Rivers in the sky

Atmospheric rivers are described in the American Meteorological Society’s Glossary of Meteorology as filamentary atmospheric flows carrying intense amounts of water vapor, usually associated with a low-level jet ahead of the cold front of an extratropical low. These flows are also associated with the ascent of large masses of warm, moist air from the lower layers of the warm sector of the low, rising rapidly to the upper troposphere as they move poleward. These events are infrequent and occur between two and ten times per year in a given region of Antarctica.

Yet, atmospheric rivers account for :

  • about 90% of the meridional transport of water vapor, even though they cover only about 10% of the surface ; four or five atmospheric rivers in each hemisphere may thus be sufficient to transport the majority of the meridional fluxes over the globe
  • 70% of the most intense precipitation events - in this case, precipitation above the 99th percentile - occur during atmospheric rivers. The associated precipitation totals represent up to 20% of annual precipitation in the regions concerned, particularly in East Antarctica
  • the majority of summer melt events over West Antarctica and the Ross Ice Shelf, including the most intense events.
  • Atmospheric rivers were the cause of the vast majority of temperature and precipitation extremes over the Antarctic Peninsula, including the absolute temperature record for the entire Antarctic continent (18.3°C), set at the Esperanza station on February 6, 2020
  • The most intense atmospheric rivers cause a series of impacts such as temperature extremes, surface melt and runoff, sea ice disintegration and intense wave generation ; all of these processes are known to destabilize ice shelves.

Atmospheric rivers thus play both positive and negative roles on the continental surface mass balance. Today, the positive effects (increased precipitation) outweigh the negative ones (melting and surface runoff), but we do not know how these respective impacts will change by the end of the 21st century. To answer this question, it is essential to understand the physical processes that drive atmospheric rivers. It is also necessary to verify that climate models are able to reproduce them correctly for the current climate, before analyzing their evolution by the end of the century. This is one of the main objectives of the ARCA project

Updated on 20 août 2022