• Observations of Convective Clouds by Means of Pulsed-Doppler Radar

      Battan, Louis J.; Kassander, A. Richard, Jr.; Theiss, John B.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1963-01-15)
      A new pulsed-doppler radar set designed for measuring the vertical distribution of the particle size and vertical-velocity spectra is briefly described. The X-band radar set employs a vertically-pointing antenna producing a 1.3 degree beam. Measurements of the properties of the hydrometeors are made at 500-ft. intervals from 500 ft. to a maximum altitude of 63,000 ft. The intensities of the radar return from particles in each of ten velocity channels are recorded digitally. The analysis of echo returns from showers is discussed in some detail. The data allow inferences of the change of particle size as a function of altitude and time, as well as of the vertical air motions in the cloud. New observations of so-called "angel echoes" are presented. Most often the vertical velocities of the angel echoes were positive. These observations can be used to infer information about clear air convection.
    • Observations of Freezing Nuclei over the Southwestern U.S.

      Kassander, A. Richard, Jr.; Sims, Lee L.; McDonald, James E.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1956-11-01)
      The results of daily flights in January, 1955 in the vicinity of Tucson, Arizona tor the purpose of detecting natural freezing nuclei are presented. Samples were taken each day at 15,000 feet, 5,000 feet and at the surface. No systematic correlation was noted with the longNterm total rainfall record according to the Bowen meteoric dust hypothesis, However, the fact that average temperatures for given concentrations of nuclei were found to be within 2C 0 of temperatures for the same concentrations over Sydney, Australia is noted. Certain interesting observations on natural ice crystal clouds are also discussed.
    • Observed Doppler Spectra of Hail

      Battan, Louis J.; Theiss, John B.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1971-06-15)
      Observations of Doppler spectra from particles 610 m above the ground were obtained by means of a vertically pointing X-band radar during a period when large hail was falling at the ground. It was found that the variance of the Doppler spectrum was a fairly good indicator of maximum hailstone sizes. Calculations of ice-particle size spectra were made on the basis of assumptions of particle shape, composition and fall speed. The many assumptions needed to bring calculated ice-sphere spectra into approximate conformity with observations indicates the complexity of this procedure and the need for at least one more independent observation of the properties of the hailstones. Measurements of depolarization might yield an independent estimate of particle shape. It is concluded that the pronounced minima in the backscattering curves of large ice spheres should serve as an independent indicator of the speed of vertical air motions.
    • Probabilities of Drought and Rainy Periods for Selected Points in the Southwestern United States

      Green, Christine R.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1960-01-31)
      This report presents the results of an investigation of rainfall and drought probabilities in the southwestern United States. Daily weather records for ten weather stations were used to compute the empirical probabilities that droughts of 5, 10, 15, 20, or 25 days or rainy periods of 3, 5, 10, or 15 days will start on any day between April 15 and September 15. The results are presented graphically in smoothed form in 24 figures.
    • Randomized Seeding of Orographic Cumuli, 1957: Part II

      Battan, Louis J.; Kassander, A. Richard, Jr.; Sims, Lee L.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1958-10-01)
      During July and August 1957, orographic cumuli over the Santa Catalina Mountains of southeastern Arizona were seeded from an airplane with silver iodide. The experimental design of the program involved the randomized seeding by pairs of days; one of two days with suitable clouds was seeded on a random basis. On seven pairs of days, observations were made of the cumuli with a pair of K-17 cameras on a 1.3 mi baseleg. At the same time, radar observations were made with a 3-cm vertically-scanning radar set. On the basis of the analysis of the camera and radar observations an investigation has been made of the occurrence of precipitation as a function of cloud size and temperature. It was found that there is a large variability in cloud behavior from year to year. Natural clouds in the arid southwest do not produce precipitation until their vertical thicknesses are of the order of at least 8 to 10,000 feet. From a comparison of seeded and non-seeded clouds it appears that the silver iodide particles may have produced changes in the precipitation formation mechanisms in orographic cumuli.
    • Recent Studies on Hail and Hail Modification in the Soviet Union

      Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1965-10-05)
    • Report of Evaluation of Meteorological Program, Aviation and Meteorology Department, Army Electronic Proving Ground, Fort Huachuca, Arizona

      McDonald, James E.; Kassander, A. Richard, Jr.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1956-05-10)
    • Seasonal Precipitation and Temperature Data for Selected Arizona Stations

      Green, Christine R.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1964-07-15)
      Annual tabulations of winter (November through April) and summer (May through October) precipitation and temperature for 23 Arizona weather stations have been analyzed in this report. Their relationships are shown and discussed briefly.
    • Seeding of Summer Cumulus Clouds

