An experiment by the Naval Postgraduate School and the National Data Buoy
Center was performed in the Gulf of Mexico to characterize the underwater sound
generated by heavy precipitation and to determine if rainfall rates of heavy precipitation
can be measured using underwater sound. During this stage of the experiment, twentytwo
data sets were recorded with rainfall rates up to 340 mm/hr. For a given rainfall rate,
it is found that sound levels from heavy convective precipitation are higher at the
beginning of the storm and when the rainfall rate is increasing than at the end of the
storm event or when rainfall rates are decreasing. This may be due to changes in the
drop size distribution during the life cycle of the storm or to variations in the temperature
difference between the raindrop and the ocean surface. Very heavy rainfall (rate > 150
mm/hr) generates near surface bubble layers or bubble clouds which attenuate sound
energy at higher frequencies (>15 kHz). The distinctive 15 kHz peak in the sound
spectrum for light rain is absent during heavy rain suggesting that the sound production
mechanism previously identified for small drops (0.8 - 1.1 mm in diameter) is suppressed
by heavy rain even though those small drops are undoubtedly present during heavy
rainfall rates. These data show a very high correlation between underwater sound level
and the logarithm of the rainfall rate except when high wind speeds (> 10 m/s) and high
rainfall rates (> 150 mm/hr) are present. An empirical rainfall rate algorithm for
con-vcctive precipitation is proposed suggesting that sound energy is directly proportional to rainfall rate, however any empirical algorithm which does not adjust for changing.
storm characteristics should be used with caution.
| Identifer | oai:union.ndltd.org:nps.edu/oai:calhoun.nps.edu:10945/26348 |
| Date | 06 1900 |
| Creators | McGlothin, Charles C. |
| Contributors | Nystuen, Jeffrey A., Medwin, Herman, Naval Postgraduate School, Naval Postgraduate School, Physical Oceanography, Meteorology |
| Publisher | Monterey, California. Naval Postgraduate School |
| Source Sets | Naval Postgraduate School |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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