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THE PREDICTION OF SURGES IN THE SOUTHERN BASIN OF LAKE MICHIGAN
Part III. The Operational Basis for Prediction
Abstract
The development of operational surge prediction in southern Lake Michigan is reviewed through the 10-year span starting with the disastrous surge of June 26, 1954 which took several lives in the Chicago area. Particular emphasis is given to the application of the work of others, especially Platzman, to the surge-prediction problem. Considerable detail is given on the surge of August 3, 1960, for which a successful prediction was made. This example, with its messages to the public, could serve as a model for future surge predictions. Finally a set of steps is given by which a prediction is made, followed by comments on those items still needing research before we can evaluate all parameters for an operational surge prediction.
Abstract
The development of operational surge prediction in southern Lake Michigan is reviewed through the 10-year span starting with the disastrous surge of June 26, 1954 which took several lives in the Chicago area. Particular emphasis is given to the application of the work of others, especially Platzman, to the surge-prediction problem. Considerable detail is given on the surge of August 3, 1960, for which a successful prediction was made. This example, with its messages to the public, could serve as a model for future surge predictions. Finally a set of steps is given by which a prediction is made, followed by comments on those items still needing research before we can evaluate all parameters for an operational surge prediction.
The methods for computing “instantaneous” upper-level pressure or height tendencies are revised to allow computation of the 500 mb height tendency using the observed surface (or sea-level) pressure tendency and an appropriate portion of the 1000–500 mb thickness advection. An evaluation is made as to what constitutes an appropriate portion of the thickness advection. Use of the method is discussed and an example is given.
The methods for computing “instantaneous” upper-level pressure or height tendencies are revised to allow computation of the 500 mb height tendency using the observed surface (or sea-level) pressure tendency and an appropriate portion of the 1000–500 mb thickness advection. An evaluation is made as to what constitutes an appropriate portion of the thickness advection. Use of the method is discussed and an example is given.
Abstract
Data from a number of reconnaissance flights into large Pacific tropical cyclones are combined to obtain a generalized pattern of winds at low level (about 1000 feet) under both stationary and non-stationary conditions. With these winds, a number of dependent computations are made including relative trajectories, divergence, vertical motion, rainfall, energy, and relative vorticity.
Abstract
Data from a number of reconnaissance flights into large Pacific tropical cyclones are combined to obtain a generalized pattern of winds at low level (about 1000 feet) under both stationary and non-stationary conditions. With these winds, a number of dependent computations are made including relative trajectories, divergence, vertical motion, rainfall, energy, and relative vorticity.
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A theory of barotropic, nondivergent, zonally propagating waves on an equatorial beta-plant with topography is presented. The bottom contours are assumed to be parallel to the equator, so that the depth profile H is a function only of y, the northward coordinate. Solutions for trapped waves are derived for the following depth profiles: 1) a single-step escarpment, 2) a flat continental shelf, 3) a semi-infinite sloping beach. and 4) an exponentially varying continental shelf/slope region that monotonically increases to a constant depth far from the shoreline. For each wave solution presented. numerical examples of typical periods and phase speeds are also given. The eigenfrequencies ω n for the waves trapped on a sloping beach with depth profile H=H 0+αy take a particularly simple form: ω n =−βH 0/|α|(2n+3), where n=0,1,2,..., and β=2Ω E /R (Ω E and R are the earth's angular speed of rotation and radius, respectively). A number of qualitative results are also derived. For example, a WKB-type argument is used to show that equatorial trapping will always occur over any monotonic depth profile that straddles the equator. Also, it is proved that the phase of an equatorial topographic wave propagates westward or eastward according to whether the equilibrium potential vorticity βy/H(y) is a monotonic increasing or decreasing function of y.
Abstract
A theory of barotropic, nondivergent, zonally propagating waves on an equatorial beta-plant with topography is presented. The bottom contours are assumed to be parallel to the equator, so that the depth profile H is a function only of y, the northward coordinate. Solutions for trapped waves are derived for the following depth profiles: 1) a single-step escarpment, 2) a flat continental shelf, 3) a semi-infinite sloping beach. and 4) an exponentially varying continental shelf/slope region that monotonically increases to a constant depth far from the shoreline. For each wave solution presented. numerical examples of typical periods and phase speeds are also given. The eigenfrequencies ω n for the waves trapped on a sloping beach with depth profile H=H 0+αy take a particularly simple form: ω n =−βH 0/|α|(2n+3), where n=0,1,2,..., and β=2Ω E /R (Ω E and R are the earth's angular speed of rotation and radius, respectively). A number of qualitative results are also derived. For example, a WKB-type argument is used to show that equatorial trapping will always occur over any monotonic depth profile that straddles the equator. Also, it is proved that the phase of an equatorial topographic wave propagates westward or eastward according to whether the equilibrium potential vorticity βy/H(y) is a monotonic increasing or decreasing function of y.
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[Reprinted at author's request from Boston Transcript of January 20, 1909.]
January 18, 1909
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[Reprinted at author's request from Boston Transcript of January 20, 1909.]
January 18, 1909
