Institute of Atmospheric Sciences and Climate
Historical Climatology Group
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Istituto di Scienze dell'Atmosfera e del Clima Institute of Atmospheric Sciences and Climate Historical Climatology Group |
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| Program | List of Participants | Contributions | Final Report | Press Release |
Teresa Nanni (ISAC-CNR, Bologna) t.nanni@isac.cnr.it
Michele Brunetti (ISAC-CNR, Bologna) m.brunetti@isac.cnr.it
Dario Camuffo (ISAC-CNR, Padova) d.camuffo@isac.cnr.it
Maurizio Maugeri (Milan University) maurizio.maugeri@unimi.it
Antonio Speranza (Camerino University) antonio.speranza@unicam.it
Valerio Lucarini (Camerino University) valerio.lucarini@unicam.it
Reinhard Böhm (ZAMG, Vienna) r.boehm@zamg.ac.at
Ricardo Garcia (University of Madrid) rgarciah@fis.ucm.es
Elena Xoplaki (University of Bern) elena.xoplaki@giub.unibe.ch
Jürg Luterbacher (University of Bern) juerg@giub.unibe.ch
Murat Türkes (University of Canakkale, Turkey) mturkes@meteor.gov.tr
Pinhas Alpert (University of TelAviv) pinhas@post.tau.ac.il
Henry Diaz (NOAA/CDC) Henry.F.Diaz@noaa.gov
Connie Woodhouse (NOAA/CDC) Connie.Woodhouse@noaa.gov
Marty Hoerling (NOAA/CDC) martin.hoerling@noaa.gov
Drew Shindell (NASA/GISS) dshindell@giss.nasa.gov
Mike Mann (University of Virginia) mann@virginia.edu
Cary Mock (University of South Carolina) MockCJ@gwm.sc.edu
Back to Top M. Brunetti*, M. Maugeri**, F. Monti** and T. Nanni* * ISAC-CNR - via Gobetti 101, I-40129 Bologna, Italy ** Instituto di Fisica Generale Applicata - Milan University - via Brera 28, I-20121 Milan, Italy The awareness of the importance of data quality and homogeneity issues in the correct detection of climate change has increased rapidly in the last few years. Most of the contributions have addressed upper air data, however errors and inhomogeneities also concern surface ones. At surface level it is often assumed that they have random disposition and that, considering a large number of series, average records with negligible bias can be obtained. This assumption is probably correct if global or hemispheric averages are considered, but it may not be correct on a regional scale. The aim of the work is a rigorous reconstruction of the Italian climate for the last centuries (the longest series start in the late 1700s), with particular attention to the identification of spurious non-climatic signals introduced by changing instruments and methods in the measurement procedures. A data set of about 100 precipitation series and from 40 to 60 minimum, maximum, and mean temperature series was set up, together with the information about the station history (metadata). The records were subjected to a detailed quality control and homogenisation procedure that was extensively supported by wide metadata availability. The series were grouped by means of Principal Component Analysis, and regional average records were obtained and analysed for trends. A comparison between the homogenized and the original series and the preliminary results of the analysis are presented. Particular emphasis is given to the importance of data homogenisation in the correct detection of long-term trends.  view moreBack to Top Reinhard Böhm Central Institute for Meteorology and Geodynamics (ZAMG), Climate Department Hohe Warte 38, A-1190 Vienna, Austria Reinhard.boehm@zamg.ac.at During the past decade, the work of the climate variability group of ZAMG has concentrated on data discovery, digitizing, quality improvement (homogenization, outlier correction and gap filling) in the "Greater Alpine Region" (GAR, 4 to 19deg E, 43 to 49deg N). It was possible so far to create highly resolved (100 to 200 single series), homogenized (more than 1000 single inhomogeneities detected and removed), outlier corrected (several 1000 outliers detected and removed) and gap-filled (annual gap rate in the original data varying between 1 and 10%) monthly long-term datasets (several series starting in the 18th century) for the climate elements temperature, precipitation and air pressure. Other elements like humidity, snow, sunshine and cloudiness are still under way. The GAR allows one to study the transition between three leading climate regions of Europe, Mediterranean - Atlantic - continental. The transition is most accentuated here through the barrier of the Alps. Compared to the typical series of global coverage (not before 1850, in most cases for 20th century only or even shorter) the GAR provides another 100 years of early instrumental data in high quality. The presentation is going to show examples for the temperature and the precipitation variability in the region. For both elements distinctive seasonally different evolutions are typical (e.g.: sharp recent wetting trends in autumn in the past 20 years, wet summers, autumns and winters versus dry springs in the 1800 to 1850 period, warm springs and summers versus cool winters near 1800, mild winters-cool summers in the 1910s). In regard to regional differences long-term temperature variability is regionally highly similar for the entire GAR (the Mediterranean parts not different to the Atlantic - continental sector), whereas long-term precipitation variability shows several subregionally