Observation and modeling of stable water isotopes as diagnostics of rainfall dynamics over southeastern Australia (original) (raw)
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Spatial and temporal variation in precipitation isotopes in the Sydney Basin, Australia
Journal of Hydrology, 2013
The δ 2 H and δ 18 O composition of 816 precipitation samples collected between February 2005 and October 2009 from four sites across the Sydney Basin, Australia, were analysed, representing the first published precipitation isotope dataset for the region. Monthly values, weighted averages and local meteoric water lines are presented for use in hydrological applications. The four year precipitation weighted average values ranged from δ 2 H=−20.16‰, δ 18 O=−4.50‰ and d=15.88‰ for Lucas Heights in the coastal region to δ 2 H=−29.48‰, δ 18 O=−5.97‰ and d=18.33‰ for Mt Werong in the highlands west of Sydney. For the Sydney Basin as a whole we recommend an overall local meteoric water line of δ 2 H=8.01±0.05·δ 18 O+16.8±0.3. Precipitation in the Sydney Basin is isotopically different from the nearest GNIP sites with a significantly higher D-excess. High D-excess values may be the result of low humidity at the sea surface during evaporation at mid latitude sources, however recycling of moisture either locally or along a moisture transport trajectory may also be an important factor. A clear coastal effect was observed but generally temperature and amount effects were found to be weak. Please download published original from http://dx.Please download published original from http://dx.
Proportions of convective and stratiform precipitation revealed in water isotope ratios
Nature Geoscience, 2016
Tropical and midlatitude precipitation is fundamentally of two types, spatially limited and high-intensity convective or widespread and lower-intensity stratiform, owing to di erences in vertical air motions and microphysical processes governing rain formation. These processes are di cult to observe or model and precipitation partitioning into rain types is critical for understanding how the water cycle responds to changes in climate. Here, we combine two independent data setsconvective and stratiform precipitation fractions, derived from the Tropical Rainfall Measuring Mission satellite or synoptic cloud observations, and stable isotope and tritium compositions of surface precipitation, derived from a global network-to show that isotope ratios reflect rain type proportions and are negatively correlated with stratiform fractions. Condensation and riming associated with boundary layer moisture produces higher isotope ratios in convective rain, along with higher tritium when riming in deep convection occurs with entrained air at higher altitudes. On the basis of our data, stable isotope ratios can be used to monitor changes in the character of precipitation in response to periodic variability or changes in climate. Our results also provide observational constraints for an improved simulation of convection in climate models and a better understanding of isotope variations in proxy archives, such as speleothems and tropical ice.
Extreme short-term stable isotope variability revealed by continuous rainwater analysis
The continuous real-time analysis, at 30-s intervals, of precipitation at an Australian tropical location revealed extreme and rapidly changing d 18 O and dD values related to variations in moisture source areas, transport paths and precipitation histories. The range of d 18 O (À19.6% to +2.6%) and dD (À140% to +13%) values from 5948 measurements of nine rain events over 15 days during an 8-month period at a single location was comparable with the range measured in 1532 monthly samples from all seven Australian Global Network of Isotopes in Precipitation stations from 1962 to 2002. Extreme variations in d 18 O (À8.7% to À19.6%) and dD (À54% to À140%) were recorded within a single 4-h period. Real-time stable isotope monitoring of precipitation at a high temporal resolution enables new and powerful tracer applications in climatology, hydrology, ecophysiology and palaeoclimatology.
Synoptic controls upon δ 18 O in southern Tasmanian precipitation
Geophysical Research Letters, 2008
1] An event-based record of 18 O in precipitation at Margate in Tasmania, Australia, was analysed using 3d Lagrangian trajectories and composites of ERA40 850hPa geopotential height for the years 1994 -2002. Trajectory analysis found that moisture entrainment occurs during the 48 hour period prior to arrival for all precipitating air masses at Margate. The rate of entrainment was greatest for events of high rainfall/high depletion, contributing up to 19% of vapour in the air mass in summer and up to 47% in winter. The majority of air masses were found to be advected from the Southern Ocean, however, for high rainfall/high depletion events during summer 30% of air masses were found to approach from the Tasman Sea (east of 155E longitude). Mean isotope ratios were less depleted by 1.4% for these events indicating mixing with less depleted air. High rainfall/high depletion events were also associated with negative geopotential anomalies east of Tasmania.
