Role of Mixed Layer Depth in the Location and Development of the Northeast Pacific Warm Blobs. Issue 16 (23rd August 2022)

• Record Type: Journal Article
• Authors: Shi, Jian; Tang, Cong; Liu, Qinyu; Zhang, Yu; Yang, Haocheng; Li, Chun
• Is Part Of: Geophysical research letters. Volume 49:Issue 16(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-23
• Subjects: warm blob -- mixed layer depth -- Northeast Pacific -- heat flux -- heat budget; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098849
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Warm blobs are persistent warm anomalies in the Northeast Pacific (NEP) upper ocean. Here, we assess the role of mixed layer depth (MLD) in their location and development based on ocean‐atmosphere reanalysis data. We find that warm blobs occur more frequently over 165°–130°W and 35°–50°N with shallow MLD. They are largely confined to the mixed layer, although substantial portions exist beneath it in summer when the MLD shoals. Based on a mixed‐layer heat budget analysis, we reveal that anomalous MLD and heat flux contribute dominantly to the surface heat flux term over the study area from May to July and from September to March, respectively, and have a large effect on warm blob development. Therefore, the MLD has important implications for the location and seasonal evolution of warm blobs and temperature diagnosis over the NEP. Plain Language Summary: Warm blobs are anomalous warm waters in the upper ocean of the Northeast Pacific (NEP). Oceanic mixed layer is the warm surface layer that maintains homogeneous temperature or density. This study aims to clarify the role of mixed layer depth (MLD) in the location and development of warm blobs. First, we determine a region of 165°–130°W and 35°–50°N in which warm blobs are most likely to occur due to strong sea surface temperature variability and shallow MLD. In this region, temperature anomalies of the warm blobs are largely confined to the mixed layer, although parts of the anomalies are beneath it when MLD shoals in summer. Then, we separate and quantify the relative contributions of MLD and surface heat flux anomaly to the development of the warm blobs from the surface heat flux term in a mixed‐layer heat budget. We find that the contribution of MLD anomaly is dominant from May to July, while that of surface heat flux anomaly (i.e., less ocean heat loss) is pronounced from September to the following March. Therefore, the effect of MLD on the location and seasonal evolution of the warm blobs gives implications for the temperature diagnosis over the NEP. Key Points: Northeast Pacific warm blobs appear more frequently in areas with a shallow mixed layer Temperature anomalies of warm blobs are not only largely confined to the mixed layer but also stored beneath the mixed layer in summer Mixed layer depth anomalies are the dominant contributor to the temperature anomalies over the warm blob area from May to July