Three-dimensional semi-idealized model for tidal motion in tidal estuaries

In this study, the method for damped co-oscillating tides is used to evaluate damping and energy dissipation characteristics for various estuaries of different geometry and depth. Of special interest are the damping and energy dissipation characteristics of the German tidal rivers such as Elbe, Weser and Ems in comparison with North-American tidal estuaries, since the former are characterized by deep navigation channels and relatively flat wadden areas at their lateral boundaries. Harleman and Ippen have applied a mathematical model for co-oscillating tides to the Bay of Fundy and the Delaware estuary. This model gives information about the damping behaviour and energy distribution in the tidal estuaries. Both of the above mentioned estuaries represent special cases since the geometric form of the Bay of Fundy allows it to be approximately represented as a rectangular canal of constant width and depth, whereas for the Delaware Estuary one can assume a constant depth of water. Partenscky has applied an extended form of this model to the St. Lawrence Estuary. The method of co-oscillating tides has now also been used in a mathematical model for the German tidal rivers such as Elbe, Weser and Ems. This method takes into account the influence of geometry and depth on the tidal motion and also the damping of the tidal wave due to friction and partial reflection. Data from gauges situated along the estuaries are needed as initial input for the calculation of the damping coefficient and the phase change. The wave amplitude and the time of highwater must be known from these stations.

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The Circulation Response of a Two-Dimensional Frontogenetic Model to Optimized Moisture Perturbations

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0102.1 ◽

2020 ◽

Author(s):

Reuben Demirdjian ◽

Richard Rotunno ◽

Bruce Cornuelle ◽

Carolyn A. Reynolds ◽

James D. Doyle

Keyword(s):

Three Dimensional ◽

Static Stability ◽

Two Dimensional ◽

Mixing Ratio ◽

Physical Processes ◽

Low Level ◽

Nonlinear Growth ◽

Idealized Model ◽

The Impact ◽

Transverse Circulation

AbstractAn analysis of the influence and sensitivity of moisture in an idealized two-dimensional moist semigeostrophic frontogenesis model is presented. A comparison between a dry (relative humidity, RH=0%) and moist (RH=80%) version of the model demonstrates that the impact of moisture is to increase frontogenesis, strengthen the transverse circulation (??????,??), generate a low-level potential-vorticity anomaly and develop a low-level jet. The idealized model is compared to a real case simulated with the full-physics three-dimensional Coupled Ocean-Atmospheric Mesoscale Prediction System (COAMPS) model establishing good agreement and thereby confirming that the idealized model retains the essential physical processes relevant for improving understanding of midlatitude frontogenesis. Optimal perturbations of mixing ratio are calculated to quantify the circulation response of the model through the computation of singular vectors, which determines the fastest-growing modes of a linearized version of the idealized model. The vertical velocity is found to respond strongly to initial-condition mixing-ratio perturbations such that small changes in moisture lead to large changes in the ascent. The progression of physical processes responsible for this nonlinear growth is (in order): jet/front transverse circulation → moisture convergence ahead of the front → latent heating at mid-to-low elevations → reduction in static stability ahead of the front → strengthening of the transverse circulation, and the feedback cycle repeats. Together, these physical processes represent a pathway by which small perturbations of moisture can strongly impact a forecast involving midlatitude frontogenesis.

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