Showing papers on "Precipitation published in 1975"

Diurnal Variations in Precipitation and Thunderstorm Frequency over the Conterminous United States

Abstract: Hourly data on the frequencies of all types of precipitation events, heavy precipitation events, trace precipitation events and thunderstorms for more than 100 stations in the United States were processed to generate statistics on the amplitude and phase of the diurnal and semidiurnal cycles at each station. Results are displayed on seasonal maps in a vectorial format that emphasizes the large scale geographical consistency of the diurnal variations. During summer each of the four parameters listed above displays a distinctive geographical pattern of diurnal variations. Thunderstorm frequency tends to be the most strongly modulated by the diurnal cycle; trace precipitation the least strongly modulated. Over the central United States the maximum frequency of severe convective storms occurs during the early evening; thunderstorms exhibit their maximum frequency around midnight, while most precipitation falls later in the night. These amplitude and phase differences offer some insight into the relat...

A Stochastic Model of n-Day Precipitation

Abstract: General expressions are derived for the distribution functions of the total amount of precipitation and the largest daily precipitation occurring in an n-day period. Two special cases are considered: (i) the probability of occurrence of precipitation on any day in an n-day period is a constant (binomial counting process) and (ii) the probability of occurrence of precipitation on any day depends on whether the previous day was wet or dry (Markov chain counting process). The distribution function for daily precipitation was assumed to be exponential. Analytic expressions are derived for the distribution functions for total precipitation or precipitation greater than a threshold. For the numerical example chosen, the Markov chain-exponential model is slightly superior to the binomial-exponential model. This stochastic model seems to have several advantages over present approaches.

The seasonal variation of the hydrologic cycle as simulated by a global model of the atmosphere

Abstract: A numerical model of the atmosphere with a seasonal variation of insolation and sea surface temperature is time integrated for over 3 simulation years on a finite difference grid network having a nearly uniform horizontal resolution of approximately 265 km. There are 11 levels in the model from 80 m to 31 km above the ground. The model has realistic continents with smoothed topography. In addition to wind, temperature, pressure, and water vapor, the model simulates rainfall, snowfall, and evaporation at the surface. The runoff rate and the rates of change of soil moisture and snow depth are determined by a budget of liquid water, snow, and heat at the ground surface. The simulated precipitation and other hydrologic quantities are compared with those derived from observed data. In addition, the correspondence between the distribution of precipitation rate and those of other relevant quantities, such as sea level pressure and kinetic energy of transient disturbances, is examined. To obtain an overall impression of the climate simulation, a map of Koppen climate types, which is obtained from simulated temperatures and precipitation rates throughout the year, is compared with a similar map based upon observed climatic data. It is shown that the model locates the major arid regions of the earth, such as the Sahara Desert in northern Africa and the deserts of central Asia and Australia. Furthermore, the tropical rain belt and its seasonal movement are well reproduced. The model approximately simulates the changeover from dry winter to wet summer conditions in southern Asia and the seasonal reversal of the monsoon wind system over Asia. The wet zone in middle and high latitudes, such as in Canada, Europe, and western Siberia, is also simulated by the model. Examination of the distribution of runoff over continents of the model reveals that the watersheds of many important rivers of the world are correctly positioned in the simulation. In general, the quality of the simulation tends to deteriorate in the neighborhood of major mountain ranges. Furthermore, the rate of precipitation and that of runoff over continental regions in the model tropics is much larger than estimates of the actual rates of these quantities. Nevertheless, this study demonstrates that the model is capable of reproducing many of the basic features of the seasonal variation of hydrology and climate on a global scale.

The Nature of Winter Clouds and Precipitation in the Cascade Mountains and their Modification by Artificial Seeding. Part I: Natural Conditions

Abstract: This is the first of three papers describing field investigations, carried out from 1969 to 1974, of winter clouds and precipitation in the Cascade Mountains of Washington State, and physical evaluations of their modification by artificial seeding. The present paper describes airborne and ground observations of the natural clouds and precipitation.It has been observed that (i) in pre-frontal conditions ice particles dominate over water droplets above the −10°C level, but the ratio of ice to water is lower in post-frontal conditions; (ii) the passage of an occluded or warm front causes a sharp lowering of the diffusional growth layers of the ice crystals, so that particles reaching the ground change from unrimed crystals which grow at low temperatures to rimed crystals which form at higher temperatures; (iii) the maximum ice particle concentrations in the clouds are often several orders of magnitude greater than measurements of ice nuclei would suggest; (iv) the growth of precipitation particles b...

