- 著者
- Takeshi ENOMOTO Shozo YAMANE Wataru OHFUCHI
- 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.2, pp.199-213, 2015 (Released:2015-05-14)
- 参考文献数
- 31
- 被引用文献数
- 8 10
Simple methods are formulated using an ensemble forecast to identify the sensitive initial perturbations that grow in a specified region at the verification time. These methods do not require the tangent-linear or adjoint models, but use an ensemble forecast to obtain approximated solutions. Input to the sensitivity calculation can be any ensemble forecast integrated from initial conditions perturbed with the bred vector, singular vector, or ensemble Kalman filter methods. Two formulations are presented here to approximate the adjoint and singular vector methods using an ensemble forecast. The ensemble singular vector sensitivity, which has already been applied in previous studies, is obtained with a single eigenvector calculation. The ensemble adjoint sensitivity only requires an even simpler matrix-vector multiplication. To validate the formulations, ensemble-based sensitivity analysis has been conducted in a few cases. First, the two methods were applied to identify the sensitive initial perturbations that grow in the verification region over Japan in January and August 2003. The first singular vector mode indeed achieves the largest amplitude at the verification time, but that is not necessarily true after the verification time. Both methods can identify the sensitive regions more specifically than the regions with large ensemble spread in cases with a mid-latitude cyclone and with a tropical cyclone. The monthly-mean sensitivity in January 2003 indicates the effect of Rossby waves and synoptic disturbances in upstream sensitive regions over Siberia, Tibet, and a downstream sensitive region in the north-western Pacific; the sensitivity in August 2003 suggests the influence of the Asian summer monsoon. Next, for an August 2002 storm case in Europe, global 20-km resolution simulations were conducted from the initial conditions perturbed by the ensemble singular vector method to compare with the unperturbed simulation. In the perturbed simulation, the cyclone is deeper by a few hPa in its north-east sector with more precipitation north of the Alps more consistently with observations. These results indicate that reasonable sensitive regions can be identified with our methods.
- 著者
- Takeshi ENOMOTO Hirokazu ENDO Yayoi HARADA Wataru OHFUCHI
- 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.87, no.1, pp.139-156, 2009 (Released:2009-03-07)
- 参考文献数
- 43
- 被引用文献数
- 13 14
In July 2004, torrential rainfalls caused significant damages in parts of Japan, followed by heat waves. Our data analysis shows that both rainfall and heat wave events in late Baiu season were caused by the intensification of the subtropical anticyclone near Japan (Bonin high) and that intensity of the Bonin high was significantly influenced by propagation of Rossby waves along the subtropical jet. Hindcast experiments from 15 July were conducted to study the mechanisms and predictability of these high-impact weather events. On 17-18 July, localized rainfalls at a few locations along the coast of the Sea of Japan including Sakata and Fukui were successfully simulated in a high-resolution (21-km mesh) global hindcast simulation. These rainfall events were found to occur near the leading edge of a filament of moist and warm air advected clockwise. On 20 July, anomalously high temperature was reproduced in the high-resolution hindcast simulation. With a moderate resolution of 83 km, the intensification of the subtropical anticyclone was reproduced although the föhn was much weaker. This result indicates that temperature distribution associated with föhn requires a resolution high enough to resolve major mountains. In order to investigate the predictability of propagation of Rossby waves and intensification of the Bonin high, 25-member ensemble experiments from 1 July 2004 were conducted using the moderate-resolution model. It is shown that the region along the Asian jet has twice as long predictability as the entire Northern Hemisphere. This case study suggests that the intensification of the Bonin high associated with the propagation of Rossby waves along the Asian jet could be predicted a few weeks in advance with an ensemble forecast at a moderate resolution.