Spatial scale dependence of the relationship between turbulent surface heat flux and SST

Xiaoshan Sun,Renguang Wu

doi:10.1007/s00382-021-05957-9

Abstract

This study investigates the spatial scale dependence of relationship between turbulent surface heat flux (SHF) and sea surface temperature (SST) variations in the mid-latitude frontal zones, subtropical gyres, and tropical Indo-western Pacific region in winter and summer with daily observational data. A comparison of the SHF and SST/SST tendency correlation between 1° and 4° spatial scale displays a decrease of the positive SHF–SST correlation and an increase of the negative SHF–SST tendency correlation as the spatial scale increases in all the above regions. The lead–lag SHF and SST/SST tendency correlation at different spatial scales illustrates an obvious transition from the oceanic forcing to the atmospheric forcing in the western boundary currents (WBCs) and the Agulhas Return Current (ARC) in both winter and summer. The transition length scale is smaller in summer than in winter, around 2.6°–4.5° in winter and around 0.8°–1.3° in summer based on the OAFlux data. In the subtropical gyres and tropical Indo-western Pacific region, atmospheric forcing dominates up to 10° spatial scale with the magnitude of forcing increasing with the spatial scale in both winter and summer except for the Arabian Sea in summer. The Arabian Sea distinguishes from the other tropical regions in that the SST forcing dominates up to more than 10° spatial scale in summer with the magnitude of forcing decreasing slowly with the spatial scale increase.

Highlights

Ocean and atmosphere interacts closely with each other
The above differences in the magnitude, scale and lead time of the maximum surface heat flux (SHF)–sea surface temperature (SST) correlation and in the magnitude of the maximum SHF–SST tendency correlation are all indicative of a weakening of the oceanic forcing from winter to summer, which is similar to the conceptual model results (Fig. 1)
To further illustrate the effect of the spatial scale and the seasonal difference, we show in Figs. 6, 7 and 8 the SHF–SST/SST tendency correlation at the western boundary currents (WBCs) and Agulhas Return Current (ARC) at three spatial scales in winter and summer, which is extracted from Figs. 4 and 5

Summary

Introduction

Ocean and atmosphere interacts closely with each other. As the largest underlying surface of the atmosphere, the ocean absorbs large amount of solar energy and releases most of the energy to the atmosphere to drive the atmospheric variability. The relationship between SST and SHF variations changes with temporal and spatial scales (Wu et al 2015; Bishop et al 2017; Small et al 2019; Sun and Wu 2021) examined the changes of SST and SHF relationship with temporal scales using daily data and identified several transitions between the atmospheric and oceanic forcing at submonthly time scales that cannot be resolved based on monthly data. They revealed seasonal differences of the temporal scale dependence of the SST and SHF relationship.

Datasets and methods

Conceptual model simulations

Spatial scale dependence of lead–lag correlation in winter and summer

Transition length scale at different locations and seasons

Findings

Summary and discussions