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Atmospheric rivers (ARs), and frontal systems more broadly, tend to exhibit prominent “V” shapes in time series of stable isotopes in precipitation. Despite the magnitude and widespread nature of these “V” shapes, debate persists as to whether these shifts are driven by changes in the degree of rainout, which we determine using the Rayleigh distillation of stable isotopes, or by post-condensation processes such as below-cloud evaporation and equilibrium isotope exchange between hydrometeors and surrounding vapor. Here, we present paired precipitation and water vapor isotope time series records from the 5–7 March 2016, AR in Bodega Bay, CA. The stable isotope composition of surface vapor along with independent meteorological constraints such as temperature and relative humidity reveal that rainout and post-condensation processes dominate during different portions of the event. We find that Rayleigh distillation controls during peak AR conditions (with peak rainout of 55%) while post-condensation processes have their greatest effect during periods of decreased precipitation on the margins of the event. These results and analyses inform critical questions regarding the temporal evolution of AR events and the physical processes that control them at local scales.
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An unmanned aerial vehicle sampling platform for atmospheric water vapor isotopes in polar environments
Abstract. Above polar ice sheets, atmospheric water vapor exchangeoccurs across the planetary boundary layer (PBL) and is an importantmechanism in a number of processes that affect the surface mass balance ofthe ice sheets. Yet, this exchange is not well understood and hassubstantial implications for modeling and remote sensing of the polarhydrologic cycle. Efforts to characterize the exchange face substantiallogistical challenges including the remoteness of ice sheet field camps,extreme weather conditions, low humidity and temperature that limit theeffectiveness of instruments, and dangers associated with flying mannedaircraft at low altitudes. Here, we present an unmanned aerial vehicle (UAV)sampling platform for operation in extreme polar environments that iscapable of sampling atmospheric water vapor for subsequent measurement ofwater isotopes. This system was deployed to the East Greenland Ice-coreProject (EastGRIP) camp in northeast Greenland during summer 2019. Foursampling flight missions were completed. With a suite of atmosphericmeasurements aboard the UAV (temperature, humidity, pressure, GPS) wedetermine the height of the PBL using online algorithms, allowing forstrategic decision-making by the pilot to sample water isotopes above andbelow the PBL. Water isotope data were measured by a Picarro L2130-iinstrument using flasks of atmospheric air collected within the nose cone ofthe UAV. The internal repeatability for δD and δ18O was2.8 ‰ and 0.45 ‰, respectively,which we also compared to independent EastGRIP tower-isotope data. Based onthese results, we demonstrate the efficacy of this new UAV-isotope platformand present improvements to be utilized in future polar field campaigns. Thesystem is also designed to be readily adaptable to other fields of study,such as measurement of carbon cycle gases or remote sensing of groundconditions.
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- Award ID(s):
- 1833165
- PAR ID:
- 10329618
- Date Published:
- Journal Name:
- Atmospheric Measurement Techniques
- Volume:
- 14
- Issue:
- 11
- ISSN:
- 1867-8548
- Page Range / eLocation ID:
- 7045 to 7067
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/amt-14-7045-2021
