Morton G. Wurtele

THE USE OF OPEN BOUNDARY CONDITIONS WITH THE STORM-SURGE EQUATIONS

Abstract Open boundaries are desirable when the region of interest of a computation is a localized area of a much larger domain. Boundary conditions are developed for the linear storm-surge equations (without Coriolis effects) that permit disturbances to pass out of the region of computation with negligible reflection. These conditions, based on the concept of Riemann invariants, are applied in one- and two-space dimensions. Examples of the flow around a sea mound, a shelf, and an island are given. Selected comparisons are made with Sommerfelds radiation condition, advanced by Vastano and Reid.

Impact of Scatterometer Winds on Hydrologic Forcing and Convective Heating through Surface Divergence

Abstract One of the difficulties in estimating atmospheric heat and moisture budgets lies in resolving the near-surface heat and moisture convergence and vertical velocities, each of which is highly dependent on the divergence of the surface wind. A kinematic approach is proposed to utilize scatterometer winds to improve the estimate of surface wind divergence, the omega profile, and, therefore, estimates of the hydrologic forcing and convective heating over the tropical ocean. Improvements in these estimates over those obtained using analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) alone are found when the ERS-1 scatterometer ground tracks passed over the TOGA COARE intensive flux array. The spatial patterns of precipitation estimated from GMS IR temperatures and radar reflectivities agree better with the divergence fields derived from the ERS-1 scatterometer winds than with those derived from either ECMWF or rawinsonde winds. The use of ERS-1 surface winds also changes the omeg...

Construction of Marine Surface Pressure Fields from Scatterometer Winds Alone

Abstract A series of 6-h, synoptic, gridded, global surface wind fields with a resolution of 100 km was generated using the dataset of dealiased Seasat satellite scatterometer (SASS) winds produced as described by Peteherych et al. This paper is an account of the construction of surface pressure fields from these SASS synoptic wind fields only, as carried out by different methods, and the comparison of these pressure fields with National Centers for Environmental Prediction (NCEP) analyses, with the pressure fields of the European Centre for Medium-Range Weather Forecasts (ECMWF), and with the special analyses of the Gulf of Alaska Experiment. One of the methods we use to derive the pressure fields utilizes a two-layer planetary boundary layer (PBL) model iterative scheme that relates the geostrophic wind vector to the surface wind vector, surface roughness, humidity, diabatic and baroclinic effects, and secondary flow. A second method involves the assumption of zero two-dimensional divergence, leading to...

Investigation of a Complex Mountain Wave Situation

Abstract A complex mountain lee wave was recorded by radar-tracked superpressure balloons at White Sands Missile Range on 6 May 1965 at a mean altitude of 3.5 km MSL; simultaneously, a very weak wave was recorded at 7 km. The lower complex wave showed variable wavelengths, amplitudes, and increasing vertical velocities with time. Several of the better existing mountain wave theories were tested against the data to determine which theory or theories, if any, could explain the physical cause of the particular features of the complex wave. It was found that existing theoretical models are too simplified to apply to the condition in the observed wave and explain only its grosser features. If our understanding of gravity waves is to be adequate to explain quantitatively what we are capable of observing quantitatively, we must begin the anlysis of more realistic models or turn to numerical integration of the relevant equations.

MOUNTAIN LEE WAVES AT WHITE SANDS MISSILE RANGE

Abstract : The need for knowledge of wind effect and its variability is well known to all who have worked in the field of unguided missiles. To meet this need, a study of mountain lee waves is now being conducted at White Sands Missile Range. The basic observational technique consists of releasing superpressure balloons, with radar targets and radiosondes attached, at points west of the range and following their trajectories with radars while simultaneously recording temperatures on the GMDs. The balloons are assumed to follow isopycnic surfaces as they float across the range and to trace out the shape of the lee wave. Two balloons are usually released to float simultaneously over the range at two heights and yield a vertical profile of the wave.

A Frontal Cyclogenesis Case Study From Seasat Scatterometfer Data

In June 1978, the Seasat satellite was launched carrying, among other instruments, the Seasat-A scatterometer system (SASS), which produced ambiguous wind speed and direction data at the ocean surface. A fifteen day subset of dealiased wind vector data with the inherent ambiguities removed was produced for the period of September 6-20, 1978. On September 8, SASS began to observe a development of frontal cyclogenesis in the South Pacific off the east coast of New Zealand, in an area of few surface observations. A large mature cyclone contained weak warm and cold fronts and an occlusion with a strong horizontal wind shear. Satellite imagery shows that a strong upper-level jet streak was moving rapidly over the area of the surface frontal occlusion and as the jet passed over this area a new vortex formed. This cyclogenesis event was studied using 50-km resolution scatterometer surface wind data. High-resolution fields of wind vectors, divergence and vorticity are computed and plotted from the scatterometer data to study the structure and development of the newly formed cyclonic vortex, not otherwise possible using conventional observations.

Construction Of Surface Pressure Field From Scatterometer Wind Field

An account of the construction of surface pressure fields from Seasat-A satellite scatterometer (SASS) winds as carried out by different methods, and the comparison of these pressure fields with those derived from in situ ship observations is presented. On the assumption that the pressure adjusts itself instantaneously to the motion field, it may be computed by various methods. One of these makes use of planetary boundary theory, and of the possible techniques in this category a two-layer iterative scheme admitting of the parametrization of diabatic and baroclinic effects and of secondary flow was chosen. A second method involves the assumption of zero two-dimensional divergence, leading to a Laplaces equation (the balance equation) in pressure, with the wind field serving as a forcing function. This method does not accommodate adiabatic or baroclinic effects, and requires a knowledge of the pressure at all boundary points. Two comparison fields are used for validation: the conventional operational analyses of the US National Meteorological Center (NMC), and the special analyses of the Gulf of Alaska Experiment (GOASEX), which were done by hand. The results of the computations were as follows: (1) The pressure fields, as computed from the SASS winds alone, closely approximated the NMC fields in regions where reasonable in situ coverage was available (typically, one or two mb differences over most of the chart, three to four mb in extreme cases); (2) In some cases the SASS-derived pressure fields displayed high-resolution phenomena not detected by the NMC fields, but evident in the GOASEX data; and, (3) As expected, the pressure fields derived from the balance equation were much smoother and less well resolved than the SASS-derived or NMC fields. The divergence as measured from the SASS winds is smaller than, but of the same order of magnitude as, the vorticity.