Research-Paleoclimate modeling

 

The Tibetan Plateau as an amplifier of the orbital-scale variability of the East Asian monsoon

 
 

    Asian monsoon climate variability at geological time scales is modulated by both the Earth¨s orbital changes and tectonic uplift of the Tibetan Plateau (TP). Here, using the band-pass filtered versions of previously-published high resolution geological records from the Chinese loess, we show that the orbital-scale variability of the East Asian summer monsoon (EASM) has increased dramatically since the late Pliocene. Climate model simulations indicate that the increase in the variability of the northern EASM at both the precession and tilt time scales may be, at least partially, attributed to the uplift of the TP.

Liu X.D., J.E. Kutzbach, Z. Liu, Z.S. An and L. Li, 2003: The Tibetan Plateau as amplifier of orbital-scale variability of the East Asian monsoon, Geophysical Research Letters, 30(16), 1839, doi:10.1029/2003GL017510.

 

Linearly-detrended precessional and obliquity periodic components of the East Asian summer (JJA) monsoon reflected by magnetic susceptibility (MS) of loess at two sites on the Chinese Loess Plateau and the corresponding orbital parameters during the past 6 million years. (a) 14C28 kyr bandpass-filtered MS at Hejiayao (HJY, 3520N, 107<E); (b) 14C28 kyr band-pass filtered MS at Zhaojiachuan (ZJC, 35<53>N, 107<58>E); (c) parameter of climatic precession (eccentricity times sine of longitude of perihelion); (d) 33C49 kyr bandpass-filtered MS at HJY; (e) 33C49 kyr band-pass filtered MS at ZJC; (f ) parameter of obliquity (degrees of tilt of Earth¨s axis) (the data of the two orbital parameters from Berger and Loutre [1991]). Standard low-pass and high-pass filters were used to construct the band-pass filtered time series.

 

Simulated summer-averaged (JJA) horizontal winds (m/s, see vector length keys) in the lower troposphere (~867 hPa, i.e., the 4th sigma level of the model¨s atmosphere) and mass-weighted averaged vertical velocity from the surface to 300 hPa for experiments with mountains (M) (left) and without mountains (N) (right). (a) MPW (modern control run). The solid line indicates the 2000m contour of the Tibetan Plateau (same in (c) and (e)); (b) NPW (modern insolation but no mountains). The box defines the northern East Asia (NEA) region used for statistics in Figure 3; (c) MPS-MPW; (d) NPS-NPW; (e) MTH-MTL; (f ) NTHNTL. Here (c) and (d), and (e) and (f ) show, respectively, the differences between the two experiments with strong and weak insolation forcing over Asia in JJA. See text. Only the areas with prominently enhanced upward motion are shaded (light -5 ~ -10*1000 kPa/s; medium -10 ~ -20*1000 kPa/s; heavy < -20*1000 kPa/s).

Simulated changes in the summer monsoon rainfall (a) and intensity (b) over the northern East Asian (NEA, 40.82C51.95<N, 103.13<C121.88<E) region. The change of rainfall is represented in regionally-averaged percentage. The monsoon intensity is measured with the mean low-level meridional wind at the southern boundary for NEA. For the purpose of plotting, the differences of monsoon indexes are normalized for each region.