Abstract: The combined representation of fields of three climatic variables with empirical orthogonal functions, herein referred to as eigenvectors, is discussed. The eigenvectors are derived from measurements of monthly mean sea-level pressure, surface temperature and precipitation at 23 points in North America for 25 Januarys. Selected eigenvectors of the individual climatic variables are presented; however, the major part of the paper is devoted to the presentation of eigenvectors consisting of combinations of three climatic variables. Empirical eigenvectors derived from fields of two or more meteorological variables have been used in statistical prediction models, but none of the studies to date displayed examples of these eigenvectors or discussed the internal consistency of the combined representations. In this paper it is shown that the structure of the covariances between the three climatic variables,as portrayed by the combined representations, is consistent with synoptic experience. This result i...

Abstract: Daily estimates of morning and afternoon mixing depths and average wind speeds through the mixing layers were calculated and summarized for seven locations in several climatic regions of the contiguous United States. Mixing depth and wind speed estimates were based on regular surface (airways) and upper air (rawinsonde) observations of the Weather Bureau and on the assumption of a dry-adiabatic lapse rate in the mixing layer. Monthly averages of morning and afternoon mixing depth and wind speed are presented graphically. The frequency of occurrence of various combinations of mixing depth and wind speed classes were used in an urban diffusion model to calculate theoretical values of relative pollutant concentration for four major cities. These relative pollutant concentrations, which also depend upon city size, are compared among the cities on the bases of their current sizes and a common size.

Abstract: Charts showing the seasonal frequency distribution of anticyclones, cyclones and cyclogeneses (centers of cyclogenesis) in the Southern Hemisphere south of 15S during the International Geophysical Year are presented. Meridional profiles of the zonal frequencies of the systems are compared with corresponding profiles of sea level pressure and wind, 1000–500 mb thermal wind and 500-mb geostrophic wind. Examples of typical cyclone and anticyclone tracks and of the movement of systems during periods with anomalous circulation are given.

Abstract: A formula for estimating the evapotranspiration rate from temperature and relative humidity data is given. Results of some tests of the accuracy of the equation indicate that it is better than other equations based on a similar number of variables. The accuracy was not as good as equations requiring more variables for their utilization, however. It was found from an investigation of the amount of water required for crop production that average yields of corn, soybeans and wheat were obtained when the total precipitation during the growing season averaged 72% of the maximum evapotranspiration. This average actual evapotranspiration rate may be more appropriate than potential evapotranspiration for some general purposes such as assessing the water resources of undeveloped countries, or determining the aridity indices in climatic studies.

Abstract: An urgent need exists for a technique of rapid and economical measurement of vertical profiles of atmospheric particulate concentration. It is shown in this paper that the lidar, or optical radar, is capable of meeting this need. The first part of the paper presents the physical basis of the technique wherein equations based on the Mie scattering theory and the radar equation are derived which permit quantitative calculation of the particulate concentration, turbidity index, and horizontal visibility from the lidar data as functions of height. The remainder of the paper is devoted to a brief description of an operational lidar system, some examples of results obtained with it, and an evaluation of its performance during six months of use. A subsequent paper will present some detailed case studies of pollution episodes in the Chicago Metropolitan area.

Abstract: Eigenvectors may be used in the same way as orthogonal polynomials. They have an advantage over those orthogonal functions expressible by simple formulas, however, in that they are derived from the data being studied and strongly resemble the important features of the data, so that the first several eigenvectors contain a much higher percentage of “variance” than would be contained in an equal number of ordinary orthogonal polynomials. This paper describes the process by which a matrix of eigenvectors was derived from the sets of 12 mean-monthly precipitation values for 60 stations in Nevada. The first three eigenvectors (in order of importance) were found to account for 93% of the “variance” in the original 12 × 60 matrix of raw data and they are also found to have features in common with three natural cycles of annual precipitation in Nevada. The effect of station elevation on each eigenvector is determined by linear correlation. The station multipliers, corrected to a mean elevation, are plott...

