As part of PACS, Acoustic Rain Gauges (ARGs) were deployed on the NOAA TAO moorings at 8º, 10º, 12º N, 95º W and at 18º S, 85º W. Data from these moorings are available from Dec 1999 and will continue to the Nov 2003. Over 60 months of data from the 95W moorings are currently available for analysis, and one year of data from the 18S mooring. Rainfall data have been compared to co-located R.M. Young rain gauge data and to TRMM satellite rainfall products (3B42). Rainfall detection and accumulation are in good agreement, although limitations for each system have been identified. The acoustic system has excellent temporal resolution, but occasionally mooring noise inhibits measurements. The R.M. Young gauges are occasionally affected by fouling and piracy. The satellite measurement has a very different sampling strategy than the surface instruments and thus agreement is observed over monthly to seasonal time periods rather than individual rain events. During periods of no rain, good wind speed measurements are available from the ARGs. These data demonstrate that oceanic rainfall measurements can be made from underwater sound. The acoustic technology can be deployed on less expensive sub-surface moorings or even bottom-mounted observation systems with no instrumentation exposed at the sea surface.
During EPIC 2001, Acoustic Rain Gauges (ARGs) were present on the NOAA TAO moorings at 10º and12º N, 95º W. These instruments provide high temporal resolution rainfall measurements, including detection, rainfall rates and accumulations. Because different drop sizes have different acoustic signals underwater, drop size distributions estimates are also obtained. Comparisons to R.M. Young rain gauges show accumulation agreement over individual events. The accumulation comparisons are improved when the acoustic drop size distributions are used, versus a single frequency inversion for rainfall rate. Convective and stratiform portions of the rain events are identified acoustically. Comparison to the R.H. Brown shipboard radar also show some agreement. Temperature and salinity measurements from the mooring document fresh water penetration into the ocean surface layer during these rainfall events. Examples for several events are presented. These data are available to support 1-dimensional modeling of fresh water flux into the ocean surface layer.