Atmospheric Rivers over the Northwestern Pacific: Climatology and Interannual Variability

Abstract

Atmospheric rivers (ARs), conduits of intense water vapor transport in the midlatitudes, are critically important for water resources and heavy rainfall events over the west coast of North America, Europe, and Africa. ARs are also frequently observed over the northwestern Pacific (NWP) during boreal summer but have not been studied comprehensively. Here the climatology, seasonal variation, interannual variability, and predictability of NWP ARs (NWPARs) are examined by using a large ensemble, high-resolution atmospheric general circulation model (AGCM) simulation and a global atmospheric reanalysis. The AGCM captures general characteristics of climatology and variability compared to the reanalysis, suggesting a strong sea surface temperature (SST) effect on NWPARs. The summertime NWPAR occurrences are tightly related to El Niño–Southern Oscillation (ENSO) in the preceding winter through Indo–western Pacific Ocean capacitor (IPOC) effects. An enhanced East Asian summer monsoon and a low-level anticyclonic anomaly over the tropical western North Pacific in the post–El Niño summer reinforce low-level water vapor transport from the tropics with increased occurrence of NWPARs. The strong coupling with ENSO and IPOC indicates a high predictability of anomalous summertime NWPAR activity.

Identifying strong signals between low‐frequency climate oscillations and annual precipitation using correlation analysis

“…For example, atmospheric rivers have been found to be a major contributor of extreme precipitation events and flooding throughout California and the Pacific Northwest (Ralph et al, ; Dettinger et al, ). Several studies have demonstrated that various large‐scale climate modes affect the frequency and position of atmospheric rivers along the West Coast, including the AO (Guan and Waliser, ); ENSO (Guan and Waliser, ; Mundhenk et al, ; Kamae et al, ), the MJO (Ralph et al, ; Guan et al, ; Mundhenk et al, ; Mundhenk et al, ), and the PNA (Guan and Waliser, ), while it has also been shown that the relationship between the MJO and atmospheric river activity is further modulated by the phase of other HCIs, such as ENSO (Mundhenk et al, ) and the QBO (Baggett et al, ; Mundhenk et al, ). Additional investigation is required in order to shed more light on the impact of the lower‐frequency variability of the MJO, ENSO, and the EAWR, on long‐term precipitation variability along both coasts and the potential modulation of the these HCIs by the other dominant interannual modes of variability as mentioned above.…”

Precipitation Changes in a Climate With 2‐K Surface Warming From Large Ensemble Simulations Using 60‐km Global and 20‐km Regional Atmospheric Models

“…Recently, Mizuta et al (2017) performed large ensemble 4-K warming climate and historical climate experiments (the database for Policy Decision making for Future climate change: d4PDF) using a 60-km atmospheric general circulation model (AGCM) and 20-km regional model. This data set has enabled examination of future change in extreme events at the end of the century such as tropical cyclone activity (Yoshida et al, 2017), extreme snow events (Kawase et al, 2016), East Asian monsoon precipitation , Northern Hemisphere blocking (Matsueda & Endo, 2017), and the reproducibility of atmospheric rivers in the d4PDF historical climate experiment (Kamae et al, 2017).…”

Ocean warming pattern effects on future changes in East Asian atmospheric rivers

“…The ensemble simulations were developed with random initial and SST perturbations (Hirahara et al 2014). In this study, a 10-member ensemble mean was examined to reduce the effect of atmospheric internal variability (Kamae et al 2017a(Kamae et al , 2017b.…”

“…Hawkins andSutton 2009, Thompson et al 2015) by using large-member ensemble simulations (e.g. Deser et al 2012, Hagos et al 2016, Kamae et al 2017a, 2017b for quantitative evaluation of forced response to global warming.…”

“…Shin and Sardeshmukh 2011, Ma and Xie 2013, Shepherd 2014, He and Zhou 2015, Choi et al 2016 and statistics of extratropical cyclones (Langenbrunner et al 2015). SST anomalies over the tropical Indo-Pacific regions are also closely linked to interannual variability in atmospheric circulation over Asia and the western North Pacific (Xie et al 2009, Wang et al 2013, Song and Zhou 2014a, 2014b, Kamae et al 2017b, Paek et al 2018. However, it is not easy to evaluate the effect of SST warming pattern uncertainty, because other factors (e.g.…”