Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
In, Teiji*; Nakayama, Tomoharu*; Matsuura, Yasutaka*; Shima, Shigeki*; Ishikawa, Yoichi*; Awaji, Toshiyuki*; Kobayashi, Takuya; Kawamura, Hideyuki; Togawa, Orihiko; Toyoda, Takahiro*
no journal, ,
The Shimokita Peninsula (hereafter SP)is located at the northeast tip of Honshu (the main island of Japan) and borders on the northwestern part of the North Pacific Ocean (hereafter NWNP) in the east and the Tsugaru Strait (hereafter TS) in the north. It is known that the NWNP off the SP assumes a complex water mass structure. Seawater of Japan Sea origin, called the Tsugaru Warm Water (TWW) component, takes on a characteristic seasonal variation. Conlon (1982) pointed out that during winter and spring, the TWW in the NWNP propagates southward along the coast of the peninsula (the coastal mode), and swirls off the peninsula from summer to autumn (the gyre mode). It is necessary to accurately reproduce the striking circulation patterns and the complicated water mass structures in this area with an ocean general circulation model (OGCM). We need to use a fine-scale grid, probably such as 1-2 km in size to reproduce the water mass structure around the TS and the off the SP in detail. To initialize the forecast system, we use a 4-dimensional variational method of data assimilation. A forecast experiment on the basis of oceanographic observations made in 2003 (a hindcast experiment) illustrates the good performance of our system. We shall focus, in particular, on the shift from the coastal mode to the gyre mode and vice versa.
Hirose, Naoki*; Kawamura, Hideyuki; Yamamoto, Masaru*
no journal, ,
This presentation reports our assimilation modeling efforts in the Japan/East Sea. An eddy-resolving, free-surface ocean circulation model is driven by daily meteorological forcing of JMA regional forecast at the surface and monthly measurement data at the horizontal boundary. The top layer is restored to the remotely-sensed temperature. The SST assimilation reduces the average residual variance from 4.55 to 2.09 degC
and presents small-scale features even finer than the original data set. An approximate Kalman filter corrects the subsurface density and velocity conditions based on the difference between the observation and the model at the sea surface height. The sequential updates of the error covariance require more computational overheads than the steady covariance but significantly corrects high-frequency barotropic changes of the northern waters. The assimilated results show realistic upper circulations such as the separation of the East Korean Warm Current or the quasi-biennial oscillation in comparison to in-situ subsurface measurements. The study also demonstrates that the assimilated estimates of the JES improve winter atmospheric conditions from meso to seasonal scales. The sharp frontal structure of the assimilated SST strongly modifies the mesoscale features over the southern JES as simulated by a non-hydrostatic atmospheric model. It is also found that the total amount of the DJF precipitation is lead by the regional NDJ SST and is further controlled by autumn transport of the Tsushima Warm Current.