著者

Yousuke Yamashita Hideharu Akiyoshi Makoto Inoue

出版者

公益社団法人 日本気象学会

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

pp.19B-002, (Released:2023-10-18)

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The dynamical response of the southern hemisphere stratosphere to the ocean-surface conditions in 2002 and 2019, when exceptional sudden stratospheric warming (SSW) events occurred, was examined through the chemistry–climate model and experiments with 1,000 ensemble members using the sea-surface temperature (SST) and sea-ice conditions. Planetary waves propagating from the troposphere to the stratosphere in experiments using the ocean-surface conditions in 2002 and 2019 were markedly enhanced compared to those in experiments using climatological ocean conditions, owing to the enhancement of the zonal wavenumber-2 component in August 2002 and the wavenumber-1 component from August to November 2019. The distribution function from the ensemble members of the Antarctic polar-vortex intensity shifted to a weaker side in the 2002 and 2019 experiments relative to that of the climatological ocean conditions. The planetary wave propagation to the stratosphere was more enhanced in 2019 than in 2002 from austral winter to spring. This result is consistent with the weakening of the Antarctic polar-vortex intensity in the 2019 experiment relative to the 2002 experiment. These results suggest that the SSWs in 2002 and 2019 are closely related to the ocean surface conditions in these years through wave propagation in the troposphere and stratosphere.

著者

Prabir K. Patra Masayuki Takigawa Shingo Watanabe Naveen Chandra Kentaro Ishijima Yousuke Yamashita

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.91-96, 2018 (Released:2018-07-21)

参考文献数

37

被引用文献数

42

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The accuracy of chemical tracer simulations by atmospheric general circulation model (AGCM)-based chemistry-transport models (ACTMs) depends on the quality of AGCM transport properties, even when the meteorology is nudged towards the reanalysis fields. Here we show that significant improvements in tracer distribution are achieved when hybrid vertical coordinate is implemented in MIROC4.0 AGCM, compared to its predecessors AGCM5.7b based on sigma coordinate. Only explicitly resolved gravity waves are propagated into the stratosphere in MIROC4-ACTM. The MIROC4-ACTM produces “age-of-air” up to about 5 years in the tropical upper stratosphere (∼1 hPa) and about 6 years in the polar middle stratosphere (∼10 hPa), in agreement with observational estimates. Comparisons of MIROC4-ACTM simulation with observed sulphur hexafluoride (SF6) in the troposphere also show remarkable improvements over the AGCM57b-ACTM simulation. MIROC4-ACTM is characterized by weaker convective mass flux and thus older age of air in the tropical troposphere, relative to AGCM57b-ACTM. The role of convective transport on tracer simulations is depicted using vertical cross-sections of 222Rn (radon) distributions. Both the ACTM versions show similar results when compared with 222Rn measurements at remote sites. All aspects of tracer transport in MIROC4-ACTM is promising for inverse modelling of greenhouse gases sources and sinks at reduced bias.

著者

Kentaro Ishijima Masayuki Takigawa Yousuke Yamashita Hisashi Yashiro Chihiro Kodama Masaki Satoh Kazuhiro Tsuboi Hidekazu Matsueda Yosuke Niwa Shigekazu Hirao

出版者

Meteorological Society of Japan

雑誌

SOLA (ISSN:13496476)

巻号頁・発行日

vol.14, pp.111-115, 2018 (Released:2018-08-21)

参考文献数

27

被引用文献数

3

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Atmospheric radon-222 (222Rn) variability is analyzed and compared with model simulations made by the Nonhydrostatic Icosahedral Atmospheric Model (NICAM), with three horizontal resolutions (223, 56, and 14 km), in order to understand high 222Rn events predominantly caused by frontal activities. Seasonal variations of event frequency are well reproduced by the model, with correlation coefficients of 0.79 (223 km) to 0.99 (14 km). The three horizontal resolutions can reproduce general features of the observed peak shapes of events in winter, which dominantly reflect the passage of cold fronts that trap dense amounts of 222Rn. Peak height and width are well reproduced by the 56 km and 14 km resolution models, while the 223 km resolution model shows much lower and broader peaks due to insufficient resolution. We also find that simulations of 222Rn and equivalent potential temperature gradient (|∇θe|) during the events show similar horizontal distributions around the 222Rn observation station, suggesting |∇θe| is a useful tool to understand the variability of atmospheric components around fronts. Consequently, model with horizontal resolution of 56 km and 14 km can well simulate spatiotemporal variations of atmospheric components driven by frontal activities, while 223 km resolution is not enough to reproduce them.

著者

Yousuke YAMASHITA Hideharu AKIYOSHI Theodore G. SHEPHERD Masaaki TAKAHASHI

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

vol.93, no.6, pp.629-644, 2015 (Released:2016-01-13)

参考文献数

52

被引用文献数

7 9

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The combined influences of the westerly phase of the quasi-biennial oscillation (QBO-W) and solar maximum (Smax) conditions on the Northern Hemisphere extratropical winter circulation are investigated using reanalysis data and Center for Climate System Research/National Institute for Environmental Studies chemistry climate model (CCM) simulations. The composite analysis for the reanalysis data indicates strengthened polar vortex in December followed by weakened polar vortex in February-March for QBO-W during Smax (QBO-W/Smax) conditions. This relationship need not be specific to QBO-W/Smax conditions but may just require strengthened vortex in December, which is more likely under QBO-W/Smax. Both the reanalysis data and CCM simulations suggest that dynamical processes of planetary wave propagation and meridional circulation related to QBO-W around polar vortex in December are similar in character to those related to Smax; furthermore, both processes may work in concert to maintain stronger vortex during QBO-W/Smax. In the reanalysis data, the strengthened polar vortex in December is associated with the development of north-south dipole tropospheric anomaly in the Atlantic sector similar to the North Atlantic oscillation (NAO) during December-January. The structure of the north-south dipole anomaly has zonal wavenumber 1 (WN1) component, where the longitude of anomalous ridge overlaps with that of climatological ridge in the North Atlantic in January. This implies amplification of the WN1 wave and results in the enhancement of the upward WN1 propagation from troposphere into stratosphere in January, leading to the weakened polar vortex in February-March. Although WN2 waves do not play a direct role in forcing the stratospheric vortex evolution, their tropospheric response to QBO-W/Smax conditions appears to be related to the maintenance of the NAO-like anomaly in the high-latitude troposphere in January. These results may provide a possible explanation for the mechanisms underlying the seasonal evolution of wintertime polar vortex anomalies during QBO-W/Smax conditions and the role of troposphere in this evolution.