Atmospheric Rivers

Integrated water vapor on December 5, 2015. Particularly high values of over 40 kg/m2 are shown in red.- Image source: (US) National Weather Service, public domain via Wikimedia Commons

"Atmospheric Rivers” (ARs) transport huge amounts of water vapor from the tropics to mid and high latitudes. When they hit land, extreme precipitation often occurs. Even a medium-sized example transports twice as much water as the Amazon River. The illustration shows an extreme case in the Atlantic, which caused severe devastation in Great Britain as storm “Desmond” and then hit Norway as storm “Synne”.

As ARs mainly extend over the oceans, they are primarily observed by satellites, especially with passive microwave sensors. These data allow a good estimate of the total water vapor content, but do not provide any information on its vertical distribution. However, this would be important in order to better understand the dynamics – even more so as ARs are expected to increase further in strength as a result of climate change.

In an article in Atmospheric Measurement Techniques, Bahareh Rahimi and Ulrich Foelsche from the Institute of Physics and Wegener Center at the University of Graz have now been able to show for the first time that this important information about the vertical structure can be obtained using the radio occultation method. The article was therefore recognized by the editors as a “Highlight Paper” (along with just two others so far in 2025).

Until now, mainly ARs over the Pacific that hit the west coast of the USA have been researched. Other regions of the world are still largely unexplored in this respect. In a parallel study, Linda M. Maier, Bahareh Rahimi and Ulrich Foelsche have systematically investigated ARs that hit Africa for the first time ever.

The potential of observing atmospheric rivers with Global Navigation Satellite System (GNSS) radio occultation
Bahareh Rahimi and Ulrich Foelsche
Atmos. Meas. Tech., 18, 2481–2507, doi.org/10.5194/amt-18-2481-2025, 2025

amt.copernicus.org/editors_choice.html

Atmospheric Rivers in Africa observed with GNSS RO and reanalysis data
Linda M. Maier, Bahareh Rahimi and Ulrich Foelsche
Remote Sensing, 17, 1273, https://doi.org/10.3390/rs17071273, 2025

Ulrich Foelsche

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