Roy M. Endlich

An Iterative Method for Altering the Kinematic Properties of Wind Fields

Abstract Grid-point values of eastward and northward wind components imply that specific fields of divergence, vorticity and deformation exist. For certain purposes, one may wish to change the winds slightly to make them non-divergent, or to make them conform to fields of vorticity or deformation somewhat different than the original values. Control over the kinematic properties of a wind field can be exercised by the procedure given in this paper. The desired wind fields are obtained by a point iterative method applied to the two simultaneous linear partial differential equations that define horizontal divergence and relative vorticity, or stretching and shearing deformation. Some possible applications of this technique in analysis and forecasting are described briefly.

The Mesoscale Structure of Some Regions of Clear-Air Turbulence

Abstract The structure of the atmosphere in regions of clear-air turbulence is investigated by means of aircraft observations of wind and temperature in combination with objective and subjective turbulence records. The nature of the aircraft data and the assumptions inherent in the analyses are described. The detailed fields of vertical and horizontal wind shear, stability and Richardson number are presented for turbulence encountered in three different patterns of flow, viz., a sharp trough, an anticyclonic jet stream, and an intense straight jet. Severe turbulence (equivalent in intensity to that measured by the same aircraft in a mature thunderstorm) was found in certain portions of the trough and ridge, and moderate turbulence existed in the straight jet. Comparison of these cases and of twenty other flights indicates certain similarities and certain differences of the flow conditions in the turbulent regions. The necessary and sufficient conditions for the existence of clear-air turbulence have not b...

Use of a Pattern Recognition Technique for Determining Cloud Motions from Sequences of Satellite Photographs

Abstract Recent geosynchronous satellites (ATS-I and ATS-III) have obtained photographs of clouds over broad regions of the earth at intervals of ∼20 min. Sequences of such photographs show the direction and speed of cloud motions. To extract the motion information in real time it is desirable to process the raw data by computer methods. One approach to this problem is to locate a limited number of centers of brightness that represent the cloud patterns in a photograph. Such centers, which am determined on the basis of area and quantified brightness, are analogous to centre of gravity in mechanics. Measurements of displacements of these centers in successive photographs provide an indication of cloud motion. Brightness centers are found by an objective computer technique called “ISODATA” that was developed in an earlier program of pattern recognition. The average distance between brightness centers is determined in part by specifying values of certain parameters in the ISODATA program. This average distan...

Use of Mass Conservation and Critical Dividing Streamline concepts for Efficient Objective Analysis of Winds in Complex Terrain

Abstract Observed winds and temperature profiles can be used to generate three-dimensional, mass-conserving wind fields that reflect topographical influences. The concept of critical dividing streamlines is used to define quasi-horizontal, flow-confining two-dimensional surfaces. Adjustment toward two-dimensional nondivergence on those surfaces forces flow around obstacles under stable conditions when some flow surfaces intersect higher terrain features. Unlike most mass-conserving wind models, the approach described here includes objective evaluation of the effects of atmospheric stability. Efficiency is achieved by casting the three-dimensional problem as several two-dimensional problems and by using an iterative scheme to adjust toward nondivergence. A 20 × 20 × 5 gridpoint analysis requires approximately 2 min on an IBM-AT personal computer.

Automatic cloud tracking applied to GOES and Meteosat observations

Abstract Improvements to the SRI automatic cloud-tracking system are described that enable it to operate on multilayer clouds associated with severe storms. The improved method has been tested using rapid-scan observations of Hurricane Eloise obtained by the GOES satellite on 22 September 1975. We performed cloud tracking using target selection (clustering) based either on visible or infrared data and tracked the targets using a pattern recognition technique. The technique matches targets with their best likeness (in terms of size, brightness and shape) at successive times in a manner analogous to human pattern recognition, and also rejects vectors in disagreement with the predominant motion in their height (infrared) category. For data of 4 and 8 km resolution, the automatic system gave results very comparable in accuracy and coverage to those obtained by NASA analysts using the Atmospheric and Oceanographic Information Processing System (AOIPS). We also tracked the same targets using a cross-correlation...

