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Many of the atmospheric anomalies that occur around built-up areas were described qualitatively in the last century. Stimulated no doubt by the 1968 WMO Brussels Symposium on Urban Climates and by the present widespread interest in the environment of “human settlements,” there has been a recent quantum jump in the number of published papers on urban meteorology, including many attempts to model and quantify the anomalies. This short paper, which is not intended to be a survey, contains some thoughts an a few selected topics. The importance of monitoring beyond the suburban limits is stressed, in view of the interactions between the urban and regional fields of motion. Despite the fact that cities are usually located in irregular terrain, the value of searching for universal results is stressed both on the micro- and mesoscales within and near cities. As part of the design of new studies, inventories of existing data should be made. In many cases, the data banks deserve reexamination from time to ...

A hybrid analog-digital computer has been established in the Department of Meteorology and Oceanography of the University of Michigan. It comprises three medium size analog computers, a small, general purpose digital computer, and an analog/digital linkage so that all of the computers can be operated together as a hybrid system. The primary functions of the computer are acquisition and reduction of field data and research in meteorological simulation. It is capable of accepting data acquired on-line from local instruments, or recorded in the field on analog magnetic tape, digital magnetic tape or punched paper tape. These data can then be processed in either analog or digital form or transmitted to a large digital computer via magnetic tape. The analog computers are versatile and of sufficient capacity to be useful for many analog data processing tasks as well as for simulation of atmospheric models such as those used in the study of diffusion and micrometeorology.

Summary Supplementary to an earlier paper in the Review of Scientific Instruments for August, 1940, this paper gives additional technical data on the construction and a discussion of important applications of a Wheatstone bridge type of balanced direct-current photoelectric amplifier adapted for use on 110-volt a-c commercial power lines. This instrument is especially adapted for use with the standard recorders now employed by the U. S. Weather Bureau in the study of Solar radiation. The determination of the amount and variation of ozone in the stratosphere, and of the total intensity of ultraviolet solar radiation in a definite wave band, are discussed as the important applications of the instrument. Performance tests indicate that the instrument is equivalent to the older battery type in sensitivity and precision. It is, furthermore, free from the disadvantages of requiring frequent voltage adjustments, sensitivity tests, and the continual attention of an experienced operator.

The following short paper was read by Dr. Baur at the Edinburgh Meeting of the Meteorology Association of the International Geodetic and Geophysical Union in July 1936; it gives his views on two of the Themes (A and B) on the Agenda of the meeting (see Bulletin, Feb., 1936, p. 53–4). Dr. C. F. Brooks and Mr. I. I. Schell have rendered the translation from the original German MS, loaned us by Mr. R. H. Weightman of the U. S. Weather Bureau, Washington. Appended to the article are some abstracts and comments on Dr. Baur's paper on the importance of the stratosphere in the broad-weather situations in Western Europe published in 1936 (Met. Zts., p. 237) which shows the same ideas used in application to long-range (10-day) forecasting. We print the article with the kind permission of Dr. Baur. See also Dr. Baur's latest paper in Met Zts., Dec. 1937.

This paper is a summary of cloudiness over the Greenland icecap route from Sondrestrom Air Base, approximately 67N–51W, to Angmagssalik, approximately 65.5N–37.5W. Four types of synoptic systems were chosen and cloudiness summarized by types both annually and for the summer season. Total cloudiness annually and for the summer season without regard to synoptic types is also presented. Data for this paper consisted of 511 flight cross sections made by Scandinavian Airlines System flight crews in scheduled air service over the icecap route. It is presented in the form of a cross-section grid with isopleths showing the percentage of time cloudiness was observed at each grid point. These cross sections are of particular value in that they are the first source of systematic, observed weather data over this area. An attempt is made to explain icecap cloud distribution by correlation with system type in order to provide a practical forecasting aid for the Greenland air-route forecasters.

