Abstract. From the fact that the Garrett-Munk-like (GM-like) internal wave spectrum is maintained even in regions of weak local energy sources, it is believed that energy is continuously supplied to the local wave spectrum by internal waves propagating from source regions where they are generated by wind stress fluctuations or tide-topography interactions. In order to examine how the energy thus supplied by propagating internal waves cascades through the local wave spectrum down to small dissipation scales, we carry out three sets of numerical experiments where the quasi-equilibrium internal wave spectrum obtained by Hibiya et al. [1996] is perturbed with forcing applied to different parts of the low-frequency low-wavenumber portion. The evolution of the internal wave spectrum is examined over eight inertial periods after the forcing is applied. First, in experiment I the forcing is applied to the low-vertical-wavenumber inertial-frequency (to --f) portion of the spectrum. In this case, no significant increase or decrease of spectral intensity can be seen within the two-dimensional wavenumber spectrum. Next, in experiment II the forcing is applied at low-vertical wavenumbers in the frequency range of 2f < to < 3f. In contrast to the result of experiment I, high-vertical-wavenumber nearinertial spectral values are seen to increase, exceeding the GM level as time progresses. Finally, in experiment III the forcing is applied at low-vertical wavenumbers in the frequency range of 1.6f < to < 2f. Although the spectral location of the forcing is very close to that assumed in experiment II, no appreciable energy transfer to high-vertical wavenumbers occurs in this case. From the results of these numerical experiments it is shown that the energy transfer to the small dissipation scales is dominated by parametric subharmonic instability which transfers energy from low-vertical-wavenumber waves with frequencies over 2f to high-vertical-wavenumber near-inertial (f < to < 2f) waves. This supports the model for the dynamic balance of the internal wave spectrum proposed by Hibiya et al. [1996] that with the increase (or decrease) of energy supply to the local internal wave spectrum, high-vertical-wavenumber near-inertial current shear is enhanced (or diminished) leading to an increase (or decrease) in the rate of energy dissipation at critical layers. IntroductionThe pattern and magnitude of the numerically reproduced general ocean circulation strongly depend on the values of eddy viscosity and diffusivity coefficients. This indicates that the evaluation of the intensity of turbulent vertical mixing at depth is crucial to accurate modeling of the large-scale general circulation [Bryan, 1987]. Mixing in the stratified ocean interior is generally considered to be associated with sporadic overturning and breaking of internal waves.The energy available for the mixing processes is originally supplied at large scales (a few tens of kilometers) and then transferred across the internal wave spectrum down to small dissipation scales ...

Synergistic applications of multi-resolution satellite data have been of a great interest among user communities for the development of an improved and more effective operational monitoring system of natural resources, including vegetation and soil. In this study, we conducted an inter-comparison of two remote sensing products, namely, visible/near-infrared surface reflectances and spectral vegetation indices (VIs), from the high resolution Advanced Thermal Emission and Reflection Radiometer (ASTER) (15 m) and lower resolution Moderate Resolution Imaging Spectroradiometer (MODIS) (250 m – 500 m) sensors onboard the Terra platform. Our analysis was aimed at understanding the degree of radiometric compatibility between the two sensors' products due to sensor spectral bandpasses and product generation algorithms. Multiple pairs of ASTER and MODIS standard surface reflectance products were obtained at randomly-selected, globally-distributed locations, from which two types of VIs were computed: the normalized difference vegetation index and the enhanced vegetation indices with and without a blue band. Our results showed that these surface reflectance products and the derived VIs compared well between the two sensors at a global scale, but subject to systematic differences, of which magnitudes varied among scene pairs. An independent assessment of the accuracy of ASTER and MODIS standard products, in which “in-house” surface reflectances were obtained using in situ Aeronet atmospheric data for comparison, suggested that the performance of the ASTER atmospheric correction algorithm may be variable, reducing overall quality of its standard reflectance product. Atmospheric aerosols, which were not corrected for in the ASTER algorithm, were found not to impact the quality of the derived reflectances. Further investigation is needed to identify the sources of inconsistent atmospheric correction results associated with the ASTER algorithm, including additional quality assessments of the ASTER and MODIS products with other atmospheric radiative transfer codes.

The experimental study of distributed systems and algorithms for large-scale internet platforms typically requires simulation of compute and network resources. This paper focuses on network simulation issues. While many packet-level network simulators are available and enable high-accuracy simulation, they can lead to prohibitively long simulation times. Consequently, a number of simulation frameworks have been developed that simulate networks at higher levels, thus enabling fast simulation but losing accuracy. One such framework, SimGrid, uses a flow-level approach that approximates the behavior of TCP networks, including TCP's bandwidth sharing properties.In this paper we perform a quantitative evaluation of Sim-Grid and compare it to popular packet-level simulators. We identify the regimes in which SimGrid's accuracy is comparable to that of these packet-level simulators, and the regimes in which SimGrid's accuracy may not be acceptable. We then describe an integration of the GTNetS packet-level simulator and SimGrid, which allows SimGrid users to easily opt either for fast but potentially inaccurate flow-level simulation or for accurate but potentially prohibitively slow packet-level simulation.

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