Annual variation in event-scale precipitation <i>δ</i><sup>2</sup>H at Barrow, AK, reflects vapor source region

Abstract

Abstract. In this study, precipitation isotopic variations at Barrow, AK, USA, are linked to conditions at the moisture source region, along the transport path, and at the precipitation site. Seventy precipitation events between January 2009 and March 2013 were analyzed for δ2H and deuterium excess. For each precipitation event, vapor source regions were identified with the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) air parcel tracking program in back-cast mode. The results show that the vapor source region migrated annually, with the most distal (proximal) and southerly (northerly) vapor source regions occurring during the winter (summer). This may be related to equatorial expansion and poleward contraction of the polar circulation cell and the extent of Arctic sea ice cover. Annual cycles of vapor source region latitude and δ2H in precipitation were in phase; depleted (enriched) δ2H values were associated with winter (summer) and distal (proximal) vapor source regions. Precipitation δ2H responded to variation in vapor source region as reflected by significant correlations between δ2H with the following three parameters: (1) total cooling between lifted condensation level (LCL) and precipitating cloud at Barrow, ΔTcool, (2) meteorological conditions at the evaporation site quantified by 2 m dew point, Td, and (3) whether the vapor transport path crossed the Brooks and/or Alaskan ranges, expressed as a Boolean variable, mtn. These three variables explained 54 % of the variance (p<0. 001) in precipitation δ2H with a sensitivity of −3.51 ± 0.55 ‰ °C−1 (p<0. 001) to ΔTcool, 3.23 ± 0.83 ‰ °C−1 (p<0. 001) to Td, and −32.11 ± 11.04 ‰ (p = 0. 0049) depletion when mtn is true. The magnitude of each effect on isotopic composition also varied with vapor source region proximity. For storms with proximal vapor source regions (where ΔTcool <7 °C), ΔTcool explained 3 % of the variance in δ2H, Td alone accounted for 43 %, while mtn explained 2 %. For storms with distal vapor sources (ΔTcool > 7°C), ΔTcool explained 22 %, Td explained only 1 %, and mtn explained 18 %. The deuterium excess annual cycle lagged by 2–3 months during the δ2H cycle, so the direct correlation between the two variables is weak. Vapor source region relative humidity with respect to the sea surface temperature, hss, explained 34 % of variance in deuterium excess, (−0.395 ± 0.067 ‰ %−1, p<0. 001). The patterns in our data suggest that on an annual scale, isotopic ratios of precipitation at Barrow may respond to changes in the southerly extent of the polar circulation cell, a relationship that may be applicable to interpretation of long-term climate change records like ice cores.

Seasonal Deuterium Excess Variations of Precipitation at Summit, Greenland, and their Climatological Significance

“…For each event, GDAS reanalysis data were used to determine the range of altitudes where condensation occurred, and this range was divided into 1,000 air parcels, each representing an equal proportion of condensing water. The method for dividing the parcels and identifying the moisture source is described by Putman, Feng, Sonder et al () and Putman, Feng, Posmentier et al (). All 1,000 parcels were tracked backward in time for 240 hr, and the water vapor source for a given trajectory was taken to be the first location where the back trajectory sank into the planetary boundary layer (as defined by GDAS).…”

Patterns of Evaporation and Precipitation Drive Global Isotopic Changes in Atmospheric Moisture

“…Indeed, precipitation and ice cores in Alaska sometimes show stronger correlations between water isotope ratios and moisture source region than temperature (Fisher et al, 2004;Putman et al, 2017), and modern precipitation measurements in the tropical Pacific suggest that isotope ratios respond more sensitively to variations in the intensity and organization of convection regionally than to the amount of local precipitation (Conroy et al, 2016;Kurita, 2013;Kurita et al, 2009;Moerman et al, 2013). More recently, studies have shown correlations between isotope ratios and regional imbalances in E and P (Feng et al, 2009;Lee et al, 2007;Moore et al, 2014) or associated variations in atmospheric residence time and moisture transport (Aggarwal et al, 2012;Bailey et al, 2017;Putman et al, 2017). Nevertheless, to decipher changes in hydrologic balance from isotope ratios, a strong theoretical framework that can explain these correlations is necessary.…”

Synoptic and Mesoscale Mechanisms Drive Winter Precipitation δ18O/δ2H in South‐Central Alaska

“…Furthermore, existing data typically represent isotopic measurements of monthly composited precipitation samples (IAEA/ WMO, 2018), thereby precluding any ability to identify process-based mechanisms that influence individual precipitation events. While some efforts to delineate spatial patterns of δ 18 O P and δ 2 H P have been carried out using measured and/or modeled data (Anderson et al, 2016;Bailey et al, 2015;Berkelhammer et al, 2012;Field et al, 2010;Putman et al, 2017), longterm empirical data from Alaska are severely lacking in comparison to the contiguous United States (Akers et al, 2017;Liu et al, 2010;Vachon et al, 2010aVachon et al, , 2010bWelker, 2000Welker, , 2012.…”