This paper covers the general requirements and restraints of a global meteorological sounding network, and presents the gun-launched meteorological probe as a system adaptable to such requirements, with demonstrable operational experience already established. The paper deals with the network requirements in three categories; required surface areas (land or water), payload carriers, and associated data collection and handling facilities. It then discusses the role of the gun-launched probe within the outline of these requirements. Certain sensors are also briefly discussed. The role of the gun-launched probe as a concept applicable to global expansion is presented as one of the most promising of available systems.

A study of the history of the early developments in the theory of the saturated adiabatic process reveals that the first quantitative formulation of both the dry- and the saturated-adiabatic cooling rates were given by the British physicist, William Thomson (later Lord Kelvin), in a paper read in 1862, although the first published analysis was presented in 1864 by a Swiss meteorologist, Reye. Reye's paper presents both the differential form and the exact integrated form of the reversible saturated adiabatic relationship, which thus attained its modern form at the moment of its first appearance. Reye also gave a very clear, though brief, discussion of the concepts of atmospheric stability of both dry and saturated layers. The papers of Hann (1874) and Hertz (1884), frequently misquoted as the original treatments of the saturated adiabatic theory, are thus shown to be secondary papers in the actual history of this important theory.

This paper summarizes the responses of the forecasters of the Travelers Weather Service to a questionnaire concerning probability forecasting. The questionnaire was designed to elicit information from the forecasters relative to the process of precipitation probability forecasting (e.g., the information sources examined, their relative importance and order of examination), the relationship between judgments and forecasts, the effect of the definition of precipitation on the forecasts, the meaning of the forecasts, the effects of feedback and experience on the forecasts, and related matters. The responses to the questionnaire and subsequent discussions with Travelers Weather Service and National Weather Service forecasters suggest the presence of a number of “problems” related to probability forecasting. Several of these “problems” are considered in some detail in a separate paper (Murphy and Winkler, 1971).

When fully implemented, Omega will be a system of eight very low frequency (VLF) transmitters providing global coverage for navigation. Recently, intensive design and development has exploited Omega for tracking sondes (both free-rising and free-falling) to determine wind velocity as a function of height. During the summer of 1974, several GATE measurement systems, including radiosondes launched from ships and dropsondes released from both aircraft and constant level balloons, will provide winds derived from Omega signals. While some GATE ship radiosonde systems will use other VLF transmitters for windfinding, the principles involved are essentially identical to those required for Omega windfinding. This paper formulates the analytical techniques needed to use Omega or other VLF transmitters for windfinding, discusses sources of measurement errors, reviews Omega wind measurement error experiments, and projects wind errors into the GATE “B” area near 10N latitude and 25W longitude.

Few would question such doggerel as “no two snow crystals are alike and in infinite variety they fall.” Conversely, many might challenge the statement that individual crystals are relatively scarce by comparison with snowflake aggregates, rimed crystals, and irregular forms; but they are. The types of snow occurring in a storm are a function of many variables including updraft strength, temperature, cloud moisture, liquid water content, cloud thickness, and ice nuclei and crystal concentrations. Some of the relationships are obvious, others more obscure, still others unknown. This paper describes ground observations and calculations that attempt to clarify certain snowfall forms in terms of the cloud conditions likely to produce them.

The METRAC™ positioning system is a ground-based radio location system that makes use of the Doppler principle in order to track an inexpensive, expendable transmitter. A prototype system has recently been built and evaluated for the Environmental Protection Agency for possible use in the Regional Air Pollution Study Program. This paper presents a brief description of the METRAC system and some of the results of a field test of the prototype system conducted in Minneapolis. The field test consisted of a comparison of wind profiles derived from the METRAC system with wind profiles derived from simultaneous rawinsonde and theodolite tracking. The results of this test demonstrate the great accuracy and high-resolution of winds measured by the prototype system.

