Surface Gradient PDF Figure List

PDFs of Surface T and S Differences

These figures show probability density functions (PDFs) of the near-surface temperature and salinity differences measured from TAO buoys in the COARE region. These buoys made hourly observations of T and S (using Seacats) at 1m and either 5m or 10m for up to 19 months during late 1992 - early 1994. Buoys studied included those at 0,156E, 0,165E and 2S,156E (all those with 1m instruments). The PDFs show the frequency of differences between the top two instruments during the period of observation, divided into 0.1 deg C or 0.1 PSU interval classes. Dots mark the center of each interval, representing the number of occurrences within 0.05 deg C or 0.05 PSU of either side of the dot. Each PDF is plotted three times: for the entire range of values (these mostly show the large spike near zero difference); "Truncated" which limit the y-axis to show detail of the smaller classes; and "Combined" to show PDFs at the 3 locations overlaid, scaled to 1000 total obs in each case for comparison.

It is worth noting that other buoys (at 0,154E, 0,161E and 2N,165E (not shown)) had 3m and 5m Seacats (with no 1m instrumentation) but in the course of this investigation it was found that the differences between 3 and 5m were much smaller than those below 1m. In addition, the mooring at 2S,156E had Seacats at 1, 3, 5 and 10m for various periods, but most of the 1-10m difference occurred between the top two instruments. Therefore the 3m observations were not revealing (except in the negative sense). Consistent with this, there was also little difference in the statistics between the 1 to 5m and 1 to 10m S and T differences shown in the figures below. It also may be that substantial gradients occurred above 1m, but this cannot be determined here.

In general, the PDFs are similar at all three locations. They tend to be skewed, with T and S warmer and fresher at the surface, respectively. The warmer/fresher side of the PDF is roughly five or more times as large as the colder/saltier side, and the tail is several times longer. Mean differences are about -0.04 PSU and 0.1 deg C, with standard deviation about 0.1 PSU and 0.25 deg C.

Salinity PDFs

Temperature PDFs

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