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CHAPTER 4 Climate modelling studies on the Holocene climate change in the African monsoon region reveal that the strengthening of the North African monsoon system during the mid- Holocene cannot be explained by orbital forcing alone (e.g. Joussaume et al., 1999). Internal feedbacks between the atmosphere and the ocean or the land-surface (including vegetation) have probably strongly enhanced the mid- to late-Holocene monsoon change in North Africa (e.g. Claussen and Gayler, 1997; Kutzbach and Liu, 1997; Broström, et al., 1998; Braconnot et al., 2000; Levis et al., 2004; Liu Z. et al., 2004). Fewer studies exist concerning the role of interactions in the Holocene Asian monsoon climate change and these studies futhermore show contradictory results that probably contribute to the above mentioned discrepancy between the model simulations within PMIP (Braconnot et al., 2007b), for instance. In some climate models, the ocean-atmosphere interaction results in an increase of the Asian monsoon precipitation (e.g. Hewitt and Mitchell, 1998; Braconnot et al., 2000; Wei and Wang, 2004). Other climate modelling studies reveal a decrease of precipitation related to the ocean-atmosphere interaction (e.g. Voss and Mikolajewicz, 2001; Ohgaito and Abe-Ouchi, 2007; Li and Harrison, 2008; Marzin and Braconnot, 2009). Regarding the vegetation and land-surface interaction with the atmosphere, the climate model results are in better agreement and suggest an enhancement of the Asian summer monsoon due to these interactions (e.g. Claussen, 1997; Wang H.-J., 1999; Diffenbaugh and Sloan, 2002, Li and Harrison, 2009). However, fully coupled atmosphere-ocean- vegetation models have been applied only in a few studies and these studies do not follow a consistent methodology to derive the interactions of the atmosphere with the other compartments of the climate system. Therefore, none of the simulations conducted in previous studies or in PMIP are designed to derive the pure contributions of the atmosphere-ocean and the atmosphere-vegetation interactions as well as their synergy to the mid- to late-Holocene Asian monsoon climate change. In Chapter 4, we assess the contribution of the ocean-atmosphere and vegetation atmosphere interaction as well as their synergy to the Holocene climate change. For this purpose, we analyse a set of coupled simulations conducted by Otto et al (2009a) in the comprehensive Earth system model ECHAM5/JSBACH-MPIOM. These simulations have been designed to allow the application of the factor-separation technique (Stein and Alpert, 1993) and therefore provide the opportunity to separate the pure contribution of the different interactions. The main research question of this chapter is: (VI) How strong is the contribution of ocean-atmosphere and vegetation-atmosphere 4 interactions as well as their synergy to the mid- to late-Holocene climate change? This chapter has been published in Climate of the Past (Dallmeyer et al., Clim. Past, 6, 195-218, 2010).
CHAPTER 5 The Tibetan Plateau exerts a strong influence on the regional as well as the global climate (e.g. Ye and Wu, 1998; Duan and Wu, 2005; Wu et al., 2007). It plays an important part in the Asian monsoon dynamics as it, for instance, forms an elevated heat source for the atmosphere in spring and summer and thus modifies and enhances the thermal contrast between the land and the ocean (e.g. Liu Y. et al., 2007). Due to its height, the Tibetan Plateau furthermore transfers this contrast to the upper troposphere where it can strongly influence the atmospheric large-scale circulation. The strong convective activity on the Plateau induces a huge air-pump and a strong vertical circulation leading to subsidence north and west of the Plateau and even in the Sahara (e.g. Rodwell and Hoskins, 1996). As the energy balance at the surface and the transfer of energy and momentum between the atmosphere and the land depends to a large part on the land cover, land cover changes on the Tibetan Plateau may have strongly affected the Holocene climate change in the Asian monsoon domain. The Tibetan Plateau is very sensitive to climate change and reconstructions have reported strong natural land cover changes on the Plateau since the early and mid-Holocene (Gasse et al, 1991, Shen et al., 2005 and 2006, Herzschuh 2010a). In Chapter 5, we compare simulated vegetation trends for different regions on the Tibetan Plateau with pollen-based vegetation reconstructions. For this purpose, we analyse the transient mid-to late-Holocene simulation performed with the comprehensive Earth system model ECHAM5/JSBACH-MPIOM by Fischer and Jungclaus (2011) that was forced with orbital forcing alone. We raise the question: (VII) Is the model able to capture the reconstructed mid- to late-Holocene vegetation trend? (VIII) Which climatic mechanisms have caused the vegetation change on the Tibetan Plateau? This Chapter is a joint work of our group and U. Herzschuh from the Alfred-Wegner- <strong>Institut</strong>e in Potsdam, Germany, and has been published in Climate of the Past (Dallmeyer et al., Clim. Past, 7, 881-901, 2011). The parts of the text that have been written by U. Herzschuh are marked. CHAPTER 6 Land cover changes are accompanied by a modification of the physical surface properties such as roughness length or surface albedo and therefore have a direct effect on the surface energy, momentum and water balance (biogeophysical effects). Land cover changes may, thus, exert a strong influence on the monsoon dynamics (Yasunari, 2007). According to reconstructions, the Holocene was characterised by large-scale natural land cover changes that are often related to the decreasing summer monsoon strength entailing shifts in the 5
Page 1: Holocene climate and vegetation cha
Page 4 and 5: Anne F. Dallmeyer Max-Planck-Instit
Page 6 and 7: Overleaf Sutlej Valley, Kalpa (31°
Page 8 and 9: Zusammenfassung Mittels verschieden
Page 10 and 11: II 3.5 Summary and conclusion of Ch
Page 12 and 13: List of Figures Figure 2.1: Simulat
Page 14 and 15: Figure 4.7: Simulated differences i
Page 16 and 17: Figure A.1: The Asian monsoon regio