different evolutions. Especially the Mediterranean part shows sometimes even opposite trend signs versus the Atlantic subregion for several decades. Concerning interannual variability rotated EOF-based regionalisations produced 4 to 6 subregions - being typical also for different long-term precipitation trends, not for temperature trends. The extensive outlier detection work on outliers in the datasets (an interactive procedure based on monthly anomaly fields applied for each single month of the series) made them fit also for extreme event studies (based on time resolutions of one month at least). In general the first analyses (based on variance-time series in moving windows) point at stable to decreasing long term variability trends in all sub-regions of the GAR. Finally the experience of our group about the "homogenisability" of daily series versus spatial dataset density will be discussed - showing the clear result that the already existing daily climate datasets (e.g. ECA, some national subsets…) are, for precipitation, still not dense enough to be homogeneity tested and adjusted directly. On the other hand a direct application of the test and adjusting results from monthly series on daily series is not feasible (e.g., daily temperature minima behave different to monthly mean). For temperature and air pressure (which are spatially decorrelating much slower than precipitation) the chances are better. Anyway the already digitised daily series in the region (and also elsewhere) represent only a small fraction (5 to 10%) of the data existing in non-digitised archives view moreBack to Top V. Lucarini Department of Mathematics and Informatics, University of Camerino, Italy We present a statistical analysis of the seasonal cycle of the 1951-2000 surface temperature data in Italy and of the corresponding surface and upper air temperature for the Mediterranean region as reconstructed by the NCEP reanalysis. In the case of the Italian records, we consider two data sets which synthesize the surface temperature fields of Northern and Southern Italy. We compute the best estimate of the seasonal cycle of the variables considered by adopting the cyclograms? technique. In general the cycles of the Southern Italy temperatures records lag behind the corresponding cycles referring to Northern Italy. All seasonal cycles lag considerably behind the solar cycle. The estimated amplitude of the seasonal cycle is larger in Northern Italy. These results are consistent with the hypothesis that land-sea differences in terms of thermal inertia play a relevant role in the determination of the properties of the seasonal cycle. The amplitude and phase of the seasonal cycle do not show any statistically significant trend in the time interval considered. In the case of the NCEP data for the Mediterranean region, we follow the same methodological approach. When analyzing surface temperature data, there is an excellent agreement with the above mentioned picture: we have a clear signature of the influence of the Mediterranean sea in the phase delay and amplitude of the seasonal cycle, which have strong negative spatial correlation. When considering upper air data, we do not observe such signature. Moreover, the spatial correlation of the phase delay and amplitude signal is not statistically significant at each given level. The spatial correlation between the phase delay signal of the various levels is significant only when considering nearby levels. The same occurs for the amplitude signal. Only very limited regions seems to show statistically significant trends in the phase delay and/or amplitude in the time frame considered. This work wishes to emphasize the relevance of considering upper air climatological data when characterizing the climate of a given geographical area and when assessing climate change signals at regional as well as global scale. view moreBack to Top M. Colacino1, D. Camuffo2, S. Enzi3 1,2 ISAC-CNR, Roma1 Padova2 3 KLEIO', Padova After a short introduction about the availability of historical data in Italy, the program, promoted by CNR in 1934 in order to collect historical information published or hand written on the meteorological events and climate in our country is recalled. Then are presented different examples of past climate reconstruction: the first one is referred to North-Eastern Italy and is based on the documents concerning the region Venezia Giulia gathered from 534 to 1958 a.D. in a book published in 1934. Another example summarizes the researches carried out on the Alps and based on documents relative to old irrigation channels, old ways crossing the mountain chain, limit of forest and variations on glaciers extension: the results show that before the half of XVI century the alpine climate was warmer and drier than in the following centuries. The third one is devoted to the study of droughts in western Sicily, based on the dates of processions effected in Erice, a small town near Palermo and Trapani, to pray for rainfall. Some concluding remarks about this kind of research close the paper. view moreBack to Top D. Camuffo1, M. Colacino2, S. Enzi3, E. Pagan1, G. Sturaro1, C. Cocheo4 1,2 ISAC-CNR, Padova1, Roma2 3 KLEIO', Padova 4 Fondazione Salvatore Maugeri, Padova Venice risks being