Observations of the equatorial current system have revealed that its structure is subject to considerable variations. To clarify the nature of these variations and their dependence on the surface winds, measurements on a spatial and time scale much greater than that which can be covered by a single ship are necessary. Such experiment must obviously coincide with a meteorological one that will furnish detailed wind data. GATE affords a unique opportunity for an oceanographic experiment which is described in this paper. It is the aim of the experiment to study the dynamics of the equatorial current system with particular emphasis on the Equatorial Undercurrent and to determine the scales of transient equatorial phenomena such as trapped waves, instabilities, and meanders. Though a number of separate experiments are described, it should be kept in mind that they are all interrelated and that they are not independent.

The zonally asymmetric climatology of the tropical large-scale motion field is an interesting GARP topic. Understanding of the maintenance of various quasi-stationary features will be a challenging problem during the FGGE (the First GARP Global Experiment) and Monex (the Monsoon Experiment). In this paper we present some current thoughts that are relevant to the climatology of the tropical upper troposphere during the northern summer. A review of some of the results from various numerical general circulation models and theoretical studies is presented for northern summer conditions. The relative success or failure of simulations of 200-mb climatology is discussed. It is pointed out that a proper simulation of the belt of anticyclones over the Asian highlands is somewhat crucial for a proper simulation of the summer climatology over the rest of the tropics. Observations of the semipermanence of the Tibetan high pressure cell during northern summer at 200 mb suggests that it acts somewhat like a barrier. In order to illustrate this we consider a problem related to the evolution of barotropic non-divergent flows past a barrier. The flows are initially zonal, with speeds varying in the north-south direction according to northern summer observations. The barrier, whose shape is based on observations of a blocking thermal high, is impulsively introduced at initial time. The flows are kept zonal at frictionless walls at 25S and 45N. The initial north-south distribution of the zonal flows is shown to have no inflection point in its profile, thus it does not satisfy the necessary condition for barotropic instability. The presence of an impulsively introduced barrier, however, results in the evolution of transient as well as steady wave motions in long term numerical integrations. It is shown that a 30-day mean motion field contains many of the well known climatological features such as the African high, the mid-Atlantic trough, the mid-Pacific trough, the Mexican high and a weak easterly jet south of the Tibetan high. Calculations of kinetic energy exchanges between waves and zonal flow in this simple experiment is compared with corresponding calculations for tropical observations and recent general circulation experiments carried out by Abbott. The impulsively introduced barrier simulates an energy source for zonal wavenumber 1, quite similar to observations in a tropical belt. Although this experiment is fairly crude, it is found to be very illustrative in many respects. Many diverse experiments along these lines can be carried out to reveal various aspects of atmospheric circulations.

Experience with the operational application of the U.S. Air Force Weather Service's Data Acquisition and Processing Program (DAPP) has shown that satellite imagery requires many different processing and enhancement techniques in order to be fully utilized. Modern imaging scanners provide more information than can be adequately revealed with conventional “cloud pictures”; the value of imagery can be greatly increased by enhancement modes directed toward specific applications. Although complete utilization demands computer processing, much of the information content can be made available to the meteorological analyst by application of electro-optical enhancement techniques. This paper illustrates some of those electro-optical enhancement techniques, both for those who may wish to better understand DAPP and for those who wish to adapt these enhancement techniques to their own applications.

Experience over the past decade has shown that objective forecasts of local weather elements can best be obtained by using statistical methods to complement the raw output of numerical prediction models. One of the most successful techniques for accomplishing this is called Model Output Statistics (MOS). The MOS method involves matching observations of local weather with output from numerical models. Forecast equations are then derived by statistical techniques such as screening regression, regression estimation of event probabilities, and the logit model. In this way the bias and inaccuracy of the numerical model, as well as the local climatology, can be built into the forecast system. MOS has been applied by the Techniques Development Laboratory to produce automated forecasts of numerous weather elements including precipitation, temperature, wind, clouds, ceiling, visibility, and thunderstorms. In this paper, the derivation and operational application of MOS forecasts for each of these elements...

