Analysis of Temperature and Salinity Variability in the Upper Ocean Caused by Rainfall in the ITCZ

H. Wijesekera, C. A. Paulson and W. S. Pegau, Oregon State University

D. Rudnick, Scripps Institution of Oceanography

As part of the EPIC field experiment, atmospheric and oceanic observations were made in the eastern tropical Pacific from the R/V New Horizon.  Atmospheric observations included wind speed and direction, temperature, humidity, incoming short and long wave radiation and rainfall rate.  Oceanic observations included temperature and salinity measured from the surface down to a depth of 250 m with a towed profiling vehicle (SeaSoar).  Measurements were typically made underway at a speed of 4 m/s around a 146-km butterfly pattern centered near 10N, 95W.  Atmospheric and oceanic measurements were also made on the R/V Brown located near the center of the butterfly pattern.  Measurements from the Brown included estimates of rainfall from a scanning radar, which encompassed the butterfly pattern.  Rainfall over the butterfly pattern was particularly heavy on two days (23 and 24 Sep) during the observational period (13 Sep to 01 Oct 2001).  Measurements on the New Horizon indicated a total rainfall of 0.4 m on 23 and 24 Sep compared to a total of 0.65 m for the entire 18-day period.  The two-day period of heavy rainfall was preceded and succeeded by periods of relatively light rainfall.  Hence the effect of the heavy rainfall on the structure of temperature (T)  and salinity (S) in the upper ocean could be assessed unambiguously.  We describe the evolution of T-S structure in the upper ocean and relate it to the structure of the rainfall and subsequent atmospheric forcing.