The influence of subsurface conditions on the spatial and temporal variability of SST and rainfall over the global tropics in the Past 57 Years (1958–2014) reforecasts

Abstract:

This study examines the potential impact of sub-surface potential temperature and current conditions on the sea surface temperature (SST) and rainfall over tropical region using Climate Forecast System version-2 (CFSv2) ensemble seasonal reforecasts for 1958-2014. The climatological difference of earlier period (1958–78; P58-78) and later period (1994–2014; P94-14) in January initialized reforecasts (JIR) depicts mild-warm SST over the equatorial eastern Pacific in January but its magnitude becomes larger over there from May to August. The difference between JIR P58-78 and P94-14 depicts warm potential temperature (PT) up to 3^oC over the equatorial central and eastern Pacific at depth from 155m to 70m in January therefore 20°C isotherm of JIR P58-78 in January tends to be deeper in the equatorial eastern Pacific than JIR P94-14. Magnitude of equatorial undercurrent (EUC) in JIR P58-78 is larger in the eastern Pacific at depth from 125m to 35m from January to February than JIR P94-14. Therefore, water upwelled to the surface through EUC was usually warm in January of JIR P58-78. As lead months increase, the center of warm PT gradually moves upward in the eastern Pacific than its location in January, resulting in development of warm SST in the eastern Pacific in March. The difference between April initialized reforecasts P58-78 and P94-14 depicts warm PT up to 1.5 ^oC in the eastern Pacific at depth from 135m to 35m in April but as lead months increase, the magnitude of warm PT gradually decreases, resulting negligible difference SST over the eastern Pacific. The results of this paper provide the importance of sub-surface potential temperature and current conditions in the state-of-the-art coupled general circulation model.

References:

Shukla R. P., (2020) The influence of subsurface conditions on the spatial and temporal variability of SST and rainfall over the global tropics in the Past 57 Years (1958–2014) reforecasts (Under revision: Journal of Geophysical Research – Oceans)