submerged as a consequence of two problems: local land subsidence and sea level rise due to global warming. They both contribute to what is referred as Apparent Sea Level Rise (ASLR). Flooding Tides (locally: 'Acqua Alta') submerge Venice with an exponentially increasing frequency. The Acqua Alta is generated by a number of factors, the main of them is the Sirocco wind blowing over the Adriatic Sea, that ultimately displaces waters towards Venice. These extreme events have been investigated by using the documentary description of past floods, accurately reported over the last millennium and tide gauge records for the recent period. A fundamental problem is to know the trend of the ASLR, possibly distinguishing between land subsidence and sea level components. Instrumental data go back to 1872 and a key point is to extend our knowledge back in time. Long-term ASLR has been investigated with the help of a biological indicator, i.e. the height of the green belt of the algae that live in the tidal range and whose upper front shows the average high tide level. Fortunately, in the first half of the 18th century, this indicator was accurately drawn by Antonio Canaletto (1697-1768) and his pupils, mainly Bernardo Bellotto (1722-1780), in their 'photographic' paintings made with an optical camera obscura. It has been possible to compare the tidal level, as it was in the 1700s and today. After careful spot investigation and minor corrections for some changes to the hydrological system occurred in the meantime, the bulk submersion of Venice estimated from the paintings is 61±11 cm with average yearly trend 1.9 mm yr-1. The contributions of the deep tectonic subsidence and eusthatism are of the same order of magnitude. view moreBack to Top Ricardo García-Herrera Departamento Física de la Tierra II, Facultad de Físicas, Universidad Complutense 28040 Madrid Weather observations on sailing ships were taken daily, with almost military routine since the mid seventeenth century; however they have been poorly used with climatic purposes, mostly because on board observation were not first standardized until 1853. Recently, the EU funded CLIWOC has shown that the quality of these observations is much higher than previously expected and can be applied to extend back current climatic databases, such as ICOADS by almost a century. CLIWOC has allowed the construction of a database with more than 280,000 entries of daily observations of wind force and direction covering the North and South Atlantic and the Indian Oceans during the period 1750-1850. But, even more importantly, this project provides the tools to properly interpret and process pre-1850 onboard weather observations and make them directly comparable with instrumental observations. However, the logbook abstraction has, by no means, been completed with CLIWOC. It is estimated that more than 130,000 logbooks are still available in different European archives and that they may contain more than 106 individual observations for the period 1650-1850. Most of them correspond to the British archives and only 10% of them have been abstracted. As previously mentioned, they only cover big open oceans. However, during the period 1700-1850, the Mediterranean Sea was especially busy, not only with ships from the coastal nations, but also with the English fleets, which possessed different ports in the area, especially in the Western Mediterranean. So the whole climatic potential of these sources for the Mediterranean has not been yet explored. This paper examines the availability of logbooks covering the Mediterranean area during the period 1650-1850 and discusses how they could be analyzed and interpreted jointly with other data sources. view moreBack to Top Elena Xoplaki1, Jürg Luterbacher1,2, J. Fidel González-Rouco3, Andreas Pauling1,2 and Ramzi Touchan4 1 Institute of Geography, University of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland 2 National Competence Center of Research in Climate, University of Bern, Bern, Switzerland 3 Departamento de Astrofísica y Ciencias de la Atmósfera, Universidad Complutense de Madrid, Spain 4 Laboratory of Tree-Ring Research, The University of Arizona, Tucson, USA The understanding and knowledge of spatio-temporal patterns of climate change for the last centuries remain a major task in assessing the degree to which the twentieth century was unusual in view against a background of pre-industrial climate variability. Further, there is an ongoing discussion on the vulnerability of ecosystems due to global change and increasing drought risk. The Mediterranean is a climate-sensitive and stressed region by limited water resources and extremes of summer heat assisting the creation or exacerbation of existing sociopolitical tensions. Here we discuss the Mediterranean winter precipitation and summer temperature variability in space and time, trends and the influence of the large scale atmospheric circulation and SSTs over the last few decades and finally provide preliminary seasonal multiproxy temperature and precipitation reconstructions and extremes for the last five centuries together with associated uncertainties. The larger Mediterranean summer temperature trends over the last 50 years based on station data from 32 countries