Climatology of deep cyclones over Asia and the Northwest Pacific

Summary A frequency analysis of deep cyclones with central pressure less than or equal to 990 hPa over Asia and the Northwest Pacific in the period 1958–1989 is presented. The most active areas of deep cyclones are: 1) Western Siberia, east of the Ural Mountains; 2) Northeastern China, east of the Mongolia Plateau and, 3) South-west of the Kamchatka Peninsula. The first most active area is related to European cyclones (Schinke, 1993) and starts in the lee of the Ural Mountains; the second is related to cyclones in the lee of Altai-Sayan and the third to East Asian coastal cyclones. After zonal averaging, two frequency maxima of deep cyclones emerged, one between 62.5–67.5° N and the other between 47.5–52.55° N. This is different from the European and North Atlantic regions where only one maximum occurs. The seasonal frequency deep cyclones in Northeastern China reaches maximum in spring and summer while in western Siberia and the Northwest Pacific deep cyclones are more frequent in winter. The annual trend of deep cyclones over the Northwest Pacific shows an increase from the sixties to the eighties while deep cyclones over East Asia decreased during this period. In the 1980's, more deep cyclones occurred over the Northwest Pacific and less deep cyclones over main land Asia which may be associated with the northern hemisphere warming. The monthly number of oceanic deep cyclones in December and January appeared to be positively correlated with the August and September sea surface temperatures over the East Pacific (El Nino regions 1 + 2).With 7 Figures     

Long-term changes in annual rainfall patterns in southern Israel

Summary Within the study region in southern Israel, the annual average rainfall during the period 1961–1990 increased by up to ~ 30%, with only minor changes in the control stations representing the central and northern parts of the country. The retreat of aridity is made even more pronounced by an appreciable decrease in the coefficient of variation (CV) in nearly all of the 30 rain stations within the study region. The geographical area where maximum CV reductions were found correlates well with the area where intensive land-use variations took place with the initial operation of the National Water Carrier in 1964. A global climate change in the sea surface temperatures starting in the early 1960's may have had an effect to increase seasonal rainfall. Current research is aimed at resolving this issue.With 6 Figures     

Limatic variables that control development of stripe rust disease on winter wheat

The frequency and severity of the stripe rust disease (caused byPuccinia striiformis) on winter wheat in the Pacific Northwest of the U.S.A. has increased since 1958 in association with climatic variation. From 1968–1979, rust intensities on ‘Gaines’ wheat were most highly correlated with accumulated negative degree days (NDD) between 1 December and 31 January and positive degree days (PDD) between 1 April and 30 June. NDD and PDD were calculated from a 7 °C base. Linear regression equations using NDD alone accounted for 76% of the variation in stripe rust. When NDD and PDD were combined, 88% of the variation in stripe rust was explained. When a growth index (GI), and NDD plus PDD were used as independent variables in a multiple regression analysis, 91% of the variation in disease was explained. Frequency of precipitation in June was correlated with stripe rust intensity, but when it was added to the multiple regression analysis, it explained less than an additional 1% of the variation. The relationships between NDD, PDD, and disease index help to explain why stripe rust was not severe from 1941 to 1957. Methods used in this research should be applicable to similar studies of the effect of climatic variation on other pests. This research was supported by a National Science Foundation Grant (ATM 76-21725), Climate Dynamics Program, Division of Atmospheric Sciences.     

REGIONAL SNOWFALL PATTERNS IN THE HIGH, ARID ANDES

Since 1990 the project Climate Change in the Arid Andes has been focusing on past climate and environmental conditions in the high mountain range of the north Chilean Andes (18° S–28° S). The extreme aridity of this region is shown by the absence of glaciers, even at the highest altitudes above 6700 m a.s.l. More knowledge of the present climatic situation is needed to interpret the proxy data of different paleoarchives in this transition belt between tropical and extratropical circulation. Precipitation events in this arid region are mainly registered during southern hemisphere summer, when the ITCZ reaches its southernmost position. Winter precipitation (snowfall) has so far not been considered an important factor in the hydrologic system of the area, because snow is seldom accurately registered by climatic stations. To fill this gap in our information, winter snowfall activity was analysed for a period of 6 years using digital NOAA/AVHRR satellite data. The results show that snowfall during winter (May–September) is a quite regular phenomenon, mainly linked to northward displacements or cut-offs of cold air-masses from the Pacific. The areal distribution of snowfall is determined by the synoptic situation that produces precipitation. During cold frontal events, snowfall is most frequent in the southernmost part of the research area and on the western Chilean side of the Andes. Cold air that has been cut off from the westerlies often interacts with warmer and more humid air over the continent and therefore gives rise to a different snowfall distribution, with the greatest snowfall frequency between 23° S–25° S, decreasing polewards as well as towards the equator. These two winter snowfall patterns show that reconstruction of paleoclimate has to take into account the different mechanisms that may cause precipitation in the research area. Intensification of winter precipitation (e.g., the west wind zone) can induce largely different precipitation patterns, depending on which mechanisms (cut-offs, cold-fronts or both) within the west wind zone are strengthened.     

