Seminar Schedule
64th APL Open Forum
- Date & Time:
- 15 May, Friday, 14:30-16:00
- Place:
- Remote telecon by Zoom
- Speaker 1:
- Yasumasa Miyazawa
- Title:
- Future directions of JCOPE ocean model development
- Abstract:
- Now JCOPE group is restructuring all models based on a code (JCOPE-T) developed for high-resolution tide resolving simulations targeting Japan coastal seas. JCOPE-T is well designed for MPI-base parallelization and use of various kinds of atmospheric forcing data. By fully utilizing these aspects of the JCOPE-T code, we are planning design of a new ensemble prediction system targeting longer-term Kuroshio path variations and other large-scale oceanic phenomena possibly driven by the predictable climate modes.
- Speaker 2:
- Yushi Morioka
- Title:
- Remote and local processes controlling decadal sea-ice variability over the Weddell Sea
- Abstract:
- Antarctic sea ice undergoes remarkable seasonal-decadal variations during the satellite period, although it does not show any significant decreasing trend in contrast to Arctic sea ice. Among the Antarctic Seas, the Weddell Sea, located east of the Antarctic Peninsula, represents pronounced decadal sea-ice variability, but the underlying physical mechanisms are poorly understood. Observational analysis shows that decadal increase in sea-ice concentration (SIC) over the Weddell Sea is preceded by easterly wind anomalies. The observed relationship is confirmed in a 300-yr simulation of the SINTEX-F2 model, demonstrating that the easterly wind anomalies act to weaken upwelling of warm water from the subsurface ocean and the associated ocean mixing/diffusion, and lower the near-surface ocean temperature thereby inducing the SIC increase. The zonal wind variability has a close relation to atmospheric intrinsic variability in the mid-high latitudes, called the Southern Annular Mode (SAM). Another sensitivity experiment, in which interannual SST variations are suppressed outside the Weddell Sea and the South Atlantic, reveals that anomalous cooling of near-surface ocean temperature is induced by anomalous northward outflow of warm water from the northern Weddell Sea linked with the zonal wind variability and anomalous westward inflow of cold water from the eastern Weddell Sea accompanied by strengthening of the clockwise Weddell Gyre. The strengthening of the Weddell Gyre is associated with an increase in ocean density, which is mostly due to an increase in salinity induced by enhanced surface evaporation during the transition period of low-to-high sea ice. These results indicate that remote atmospheric forcing together with the local ice-ocean interaction is greatly important for generation of decadal sea-ice variability over the Weddell Sea.
63th APL Open Forum
- Date & Time:
- 24 April, Friday, 14:30-16:00
- Place:
- Remote telecon by Zoom
- Speaker 1:
- Swadhin Behera
- Title:
- A global wavenumber-4 pattern in SST anomalies of southern mid-latitudes
- Abstract:
- A stationary zonal wavenumber-4 pattern (W4) in sea surface temperature (SST) anomaly is found in the southern mid-latitudes during austral summer. It is found to be linked to a Rossby wave train triggered by atmospheric convections in the central tropical Pacific. The southern subtropical westerly jet acts as the wave guide to circumnavigate the signal and generate an anomalous barotropic W4 in the atmosphere. The W4 in SST anomaly is subsequently observed during the month of November-December, which persists over the region till April-May through wind-MLD-SST feedback processes. Correlation analysis suggests that this atmosphere-ocean mode is linearly independent of other natural variabilities such as El Niño Southern Oscillation and Southern Annular Mode.
- Speaker 2:
- Ryo Furue
- Title:
- Spatial, temporal, and statistical properties of the deep zonal jets in the eastern North Pacific in an eddy-resolving ocean general circulation model (OFES)
60th APL Open Forum
- Date & Time:
- 24 January, Friday, 14:30-16:00
- Place:
- Meeting Room, 6th floor, IT Building, Yokohama Institute
- Speaker 1:
- Akira Yamazaki
- Title:
- Toward practical use of EFSO for the weekly forecast: Dynamics of propagation of observation impacts
- Abstract:
- This study tests the usefulness of an ensemble-based forecast sensitivity to observations (EFSO) diagnosis implemented in an AFES-LETKF data assimilation system for the estimation of the impacts of specific observations in the quasi-operational global observing system on weekly short- and medium-range forecasts. EFSO can quantify how much each observation has improved or degraded the forecast without observing-system (data denial or addition) experiments, that is, an offline diagnosis. Here, it was examined whether the EFSO values can be used to quantify the impacts of a subset of observations done in a specific geographical spot in 6-hour–7-day forecasts. In the observing-system experiments EFSO values were compared with actual observation impacts obtained from 12 data denial experiments in each of which a subset of 3 radiosonde observations launched from a geographical spot was excluded. The 12 spots were selected from 3 latitudinal bands, which were composed of (i) 4 Arctic regions, (ii) 4 midlatitude regions in the Northern Hemisphere, and (iii) 4 tropical regions during the winter of 2015/16. The results showed that all the EFSO values reasonably estimated observation impacts on the short-range (6-hour–2-day) forecast. Furthermore, it was found that the initial Arctic observation impacts, which could be estimated by EFSO, remained in the medium-range (~7 days) forecast, because the Arctic is located at upstream of dynamical propagation toward the midlatitudes where small perturbations grow rapidly and spontaneously. It is concluded that EFSO can be useful for the weekly forecast for anticipating impacts of specific observations by considering dynamical propagation.
- Speaker 2:
- Pascal Oettli
- Title:
- Monthly mean surface air temperature prediction in the Kanto region
- Abstract:
- In Kanto region, a strong correlation exists between summer and winter temperatures and the electric power demand. Identification of the sources of variability in this region is crucial for power demand forecasting few months ahead.
Due to the ocean memory effect, sea-surface temperature (SST) anomalies are considered as a source of predictability of surface air temperature (SAT) anomalies, with different time lag. In this way, conditions in the equatorial Pacific are known to influence SAT anomalies in Japan, both in summer and winter. Thus, predicting tropical SST conditions few months ahead helps to estimate the sign of the SAT anomalies in Kanto.
Over the years, SINTEX-F2 seasonal prediction system proved its ability to accurately predict SST anomaly, particularly in the tropics, few months in advance. Nevertheless, skills drastically drops when it comes to predict SAT anomalies in the mid-latitudes, particularly because the teleconnection patterns are not well predicted by the system.
Here we try to restore the teleconnection between tropical SST and SAT in Kanto region with the help of statistics, proposing a hybrid model, combining dynamical prediction of SST by SINTEX-F2 and statistical prediction of SAT in Kanto region.