Search

This paper (part I) is a discussion of the magnitude and implication of the vertical circulation patterns of the summertime tropical atmosphere as derived from synoptic scale considerations. Part I is compared to the vertical circulation patterns derived from cumulus scale considerations as discussed by Lopez in part II, a companion paper. From the synoptic scale considerations, we show that a very significant subsynoptic or local vertical motion is occurring within the cloud regions of the Tropies. This mass-cancelling local up- and-down circulation is not resolved by the mean or synoptic scale flow patterns. The magnitude of this local or up- and-down vertical circulation can be estimated from cloud-cluster scale (approx. 4°) mass, vapor, energy, and rainfall-evaporation budgets. Results are closely comparable to those obtained by Lopez from an independent small-scale approach through modelling of individual cumulus elements. This local vertical circulation is shown to be fundamental for the ma...

Temperature and humidity fluctuation data were collected on the R/V Flip during BOMEK (Barbados Oceanographic and Meteorological Experiment) in May 1969 and during a pre-BOMEX trial cruise near San Diego in February 1969. The program was a cooperative one with a number of groups on board. In a companion paper with the personnel from the University of British Columbia, the equipment and data analysis are described in more detail and the results of measurements of the fluxes of momentum, moisture and sensible heat are given. The emphasis of this paper is on the similarities and differences between temperature and humidity and on their cospectra and correlations with the velocity fluctuations. During the San Diego experiment it was found that humidity and temperature fluctuations were very similar with only minor differences. During BOMEX the humidity fluctuations were similar to those obtained during the San Diego experiment and to measurements over land, but the low-frequency ends of the temperatu...

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...

The paper presents results of a series of studies of Upper Midwest hailstroms made between 1957 and 1962. It discusses hailstorm frequency, incidence, origins and formation in the Upper Great Plains of the United States, but omits synoptic considerations since they were discussed in an earlier paper.

The primary concern of this paper is an examination of the utility of spectral techniques in detecting wave modes of the large-scale tropospheric circulation. Sample time- and space-spectra of meridional winds in middle latitudes are presented. A maximum in the spatial spectra of the transient waves at hemispheric wave numbers 5–7 is shown, in agreement with similar, previously published spectra. The temporal spectra, unlike the spatial spectra, fail to show any significant features that can be attributed to the passage of baroclinic disturbances. (In this paper, the frequency range considered is limited to 0.03–0.50 per day.) The continuum of the coherence statistic between lower and upper tropospheric wind components is highly significant, but no significant “peaks” or maxima exist. Because of recent interest in the dynamics of tropical regions, spectral techniques are employed on meridional wind data for five tropical stations with record lengths of from 3 to 7 yr. At 850 mb, the two stations ...

The fact that the ares of the trade-wind belt of the North Atlantic is estiniated to be 10 million square miles suggests the impracticability of attempting a detailed study of the wind data over the entire region. In the monthly Pilot Charts of the United States Hydrographic Office of the Navy we have a complete set of monthly averages of these winds. Their percentages, including calms, velocities in terms of the Beaufort scale and prevailing directions, within the 8 points of the compass, are given for each 5’ of latitude by 5’ of longitude. Observations from transatlantic and coastwise ships contributed largely, and continue to do so, to the comprehensive mapping of ocean areas. On the other hand, we lack comparative data for different years, a t least in assembled form. The present paper gives a more or less detailed arrangement of the wind data by months and years for one station (San Juan, Puerto Rico) in the trade-wind belt. It includes the variations from year to year in total wind movement; treats of the “trades” as a separate entity; gives the wind velocities and notes the percentage of winds from the east, northeast and southeast. These data also are compared with their normal or average values. Beals has given an interesting survey of “The Northeast Trades of the North Pacific ” from which suggestions have been obtained for the present paper. In referring to the general world pressure system, the following is quoted as applying with equal force to both areas

Notable asymmetric features of an early experiment with a three-dimensional hurricane model were spiral bands of convection and large-scale asymmetries (eddies) in the outflow layer. Using an improved version of the model, we describe the formation and maintenance of these features in greater detail in this paper. The spiral bands in the model propagate cyclonically outward in agreement with bands in nature. The breakdown of symmetry into a chaotic pattern of eddies in the outflow region is shown to be the result of dynamic (inertial) instability, with the eddy kinetic energy derived from the kinetic energy of the azimuthal flow. This instability does not contribute to the overall intensification of the model storm, however. We observe a curious anticyclonic looping of the vortex center in these experiments. This looping appears to be associated with asymmetries in the divergence pattern associated with the eddies in the outflow layer. This paper also summarizes improvements made in the original ...