The Illinois State Water Survey, a state water resources research agency, initiated efforts in 1971 to develop and secure a law for Illinois that would permit and regulate weather modification activities. Such legislation was deemed a prime requirement, not only for the proper execution of scientific experiments on weather modification in Illinois but for the general benefit of citizens of Illinois through encouragement to properly conducted activities and protection from improperly conducted weather modification operations. (It was our intention to develop a “model law” that reflected the best aspects of weather modification legislation and experience in other states, and which would serve as a model for future legislation in other states.) The efforts began in October 1971 and were completed in September 1973 with the signing of the Illinois Weather Modification Control Bill and its accompanying appropriation bill. This paper describes the type of law desired, the activities performed to secure...

Diurnal variations in outdoor air temperature, wind velocity and intensity of solar radiation cause a diurnal variation in the rate of heat flow into or out from a building. This variation is strongly influenced by the heat capacity of the structure and the ventilation rate. Thus it is difficult to estimate accurately the loads on heating and cooling systems or to predict the indoor climate of buildings not provided with such systems. This paper shows how the complex thermal system of building and outdoor environment can be represented by a thermal circuit. Analysis of such circuits by mathematical or analog methods provides a practical rational means of predicting the thermal performance of buildings.

The past 20 years have encompassed remarkable scientific and technical advances in the atmospheric and oceanic sciences which herald a new era for deterministically predicting atmospheric behavior. Many of the key innovations were directly influenced, if not originated by Harry Wexler during his very productive career. This paper will deal with a critique of recent progress in modelling the atmosphere-ocean system, some of the newly exposed problems, and the needs and expectations for the future.

The Microseismic Research Project, initiated by the Naval Aerological Service, has recently completed a detailed study of microseisms associated with cold fronts. The data presented in this paper concerning frontal microseisms, together with data previously published concerning tropical storm microseisms, lead to the conclusion that most microseismic storms are a direct function of the wind force, the density of the air mass involved and the area over which the force acts. Most reliable sources of information also lead to the conclusion that microseismic storms are generated on the ocean bottom directly under the storm area, probably by means of compressional water waves set up by the storm.

This paper summarizes some of the weather conditions which cause blowing dust in the Southern High Plains of Texas. These conditions include diurnal winds, whirlwinds and thunderstorms. A tentative classification of dust storms in this area is given in table form. The terms dust lift, dust swath, and dust ring are introduced.

In the near future wind and temperature data at heights above 200,000 ft will be made generally available. This paper is designed to acquaint meteorologists with vehicles, sensors and reduction techniques used in collecting these data. The problems involved in establishing a rocketsonde network modeled after the radiosonde network are discussed.

The results of a questionnaire designed to gather information on how nonmeteorological scientists and engineers view meteorology and weather forecasting are summarized in this paper. The respondents were from two organizations, Texas A & M University and NASA's Marshall Space Flight Center, the first representing the academic community and the latter the engineering community. While there were some differences between the groups, in most cases answers expressed in the opinionnaire by the two groups were essentially identical. The results revealed the following: Approximately three-fourths of the respondents use meteorological data and/or weather forecasts in their profession; the meaning of probability forecasts is very unclear with only 13% indicating the correct answer; television is the main source of weather information; approximately half of the respondents had never heard of the Global Atmospheric Research Program; and the opinion was almost unanimous that satellites had contributed significantly to weather observations and/or forecasts. Also, the results indicated a number of other ?problem' areas where some improvements are desired.

The need for reliable determination of the temperature of the air very near the ground and the difficulties inherent in measurement of this quantity by the ordinary indirect methods are pointed out. It is suggested that the dependence of the speed of light on air density provides a convenient method for the determination of the temperature near the ground by direct measurement of the lapse rate, and evidence is given from other papers to show that this is feasible where the vertical gradient of humidity is not great. The relationship between apparent elevation and lapse rates of temperature and vapor pressure is derived, and the relationship is illustrated by the results of computations.

