Showing papers in "Monthly Weather Review in 1970"

Some basic formalisms in numerical variational analysis

Abstract: This study aims at the theoretical development of a method of “four-dimensional analysis,” namely the numerical variational analysis. The three basic types of variational formalism in the numerical variational analysis method are discussed. The basic formalisms are categorized into three areas: (1) “timewise localized” formalism, (2) formalism with strong constraint, and (3) formalism with weak constraint. Exact satisfaction of selected prognostic equations were formulated as constraints in the functionals for the first two formalisms. However, only the second formalism contains explicitly the time variation terms in the Euler equations. The third formalism is characterized by the subsidiary condition which requires that the prognostic or diagnostic equations must be approximately satisfied. The variational formalisms and the associated Euler-Lagrange equations are obtained in the form of finite-difference analogs. In this article, the filtering of cach formalism and the uniqueness of solutions o...

Large-scale features of monthly mean northern hemisphere anomaly maps of sea-level pressure

Abstract: Spatial patterns of circulation variability over the Northern Hemisphere and their changes during the past 70 yr (1899–1969) are examined using eigenvector analyses of mean January and July sea-level pressure maps. The first several eigenvectors display variability associated with the major centers of action (the subpolar oceanic Lows, the subtropical oceanic Highs, the winter Siberian High, and the summer Asiatic Low). The pattern of the first eigenvector of January suggests that the intensity and latitudinal position of the major circulation features over the North Atlantic are associated with the intensity and position of the Aleutian Low over the North Pacific. The time series of the coefficients of the hemispheric eigenvectors are used to identify intervals of change in the hemispheric circulation associated with features on the scale of thc major centers of action. These time series provide a more general description of circulation change than that obtained from local or regional indices; b...

Atlantic tropical systems of 1969

Abstract: A census of Atlantic tropical systems of 1969 presents information on the history of each tropical wave or disturbance, including the dates these systems passed three key stations: Dakar, Barbados, and San Andres Island.

Diurnal variations in boundary layer winds over the south-central united states in summer

Abstract: Analysis of 1 week's data in August 1960 shows significant diurnal variations in surface geostrophic wind over the south-central United States. The oscillation in the southerly component (Vg) is driven by the response of the thermal wind to the diurnal temperature cycle over sloping terrain. A smaller oscillation in Ug derives from spatial variations in the amplitude of the diurnal pressure wave. The amplitude of the oscillation in Vg is about 3 to 5 m sec–1 at the surface, decaying exponentially with height to near 0 at 2 km. Examination of 11 yr of summertime rawinsonde data at Fort Worth, Tex., shows a very regular diurnal variation in boundary layer wind with maximum amplitude of about 3 m sec–1 at 600 m above the ground. This oscillation is forced by periodic variations in both eddy viscosity and geostrophic wind. Using a simplified model of the boundary layer, we obtain solutions for the diurnally periodic wind resulting from “reasonable” variations in eddy viscosity and “observed” variatio...

The estimation of monthly rainfall from satellite data

Abstract: The global distribution of precipitation is an outstanding example of a pattern whose form cannot be deduced very satisfactorily from conventional observational data. Many investigations of the global hydrological cycle across real periods of time are based on broadly generalized assumptions concerning rainfall patterns, especially over the world's oceans. This paper explores the feasibility of employing observational data from meteorological satellites to yield more acceptable maps of rainfall across periods of 1 mo and upward than is possible using conventional surface measurements, whose distributions are less uniform, and whose derivations are more heterogeneous, than the satellite data coverage. The central problem is related to the fact that satellites cannot measure rainfall directly, and the solution of this problem necessitates the construction of a rainfall coefficient equation to be evaluated from nephanalysis indications of cloud cover. Evaluated coefficients for the months of March, ...