Freezing nuclei in marine waters

Abstract: Inorganic soil materials (Isono et al., 1959; Mason, 1960) and extraterrestrial meteoritic particles (Bowen, 1956; Bigg, 1963) have been suggested as possible sources of atmospheric ice nuclei which play important roles in the production of precipitation. DOI: 10.1111/j.2153-3490.1975.tb01682.x

Possible climatic impact of tropical deforestation

Abstract: OF the various mechanisms suggested by which man might change the planetary climate, the removal of tropical rain forests to increase arable acreage seems to be one of the more imminent For this reason we selected this as one of the first problems to be tested in our recently updated climate model Bearing in mind the fallibility of computer simulations, we find overall global cooling and a reduction in precipitation: a larger tropical reduction being almost balanced by a subtropical increase

Precipitation characteristics in the northeast Brazil dry region

Abstract: The general meteorological conditions and precipitation characteristics in the Northeast Brazil dry region during its rainy season from December through April are discussed. It is found that most of the yearly rainfall comes in six to eight episodes from organized weather systems which move from east to west with about the same speed (∼5 m s−1) as the lower tropospheric wind flow. These systems appear not to be of local origin. Rainfall is shown to be inversely correlated with the regional subsidence. An interesting and previously unknown diurnal rainfall variation is found. Orographic influences appear to act to modulate the weather systems and develop upslope and downslope winds. This produces rainfall in the morning over the lowland regions and in the afternoon over the hills and more elevated regions. Extensive comparisons of the rain systems with other tropical regions are made. Other characteristics are discussed.

Growth of the desert tortoise (Gopherus agassizi) in Nevada

Abstract: Between 1963 and 1973, growth of the desert tortoise (Gopherus agassizi) in southern Nevada averaged about 9 mm per year. Yearly increments were estimated for 5 years (1969 to 1973) and ranged from a low of 1.8 mm in 1972 to a high of 12.3 mm in 1969. Growth was greatest following winters of high precipitation, which resulted in increased production of winter annuals in the spring. Growth of tortoises generally occurred between April and July. The weight, W(g), of tortoises may be estimated as W =0.000258X/sup 2.98/ with X the plastron length in mm. (auth)

Optimal risk based design of storm sewer networks

Abstract: Optimal design of sewer network has conventionally been pursued within a deterministic framework. However, such design may be appropriate because of existence of uncertainties affecting the performance of a storm sewer system, e.g., precipitation rate, insufficient data, errors in design equations, and other factors. These uncertainties are systematically evaluated and incorporated in the proposed design of a storm sewer system. The optimal choice of slopes and diameters of the entire sewer network is based on a tradeoff between risk due to potential flood losses and the cost of installation of the sewers. Discrete differential dynamic programming technique is used in the risk-based design.

Rainfall Characteristics and Soil Erosion in the Rainforest Area of Western Nigeria

Abstract: Precipitation in Western Nigeria is principally from thunderstorms with sharp, high-intensity rainfall peaks. The time of occurrence of the peak intensity period in a rainstorm has an influence on whether or not runoff occurs in smaller storms. Runoff and soil loss on bare, cultivated Iwo soil are closely related to an EI 30 erosivity index, modified by the time-position of the peak intensity. The soil erodibility factor in the universal soil-loss equation could be reasonably estimated from easily measured soil parameters.

Summer Ice Crystal Precipitation at the South Pole

Abstract: Ice crystal precipitation was observed and the crystals replicated, at the South Pole during January and February 1974. The crystals were of columnar form. These columns were hollow or prismatic, and sometimes were in the form of combinations of bullets. These combinations were very fragile, disintegrating into individual bullets upon impaction. Smaller “diamond dust” crystals were observed on two occasions. NOAA-NWS radiosonde data showed that the air was supersaturated with respect to ice at 650 to 600 mb (i.e., just above the surface) throughout the period. Ice crystal precipitation was only observed at the surface when cirrus bands were present at higher altitudes. It is likely that ice crystals, descending from the cirrus only a short distance above, grew to the larger columnar crystals while falling through the moist layer. As these layers were able to remain saturated, without precipitating or forming ice fogs or clouds at temperatures of −35°C, heterogeneous freezing nuclei were probably ...

Formation of Graupel.

Abstract: Measurements were made of the sizes and concentrations of graupel and snow crystals occurring in seeded and untreated winter storms of the Sierra Nevada. The amounts of rime on individual snow crystals were also determined. The observations show that crystal riming, and formation and precipitation of graupel, are common to all stages of Sierran snowstorms. Graupel occurs simultaneously with all types of snow crystals, but individual crystal types do not consistently occur with or serve as kernels for particles of graupel.Graupel particles do not develop predominantly on kernel snow crystals that grow to relatively large sizes over relatively long periods by deposition and accretion. Graupel often forms instead on a select few small crystals, when it forms utilizing regular crystals as kernels. Graupel frequently develops without kernels, by alternate riming processes. One possible alternative is a mechanism that produces graupel from rime accumulated at localized points on parent snow crystals.

Precipitation: its acidic nature.

Abstract: A comparison of the free hydrogen ion concentration and the total hydrogen ion concentration of rain samples shows that rain is a weak acid. The weak acid nature of rain casts doubt on the concepts that the acidity of rain is increasing and that these increases are due to strong acids such as sulfuric acid.