The Microseismic Research Project described in this paper was started by the U. S. Navy in 1943 in an effort to find a better and cheaper method of locating and tracking severe tropical disturbances when several hundred miles from land. The microseismic data prove that a storm causes the ocean bottom over which it passes to vibrate and these more or less regular oscillations are called microseisms. They travel outward from the storm center in concentric circles and can be recorded on a microseismic seismograph. The amplitude of the microseisms recorded for a particular storm appears to depend principally on the storm's intensity and distance from a recording seismograph and to a less degree on the depth of the water over which it passes and on the position of certain deep discontinuities of the earth's crust. The maximum effective distance a storm can be detected in the Caribbean is about 600 miles while in the Pacific it is at least 1000 miles.

This is an eye-witness account of a series of six tornadoes observed in extreme northeastern Colorado and western Nebraska on June 7, 1953. The author's illustrations, developed from his pencil sketches made while the tornadoes were being observed, show details of their appearance. Of special interest to meteorologists may be the remarks and illustrations pertaining to the formation and dissipation of the tornadoes. Another section of the paper gives a description of the synoptic features associated with the tornadoes.

Relationships between smoke concentration and visibility, wind direction, wind speed, and temperature stratification are discussed with some references to previous investigations which have related these factors. The paper deals with smoke pollution such as exists in an industrial city, rather than with the effluent from a point- or line-source drifting over an area of constant surface roughness. The review includes some of the findings of the writers, who have made a number of correlations between Weather Bureau meteorological data and Davidson's New York City smoke data of 1939–40. The best of these correlations resulted when the wind direction and wind speed were considered hour by hour for each day, and when a straight-line regression formula was fitted to the data. It is brought out that isobaric curvature, as shown on the weather maps, seems to be a significant factor in the smoke-spreading problem.

This paper presents the concept, design, and development of a novel type combination fast-rising, high-altitude meteorological balloon. The design consists of an inner high-altitude balloon and an outer streamline balloon. The assembly is so designed that it will ascend rapidly to approximately 50,000 ft. At this altitude, the streamline balloon bursts and falls away from the inner balloon. The inner balloon now, by virtue of its increased free lift, proceeds to accelerate at the upper level of flight, providing a faster ascent rate throughout most of the flight than that attainable by individual component balloons. The balloon provides an ascent rate in excess of 1700 ft min−1 in the daytime and 1600 ft min-1 at night to altitudes in excess of 100,000 ft.

SUMMARY This paper describes a new light weight anemometer and wind vane, together with associated equipment. The characteristics of pitot static, bridled, cup wheel, and propeller anemometers are discussed and reasons given for using a propeller in the new equipment. This propeller anemometer is characterized by accuracy, linearity, and generally excellent performance as determined by wind tunnel and other tests. The anemometer is adaptable to wind speed measurement by means of magneto and voltmeter, disc and roller tachometer mechanism, contacts or electronic devices. While primarily designed for fixed station and marine use, the equipment is suitable where portability is required.

The results presented in this paper were obtained in a statistical investigation made to determine the meteorological conditions of air temperature and stability under which the occurrence of aircraft icing is most likely to occur over the route flown by a scheduled air line in the Rocky Mountain region of southern British Columbia. The investigation was limited to the fall, winter and spring seasons. The results obtained show that, during the seasons studied, the greatest frequency of icing occurs at temperatures in the vicinity of 8°F. and that air masses most favourable for icing are originally potentially unstable, which instability is realized when they are lifted over the higher terrain of the region considered. Icing may occur with lift of stable air provided the relative humidities of the lower levels are near 100 per cent.

Aristotle's Meteorologica dominated the development of the science of meteorology during the nearly 2000-year period from antiquity up to the seventeenth century. This paper presents a survey of the history of meteorology during this often called “Era of Speculation”.

The development of turbo-jet aircraft has made high-level clear air turbulence a major problem for aviation interests. This paper emphasizes the association of the majority of this turbulence with the pronounced vertical wind shear in and near the maximum wind speed centers that move along the jet stream. A physical model is proposed as a possible explanation of clear air turbulence, the associated cirrus bands and wind streaks in the jet maxima. This model is supported by an analogy drawn with similar low-level phenomena studied by Woodcock and others. The model can explain distribution of these features in the horizontal by means of helical vortices which are dependent upon proper vertical wind shear and stability conditions. The observed multiple layers in the vertical are also explained by this model. It is believed that the reason why most of the clear-air turbulence is found near the jet-stream maxima is simply because the necessary shear and stability conditions associated with this turbulence are most frequently fulfilled in that region.

