Local and remote forcing effects of oceanic eddies in the subtropical front zone on the mid-latitude atmosphere in Winter

Haibo Hu,Ning Zhang,Feifei Chen,Haokun Bai,Yihang Zhao

doi:10.1007/s00382-021-05877-8

Abstract

Multiple oceanic eddies coexist in the North Pacific subtropical front zone (STFZ) in winter, which can be classified into the isolated single eddies, the combined double isotropic eddies and pairs of anisotropic eddies. The forcings of these eddies on the mid-latitude atmosphere are investigated using Climate Forecast System Reanalysis (CFSR) data from year 1979 to 2009, which are divided into the remote and local effects in this research. In the years with a stronger subtropical front, there are more cyclonic isolated and double eddies to the north, more anticyclonic isolated and double eddies to the south of the STFZ, and more eddy pairs with cold to the north and warm to the south concentrated around the main axis of the STFZ. These eddy distributions enhance the strength of the subtropical front, intensify the propagation of upwards baroclinic waves in the lower atmosphere, and finally enhance the zonal wind at upper atmosphere, which is defined as the remote effects of the eddies. However, distinct from this basin-scale remote forcings, three types of oceanic eddies also have different local forcings on the marine atmospheric boundary layer (MABL) above and on the middle atmosphere as expressed in local precipitation difference. The local effects of the isolated single eddies and combined double isotropic eddies take place near the eddy center, whereas that of the pairs of anisotropic eddies at the boundary of the two eddies.

Highlights

The interaction between the ocean and the atmosphere is the focus of attention in atmospheric dynamics and climate research
The most notable mesoscale air-sea interaction characteristic is the positive statistical correlation between SST and near-surface wind speed anomalies (Chelton et al, 2001; Xie, 2004; Small et al 2005), which was found in global oceanic front regions with large SST gradients and multiple oceanic eddies, including the Kuroshio Extension (KE) (Nonaka and Xie, 2003), the Gulf Stream (Minobe et al, 2008; Small et al, 2014), the Antarctic Circumpolar Current (O'Neill et al, 2003) and the Somali Current (Vecchi et al.,2004; Mafimbo et al, 2010)
Their researches revealed that the stronger year of the subtropical front zone (STFZ) intensity was accompanied by the Pacific DecadalOscillation (PDO) warm phase sea temperature anomaly with the colder north and the warmer south, which increased the baroclinity of the lower atmosphere and might affect the upper atmosphere

Summary

Introduction

The interaction between the ocean and the atmosphere is the focus of attention in atmospheric dynamics and climate research. Wang et al (2016; 2019) pointed out that the southern STFZ, which is located between 28°N and 32°N, has the closest relationship with the most significant SST anomaly mode (PDO) in the North Pacific Their researches revealed that the stronger (weaker) year of the STFZ intensity was accompanied by the PDO warm (cold) phase sea temperature anomaly with the colder (warmer) north and the warmer (colder) south, which increased (weakens) the baroclinity of the lower atmosphere and might affect the upper atmosphere. Considering the large number of oceanic eddies in the STFZ region, it is natural to wonder what the relation is between these eddy activities and the STFZ intensity on the interannual time scale This promising relation may reveal the remote effects of oceanic eddies on mid-latitude upper atmosphere.

Data and Analysis Method

Findings

Conclusion and Discussion