Search Results
Abstract
The tendency for the recurrence of weather events on or near the same calendar date has been the subject of controversy for many years. The statistical evidence has been far from conclusive, and no generally acceptable physical explanation of such phenomena, if real, is available. Dr. E. G. Bowen has advanced the meteoritic-dust hypothesis to explain singularities in the number of ice nuclei and in world rainfall amounts. This paper describes a statistical test comparing three independent series of daily rainfall: (1) world rainfall amounts determined from several hundred stations assembled by Bowen for the period 1880 to 1950; (2) average daily precipitation amounts during the period 1952 to 1957 for a network of approximately 150 stations distributed over the United States; and (3) average daily precipitation amounts for the same United States network during the year 1958. A non-parametric test, made possible through, use of an electronic computer, shows a highly significant association among these series. These results lead to the conclusion that there has been a strong tendency for precipitation anomalies (both high and low) to occur on specific calendar dates.
Abstract
The tendency for the recurrence of weather events on or near the same calendar date has been the subject of controversy for many years. The statistical evidence has been far from conclusive, and no generally acceptable physical explanation of such phenomena, if real, is available. Dr. E. G. Bowen has advanced the meteoritic-dust hypothesis to explain singularities in the number of ice nuclei and in world rainfall amounts. This paper describes a statistical test comparing three independent series of daily rainfall: (1) world rainfall amounts determined from several hundred stations assembled by Bowen for the period 1880 to 1950; (2) average daily precipitation amounts during the period 1952 to 1957 for a network of approximately 150 stations distributed over the United States; and (3) average daily precipitation amounts for the same United States network during the year 1958. A non-parametric test, made possible through, use of an electronic computer, shows a highly significant association among these series. These results lead to the conclusion that there has been a strong tendency for precipitation anomalies (both high and low) to occur on specific calendar dates.
Abstract
Recently published data on the average hourly rates of visual meteors for each night of the year have been compared with the average daily precipitation of a number of stations for a 50-year period. No significant relation was found between meteor showers and precipitation although there was a very slight suggestion of a maximum in precipitation around 30 days after peak meteor activity.
Abstract
Recently published data on the average hourly rates of visual meteors for each night of the year have been compared with the average daily precipitation of a number of stations for a 50-year period. No significant relation was found between meteor showers and precipitation although there was a very slight suggestion of a maximum in precipitation around 30 days after peak meteor activity.
Abstract
Developments in the statistical theory of turbulence during the past thirty years have been used by a number of investigators studying the problem of eddy diffusion. Taylor has derived a formula for the diffusion of particles from a point source. This formula and its extension by Sutton make use of a Lagrangian correlation coefficient Rξ defined as the correlation between the velocity of a fluid particle at any instant and that of the same particle after a time interval ξ. A more general formula that takes account of the initial distance between the particles is presented here and it is shown that the Taylor formula can be derived as a special case of this formula.
An experiment is described where modern radar equipment was used to measure the scatter of a cluster of balloons released simultaneously in the free atmosphere. Questions are raised as to the usefulness of balloon data in obtaining estimates of the rate of diffusion, due to such factors as variable ascension rates of balloons, the change of wind speed and direction with height, and the failure of large balloons to respond to smaller-scale eddies that might contribute considerably to the diffusion of small particles such as smoke.
Abstract
Developments in the statistical theory of turbulence during the past thirty years have been used by a number of investigators studying the problem of eddy diffusion. Taylor has derived a formula for the diffusion of particles from a point source. This formula and its extension by Sutton make use of a Lagrangian correlation coefficient Rξ defined as the correlation between the velocity of a fluid particle at any instant and that of the same particle after a time interval ξ. A more general formula that takes account of the initial distance between the particles is presented here and it is shown that the Taylor formula can be derived as a special case of this formula.
An experiment is described where modern radar equipment was used to measure the scatter of a cluster of balloons released simultaneously in the free atmosphere. Questions are raised as to the usefulness of balloon data in obtaining estimates of the rate of diffusion, due to such factors as variable ascension rates of balloons, the change of wind speed and direction with height, and the failure of large balloons to respond to smaller-scale eddies that might contribute considerably to the diffusion of small particles such as smoke.
Abstract
A cycle of 14.765 days, one-half of the lunar synodic month, can be demonstrated in the precipitation data for the United States for the period 1871–1961. Numerous rigorous statistical tests show that association is real and an estimate is obtained of the magnitude of the lunar effect. Geographical, seasonal and other sources of variation in the effect are suggested by the data. No other periodicity with comparable amplitude was found by the statistical analysis, but there is evidence that the lunar synodic cycle interacts with the nodical cycle.
