著者

NAKAMURA Yuhi MIYAKAWA Tomoki SATOH Masaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2020-046, (Released:2020-06-02)

---

From 9 to 11 September 2015, the Kanto and Tohoku regions of Japan experienced an extremely heavy rainfall event. The synoptic-scale field was characterized by two typhoons, Etau (T1518) and Kilo (T1517). After Etau made landfall in the Tokai region and transformed into an extra-tropical cyclone over the Sea of Japan, meridionally oriented rain bands persisted over the Kanto region for about 12 hours and caused heavy rainfall, particularly over the Tochigi prefecture. During this time, Kilo approached the eastern ocean of the Kanto region. In this study, we examine the role of Kilo in this event by conducting numerical experiments using a stretched version of the Nonhydrostatic Icosahedral Atmospheric Model configured with a minimum grid interval of about 5.6 km. The control experiment reproduced intense rain bands around the same period and place as the observed event, although they were not reproduced in an experiment with a longer lead time. Sensitivity experiments were conducted in which Kilo was weakened by removing moisture in its central region with a longer lead time. In contrast to the expectation that reduced moisture would lead to a weaker typhoon and hence weaker rain, the sensitivity experiment reproduced the rain band with realistic location but 5 % less precipitation than the control experiment. Furthermore, this experiment indicated that precipitation over the outer band of Etau, which covers the Kanto region, increased by 10 % compared to the control experiment. We found that a southeasterly wind induced by a high-pressure ridge between Kilo and the Kanto region played a greater role in supplying moisture to the Kanto region than the strong easterly wind produced by the pressure gradient between Kilo and the Okhotsk high. In this case, weaker Kilo resulted in enhanced northwestward moisture flux associated with the ridge, thereby inducing heavier rainfall over the Kanto region.

著者

JINNO Takuya MIYAKAWA Tomoki SATOH Masaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-017, (Released:2018-12-07)

被引用文献数

3

---

In August 2016, a monsoon gyre persisted over the western North Pacific and was associated with the genesis of multiple devastating tropical cyclones. A series of hindcast simulations was performed using the nonhydrostatic icosahedral atmospheric model (NICAM) to reproduce the temporal evolution of this monsoon gyre. The simulations initiated at dates during the mature stage of the monsoon gyre successfully reproduced its termination and the subsequent intensification of the Bonin high, while the simulations initiated before the formation and during the developing stage of the gyre failed to reproduce subsequent gyre evolution even at a short lead time. These experiments further suggest a possibility that the development of the Bonin high is related to the termination of the monsoon gyre. High predictability of the termination is likely due to the predictable mid-latitudinal signals that intensify the Bonin high.

著者

MIYAKAWA Tomoki MIURA Hiroaki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2019-034, (Released:2019-02-11)

被引用文献数

7

---

The properties of tropical convection are evaluated using one-month long simulation datasets produced by the non-hydrostatic icosahedral atmospheric model (NICAM) using 3.5-, 7-, and 14-km horizontal meshes with identical cloud-microphysics configurations. The simulations are targeted on the 2nd Madden-Julian oscillation (MJO) event observed in the CINDY2011/DYNAMO field campaign. An increase of high cloud fraction at 200 hPa level and a reduction of surface precipitation occur as the horizontal resolution increases, corresponding to the reduction of precipitation efficiency due to the shorter residence time inside stronger updrafts that occur at the higher resolution. The increase of high cloud fraction is followed by the warming of the troposphere, which results in an increase in the column water vapor and an elevation of the freezing level. The total water condensation is decreased at higher resolutions, which is likely due to a balance with the decreased outgoing longwave radiation (OLR). The reproduced MJOs, which accounted for a large portion of the tropical convections, were similar in the 3.5-km and 14-km simulations in terms of eastward propagation speeds and structures, including the characteristic westward tilt of the moisture anomaly with height. However, the amplitude of the anomalous MJO circulation was considerably smaller in the 3.5-km simulation. The robust resolution dependence and the interpretations presented in this study underline the necessity for a resolution-aware cloud-microphysics optimization method that will have value in the coming era of global cloud-resolving simulations.

著者

SHIBUYA Ryosuke NAKANO Masuo KODAMA Chihiro NASUNO Tomoe KIKUCHI Kazuyoshi SATOH Masaki MIURA Hiroaki MIYAKAWA Tomoki

出版者

Meteorological Society of Japan

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2021-046, (Released:2021-04-08)

被引用文献数

5

---

In this study, we assessed the prediction skill of the Boreal Summer Intra-Seasonal Oscillation (BSISO) mode of one-month simulations using a global non-hydrostatic atmospheric model (NICAM) with explicit cloud microphysics and with a grid spacing of 14 km. The simulations were run as a series of hindcast experiments every day of August during 2000-2014; a total of 465 simulations were run with a 13950-day integration. On using forecast skill scores for statistical measurements, it was found that the model showed an overall BSISO prediction skill of approximately 24 days. The prediction skill tended to be slightly higher (∼ 2 days) when BSISO events began in the initial phases 7 to 1, which corresponded to the re-initiation phase of the BSISO, where a major convective center over the Philippine Sea decayed and a new convective envelope began aggregating over the western Indian Ocean. The phase speed and the evolution of the amplitude of the BSISO were well simulated by the model with a clear northwestward-southeastward tilted outgoing longwave radiation (OLR) structure over the Maritime continent and the western Pacific. However, the propagation speed was slower during phases 6-7, and the amplitude of the BSISO largely decayed during phases 8-1, which was likely to have been associated with the stagnant behavior of the convective cells over the Philippines. This stagnation of the propagation over the Philippines may be largely attributed to the small background southerlies bias in the model over the Philippines based on regression coefficient analysis using the moist static energy. The bias in the large-scale circulation was likely to have been associated with the bias in the moisture field and the associated background monsoonal circulation. We concluded that the model physics controlling the background fields are important factors for improving the BSISO prediction skill.

著者

MASUNAGA Ryusuke MIYAKAWA Tomoki KAWASAKI Takao YASHIRO Hisashi

出版者

公益社団法人 日本気象学会

雑誌

気象集誌. 第2輯 (ISSN:00261165)

巻号頁・発行日

pp.2023-010, (Released:2023-02-07)

---

High-resolution atmosphere–ocean coupled models are the primary tool for sub-seasonal to seasonal-scale (S2S) prediction. Seasonal-scale sea surface temperature (SST) drift is, however, inevitable because of the imbalance between the model components, which may deteriorate the prediction skill. Here, we examine the performance of a simple flux adjustment method specifically designed to suppress seasonal-scale SST drift through case studies. The Nonhydrostatic Icosahedral Atmospheric Model (NICAM)–Center for Climate System Research Ocean Component Model (COCO) coupled weather/climate model, named as NICOCO, was employed for wintertime 40-day integrations with a horizontal resolution of 14 km for the atmosphere and 0.25° for the ocean components. The coupled model with no flux adjustment suffers SST drift of typically -1.5–2°C in 40 days over the tropical, subtropical, and Antarctic regions. It is found that simple flux adjustment sufficiently suppressed the SST drift. Nevertheless, the lead-lag correlation analysis suggests that air–sea interactions are likely to be appropriately represented under flux adjustment. Thus, high-resolution coupled models with flux adjustment can substantially improve S2S prediction.