Experiments In Automatic Cloud Tracking Using SMS-GOES Data

Abstract A description is given of the component parts of a computer system for automatically tracking clouds shown by sequences of pictures obtained by geostationary weather satellites. The component programs perform the following functions: separation of clouds from background; subdivision of the cloud data into groups (which are potential tracers); computation of the location, size, brightness and infrared values of each group: matching groups at two different times to give cloud motion vectors;and conversion of motions from the row and column coordinates of recorded data to earth coordinates. In this paper, the emphasis is on the automatic grouping and tracking functions. Some recent tests of the method are described and illustrated. These tests used SMS-GOES data in both visible and infrared channels for several different types of clouds, including low clouds, convective clouds and cirrus. Using 4 mi resolution data at one-half hour intervals, and with no initial information about the expected motion...

Direct Computation of Geostrophic Winds from Observed Winds Using the Balance Equation

Abstract In certain meteorological problems it is desirable to make a grid-point analysis of observed winds. In order to combine a wind analysis with other quantities, or to use the wind analysis in a numerical model, one may wish to know the geostrophic winds (or the heights) that conform to the analyzed winds. Many previous studies have shown that the balance equation accurately describes relationships between winds and the height field. In this paper the balance equation is used to equate geostrophic vorticity at each grid point to a sum of terms evaluated from the wind analysis. Then the geostrophic winds are found by altering an initial guess field of zonal and meridional wind components until the geostrophic vorticity and divergence required at each point are met within a close tolerance. The final wind vectors are a geostrophic field that conforms to the original wind analysis according to the balance equation. Typical examples are shown of geostrophic wind vectors computed by this method in a slop...

Evaluation of the WOCSS Wind Analysis Scheme for the San Francisco Bay Area

Abstract Applications of the Winds on Critical Streamline Surfaces (WOCSS) model in the San Francisco Bay Area are described. Three case studies, chosen to represent important classes of airflow in the region, were conducted. Two cases involved a prevailing northeasterly flow with or without an inversion, and the third case involved northeasterly flow at the time of the Oakland hills firestorm of 20 October 1991. The dependence of model results (surface winds) on input winds and on the specification of inversion topography is discussed. Dependable results are produced with relatively few well-placed surface observations and with a single sounding. The results suggest that the model is quite suitable for routine, real-time analyses and other practical applications.

Statistical Analysis of Precipitation Chemistry Measurements over the Eastern United States. Part III: The Ionic Balance among Chemical Constituents

Abstract The relationships between acidity and the principal chemical constituents of precipitation (including sulfate, nitrate, ammonium, calcium, magnesium, sodium, and chloride) were investigated using a new archive of daily precipitation chemistry measurements for the eastern United States. This archive consist of measurements from three networks during the period 1979 through 1983. The chemical relationships between acidity (hydrogen ion concentrations) and the other chemical constituents were studied using six sites that span the eastern United States and represent geographic variations. At these sites, the two predominant cations were hydrogen and ammonium, and the predominant anions were sulfate and nitrate; these four largely controlled the ionic balance, particularly at locations where the precipitation was most acidic. When other less predominant analytes (sodium, magnesium, potassium, chloride, and phosphate) were also considered, the average ionic balance indicated an apparent excess of catio...

The Relationship of Satellite-Inferred Stratospheric Aerosol Extinction to the Position of the 50-mb North Polar Jet Stream

The relationship between stratospheric aerosols and the location of the north polar night stratospheric jet stream was investigated for selected periods of four successive winters (1979-1982), using measurements from SAM II (Stratospheric Aerosol Measurement II) and SAGE I (Stratospheric Aerosol and Gas Experiment I) satellite-borne sun photometers and corresponding meteorological observations. Each period investigated included a polar stratospheric warming during which major dynamic meteorological changes are known to have perturbed the structure of the polar vortex. The analysis of variations in aerosol extinction mixing ratio patterns among winters and during major stratospheric warming events within separate winters showed a well-defined positive gradient in extinction mixing ratio and temperature across the jet stream from the cyclonic side to the anticyclonic side at altitudes between 20 and 30 km during each winter period. Estimates of extinction mixing ratio profiles measured near the center of the polar vortex suggest that a gradual subsidence took place within the polar vortex during at least three of the four winter periods.