Evaluating the Roles of Rainout and Post-Condensation Processes in a Landfalling Atmospheric River with Stable Isotopes in Precipitation and Water Vapor

Abstract

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.

Variations of Stable Isotopic Composition in Atmospheric Water Vapor and their Controlling Factors—A 6‐Year Continuous Sampling Study in Nanjing, Eastern China

“…The large range of raindrop evaporation fraction suggests that the isotopic composition ( δ 18 O and d ‐excess) in precipitation or water vapor can be significantly impacted by the subcloud evaporation at the event timescale. Thus, concurrent monitoring of precipitation and water vapor isotopes is beneficial to constrain both the rainout and postcondensation processes such as below‐cloud evaporation (Mix et al, 2019). On the other hand, the effects of subcloud evaporation on precipitation isotopes at climate scale in the warm and humid Asia monsoon region have drawn little attention probably because of the relatively high precipitation amount in this region.…”

“…Such new techniques have been used in the past decade to monitor water vapor isotopes in different climatic regions around the world. Based on these new data, previous studies examined a variety of hydrological processes, such as moisture sources (e.g., Salamalikis et al, 2015; Steen‐Larsen et al, 2013), convective activities (e.g., Lacour et al, 2018; Rahul et al, 2016; Saranya et al, 2018), water vapor transport (e.g., Bonne et al, 2015; Cai & Tian, 2016), water vapor mixing (e.g., Brown et al, 2008; Galewsky & Samuels‐Crow, 2015; Welp et al, 2012), precipitation processes (e.g., Laskar et al, 2014; Mix et al, 2019; Wei et al, 2016), raindrop evaporation (e.g., Rahul et al, 2016; Worden et al, 2007), local meteorological factors such as specific humidity and air temperature (e.g., Sun et al, 2014; Wen et al, 2010), and land evapotranspiration (e.g., Brown et al, 2008; Wei et al, 2016). These studies confirm the great potential of using water vapor isotopes to trace and examine atmospheric hydrological processes.…”

Controls on stable isotopic characteristics of water vapour over Thailand

“…For condensation, the isotopic fractionation is due to a rapid molecular exchange between liquid precipitation and vapour, which predominates over the separation effect of removing moisture content in the air (Craig et al, 1963). Equilibrium fractionation describes the isotopic exchange reactions between two different phases of a compound at a rate that maintains equilibrium, such as transforming water vapour to liquid precipitation (Mix et al, 2019). Although the exchange rate ( k ) remains constant, it varies for different isotopic compositions (Sharp, 2017).…”

Evaluation of physicochemical and trace metal qualities of rainwater in the south-eastern region of Bangladesh

“…Consequently, different locations may have different elemental concentrations that are key to the quality and suitability of uses. Rainwater chemistry is formed through the dynamic interaction between atmospheric (e.g., cloud) dynamics and microphysical actions together with a sequence of chemical reactions in the atmosphere caused by rainout and washout (Bertrand et al 2008;Mohanakumar 2008;Al-Khashman 2009;Mix et al 2019). As noted by Wang & Han (2011), rainwater chemistry signifies the chemical characteristics of the atmosphere through which it falls, which helps to understand and investigate the soluble elements that exist in rainwater.…”