The spatio-temporal evolution of the Asian monsoon climate in the Late Miocene and its causes: A regional climate model study

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http://urn.fi/URN:ISBN:978-952-10-6326-8
Title: The spatio-temporal evolution of the Asian monsoon climate in the Late Miocene and its causes: A regional climate model study
Author: Tang, Hui
Contributor: University of Helsinki, Faculty of Science, Department of Geosciences and Geography, Division of Geology
Publisher: Helsingin yliopisto
Date: 2013-06-15
Belongs to series: Department of Geosciences and Geography A21 - URN:ISSN:1798-7911
URI: http://urn.fi/URN:ISBN:978-952-10-6326-8
http://hdl.handle.net/10138/39411
Thesis level: Doctoral dissertation (article-based)
Abstract: Late Miocene (11-5 Ma) is a crucial period for Asian monsoon evolution. Significant changes of both the India and East Asian monsoons in this period have been documented in geological records. In this study, a high-resolution regional climate model COSMO-CLM driven by a fully coupled atmosphere-ocean general circulation model ECHAM5/MPI-OM is employed to investigate the monsoon climate change in the early Late Miocene (i.e. Tortonian) and its mechanisms. Our results suggest a generally weaker (stronger) summer (winter) monsoon circulation over East Asia and India in the Tortonian than today. The monsoon rainfall changes, however, might have exhibited great regional differences. The modern-like monsoonal climate may have existed in southern China and India in the Tortonian, while the monsoonal climate in northern China and northwestern India may have not fully developed at that time. Sensitivity experiments with different orographic configurations in our regional model shows that different from the effect of the uplift of the entire Asian orography (i.e. bulk mountain uplift) which strengthens both the Indian and East Asian summer monsoons (ISM and EASM), the diachronous growth of different part of the Asian orography (i.e. regional mountain uplift) can lead to an asynchronous development of the ISM and EASM. While the ISM is primarily intensified by the presence of the southern TP (Zagros Mountains) due to its thermal insulation (mechanical blocking) effect, the EASM is mainly strengthened by the presence of the central and northern TP and the Tianshan Mountains owing to their strong diabatic heating effect. Such effects offer explanations to the asynchronous development of the ISM and EASM during the Middle Miocene (15 Ma), the Late Miocene (8 Ma) and Pliocene (4 Ma). In addition to the mean monsoon climate, the interannual variability of the ISM in the Late Miocene is also explored by analyzing our model experiments for the Tortonian. It reveals that the interannual variability of the ISM in the Late Miocene may have been as strong as, or even stronger than at present. This can be attributed to the strong El Niño Southern Oscillation (ENSO) at that time. In addition, the extratropical influence, such as summer North Atlantic Oscillation, on the ISM might have been weak. This may have facilitated a stronger ENSO-ISM teleconnection in the Late Miocene. We note that although the Late Miocene Asian monsoon climate is strongly influenced by regional tectonic changes (e.g. the lower northern TP), it still exhibits great resemblance to that projected under the future global warming conditions. Better knowledge and model simulations on the Late Miocene monsoon climate may provide useful constraints on the prediction of the future Asian monsoon changes.Aasian monsuuni on ilmastosysteemin aktiivisimpia osia ja yli kolmannes ihmiskunnasta elää sen vaikutuksen alaisena. Sen luonnollisen vaihtelun ja mekanismien ymmärtäminen on tärkeää sekä tieteellisesti että käytännön kannalta. Tässä tutkimuksessa käytin erilaisia laskennallisia ilmastomalleja Aasian monsuunin kehityksen selvittämiseen sen syntyaikana myöhäismioseenissa (11-5 miljoonaa vuotta sitten). Tulokset osoittavat, että modernin kaltainen monsuuni-ilmasto on saattanut olla olemassa Etelä-Kiinassa ja Intiassa jo varhaisen myöhäismioseenin aikaan (11-7 miljoonaa vuotta sitten) Pohjois-Kiinassa ja Luoteis-Intiassa se ei kuitenkaan vielä tuolloin ollut täysin kehittynyt. Monsuuni-ilmaston ylläpitämiseksi erityisesti Aasian vuoristot ovat kriittisiä. Niiden eri osien eriaikainen kasvu geologisessa menneisyydessä on saattanut johtaa monsuuni-ilmaston eriaikaiseen kehittymiseen Intiassa ja Itä-Aasiassa. Monsuunin voimakkuuden vuotuinen vaihtelu on myöhäismioseenissa saattanut olla yhtä vahva, tai jopa vahvempi, kuin nykyään., Tämä johtuu mioseenin voimakkaasta El Niño -ilmiöstä. Myöhäismioseenin maailman keskilämpötila oli lähellä sitä, mikä on odotettavissa tulevaisuuden olosuhteiksi antropogeenisten kasvihuonekaasupäästöjen johdosta. Parempi ymmärrys myöhäismioseenin monsuuni-ilmaston mekanismeista helpottaa tulevaisuuden monsuuni-ilmaston ennustamista.
Subject: palaeoclimate modeling
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