• Doppler Radar Observations of a Hailstorm

      Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1974-02-01)
      A severe hailstorm, occurring on 10 August 1966, passed over a zenith pointing, X-band, pulsed-Doppler radar located on a mountain in southeastern Arizona. An analysis was made of measurements of radar reflectivity, mean Doppler velocity, variance of the Doppler spectrum and calculated updraft velocity. The vertical air motions and characteristics of the hydrometeors within the storm were highly variable over distances of a few hundred meters to a few kilometers. The storm consisted of a series of updraft cores containing a number of discrete volumes, 1 to 2 km in diameter, of rapidly rising air with smaller accompanying eddies. The updraft cores were separated by regions of weak updrafts or downdrafts. For the most part, the highest reflectivitives were outside the updraft cores. It is visualized that the hailstone growth was initiated within the updraft, not as a continuous process, but rather as pockets of hailstones within the fast rising distinct volumes. This process could account for the layers of clear and opaque ice within large stones by allowing them to pass through several rising volumes. It might also account for brief bursts of hail and short hailstreaks observed at the ground.
    • Doppler Radar Observations of a Mountain Hailstorm

      Battan, Louis J.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1975-08-01)
      By means of an X-band, vertically pointing Doppler radar observations were made of a thunderstorm on 20 August 1973 producing hail about 6 mm in diameter. The observations confirm earlier ones showing a highly variable internal structure. Updrafts are composed of high velocity "eddies" having diameters of about a few 100 m to a kilometer. It is speculated that such hailstorm features as the size and layering of ice type and the sporadic nature of hail showers are explained by the highly variable character of each updraft region and the sequence, at periods of 3 to 4 minutes, of updraft formation.
    • Evaluation of Effects of Airborne Silver-Iodide Seeding of Convective 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), 1962-03-01)
      Observations of the convective clouds over the mountain ranges of southeastern Arizona show that a large fraction of them reach temperatures far below freezing but fail to produce precipitation. During the summer periods of the years 1957 through 1960, a randomized cloud seeding experiment was conducted to test if these clouds could be modified by airborne silveriodide seeding. The essential features of the experimental design were the following: 1) An objective technique was evolved for predicting days with suitable clouds; 2) one of a pair of two adjacent days was seeded on a random basis; 3) measurements on all days were made with rain gages, radar and a pair of ground-located aerial cameras mounted at the ends of a 3-mile base leg, and visual observations were made of cloud-to-ground lightning; 4) the signrank test was used to make statistical evaluation of the effects of seeding. The results after four years are the following: 1, The rainfall statistics do not allow a conclusion that seeding had any effect. Statistically, the rainfall on both seeded and not-seeded days was the same. However, the sensitivity of the tests to changes in the quantity of precipitation was quite low. 2. The frequency of occasions of large thunderstorm echoes was statistically the same on seeded and not-seeded days. 3. The cloud-census and radar studies suggest that in some cases, seeding may have led to the initiation of precipitation echoes. 4. Although there were more cloud-to-ground lightning strokes on seeded days, the differences between their occurrence on seeded and not-seeded days were not statistically significant. Evidence is presented indicating that precipitation in convective clouds is not initiated by the ice-crystal process. Samples of days with heavy rain and light rain were compared in order to study the factors governing the quantity of rain. It was not possible to show that there was any relation between the region of echo initiation and the quantity of precipitation. On the other hand, it is clear that on days with heavy rain there were many more large clouds. The observations are best explained if it is assumed that the quantity of rain is governed by those properties of the atmosphere which determine the number and size of the convective clouds. The microphysical processes which determine the region of precipitation initiation do not appear to be as important as was once suspected. A new program of seeding tests is described which should be more sensitive to changes in quantity of rainfall. It differs in several fundamental aspects from the program conducted during the period 1957 to 1960.
    • Evaluation of Potential Vorticity Changes Near the Tropopause, and the Related Vertical Motions, Vertical Advection of Vorticity and Flow of Radioactive Debris from Stratosphere to Troposphere