Abstract: A combination formula for evaporation that uses the surface temperature measured by infrared thermometers as a boundary condition is successfully tested against the evaporation obtained from a detailed energy balance and Bowen ratio measurements The transfer coefficients used in the combination formula are obtained from aerodynamic similarity and include the effect of the diabatic turbulence Two simple resistive models which attempt to account for the reduction of evaporation due to the water vapor desaturation of the soil surface are analyzed, but fail to describe correctly the transfer processes through the dry upper layer of the soil

Abstract: Evidence from locations in the north central region of the United States indicates that a rainy spell is more likely to terminate after at least two wet days than after one wet day during early spring. However, the departure from a first-order Markov chain model has only minor effects when estimating probabilities of specified sequences of wet and dry days.

Abstract: The results of a heat flux comparison experiment carried out at Hay, New South Wales, Australia, during May 1966 using a sonic anemometer thermometer (SAT), Fluxatron and Evapotron are reported. The instruments agree with each other to within a factor of 2 for individual runs. The large fluctuations from run to run of the individual estimates are mainly caused by the fact that the Eulerian point average does not provide an adequate statistical sample of the heat flux. This point is illustrated by the non-stationary behavior of the instantaneous product of vertical wind and temperature. As auxiliary results, values of σw/u* and σT/T* have been obtained which are somewhat higher than, but in general agreement with, observations reported by Mordukhovich and Zwang.

Abstract: The silicon photovoltaic solar cell has made possible the construction of simple pyranometers of reasonable accuracy. Cell response is linear, temperature sensitivity is low, and spectral response does not cause serious error, provided the cell is used in open sunlight. The solar cell has been mounted beneath a special diffusing unit to obtain a rugged pyranometer with excellent cosine response. This pyranometer has been coupled with a solid state integrator developed for this purpose. The integral is recorded with either visual or printing counters. Tests were made during September 1965 through February 1966 when low solar altitude and severe operating conditions would cause greatest error; and again during March 1966 through July 1966 when solar radiation intensities were high. For the first period the standard error of estimate and the solar radiation means were, respectively, 84 and 2200 Wh m−2 day−1. For the second period the corresponding values were 158 and 5630 Wh m−2 day−1.

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.

Abstract: The temperature of a naturally exposed, bare wet soil surface was measured with a narrow bandpass infrared radiation thermometer. Corrections were made for actual sky radiance and for surface emittance, the latter also determined in the field. When used to calculate evaporation rates with a Dalton-type equation containing a log-law wind function (drag coefficient × windspeed), excellent agreement was found with lysimeter values on both an hourly and daily basis. The results demonstrate the feasibility of surface temperature measurements and support the validity of the log law for describing transfer in the surface layer.

Abstract: During the summer of 1966 from Bemidji, Minn., aircraft collections of cirrus crystals were made with a continuous particle replicator. Actual samples show that cirrus crystal trails with a concentrations of 105–106 m−3 can survive a fall of 20,000 ft in clear air with a temperature/dew point spread of 15C. Computations of evaporation rates for falling crystals suggest that it is somewhat surprising that the crystals could have survived under the observed conditions; however, this may have been because input data for the calculations are inadequate.

Abstract: Radar echoes over the Florida peninsula have been recorded manually every 3 hr on a 7.5 by 7.5 mi grid during the past three summers. This note summarizes the echo distribution for the period May through August 1963. The spatial and temporal variations of convective activity were found to be highly correlated with the sea breeze.

Abstract: Wind vane motion constants (damping ratio, natural wavelength and decay distance) are derived in a way which can accomodate both mechanical friction and the presence of a propeller. The motion is shown to be insufficiently described by a second order equation because of the way in which the aerodynamic torque changes with angle of attack. This implies that any measurements of vane constants made in the wind tunnel at initial angles of attack above 20° are not representative for the vane. Simple relations between easily measured vane dimensions and motion constants are derived, and vane motion is proved to be independent of the fin area. The WMO requirement for wind vanes is translated into motion constants and shown to be fulfilled for any vane with a damping ratio of 0.30. For turbulence measurements a certain short-wavelength reliability limit for vane-measured spectra is proposed. Experimental comparison of basic fin configurations shows the inferiority of streamlined and splayed fins. General...

