Atmospheric Rivers and Surface Melt Events Over the Greenland Ice Sheet

In the summer of 2012, nearly the entire Greenland Ice Sheet (GIS) melted  as warm air and thin clouds moved over the GIS in association with an Atmospheric River (AR) (Bennartz et al. 2013, Neff et al. 2014).  More recently surface melt as well as rainfall have been observed at Summit Station Greenland.  While these events garner much media attention, systematic mass loss in the ablation zones around the ice sheet (particularly along the southwest coast), in the transition to the accumulation zone and vulnerable glacier systems (Mattingly et al. 2021) is important to forecast sea level rise.  In this analysis, we use a simple detection method to identify ARs along the Greenland west coast using reanalysis data at two points (60N/310W and 65N/305W) at 850 hPa, namely wind speed and direction and total integrated water vapor.  We show a comparison between ERA5, NCEP/NCAR, and the Twentieth Century Reanalysis to show the efficacy of this approach and the ability to track ARs over the past hundred years. The approach exploits the barrier effect of the GIS, which extends to about 700 hPa.
This use of reanalysis data is then coupled with the calculation of the fraction of melt in a series of latitude-longitude boxes at various locations around the ice sheet using the MEaSURES data set (Mote 2016) for the period 2000-2012. We then develop composite synoptic maps for geopotential height, total column water vapor, and Omega (for vertical velocity) for each class of event (e.g. strong ARs) and their subsequent evolution over 3 to 5 days. A key finding is that ARs that first impact the west coast later transport moisture to the SE coast leaving a residue of moisture along the west coast as the associated blocking high moves to the east.  In addition, we show how strong ARs along the west coast reflect geopotential height patterns very similar to those presented in (Gallagher et al. 2018) that are also associated with warmer temperature and increased opaque cloudiness at Summit Station.  Finally, we examine how various extreme events fit into this picture and affect the meteorology at Summit Station, including dramatic changes in boundary layer structure.

References

Bennartz, R., M. D. Shupe, D. D. Turner, V. P. Walden, K. Steffen, C. J. Cox, M. S. Kulie, N. B. Miller and C. Pettersen (2013). Nature 496(7443): 83-86.Gallagher, M. R., M. D. Shupe and N. B. Miller (2018. Journal of Climate."  31(21): 8895-8915.

Mattingly, K. S., T. L. Mote and X. Fettweis (2018). Journal of Geophysical Research: Atmospheres.

Mote, T. L. (2016). MEaSUREs Greenland Surface Melt Daily 25 km EASE-Grid 2.0, version 1. https://doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0533.001.

Neff, W., G. P. Compo, F. M. Ralph and M. D. Shupe (2014). Journal of Geophysical Research-Atmospheres 119(11): 6520-6536.

Mattingly et al., EGU General Assembly 2021