Elevation Dependence of Winter Wheat Production in Eastern Washington State with Climate Change: A Methodological Study

Crop growth models, used in climate change impact assessments to project production on a local scale, can obtain the daily weather information to drive them from models of the Earth's climate. General Circulation Models (GCMs), often used for this purpose, provide weather information for the entire globe but often cannot depict details of regional climates especially where complex topography plays an important role in weather patterns. The U.S. Pacific Northwest is an important wheat growing region where climate patterns are difficult to resolve with a coarse scale GCM. Here, we use the PNNL Regional Climate Model (RCM) which uses a sub-grid parameterization to resolve the complex topography and simulate meteorology to drive the Erosion Productivity Impact Calculator (EPIC) crop model. The climate scenarios were extracted from the PNNL-RCM baseline and 2 × CO₂ simulationsfor each of sixteen 90 km² grid cells of the RCM, with differentiation byelevation and without correction for climate biases. The dominant agricultural soil type and farm management practices were established for each grid cell. Using these climate and management data in EPIC, we simulated winter wheat production in eastern Washington for current climate conditions (baseline) and a 2 × CO₂ `greenhouse' scenario of climate change.Dryland wheat yields for the baseline climate averaged 4.52 Mg ha^–1 across the study region. Yields were zero at high elevations where temperatures were too low to allow the crops to mature. The highest yields (7.32 Mgha^–1) occurred at intermediate elevations with sufficientprecipitation and mild temperatures. Mean yield of dryland winter wheat increased to 5.45 Mg ha^–1 for the 2 × CO₂ climate, which wasmarkedly warmer and wetter. Simulated yields of irrigated wheat were generally higher than dryland yields and followed the same pattern but were, of course, less sensitive to increases in precipitation. Increases in dryland and irrigated wheat yields were due, principally, to decreases in the frequency of temperature and water stress. This study shows that the elevation of a farm is a more important determinant of yield than farm location in eastern Washington and that climate changes would affect wheat yields at all farms in the study.     

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.     

天水地区条锈病的发生与气象条件关系研究

利用1994～2006年天水市条锈病监测资料、天水市7县（区）气象站的常规观测资料和冬小麦生长发育期资料,用数理统计方法分析条锈病的发生发展特征及气象因子与冬小麦生长发育期的关系。结果表明：全球气候变暖使条锈病的越冬、越夏条件优越,自1994年以来发生面积呈线性增长,发病程度天水市东南部重于西北部。条锈病的爆发流行既受当时气象条件制约,又受周边地区条锈病发生发展趋势的影响。根据分析制作的条锈病预测预报模型,为条锈病的积极防治及科学决策生产提供了依据。     

阿勒泰地区冬季降雪的集中度和集中期变化特征

利用1961~2010年阿勒泰地区冬季台站降水资料,计算并分析了阿勒泰地区降雪集中度和集中期的时空变化特征。结果表明:降雪集中度(PCD)和集中期(PCP)能够定量表征降雪量在时空场上的非均一性。阿勒泰地区降雪平均集中度为0.27,平均集中期为第7.8候(12月上旬)。平均集中度和集中期空间分布不均匀,东部的降雪集中度和集中期较西部大。Morlet小波分析表明,阿勒泰地区降雪集中度和集中期存在各自的年际尺度周期变化。通过降雪量与集中度和集中期的合成分析表明,多雪年集中度较少雪年偏小,集中期较少雪年偏早。     

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     

我国强降雪气候特征及其变化

基于全国气象台站逐日地面降雪观测数据,对我国25°N以北不同气候区强降雪事件的地理分布和年内旬、月变化等气候特征进行分析,并探讨1961—2008年其时间序列演变特征,及1961—2008年和1981—2008年 (气候变暖后) 气候变化趋势。结果表明:强降雪量和强降雪日数在青藏高原东部、新疆和东北北部最多;强降雪强度高值中心出现在云南。东北北部、华北、西北、青藏高原东部强降雪事件多发生于初冬和初春,年内分布呈双峰型;新疆和黄淮地区年内分布呈单峰型,前者多发生在隆冬时节,后者多发生于晚冬;1961—2008年东北北部、新疆、青藏高原东部平均强降雪量和强降雪日数呈明显增加趋势;气候变暖后我国大部年强降雪量增多,强降雪日数增加,强降雪强度增强。     

Twenty-first century changes in snowfall climate in Northern Europe in ENSEMBLES regional climate models

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.     