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.

During the weekend of May 26-28, 1956, a large, cold, high pressure system moved slowly off the east coast of the United States followed by a broad current of moist tropical air from the Gulf of Mexico. As this moist current overran the retreating cold air mass, widespread warm-frontal-type rains spread over the northeastern United States. The warm front was poorly defined at the surface, with a broad zone of gradual transition. Aloft the front was somewhat more distinct but still quite broad. To the rear of this frontal zone the warm sector air mass extended uninterruptedly to the Gulf of Mexico. The synoptic situation on May 27 is presented in figure 1A. It was in the extensive belt of mT air that the rains described in this paper occurred. The rains began in Illinois early Saturday morning of May 26 and spread eastward with the warm front to the coast by Sunday morning. Surprisingly enough, however, they continued throughout a broad strip from central Illinois eastward all day Saturday, Sunday, and part of Monday. The rain over most of this area ceased when a southwardmoving cold front brought dry air and subsiding currents to the region. East of the Appalachian Mountains the warm-sector rains were accompanied by a deepening trough at the surface and aloft. Here the rains began when the flow at the 700-mb. level became cyclonic and ended when the warm-sector flow lost its cyclonic curvature after passage of the 700-mb. trough. The principles relating surface precipitation to cyclonic curvature aloft [l] have long been recognized so the rains occurring in this part of the country were not unusual. Development of heavy rains which fell farther to the west in the warm sector were not so easily explained. The upward motion in the warm sector must have been quite widespread to produce such a large area of precipitation and therefore should be subject to detection or computation by several of the methods which have been developed for the study of vertical motions. The cause and distribution of these vertical motions will be investigated in this paper by examination of each of the following types of charts: 1. precipitable moisture, 2. Showalter stability index, 3. differential advection, 4. surface isobaric convergence, 5. sea level pressure change (Laplacian of), 6. curvature of flow pattern at 700 mb. and higher, 7. jet stream, 8. tropopause, and 9. JNWP vertical motion computations (900400 mb.).

This paper is a review and compilation of information concerning the incidence and frequency of hail fall in tropical areas. The authors have gathered the data over a period of years from literary sources and by extensive correspondence with private individuals and government meteorological services. The four areas under which the various hail reports are grouped, viz., the American, African, Asian, and Australian, together form a total band around the Earth within latitudes 23½ degrees north and south of the equator. Attempts have been made to systematize presentation of the information. This is possible only up to a point, however, since it was received in a multiplicity of forms, some of which defy conventional climatological handling. Nevertheless, the paper makes possible for the first time a comprehensive assessment of the tropical hail phenomenon. Moreover, a great deal can be learned from it about seasonality of hail fall in specific areas and about the occurrence of hail at sea level and...

An experiment to investigate the structure of the oceanic mixed layer was conducted between 28 September and 14 October, 1971, at 21N and between 66 and 67W aboard the NOAA Discoverer. During the experiment a quartz thermometer system capable of measuring temperature changes to within 0.001C was deployed from a surface buoy. Time-series temperature data were obtained from 10, 20, 30, 40 and 50 m depths and digitally recorded with a sampling interval of 1.1 min. This paper presents the results of an analysis of the temperature fluctuations in the mixed layer at selected levels for a three-day period characterized by fair weather conditions. STD measurements indicate there were no observable changes in salinity during this period. The observations show downward propagation of the diurnal heat wave at a rate of about 5 m hr−1 resulting in a turbulent exchange coefficient for the diurnal cycle of the order of 100 cm2 sec−1. During the heating portion of the cycle, which occurs during the day, the mix...