A regression method for obtaining real-time temperature and geopotential height profiles from satellite spectrometer measurements and its application to nimbus 3 “sirs” observations

Abstract: A least squares regression method is formulated for obtaining global temperature and geopotential height profiles from satellite radiation measurements, particularly those obtained by the Sate1lite Infra-Red Spectrometer (SIRS) aboard the Nimbus 3 satellite launched Apr. 14, 1969. Regression equations relating temperature and geopotential height to spectral radiance observations are derived. A method accounting for the influence of clouds, mountains, and hot terrain on the solutions is described. Results obtained from Nimbus 3 radiance data are presented. The procedure described herein has been successfully applied to Nimbus 3 SIRS observations on a real-time basis. The temperature and geopotential heights obtained are being used operationally by the National Meteorological Center in their objective constant pressure analyses. Numerous meteorological results are given to demonstrate the usefulness of this new sounding tool.

On the annual variation of the monthly mean meridional circulation

Abstract: Data for a 5-yr period from a dense network of upper air stations have been used to determine the annual cycle in the mean meridional circulation north of 15°S. Only during the transition months April, May and October, November is there some degree of symmetry with respect to the Equator. During the other months of the year, the Hadley cell of the winter hemisphere with a maximum strength of about 23 × 1013 gm sec–1 appears always to dominate the circulation. The Hadley cell of the summer hemisphere practically disappears, except possibly near the surface. Maximum meridional velocities connected with the winter Hadley cell are about 2.5 m sec–1 near 1000 mb and over 3 m sec–1 near 200 mb. Mean vertical velocities attain values of about 5 and 8 mm sec–1 in the downward and upward branches of the winter Hadley cells. A rather weak Ferrel circulation (about 4 × 1013 gm sec–1) and a very weak polar circulation (about 1 × 1013 gm sec–1) are computed in middle and high latitudes throughout the year. Wi...

The determination of sea-surface temperature from satellite high resolution infrared window radiation measurements

Abstract: A statistical histogram method is developed to objectively determine sea-surface temperature from satellite high resolution window radiation measurements. The method involves inferring the distribution of surface radiances for the clear atmospheric case from observed histograms of generally cloud-contaminated radiances. The brightness temperature associated with the clear atmosphere modal peak radiance is the statistically most probable surface temperature. The reliability of the inferred surface temperature depends upon the number of cloud-free measurements available to define the clear mode. The method accounts for atmospheric attenuation and instrumental noise and also objectively discriminates cloud-free from cloud-contaminated observations. The statistical histogram method is applied to 3.8 micrometer window radiation data obtained by the High Resolution Infrared Radiometer flown on the Nimbus 2 and Nimbus 3 satellites. Examples of sea temperatures inferred over both small and large areas ar...

Palm sunday tornadoes of april 11, 1965

Abstract: An extensive aerial survey was made over a large portion of the area affected by the outbreak of tornadoes on Palm Sunday on Apr. 11, 1965. The destruction from the tornadoes extended over parts of six Midwestern States. Aerial and ground damage surveys were combined with eyewitness reports to determine the exact location and time of each tornado occurrence and its path. Radar pictures of the squall line clouds were used to verify the direction and speed of the tornado-producing clouds. Almost simultaneously with the first tornado touchdown in eastern Iowa, TIROS IX took pictures of the Midwest United States that showed a large tongue of cloud-free dry air behind the cold front. The vertical structure of the cold dome is discussed in connection with its role in the development of the tornadoes. Two predictive parameters, namely, the best lifted index (BLI) and material differential advection (MDA) were developed and evaluated with data gathered on this outbreak of tornadoes. The wind speed of a t...

