In order to understand the fluctuations imposed upon low frequency (50 to 500 Hz) acoustic signals due to coastal internal waves, a large multilaboratory, multidisciplinary experiment was performed in the Mid-Atlantic Bight in the summer of 1995. This experiment featured the most complete set of environmental measurements (especially physical oceanography and geology) made to date in support of a coastal acoustics study. This support enabled the correlation of acoustic fluctuations to clearly observed ocean processes, especially those associated with the internal wave field. More specifically, a 16 element WHOI vertical line array (WVLA) was moored in 70 m of water off the New Jersey coast. Tomography sources of 224 Hz and 400 Hz were moored 32 km directly shoreward of this array, such that an acoustic path was constructed that was anti-parallel to the primary, onshore propagation direction for shelf generated internal wave solitons. These nonlinear internal waves, produced in packets as the tide shifts from ebb to flood, produce strong semidiurnal effects on the acoustic signals at our measurement location. Specifically, the internal waves in the acoustic waveguide cause significant coupling of energy between the propagating acoustic modes, resulting in broadband fluctuations in modal intensity, travel-time, and temporal coherence. The strong correlations between the environmental parameters and the internal wave field include an interesting sensitivity of the spread of an acoustic pulse to solitons near the receiver.
The evaluation of hurricane forecast skill requires ensembles of historical forecasts. The purpose of this article is not to undertake such an evaluation, but rather to demon strate the current status of satellite physical retrievals and their potential to provide valu able information for such evaluations and contribute to model improvements. Figure 3 shows a pictorial example of the 120-hour accumulated surface rainfall from satellite retrievals, and from single high-resolution forecasts from ECMWF and NASA models.Predictions The hurricane in the ECMWF forecast, though, deviates by two to three degrees east of the best track, and makes landfall between Ala bama and Florida about 12 hours late. These differences in the hurricane track and accu mulated precipitation may reflect inadequa cies in the large-scale circulation provided in the initial conditions, or imperfect model physical parameterizations, but also may be due to the system's lack of predictability.
Developments in Hurricane ForecastsAdvances in spaceborne observations and numerical weather prediction (NWP) models provide new opportunities for improving hurricane forecasts. Apart from their impor tance for NWR global atmospheric models of hurricanes and their forecasts represent an important and unique test bed of model formulations.Recent developments that include moving from synoptic-scale-resolving to mesoscaleresolving global models show some very encouraging results. In addition to increasing resolution and including more physically based parameterizations on mesoscale effects in conventional general circulation models, cloud-scale-resolving global models-in which the cloud dynamics and mesoscale processes are explicitly resolved-also are being devel oped and could be used as a parallel approach to more realistically simulate hurricanes in global models in the future.Better resolution of the hurricane struc ture and larger-scale steering circulation, along with improved initial conditions pro vided by high-resolution satellite data and sophisticated data assimilation systems, could lead to better detection, monitoring, under standing, and prediction of the genesis and development of hurricanes that have such a devastating impact on society.
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