Journal of the Meteorological Society of Japan, 2011
Isotopic and meteorological observations in November 2006 on the west coast of Sumatera, Indonesia during the intense observation period of the Hydrometeorological ARray for Intraseasonal Variation-Monsoon AUtomonitoring (HARIMAU2006), revealed the impacts of large-scale moisture transport and mesoscale processes on precipitation isotope ratios. Intraseasonal changes in the precipitation d 2 H in November had large variability ranging from þ10 to À65 per mil, as a result of the changes in the large-scale moisture transport associated with the intraseasonal oscillation with a time-scale of 10-15 day over Sumatera. The isotopic composition of precipitation was independent from di¤erence in precipitation type (convective or stratiform precipitation). An isotope circulation model reproduced the observed isotopic changes, supporting that the isotopic e¤ect of large-scale moisture transport was the main contributor to intraseasonal isotopic changes.
Water isotopes in precipitation
Quaternary Science Reviews, 2000
O concentrations are observed in precipitation both on a geographical and on a temporal basis. These variations, resulting from successive isotopic fractionation processes at each phase change of water during its atmospheric cycle, are well documented through the IAEA/WMO network. Isotope concentrations are, in middle and high latitudes, linearly related to the annual mean temperature at the precipitation site. Paleoclimatologists have used this relationship to infer paleotemperatures from isotope paleodata extractable from ice cores, deep groundwater and other such sources. For this application to be valid, however, the spatial relationship must also hold in time at a given location as the location undergoes a series of climatic changes. Progress in water isotope modeling aimed at examining and evaluating this assumption has been recently reviewed with a focus on polar regions and, more speci"cally, on Greenland. We extend this review in comparing the results of two di!erent isotopic AGCMs (NASA/GISS and ECHAM) and in examining, with a more global perspective, the validity of the above assumption, i.e. the equivalence of the spatial and temporal isotope}temperature relationships. These results con"rm the dominating role of local temperature changes on the paleo isotope signal in most regions. However, the exact calibration of this valuable paleothermometer is biased by, for example, the seasonality of precipitation and other factors. We forced the two models by the climatic boundary conditions of the mild-holocene at 6 kyr BP which only slightly di!ers from today's climate. The isotope response on this weak forcing is quite heterogeneous. The only robust common response is the intensi"cation of the hydrological cycle in low latitudes and, therefore, isotopically more depleted precipitation in the tropics and subtropics. We also examine recent progress made in modeling: the relationship between the conditions prevailing in moisture source regions for precipitation and the deuterium excess of that precipitation.
Stable isotope anatomy of tropical cyclone ita, north-eastern australia, april 2014
PloS one, 2015
The isotope signatures registered in speleothems during tropical cyclones (TC) provides information about the frequency and intensity of past TCs but the precise relationship between isotopic composition and the meteorology of TCs remain uncertain. Here we present continuous δ 18 O and δ 2 H data in rainfall and water vapour, as well as in discrete rainfall samples, during the passage of TC Ita and relate the evolution in isotopic compositions to local and synoptic scale meteorological observations. High-resolution data revealed a close relationship between isotopic compositions and cyclonic features such as spiral rainbands, periods of stratiform rainfall and the arrival of subtropical and tropical air masses with changing oceanic and continental moisture sources. The isotopic compositions in discrete rainfall samples were remarkably constant along the~450 km overland path of the cyclone when taking into account the direction and distance to the eye of the cyclone at each sampling time. Near simultaneous variations in δ 18 O and δ 2 H values in rainfall and vapour and a near-equilibrium rainfall-vapour isotope fractionation indicates strong isotopic exchange between rainfall and surface inflow of vapour during the approach of the cyclone. In contrast, after the passage of spiral rainbands close to the eye of the cyclone, different moisture sources for rainfall and vapour are reflected in diverging d-excess values. High-resolution isotope studies of modern TCs refine the interpretation of stable isotope signatures found in speleothems and other paleo archives and should aim to further investigate the influence of cyclone intensity and longevity on the isotopic composition of associated rainfall.
