The South Pacific Ocean Climatology (SPOC)

The interaction of tropical cyclones (TC) with the ocean is part of an important dynamic process to understand due to their impact on the local ecosystems and economies. The South Pacific basin, an area between the Australian coast and 120°W monitored by both Fiji Meterological and the Australia Meteorology Bureau, is home to approximately 2 to 16 cyclones per year, where several of those reach severe TC status. These storms induce a thermal response for several weeks after storm passage due to vertical mixing. During the Austral summer months, sea surface temperatures (SST) in this area can reach over 30°C and warm waters extend deep into the water column. Severe TC Evan, Ian, and Pam are investigated using the South Pacific Ocean Climatology (SPOC).

SPOC was developed to estimate ocean heat content (OHC) variability in the South Pacific Ocean. SPOC is a blend of temperature and salinity fields from the World Ocean Atlas 2001 (WOA) and Generalized Digital Environmental Model v.2.1 (GDEM) at 1/4° resolution. Monthly mean isotherm depths of the 20°C (D20) and 26°C (D26) (and their mean ratios), reduced gravities, and mixed layer depth (MLD) were estimated for both GDEM and WOA climatologies. Daily fields were created by applying a 15-day running average to the monthly fields to eliminate discontinuities when transitioning between months. To blend the two climatologies and create SPOC, a weighting scheme was developed by minimizing the residual covariances between in-situ and satellite-derived fields.

Using a 2.5 layer model approach together with SPOC, and satellite-derived sea surface height anomaly (SHA) and SST fields, daily D20, D26, MLD, and OHC were estimated from 1998 to 2014. In addition, the SHA product includes mapping errors given the diverse repeat tracks from the various satellite platforms and the altimeter sensor accuracies. This is especially important across the eddy-rich regimes in the western Pacific Ocean and the complex equatorial wave guide. To assess uncertainties in SPOC and the daily fields, ship-deployed profilers, TAO moorings, and Argo profiling floats provided more than 240,000 quality controlled in situ thermal profiles. This carefully constructed climatology creates an accurate estimate of OHC from satellite-based measurements to build evaluated ocean products in the South Pacific Ocean for multiple applications, including model assimilation, hurricane intensity forecasting, and climate research.