ALBERT

Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Suo, L., Gastineau, G., Gao, Y., Liang, Y.-C., Ghosh, R., Tian, T., Zhang, Y., Kwon, Y.-O., Otterå, O., Yang, S., & Matei, D. Simulated contribution of the interdecadal Pacific oscillation to the west Eurasia cooling in 1998–2013. Environmental Research Letters, 17(9), (2022): 094021, https://doi.org/10.1088/1748-9326/ac88e5.

Description: Large ensemble simulations with six atmospheric general circulation models involved are utilized to verify the interdecadal Pacific oscillation (IPO) impacts on the trend of Eurasian winter surface air temperatures (SAT) during 1998–2013, a period characterized by the prominent Eurasia cooling (EC). In our simulations, IPO brings a cooling trend over west-central Eurasia in 1998–2013, about a quarter of the observed EC in that area. The cooling is associated with the phase transition of the IPO to a strong negative. However, the standard deviation of the area-averaged SAT trends in the west EC region among ensembles, driven by internal variability intrinsic due to the atmosphere and land, is more than three times the isolated IPO impacts, which can shadow the modulation of the IPO on the west Eurasia winter climate.

Description: This work is funded by the JPI Climate-Oceans ROADMAP and the Blue‐Action Project (European Union's Horizon 2020 research and innovation program, 727852). The CAM6-Nor simulations were performed on resources provided by UNINETT Sigma2—the National Infrastructure for High Performance Computing and Data Storage in Norway (nn2343k, NS9015K). The simulations of IAP4.1 were supported by National Key R&D Program of China 2017YFE0111800.

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Yamamoto, A., Nonaka, M., Martineau, P., Yamazaki, A., Kwon, Y.-O., Nakamura, H., & Taguchi, B. Oceanic moisture sources contributing to wintertime Euro-Atlantic blocking. Weather and Climate Dynamics, 2(3), (2021): 819–840, https://doi.org/10.5194/wcd-2-819-2021.

Description: Although conventionally attributed to dry dynamics, increasing evidence points to a key role of moist dynamics in the formation and maintenance of blocking events. The source of moisture crucial for these processes, however, remains elusive. In this study, we identify the moisture sources responsible for latent heating associated with the wintertime Euro-Atlantic blocking events detected over 31 years (1979–2010). To this end, we track atmospheric particles backward in time from the blocking centres for a period of 10 d using an offline Lagrangian dispersion model applied to atmospheric reanalysis data. The analysis reveals that 28 %–55 % of particles gain heat and moisture from the ocean over the course of 10 d, with higher percentages for the lower altitudes from which particles are released. Via large-scale ascent, these moist particles transport low-potential-vorticity (PV) air of low-altitude, low-latitude origins into the upper troposphere, where the amplitude of blocking is the most prominent, in agreement with previous studies. The PV of these moist particles remains significantly lower compared to their dry counterparts throughout the course of 10 d, preferentially constituting blocking cores. Further analysis reveals that approximately two-thirds of the moist particles source their moisture locally from the Atlantic, while the remaining one-third of moist particles source it from the Pacific. There is also a small fraction of moist particles that take up moisture from both the Pacific and Atlantic basins, which undergo a large-scale uplift over the Atlantic using moisture picked up over both basins. The Gulf Stream and Kuroshio and their extensions as well as the eastern Pacific northeast of Hawaii not only provide heat and moisture to moist particles but also act as “springboards” for their large-scale, cross-isentropic ascent, where its extent strongly depends on the humidity content at the time of the ascent. While the particles of Atlantic origin swiftly ascend just before their arrival at blocking, those of Pacific origin begin their ascent a few days earlier, after which they carry low-PV air in the upper troposphere while undergoing radiative cooling just as dry particles. A previous study identified a blocking maintenance mechanism, whereby low-PV air is selectively absorbed into blocking systems to prolong blocking lifetime. As they used an isentropic trajectory analysis, this mechanism was regarded as a dry process. We found that these moist particles that are fuelled over the Pacific can also act to maintain blocks in the same manner, revealing that what appears to be a blocking maintenance mechanism governed by dry dynamics alone can, in fact, be of moist origin.

Description: This research has been supported by the Japan Society for the Promotion of Science (JSPS) (grant nos. JP19H05701, JP19H05702, JP19H05703, JP19H05704 on Innovative Areas 6102, and JP20H01970), the Japan Science and Technology Agency through Belmont Forum CRA “InterDec” and COI-NEXT (grant no. JPMJPF2013), the Japanese Ministry of Environment through the Environment Research and Technology Development Fund (grant no. JPMEERF20192004), the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) through the Arctic Challenge for Sustainability (ArCS and ARCS II; grant nos. JPMXD1300000000 and JPMXD1420318865) programmes, the Japanese Ministry of Environment through the Environment Research and Technology Development Fund (grant no. 2-1904), the US NSF Climate & Large Scale Dynamics Program (grant no. AGS-2040073), and the US DOE CESD Regional and Gloabal Model Analysis programme (grant no. DE-SC0019492). Patrick Martineau was partly supported by Grant-in-Aid for JSPS Research Fellows.

Description: A regime shift in the formation mechanisms of the North Pacific subtropical mode water (NPSTMW) and its causes were investigated using a 2,000-year-long pre-industrial control simulation of a fully coupled atmosphere-ocean-sea ice model. The volume budget analysis revealed that the air-sea flux and ocean dynamics (OD) were the two primary driving mechanisms for NPSTMW formation, but their relative importance has periodically alternated in multidecadal timescales of approximately 50–70 years. The regime shift of the NPSTMW formation was closely related to the meridional (50 years) and zonal (70 years) movements of the Aleutian Low (AL). When AL shifted to the south or east, it induces the sea surface height anomalies propagating westward from the central North Pacific and preconditions the NPSTMW formation, thus the OD become relatively more important. Key Points: - Driving mechanisms for the North Pacific subtropical mode water formation exhibit a regime shift with a periodicity of about 50–70 years - Multidecadal regime shifts are associated with meridional and zonal shifts in the Aleutian Low (AL) - Position shift of the AL affects the variability of the local air-sea flux and remotely driven oceanic dynamics