This paper presents a non-technical survey of the research being done on the meteorological aspects of aircraft icing. The organization of the program and functions of four installations in the U. S. are indicated. After a short qualitative discussion of the flow around cylinders, several new specialized instruments are described, and some of the theory developed to interpret their data is treated briefly.

This paper outlines current and proposed meteorological research under consideration by the Planning Division, Office of Research and Inventions. The projects discussed include fundamental studies of atmospheric dynamics, atmospheric thermodynamics, high-altitude meteorological research, experimental meteorology, and Arctic meteorology.

This paper constitutes a brief review of the main concepts relating to dynamic response characteristics.1 It gives the quantities used to define the characteristics (a response time or distance for devices like a simple temperature probe or rotating cup anemometer; both a delay factor and a damping ratio for a direction vane). It shows how to obtain these quantities experimentally by noting the sensor response to a step change of the variable being measured. Graphs are presented, showing the response of the sensors to sinusoidal inputs, by which measured statistical data can be corrected for the sensor characteristics.

Non-Technical Summary Why cyclones deepen and fill up is one of the fundamental problems in meteorology that still largely resists theoretical treatment; but it is a matter of great practical importance because it does not seem that our daily forecasts will improve greatly until we find quantitative expressions for the factors leading to development as well as mere translation of pressure systems. Mr. Gringorten in this paper follows up a line of attack already laid down by several European investigators to see how well it may agree with reality. While he does not offer us a new principle the result is very interesting because he shows that the familiar conception of the isallobaric wind component, i.e. the small departure of the wind from the “gradient wind” which follows the isobars (except with surface friction), must play an important role in the pressure changes observed on the weather maps or the barograms every day. Qualitatively we have believed this for some time but Mr. Gringorten has computed the expected pressure change, from formulae proposed by Bjerknes and by Sutcliffe, for a particular time and place. This case was for the layers between 2000 and 8000 feet above Detroit between 7:30 p.m. Feb. 2 and 7:30 p.m. Feb. 3, 1940. The computed pressure change at 2000 feet was at the rate of 22.8 millibars in 12 hours but the observed change was only 5 mb. The practical meteorologist will not regard this as very good agreement but in view of the great difficulties in the theoretical treatment of such a problem the theoretician finds some consolation in that at least the computation gives results in the right direction. Of course, as Mr. Gringorten points out, it was obvious on Feb. 3 from the A. M. weather map that the pressure would fall at Detroit by that evening, and no one would suggest that the theory be used for forecasting.—R. G. S.

Squall lines are among the most severe but least understood weather phenomena. They are difficult to identify on the usual synoptic charts, and there has been some confusion concerning the definition of the terms “squall line” and “instability line.” The primary purpose of this paper is to show that squall lines can be defined and identified by the surface windshift, and that the surface windshift is highly informative as to the location of areas of severe turbulence. Characteristies of squall lines and synoptic conditions favorable for their development are discussed.

A modification to the radiosonde humidity channel to eliminate a temperature induced bias is described. Data are presented from Right test comparisons of radiosondes so modified and standard unmodified radiosondes. It is anticipated that the redesign of the current, standard radiosondes will reflect essentially the modifications described herein and consequently the data indicate the type and magnitude of change in the reported humidifies which may be expected. The data are essentially in agreement with predicted changes from a previous paper (Morrissey and Brousaides. 1970). Further field testing of this and other modifications is proposed to determine residual error. Similar tests to standard instrumentation would permit corrections to archived data.

Studies of the heat island effect produced by urban centers have focused almost exclusively on large cities. Knowledge concerning the extent to which small places. i.e., towns with less than 50,000 people, exert a similar effect on their atmospheric environment is limited in this country. Only at Palo Alto, Calif., and Corvallis, Oreg., have such studies been conducted. This paper reports the results of temperature measurements and their spatial patterns taken by mobile traverses during the course of three seasons at Chapel Hill, N. C., and compares the heat island effect identified in this small university town with previous studies. The comparison shows a similarity among derived data which lends support to the ranking of urban places by population size as a climatic parameter.

