when taking into account the fact that the two methods are quite different, as well as the complex nature of pressure systems.  相似文献   

14.
Local to regional climate anomalies are to a large extent determined by the state of the atmospheric circulation. The knowledge of large-scale sea level pressure (SLP) variations in former times is therefore crucial when addressing past climate changes across Europe and the Mediterranean. However, currently available SLP reconstructions lack data from the ocean, particularly in the pre-1850 period. Here we present a new statistically-derived 5° × 5° resolved gridded seasonal SLP dataset covering the eastern North Atlantic, Europe and the Mediterranean area (40°W–50°E; 20°N–70°N) back to 1750 using terrestrial instrumental pressure series and marine wind information from ship logbooks. For the period 1750–1850, the new SLP reconstruction provides a more accurate representation of the strength of the winter westerlies as well as the location and variability of the Azores High than currently available multiproxy pressure field reconstructions. These findings strongly support the potential of ship logbooks as an important source to determine past circulation variations especially for the pre-1850 period. This new dataset can be further used for dynamical studies relating large-scale atmospheric circulation to temperature and precipitation variability over the Mediterranean and Eurasia, for the comparison with outputs from GCMs as well as for detection and attribution studies.  相似文献   

15.
We examine summer temperature patterns in the Wenatchee River and two of its major tributaries Icicle and Nason Creeks, located in the Pacific Northwest region of the United States. Through model simulations we evaluate the cooling effects of mature riparian vegetation corridors along the streams and potential increases due to global warming for the 2020s–2080s time horizons. Site potential shade influences are smaller in the mainstream due to its relatively large size and reduced canopy density in the lower reaches, proving a modest reduction of about 0.3°C of the stream length average daily maximum temperature, compared with 1.5°C and 2.8°C in Icicle and Nason Creeks. Assuming no changes in riparian vegetation shade, stream length-average daily maximum temperature could increase in the Wenatchee River from 1–1.2°C by the 2020s to 2°C in the 2040s and 2.5–3.6°C in the 2080s, reaching 27–30°C in the warmest reaches. The cooling effects from the site potential riparian vegetation are likely to be offset by the climate change effects in the Wenatchee River by the 2020s. Buffers of mature riparian vegetation along the banks of the tributaries could prevent additional water temperature increases associated with climate change. By the end of the century, assuming site potential shade, the tributaries could have a thermal condition similar to today’s condition which has less shade. In the absence of riparian vegetation restoration, at typical summer low flows, stream length average daily mean temperatures could reach about 16.4–17°C by the 2040s with stream length average daily maxima around 19.5–20.6°C, values that can impair or eliminate salmonid rearing and spawning. Modeled increases in stream temperature due to global warming are determined primarily by the projected reductions in summer streamflows, and to a lesser extent by the increases in air temperature. The findings emphasize the importance of riparian vegetation restoration along the smaller tributaries, to prevent future temperature increases and preserve aquatic habitat.  相似文献   

16.
Inclusion of the effects of vegetation feedback in a global climate change simulation suggests that the vegetation–climate feedback works to alleviate partially the summer surface warming and the associated heat waves over Europe induced by the increase in atmospheric CO2 concentrations. The projected warming of 4°C over most of Europe with static vegetation has been reduced by 1°C as the dynamic vegetation feedback effects are included.. Examination of the simulated surface energy fluxes suggests that additional greening in the presence of vegetation feedback effects enhances evapotranspiration and precipitation, thereby limiting the warming, particularly in the daily maximum temperature. The greening also tends to reduce the frequency and duration of heat waves. Results in this study strongly suggest that the inclusion of vegetation feedback within climate models is a crucial factor for improving the projection of warm season temperatures and heat waves over Europe.  相似文献   

17.
The wet/dry spells of the Indian summer monsoon (ISM) rainfall are governed by northward propagating boreal summer monsoon intraseasonal oscillations (MISO). Unlike for the Madden Julian Oscillation (e.g. RMM indices, Wheeler and Hendon in Mon Weather Rev 132:1917–1932, 2004), a low dimensional real-time monitoring and forecast verification metric for the MISO is not currently available. Here, for the first time, we present a real time monitoring index developed for identifying the amplitude and phase of the MISO over the ISM domain. The index is constructed by applying extended empirical orthogonal function (EEOF) analysis on daily unfiltered rainfall anomalies averaged over the longitudinal domain 60.5°E–95.5°E. The gravest two modes of the EEOFs together explain about 23 % of the total variance, similar to the variance explained by MISO in observation. The pair of first two principal components (PCs) of the EEOFs is named as MISO1 and MISO2 indices which together represent the evolution of the MISOs in a low dimensional phase space. Power spectral analysis reveals that the MISO indices neatly isolate the MISO signal from the higher frequency noise. It is found that the current amplitude and phase of the MISO can be estimated by preserving a memory of at least 15 days. Composite pictures of the spatio-temporal evolution of the MISOs over the ISM domain are brought out using the MISO indices. It is further demonstrated that the MISO indices can be used in the quantification of skill of extended range forecasts of MISOs. Since the MISO index does not rely on any sort of time filtering, it has great potential for real time monitoring of the MISO and may be useful in developing some prediction scheme.  相似文献   

