Seasonal thermocline in the China Seas and northwestern Pacific Ocean

Abstract

.[1] Climatological seasonal variations of the thermocline in the China Seas and northwestern Pacific Ocean were studied using historical data from 1930 through 2001 (707,624 profiles). The quantitative roles of surface thermal buoyancy (B q ), haline buoyancy flux (B p ), and total buoyancy flux (B) against the wind-induced mixing (t) in different seasons and regions were also explored using the buoyancy ratio (R = |B q /B p |) and the Monin-Obukhov depth ratio (d), respectively. The thermocline has obvious seasonal variations in the study area north of 20°N. There is no thermocline along the west coast of the Bohai Sea (BS), Yellow Sea (YS), and northern East China Sea from December to March resulting from surface cooling and wind mixing. The significantly different variation of the thermocline strength on and off the Chinese shelf is mainly caused by the fact that the thermal stratification is enhanced by bottom tidal mixing on the shelf. The d indicates that the thermocline depth on the Chinese shelf is mainly dominated by B in summer, while it is dominated by t in winter. It reveals an opposite feature in the Kuroshio region; the dominating factor is B in winter, associated with the large heat buoyancy loss there. South of 20°N, the dominating factor is similar to that on the shelf, with the more obvious B dominant characteristic during the monsoon transition periods. The R demonstrates that B is mainly controlled by B q all year round, with some sporadically B p -dominated regions in the tropical area in winter and in the BS and eastern YS in September.

Thermal structure and response to long‐term climatic changes in Lake Qiandaohu, a deep subtropical reservoir in China

“…However, there is no objective way to determine the criterion, which ranges from 0.05uC m 21 to 2uC m 21 (Coloso et al 2011;Hao et al 2012). For example, the criterion value of 0.05uC m 21 is used for the Chinese shelf (.…”

“…For example, the criterion value of 0.05uC m 21 is used for the Chinese shelf (. 200 m; Zou et al 2001), 0.2uC m 21 is used for the Chinese shelf (# 200 m; Hao et al 2012), and 1uC m 21 is used in Canadian Shield lakes (Fee et al 1996).…”

Upper water structure and mixed layer depth in tropical waters: The SEATS station in the northern South China Sea

“…6, 1019-1032, December 2017 general categories: (1) fixed temperature difference (FTD) methods -the depth at which the potential temperature, θ, has decreased by a prescribed amount relative to a reference depth, preferably the sea surface; (2) fixed density difference (FDD) methods -the depth at which the potential density, σ θ , has increased by a prescribed amount relative to a reference depth, again preferably the sea surface; (3) fixed temperature gradient (FTG) methods -the depth at which the gradient in θ with depth z, δθ/δz, has increased to a prescribed value; and (4) fixed density gradient (FDG) method -the depth at which the gradient in σ θ with depth, δσ θ /δz, has risen to a prescribed value. The prescribed values that have been used varied, for example, a drop in θ of 0.2 (Thompson 1976), 0.5 (Price et al 1986;Kelly and Qiu 1995;Obata et al 1996;Monterey and Levitus 1997), 0.8 (Kara et al 2000;Qu et al 2007) or even 1.0°C (Lamb 1984;Wagner 1996), an increase in σ θ of 0.125 or 0.13 σ θ unit (Miller 1976;Levitus 1982;Spall 1991;Huang and Russell 1994), an increase in -δθ/δz to 0.05°C m -1 (Qu 2001;Hao et al 2012) and an increase in δσ θ /δz to 0.01 (Lukas and Lindstrom 1991), 0.05 (Tseng et al 2007) or 0.1 σ θ unit m -1 (Tseng et al 2005;Wong et al 2007a, b) in the FTD, FDD, FTG, and FDG methods, respectively. The reference depths used include the sea surface (Miller 1976;Thompson 1976;Levitus 1982;Lamb 1984;Price et al 1986;Spall 1991;Huang and Russell 1994;Kelly and Qiu 1995;Obata et al 1996;Wagner 1996;Monterey and Levitus 1997) and 10 m below the sea surface …”

“…As a result, MLD generally tends to decrease with decreasing latitude, and, the seasonal variations in MLD in the tropical waters tend to be smaller (Monterey and Levitus 1997;Montégut et al 2004). As a part of several studies for diverse purposes, the MLD in the tropical northern South China Sea (SCS) has been estimated by various investigators using a variety of different methods: a FTD method with a drop in θ of 0.8°C relative to that at 10 m (Qu et al 2007); a FTG method at a temperature gradient of 0.05°C m -1 (Qu 2001;Ge et al 2003;Hao et al 2012); a FDG method at density gradients of 0.05 (Tseng et al 2007) or 0.1 σ θ unit/m (Tseng et al 2005(Tseng et al , 2009Wong et al 2007b). Wong et al (2007b) reported that, unlike what is expected in tropical waters, the MLD in the northern SCS varies over a relatively wide range seasonally, from 20 m in the summer to 90 m in the winter.…”

Integrated 3D numerical modeling during La Niña and El Niño events using Regional Ocean Modeling System (ROMS) in Makassar Strait: preliminary study

“…We collected 7 random points in the model from north part to south part to see the vertical profiles and compared them between La Niña, El Niño, and normal scenario. Thus thermocline layer calculate using gradient criterion 0.05 o C/m to determine the depth of upper and lower threshold of thermocline layer [22].…”