Abstract: A rather general formulation is utilized for the stability dependence of the eddy coefficient for heat KH above the lowest 50 m. It contains five empirical parameters which pertain to the magnitude of KH in neutral conditions, its variation with increasing stability, its variation with increasing instability, the extent of a slightly countergradient upward heat flux, and the height variation of KH in stable air above hilly terrain or above a cloud-capped inversion base. The five parameters were evaluated or checked against observations of the thermal modification of polar air moving from New England towards Bermuda, and of the diurnal temperature wave at O'Neill, Nebr. A detailed study of the effects of variation of any of the parameters upon the resultant potential temperature profile is included, as is also the effects of different rates of long-wave radiation, of different cloudiness, and of different large-scale subsidence than those assumed. The empirically obtained formulation for KH giving...

Abstract: Four types of chinook winds are described and features detectable in satellite pictures are shown. The hypothesis that large amplitude lee waves could be a possible driving mechanism for chinook winds is investigated for a case occurring in the Rocky Mountains during April 1963. It is shown that the stability of the surface inversion layer on the windward side of a mountain is related to the occurrence of chinook winds to the leeward side. This relationship leads to the speculation that chinook winds may undergo a quasi-diurnal fluctuation, in phase with the onset of the windward surface inversion.

Abstract: A continuous, automatic, and portable instrument was developed for detecting and counting ice nuclei in the field and laboratory. The nuclei are activated in a cloud chamber and the resulting ice crystals are counted by an acoustic particle sensor while the water drops are ignored. The instrument is used in aircraft, trucks, and at fixed sites to track silver iodide and natural ice nuclei.

Abstract: Most current objective analysis schemes require a rather subjective pre-specification of “weight curves” in their interpolation formulae. This has the effect of preordaining, to a certain extent, the manner in which the variance will be distributed among the component perturbations. An objective analysis technique is presented wherein the data define their own “weight curves” and, consequently, their own variance partitioning procedures. The possible stochastic or periodic nature of the data field is discussed by means of the power spectrum. As a companion map to the final analysis, a map estimating the accuracy of the analysis at each grid point is presented.

Abstract: A numerical procedure is described for computing a stream-function field from the vorticity of the horizontal wind field. The method was developed for use in meteorological studies which require analyses based solely on wind observations, or for use in the construction of balanced fields of winds and heights. The boundary of the net region is treated by specifying the gradients of the stream function normal to the boundary. The solution for the stream-function field is achieved relatively quickly by the iterative process known as the implicit alternating-direction method. The same procedure is also used to calculate a velocity-potential field from the divergence of the wind field. The computations are performed on a spherical net and have been tested on wind fields over both the United States and the Caribbean. The computed stream-function fields have been found to provide reliable and sufficiently accurate representations of the non-divergent wind field.

Abstract: The seasonal variations during the IGY of sea-level pressures, 500-mb heights, and 1000-500 mb thickness in the Southern Hemisphere are examined to see if they conform to patterns which are deemed intrinsic to the hemisphere. These are: 1) the arrangement of the annual temperature range in four concentric zones of alternating low and high range; 2) the coldness of the lower and middle troposphere over Australasia in winter compared with South America and Africa; 3) the positive temperature isanomals in middle and high latitudes over the South Pacific Ocean in both summer and winter; and 4) the sea-level pressure and 500-mb height variations of opposite sign in middle and high latitudes which give rise to a second harmonic of large amplitude in temperature and height gradients, and in winds and sea-level pressure. The speed of movement of lows between 30 and 70S was, on the average, only slightly lower in the IGY summer than in the winter. A comparison between the standard deviations of daily sea-...

