The Influence of Subsurface Conditions on the Spatial and Temporal Variability of Tropical SST and Rainfall in CFSv2 Reforecasts

This study examines the potential impact of subsurface potential temperature and current conditions on the sea surface temperature (SST) and rainfall over the 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°C over the equatorial central and eastern Pacific at depth from 155 to 70 m 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. The magnitude of equatorial undercurrent (EUC) in JIR P58‐78 is larger in the eastern Pacific at depth from 125 to 35 m 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°C in the eastern Pacific at depth from 135 to 35 m in April but as lead months increase, magnitude of warm PT gradually decreases, resulting in negligible difference SST over the eastern Pacific.