Bjerknes’ hypothesis on the coldness during AD 1790–1820 revisited

The aim of this paper is to re-examine and quantify a hypothesis first put forward by J. Bjerknes concerning the anomalous coldness during the AD 1790–1820 period in western Europe. Central to Bjerknes hypothesis is an anomalous interaction between ocean and atmosphere studied here using an ocean-atmosphere coupled climate model of intermediate complexity. A reconstruction of the sea-level pressure pattern over the North Atlantic sector averaged over the period 1790–1820 is assimilated in this model, using a recently developed technique which has not been applied to paleoclimatic modelling before. This technique ensures that averaged over the simulation the reconstructed pattern is retrieved whilst leaving atmospheric and climatic variability to develop freely. In accordance with Bjerknes hypothesis, the model results show anomalous southward advection of polar waters into the northeastern North Atlantic in the winter season, lowering the sea-surface temperatures (SSTs) there with 0.3–1.0°C. This SST anomaly is persistent into the summer season. A decrease in western European winter surface air temperatures is found which can be related almost completely to advection of cold polar air. The decrease in summer surface air temperatures is related to a combination of low SSTs and anomalous atmospheric circulation. The modelled winter and summer temperatures in Europe compare favourably with reconstructed temperatures. Enhanced baroclinicity at the Atlantic seaboard and over Baffin Island is observed along with more variability in the position of the North Atlantic storm tracks. The zone of peak winter storm frequency is drawn to the European mid-latitudes.     

Wintertime European circulation patterns during the Late Maunder Minimum cooling period (1675–1704)

Summary The North Atlantic and Western Europe regions comprise a key area to study climate variations in the form of cold relapses which may be a possible manifestation of reduced ocean circulation. By using multi-proxy data of the late Maunder Minimum period, temperature and precipitation distribution during winter was studied in connection with atmospheric circulation, with the goal of obtaining an insight into the feedbacks between ocean, sea ice and temperature. The study shows that the Late Maunder Minimum was a relatively cool and dry period with low ocean temperatures and a large sea ice extent, although Alpine glaciers did not grow during this time. A comparison of the winter weather types of the three decades from 1675 to 1704 with the recent 30 year period (1961–1990) shows that the late Maunder Minimum was characterized by strong sea level pressure reversals with high pressure centres over Northern or Northwestern Europe and large outbreaks of northeasterly cold continental air.With 3 Figures     

Trends of Extreme Temperatures in Europe and China Based on Daily Observations

Ten of the longest daily temperature series presently available in Europe and China are analysed, focusing on changes in extremes since pre-industrial times. We consider extremes in both a relative (with respect to the time of year) and an absolute sense. To distinguish changes in extremes from changes affecting the main part of the temperature distribution, a percentile smaller than 10 (and/or larger than 90) is recommended for defining an extreme. Three periods of changes in temperature extremes are identified: decreasing warm extremes before the late 19th century; decreasing cold extremes since then and increasing warm extremes since the 1960s. The early decreases and recent increases of warm extremes dominate in summer, while the decrease of cold extremes for winter persists throughout the whole period. There were more frequent combined (warm plus cold) extremes during the 18th century and the recent warming period since 1961 at most of the ten stations, especially for summer. Since 1961, the annual frequency of cold extremes has decreased by about 7% per century with warm extremes increasing by more than 10% per century but with large spatial variability. Compared with recent annual mean warming of about 2–3 ° C/century, the coldest winter temperatures have increased atthree times this rate, causing a reduced within-season range and therefore less variable winters. Changes in the warmest summer temperatures since 1961 exhibit large spatial variability, with rates of change ranging from slightly negative to 6 ° C/century. More extensive station observations since 1961 indicate that the single site results are representative of larger regions, implying also that the extremes studied are the result of large-scale changes. Recent circulation changes in daily gridded pressure data, used as an indicator of wind speed changes, support the results by explaining some of the trends.     

The NPO/ NAO and interdecadal climate variation in China

This article discusses the interannual variation of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO), its relationship with the interdecadal climate variation in China which is associated with the climate jump in the Northern Hemisphere in the 1960’s, using the data analyses. It is clearly shown that both the amplitudes of the NAO and NPO increase obviously in the 1960’s and the main period of the oscillations changes from 3-4 years before the 1960’s to 8-15 years after the 1960’s. Therefore, interdecadal climate variation in China or the climate jump in the 1960’s is closely related to the anomalies of the NAO and NPO.     