The tropical rainstorm over land is extremely variable in both temporal and areal distribution. Usually only one rainstorm (defined to deposit > 10 mm of rain) occurs a day at one place. This paper is restricted to the tropical rainstorm as it occurs over Southeast Asia, Colombia, Panama, and Costa Rica. The size and duration of the rainstorms are discussed. A typical tropical rainstorm is about 30 km in diameter and the core rainfall exceeds 25 mm. More than 60% of the daily rain falls from the rainstorm within a period of one hour. The rainstorms are separated from each other with the area in between receiving little or no rain. Some effects of terrain on the size of the rainstorm and the time of day it occurs are discussed.

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.

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.

Hurricane-spawned tornadoes are most frequent at the time when hurricanes initially cross land and undergo rapid filling. This paper presents data composite information on all available rawinsonde and pibal reports surrounding this type of tornado genesis in the United States and Japan. Information has also been gathered on tropical storms entering land which did not produce tornadoes. The most important difference between storms which produce tornadoes and those which do not is a very large increase of the vertical shear of the horizontal wind between the surface and 4–5 thousand feet. This averages about 40 knots for the tornado cases, but is much less in the cases which do not produce tornadoes. Differences in vertical stability are observed to be small. An overland hurricane dissipation model is proposed whereby the boundary layer frictional inflow towards the hurricane center occurs without the usual ocean sensible heat gain and is not, as over the ocean, isothermal. Over land the inward spi...

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.

A common observation in major coastal upwelling regions is a reversal of the mean longshore current with depth during active upwelling. A numerical model and a simple analytical model applied to a two-layer ocean on a beta-plane indicate that this undercurrent cannot exist for upwelling off an east-west (zonal) coastline. The models are applied to the coastal upwelling occurring on the Campeche Bank during the period from March to September. The beta-plane solutions for upwelling along an east-west coastline resemble f-plane solutions for a meridional (N–S) coastline. In particular, the hypothesis explaining the undercurrent of Hurlburt and Thompson cannot hold for upwelling along a zonal coastline. The results in this paper form a new hypothesis which could be tested by measuring currents on the Campeche Bank during active upwelling.

Data from the 1972 International Field Year on Lake Ontario have been used to test the performance of three-dimensional hydrodynamical models of large lakes. The models vary with regard to computational details, but their common purpose is to predict water levels, currents and temperatures in the Great Lakes on the basis of prescribed atmospheric conditions. The period of observations dealt with in the present paper includes the passage of tropical storm Agnes during the latter part of June 1972. Data from the meteorological buoy network on Lake Ontario are combined with routine observations at first-order synoptic stations around the lake to obtain hourly values of wind-stress and pressure fields. Initial temperature distributions as a function of depth and horizontal coordinates are derived from quasi-synoptic ship cruises. Verification of model results is based on hourly values of water level data from stations on the perimeter of the lake and currents and temperatures measured by the buoy net...

This paper illustrates how the ocean can affect and be affected by the overlying atmosphere over time periods of months and seasons and how these effects are transmitted by the atmosphere to North America. The period from September 1972 through August 1973 shows the remarkable continuity of a monthly-mean mid-tropospheric trough which can be traced from 155E in September to 90W in May. The development and motion of the trough over the ocean is associated with and perhaps explained by sea-surface-temperature (SST) contrasts which supply a baroclinic source of energy to the overlying atmosphere. Estimates of ocean-surface flow around the North Pacific gyre suggest that the zone of SST contrast was advected the proper distance to account for the observed displacement. The SST contrast was enhanced, meanwhile, by the cyclonic activity. After reaching the west coast in March, the trough was supplied with a new source of baroclinic energy by the contrast between a cold polar-Pacific air mass, kept cold...

Increasing indication of interaction between the stratosphere and mesosphere makes it seem probable that effects from the lower atmosphere will not be uncommon among the variations of the earth’s magnetic field especially in the form and range of the daily variation of the field. Meteorology may be able to aid space research by identifying effects in the magnetic records that may be of atmospheric origin in order that they not be mistaken for direct solar effects. Extending the work of two earlier articles this paper gives the daily variation of the horizontal intensity of the earth’s field for San Juan, Puerto Rico, as the quiet-day average for the 11 years 1948-58 in a form which illustrates seasonal features that the author believes arise from prevailing ionospheric winds. Further, semi-monthly individual 5-day averages of the daily variation are given for San Juan for a period of 12 months in 1957-58 for which a description of the stratospheric circulation at roughly 30 km. altitude (10 mb.) was available.

