The stable isotopic composition of water vapour above Corsica during the HyMeX SOP1 campaign: insight into vertical mixing processes from lower-tropospheric survey flights

Abstract. Stable isotopes of water vapour are powerful indicators of meteorological processes on a broad range of scales, reflecting evaporation, condensation, and air mass mixing processes. With the recent advent of fast laser-based spectroscopic methods, it has become possible to measure the stable isotopic composition of atmospheric water vapour in situ at a high temporal resolution. Here we present results from such comprehensive airborne spectroscopic isotope measurements in water vapour over the western Mediterranean at a high spatial and temporal resolution. Measurements have been acquired by a customized Picarro L2130-i cavity-ring down spectrometer deployed onboard the Dornier 128 D-IBUF aircraft together with a meteorological flux measurement package during the HyMeX SOP1 (Hydrological cycle in Mediterranean Experiment special observation period 1) field campaign in Corsica, France, during September and October 2012. Taking into account memory effects of the air inlet pipe, the typical time resolution of the measurements was about 15–30 s, resulting in an average horizontal resolution of about 1–2 km. Cross-calibration of the water vapour measurements from all humidity sensors showed good agreement under most flight conditions but the most turbulent ones. In total 21 successful stable isotope flights with 59 flight hours have been performed. Our data provide quasi-climatological autumn average conditions and vertical profiles of the stable isotope parameters δD, δ18O, and d-excess during the study period. A d-excess minimum in the overall average profile is reached in the region of the boundary-layer top, possibly caused by precipitation evaporation. This minimum is bracketed by higher d-excess values near the surface caused by non-equilibrium fractionation, and a maximum above the boundary layer related to the increasing d-excess in very depleted and dry high-altitude air masses. Repeated flights along the same pattern reveal pronounced day-to-day variability due to changes in the large-scale circulation. During a period marked by a strong inversion at the top of the marine boundary layer, vertical gradients in stable isotopes reached up to 25.4 ‰ 100 m−1 for δD and 24.0 ‰ 100 m−1 for the d-excess.

Download Full-text

The stable isotope composition of water vapour above Corsica during the HyMeX SOP1: insight into vertical mixing processes from lower-tropospheric survey flights

10.5194/acp-2016-728 ◽

2016 ◽

Author(s):

Harald Sodemann ◽

Franziska Aemisegger ◽

Stephan Pfahl ◽

Mark Bitter ◽

Ulrich Corsmeier ◽

...

Keyword(s):

Boundary Layer ◽

Stable Isotope ◽

Water Vapour ◽

Isotope Composition ◽

Water Isotopes ◽

High Temporal Resolution ◽

Stable Isotope Composition ◽

Stable Water Isotopes ◽

Mixing Processes ◽

Strong Inversion

Abstract. Stable water isotopes are powerful indicators of meteorological processes on a broad range of scales, reflecting evaporation, condensation, and airmass mixing processes. With the recent advent of fast laser-based spectroscopic methods it has become possible to measure the stable isotopic composition of atmospheric water vapour in situ at high temporal resolution, enabling to tremendously extend the measurement data base in space and time. Here we present the first set of airborne spectroscopic stable water isotopes measurements over the western Mediterranean. Measurements have been acquired by a customised Picarro L2130-i cavity-ring down spectrometer deployed onboard of the Dornier 128 D-IBUF aircraft together with a meteorological flux measurement package during the HyMeX SOP1 field campaign in Corsica, France during September and October 2012. Taking into account memory effects of the air inlet pipe, the typical time resolution of the measurements was about 15–30 s, resulting in an average horizontal resolution of about 1–2 km. Cross-calibration of the water vapour measurements from all humidity sensors showed good agreement in most flight conditions but the most turbulent ones. In total 21 successful stable isotope flights with 59 flight hours have been performed. Our data provide quasi-climatological autumn average conditions of the stable isotope parameters δD, δ18O and d-excess during the study period. A time-averaged perspective of the vertical stable isotope composition reveals for the first time the mean vertical structure of stable water isotopes over the Mediterranean at high resolution. A d-excess minimum in the overall average profile is reached in the region of the boundary layer top due to precipitation evaporation, bracketed by higher d-excess values near the surface due to non-equilibrium fractionation and above the boundary layer due to the non-linearity of the d-excess definition. Repeated flights along the same pattern reveals pronounced day-to-day variability due to changes in the large-scale circulation. During a period marked by a strong inversion at the top of the marine boundary layer, vertical gradients in stable isotopes reached up to 25.4 ‰ 100 m−1 for δD.

