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height (SSH) and SST estimates provided by satellites, if correctly incorporated into the assimilation system, can be used to provide skillful forecast of the three-dimensional circulation up to 2 weeks into the future using ROMS. To provide a robust evaluation of the assimilation system, we study 2 yr of mesoscale ocean circulation in the EAC ( sections 2 ). The observations used for assimilation and validation during the 2-yr period are described in section 3 , and the IS4DVAR assimilation
height (SSH) and SST estimates provided by satellites, if correctly incorporated into the assimilation system, can be used to provide skillful forecast of the three-dimensional circulation up to 2 weeks into the future using ROMS. To provide a robust evaluation of the assimilation system, we study 2 yr of mesoscale ocean circulation in the EAC ( sections 2 ). The observations used for assimilation and validation during the 2-yr period are described in section 3 , and the IS4DVAR assimilation
AUGUST I987 RIENECKER, MOOERS AND ROBINSON 1189Dynamical Interpolation and Forecast Of the Evolution of Mesoscale Features off Northern CaliforniaMICHELE M. RIENECKERl AND CHRISTOPHER N. Ko MOOERS1 Dept. of Oceanography, Naval Postgraduate School, Monterey, CA 93943 ALLAN R. ROBINSONCenter for Earth and Planetary Physics, Harvard University, Cambridge, MA 02138
AUGUST I987 RIENECKER, MOOERS AND ROBINSON 1189Dynamical Interpolation and Forecast Of the Evolution of Mesoscale Features off Northern CaliforniaMICHELE M. RIENECKERl AND CHRISTOPHER N. Ko MOOERS1 Dept. of Oceanography, Naval Postgraduate School, Monterey, CA 93943 ALLAN R. ROBINSONCenter for Earth and Planetary Physics, Harvard University, Cambridge, MA 02138
covariances between modalstreamfunction and velocity fields. The former is found to be approximately zero and the latter havesignificant extrema at lag distances comparable to an eddy radius. Furthermore, the dominant contribution to these coupling signals comes from the time-averaged (over a little more than two months) mesoscale field, which from lengthy moored observations we can identify as an instantaneous realization ofthe very low frequency "secular scale" described by Schmitz (1978). Forecasts
covariances between modalstreamfunction and velocity fields. The former is found to be approximately zero and the latter havesignificant extrema at lag distances comparable to an eddy radius. Furthermore, the dominant contribution to these coupling signals comes from the time-averaged (over a little more than two months) mesoscale field, which from lengthy moored observations we can identify as an instantaneous realization ofthe very low frequency "secular scale" described by Schmitz (1978). Forecasts
the boundaryconditions and .the interior evolves as determined by dynamics. Away from boundary condition induced errors,the dynamical model is able to maintain a high level of correlation between the forecast and analyzed fields for20 days. Also, the accuracy may be affected by the position of the data relative to the forecast domain. Theimplications for sampling strategies are discussed. These results are important to ocean scientists on several fronts. In studying mesoscale processes, a
the boundaryconditions and .the interior evolves as determined by dynamics. Away from boundary condition induced errors,the dynamical model is able to maintain a high level of correlation between the forecast and analyzed fields for20 days. Also, the accuracy may be affected by the position of the data relative to the forecast domain. Theimplications for sampling strategies are discussed. These results are important to ocean scientists on several fronts. In studying mesoscale processes, a
level of no motion, 3) the effects of surrounding mesoscale activity, 4) variations in the boundaryconditions, and 5 ) simple assimilation of newly acquired data into the forecasts are carded out. Using a feature validation technique, which incorporates a 1 ) validating hydrocast survey, 2) satellite SSTimages, and 3 ) surface drifter observations, most of the forecasts are found to perform well in capturing the keyevents of the validation strategy, particularly the development of the cold tongue
level of no motion, 3) the effects of surrounding mesoscale activity, 4) variations in the boundaryconditions, and 5 ) simple assimilation of newly acquired data into the forecasts are carded out. Using a feature validation technique, which incorporates a 1 ) validating hydrocast survey, 2) satellite SSTimages, and 3 ) surface drifter observations, most of the forecasts are found to perform well in capturing the keyevents of the validation strategy, particularly the development of the cold tongue