The ranked probability score and the probability score: a comparison1,, 2

Abstract: In this paper, we compare the ranked probability score (RPS) and the probability score (PS) and examine the nature of the sensitivity of the RPS to distance. First, we briefly describe the nature of and the relationship between the frameworks within which the RPS and the PS were formulated. Second, we consider certain properties of the RPS and the PS including their range, their values for categorical and uniform forecasts, and their “proper” nature. Third, we describe the RPS and the PS in a manner that reveals the structure of and the relationship between these scoring rules. Fourth, we considered the RPS with reference to two definitions of distance and examine the nature of the sensitivity of the RPS to distance. The comparison of the RPS and the PS suggests that the RPS rather than the PS should be used to evaluate probability forecats, at least in those situations in which the variable of concern is ordered.

Numerical variational analysis formulated under the constraints as determined by longwave equations and a low-pass filter

Abstract: The “timewise localized” variational formalism of the numerical variational analysis method is used (1) to filter and suppress unnecessary high-frequency noises contained in initial and forecast fields and (2) to obtain dynamically sound initial values in the areas lacking data. A set of nonlinear longwave equations and a low-pass filter minimizing local changes are used in this paper as dynamical constraints. Also proposed in this study is a technique to assure the convergence of a numerical solution of the nonlinear Euler equations by an iterative process. Three applications of the method are presented. The first two examples demonstrate that the initial guess in the iterative process influences significantly the speed of convergence. The last example is an application to the 500-mb analysis of hurricane Dora, 1964, and demonstrates a reasonable analysis in the data-sparse area where the hurricane was located at 1200 GMT on Sept. 8, 1964.

“bottom stress time-history” in linearized equations of motion for storm surges1

Abstract: A transient Ekman's transport equation, in which bottom stress is formed as a convoluted integral in terms of surface stress and surface slope, and a continuity equation are used as predictors to compute storm surges in a model basin. Driving forces in the basin are analytically computed, using a model storm to represent actual meteorological conditions. A coastal boundary condition that relates surface slope to surface stress is developed by balancing slope and drift transports normal to a vertical wall. At interior grid points of the basin, sea-surface heights are computed by numerical means, using the prediction equations. These sea-surface heights are then extrapolated to the coast to agree with the coastal surface slope given by the boundary condition. Coastal storm surges computed in this manner are compared with observed surges to test the model developed in this study.

The climate of the midnineteenth century united states compared to the current normals

Abstract: Climatic data for the Continental United States for the 1850's and 1860's are compared with the currently valid normals. In the eastern half of the United States, these two decades continue the cooler and somewhat wetter character found in an earlier investigation, while in the western half, a distinctly warmer and decisively wetter climate existed in the mid-19th century, as compared to the conditions in the first half of the 20th century.

Integration of the primitive barotropic model over a spherical geodesic grid

Abstract: Conservative finite-difference approximations are developed for the primitive barotropic model over a spherical geodesic grid. Truncation error considerations show that the grid resolution must be at least as fine as 2½° in order for the error not to dominate the mass flux calculations. When the fine resolution is used, the approximations are seen to be quite good. Comparisons are made with schemes in use today with approximately the same resolution applied to the same initial condition.

Coastal air-circulation system: observations and empirical model 1,, 2

Abstract: Three consecutive early summer studies on the upper Texas coast have produced data that afford a much clearer view of the land and sea breeze system than was previously held. Networks of surface observations, pibal and radiosonde ascents, and aircraft flights have produced observations that are integrated to give a synthesized model of the coastal air-circulation system as a function of space and time.

An operational technique for relating the movement of existing tropical cyclones to past tracks1

Abstract: The HURRAN (hurricane analog) technique for selecting analogs for an existing tropical storm or hurricane is described. This fully computerized program examines tracks of all Atlantic tropical storms or hurricanes since 1886, and those that have designated characteristics similar to an existing storm are selected and identified. Positions of storms selected as analogs are determined at 12, 24, 36, 48, and 72 hr after the initial time. Probability ellipses are computed from the resulting arrays and plotted on an x, y (CALCOMP) offline plotter. The program also has the option of computing the probability that the storm center will be located within a fixed distance of a given point at a specific time. Operational use of HURRAN during the 1969 hurricane season, including both its utility and limitations, is described.