Download Full-text

Continuous, near-real-time observations of water stable isotope ratios during rainfall and throughfall events

Hydrology and Earth System Sciences ◽

10.5194/hess-23-3007-2019 ◽

2019 ◽

Vol 23 (7) ◽

pp. 3007-3019 ◽

Cited By ~ 1

Author(s):

Barbara Herbstritt ◽

Benjamin Gralher ◽

Markus Weiler

Keyword(s):

Stable Isotope ◽

Isotopic Composition ◽

Real Time ◽

Temporal Resolution ◽

Tree Canopy ◽

Dead Volume ◽

High Temporal Resolution ◽

Time Lags ◽

Mixing Processes ◽

Water Stable Isotope

Abstract. The water isotopic composition of throughfall is affected by complex diffusive exchange with ambient water vapour, evaporative enrichment of heavy isotopes, and mixing processes in the tree canopy. All interception processes occur simultaneously in space and time, generating a complex pattern of throughfall depth and water isotopic composition. This pattern ultimately cascades through the entire hydrologic system and is therefore crucial for isotope studies in catchment hydrology, where recharge areas are often forested, while reference meteorological stations are generally in the open. For the quasi real-time observation of the water isotopic composition (δ18O and δ2H) of both gross precipitation and throughfall, we developed an approach combining a membrane contactor (Membrana) with a laser-based Cavity Ring-Down Spectrometer (CRDS, Picarro), obtaining isotope readings every 2 s. A setup with two CRDS instruments in parallel analysing gross precipitation and throughfall simultaneously was used for the continuous observation of the temporal effect of interception processes on the stable isotopes of water. All devices were kept small to minimize dead volume with time lags of only 4 min for water from the rainfall collectors to the isotope analysers to increase the temporal resolution of isotope observations. Complementarily, meteorological variables were recorded at high temporal resolution at the same location. The achieved evolution from discrete liquid or event-based bulk samples to continuous measurements allows for direct comparison of water stable isotope data with common meteorological measurements. Future improvements of the spatial representativeness will make our approach an even more powerful tool towards detailed insight into the dynamic processes contributing to interception during rainfall events.

Download Full-text

Effects of changes in moisture source and the upstream rainout on stable isotopes in summer precipitation – a case study in Nanjing, East China

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-3919-2015 ◽

2015 ◽

Vol 12 (4) ◽

pp. 3919-3944 ◽

Cited By ~ 6

Author(s):

Y. Tang ◽

H. Pang ◽

W. Zhang ◽

Y. Li ◽

S. Wu ◽

...

Keyword(s):

Stable Isotopes ◽

Isotopic Composition ◽

Asian Monsoon ◽

Summer Precipitation ◽

Monsoon Region ◽

Asian Monsoon Region ◽

Moisture Source ◽

Source Regions ◽

Stable Isotopic Composition ◽

Stable Isotopic

Abstract. In the Asian monsoon region, variations in the stable isotopic composition of speleothems have often been attributed to the "amount effect". However, an increasing number of studies suggest that the "amount effect" in local precipitation is insignificant or even non-existent. To explore this issue further, we examined the variability of daily stable isotopic composition (δ18O) in summer precipitation of 2012–2014 in Nanjing, East China. We found that δ18O was not significantly correlated with local rainfall amount, but could be linked to changes in the location and rainout processes of precipitation source regions. Our findings suggest that the stable isotopes in precipitation could signal the location shift of precipitation source regions in the intertropical convergence zone (ITCZ) over the course of the monsoon season. As a result, changes in moisture source location and upstream rainout effect should be taken into account when interpreting the stable isotopic composition of speleothems in the Asian monsoon region.

