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Lanzhou University (2007)

Reconstruction Of Temperature Variation Since 1500AD In The Arid-semiarid Central-eastern Asia Using Tree-ring Chronology Based On EOF Iteration Scheme

Ding Xiao Jun

Titre : Reconstruction Of Temperature Variation Since 1500AD In The Arid-semiarid Central-eastern Asia Using Tree-ring Chronology Based On EOF Iteration Scheme

Auteur : Ding Xiao Jun

Grade : Master’s Theses 2007

Université : Lanzhou University

Résumé
The arid-semiarid central-east Asian (ACEA), which is a transition between equatorial and extratropical regions, also called mid-latitude Asian inland arid band, is a region for interactions between westerly and monsoon ciimates, and responds sensitively to global climate change. It’s known that recent global warming is obvious, and how does the ACEA respond to the global warming ? And besides, what are the basic features of ACEA climate change during past several hundred years ? Answering this question will be benefit to understand the mechanism and reason of the ACEA climate change, and to make ready for best understand the ACEA climate change in the past millennium even ten millenaries, thus to provide reference for region climate research as well as the future climate forecast.In this study using the surface ground temperature from 1961 to 2003 over 67 observation sites and NCEP/NCAR 500hpa height re-analysis data as well as the tree-ring width index data which comes from ITRDB, firstly the instrumental temperature variation is analyzed to know about the responds to the global warming. Then an ACEA temperature reconstruction is established based on the empirical orthogonal function (EOF) iteration scheme and the variability is analyzed, and compared with other reconstructions and some history documents. In addition, the winter and summer atmospheric circulation fields at 500hpa height over Europe-Asia continent (0-150°E, 20-70°N) are also reconstructed so that the circulation context during the warmer and colder periods is analyzed to verify the reliability of the temperature reconstruction. Some preliminary conclusions are as follows:1、The geography and the terrain have influence on the spatial distribution of the mean annual temperature greatly in ACEA. The difference of the mean annual temperature between the south and the north of ACEA is obvious. The elevation plays an important role on the mean annual temperature variation. The lowest temperature appears in the Tienshan mountains and the Mongol plateau as well as Qilian Mountains. During 1961-2003 a rise trend is indicated in the mean annual instrumental temperature series and the increase rate is about 0.39℃/10a. The warming is very evident in the recent twenty years. The results of the estimating red-noise spectra of the time series method show that there exist quasi-periodicities of 10a and 2.4-2.6a. The increase rate of mean annual temperature is largest in the Eastern monsoon area while smallest in the Central Asia.2、Numerical experiments show that it is feasible to reconstruct the temperature series and atmospheric circulation fields with the EOF iteration scheme using tree-ring data.3、The mean annual temperature variation during the last 1500 years is reconstructed with the EOF iteration scheme using tree-ring data. The results show that there is a colder period than modern climate period (i.e. 1971a-2000a) from late 17th century to early 19th century and a weakly warmer condition in the 1930s. In detail, the ACEA mean annual temperature experienced four colder periods in the years of 1533-1573, 1657-1711, 1718-1823 and of 1887-1979, as well as three warmer periods in the years of 1502-1532, 1574-1656, and of 1824-1886.There exist pronounced lower-frequency periodicities of 250a and higher-frequency variations of 4.3a and 2.2a in the mean annual temperature reconstruction in study area, respectively exceeding 99% and 95% red-noise significance level.The mean annual temperature variation in each subarea agrees with that in the whole area in most cases.4、Furthermore, the winter and summer atmospheric circulation fields at 500hpa height are also reconstructed using tree-ring data and NCEP re-analysis data with EOF iteration scheme. The temperature variation has a good response to the atmospheric circulation fields over the study region.

Mots clés : the Arid-semiarid Central-East Asia (ACEA), paleoclimate reconstruction, EOF iterative scheme, tree-ring chronology

Présentation (Dissertationtopic)

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