A circularly symmetric primitive equation model of tropical cyclone development containing an explicit water vapor cycle

Abstract: The tropical cyclone model described in previous reports is extended to include an explicit water vapor cycle. Results of experiments that examine effects due to initial humidity conditions, radial resolution, and the finite-difference scheme are discussed. Growth to the mature stage is more rapid in the moist environment, but peak intensity is not strongly affected by the initial moisture content. Rainfall rates are quite reasonable, and nonconvective precipitation is found to be a significant proportion of the total rainfall, in agreement with recent empirical results. Experiments with upstream differencing yield more realistic solutions than do experiments with centered differences. This surprising result is discussed in detail.

Numerical models of a tropical cumulus cloud with bilateral and axial symmetry1

Abstract: Two versions of a numerical model for cumulus convection are compared. One is symmetrical about a vertical plane, the other about a vertical axis. It is found that the axisymmetric model grows more vigorously than the other and more realistically represents the relations between updraft and downdraft, the shape, and other characteristics. The previous findings of Ogura are generally confirmed and extended.

Numerical variational analysis with weak constraint and application to surface analysis of severe storm gust

Abstract: An investigation of the numerical variational analysis method is made for a case of “weak constraint” where the subsidiary condition is given in the form of an approximation. The simple example of a system moving with an optimized velocity is used to illustrate the theoretical development. The method is applied to analysis of the National Severe Storms Laboratory mesonetwork data of the severe storm gust that passed over the network on May 31, 1969.

The unprecedented rains in virginia associated with the remnants of hurricane camille

Abstract: The rainfall and synoptic features of the unprecedented Virginia storm associated with the remnants of hurricane Camille are analyzed. Comparisons with alltime record-breaking rains in the United States and probable maximum precipitation estimates are made. The rains of this storm are shown to come within 80 to 85 percent of the probable maximum precipitation for a duration of 12 hr for areas up to 1,000 mi2. Persistent low-level moisture feeding into the remains of Camille's cyclonic circulation was found to be close to the maximum persisting value for the season and location. The passage of the remnant low-pressure system a little to the south of the rain area resulted in low-level flow from the southeast which made it possible to utilize the high moisture, with some orographic intensification, without depletion by upwind barriers. Apparently, in addition to the very high moisture values, a number of synoptic and mesoscale weather factors operated properly to produce the remarkable rainfall.

A january simulation experiment with the two-layer version of the ncar global circulation model

Abstract: Results of a January simulation experiment with the two-layer version of the NCAR global circulation model are discussed. The model includes a hydrological cycle, horizontal and vertical turbulent transports of momentum, heat, and water vapor from the lower boundary and within the atmosphere, and calculations of solar and terrestrial radiation. Although the water vapor field interacts with the radiation calculations, the cloud distribution is a function of latitude and season. In this version of the model, the earth's orography is omitted as well as an explicit calculation of the surface temperature. This version of the model has a spherical horizontal mesh spacing of 5° in both longitude and latitude and two vertical layers at 6-km height, increments. The details of the finite-difference scheme for the model are presented. The initial conditions for this experiment are based on an isothermal atmosphere at rest. The zonal mean cloudiness, the mean sea level temperature distribution, and the sun's...

The dynamic structure of lee wave flow as obtained from balloon and airplane observations

Abstract: The lee flow disturbances produced by the Front Range of the Colorado Rockies have been quantitatively observed in a continuing program at the National Center for Atmospheric Research. The results of midtroposphere constant-volume ballon and aircraft flights in the winter of 1966/67 are here presented. The relative merits and limitations of the two methods are compared with respect to various operational and inherent phenomenological difficulties of the subject. The nonstationarity of many flow features is inescapable and poses serious problems for data evaluation and theory. Schematically, we distinguish between smooth, wavy, and hydraulic jump-type flow patterns, but also observe some cases that do not fit well into any of these categories. The stronger stationary wave features can be compared with the “stable” resonance modes computed from stationary linear theory, that is, those modes which are insensitive to small changes in the upstream flow. The frequent occurrence of erratic and nonstatio...

