To What Extent Aquarius’ Sampling Pattern Affects the Estimated Amplitude of Tropical Instability Waves?

Abstract:

Tropical instability waves (TIWs) are important to ocean dynamics, air-sea interaction, and biogeochemistry. Measurements of sea surface salinity (SSS) from the Aquarius/SAC-D and SMOS missions have demonstrated their capabilities to detect TIWs both in the Pacific and the Atlantic Oceans. The accuracy of satellite SSS in representing TIW amplitudes has strong implication to the assimilation of these data in ocean models. The amplitude of SSS variability associated with TIWs inferred from Aquarius Version 2 gridded data has been found to be smaller than that derived from tropical mooring measurements by approximately 25%. One of the potential causes for this difference is the accuracy of the meridional gradients of SSS inferred from Aquarius data. However, existing in-situ data (e.g., from Argo floats) do not provide fine enough spatial resolution to evaluate the relatively fine SSS gradients inferred from Aquarius systematically. Another potential cause is that mooring data are point-wise measurements while Aquarius data represent spatial and temporal averages that are characteristic of Aquarius footprint and sampling pattern. Because high-resolution SST products are available and TIW-related SSS and SST are highly correlated, we examine the effect of Aquarius’ sampling pattern on the estimated TIW amplitude indirectly by sampling a high-resolution SST product based on Aquarius’ spatial and time sampling characteristics then re-create gridded SST maps to estimate the TIW amplitudes. The results suggest that, to a large extent, the smaller amplitudes of TIWs inferred from Version 2 of the Aquarius’ gridded data can be explained by Aquarius’ spatial and temporal sampling.