      Battan, Louis J.; Kassander, A. Richard, Jr.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1959-07-01)
      A description is given of a program of randomized seeding of orographic cumuli over southeastern Arizona. This investigation, started in 1957, is still in progress. The aims have been to learn more about natural cloud processes and to ascertain if airborne silver iodide seedings can modify them. It will be shown that analyses of cloud photographs, radar observations, lightning observations and rainfall data suggest that cloud seeding modified the natural cloud processes. However, the changes observed so far have not been large enough to conclude that effects have positively been established.
    • Separate Component Multiple-Effect Solar Distillation

      Hodges, Carl N.; Thompson, T. Lewis; Groh, John E.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1962-11-01)
      Research concerning a desalting system which utilizes solar energy and separate components for evaporation and condensation has been conducted by The University of Arizona for the Office of Saline Water during the period from April 28 to October 28, 1962. While cost optimization has not been completed, equations have been developed for solar collector performance and specific productivity. Items of equipment, such as heat exchangers, packed towers, spray chambers, etc., have also received careful investigation. A model plant has been constructed and is presently being operated. I
    • Significance of Different Vertical Distributions of Water Vapor In Arid and Humid Regions

      Byers, Horace R.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1957-03-15)
      The vertical distribution of water vapor can be expressed by an index coefficient which provides information about eddy and advective transports in a region or in an air mass. The relationship between evapotranspiration and eddy diffusivity of water vapor can be studied in this way. Striking differences in conditions between the arid Southwest and the remainder of the country are shown.
    • Silver Iodide Seeding and Radar Echoes from Convective Clouds

      Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1967-10-15)
      Summer convective clouds over a fairly isolated mountain range over southeastern Arizona were seeded by means of airborne silver iodide generators. The selection of days to be seeded was made according to a randomization scheme involving pairs of days. A 3-cm vertically scanning radar set was used to observe the maximum echo height over the "target" area at 30 minute intervals. The data so obtained were used to examine the effects of the seeding on the vertical extent of the cloud echoes. Although there is a suggestion that the silver iodide nuclei may have initiated precipitation in some clouds and caused small vertical echo growths, the statistical analyses, for the most part, showed that the observed differences could easily have been caused by chance.
    • Some Factors in Tucson Summer Rainfall

      Bryson, Reid A.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1957-05-31)
      This report describes an investigation of several synoptic and airmass factors as they relate to the occurrence and amount of daily rainfall at Tucson, Arizona. Of the variables considered as predictors of rain later the same day, three stand out as useful: total precipitable water, Shownlter Stability Index, and distance south of the last closed contour of the circumpolar vortex at 500 mb. Better than 90 percent correct short-term forecasts appear attainable for occurrence of rain, while about twice as many correct forecasts as might be expected by chance were obtained in forecasting rain amount class.
    • Summer Rainy Days in Arizona

      Green, Christine R.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1963-01-15)
      June through September rainy days for 22 Arizona weather stations with 50 or more years of record are tabulated, graphically presented, and discussed.
    • Survey of Weather Modification in the Soviet Union

      Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1973-05-15)
      On the basis of a review of abstracts of articles published mostly since 1969, a summary has been prepared of Soviet research in weather modification. Hail suppression and precipitation stimulation still are major areas of activity in the USSR, but in recent years they have begun to do research on lightning suppression and the use of heat for the dissipation of warm fog in stratus. The articles surveyed show little evidence that Soviet scientists, unlike their American counterparts, are convinced of the value of randomized experiments in the evaluation of cloud seeding hypotheses and there is no evidence in this literature that Soviet scientists have been tackling the modification of large scale weather phenomena.
    • Tables of the Radar Cross Sections of Water Spheres

      Herman, Benjamin M.; Browning, Samuel R.; Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1961-12-01)
    • The Annual and Diurnal Variations of Cloud Amounts and Cloud Types at Six Arizona Cities

      Sellers, William D.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1958-09-01)
      The annual and diurnal variations of cloud types and cloud amounts are described for six first-order weather stations in .Arizona. These stations are Flagstaff, Winslow, Prescott, Phoenix, Tucson, and Yuma. Most of the data analysed were obtained on punched-cards from the National Weather Records Center at Asheville, North Carolina. The period of record was from January 1, 1948 through December 31, 1955. This information was supplemented by cloud amount data for the period from July 1, 1956 through March 31, 1958 taken from the supplement to the Local Climatological Data for the six stations. After a brief outline of the terrain features in the vicinity of the stations (section II), the type, quantity, and quality of the data are discussed. Emphasis is put on the homogeneity of the records, both temporally at a single station and spatially from one station to another. In section rv the annual variations of cloud amounts, cloud types, and thunderstorms are described, without any reference to the more detailed diurnal variations, which are discussed later, month by month, in section V. Part of the summary (section VI) is devoted to an investigation of the relation between the average cloud cover and the frequencies of occurrence of both clear and overcast skies at a "typical" .Arizona city.
    • The Annual March of Precipitation in Arizona, New Mexico, and Northwestern Mexico