Numerical experiments with a two-dimensional horizontal variable grid

Abstract: A two-dimensional horizontal variable grid is derived that has maximum resolution at the center and minimum resolution near the boundaries of the grid By using the analytic transformation that defines the variable grid, the equations of motion for a free-surface model are transformed in terms of new independent space variables in a computational domain with constant resolution Numerical experiments utilize the variable grid to (1) increase the domain size with a fixed resolution at the center and (2) increase the resolution at the center with a fixed domain size Several finite-difference analogs and three time-integration schemes are tested For a given domain size and number of grid points, several variable grid experiments show superior results in the mass and momentum fields compared to constant grid results Most variable grid experiments, however, show a small (less than 1 percent) increase in total energy after 2000 time steps due apparently to the presence of additional nonlinear terms

A quasi-geostrophic model of the winter stratospheric circulation

Abstract: A six-level quasi-geostrophic model including radiative and photochemical processes in the manner suggested by Lindaen and Goody is run from a state of joint radiative-photochemical equilibrium for midwinter conditions. The spectral method is used to integrate the equations where all dependent variables are represented by a set of spherical harmonics with east-west wave numbers 0, 1, 2, 3, and 6 included. The winter storage of ozone in the polar lower stratosphere is simulated, and the importance of horlzontal planetary scale transports and the vertical eddy diffusion of ozone is demonstrated. The rapid dissipation of upper stratospheric temperature disturbances by joint radiative-photochemical relaxation is discussed, and the importance of tropospheric forcing and nonlinear exchanges of kinetic energy between the planetary scale waves is demonstrated. The energetics of downward-propagating spontaneous warmings is discussed. A full-scale warming is triggered by strengthening the north-south lower tropospheric temperature gradient. Its main energy source is found to be a greatly increased forcing of the stratosphere from below.

The atlantic hurricane season of 1969

Abstract: The 1969 hurricane season in the North Atlantic area, considered in its entirety, and synoptic and statistical aspects of individual storms are discussed.

a Generalized Probability Model for Sequences of Wet and Dry Days

Abstract: A generalization of the two main probability models used to describe runs of wet days or of dry days is given. The new model depends on only two parameters and is shown to fit a large proportion of available sets of data.

On partial difference equations in mathematical physics

Abstract: A rather general theory of nonlinear computational stability is reported. Instability is caused by both spatial and temporal high frequencies that, if not present initially, will appear from nonlinear interactions. It appears that through simple remedies relative stability, if not perfect stability, can be achieved.

On the possibility of weather modification by aircraft contrails

Abstract: The possible effect of contrails in modifying the weather is reconsidered in the light of information obtained from ground-level contrails in Alaska. It appears likely that inadvertent cloud seeding by jet aircraft may be of the same order of magnitude as that attained in commercial cloud seeding operations. Further investigation is needed; but in the meantime, the possibility of contrail contamination should be kept in mind when evaluating the results of seeding operations.

Tornadoes associated with hurricane beulah on september 19–23, 1967

Abstract: One hundred fifteen tornadoes are known to have occurred in association with hurricane Beulah. The total was far greater than the number reported with any previous North Atlantic tropical cyclone in history. The spatial distribution of the tornadoes with reference to the hurricane center was examined, and it is shown that the best relationships on location of the hurricane-tornado within the parent cyclone are obtained with respect to true azimuth and are superior to those obtained using an orientation from a heading along the tropical cyclone track. With few exceptions, the tornadoes associated with hurricane Beulah occurred outside the area of known hurricane-force winds. The period of the day, the orientation of the Texas coastline in relation to the hurricane's path, and the length of time Beulah lingered near the coast may have contributed to the record number of occurrences of hurricane-tornadoes.