| The residence time was defined as the time taken for a parcel to leave the domain of interest, which could represent the timescale of water exchange. However, there are few studies on the intra-tidal variation of residence time. Based on constituent-oriented age and residence time theory (CART), the spatial distribution of average residence time (ART) with different initial time in Jiaozhou Bay (JZB) was calculated by solving its adjoint equation in this study. Special attention was paid on the formation mechanism of ART, together with its uncertainty owing to the impact of external disturbance on advection transport path. Significant results and useful conclusions have been achieved in the following aspects:A three-dimensional hydrodynamic model was applied to calculate the tide and tidal current in Jiaozhou Bay. The simulation results of tidal elevation and current of M2constituent agreed quite well with observation and existing studies, indicating that the modelled flow field used to calculate ART is reliable.The ART was about60days. EOF analysis showed that the first mode of ART can be capable of satisfactorily describe the spatiotemporal variation, since its accumulated variances was larger than99%. The time coefficients shows semi-diurnal period same to the tidal elevation, but their phase difference is180degrees. For instance, maximal ART (about64days) occurred at low tide, while minimal ART (about54days) at high tide. Intra-tidal variation of ART in JZB nearby Tuandao was quite significant,(over20days). Spatially, ART decreases from bay head to bay mouth, and there is a obvious stagnant zone about water exchange between the southwest of Huangdao and Xuejiadao. ART would be increased by24days in the calculation with re-entry process considered, and the return rate is all about90%at different initial time, so that the increment did not vary with initial time. The residence time in previous studies were always defined as the time for the water of local area to be replaced by outer sea water. That definition was called ART’to distinguish with ART in this study. Consequently, the difference between ART and ART’was negative in west of the JZB and north of Tuandao, and positive in other areas. Spatial and temporal distribution of ART was closely related to the Lagrangian residual current field. It had been founded that strong nonlinear effects of M2tidal system in JZB would result in significant intra-tidal variation of Lagrangian residual circulation there, which could be used to explain the strong dependence of ART on the initial tidal phase. The largest intra-tidal variation of ART was located near the bay mouth, where there was particularly strong nonlinear effect. Two counterclockwise eddies in the inner bay hindered water exchange there. Being different with Euler residual current, the Lagrange residual current flowed out the bay in west of the bay and north of Tuandao. Therefore, ART in these areas was lower than ART’.On one hand, the accuracy of ART depends on the reliability of the simulated flow field; on the other hand, the flow field is inevitably affected by the external disturbance. The influence of disturbance on current field was analyzed in Monte Carlo experiments by particle tracking method. The results showed that JZB could be divided into AREA I where flow field is not sensitive to disturbance, and AREA II where flow field is sensitive. The boundary between I and II area is close to the bay mouth (about3km) at low tide, and far from the bay mouth (about8km) at high tide. The uncertainty of the flow field was also associated with the nonlinear effect of M2tidal system. The higher nonlinearity, the higher uncertaint.Taking Jiaozhou Bay as an example, the intra-tidal variation of ART is obtained for the first time, and ART is minimal at high tide is revealed. The spatial and temporal distribution of ART was determined by tide-induced Lagrange residual current instead of Euler residual current. |
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