observations over strong SST fronts throughout the world’s oceans (see reviews by Xie 2004 ; Chelton et al. 2004 ; Small et al. 2008 ). Previous evaluations of mesoscale, global, and climate numerical model forecasts, however, indicate that the models underrepresent the small-scale (∼25 km) interaction between the ocean and atmosphere. Coupling coefficients are only about half, or less, of those inferred from satellite observations ( Chelton 2005 ; Maloney and Chelton 2006 ; Chelton et al. 2007 ; Seo
observations over strong SST fronts throughout the world’s oceans (see reviews by Xie 2004 ; Chelton et al. 2004 ; Small et al. 2008 ). Previous evaluations of mesoscale, global, and climate numerical model forecasts, however, indicate that the models underrepresent the small-scale (∼25 km) interaction between the ocean and atmosphere. Coupling coefficients are only about half, or less, of those inferred from satellite observations ( Chelton 2005 ; Maloney and Chelton 2006 ; Chelton et al. 2007 ; Seo
for the waves to adjust to the wind changes; that is, the sea has not had a chance to become well developed. 4. Summary and conclusions In this study the impact of coupled atmospheric–ocean wave models was examined in the context of mesoscale short-term forecasts with real cases of rapidly developing storms, thus extending previous studies on idealized cases. It should be emphasized here that the results obtained in this study are valid for the temporal scale ∼2 days and a spatial scale in the
for the waves to adjust to the wind changes; that is, the sea has not had a chance to become well developed. 4. Summary and conclusions In this study the impact of coupled atmospheric–ocean wave models was examined in the context of mesoscale short-term forecasts with real cases of rapidly developing storms, thus extending previous studies on idealized cases. It should be emphasized here that the results obtained in this study are valid for the temporal scale ∼2 days and a spatial scale in the
energctics and spectra of the simulatedenvironments have confirmed the effect ofbiharmonic friction in suppressing small-scale motion while maintainingthe mesoscale. However, a new result concerns the impact of this scale selectivity on simulated underwateracoustic fields and the possible consequences of this for ocean forecast models and acoustic tomography applications. Acoustic effects have been quantified in terms of the differences in predicted sound intensity levels betweenharmonic and
energctics and spectra of the simulatedenvironments have confirmed the effect ofbiharmonic friction in suppressing small-scale motion while maintainingthe mesoscale. However, a new result concerns the impact of this scale selectivity on simulated underwateracoustic fields and the possible consequences of this for ocean forecast models and acoustic tomography applications. Acoustic effects have been quantified in terms of the differences in predicted sound intensity levels betweenharmonic and
real cases of developing systems. The results indicate that the effects of coupling on the evolution and synoptic-scale aspects of the storm are rather weak, while small beneficial effects are noted on surface parameters. The study also demonstrates that the present generation of atmospheric mesoscale models does not need to know precisely the sea state, at such resolution, in order to produce reasonably accurate short-term forecasts. Knowledge of the sea state certainly does not deteriorate the
real cases of developing systems. The results indicate that the effects of coupling on the evolution and synoptic-scale aspects of the storm are rather weak, while small beneficial effects are noted on surface parameters. The study also demonstrates that the present generation of atmospheric mesoscale models does not need to know precisely the sea state, at such resolution, in order to produce reasonably accurate short-term forecasts. Knowledge of the sea state certainly does not deteriorate the
.e,,a pure forecast), Although some mesoscale meanders and rings are not well produced by the assimilation model,consistent reduction of errors by the assimilation is demonstrated. The vertical distribution of errors revealsthat the scheme is most effective in nowcasting temperatures at middepth (around 500 m) and less effectivenear the surface and in the deep ocean. The scheme is also more effective in nowcasting the Gulf Stream axislocation than in nowcasting temperature variations. A comparison of the
.e,,a pure forecast), Although some mesoscale meanders and rings are not well produced by the assimilation model,consistent reduction of errors by the assimilation is demonstrated. The vertical distribution of errors revealsthat the scheme is most effective in nowcasting temperatures at middepth (around 500 m) and less effectivenear the surface and in the deep ocean. The scheme is also more effective in nowcasting the Gulf Stream axislocation than in nowcasting temperature variations. A comparison of the