show a clear east-west differentiation. Cooling, though mostly not significant, was experienced over the Balkans, and parts of the eastern basin. In the other areas, there is a significant warming trend of up to 3°C/50yr. However, the warming in these regions did not occur in a steady or monotonic fashion. Over most of western Mediterranean for instance, it has been mainly registered in two phases: from the mid-1920s to 1950 and from the mid-1970s onwards. It has been found that the overall summer warming of around 0.4°C can be mainly attributed to the first Canonical mode, associated with blocking conditions, subsidence, stability and above normal Mediterranean Sea Surface temperatures. The rainfall totals during the wet season from October to March constitute a very important proportion of the annual precipitation amount in the Mediterranean area. The wet season amount varies between 30% in the northwestern Mediterranean with continental climate and more than 90% in the Near East and Northern Africa. The wet season precipitation steadily increased from the mid-19th century until around 1960 and decreased since then. The decadal and long term trends follow those of the NAO, suggesting that long term changes in Atlantic variability, among other processes, govern Mediterranean precipitation. The understanding of the climate variability in the Mediterranean area during the twentieth century and the responsible physical mechanisms can help interpreting the past climate variability. In order to address the current changes in winter precipitation and summer temperature in a longer time context, we present preliminary reconstructed entire climate fields, averaged time series over the Mediterranean through multivariate statistical climate fields reconstruction (CFR) approaches. CFR seeks to reconstruct a large-scale field of surface air temperature and precipitation using a spatial network of proxy indicators, performing a multivariate calibration of the large-scale information in the proxy data network (documentary evidence, natural proxies) against the gridded (60kmx60km resolution) land-based data of the Climatic Research Unit. Results indicate strong decadal to interdecadal summer temperature variability on which shorter period quasi oscillatory behavior is superimposed. Averaged Mediterranean summer temperatures from 1500 to the late 19th century were not distinctly cooler compared to the 20th century. However, the late 20th century/early 21st century turns out to be the hottest period in the 500 year time series. As for the whole of Europe, the summer of 2003 was by far the hottest over the last centuries. The winter precipitation uncertainty of the first centuries is rather high due to the small number of predictors around the Mediterranean. The recent downward trend does not seem to be unusual compared to previous centuries. Finally, we provide first results on late spring-summer precipitation variability over Greece, Turkey and the Near East over the last 600 years based on tree-ring data. view moreBack to Top Cary J. Mock Department of Geography, University of South Carolina, Columbia, SC 29208, U.S.A. The Mediterranean climate region of California possesses some of the longest documentary and early instrumental climatic data for the western United States, well before the modern (twentieth century) record. Although extensive temporal coverage is generally less than 200 years, the data are particularly dense spatially after 1860 and provide important information on verifying climatic reconstructions from tree-ring data, examining spatial variations of climate in response to teleconnections such as ENSO (El Nino/Southern Oscillation) and the PDO (Pacific Decadal Oscillation), on assessing extreme meteorological events such as floods and snowstorms, and reconstructing the length of the growing season. This study provides an overview on some historical climate reconstructions done for the Mediterranean climate region, focusing mostly on winter climate given the strongest teleconnection signals for this season. The climatic data consist of early instrumental data from the U.S. Army Surgeon General from military forts, observers of the Smithsonian Institution, the Signal Service, and some private observers. Daily original records of these data were carefully assessed for discontinuities from examining diurnal temperature ranges and daily precipitation amounts. Corrections on nineteenth century precipitation and temperature records were conducted, based on hourly weather data of the last 40 years. Some documentary (non-instrumental) data were utilized as well, coming mostly from diaries and newspapers. A few previous reconstructions conducted to date were also reassessed in this study, such as those from Spanish documentary sources. The climatic reconstructions conducted were as follows: 1) winter precipitation time series of amounts and rain days for selected locations since the 1840s, particularly from Sacramento and San Francisco, 2) maps of precipitation anomalies for selected extreme winters that are suspected ENSO and flood extremes, 3) growing season time series for selected locations since 1850, 4) winter temperature time series for selected locations since 1850, and 5) analysis of