This paper describes an attempt to find systematic errors in the sea-level forecasts produced by the operational six layer primitive-equation model of the National Meteorological Center, Suitland, Md. The sample of cases studied contains 417 storms from the winter of 1969–1970. Several systematic errors exist. Over the oceans, the model does not forecast storms deep enough. Storms forming on the lee slopes of the Rocky Mountains are forecast too deep and too warm. Storms fill more slowly and deepen more rapidly than the model predicts. Strongly deepening cyclones move to the left of the forecast track.

SYNOPSIS This paper is in the nature of a preliminary report on the period of abnormal warmth in the United States and Canada which began in September, 1920, and ended with July, 1921. The location of the areas of maximum positive departure of temperature from the normal from month to month are traced and three periods of abnormal warmth are distinguished. The end of each period of abnormal warmth is evidently marked by a brief and ineffective reaction to lower temperature which soon gave way to a second and third period of unusual warmth. The meteorological conditions as to pressure, over the United States and the adjacent oceans, the prevailing winds, the number of areas of low pressure (cyclones) plotted during the 11 months are briefly discussed and the most important conclusion reached will be found in the closing paragraph.

Mid-tropospheric cyclones are an important part of the tropical general circulation of the summer season. These are synoptic-scale disturbances which appear in the daily and monthly mean circulation maps with greatest intensity at levels near 500 mb. The structure and energetics of this type over southeast Asia are discussed in this paper. Interesting features include a warm anomaly above the cyclone and a cold anomaly below. A five-level non-geostrophic balanced model is used in this study to obtain the distribution of vertical motion. The model includes a parameterization of cumulus-scale convection. In the middle levels, rising motions are found west of the cyclone and sinking motions to the east. This is primarily due to the thermal structure of the atmosphere and associated advection of colder air from the oceanic regions and warmer air from land areas. A marked diurnal change in the vertical velocity is noted in the computations; magnitudes are large at 0700 local time compared to 1900. Thi...

SYNOPSIS This paper is an attempt to show the relation between the pressure distribution over the North Pacific Ocean, east of about the 180th meridian of west longitude, and the weather of the United States for corresponding periods. The pressure charts used were those for the Northern Hemisphere prepared twice daily in the Forecast Division of the central office of the Weather Bureau. It is fully realized that useful precepts for forecasting weather some days in advance, or other form of generalization can not safely be drawn from the record of a single month or so; nevertheless the most important tendencies may be pointed out. These are: (1) A barometric minimum over the Gulf of Alaska or the Aleutians with fully developed cyclonic wind circulation does not readily pass inland as such, but rather oscillates back and forth with at times increasing and at times decreasing pressure at its center, until the conditions are favorable for (a) the passage of the cyclone in its entirety inland, evident...

This paper summarizes certain facts of observation, as reported by a number of investigators, concerning the nature of climatic variations on the earth's surface during observational time, during postglacial or historical time, and during the geological past. Particular emphasis is placed on possible interpretations or explanations of these changes. The discussion of the secular variations of the world weather patterns during observational time stresses on the one hand apparent relationships between these variations and solar activity, as indicated by sunspots, and on the other hand the essential similarity of these secular variations to those which occur from week to week and month to month in the fluctuation of the general-circulation pattern between more zonal (high index) and more cellular (low index) characteristics. The discussion of the variations of world climate during geological time is concerned primarily with the relative merits of the three principal theories which currently attempt ...

The period July–December 1964 in the tropical western Pacific was marked by strong fluctuations in the meridional wind component with periods ranging from 4–6 days. This paper describes an intensive study of these disturbances, using spectrum-analysis techniques on time series of radiosonde data. Two types of disturbances appear to be involved. One of these, prevalent at Canton Island, is characterized by upward phase propagation in the lower troposphere and downward phase propagation above 200 mb. It has previously been suggested that this wave may be the tropospheric manifestation of the mixed Rossby- gravity wave. A second type of disturbance, prevalent at stations further west, is marked by an absence of vertical phase propagation. Latent heat release may be important in its energetics.