Page 19 and 20: 1. Introduction Like all monsoon sy
Page 21: (I) How well is the present-day Asi
Page 25 and 26: 2. Simulated present-day Asian mons
Page 27 and 28: In this study, we assess the perfor
Page 29 and 30: in the local summer season. This la
Page 31 and 32: Figure 2.2: Hovmöller diagram show
Page 33 and 34: 2.3.2 Monsoon onset and withdrawal
Page 35 and 36: to observations and reanalysis data
Page 37 and 38: and as indices the method of prescr
Page 39 and 40: investigated by comparing atmospher
Page 41 and 42: T 3 1 _ A _ A M I P [ °C ] T 6 3 _
Page 43 and 44: - Overall, the simulation T31AV0k a
Page 45 and 46: 3. Simulated mid-Holocene Asian mon
Page 47 and 48: Values were taken from a course res
Page 49 and 50: To further analyse the differences
Page 51 and 52: Figure 3.6: Simulated difference in
Page 53 and 54: Figure 3.8: Annual cycle of precipi
Page 55 and 56: in these regions during the pre-mon
Page 57 and 58: positive anomaly (more divergent) i
Page 59 and 60: our results, we compare the reconst
Page 61 and 62: Figure 3.15: Differences in the sea
Page 63 and 64: mid-Holocene climate north of 40°N
Page 65 and 66: 4. Contribution of the atmosphere-o
Page 67 and 68: includes the dynamic vegetation mod
Page 69 and 70: Region Approximate longitude (°E)
Page 71 and 72: Figure 4.2: Seasonal and annual ave
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Figure 4.3: Same as Figure 4.2, but
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nearby desert or sparsely vegetated
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Figure 4.5: Factors contributing to
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spring summer autumn winter spring
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In autumn, the contribution of the
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Figure 4.8: Same as Figure 4.5 but
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The atmospheric response to the orb
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Due to the thermal inertia of the o
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eduction of -0.97K (on average) is
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climate in 6k. Whether the ocean-at
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econstructions (Yu et al., 2000). T
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5. Comparison of the simulated Holo
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ased vegetation reconstructions for
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(Zhang et al. 2000; Fang et al. 200
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Figure 5.2: ECHAM5 orography (eleva
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unfavourable climate conditions, i.
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vegetation type exists and the land
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etreat and were replaced by steppes
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exceeds 4000m in reality (cf. Fig.
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5.5.2 Site-specific discussion of t
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Figure 5.7: Change of the climate f
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Figure 5.8: Simulated change of sum
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Overall, the simulated forest fract
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simulated climate for SETP strongly
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6. Sensitivity of the Asian monsoon
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6.5k. Afterwards, land cover gradua
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additionally accounted for. The soi
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total grass sum per grid-box is sca
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In the dry/cold season, the strong
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6.4.1 Change of circulation and wat
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Figure 6.7: Simulated change of dif
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6.4.2 Change of albedo and turbulen
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In the dry/cold season, deforestati
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Figure 6.13: Simulated change in mo
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Northeast China (increase), regardl
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a.) Local effect: - The impact of l
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7. Summary and Conclusion 7.1 Summa
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strongest temperature change in the
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suggested in previous paleo-reconst
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Bibliography Adler, R.F., Huffman,
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Claussen, M.: Late Quaternary veget
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Gasse, F., Arnold, M., Fontes, J.Ch
Page 157 and 158:
Joussaume, S., and Braconnot, P.: S
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Marsland, S. J., Haak, H., Jungclau
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Roeckner, E., Brokopf, R., Esch, M.
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Ueno, K., Fujii, H., Yamada, H., an
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Wu, G.X., Wang, J., Liu, X., and Li
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Appendix A: Additional figures A.I
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Figure A.4: Sketch of the main mean
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Figure A.7: Same as Figure A.6, but
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Appendix B: Additional tables B.I S
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Appendix C: Summary of the simulate
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Figure C.4: Same as Figure C.1, but
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Figure C.7: Same as Figure C.5, but
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Acknowledgements I would like to ac
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