Abstract
A cycle of 14.765 days, one-half of the lunar synodic month, can be demonstrated in the precipitation data for the United States for the period 1871–1961. Numerous rigorous statistical tests show that association is real and an estimate is obtained of the magnitude of the lunar effect. Geographical, seasonal and other sources of variation in the effect are suggested by the data. No other periodicity with comparable amplitude was found by the statistical analysis, but there is evidence that the lunar synodic cycle interacts with the nodical cycle.
Abstract
A randomized seeding experiment was carried out on 23 tropical oceanic cumulus clouds on 9 days in the summer of 1965 as part of the joint Navy-ESSA Project Stormfury. Following instructions in sealed envelopes, an aircraft seeded 14 of the clouds with 8-16 pyrotechnic silver iodide generators called Alecto units. Each unit releases about 1.2 kg of silver-iodide smoke. The nine remaining clouds were studied in an identical manner as controls, using the same stack of four instrumented aircraft to penetrate the cloud before and after the seeding run. Cloud growth was documented by aircraft, radar and photogrammetry. The seeded clouds grew vertically an average of 1.6 km more following the seeding run than did the control clouds; the difference is significant at the 0.01 level.
A numerical model of cumulus dynamics was specified in advance of the field program. This model integrates the equation for the vertical acceleration of an entraining cumulus tower, predicting top heights of unseeded and seeded clouds as a function of ambient sounding and horizontal tower dimension. Seedability is defined as the predicted difference between the seeded and unseeded top of the same cloud. Effect of seeding is defined as the difference between the observed top and the predicted unseeded top of the same cloud. Both parameters are computed and graphed for all 23 clouds. Seeded and unseeded clouds separate into distinct populations. This statistical analysis demonstrates that 1) seeding has a clear effect on cumulus growth under specifiable conditions and 2) the model has considerable skill in predicting the amount of growth and in specifying the conditions.
Sources of subjectivity and bias are shown to be small and not to affect the results. The sensitivity of the model predictions to variations in input data is investigated with two examples, one each of large and of negligible cloud growth following seeding. Some possible effects of natural glaciation are examined with the model and future phases of the program are described.
Abstract
A randomized seeding experiment was carried out on 23 tropical oceanic cumulus clouds on 9 days in the summer of 1965 as part of the joint Navy-ESSA Project Stormfury. Following instructions in sealed envelopes, an aircraft seeded 14 of the clouds with 8-16 pyrotechnic silver iodide generators called Alecto units. Each unit releases about 1.2 kg of silver-iodide smoke. The nine remaining clouds were studied in an identical manner as controls, using the same stack of four instrumented aircraft to penetrate the cloud before and after the seeding run. Cloud growth was documented by aircraft, radar and photogrammetry. The seeded clouds grew vertically an average of 1.6 km more following the seeding run than did the control clouds; the difference is significant at the 0.01 level.
A numerical model of cumulus dynamics was specified in advance of the field program. This model integrates the equation for the vertical acceleration of an entraining cumulus tower, predicting top heights of unseeded and seeded clouds as a function of ambient sounding and horizontal tower dimension. Seedability is defined as the predicted difference between the seeded and unseeded top of the same cloud. Effect of seeding is defined as the difference between the observed top and the predicted unseeded top of the same cloud. Both parameters are computed and graphed for all 23 clouds. Seeded and unseeded clouds separate into distinct populations. This statistical analysis demonstrates that 1) seeding has a clear effect on cumulus growth under specifiable conditions and 2) the model has considerable skill in predicting the amount of growth and in specifying the conditions.
Sources of subjectivity and bias are shown to be small and not to affect the results. The sensitivity of the model predictions to variations in input data is investigated with two examples, one each of large and of negligible cloud growth following seeding. Some possible effects of natural glaciation are examined with the model and future phases of the program are described.
Abstract
A statistical analysis is applied to 63 years of daily United States precipitation data to determine whether a tendency exists for rainfall anomalies to occur near specific calendar dates. The results clearly indicate no tendency for rainfall anomalies near specific calendar dates.
Abstract
A statistical analysis is applied to 63 years of daily United States precipitation data to determine whether a tendency exists for rainfall anomalies to occur near specific calendar dates. The results clearly indicate no tendency for rainfall anomalies near specific calendar dates.