This paper discuses the solar radiation data assembled during the two recent expeditions to the Everest area. These were the Himalayan Scientific and Mountaineering Expedition of 1960–61, led by Sir Edmund Hillary, and the American Mount Everest Expedition of 1963, led by Norman Dyhrenfurth. Measurements were made at about 19,000 and 18,000 ft, respectively, in the Northern Hemisphere spring, the first series being conducted under generally cloudless conditions and the second with mainly cloudy skies. The observations included not only (a) total incoming sun and sky radiation received on a horizontal surface (global radiation), but also (h) the reflected component (short-wave albedo) from glacial and firm surfaces under different snow conditions, and (c) the subdivision of the radiant fluxes into spectral bands. The 1961 series extended over about 20 days and the 1963 series over 50 days. It is believed that the figures presented here are the first to be published for this type of information at ...

Recent studies have revealed a relationship between variations in gravitational tidal forces and rainfall. A possible mode of interaction of the tidal forces on atmospheric processes is suggested to explain how the tidal forces which are small may induce detectable effects on atmospheric circulation, considering both synoptic-scale and short-period processes in the atmosphere. The variability of gravitational tidal forces is compared with variations in precipitation as revealed by statistical studies. The interrelation between thermal and tidal forces is brought out to account for the anomalous distribution of maximum precipitation in the United States during the synodic month when classified according to seasons, geographical areas, and periods of high versus low solar activity. The model suggested in this paper is based on an intuitional approach to the problem. Its usefulness or validity can be ascertained only by further investigations of rainfall variations; in addition there is the need to ...

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.

The growth of small errors in numerical models of the atmospheric circulation destroys the detailed predictive capability of those models within a few days. Despite the failure of the models to produce accurate local predictions, it was hypothesized that a change in the equator-to-pole temperature gradient would produce discernible effects in average conditions. This paper presents the results of an experiment to test this hypothesis. The Mintz-Arakawa model was started with a standard set of initial conditions and was run 60 days. The experiment was then replicated twice, with two independent sets of random temperature variations superposed on the temperatures at the σ = 0.25 and σ = 0.75 levels. At this point, the ice of the Arctic Ocean was replaced with water at the freezing temperature. Again the model was run, starting once with the standard initial conditions (other than the ice removal) and once each with the two sets of temperature “errors” added. For the four replications with temperatu...

An attempt is made in this paper to examine Nigerian rainfall patterns within the framework of the dominant influence of the Intertropical Discontinuity (ITD), defined here as a moisture boundary separating dry northern air from moist southern air. The characteristics of this moisture boundary are discussed with respect to its influence on the distribution patterns of rainfall. The dynamic factors affecting the rainfall are then synthesized into an ITD plus coastal rainfall model but with an implicit recognition of the modifying effects of such terrain features as the windward, leeward, and valley locations of stations and elevation. The model is shown to have some predictive value, particularly in Nigeria and adjacent territory.

The lunar semidiurnal barometric tide Lz and the solar 24, 12-, and &hr. oscillations of the surface pressure have been determined for 10 stations in Australia and on adjacent islands. At Rabaul and Moresby L2 is considerably smaller than elsewhere in these latitudes. The characteristic annual variation of the phase-late high tide during the D season-is found at most Australian stations. But the annual amplitude minimum occurs only at half the Australian stations during this season, contrary to the behavior of LZ over most of the globe. In order to obtain a more complete and reliable picture of the global distribution of the lunar barometric tide, hereafter called L.2, 10 determinations have been made for stations in Australia and on some nearby islands (table 1). In this region of the world the tide has heretofore only been determined for Melbourne and Wellington by Chapman and collaborators [l, 21. With these 10 additional Australian stations lunar barometric tidal determinations are now available for 102 stations. Of these, 67 are in the Northern Hemisphere, 35 in the Southern Hemisphere, so that it will be possible to make a reasonably satisfactory spherical harmonic analysis of LZ and its remarkable seasonal variation. Such an analysis will be carried out in 8: subsequent paper. Here, a report on the analysis of the lunar semidiurnal barometric oscillations in Australia will be given. The data for this investigation, 14 yr. of surface pressure observations (from July 1951 through June 1965), were made available by the Australian Bureau of Meteorology to whom we are indebted for their assistance. The observations were taken at 3-hr. intervals (solar time) except for 1 night hr. at which observations were not made. Under these circumstances the customary formulae for harmonic analysis, based on equidistant values, are not applicable. Instead, if we wish to determine the harmonic coefficients of the fist three waves, that is for the diurnal, semidiurnal, and terdiurnal solar oscillation we have, with the mean value and the two harmonic constants for each of the three oscillations seven constants which are to be determined from only seven equations

