A Hot Blob Eastward of New Zealand in December 2019.

A hot blob for near-surface water was identified eastward of New Zealand in the South Pacific in December 2019, which was the second strongest event on record in this region. Its sea surface temperature anomalies reached up to 5 °C, and the anomalous warming penetrated around 40 m deep vertically. From the atmospheric perspective, the anomalous high-pressure system from the surface up to 300 hPa lasted for about 50 days, accompanied by the blocking pattern at 500 hPa and a deep warming air column extending downward to the surface. A mixed-layer heat budget analysis revealed that the surface heat flux term was the primary factor contributing to the development of this hot blob, with more shortwave radiation due to the persistent high-pressure system and lack of clouds as well as higher temperature of the troposphere aloft denoted by sensible heat. The oceanic contribution including the horizontal advection and vertical entrainment was changeable and accounted for less than 50%. Moreover, we used the strongest hot blob event which peaked in December 2001 as another example to evaluate the robustness of results derived from the 2019 case. The results show similar circulation features and driving factors, which indicate the robustness of the above characteristics. [ABSTRACT FROM AUTHOR]