宁夏近百年来的气候变化及突变分析

以宁夏北部地区近百年来的降水量、气温距平资料以及全区各季有仪器观测以来的温度降水资料为基础，利用Mann-Kendall突变检验法和滑动t检验法，分析了宁夏近百年来气候变化的阶段性和突变特点。结果表明：近百年来宁夏气候大概经历了五个主要阶段；80年代中期年平均气温及秋冬季平均气温发生改变；60年代左右年降水量发生突变；70年代中后期全区秋季降水量出现突变。     

Analysis of recent climatic changes in the Arabian Peninsula region

Summary Interest in the potential climatic consequences of the continued buildup of anthropo-generated greenhouse gases has led many scientists to conduct extensive climate change studies at the global, hemispheric, and regional scales. In this investigation, analyses are conducted on long-term historical climate records from the Arabian Peninsula region. Over the last 100 years, temperatures in the region increased linearly by 0.63 °C. However, virtually all of this warming occurred from 1911–1935, and over the most recent 50 years, the Arabian Peninsula region has cooled slightly. In addition, the satellite-based measurements of lower-tropospheric temperatures for the region do not show any statistically significant warming over the period 1979–1991. While many other areas of the world are showing a decrease in the diurnal temperature range, the Arabian Peninsula region reveals no evidence of a long-term change in this parameter. Precipitation records for the region show a slight, statistically insignificant decrease over the past 40 years. The results from this study should complement the mass of information that has resulted from similar regional climate studies conducted in the United States, Europe, and Australia.With 5 Figures     

CLIMATE CHANGE AND THE BATHURST CARIBOU HERD IN THE NORTHWEST TERRITORIES, CANADA

The Bathurst barren-ground caribou herd was chosen as the focus of a study of the possible effects of a changed climate on hunting of a caribou herd in the Northwest Territories. Four climate change scenarios representing conditions under a doubling of atmospheric carbon dioxide concentrations were used in the study. The locations of the Bathurst herd throughout the year were determined, and the 1951 to 1980 average monthly temperatures and total monthly precipitation amounts were ascertained at those locations. The four climate change scenarios were applied, with changes in average monthly temperatures and in total monthly precipitation amounts noted. Analyses indicate a possible increase in winter snowfall, and increased insect harassment of caribou in the summer, due to an increase in average monthly temperatures. The reduced accessibility and health of caribou in the Bathurst herd suggest a reduced hunting potential. Management options are briefly discussed.     

Future change of climate in South America in the late twenty-first century: intercomparison of scenarios from three regional climate models

Regional climate change projections for the last half of the twenty-first century have been produced for South America, as part of the CREAS (Cenarios REgionalizados de Clima Futuro da America do Sul) regional project. Three regional climate models RCMs (Eta CCS, RegCM3 and HadRM3P) were nested within the HadAM3P global model. The simulations cover a 30-year period representing present climate (1961–1990) and projections for the IPCC A2 high emission scenario for 2071–2100. The focus was on the changes in the mean circulation and surface variables, in particular, surface air temperature and precipitation. There is a consistent pattern of changes in circulation, rainfall and temperatures as depicted by the three models. The HadRM3P shows intensification and a more southward position of the subtropical Pacific high, while a pattern of intensification/weakening during summer/winter is projected by the Eta CCS/RegCM3. There is a tendency for a weakening of the subtropical westerly jet from the Eta CCS and HadRM3P, consistent with other studies. There are indications that regions such of Northeast Brazil and central-eastern and southern Amazonia may experience rainfall deficiency in the future, while the Northwest coast of Peru-Ecuador and northern Argentina may experience rainfall excesses in a warmer future, and these changes may vary with the seasons. The three models show warming in the A2 scenario stronger in the tropical region, especially in the 5°N–15°S band, both in summer and especially in winter, reaching up to 6–8°C warmer than in the present. In southern South America, the warming in summer varies between 2 and 4°C and in winter between 3 and 5°C in the same region from the 3 models. These changes are consistent with changes in low level circulation from the models, and they are comparable with changes in rainfall and temperature extremes reported elsewhere. In summary, some aspects of projected future climate change are quite robust across this set of model runs for some regions, as the Northwest coast of Peru-Ecuador, northern Argentina, Eastern Amazonia and Northeast Brazil, whereas for other regions they are less robust as in Pantanal region of West Central and southeastern Brazil.     

Indications of change of climate from the analysis of air temperature time series in Athens,Greece

Air temperature data of Athens are analysed to point out the variations caused by natural controls and anthropogenic activities. The study of the temperature records from 1858 to 1982 at Athens, on the southeast coast of Greece, supports the findings of earlier studies which indicate that the period of the 1920's to the 1950's were, climatologically, warmer than the preceding 60 yr and after about 1960. In particular, minimum temperatures show an increase from the 1920's to the 1980's, possibly due to the urbanization of the area. The climatological trends are clearly indicated in the data, when averaged over 30 yr and/or a numerical low-pass filtering technique is used. However, the sizes of the trends in climate are smaller than the interannual variations in the temperature measures. Over periods of several generations these small variations in climate cannot have had any effect on human activity when compared with the large effects caused by the interannual variability in the temperature.