In this Paper we present the geometry and intensity of the mean east–west circulation during the northern winter. We show that near the equatorial latitudes two pronounced regions of divergent mass outflow in the upper troposphere are found near the convective regions over the northwestern part of South America and Indonesia. The intensity of the east–west circulation is shown to be of the order of 1 m sec−1 which is comparable to the intensity of the Hadley circulation. The divergent streamlines are shown to be important for the maintenance of the three waves of the subtropical westerly jet in the Northern Hemisphere, and are shown to exhibit asymptotes of convergence in the regions of mid-oceanic upper tropospheric troughs over the tropical southern oceans. Kinetic energy exchanges for a tropical belt 15S to 15N at 200 mb are expressed as a function of zonal wavenumber. Results for northern summer and winter seasons are compared. We find that wave interactions with the mean zonal flow differ in...

SYNOPSIS Not enough attention has been paid in the past to locating crops subject to damage by frost on the more frost-free hillsides; and at the present day the phenomenon of nocturnal temperature inversion is not well understood by most fruit growers. Orchards set out 20 years ago in some of the coldest sections in several fruit districts on the Pacific coast are still being operated at a lose, while others have been removed only during the last two or three years. Detailed records of nocturnal temperature differences on slopes, covering entire frost seasons, are scarce. Observations of nocturnal temperature inversions, made at Pomona, Calif., and Medford, Oreg., during the frost seasons of 1918, 1919, and 1920, are given in detail and discussed in this paper. Inversions at Pomona during the winter are compared with those at Medford during the spring. Differences in minimum temperature as great as 28° F. were observed between stations at the base and 225 feet above the base, on a hillside at Po...

The occurrence of large surface hail is extremely rare in low latitudes. In an effort to explain this deficiency, this paper presents a mesoscale analysis of an isolated case of large hail over Miami, Florida, in March 1963. For this analysis, a dense network of hail size and frequency sensors was conveniently provided by the hall-punctured overhead portions of the many screened patio and swimming pool enclosures which are part of the Miami environment. A study of this damage pattern along with considerable mesosynoptic data on pressure, rainfall and wind revealed intimate details of the storm's behavior and showed that it displayed many of the features generally associated with Midwest tornadic hailstorms.

The lake-breeze circulation on the Great Lakes is often as vigorous as its oceanic counterpart. This paper shows that lake breezes frequently exert drastic control on mesoscale air pollution patterns in urbanized shore-line areas, in this case, Chicago, Ill. Observational data were gathered from a surface mesonetwork, surface and satellite cloud photography, a chain of pilot balloons normal to the shore, optically tracked constant-level balloons, and aircraft measurements of suspended particulate concentrations in several size ranges. On the 2 late summer days studied, the lake breezes were extremely well developed. Inflow depths ranged from 500 to 1000 m, with peak inflow velocities of 6–7 m/s. Beginning at the shore-line between 0800 and 0900 LST, the breezes penetrated inland over 40 km. Clearly defined return flow layers were present both days. Eulerian wind field measurements from serial pilot, balloon releases were used to make cross sections of the u wind component. Computed one-dimensiona...