a strong landfalling tropical cyclone in southern California during September 1939. Some results to date indicate that extraordinary positive precipitation anomalies, including its spatial extent, occurred in the winter of 1861-1862, which covered about two-thirds of California. The floods from this winter are considered 'unprecedented' when compared with the climate record of the last 130 years. Also, widespread positive precipitation anomalies are evident during prominent strong warm ENSO events, such as 1877-78 and 1884-85. Some other warm ENSO events such as 1867 and 1871 indicate weaker positive anomalies and vary spatially, and southern California locations generally exhibit more homogeneous positive anomalies. These anomaly patterns are mostly consistent with expected 20th century anomalies during ENSO. Precipitation frequencies (rain days) generally correspond with results from precipitation amounts and exhibit distinctive decadal variability, with the period 1865-1875 being anomalously high for central California. A reconstruction of a landfalling tropical cyclone for September 1939 at Los Angeles from newspaper and ship log data suggest a strength of 50-55 knots. The $2 million in damages from this storm would likely be over $100 million today if it occurred, given higher population densities along with inflation adjustments. view moreBack to Top Connie Woodhouse NOAA National Climatic Data Center, Paleoclimatology Branch and INSTAAR, University of Colorado, Boulder, CO Central and southern California contain 10% of the global area classified as Mediterranean climate. Although a relatively small area, the region is extremely important for its agriculture. California leads the United States in agriculture, producing over 50% of the nation's fruits, vegetables, and nuts, and is also the nation's biggest farm products exporter. This superiority is in large part due to a Mediterranean climate, along with fertile soils and diverse land resources. Most of central and southern California's annual precipitation falls between November and April. El Niño/Southern Oscillation (ENSO) events have significant impacts on winter precipitation in this region. In general, El Niño brings above average precipitation to the entire region, while La Niña's have a more variable impact on regional precipitation. During La Niña's, the southern coast is most often dry while the northern coast tends to be wet. However, the spatial rainfall response is highly variable from event to event. Because of the short instrumental record, it is difficult to determine whether there are decadal-scale variations in the relationship between regional precipitation and ENSO. Understanding low-frequency changes in the character of ENSO and their influence on California climate are important for anticipating possible future impacts resulting from long-term climate change. In this study, the feasibility of using tree-ring data as a proxy for both regional precipitation data and ENSO events to document the relationship between ENSO and winter precipitation over three centuries is explored. A transect of moisture-sensitive tree-ring sites was selected that extends from southwestern to north-central California, encompassing the Mediterranean region. After some initial screening, the resulting network of 16 tree-ring chronologies was found to be well-correlated with divisional November-April precipitation, and adequately represented the regional precipitation, as described by the climate divisions, across the region. Spatial patterns of precipitation during ENSO winters were compared to tree-growth patterns for the same years, and, on average, the patterns were very similar. ENSO years of widespread precipitation anomalies were also well replicated. In order to extend the record of ENSO events prior to the instrumental record, three reconstructions of ENSO (Niño3 from Cook 2000, and Mann et al 2000, SOI from Stahle et al. 1998) were compared and a list was compiled of the years of extreme values (20th and 80th percentiles, 1706-1899) found in all three records. Validation of these dates was partially accomplished with historical climate data from C. Mock. Patterns of tree-growth were examined for 23 El Niño and 20 La Niña events, and compared to the patterns for events in the 20th century. In some cases, the 20th century appears to be representative of past centuries, especially with regard to periodic (although not evenly spaced) occurrences of very widespread dryness during La Niña years, and most consistent dryness in the southern part of the region. For El Niño event years, difference are subtle, but the southern part of the region appears to be more consistently wet for events in the 18th to mid-19th century, with anomalies more evenly distributed over the region in the last 150 years. References cited Cook, E.R., 2000, Nino 3 Index Reconstruction. International Tree-Ring Data Bank. IGBP PAGES/World Data Center-A for Paleoclimatology Data Contribution Series #2000-052. NOAA/NCDC Paleoclimatology Branch, Boulder CO, USA. Mann, M.E., E. Gille, R.S. Bradley, M.K. Hughes, J.T. Overpeck, F.T. Keimig, and W. Gross. 