The summer 2012 Greenland heat wave: In situ and remote sensing observations of water vapor isotopic composition during an atmospheric river event

Abstract

During 7–12 July 2012, extreme moist and warm conditions occurred over Greenland, leading to widespread surface melt. To investigate the physical processes during the atmospheric moisture transport of this event, we study the water vapor isotopic composition using surface in situ observations in Bermuda Island, South Greenland coast (Ivittuut), and northwest Greenland ice sheet (NEEM), as well as remote sensing observations (Infrared Atmospheric Sounding Interferometer (IASI) instrument on board MetOp‐A), depicting propagation of similar surface and midtropospheric humidity and δD signals. Simulations using Lagrangian moisture source diagnostic and water tagging in a regional model showed that Greenland was affected by an atmospheric river transporting moisture from the western subtropical North Atlantic Ocean, which is coherent with observations of snow pit impurities deposited at NEEM. At Ivittuut, surface air temperature, humidity, and δD increases are observed. At NEEM, similar temperature increase is associated with a large and long‐lasting ∼100‰δD enrichment and ∼15‰ deuterium excess decrease, thereby reaching Ivittuut level. We assess the simulation of this event in two isotope‐enabled atmospheric general circulation models (LMDz‐iso and ECHAM5‐wiso). LMDz‐iso correctly captures the timing of propagation for this event identified in IASI data but depict too gradual variations when compared to surface data. Both models reproduce the surface meteorological and isotopic values during the event but underestimate the background deuterium excess at NEEM. Cloud liquid water content parametrization in LMDz‐iso poorly impacts the vapor isotopic composition. Our data demonstrate that during this atmospheric river event the deuterium excess signal is conserved from the moisture source to northwest Greenland.

Regional seesaw between the North Atlantic and Nordic Seas during the last glacial abrupt climate events

“…2). Recent monitoring data have revealed that (i) deuterium excess is low for subtropical Atlantic vapour and high for vapour formed at the Arctic sea-ice margin, where high kinetic fractionation occurs due to low relative humidity, and (ii) this vapour deuterium excess is preserved during transportation towards Greenland (Jouzel et al, 2013;Bonne et al, 2015). Higher deuterium excess recorded during GS (Masson-Delmotte et al, 2005) may reflect enhanced contribution of moisture from the Nordic Seas towards Greenland (as also previously suggested for Heinrich stadial 4 interval; Wary et al, 2016), when the Norwegian Sea appears relatively warm and surrounded by sea-ice-covered areas (providing low humidity air masses), while the North Atlantic surface is cold and marked by large sea-ice expansion (Hillaire-Marcel and de Vernal, 2008).…”

Identification of Air Masses Responsible for Warm Events on the East Antarctic Coast

“…These two periods were associated with passages of strong precipitation events, so-called atmospheric river (AR): poleward moisture was organized in a filamentary structure stretching from subtropical latitudes to Antarctica, leading to heavy snow accumulation events over DML (Gorodetskaya et al 2014). Note that, in Greenland, an AR event was observed in summer 2012 (e.g., Neff et al 2014), including water vapor isotope monitoring (Bonne et al 2015), and let to widespread melt at the ice sheet surface (Nghiem et al 2012). As observed over the Greenland ice sheet, T max rose at Syowa above the melting point during these events.…”

Numerical simulation of extreme snowmelt observed at the SIGMA-A site, northwest Greenland, during summer 2012

“…Neff et al (2014) examined synoptic-scale atmospheric conditions over the GrIS during July 2012 from various aspects and summarized notable features as follows: (1) warm air originating from a record North American heat wave (the North American drought of 2012 was the worst since 1895), (2) transitions in the Arctic Oscillation, (3) transport of water vapor via an atmospheric river over the Atlantic to Greenland, and (4) the presence of warm ocean waters south of Greenland. Bonne et al (2015) clearly showed that moist air mass was advected northward following a narrow band reaching southern Greenland and then it moved northward along the western Greenland coast around 9 July. Observed features of above-mentioned meteorological properties during the IOP at the SIGMA-A site are consistent with these large-scale atmospheric conditions.…”