This paper reports the results from the latest in a series of scientific exchanges concerning the Soviet anti-hail program. Additional details on the Soviet technique of hail suppression were learned. An impression on the types of storms and the accompanying synoptic conditions was gained. In addition to visual impressions, some case studies are presented. The North Caucasus region resembles northeastern Colorado from a topographical and meteorological point of view, except that a dry line or dew-point front is not normally present north of the Caucasus Mountains. The abundance of low-level moisture in this region seems to produce storms which resemble cloud streets in that lines of storms are aligned with the wind rather than normal to the wind. Although the large supercell and multicell storms typical of the High Plains of North America do occur in the Caucasus region, they are rare and the Soviet scientists are apparently unable to suppress all the hail on these types of storms.

SYNOPSIS By a method explained in detail the probabilities of the occurences of extreme rainfalls were computed for a number of stations on Oahu. These values are given in table 3. The coefficients of variation were determined for 42 stations and plotted in figure 10. The significance of this map is discussed in the latter part of the paper.

SYNOPSIS The variations of monthly mean pressure for stations in the Northern Hemisphere, as published in Reseau Mondial for the eight years 1910–1917 were studied with a view of determining the frequency, geographic extent, and distribution in latitude and longitude of the pressure anomalies in the Northern Hemisphere for that period. The isanomalies for 67 months out of the 96 that, were available were charted and studied. Many of these were featureless in the sense that the amplitude of the anomaly was small and frequently in an opposite sense in closely adjacent regions. In about 10 per cent of the cases considered the anomalies were pronounced both as to amplitude and extent of area involved These are described in some detail, and the relation of the anomalies to current and subsequent weather in contiguous areas is discussed. The paper closes with a brief review of the method of seasonal forecasting now practiced in India and tentative suggestions are given looking to the development of a m...

SYNOPSIS In the first part of the paper effort is made to discover to what extent periods of abnormally high or abnormally low temperature in the United States synchronize and also as to whether or not there is evidence of a periodicity in the occurrence and recurrence of these phenomena. The basic material for the study was 12-month consecutive or overlapping monthly means of the temperature for fairly large geographic districts. The districts used are (1) the New England States, (2) Minnesota, (3) Colorado, (4) Washington, and (5) Louisiana. The monthly mean temperature for each of these districts was originally computed from the means of all of the individual stations therein. The period 1888–1919 furnished the data for the study. As was to have been expected, the control of the changes in temperature of the various parts of the United States is clearly that of the general circulation of the atmosphere, as modified, of course, by the secondary circulation due to the movement of cyclones and an...

This paper presents time cross-sections of vertical temperature structure during the 1966 Thanksgiving week air pollution episode in New York City, based on 6-hourly soundings at Kennedy Airport. The analyses depict numerous inversions in the lower 10,000 ft of the atmosphere, including an interesting sequence of surface-based inversions and an outstanding inversion aloft. Diurnal and daily variations in the height of the mixing layer can also be seen. Some possible influences of the vertical temperature structure on SO2 concentrations in Manhattan are discussed, and it is suggested that exceptional peak SO2 concentrations were largely due to the fumigation process.

The material contained in this paper is a description of the weather conditions over Greenland based on observations taken by exploring expeditions. It can be summarized as follows: Greenland is overlaid by a fixed glacial anticyclone of great vigor which spreads beyond its borders. Within a central cold region of Greenland is a core of descending air currents from levels above 4000 meters. The central region is sharply delimited on all its margins, which are marked by an abrupt rise of air temperature and by a fall of daily temperature range. The zone surrounding the cold central area of Greenland and extending beyond the glacial margin has at all times outblowing winds supplied from the central area. The winds centrifugal to Greenland vary in force from near-calms to surges with velocities of 100 and more miles per hour. Variations of wind velocity occur with little change in wind direction. For every point on the glacier's surface there is a wind direction which deviates from the downslope dir...

This paper describes the method of incorporating into the NCAR global circulation model the dynamic effect of mountains, the prediction of cloudiness for radiation calculations, and the calculation of ground surface temperature using a heat balance equation. Other aspects of the physics of the model and the finite-difference schemes are very similar to those discussed by the authors in 1967 and 1970. For the simulation of seasonal climate we specify two parameters: the sun's declination and the distribution of ocean surface temperatures. Since the prediction of cloudiness is parameterized in terms of the relative humidity and the vertical motion fields, solar and atmospheric radiation processes interact closely with the dynamics of the atmosphere through variations in the fields of cloudiness, temperature and water vapor. Coupling between radiation and dynamics helps to maintain stronger baroclinic activity in middle latitudes. Although a hydrologic cycle is included in the model atmosphere and t...