2000. Global temperature patterns in past centuries: An interactive presentation. Earth Interactions 4-4:1-29. Stahle, D.W., R.D. D'Arrigo, P.J. Krusic, M.K. Cleaveland, E.R. Cook, R.J. Allan, J.E. Cole, R.B. Dunbar, M.D. Therrell, D.A. Gay, M.D. Moore, M.A. Stokes, B.T. Burns, J. Villanueva-Diaz and L.G. Thompson. 1998. Experimental dendroclimatic reconstruction of the Southern Oscillation. Bull. American Meteorological Society 79: 2137-2152. view moreBack to Top Michael E. Mann Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA. I will review evidence for climate change and its causes over the interval spanning roughly the past millennium. This evidence is taken from instrumental and high-resolution climate 'proxy' data sources, and climate modeling studies. I will devote particular attention to proxy-based reconstructions of temperature patterns in past centuries, which place recent large-scale warming in an appropriate longer-term context. Several research groups have recently developed annually-resolved, quasi-hemispheric reconstructions of Northern Hemisphere mean temperature changes over the past 500-2000 years, and several modelling centres have run climate simulations based on models with varying levels of complexity, forced by estimated changes in natural and anthropogenic radiative forcing over a similar time frame. While such simulations are limited by limitations in the models and by the uncertain reliability of past forcing histories, inter-comparisons of simulated and reconstructed climates are in reasonable agreement with respect to hemispheric-scale changes over the past millennium and even some regional patterns of change. The comparisons of empirical reconstructions with proxy-based reconstructions demonstrates that natural factors appear to explain the major surface temperature changes of the past millennium reasonably well, at least through to the 19th century. Only anthropogenic forcing of climate, however, can explain the recent anomalous large-scale warming in the late-20th century. At regional scales, climate variability and change appears more closely associated with the behavior of particular modes of climate variability, such as the North Atlantic Oscillation (NAO) and the El Niño/Southern Oscillation (ENSO). These modes of variability may themselves have exhibited late-20th century behavior that is anomalous in a long-term context, but the uncertainties are considerably greater. Changes in the NAO and ENSO are especially relevant for understanding the complex patterns of climate change associated with the so-called "Little Ice Age" and "Medieval Warm Period". Significant climate changes in Europe and the Mediterranean in past centuries, such as the substantial cooling in large parts of Europe during the late 17th and early 18th century, appear closely related to long-term variations in the NAO. Coupled ocean-atmosphere processes in the North Atlantic acting on multidecadal to centennial timescales may also play a role in these changes. A substantial component of this variability appears to be associated with the large-scale dynamical response of the climate system to natural radiative forcing associated with changes in explosive volcanic activity and changes in solar output. By contrast, climate changes in the desert southwest of the U.S. appear more closely tied to changes in ENSO in past centuries, which may also represent in large part the response to such past changes in radiative forcing. view moreBack to Top Antonio Speranza Department of Mathematics and Informatics, University of Camerino, Italy Statistical inference suffers for severe limitations when applied to extreme meteo-climatic events. An old (first half of the past century) general theorem, in some sense similar to the central limit theorem, proposes a constructive theory for a "universal" distribution law (the Generalized Extreme Value distribution) of extremes. Use of this theorem and its derivations is nowadays quite common. However, when applying it we should keep in mind, among other things, that: · the selected events should be real extremes; · the theorem, strictly speaking, applies to stationary processes; · the GEV distribution is determined by three real parameters. In practical applications the major source of errors is probably the firs point: there is no strict criterion for selecting extremes and, in order to "fatten" the statistical sample very "mild" selection criteria are often used. When a trend is introduced, inference becomes even more problematic. Experience shows that any a priori knowledge concerning the system can play a fundamental role in the analysis, in particular if it lowers the dimensionality of the parameter space to be explored. The inference procedures serve, then, the purpose of testing the reliability of inductive hypothesis, rather then determining them. Within the above general context, we will discuss the hypothesis that the frequency and/or intensity of extreme weather events in the Mediterranean area may be changing. The analysis will be based on a combined deterministic-statistical approach to this specific problem. Dynamical analysis of intense perturbations will be combined with statistical techniques in order to try put the problem in the correct perspective. view moreBack to Top Pinhas Alpert, S.O. Krichak, B. Ziv, H. Saaroni & C. Price Heavy daily rainfall