Origin of summer monsoon rainfall identified by δ18O in precipitation

Abstract

A negative correlation between δ 18 O in mon-soon precipitation and f, the ratio of precipitable water in monsoon region to that in water source area, is hypothesized. Using the Rayleigh model, a new method for identifying origin of summer monsoon rainfall is developed based on the hypothesis. In order to validate the method, the isotopic data at New Delhi, a typical station in the southwest monsoon region, and Hong Kong, a typical station in the southeast monsoon region, were collected and analyzed for case studies. The case studies indicate that the water source areas of the monsoon rainfall at the two stations identified by the method are accordant with the general atmosphere circulation patterns. The method developed in this paper is significantly important for tracing the origin of summer monsoon precipitation.Identifying origin of precipitation is always a hotspot in water cycle research. It is valuable for hydrologists to further understand the processes of water cycle and its structure. Some researchers simulated the water source regions by the general circulation models (GCMs) [1][2][3] . However, the simulated results are mainly dependent on spatial and temporal resolutions of the GCMs and the validity of the models' parameterization. The stable isotopes, 18 O and 2 H, are two natural tracers in hydrological studies. Waters with different origins have distinctive isotopic ratios due to the equilibrium and non-equilibrium fractionation of stable isotopes when water phase changes, which makes it possible to study water cycle processes by stable isotopic variations in waters. A worldwide network of isotopic investigation in precipitation established by the International Atomic Energy Agency (IAEA) and the World Meteorological Organization (WMO), with about 550 IAEA/ WMO stations in different parts of the world, has provided precious isotopic data for studying global and local hydrological cycles. At present, it is an international study hotspot to identify origin of precipitation by the stable isotope method. Deuterium excess in precipitation, d (d = δ D−8δ 18 O [4] ), is mainly dependent on meteorological conditions in water source region, such as relative humidity, sea surface temperature and wind speed [5,6] . It is a useful parameter for tracing source area of precipitated water. Therefore many scientists identified origin of precipitation by the parameter [7][8][9][10][11][12] . Chinese scientists made a significant contribution to origin of precipitation in Tibetan Plateau using the stable isotope method [13][14][15][16][17] . They concluded that the distinctive origins of precipitated water result in the different isotopic patterns in the northern and southern Tibetan Plateau.It is difficult to trace origin of summer monsoon precipitation accurately and effectively by either the GCMs simulation or deuterium excess tracer because of the complexity of monsoon hydrological cycle system and its variability. There is a need to develop a new method for identifying origin of monsoon precipitation. It is ho...

Seasonal variations of major ions in fresh snow at Baishui Glacier No. 1, Yulong Mountain, China

“…Moreover, terrestrial dust had been input into the study area constantly by the plateau monsoon and west wind circulation. In the process of the strong local atmospheric motion and vapor transpiration, a large number of weathered material from igneous or metamorphic rocks, such as feldspar, mica and other substances, got into atmosphere and then returned to the surface in the form of wet and dry deposition, which resulted in higher ion concentration of fresh snow in dry season (Kang et al 2000;Pang et al 2005). …”

Numerical experiments on the impacts of surface evaporation and fractionation factors on stable isotopes in precipitation

“…Based on stable isotopic data of the Global Network of Isotopes in Precipitation (GNIP), coordinated by the International Atomic Energy Agency in cooperation with the World Meteorological Organization (IAEA/WMO), marked positive correlation between monthly stable isotopic ratio in precipitation and monthly mean temperature, the so-called temperature effect, has been reported for mid-high latitude continents (Dansgaard, 1964;Aragúas-Aragúas et al, 1998;Zhang et al, 2003); marked negative correlation between monthly stable isotopic ratio in precipitation and monthly precipitation amount, the so-called amount effect, is found for low-mid latitude oceans, islands, and monsoon areas (Dansgaard, 1964;Aragúas-Aragúas et al, 1998;Liu et al, 2010); and monthly δ 2 H and δ 18 O in precipitation are highly correlated (Dansgaard, 1964). These isotopic effects and their spatial variability are related to moisture sources, rainout history, and atmospheric conditions leading to precipitation (Dansgaard, 1964;Jouzel, 1986;Aragúas-Aragúas et al, 1998;Pang et al, 2005;Liu et al, 2014).…”

“…If the air parcel is replenished by a steady vapour supply and its vapour isotopic composition experiences little change, a higher condensation temperature can lead to a lower stable isotopic ratio in hydrometeor, owing to a smaller equilibrium fractionation factor at a higher temperature. The resulting precipitation may show an antitemperature effect (Pang et al, 2005;Liu et al, 2010).…”

“…In many isotopic simulations by land surface models and isotopic GCMs, the evaporation fractionation at the surface is thought to be associated with wind speed (Gat, 1970;Aragúas-Aragúas et al, 2000), surface temperature (Jouzel et al, 1987;Hoffmann et al, 1998), humidity (Gedzelman, 1988), turbulence at the evaporation surface (Craig and Gordon, 1965), and the atmospheric diffusion (Aragúas-Aragúas et al, 2000). Observations show that stable isotopes in water vapour evaporated from sea surface (Uemura et al, 2008), lake surface (Gibbson et al, 1993;Zhang, 1994;Zhang et al, 2005), land surface and forest canopy (Henderson-Sellers et al, 2006) have significant spatial and temporal variations.…”

A groundwater conceptual model and karst-related carbon sink for a glacierized alpine karst aquifer, Southwestern China

“…It has attracted much scientific attention, with previous studies being focused on stable isotopic variations in rainwater, snow and glacier meltwater, and river water, and on ionic compositions and d 18 O in the shallow firn profile (He et al, 2002Pang et al, 2005Pang et al, , 2006Pang et al, 2007;Zhu et al, 2013). In particular, there is a primary study of the geochemistry and chemical exchange between groundwater and surface water in the Lijiang glacial basin by stable oxygen isotope and major ion analysis (Pu et al, 2013a).…”