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Hydroclimatic contrasts over Asian monsoon areas and linkages to tropical Pacific SSTs

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ABSTRACT

Knowledge of spatial and temporal hydroclimatic differences is critical in understanding climatic mechanisms. Here we show striking hydroclimatic contrasts between northern and southern parts of the eastern margin of the Tibetan Plateau (ETP), and those between East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) areas during the past ~2,000 years. During the Medieval Period, and the last 100 to 200 years, the southern ETP (S-ETP) area was generally dry (on average), while the northern ETP (N-ETP) area was wet. During the Little Ice Age (LIA), hydroclimate over S-ETP areas was wet, while that over N-ETP area was dry (on average). Such hydroclimatic contrasts can be broadly extended to ISM and EASM areas. We contend that changes in sea surface temperatures (SSTs) of the tropical Pacific Ocean could have played important roles in producing these hydroclimatic contrasts, by forcing the north-south movement of the Intertropical Convergence Zone (ITCZ) and intensification/slowdown of Walker circulation. The results of sensitivity experiments also support such a proposition.

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Hydroclimatic contrasts between EASM and ISM areas.Arrows denote monsoon streamlines (for areas lower than 1500 m) averaged from June to August at 850 hPa during 1968–1996 based on NCEP/NCAR reanalysis data61. The blue and orange circles show wet and dry sites during the Medieval Period, respectively. The red triangles denote the sites (15 to 20) located in an ISM-EASM transitional zone. Green circles (39 to 43) show the locations of some stalagmite records in the northern India. The dashed pink line outlines the general position of the ISM boundary. Numbers denote the sites mentioned in the text (note parts of the sites are overlapped; see details in Table S3). The satellite image was drawn from the basemaps in ArcGIS 10.2 (ESRI data & maps).
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f1: Hydroclimatic contrasts between EASM and ISM areas.Arrows denote monsoon streamlines (for areas lower than 1500 m) averaged from June to August at 850 hPa during 1968–1996 based on NCEP/NCAR reanalysis data61. The blue and orange circles show wet and dry sites during the Medieval Period, respectively. The red triangles denote the sites (15 to 20) located in an ISM-EASM transitional zone. Green circles (39 to 43) show the locations of some stalagmite records in the northern India. The dashed pink line outlines the general position of the ISM boundary. Numbers denote the sites mentioned in the text (note parts of the sites are overlapped; see details in Table S3). The satellite image was drawn from the basemaps in ArcGIS 10.2 (ESRI data & maps).

Mentions: The Asian summer monsoon system is generally divided into two subsystems, namely the Indian Summer Monsoon (ISM), and the East Asian Summer Monsoon (EASM) (e.g., ref. 6 and Fig. 1), both of which play key roles in transporting heat and moisture from tropical oceans to higher latitudes. The ETP area is one of the most sensitive regions for studying the behavior of these two monsoons and their linkages to global climatic changes. Along the ETP, there prevails the EASM, the ISM, the East Asian winter monsoon, and the westerly jet stream36. Our previous work has shown clear climatic discrepancies on a decadal time scale during the past ~400 years between northern ETP (N-ETP) and southern ETP (S-ETP) areas3. A recent study compared palmer drought severity indices (PDSI) over the north and south Tibetan Plateau developed from tree ring widths during the past ~550 years, and showed two obvious contrasts in moisture stress between these two regions5, suggesting that the responses of climatic changes are sensitive and variable to different climatic forcing over the eastern Tibetan Plateau. Here, we focus on centennial/multi-decadal hydroclimatic differences along ETP areas during the past 2,000 years, then extend such hydroclimatic contrasts to the broader EASM and ISM areas, and finally we discuss possible forcing mechanisms.


Hydroclimatic contrasts over Asian monsoon areas and linkages to tropical Pacific SSTs
Hydroclimatic contrasts between EASM and ISM areas.Arrows denote monsoon streamlines (for areas lower than 1500 m) averaged from June to August at 850 hPa during 1968–1996 based on NCEP/NCAR reanalysis data61. The blue and orange circles show wet and dry sites during the Medieval Period, respectively. The red triangles denote the sites (15 to 20) located in an ISM-EASM transitional zone. Green circles (39 to 43) show the locations of some stalagmite records in the northern India. The dashed pink line outlines the general position of the ISM boundary. Numbers denote the sites mentioned in the text (note parts of the sites are overlapped; see details in Table S3). The satellite image was drawn from the basemaps in ArcGIS 10.2 (ESRI data & maps).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
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getmorefigures.php?uid=PMC5016894&req=5

f1: Hydroclimatic contrasts between EASM and ISM areas.Arrows denote monsoon streamlines (for areas lower than 1500 m) averaged from June to August at 850 hPa during 1968–1996 based on NCEP/NCAR reanalysis data61. The blue and orange circles show wet and dry sites during the Medieval Period, respectively. The red triangles denote the sites (15 to 20) located in an ISM-EASM transitional zone. Green circles (39 to 43) show the locations of some stalagmite records in the northern India. The dashed pink line outlines the general position of the ISM boundary. Numbers denote the sites mentioned in the text (note parts of the sites are overlapped; see details in Table S3). The satellite image was drawn from the basemaps in ArcGIS 10.2 (ESRI data & maps).
Mentions: The Asian summer monsoon system is generally divided into two subsystems, namely the Indian Summer Monsoon (ISM), and the East Asian Summer Monsoon (EASM) (e.g., ref. 6 and Fig. 1), both of which play key roles in transporting heat and moisture from tropical oceans to higher latitudes. The ETP area is one of the most sensitive regions for studying the behavior of these two monsoons and their linkages to global climatic changes. Along the ETP, there prevails the EASM, the ISM, the East Asian winter monsoon, and the westerly jet stream36. Our previous work has shown clear climatic discrepancies on a decadal time scale during the past ~400 years between northern ETP (N-ETP) and southern ETP (S-ETP) areas3. A recent study compared palmer drought severity indices (PDSI) over the north and south Tibetan Plateau developed from tree ring widths during the past ~550 years, and showed two obvious contrasts in moisture stress between these two regions5, suggesting that the responses of climatic changes are sensitive and variable to different climatic forcing over the eastern Tibetan Plateau. Here, we focus on centennial/multi-decadal hydroclimatic differences along ETP areas during the past 2,000 years, then extend such hydroclimatic contrasts to the broader EASM and ISM areas, and finally we discuss possible forcing mechanisms.

View Article: PubMed Central - PubMed

ABSTRACT

Knowledge of spatial and temporal hydroclimatic differences is critical in understanding climatic mechanisms. Here we show striking hydroclimatic contrasts between northern and southern parts of the eastern margin of the Tibetan Plateau (ETP), and those between East Asian summer monsoon (EASM) and Indian summer monsoon (ISM) areas during the past ~2,000 years. During the Medieval Period, and the last 100 to 200 years, the southern ETP (S-ETP) area was generally dry (on average), while the northern ETP (N-ETP) area was wet. During the Little Ice Age (LIA), hydroclimate over S-ETP areas was wet, while that over N-ETP area was dry (on average). Such hydroclimatic contrasts can be broadly extended to ISM and EASM areas. We contend that changes in sea surface temperatures (SSTs) of the tropical Pacific Ocean could have played important roles in producing these hydroclimatic contrasts, by forcing the north-south movement of the Intertropical Convergence Zone (ITCZ) and intensification/slowdown of Walker circulation. The results of sensitivity experiments also support such a proposition.

No MeSH data available.


Related in: MedlinePlus