In dealing with differences in upper-air relative humidity over short distances and during small time intervals, investigators have noted a tendency for low values to be reported by U.S. radiosondes, particularly those sent aloft in daytime. This paper summarizes the proceedings of a colloquium of experts who described the nature of the spurious diurnal variation and recommended the manner in which the radiosonde should he modified and in which archived data might he corrected. The billiard sharp whom anyone catches, His doom's extremely hard– He's made to dwell in a dungeon cell On a spot that's always barred. And there he plays extravagant matches In fitless finger stalls On a cloth untrue, with a twisted cue And elliptical billiard balls! The Mikado, Act II.

This paper presents a four year climatology of penetrations of the tropopause (of more than 5000 ft) by thunderstorms at ten locations in the United States. WSR-57 radar data for 1961 through 1964 were used to determine the vertical extent of the penetrations. Most penetrations occurred during the spring and summer months with only the central part of the United States showing penetrations in both February and October. Maximum penetrations occurred during the afternoon and evening hours with several mountain and coastal stations reporting only one or two total penetrations for a few of the night hours for the four year period. The largest number of penetrations occurred from the coast of the Gulf of Mexico northward into the center of the country, with only one-tenth as many penetrations reported at some of the coastal stations. The highest penetrations also occurred near the center of the country. Cloud tops equal to or greater than 60,000 ft MSL were found in large numbers (more than 50) from t...

This paper outlines a rainfall forecasting model involving satellite nephanalyses and certain conventional weather data for application in regions where the rain-bearing clouds are advectional rather than convectional. Essentially, the scheme depends upon the selection each day of an appropriate cloud quadrant for the station in question and the evaluation of a “rainfall prediction index” for that quadrant, embracing its synoptic weather organization, its mean cloud cover, and its included cloud types. The rainfall prediction index is then used to forecast a class of rainfall for the day ahead in terms of “no rain,” “light rain,” “moderate rain,” or “heavy rain;” being interpreted through tabulations of related rainfall measurements. The essential indices are specified for Valentia, Republic of Ireland, from January through June 1967. Rainfall “forecasts” are then made for July through December 1967 using these indices, and the results are discussed. Verification of these forecasts indicates a ra...

An investigation of tropospheric conditions before and after pronounced stratospheric midwinter warmings indicates an interdependence of developments in the two atmospheric regions. The eleven northern hemisphere winters which have been investigated show that every two years the behavior of the stratosphere is similar as regards the location of the initial warming, direction of movement of systems, and subsequent response of the troposphere. Every second year the midwinter warmings begin in the stratosphere above the eastern United States and Canada, as illustrated in the published examples from 1957 and 1963. During the alternate years of the cycle the warmings originate over central and eastern Europe. In this paper the emphasis has been placed on this type of warming. The tropospheric circulation patterns before each warming of this kind are analogous, and the warming is followed after about ten days by a blocking situation at sea level. It is likely that there is a connection between the 26-m...

In the summer of 1957, short-term weather surveys were made in four prescribed burn areas in the central Sierra Nevada foothills and in the central Coast Range in California The local fireclimate patterns were studied, a fire-weather forecast was adapted to the burn area for each fire, and attempts were made to note the effects of the fires on the fireclimate patterns. This paper describes the survey techniques used, gives an example of a forecast, and discusses some of the survey results. The latter include an increase in wind speed blowing out of the lee side of the fire, effects of the broadscale weather on the local patterns, down-canyon afternoon winds in east-facing canyons, and temperature observations and topographic effects on the lee side of a ridge.

This paper deals almost entirely with beneficial rains. Records of drought severity in the climatic divisions of the states are examined. The rainfall data from tropical cyclones which have moved over drought-stricken areas are used to tabulate in graphical form the ones which have been most beneficial. Other benefits which have, on occasion, been derived from the tropical cyclone are enumerated.