Ocean variability and air-sea fluxes produced by atmospheric rivers

Toshiaki Shinoda,Yanjuan Guo,Luis Zamudio,E Joseph Metzger,Chris W Fairall

doi:10.1038/s41598-019-38562-2

Abstract

Atmospheric rivers (ARs) cause heavy precipitation and flooding in the coastal areas of many mid-latitude continents, and thus the atmospheric processes associated with the AR have been intensively studied in recent years. However, AR-associated ocean variability and air-sea fluxes have received little attention because of the lack of high-resolution ocean data until recently. Here we demonstrate that typical ARs can generate strong upper ocean response and substantial air-sea fluxes using a high-resolution (1/12°) ocean reanalysis. AR events observed during the CalWater 2015 field campaign generate large-scale on-shore currents that hit the coast, generating strong narrow northward jets along the west coast of North America, in association with a substantial rise of sea level at the coast. In the open ocean, the AR generates prominent changes of mixed layer depth, especially south of 30°N due to the strong surface winds and air-sea heat fluxes. The prominent cooling of SST is observed only in the vicinity of AR upstream areas primarily due to the large latent heat flux. Using a long-term AR dataset, composite structure and variations of upper ocean and air-sea fluxes are presented, which are consistent with those found in the events during CalWater 2015.

Highlights

AR events observed during the CalWater 2015 field campaign produce large-scale on-shore currents toward the west coast of North America, generating strong narrow northward jets along the coast, in association with a substantial rise of sea level at the coast
The difference in evaporation between downstream and upstream areas is primarily attributed to the difference in vertical humidity gradient near the surface
The results indicate that the composite structure and evolution are all consistent with those found in the case study for the events during CalWater 2015. This suggests that oceanic processes and air-sea fluxes associated with ARs identified during the CalWater 2015 are commonly found in most AR events

Summary

Data and Methods

The data assimilated by NCODA include remotely sensed sea surface height (SSH), sea surface temperature (SST) and sea ice concentration as well as in-situ surface and subsurface observations of temperature and salinity These include synthetic temperature profiles computed using the Improved Synthetic Ocean Profile (ISOP21), in which the vertical profile at a given location is constructed by projecting remotely observed SSH and SST downward from the surface using a global database of statistical relationships. A similar method is used to construct composites of ocean variability and air-sea fluxes associated with ARs. ARs are identified based on the characteristics of the integrated water vapor transport (IVT) at 6 hourly intervals[31]. Daily variables relevant to upper ocean variability and air-sea fluxes are composited over a 60° longitude by 40° latitude domain centered at the centroid of ARs, using AR events for the 5-year period of 2011–2015. Only AR events in which IVT at the center exceeds 500 kg m−1 s−1 are used

Results

Summary and Discussion

Author Contributions

Additional Information