      Staley, D. O.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1960-03-26)
      Individual potential vorticity change, vertical motion, vertical advection of vorticity and flow from stratosphere to troposphere are evaluated at different levels and for different times in an extratropical disturbancec Vertical motions are obtained from trajectories on three isentropic surfaces for two different times. The isentropes pass through or near a front in the upper troposphere, the lower stratosphere, and the high troposphere on the cold side of the front. Vertical motion is also evaluated at 500 mb from an adiabatic method designed to give instantaneous values to the extent that the system moves without change of shapeo Negative extremes of 8 to 10 cm sec-1 occur in the upper air front, with positive extremes of the same magnitude a short distance to the northeast, coinciding with the eastern exit of the frontal zone. From theory it is shown that potential vorticity is not conserved if there is either a gradient of diabatic heating or a component of curl, normal to the isentropic surface, of frictional force. The sum of these two effects is evaluated over the United States for two 12-hr periods on two isentropic surfaces which were common to parts of the lower stratosphere, upper troposphere and a front in middle and upper troposphere. Generally large, positive potential vorticity changes occur in the lower stratosphere and in the upper troposphere on the cold side of the front. Large negative values occur in the frontal zone and around the entire periphery of the positive area, or around the periphery of the trough in the upper air. The potential vorticity changes are related to simultaneous stability and vorticity changes of like sign. The potential vorticity changes are positive in the region of the so-called 1 tropopause funnel 1 ; changes everywhere appear attributable to vertical gradient of diabatic heating rather than curl of frictional force. ' ( I The terms in the vorticity equation which contain vertical velocity (vertical advection of vorticity and tilting terms) are shown by means of the thermal wind equation to depend only on the vertical motion and temperature fields in an isobaric surface. For the frequent case where negative motion is centered in the baroclinic or frontal zone and rising motion centered at the exit of the zone, each of the vertical motion terms has the same characteristic distribution. Positive values occur on the cold side of the zone and to the right of the downwind exit of the zone, and negative values occur on the warm side of the zone and to the left of the downwind exit of the zone. The vertical advection and the sum of vertical advection and tilting terms are evaluated at 500 mb. Magnitudes obtained compare with those of the divergence term, although magnitude depends considerably on the distances over which finite differences are evaluated. Isentropic trajectories trace air initially in the lower stratosphere downward to within 5000 ft of the surface within 24 hr. Diabatic incorporation into the troposphere is also noted. The total adiabatic mass flow into the troposphere associated with the number of typical upper air disturbances in existence at any time is estimated and found to be sufficient to give the observed short residence times of a few months for radioactive debris injected into the stratosphere by nuclear detonations.
    • Fourier Analysis of the Annual March of Precipitation in Australia

      Bryson, Reid A.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1957-05-31)
      Monthly standard normal rainfall data for about 200 Australian stations was subjected to Fourier analysis. Charts were then plotted for phase angle and amplitude of each of the first four harmonics. These provide an objective description of the pattern of annual march of rainfall, and clearly delineate certain rainfall regions and climatic divides.
    • Heating and Cooling Degree-Day Characteristics in Arizona

      Green, Christine R.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1962-02)
      A twofold study of degree-day data has been made for 49 Arizona weather stations. The first section of the report analyzes the possibility of temperature trends occurring in Arizona. The second section discusses heating and cooling degree-day practical application with emphasis on the Tucson area.
    • Measurement of Atmospheric Water Vapor by a Spectrophotometric Technique

      McMurry, Earl W.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1962-09-21)
      A spectroscopic technique was used to measure the total amount of water vapor between the point of observation and the sun. Measurements were taken continuously throughout the day, yielding a detailed picture of water vapor variations as a function of time. Results from 28 days of observation over a period of a year show a wide variety of situations ranging from days of relatively stable and constant precipitable water vapor W to days in which large changes occur, sometimes quite abruptly. The median value of the range of W within successive one-hour periods was found to be 0.05 in, with ten per cent of all ranges exceeding 0.12 in, the latter amounting to about fifteen per cent of the annual mean of W at the locality in question. It is concluded that significant W-fluctuations are commonly missed in routine radiosonde practice. Natural variations of Ware, on the average, somewhat greater than the instrumental errors of radiosondes. Crude estimates of moist 11 bubble11 diameters of 0.5 to 12 kilometers were obtained.
    • Measurement of Draft Speeds in Convective Clouds by Means of Pulsed-Doppler Radar

      Battan, Louis J.; Theiss, John B.; Institute of Atmospheric Physics, The University of Arizona (Institute of Atmospheric Physics, University of Arizona (Tucson, AZ), 1967-04-01)
    • 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.