Annual, monthly and daily analyses of stable isotopes in precipitation are commonly made worldwide, yet only a few studies have explored the variations occurring on short timescales within individual precipitation events, particularly at mid-latitude locations. This study examines hydrogen isotope data from sequential, intra-event samples from sixteen precipitation events during different seasons and a range of synoptic conditions over an 18-month period in Birmingham, UK. Precipitation events were observed simultaneously using a vertically-pointing micro rain radar (MRR), which, for the first time at a mid-latitude location, allowed high resolution examination of the microphysical characteristics (e.g. rain rate, fall velocity, drop size distributions) that may influence the local isotopic composition of rainwater. The range in δD from 242 samples from 16 events was -87.0‰ to +9.2‰, whilst the largest variation observed in a single event was 55.4‰. In contrast to previous work, the results indicate that some mid-latitude precipitation events do indeed show significant intra-event trends that are strongly influenced by precipitation processes and parameters such as rain rate, melting level height and droplet sizes. Inverse relationships between rain rate and isotopic composition are observed, representing an example of a local type of ‘amount effect’, a still poorly-understood process occurring at different scales. For these particular events the mean δ value may therefore not provide all the relevant information. This work has significance for the testing and development of isotope-enabled cloud resolving models and land surface models at higher resolutions, and provides improved insights into a range of environmental processes that are influenced by sub-sampled precipitation events.
Correction to “Stable isotopic compositions in Australian precipitation”
Journal of Geophysical Research, 2011
Stable deuterium (dD) and oxygen-18 (d 18 O) isotopes in 1962 to 2002 precipitation from the seven Australian stations of the Global Network of Isotopes in Precipitation (GNIP) were used to investigate isotope characteristics including temporal and spatial distributions across different regions of Australia. On the basis of 1534 samples, the local meteoric water line (LMWL) was established as dD = 7.10d 18 O + 8.21. d 18 O showed a depletion trend from north and south to central Australia (a continental effect) and from west to east. Precipitation amount effects were generally greater than temperature effects, with quadratic or logarithmic correlations describing d/T and d/P better than linear relationships. Nonlinear stepwise regression was used to determine the significant meteorological control factors for each station, explaining about 50% or more of the d 18 O variations. Geographical control factors for d 18 O were given by the relationship d 18 O (‰) = −0.005 longitude (°) − 0.034 latitude (°)-0.003 altitude (m) − 4.753. Four different types of d-excess patterns demonstrated particular precipitation formation conditions for four major seasonal rainfall zones. Finally, wavelet coherence (WTC) between d 18 O and SOI confirmed that the influence of ENSO decreased from east and north to west Australia.
Global and Planetary Change, 2006
An integral part of isotopes in the Program for Intercomparison of Land-surface Parameterisation Schemes (iPILPS) [Henderson-Sellers, A., in press. Improving land-surface parameterization schemes using stable water isotopes; introducing the iPILPS initiative. Global and Planetary Change, in press] is that the models' outputs be evaluated against measured values of δ 2 H and δ 18 O in the various simulated environmental compartments. This paper outlines the steps taken in Australia to initiate measurement of these stable water isotopes (SWIs) in the field, at a cool-temperate forest site in S.E. Australia near Tumbarumba, specifically to facilitate the model evaluation process. The selected sampling methodologies are detailed within the context of a conceptual model developed to describe the land-atmosphere exchange systems. This model has also been used to make a priori estimations of the isotopic values to be expected in each measured sub-system. As the data resulting from the Tumbarumba field campaign emerge, they will be compared with these working hypotheses to evaluate and, where necessary, amend the conceptual model. Initial comparisons based on preliminary data are presented here. The new observations derived in March 2005 should allow the land surface schemes used in weather forecast and climate change models to better reflect the environments for which they are attempting to make predictions.