Four Types of Baroclinic Instability Waves in the Global Oceans and the Implications for the Vertical Structure of Mesoscale Eddies

Abstract

Mesoscale eddies are ubiquitous in the world's oceans and are believed to account for ∼90% of ocean kinetic energy (Wunsch & Ferrari, 2004) and to play an important role in meridional heat and mass transport (Sun et al., 2019; Zhang et al., 2014). Most eddies are initially driven by baroclinic instability (BCI) by extracting

Seasonality of Four Types of Baroclinic Instability in the Global Oceans

“…It is worth noting that BCIs always lead eddies (denoted by EKE) by the growth time scale of BCI, which, however, varies from locations to locations. In the KE regions, the growth time scale is short, ∼10 days (Feng et al., 2021); as a result, there is no obvious phase shift between the BCIs and eddies, or between BCIs and BCRs, at the seasonal time scale. Similarly, in the ACC region, because of the short growth time scale of BCI, there is no obvious phase shift between BCI and BCR at the seasonal time scales, either.…”

“…The Eady‐type BCIs are generated by a strong surface QGPV gradient and a strong bottom QGPV gradient with opposite sign, while the Charney_b‐type BCIs are generated by a strong bottom QGPV gradient and an internal QGPV gradient with opposite sign (Feng et al., 2021). Due to the stable bottom flows, the Eady‐ and Charney_b‐type BCIs are seasonally stable.…”

“…Due to the stable bottom flows, the Eady‐ and Charney_b‐type BCIs are seasonally stable. In contrast, the Charney_s‐ and the Phillips‐type BCIs are determined by the surface and subsurface QGPV gradients (Feng et al., 2021), and they can be affected by N 2 in the upper ocean as discussed in Section 4.2 for the KE and GS.…”

“…The four types of BCIs are characterized by the following distributions: the Charney_s type BCIs are ubiquitous in the ocean and prefer the mid‐latitudes and high‐latitudes (>20°); the Phillips‐type BCIs prefer low latitudes (5°–20°) and they also dominate south of the Kuroshio Extension (KE) and in most regions of the Gulf Stream (GS) (Feng et al., 2021; Tulloch et al., 2011). The Eady‐ and Charney_b‐type BCIs are mainly located in the Antarctic Circumpolar Current (ACC) region (Feng et al., 2021). The spatial distribution of BCI types is found to imply a spatial preference of different eddies: regions dominated by the Charney_s‐type BCIs usually have active surface mesoscale eddies and regions dominated by the Phillips‐type BCIs usually have active subsurface mesoscale eddies.…”

“…The four types of BCIs are characterized by the following distributions: the Charney_s type BCIs are ubiquitous in the ocean and prefer the mid‐latitudes and high‐latitudes (>20°); the Phillips‐type BCIs prefer low latitudes (5°–20°) and they also dominate south of the Kuroshio Extension (KE) and in most regions of the Gulf Stream (GS) (Feng et al., 2021; Tulloch et al., 2011). The Eady‐ and Charney_b‐type BCIs are mainly located in the Antarctic Circumpolar Current (ACC) region (Feng et al., 2021).…”