This paper presents an objective method of forecasting advective stratus and other low clouds during the summer months in the McChord-Seattle area. A relationship is shown between the 1630P pressure at North Bend, Oregon and Seattle, Washington, and the inland movement of stratus and the occurrence of other low clouds. Higher 1630P pressure at North Bend, beginning at a critical positive difference, favors the occurrence of low clouds the following day; higher 1630P pressure at Seattle, at a critical negative difference, favors clear skies or fog formation, with higher values reaching 100% verification.

References to previous papers by the author show that his ideas on typhoon origin and structure contain the following main elements:(a) Strong surface convergence of two or more humid air streams.(b) Strong upward convection in a rather narrow ring near typhoon center, giving a warm inner core, and conditions favoring a modified Rankine vortex.(c) The formation of an upper front, roughly funnel-shaped.(d) Possible divergence aloft, especially a fast upper current to dispose of the rising core air and partially at least controlling the pressure gradient and size of the convection ring. These ideas are subjected to approximate mathematical treatment, giving satisfactory magnitudes for pressure gradients and proper shape of pressure curve. A short discussion is given of what are considered the most essential elements determining typhoon origin and structure.

This paper describes some experiments on the deterioration of silver iodide freezing nuclei produced with a kerosene burner. It is found that the number of particles effective as freezing nuclei decreases with time as does the rate of decay itself. The decay rate is critically dependent on the ambient air temperature and to a lesser extent on the air pressure. The results suggest that for artificial rainmaking, silver iodide smoke released from the ground in warm climates is of little use but it may be very effective when released from high mountains or aircraft.

A disturbance of the wind field such as a hurricane inherently involves a hyperbolic point (analogous to a pressure col) in addition to the cyclonic-indraft point usually identified as the hurricane center. The entire hurricane (i.e., including the hyperbolic point) is not normally located by reconnaissance flights. Neither is the rain pattern of a hurricane over the open ocean normally included in reconnaissance reports. In this paper the complete observation of the fields of the wind and the weather to the best of our present abilities is suggested. Feasibility of these observations and possible research gains therefrom are discussed.

An attempt is made in this paper to identify the areal patterns of significant thermal influence exerted by the Great Lakes by use of the methods of anomalies and isanomal mapping. Empirical temperature models for the seasonal months of January, April, July and October were constructed and the mean monthly temperatures of some 500 stations within the Great Lakes Region were compared to these models. The same procedure was used for average annual temperature ranges. The resultant deviations were mapped and their patterns described and analyzed. Based on these patterns of mean deviations, the areal extent and seasonal variation of the Great Lakes' effect on vicinal temperature regimes is graphically shown, and the method of isanomal mapping is further substantiated as an effective climatological technique.

Studies carried out in Alaska and Canada have shown that fog is a relatively rare phenomenon at temperatures between 0° and − 30°F, with a minimum frequency between − 20° and −30°. At still lower temperatures, however, the frequency of fog increases rapidly. This effect is noted only in the immediate vicinity of inhabited areas, such as towns and airfields. The reason for the sudden increase in fog frequency at these temperatures, and the rarity or lack of fog at the higher temperatures, has not been heretofore explained. In a recent study on aircraft condensation trails, it was shown that if the temperature is sufficiently low (between − 20 and − 40°F, depending on the relative humidity), the burning of hydrocarbon fuels, such as would occur in towns and at airfields, easily results in supersaturation of the air and a “surface contrail” or ice fog. At higher temperatures, on the other hand, combustion actually reduces the relative humidity of the atmosphere, hindering the formation of fog. In this paper it is shown that low-temperature (ice) fogs form as a result of the combustion process, and curves are presented showing the temperature-dew-point relationship necessary for the formation of such fogs.