18.
H. Athar 《Climatic change》2013,119(2):333-344
Variability in the observed daily temperature for the 31-year period (1978–2008) is studied for northern Saudi Arabia (nSA) by computing the probability distribution functions (PDFs) on a seasonal basis. The 31-year base period is divided into three decades and the results for the first (1978–1987) and the last decade (1999–2008) are presented. When averaged over all seasons, mean values of the observed decadal PDFs depict a positive shift from the first to last decade in the minimum, mean, and maximum temperature of 0.81 °C, 1.03 °C, and 1.25 °C, respectively. The daily temperature datasets from a regional climate model (RCM) and two versions of a coupled atmosphere-ocean general circulation model (AOGCM) are compared with the observed daily temperature datasets. The RCM is driven by re-analysis data for the historical period and by the HadCM3 model for the future, while the AOGCMs used are the GFDL CM2.0 and 2.1 models, with both HadCM3 and the GFDL simulations corresponding to the SRES A1B scenario. The average shifts from 1978–1987 to 1999–2008 in the mean value of the PDFs for the minimum, mean and maximum temperature are 0.63 °C, 0.54 °C and 0.45 °C, respectively, for the RCM, and 0.97 °C, 0.97 °C and 0.96 °C, respectively, for the AOGCM. Thus, the RCM shows a smaller shift in the mean of PDF for maximum temperature than for mean or minimum temperature, the AOGCM shows a comparable shift for all three, and the observations show a greater shift in the PDF for maximum temperature. For the period 2070–2099 relative to 1978–2008, the three average shifts are 4.11 °C, 3.87 °C and 3.44 °C for the RCM and 3.63 °C, 3.74 °C and 3.84 °C for the AOGCM.  相似文献   

19.
We assess the depiction and prediction of blocking at 140°E and its impact on Australian intra-seasonal climate variability in the Bureau of Meteorology’s dynamical intra-seasonal/seasonal forecast model Predictive Ocean Atmosphere Model for Australia version 2 (POAMA-2). The model simulates well the strong seasonality of blocking but underestimates its strength and frequency increasingly with lead time, particularly after the first fortnight of the hindcast, in connection with the model’s drifting basic state. POAMA-2 reproduces well the large-scale structure of weekly-mean blocking anomalies and associated rainfall anomalies over Australia; the depiction of total blocking in POAMA-2 may be improved with the reduction of biases in the distribution of Indian Ocean rainfall via a tropical-extratropical wave teleconnection linking blocking activity at 140°E with tropical variability near Indonesia. POAMA-2 demonstrates the ability to skilfully predict the daily blocking index out to 16 days lead time for the ensemble mean hindcast, surpassing the average predictive skill of the individual hindcast members (5 days), the skill obtained from persistence of observed (2 days), and the decorrelation timescale of blocking (3 days). This skilful prediction of the blocking index, together with effective simulation of blocking rainfall anomalies, translates into higher skill in forecasting rainfall in weeks 2 and 3 over much of Australia when blocking is high at the initial time of the hindcast, compared to when the blocking index is small. POAMA-2 is thus capable of providing forecast skill for blocking rainfall on the intra-seasonal timescale to meet the needs of Australian farming communities, whose management practises often rely upon decisions being made a few weeks ahead.  相似文献   

20.
《大气与海洋》2013,51(2):243-256
Abstract

Trends and variations in daily temperature and precipitation indices in southern Québec are examined for the period 1960–2005. The indices are based on daily temperature and daily precipitation which have been recently adjusted at 53 climatological stations. The adjustments were made for site relocation, changes in observing programs, known instrument changes and measurement program deficiencies. The results show that the surface air temperature has increased in southern Québec over 1960–2005. Significant warming is evident in the western, southern and central parts of the province but the increasing trends become smaller toward the east. The warming is greater during the winter although many significant increasing trends are found in the summer. The analysis of the temperature extremes strongly indicates the occurrence of more nights with extreme high temperatures in all seasons. The temperature indices also suggest an increase in the number of thaw/frost days during the winter (days with maximum temperature above 0°C and minimum temperature below 0°C), a decrease in the length of the frost season, an increase in the length of the growing season, a decrease in heating degree days and an increase in cooling degree days. The precipitation indices show an increase in the annual total rainfall although many stations indicate decreasing trends during the summer. The number of days with rain has increased over the region whereas the number of days with snow and the total snow amounts have decreased over the past 46 years.  相似文献   

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