The seasonal variability of an air-sea heat flux in the northern South China Sea
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The seasonal variability of an air-sea heat flux in the northern South China Sea ZHANG Yan1,2∗ , WANG Dongxiao1 , XIA Huayong2 , ZENG Lili1 1
2
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China South China Sea Engineering Surveying Center, South China Sea Branch, State Ocean Administration, Guangzhou 510300, China
Received 3 March 2012; accepted 8 August 2012 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2012
Abstract The seasonal variabilities of a latent-heat flux (LHF), a sensible-heat flux (SHF) and net surface heat flux are examined in the northern South China Sea (NSCS), including their spatial characteristics, using the in situ data collected by ship from 2006 to 2007. The spatial distribution of LHF in the NSCS is mostly controlled by wind in summer and autumn owing to the lower vertical gradient of air humidity, but is influenced by both wind and near-surface air humidity vertical gradient in spring and winter. The largest area-averaged LHF is in autumn, with the value of 197.25 W/m2 , followed by that in winter; the third and the forth are in summer and spring, respectively. The net heat flux is positive in spring and summer, so the NSCS absorbs heat; and the solar shortwave radiation plays the most important role in the surface heat budget. In autumn and winter, the net heat flux is negative in most of the observation region, so the NSCS loses heat; and the LHF plays the most important role in the surface heat budget. The net heating is mainly a result of the offsetting between heating due to the shortwave radiation and cooling due to the LHF and the upward (outgoing) long wave radiation, since the role of SHF is negligible. The ratio of the magnitudes of the three terms (shortwave radiation to LHF to long-wave radiation) averaged over the entire year is roughly 3:2:1, and the role of SHF is the smallest. Key words: South China Sea, latent heat flux, sensible heat fluxnet heat flux
face. Numerical modeling of the atmosphere and the oceans to forecast weather and climate also requires a quantitative representation of air-sea fluxes (Stuart et al., 1996). The air-sea interaction can usually be described by mechanisms involved in the sea-surface energy budget, in which the net surface heating is estimated by the summation of four terms: latent-heat flux (LHF), sensible-heat flux (SHF), shortwave (SW) and long-wave (LW) radiations. The South China Sea (SCS; 0◦ –23◦ N, 99◦ –121◦ E) is located on the southwest side of the north Pacific Ocean. The SCS climate is an important part of the Asian monsoon system. A basin-wide surface ocean circulation changes drastically, depending on the season: a cyclonic (anticyclonic) circulation develops in winter (summer) under the northeasterly (southwest-
1 Introduction Surface heat fluxes are important in atmosphereocean interaction and climate variability. Turbulent and radiative processes exchange heat between the air and the sea. Together with evaporation, preci
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