Effects of a Cold Ocean Eddy on Local Atmospheric Boundary Layer Near the Kuroshio Extension: In Situ Observations and Model Experiments

Abstract

Shipboard observations captured clear modulations of the marine atmospheric boundary layer (MABL) over a 300‐km‐diameter cold eddy in the Kuroshio Extension in April 2014. Regional atmospheric model experiments, with 30‐km and 10‐km horizontal resolutions for outer and inner domains, respectively, are conducted to aid the interpretations of the in situ observations. Enhanced turbulent heat fluxes promoted a well‐mixed MABL up to 1900‐m deep and a stratocumulus layer over the warm water west of the eddy. Over the cold sea surface of the eddy, the MABL was free of cloud and shrank to 1,200‐m deep. In the transition zone from the warm water in the west to the cold eddy, the MABL deepened and convective cumulus developed under a temperature inversion at 2,800 m. Model results indicate that, via the vertical mixing and pressure adjustment mechanisms, low sea surface temperatures of the cold eddy drives anomalous easterly winds in the transition zone, causing surface convergence to deepen the MABL and clouds. The model further shows that the atmospheric asymmetric responses in surface divergence and secondary circulation are due to the combined effects of the vertical mixing and pressure adjustment.

Atmospheric Responses to Mesoscale Oceanic Eddies in the Winter and Summer North Pacific Subtropical Countercurrent Region

“…The results indicated that the MOEs-induced cloud and precipitation anomalies were 3.6% and 7.5% of the background values, respectively. In addition, field observations and numerical experiments showed that MOEs affect the development of clouds over them [14][15][16]. The vertical mixing and pressure adjustment mechanisms generate wind divergence anomalies, modifying the vertical motion and thus influencing the clouds and precipitation.…”

“…The MOEs in the North Pacific, characterized by strong eddy kinetic energy (EKE) [17], are prevalent in the KE region and subtropical countercurrent (STCC) region (Figure 1a). Through previous analyses of satellite data, reanalysis data, observation data and numerical simulation results, the existing literature has elucidated the atmospheric responses to the MOEs in the KE region [12][13][14][15]18,19]. In the STCC region, by analyzing satellite data, Chow and Liu (2013) [20] found that there were phase differences between the centers of SSTAs and the centers of MOEs in the spring, while the surface wind speed anomalies (SWSAs) pattern bears a discernable resemblance to the SSTAs pattern.…”

Impact of the Oyashio Extension SST Front on Synoptic Variability of Oceanic Low‐Level Cloud in Summertime Based on WRF Numerical Simulation

“…To investigate the response of oceanic low‐level cloud properties to the SST front, we use the WRF model, version 4.0 (Skamarock et al, 2008, 2019), which is a nonhydrostatic atmospheric model. The WRF has been used in numerous studies to investigate the effect of oceans on regional atmospheric circulation (Kilpatrick et al, 2014, 2016), precipitation systems (Tanimoto et al, 2011; Xu et al, 2010), and cloud (Jiang et al, 2019; Y. Kawai et al, 2015). In this study, we use the WRF model to investigate the response of low‐level cloud to the presence of an SST front.…”

“…Although the active role of SST fronts in summertime may not be substantial, recent studies based on ship‐based and satellite observations indicated that the SST front modulates the atmospheric boundary layer and low‐level clouds overlying it (Jiang et al, 2019; Liu et al, 2014; Miyamoto et al, 2018; Tokinaga et al, 2009; Y. Kawai et al, 2015, 2019). There are local effects of the SST anomaly associated with the front on the low‐level cloud and atmospheric boundary layer, such as thickness and turbulent mixing, in summertime.…”

“…Although the active role of SST fronts in summertime may not be substantial, recent studies based on ship-based and satellite observations indicated that the SST front modulates the atmospheric boundary layer and low-level clouds overlying it (Jiang et al, 2019;Liu et al, 2014;Miyamoto et al, 2018;Tokinaga et al, 2009; Y. Kawai et al, 2015Kawai et al, , 2019.…”