over the Mediterranean is observed to increase despite the decrease in the total values. The redistribution of six daily rainfall categories, i.e., torrential/heavy against moderate/light, with climate change in the recent 45 years is of major significance for flash floods impacts, water management, soil erosion, (Alpert et al., GRL, 2002). The potential relations between rainfall extremes in the Mediterranean to tropical systems, e.g. El Niño, hurricanes, Indian Monsoon, will be shown. Also, the tendency in extreme summer temperatures will be shown and the relation to the Indian Monsoon illustrated. High resolution modeling of a severe flood event on 3-5 Dec 2001 over Israel and relation to Hurricane Olga will be discussed. These studies are supported by the GLOWA Jordan River Project that P. Alpert is directing in Israel: http://www.glowa-jordan-river.de/Design/Glowa_JR.htm view moreBack to Top Martin Hoerling NOAA Climate Diagnostics Center Boulder CO USA Jim Hurrell NCAR Boulder CO USA Atmospheric responses to 20th Century warming of tropical sea surface temperatures (SSTs) are illustrated, with emphasis on their relationship to regional changes over the North Atlantic, Europe and the Mediterranean region. The question is explored whether the trend component of wintertime North Atlantic/European climate can be understood as the pattern forced by the warming trend of tropical SSTs. Results are derived from atmospheric general circulation model (GCM) experiments subjected to idealizations of the observed, tropical SST trends since 1950. It is discovered that a strong projection onto the positive polarity of the North Atlantic Oscillation (NAO) index characterizes the atmospheric response structure to the 1950-1999 trend component of tropical-wide SSTs within 25°N-25°S. This is embedded within a hemisphere-wide pattern distinguished by a meridional seesaw having lowered Arctic pressure and increased mid-latitude pressure that resembles the so-called Northern Hemisphere Annular mode. It is shown that progressive warming of the Indian Ocean since 1950, amounting to +1 °C, is the principal contributor to North Atlantic/European winter climate trends. This influence appears to be robust in so far as it is reproduced in ensembles of experiments using three different GCMs. Taken together, the North Atlantic/European response to recent Indian ocean warming replicates the pattern and amplitude of that region's 1950-99 trends occurring in earlier GCM simulations forced with the complete history of global monthly varying SSTs. Importantly, the pattern and about half the amplitude of the observed trend are found to be consistent with an Indian Ocean warming source. The presentation concludes by exploring consequences for the Mediterranean climate under the scenario of additional tropical SST warming as will likely occur during the 21st Century. view moreBack to Top M. Brunetti*, M. Maugeri **, T. Nanni * *ISAC-CNR, Bologna, Italy ** Institute of Phisics, University of Milano, Italy A new data set of daily precipitation series, covering quite uniformly Italian territory for the period 1880-2002, was recovered. The series have been homogenised on daily basis, completed by means of statistical methods and grouped into 5 regions by a Principal Component Analysis. Seasonal and yearly total precipitation, number of wet days, and precipitation intensity were analysed for each station record and averaged into 5 regional series for a synthetic description of the results. Proportion and frequency of daily rainfall amounts, belonging to 6 precipitation class-intervals, defined on the basis of some percentiles of the precipitation distribution, were also analysed. The results show a negative significant trend in the number of wet days all over Italy, and a positive trend in precipitation intensity, which is significant only in the northern regions. The negative trend in wet days has persisted since the end of 19th century and is due to the marked decrease in the number of low intensity precipitation events. An increase in the number of events belonging to the highest intensity class interval was observed too, but only in northern regions. For the last 50 years this tendency was explained in terms of atmospheric circulation changes: positive trend in the mean SLP and an increase in the frequency and persistency of anticyclonic conditions over the Mediterranean basin. The relationship between atmospheric circulation and precipitation regimes was quantified by introducing a "Mediterranean Circulation Index" constructed from Marseille and Jerusalem surface pressure records. view moreBack to Top MURAT TÜRKE1 AND ECMEL ERLAT2 1Department of Geography, Çanakkale Onsekiz Mart University, Terzioglu Campus - Çanakkale, Turkey 2Department of Geography, University of Aegean, Bornova - Izmir, Turkey Relationships between the variability of the NAO indices and the normalized precipitation at the 78 stations of Turkey, and the influences of the extreme NAO index (NAOI) episodes and the year-to-year and longer time-scale variations in the NAO on the precipitation conditions were investigated. The study also carried out analysis of the anomalous circulations at 500 hPa geopotential level during the extreme NAOI phases in order