Using CryoSat‐2 altimeter data to evaluate M2 internal tides observed from multisatellite altimetry

Abstract

AbstractThis paper evaluates M2 internal tides observed from multisatellite altimetry (MultiSat20yr) using CryoSat‐2 altimeter data. MultiSat20yr is constructed using 20 years of sea surface height measurements made by multiple satellite altimeters from 1992 to 2012. Here it is demonstrated that M2 internal tides can also be extracted using 4 years of CryoSat‐2 data from 2011 to 2014 (CryoSat4yr) by the same plane wave fit method. MultiSat20yr and CryoSat4yr are in good agreement in the central North Pacific, although they are from satellite data of different sampling patterns (1998 versus 10,688 tracks) and different observational periods (20 versus 4 years). Further comparisons are carried out for three isolated wave components. MultiSat20yr and CryoSat4yr agree very well for both Hawaiian components, suggesting that the Hawaiian Ridge is a relatively stable generation site. In contrast, the Aleutian Ridge is a relatively unstable source in that the M2 amplitudes in MultiSat20yr and CryoSat4yr are very different. With respect to MultiSat20yr, the M2 internal tide in 2011–2014 propagates slower (faster) to the south (north) of Hawaii, respectively, suggesting that the internal tide's propagation speed is subject to significant interannual variability. This feature is supported by M2 internal tides observed using multisatellite altimeter data in 2005 (MultiSat2005) and Argo measured upper ocean temperature profiles. MultiSat20yr is used to correct M2 internal tides in the CryoSat‐2 data. Significant and efficient variance reduction suggests that MultiSat20yr is a reliable internal tide model. A phase‐adjusted MultiSat20yr is built to account for the interannual variations, and it works better in internal tide correction.