Atmospheric Rivers in the Mid-latitudes: A Modeling Study for Current and Future Climates

Abstract:

Atmospheric rivers (ARs) are dynamically-driven narrow intense bands of moisture that transport significant amounts of moisture from the tropics to mid-latitudes and are thus an important aspect the Earth’s hydrological cycle. They are often associated with extratropical cyclones whose low level circulation is able to tap into tropical moisture and transport it northward. The “Pineapple Express” is an example of an AR that impacts the west coast of California predominately in the winter months and can produce heavy amounts of precipitation in a short period of time (hours up to several days).

This work will focus on three mid-latitude AR regions including the west coast of California, the Pacific Northwest, and the United Kingdom as modeled by a suite of high-resolution CESM (Community Earth System Model) simulations for 20^th century and RCP8.5 future climate scenarios. The CESM version employed utilizes half-degree resolution atmosphere/land components (~0.5^o) coupled to the standard (1^o) ocean/ice components. We use the high-resolution atmosphere because it is able to more accurately represent extreme, regional precipitation.

CESM realistically captures ARs as spatial and temporal statistics show. Projections for future climate statistics for all three regions as well as analysis of the dynamical and thermodynamical mechanisms driving ARs, such as vorticity, jets and the steering flow, and water vapor transport, and will presented. Finally, teleconnections to climate variability processes, such as ENSO will be explored.