      Bryson, Reid A.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1957-06-07)
      This report is concerned with the annual march of monthly precipitation amount in an area comprising the states of Arizona, New Mexico, Sonora, Sinaloa, Durango, and western Chihuahua. Fourier analysis was used to reduce the twentyyear mean monthly values to six harmonic terms, four of which were then plotted on charts and studied. The results of this study indicate that an area consisting largely of the Sierra Madre Occidental in northwestern Mexico, and the portion of Arizona southeast of Tucson constitute a single rainfall province with a strong summer maximum of rainfall. This province also has a winter maximum but only in Arizona does the semi-annual term exceed the annual in amplitude. Within the United States the Gila and Rio Grande valleys constitute rainfall provinces of internally similar annual march, while the upland areas tend to resemble the Pacific coastal pattern to the west.
    • The Distribution of Clouds at Tucson, Arizona, with Respect to Type, Amount, and Time of Observation

      DesJardins, Robert B.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1958-01-01)
      More than 25,000 Weather Bureau cloud observations for Tucson, Arizona, for the nine-year period from 1 July 1945 to 1 July 1954, were statistically analyzed. It was immediately obvious from this analysis that the cloud data for this period were not homogeneous. A study of the heterogeneities in the data indicated that they were probably caused by two changes which had been made in the Weather Bureau cloud observing procedures. These changes were: (1) In 1949 the descriptive material for cirrostratus clouds was changed when the revised version of the Manual of Cloud Forms and Codes for States of the Sky was published. !!his change is believed to have caused a large increase in the annual number of observations of cirrostratus clouds and a correspondingly large decrease in the annual number of observations of cirrus clouds. (2) On July 1, 1948 a new procedure for recording cloud observations on WBAN Form lOB was adopted. This new recording procedure resulted in cloud observations which were not as detailed as were the observations made before July 1, 1948. The change from the old "cloud family" recording procedure to the new "cloud layer" recording procedure resulted in a decreased number of recorded observations of cumulonimbus and altostratus clouds. The frequencies of occurrence were computed for eight types of clouds (stratocumulus, cumulus humilis, cumulus congestus, cumulonimbus, altostratus, altocumulus, cirrus and cirrostratus) and the annual and diurnal variations of these frequencies were determined. The average monthly tenths of cloud cover were also computed and the annual and diurnal variations of the amounts of cloud cover were determined. A comparison of the annual variations of these parameters showed that they were essentially the same for six of the cloud types but were notably different for the cumulus humilis and cumulus congestus cloud types. The annual variations of the frequencies of occurrence of the most common cloud types were also compared to the annual variations of three synoptic parameters (the number of frontal passages, the amount of precipitation and the amount of precipitable water). These comparisons seemed to indicate that there was a relationship between the general synoptic situation and the amount of cloudiness during some months. However, the number of synoptic parameters included in this part of the study need to be increased before any definite conclusions can be reached. For each month, the year-to-year variations in the amounts of high, middle and low cloudiness at Tucson were compared with the year-to-year variations of the average amount of precipitation for the Tucson area. In general, changes in the amount of cloudiness were of the same sign as changes in the amount of precipitation, but there were many noteworthy exceptions to this general pattern. In addition, the rank correlations -2- between the monthly amounts of precipitation and the monthly amounts of cloudiness were computed. In general, the precipitation was best correlated with the amount of low cloudiness and the highest of these correlations occurred during the winter months. However, there were many interesting deviations from this general pattern.
    • The Low-Level Wind Field at Phoenix and Tucson

      Frenzel, Carroll W.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1961-10-02)
      Resultant surface winds presented as monthly averages for each hour of the day for two years have been computed for Tucson and Phoenix and are displayed as hodographs showing the diurnal variation of the surface wind. Resultant winds for these two years were computed from upper air observations for all times and all levels of observation up to and including 4000 meters above mean sea level for both Phoenix and Tucson, and are presented in the form of tabulated listings as monthly averages. In addition, mean speeds of the upper air winds are presented and a tabulation of the occurrence of calm winds at the surface vs. month and hour is given. Results of this study show that a distinct diurnal variation in the surface winds is present at both Tucson and Phoenix. The most persistent feature of the wind field at both of these stations is the drainage wind which occurs during the early morning hours. During the warmer portions of the day air motion tends to be toward higher elevations. Thus, in general, the air motion conforms to what is expected on the basis of theory. Mean air motion for each month is presented. Considerable difference between months and between the same months of the two years is noted. High frequencies of reported calms at Phoenix for certain months lead to rather small net air movement. The diurnal variation in the number of reported calms is seen to be related to the diurnal reversal in wind direction associated with the mountain-valley circulation. The relationship of these resultant winds to the air pollution problem at these two cities is discussed.