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Monsoon

About: Monsoon is a research topic. Over the lifetime, 16087 publications have been published within this topic receiving 599888 citations.


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Journal ArticleDOI
TL;DR: In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer ''monsoon'' precipitation generally wets only surface layers as discussed by the authors. But the use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona.
Abstract: In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer ''monsoon'' precipitation generally wets only surface layers. Use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona. Mean summer precipitation ranged from 79 to 286 mm, or from 18% to 60% of the annual total across the gradient. We predicted that, along this summer rainfall gradient, populations of dominant tree species would exhibit a clinal off-on response for use of water from upper soil layers, responding at particular threshold levels of summer precipitation input. This prediction was largely supported by our observations of tree water source use over a two-year period and from irrigation ex- periments. Hydrogen and oxygen stable isotope ratios ( dD and d 18 O) of tree xylem water were compared to that of precipitation, groundwater, and deep and shallow soil water to distin- guish among possible tree water sources. dD-d 18 O relationships and seasonal xylem water potential changes revealed that trees of this ecosystem used a mixture of soil water and recent precipitation, but not groundwater. During the monsoon period, a large proportion of xylem water in Pinus edulis and Juniperus osteospermawas from monsoon precipitation, but use of this precipitation declined sharply with decreasing summer rain input at sites near the regional monsoon boundary in Utah. Quercus gambelii at most sites along the gradient used only deep soil water even following substantial inputs of summer rain. Pop- ulations of Quercus at sites with the highest average summer precipitation input, however, predominantly used water in upper soil layers from recent summer rain events. Soil tem- perature correlated with patterns of summer precipitation use across the gradient; high soil temperatures north of the monsoon boundary may have inhibited surface root activity for some or all of the three tree species. Irrigation experiments with deuterium-labeled water revealed that Quercus gambeliiin northern Arizona and southern Utah did not use water from surface layers. In contrast, Juniperus osteosperma at these sites responded significantly to the irrigations: between 37% and 41% of xylem water originated from irrigations that wetted only the top 30 cm of soil. Responses by Pinus edulis to these irrigations were variable; uptake of labeled water by this species was greater in September at the end of the summer than during the hot midsummer period. Inactivity of Pinus roots in midsummer supports the hypothesis that root activity in this species is sensitive to soil temperature. Seasonal patterns of leaf gas exchange and plant water potential corresponded to the seasonality of rainfall at different sites. However, no correlation between a species' ability to use summer rainfall and its tolerance to water deficits at the leaf level was found. Midday stomatal conductance (gs) for Pinus needles approached zero at predawn water potentials near 22 MPa, whereas gs in Quercus and Juniperus declined to zero at 22.8 and 23.7 MPa, respectively. The relationship between photosynthesis (A) and gs was similar among the three species, although Quercus maintained higher overall rates of gas exchange and tended to operate higher on the A/gs curve than the two conifers. At sites in eastern Arizona where Quercus fully used moisture from summer rains, leaf gas exchange characteristics were similar to those of Pinus and Juniperus.

284 citations

Journal ArticleDOI
TL;DR: The New Guinea Coastal Undercurrent has a maximum speed of 40-70 cm s −1 at a depth of about 200 m as mentioned in this paper, which is a permanent feature despite the reversals of the wind and the surface current during the period of the northwest monsoon in austral summer.

283 citations

Journal ArticleDOI
18 Oct 2012-Nature
TL;DR: In this paper, an East Asian winter monsoon proxy record using grain size variations in Chinese loess over the past 900,000 years was presented, showing that the weak monsoon winds maintained a mild, non-glacial climate at high northern latitudes.
Abstract: An East Asian winter monsoon proxy record using grain size variations in Chinese loess over the past 900,000 years shows that for up to 20,000 years after the interglacials at 400,000-year intervals, the weak monsoon winds maintain a mild, non-glacial climate at high northern latitudes. Qingzhen Hao and colleagues present a record of grain-size variations in the Chinese Loess Plateau — a proxy of variations in the strength of the East Asian winter monsoon — and show that relatively high insolation at 400,000-year intervals held off the inception of the subsequent ice age for about 20,000 years relative to other glacial inceptions. Mechanistically, the extension of warm conditions was probably linked to a weak Siberian high-pressure system associated with a delayed build up of northern ice and snow. The authors speculate that these observations imply that Arctic climate may remain in non-glacial mode for more than 40,000 years, even in the absence of anthropogenic greenhouse gases. Knowledge of the past variability of climate at high northern latitudes during astronomical analogues of the present interglacial1 may help to inform our understanding of future climate change. Unfortunately, long-term continuous records of ice-sheet variability in the Northern Hemisphere only are scarce because records of benthic 18O content represent an integrated signal of changes in ice volume in both polar regions2. However, variations in Northern Hemisphere ice sheets influence the Siberian High3 (an atmospheric pressure system), so variations in the East Asian winter monsoon (EAWM)—as recorded in the aeolian dust deposits on the Chinese Loess Plateau—can serve as a useful proxy of Arctic climate variability before the ice-core record begins. Here we present an EAWM proxy record using grain-size variations in two parallel loess sections representative of sequences across the whole of the Chinese Loess Plateau over the past 900,000 years. The results show that during periods of low eccentricity and precessional variability at approximately 400,000-year intervals, the grain-size-inferred intensity of the EAWM remains weak for up to 20,000 years after the end of the interglacial episode of high summer monsoon activity and strong pedogenesis. In contrast, there is a rapid increase in the EAWM after the end of most other interglacials. We conclude that, for both the 400,000-year interglacials, the weak EAWM winds maintain a mild, non-glacial climate at high northern latitudes for much longer than expected from the conventional loess and marine oxygen isotope records. During these times, the less-severe summer insolation minima at 65° N (ref. 4) would have suppressed ice and snow accumulation, leading to a weak Siberian High and, consequently, weak EAWM winds.

283 citations

Journal ArticleDOI
TL;DR: In this article, the mass balance of a glacier in the southern Tibetan Plateau is found to be due to May/June precipitation, which is controlled by mid-latitude climate and the tropical monsoon.
Abstract: The tropical monsoon is thought to play a key role in glacier change in High Asia. The mass balance of a glacier in the southern Tibetan Plateau is found to be due to May/June precipitation, which is controlled by mid-latitude climate and the tropical monsoon. Further attention should be paid to mid-latitude climate to understand glacier changes.

282 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the sea level data from Davao in the Philippines and from Darwin in Australia to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985 and concluded that the variability of the through flow can be monitored by sea level measurements.
Abstract: The flow of water from the western Pacific to the eastern Indian Ocean through the Indonesian archipelago is governed by a strong pressure gradient. Dynamic height computations determine the average sea level difference as 16 cm and show that most of the pressure gradient is contained in the upper 200 m. Sea level data from Davao in the Philippines and from Darwin in Australia are used to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985. The annual signal has a maximum during the southeast monsoon in July and August and a minimum in January and February. Interannual variations are not related to the Southern Oscillation because sea level is low at both stations during El Nino events, and thus there is little influence on the sea level difference. The mechanism of the through flow is discussed, but a determination of its numerical value will have to await direct measurements. A comparison of the sea level difference with results from a numerical model by Kindle shows satisfactory agreement. It is concluded that the variability of the through flow can be monitored by sea level measurements.

282 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,221
20222,355
2021922
2020757
2019749
2018727