Atmospheric rivers (ARs) are relatively narrow regions of concentrated water vapor (WV) responsible for horizontal transport in the lower atmosphere (Raph and Dettinger, 2011). It was shown that more than 90% of the meridional WV transport in the midlatitudes occurs in the ARs, although they cover less than 10% of the area of the globe (Zhu and Newell, 1998).
These bands of concentrated WV are typically only a few hundred kilometers wide and are located in the lower troposphere, but can stretch over thousands of kilometers across the ocean and their water transportation rate can be at times as intense as that of major terrestrial rivers (Zhu and Newell, 1998). The large amount of WV that is transported can lead to heavy precipitation and floods.
The analysis of the contribution of ARs to extreme precipitation events has been restricted to a few areas of the world, with a strong focus on the eastern North Pacific and their associated impacts on the contiguous North American west coast (Neiman et al. 2008; Ralph and Dettinger 2012). Over Europe, the large amount of WV that is transported by the ARs can also lead to extreme precipitation events and flooding as described for a number of well-known extreme events (Liberato et al. 2013; Trigo et al. 2014; Stohl et al. 2008, Lavers et al., 2011)
The detection of the ARs is usually achieved through the implementation of one of two possible main approaches. The first methodology considers the use of the IWV, acquired mainly from the SSMI (e.g. Ralph et al. 2004; Ralph and Dettinger 2011). The second approach is based on the use of the vertically integrated horizontal water vapor transport (IVT) between the 1000hPa and 300hPa, computed from different reanalysis datasets, or from general circulation models (e.g. Zhu and Newell 1998; Lavers et al. 2013). A review of the different methods to identify atmospheric rivers can be seen in Gimeno et al. (2014).
The Climatology and Climate Change group at IDL is currently studying the relationship between the ARs and the extreme precipitation events in the Iberian Peninsula (e.g. Ramos et al. 2014). Several case studies of intensive precipitation had been analysed and the importance of the ARs have been accessed and confirmed (e.g. December 1876 (Trigo et al., 2014), November 1983 (Liberato et al, 2013).
Figure 1. Example of an Atmospheric River, over the North Atlantic Ocean and making landfall over the Iberian Peninsula for 28 of March. 48-hour animation of total precipitable water derived from the SSMI/SSMIS/TMI (http://tropic.ssec.wisc.edu/real-time/mimic-tpw/natl/main.html).
Gimeno, L, R. Nieto, M. Vázquez, and D.A. Lavers, 2014: Atmospheric rivers: a mini-review. Front. Earth Sci. 2, 2. doi: 10.3389/feart.2014.00002.
Lavers, D. A., R. P. Allan, E. F. Wood, G. Villarini, D. J. Brayshaw, and A. J. Wade 2011: Winter floods in Britain are connected to atmospheric rivers. Geophys. Res. Lett., 38: L23803, doi:10.1029/2011GL049783.
Lavers, D. A., and G. Villarini, 2013: The nexus between atmospheric rivers and extreme precipitation across Europe. Geophys. Res. Lett., 40, 3259–3264.
Liberato, M. L. R., A. M. Ramos, R. M. Trigo, I.F. Trigo, A. M. Durán-Quesada, R. Nieto. And L. Gimeno, 2013: Moisture Sources and Large-Scale Dynamics Associated With a Flash Flood Event, in Lagrangian Modeling of the Atmosphere (eds J. Lin, D. Brunner, C. Gerbig, A. Stohl, A. Luhar and P. Webley), American Geophysical Union, Washington, D. C., doi: 10.1029/2012GM001244.
Neiman, P. J., F. M. Ralph, G. A. Wick, J. D. Lundquist, and M. D. Dettinger, 2008: Meteorological characteristics and overland precipitation impacts of atmospheric rivers affecting the West Coast of North America based on eight years of SSM/I satellite observations. J. Hydrometeorol., 9(1), 22–47.
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Ralph, F. M., and M. D. Dettinger, 2011: Storms, floods, and the science of atmospheric rivers, Eos Trans. AGU, 92(32), 265.
Ralph, F. M., and M. D. Dettinger, 2012: Historical and national perspectives on extreme west-coast precipitation associated with atmospheric rivers during December 2010. Bull. Amer. Meteor. Soc., 93, 783-790, doi:10.1175/BAMS-D-11-00188.1.
Stohl, A., C. Forster, and H. Sodemann, 2008: Remote sources of water vapor forming precipitation on the Norwegian west coast at 60°N: A tale of hurricanes and an atmospheric river. J. Geophys. Res., 113, D05102.
Trigo, R. M., F. Varino, A. M. Ramos, M. A. Valente, J. L. Zęzere, J. M. Vaquero, C. M. Gouveia, and A. Russo, 2014: The record precipitation and flood event in Iberia in December 1876: description and synoptic analysis. Front. Earth Sci., 2, 3, doi: 10.3389/feart.2014.00003.
Zhu, Y., R. E. Newell, 1998: A proposed algorithm for moisture fluxes from atmospheric rivers. Mon. Weather Rev., 126(3), 725–735.