Download Full-text

ENSO Effects on Annual Variations of Summer Precipitation Stable Isotopes in Lhasa, Southern Tibetan Plateau

Journal of Climate ◽

10.1175/jcli-d-16-0868.1 ◽

2018 ◽

Vol 31 (3) ◽

pp. 1173-1182 ◽

Cited By ~ 13

Author(s):

Jing Gao ◽

You He ◽

Valerie Masson-Delmotte ◽

Tandong Yao

Keyword(s):

Stable Isotopes ◽

Tibetan Plateau ◽

Isotopic Composition ◽

Southern Oscillation ◽

La Niña ◽

Annual Variations ◽

La Nina ◽

Stable Isotopic Composition ◽

Stable Isotopic ◽

Southern Tibetan Plateau

Abstract Although El Niño–Southern Oscillation (ENSO) influences the Indian summer monsoon, its impact on moisture transport toward the southern Tibetan Plateau (TP) remains poorly understood. Precipitation stable isotopes are useful indices for climate change in the TP. Classical interpretations of variations of precipitation stable isotopes focus on the local surface air temperature or precipitation amount. However, several of the latest studies suggested they may correlate with large-scale modes of variability, such as ENSO. This paper presents a detailed study of ENSO’s effect on annual variations of the oxygen stable isotopic composition of precipitation (δ18Op) at Lhasa in the southern TP for up to 10 years. The stable isotopic composition of water vapor from satellite data [Tropospheric Emission Spectrometer (TES)] and simulations from an isotopically enabled atmospheric general circulation model (zoomed LMDZiso) are used to explore the mechanism that leads to variations of δ18Op at Lhasa. Statistically significant correlations between δ18Op and ENSO indices [Southern Oscillation index (SOI) and Niño-3.4 sea surface temperature index (Niño-3.4)] are observed. This paper shows that ENSO’s effects on the location and intensity of convection over the Arabian Sea, the Bay of Bengal, and the tropical Indian Ocean, along moisture transport paths toward Lhasa, further impact convection from the northern Tibetan Plateau. The changing of this convection results in lower δ18Op at Lhasa in 2007, a La Niña year, and higher δ18Op in 2006, an El Niño year. The study presented here confirms that the regional upstream convection related to ENSO teleconnections plays an important role in variations of δ18Op at the interannual scale and that the more depleted oxygen stable isotopic composition of vapor (δ18Oυ) from the northwestern region of India during a La Niña year intensifies the lower δ18Op at Lhasa in a La Niña year. The study’s results have implications for the interpretation of past variations of archives with precipitation stable isotopes, such as ice cores, tree rings, lake sediments, and speleothems, in this region.

Download Full-text

Seasonal trends in the stable isotopic composition of snow and meltwater runoff in a subarctic catchment at Okstindan, Norway

Hydrology Research ◽

10.2166/nh.2004.0009 ◽

2004 ◽

Vol 35 (2) ◽

pp. 119-137 ◽

Cited By ~ 12

Author(s):

S.D. Gurney ◽

D.S.L. Lawrence

Keyword(s):

Isotopic Composition ◽

Mean Value ◽

Mean Values ◽

Stable Isotopic Composition ◽

Meltwater Runoff ◽

Stable Isotopic ◽

The Mean ◽

The Difference ◽

Δ18o And Δd

Seasonal variations in the stable isotopic composition of snow and meltwater were investigated in a sub-arctic, mountainous, but non-glacial, catchment at Okstindan in northern Norway based on analyses of δ18O and δD. Samples were collected during four field periods (August 1998; April 1999; June 1999 and August 1999) at three sites lying on an altitudinal transect (740–970 m a.s.l.). Snowpack data display an increase in the mean values of δ18O (increasing from a mean value of −13.51 to −11.49‰ between April and August), as well as a decrease in variability through the melt period. Comparison with a regional meteoric water line indicates that the slope of the δ18O–δD line for the snowpacks decreases over the same period, dropping from 7.49 to approximately 6.2.This change points to the role of evaporation in snowpack ablation and is confirmed by the vertical profile of deuterium excess. Snowpack seepage data, although limited, also suggest reduced values of δD, as might be associated with local evaporation during meltwater generation. In general, meltwaters were depleted in δ18O relative to the source snowpack at the peak of the melt (June), but later in the year (August) the difference between the two was not statistically significant. The diurnal pattern of isotopic composition indicates that the most depleted meltwaters coincide with the peak in temperature and, hence, meltwater production.

Download Full-text