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

Current meter, temperature and wind observations from the 1984 MMS experime nt are used to estimate the mass and heat budgets in the Santa Barbara Chan nel. The mass transports estimated at the western, eastern and southern bou ndaries of the channel are characterized by fluctuations whose energy is co ncentrated around three different periods: 5, 14 and 2.8 days respectively. These three transports fluctuate along with the dominant EOF modes obtaine d at those 3 entrances respectively. The mean transport passing through the channel from east to west is about 0.28 Sv. There rue 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 (counter clockwise) 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 w here it also shows an absolute maximum of variance. nle recirculating trans port lags the local downwelling-favorable winds by about 1.5 day and stems to be the channel response to wind relaxations with respect to its most per sistent upwelling-favorable state. The main mean balance in the channel-int egrated heat equation is between the heat transport passing through the wes tern mouth, which cools off the channel, and the heat transport caused by t he mass transport (the transport heat Bur), which warms: up the channel. Th is latter transport results from the advection of the temperature differenc e between the channel boundaries (mainly east and west) by the mass transpo rt. There are no two terms that dominate the heat equation for the time dep endent heat transports, but it can be simplified by balancing the along cha nnel heat divergence (heat transport passing through the mouth plus transpo rt 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 fou nd, in agreement with the work of Brink and Muench (1986) [Journal of Geoph ysical Research, 91, 877-895] and with the recent ADCP-CTD comparisons done by Richards (personal communication). All the terms in the heat equation s how a variance peak in the 2-4 day band. It is found that when upwelling fa vorable winds blow on the northern shelf of the channel there is first a de crease or even a reversal, with respect to its mean, in the amplitude of th r transport heat flux. Next, a cooling of the Santa Barbara Channel is obse rved, followed by a loss of heat through the western mouth first and throug h the eastern mouth later, This whole process takes about 24 h to complete. (C) 1999 Elsevier Science Ltd, All rights reserved.