Research ArticleATMOSPHERIC SCIENCE

On the crucial role of atmospheric rivers in the two major Weddell Polynya events in 1973 and 2017 in Antarctica

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Science Advances  11 Nov 2020:
Vol. 6, no. 46, eabc2695
DOI: 10.1126/sciadv.abc2695
  • Fig. 1 ARs and the Weddell Polynya.

    Cloud bands associated with ARs on 13 September 2017 (A) and on 16 September 2017 (B) observed in natural colors by the Spinning Enhanced Visible and InfraRed Imager (source, The European Organisation for the Exploitation of Meteorological Satellites). (C) The large Weddell Polynya on 23 September 1974, which initially opened on 22 November 1973 and remained open for the following three winters, and (D) the second large opening, which occurred in September 2017. The location of the polynya is indicated by the letter P on (A) and (B).

  • Fig. 2 The characteristics of the 2017 AR events.

    ERA5 reanalysis maps for 2017 of the following: (i) IVT magnitude (shaded) and direction (black vectors) and geopotential heights at 500 hPa in black contours on (A) 31 August at 0000 UTC, (C) 13 September at 0000 UTC, and (E) 16 September at 0000 UTC. (ii) Standardized anomalies of precipitable water (shaded), 1000- to 700-hPa mean winds in vectors and mean sea level pressure (MSLP) in black contours on (B) 31 August at 0000 UTC, (D) 13 September at 0000 UTC, and (F) 16 September at 0600 UTC. (iii) Standardized anomalies of total column cloud liquid water (shaded), MSLP in gray contours, and 10-m winds in black vectors on (G) 13 September at 0000 UTC and (H) 16 September at 0000 UTC. On all panels, ARs are outlined in blue contours, specific values of satellite-derived sea ice concentration (SIC) are superimposed in pink contours, and the green box corresponds to the area used to average the quantities shown in Fig. 3.

  • Fig. 3 The impact of the 2017 AR events.

    Time series from 20 August 2017 to 30 September 2017 of the following (from top to bottom): (A) Satellite-derived sea ice concentration and sea ice thickness (SIT). (B) ERA5 IVT and TCWV. (C) ERA5 2-m surface temperature and skin temperature. (D) ERA5 SHF at the surface and latent heat flux (LHF) at the surface. (E) Net longwave radiation (LWnet) and net shortwave radiation (SWnet) at the surface from ERA5 (solid lines) and from CERES (dashed lines). (F) ERA5 net radiation (Rnet) at the surface (solid lines) and from CERES (dashed lines) and ERA5 total energy flux at the surface (Fnet); positive values are toward the surface. (G) ERA5 snow accumulation rates. All quantities are averaged over the domain 2°W to 8°E, 63°S to 67°S (green box in Figs. 2 and 4). Dotted/dashed lines on panels B (D) are the 95th/99th (5th/1st) percentiles (relative to August to September climatology) showing times when IVT, TCWV, SHF, and LHF exceeded climatologically extreme values. The blue shading in the background indicates times when an AR was present over the domain. Snow accumulation is expressed in millimeter water equivalent per hour (mm w.e. hour−1).

  • Fig. 4 The impact of the ARs on 12-13 September 2017.

    ERA5 reanalysis maps for the 13 September 2017 AR event of the following: (A) All-sky upwelling LW radiation at the TOA on 13 September at 0000 UTC. The green dashed contour represents the domain shown in (D) to (F). (B) All-sky downwelling LW radiation at the surface (SFC) on 13 September at 0000 UTC. (C) Standardized anomalies of TOA LW (shaded) on 13 September 2017 at 0000 UTC. Positive values of LW fluxes are toward Earth’s surface, and negative values are away from the surface. Positive anomalies of TOA LW flux represent less outgoing LW radiation. (D) Total energy flux at the surface (shaded) on 12 September 2017 at 1300 UTC over the domain marked by the green dashed contour on (A). (E) Skin temperature anomalies on 12 September 2017 at 1300 UTC (shaded). (F) Same as (E) but on 13 September 2017 at 0000 UTC. On (D) to (F), MSLP is in gray contours and 10-m winds in gray vectors, and sea ice concentration, skin temperature, and 2-m temperature are superimposed for particular values as annotated on the figures. The green box represents the area used to average the quantities shown in Fig. 3. ARs are outlined in blue on all panels. All anomalies are calculated relative to the 1979–2017 climatological reference period.

  • Fig. 5 The exceptional nature of the 2017 AR events.

    Histograms showing the distribution of daily mean values for all August to September climatology during 1979–2017, spatially averaged over 2°W to 8E°E and 63°S to 67°S of the following: (A) IVT, (B) net radiation at the surface, (C) skin temperature, (D) 2-m surface air temperature, (E) mean hourly snow accumulation in millimeter water equivalent, and (F) 10-m wind speed. The colored vertical lines correspond to daily mean values during the 28 August–17 September 2017 period. The gray lines correspond to the 1st and 99th percentiles, the black lines correspond to the minimum and maximum values, and the dashed gray lines correspond to the 5th and 95th percentiles.

  • Fig. 6 The 1973 polynya event.

    JRA55 reanalysis maps on 18 November 1973 at 1800 UTC of the following: (A) IVT magnitude (shaded) and direction (black vectors) and geopotential heights at 500 hPa in black contours. Red contours represent areas with climatological IVT PR above the 85th percentile. (B) Standardized anomalies of precipitable water (shaded), 1000- to 700-hPa mean winds in vectors, and MSLP in black contours. (C) Total column cloud liquid water (shaded) on 19 November 1973 at 0600 UTC. (D) Standardized anomalies of TOA LW (shaded) on 19 November 1973 at 0600 UTC relative to the 1970–2000 climatological reference period. Positive anomalies of TOA LW flux represent less outgoing LW radiation. (E) Daily sea ice concentration in the small domain represented in the green box in (D) from Nimbus 5 on 19 November 1973. (F) Same as (E) but on 22 November 1973. The solid yellow line is the 15% contour, and the dotted yellow line is the 50% contour. The 15% contour of sea ice concentration was used to delineate the polynya. (A to E) The ARs are outlined in blue contours.

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