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This presentation will report on comparisons between ray travel times computed in a model and observations in the Northern Philippine Sea (NPS). The model is the MITgcm, configured with 50 vertical levels and 1/12 deg resolution in a domain covering 17–27 deg north and from the western boundary to 140 deg East. It is forced by surface fluxes from NCEP and NOGAPS products, and assimilated HYCOM 1/12 deg output is used for initial and boundary conditions. Sound speed profiles taken from the model will be compared to those from climatologies and from Argo floats in the region. Ray arrival times calculated using the time evolution of the model over several years will be calculated. The arrival pattern and its variability will be compared to observations and to calculations in climatologies. Ray arrival and ray path stability will be analyzed to assess the utility of travel time measurements for estimating ocean structure. This is a step in preparation for a model‐based analysis of the NPS.

A hydrophone was moored at mid depth in the South China Sea basin from November 2005 to October 2006. Operated with a 1‐min‐on and 14‐min‐off duty cycle and sampled at 1.6 kHz, the measured time series captures the spectral characteristics and variability of the ambient noise in the 0–800‐Hz band over an annual cycle. In this paper, we provide a description on the daily, monthly, and seasonal variabilities and variances in the measured noise spectrum and band levels. In order to gain insights into the predictability of the ambient noise field in this marginal sea, the interpretation of the data is facilitated with historical shipping density data and nowcast wind fields from the Navy Operational Global Atmospheric Prediction System (NOGAPS). Attention is made to the evolution of the ambient noise spectra during major storm events. Intermittent noises are also examined. The potential sources for these intermittent noises are discussed. [Research sponsored by the Office of Naval Research.]

Iron mines in Minnesota are ideally located to assess the accuracy of available atmospheric profiles used in infrasound modeling. These mines are located approximately 400 km away to the southeast (142) of the Lac‐Du‐Bonnet infrasound station, IS‐10. Infrasound data from June 1999 to March 2004 was analyzed to assess the effects of explosion size and atmospheric conditions on observations. IS‐10 recorded a suite of events from this time period resulting in well constrained ground truth. This ground truth allows for the comparison of ray trace and PE (Parabolic Equation) modeling to the observed arrivals. The tele‐infrasonic distance (greater than 250 km) produces ray paths that turn in the upper atmosphere, the thermosphere, at approximately 120 km to 140 km. Modeling based upon MSIS/HWM (Mass Spectrometer Incoherent Scatter/Horizontal Wind Model) and the NOGAPS (Navy Operational Global Atmospheric Prediction System) and NRL‐GS2 (Naval Research Laboratory Ground to Space) augmented profiles are used to interpret the observed arrivals.

Infrasonic waves can propagate thousands of kilometers in range and sample regions of the atmosphere from the ground up to and including the thermosphere. Conventional infrasound propagation modeling techniques rely on climatological models of mean temperatures and winds to characterize the environment. However, temperature and wind vary over temporal and spatial scales that are not captured by climatological models. Recent work addresses the integration of infrasound propagation models, such as three‐dimensional ray tracing, with numerical weather prediction models, such as the Navy Operational Global Atmospheric Prediction System (NOGAPS). Propagation results are computed using both climatological and updated atmospheric characterizations, and comparisons are presented. Implications for global infrasound monitoring are discussed. [Work supported by the Defense Threat Reduction Agency.]