Mass and heat balances in the Santa Barbara Channel : estimation, description and forcing

• Published in: Progress in oceanography 1999, Vol.43 (1), p.111-155
• Main Authors: AUAD, G, HENDERSHOTT, M. C, WINANT, C. D
• Format: Article
• Language: English
• Subjects: Earth, ocean, space; Exact sciences and technology; External geophysics; Marine; Physics of the oceans; Thermohaline structure and circulation. Turbulence and diffusion
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/S0079-6611(99)00006-3

Current meter, temperature and wind observations from the 1984 MMS experiment are used to estimate the mass and heat budgets in the Santa Barbara Channel. The mass transports estimated at the western, eastern and southern boundaries of the channel are characterized by fluctuations whose energy is concentrated around three different periods: 5, 14 and 2.8 days respectively. These three transports fluctuate along with the dominant EOF modes obtained at those 3 entrances respectively. The mean transport passing through the channel from east to west is about 0.28 Sv. There are two frequency bands where winds and mass transports are coherent: 2.5-3.0 and 4.7-5.2 day bands. Winds on the northern shelf lead the transports in both bands by about 1.0 day. At the western half of the channel there is a recirculating (counterclockwise) mean transport of about 0.30 Sv. The time dependent part of the recirculating transport is coherent with the wind in the 4.7-5.2 day band where it also shows an absolute maximum of variance. The recirculating transport lags the local downwelling-favorable winds by about 1.5 day and seems to be the channel response to wind relaxations with respect to its most persistent upwelling-favorable state. The main mean balance in the channel-integrated heat equation is between the heat transport passing through the western mouth, which cools off the channel, and the heat transport caused by the mass transport (the transport heat flux), which warms up the channel. This latter transport results from the advection of the temperature difference between the channel boundaries (mainly east and west) by the mass transport. There are no two terms that dominate the heat equation for the time dependent heat transports, but it can be simplified by balancing the along channel heat divergence (heat transport passing through the mouth plus transport heat flux), the vertical heat flux and the local change of heat. A clear thermal-wind balance at the eastern and western ends of the channel is found, in agreement with the work of Brink and Muench (1986) [Journal of Geophysical Research, 91, 877-895] and with the recent ADCP-CTD comparisons done by Richards (personal communication). All the terms in the heat equation show a variance peak in the 2-4 day band. It is found that when upwelling favorable winds blow on the northern shelf of the channel there is first a decrease or even a reversal, with respect to its mean, in the amplitude of the transport heat flux. Ne