to explain atmospheric causes of responses of the Turkish precipitation to the extreme NAO phases. An extended summary and the main conclusions of the study are as follows: When the NAO is in its extreme phases, both the Icelandic Low and the Azores High are well developed during cool/cold period of the year, especially in winter. Weak phase of the NAO indicates stronger-than-average westerly and south-westerly circulation over the subtropical north-east Atlantic, the North Africa and the Mediterranean basin towards Turkey, and the stronger-than-average north-easterly circulation across the Scandinavia and the mid-latitude and sub-Arctic north-east Atlantic particularly in winter, spring and annually. Contrary, the strong phase of the NAO shows the increased westerlies over the mid-latitudes and the Scandinavia and increased easterly and northeasterly circulation over a large conveyer zone from Turkey to the subtropical Atlantic via the Mediterranean basin and the North Africa. In summer, weak phase of the NAO indicates increased easterly/north-easterly circulation over the Northern Europe and the northeast Atlantic associated with the anticyclonic anomaly centre over the area of the Icelandic Low and the cyclonic anomaly centres over the mid-north-east Atlantic and the Western Europe. On the other hand, strong phase of the NAO indicates increased easterly and northeasterly circulation across a large region of the northern Mediterranean/southern Europe, the Balkans, the northwest Turkey and the Black Sea. Autumn, in addition to the apparent anomaly centres over the areas of the Icelandic Low and the Azores High, is only season that characterized by well-described and large-scale anomaly centres occurred in both extreme phases of the NAO, in comparison with other seasons. A negative anomaly centre is evident over north of Russia and the Eastern Europe, and an associated trough is extending from that centre to Turkey. There is a negative relationship between interannual variability of the Turkish precipitation series and the NAO indices. Negative relationships that are stronger particularly in winter and partly in autumn are detected to be weaker in spring and almost non-existent in summer. Composite precipitation means corresponding to the extreme NAOI phases mostly exhibit an apparent opposite anomaly pattern, except in summer, between the negative and positive NAOI phases. Annual, winter, spring, autumn and partly summer composite precipitation means are mostly characterised by wetter than the long-term average conditions during the negative NAOI phase, whereas the positive NAOI responses mostly exhibit drier than the long-term average conditions annually and in all seasons except summer. Spatially coherent and statistically significant changes in the precipitation amounts during the extreme NAOI phases are more apparent in the west and mid Turkey. The 500 hPa circulation corresponding to the negative NAOI phase brings above long-term average precipitation to Turkey in winter, spring and autumn and annually, associated with the NAO pattern in which the 500 hPa geopotential level is anomalously high in the area of the Icelandic Low and anomalously low across the regions of the Azores High and the Europe in general. Contrary, the NAO pattern over the North Atlantic and the Europe is responsible for the drier than long-term average precipitation conditions in Turkey during the positive NAOI phase, when the 500 hPa geopotential level is anomalously low over the area of the Icelandic Low and the anomalously high across the subtropical and mid-latitude north-east Atlantic and the Europe regions. Low-frequency fluctuations in the circulation over the Atlantic are closely linked to the coherent large-scale precipitation anomalies that have persisted, particularly in winter, over Turkey since the early 1960s. view moreBack to Top Drew Shindell NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA Analyses of observations shows correlations between the mean state of indicies representing either the North Atlantic Oscillation (NAO) or the Arctic Oscillation (AO, also called Northern Annular Mode) with various external forcings. These include volcanic eruptions, solar variability, greenhouse gas levels and stratospheric ozone depletion. Climate model simulations have been able to reproduce many aspects of these correlations over a variety of time scales ranging from interannual to century scale. This has allowed some insight to be gained into how external forcings modulate these intrinsic variability patterns. I review current understanding derived from comparisons of a range of models with observations to highlight areas of commonality as well as remaining uncertainties. Contrasts between the Northern and Southern Hemispheres suggest that much of the response to external forcing occurs via wave-driven processes. Comparison of the response to forcings at different levels in the atmosphere indicate a sizeable role for both stratospheric and surface-level perturbations. Implications for forcing of changes in Mediterranean climate are presented for pre-industrial times during the last millennium, for the twentieth century, and for the potential future view moreBack to Top Back to Top Back to Top |