Abstract: Four forms of hail data in Illinois were analyzed to obtain indirect measures of the areal and seasonal variations in hail intensity. These data were also examined to ascertain which hail characteristics correlated best with crop damage. The frequency of intense hail in the crop season (May–October) was found to increase with time, reaching a maximum in September. Insurance statistics indicated that corn damage from hail was usually greater in July than in the later months because corn was more susceptible to damage in July. Observations from a mesoscale network in central Illinois indicated that hailstone sizes and number (volume of ice) and durations of hailstorms related moderately well with crop-hail damage, but that strong surface winds were more closely related. Significant areal variations of hail intensity were found, with some portions of Illinois experiencing intense hail six times more often than other areas.

Abstract: Ninety large oblate hailstones have been photographed to display thin sections containing their minor and major axes. The ratios of their minor to major axes have been determined throughout their growth from the shapes of the layered growth transitions. It has been found that the majority of hailstones became increasingly oblate throughout growth, but that a further increase in oblateness accompanied the melting of the hailstones during their descent to the ground. Although even oblate hailstones are believed to tumble to some extent, they fall for most of the time with their minor axis vertical. Evidence is presented which suggests that during growth the proportion of unfrozen water is often greater at either end of the minor axis than at the sides of the hailstone. It is proposed that the increase in oblateness during growth is due to spongy ice on the upstream face being driven toward the sides of the hailstone, where it subsequently freezes, and that the further increase in oblateness during ...

Abstract: Study of the frequency of damaging storms along the east coast of the United States during the past 40 years has revealed a significant increase in the past decade. Reasons for this increase are analyzed. It is concluded that man's generally unrestricted development of the outer coastal margin as well as a slight intensification of coastal cyclones have both contributed. Assuming no change in coastal development or meteorological conditions in the future, a storm damaging as much of the coast as the one in March 1962 would be expected once every 20 years. Based on recent storm damage experience, the New England coastal area and the region around Cape Hatteras appear to be particularly vulnerable to storm damage. The New Jersey, Maryland, Delaware coast and the coast from South Carolina to Florida seem to have a relatively low storm damage potential.

Abstract: On the basis of satellite and other types of information, it is shown, both on observational and theoretical grounds, that cirrus clouds have a higher transmission for radiation at 10 μ than for radiation at 6 μ. Thus, in the case studied, at 10 μ the cirrus clouds had a fractional transmission of about 50%, while at 6 μ the clouds were essentially opaque. This fact has an important bearing on attempts to use a “humidity diagram” to estimate relative humidity above clouds. The satellite data show that measurements at 6 or 10 μ can be used to locate regions of substantial cloudiness, which are therefore regions of high relative humidity in the troposphere. To use these satellite measurements to estimate the relative humidity above clouds would be misleading. However, the use of radiation measurements in both channels can perhaps be helpful for specifying the transmissivity of cirrus clouds, and in the absence of clouds, for locating regions of low relative humidity.

Abstract: The visual quality of the atmosphere in terms of the meteorological range has become a frequently used working standard in aviation and air pollution. Calculations of the meteorological range based on measured size frequency distribution of aerosols in the atmosphere are compared with visibility observations and discussed with regard to existing weather conditions. The results show the existence of strong inhomogeneities in the aerosol content of air and indicate the necessity for objective means in order to quantitatively evaluate the visual quality of the atmosphere. It follows from the calculations that changes in refractive index and wavelength within their limiting values have little influence on the total extinction of any size distribution.

Abstract: Tropospheric water vapor analysis via Tiros IV SATELLITE, determining spatial and temporal temperature, humidity and mass variations

Abstract: This paper describes equipment designed to observe variations in atmospheric density at heights up to 65 km by measuring the intensity of light back-scattered from a laser beam. The basic theory of the technique is briefly described, and an expression is derived for the sensitivity of the laser radar. The design of the equipment is then discussed from the point of view of optimization of the equipmental parameters for maximum sensitivity, with a view to obtaining measurements at the greatest possible height. The paper continues with a description of the actual equipment, a discussion of problems encountered in its application, and the methods used to overcome these problems. Finally, a very brief description is given of the results obtained with the laser radar.