Numerical Simulation with the NCAR Global Circulation Model of the Mean Conditions During the Asian-African Summer Monsoon

Abstract: A global circulation model (GCM) developed at the National Center for Atmospheric Research (NCAR) has been used to simulate the large-scale features of the Asian-African summer monsoon. The model has 6 vertical layers of 3-km thickness with a 2½° horizontal latitude-longitude grid. The physical processes incorporated are solar and infrared radiation, with cloudiness explicitly calculated from a model-generated relative humidity distribution. The latent heat released from precipitation is derived from stable lifting and cumulus convection. Also included in the model are subgrid-scale vertical and horizontal transports of momentum, sensible heat, and latent heat. We compare the computed sea-level pressure, wind, cloudiness, and precipitation patterns with. observed data and, in particular, concentrate on the strong low-level monsoon jet near eastern Kenya and Somalia. The model correctly simulates this jet in position; however, the wind maxima are weaker than observed. Because of the relatively coa...

The January Global Climate Simulated by a Two-Level General Circulation Model: A Comparison with Observation.

Abstract: The mean global distributions of pressure, temperature, wind, moisture, cloudiness, precipitation, evaporation, and surface heat balance simulated for January by the two-level Mintz-Arakawa atmospheric general circulation model are compared with the corresponding observed fields. Although there are a number of shortcomings, in general the large-scale distribution of global climate is reasonably well portrayed by the model, in spite of its limited vertical resolution. The model simulates the semi-permanent cyclones and anticyclones of both the tropics and higher latitudes in approximately their correct positions, together with the associated large-scale temperature and circulation fields of the middle and lower troposphere. In comparison with models of greater resolution, these results suggest that with further selective improvements in the physical parameterizations, relatively coarse global models (of correspondingly lower computational demands) are useful tools in the study of many aspects of c...

The Nature of Winter Clouds and Precipitation in the Cascade Mountains and their Modification by Artificial Seeding. Part II: Techniques for the Physical Evaluation of Seeding

Abstract: Airborne, ground and radar techniques used for evaluating the effects of artificial seeding on winter clouds and precipitation over the Cascade Mountains are described. The clouds were seeded for 1 or 2 h with silver iodide and/or Dry Ice, dispersed from an aircraft, at locations which particle trajectory analysis, based on field data, indicated would affect precipitation in a small (90 km2) predetermined target area straddling the Cascade crest. The effects of seeding on the clouds were determined from the aircraft through visual observations, ice nuclei measurements, and measurements of the type and concentrations of cloud particles. A Doppler radar located near the Cascade crest was used to measure the spectra of fallspeeds of the precipitation particles. At manned stations within the target area on the ground, measurements and observations were made before, during and after seeding of precipitation rates, the types, concentrations and degrees of riming of snow crystals, and the concentrations...

The dynamics and thermodynamics of precipitation loading

Abstract: A one-dimensional, time-dependent numerical cloud model is used to analyze the factors in the dynamic and thermodynamic equations which lead to a steady-state or nonsteady-state solution for the cloud vertical motion, buoyancy, precipitation, and cloud water fields. ‘Bulk water’ microphysical techniques are used for the cloud, rain, and hail variables. An atmospheric sounding from a severe storm situation is used as initial and environmental conditions, yielding model updrafts of 40 m sec−1 maximum and more than 10 m sec−1 over the entire cloud region.

Isotopes in Precipitation in Northwestern North America

Abstract: Regional analyses of oxygen and deuterium isotope abundances in precipitation from selected stations of the International Atomic Energy Agency-World Meteorological Organization global netwok are presented as background for a more detailed study of the origin and history of atmospheric water in western Canada east of the Rocky Mountains. Departures from Dansgaard's regression between oxygen-18 concentrations and surface temperatures are attributed mainly to differences in intial water vapor isotope concentrations at inland stations in western Canada. Values of δO18 in rain at Edmonton are best correlated with 800 mb temperatures. However, snow data showed little variation in correlation with height up to 800 mb, and larger unexplained variance than rain, despite the fact that evaporation and isotope exchange effects are small for snow. Using simultaneous upper air temperature and wind data the δO18 variations in snow are attributed both to large condensation temperature variations that can occur i...

Precipitation Increases in the Low Hills of Southern Illinois: Part 1. Climatic and Network Studies

Abstract: Long-term precipitation records indicated that, on the average, 15% more warm season precipitation falls on the forested western Shawnee Hills of southern Illinois than falls on the rural farm flatlands at 120 m lower elevations both north and south of the hills. This precipitation difference with relatively little elevation change offered an interesting opportunity to study the effect of orographic and land-use differences upon convective precipitation. Initially, two methods differing in scale and time were used to delineate the bill anomaly and to investigate its causes. Extensive climatic studies of all available precipitation data revealed that the effect of the hills was most pronounced during the warm season when showers and thunderstorms are the major source of precipitation. A subsequent 5-yr study involving a dense recording raingage and wind recording network showed that the hill-related increases apparently came through enhancement of heavy showers, particularly those associated with ...

Two mechanisms of microbial carbonate precipitation

Abstract: Puddles formed on loess soil are known to fissure up on drying [1]. The irregular, dish-like, concave pieces thus formed may reach a 100cm 2 area and are from l m m to l c m thick (Fig. 1 a). They are formed by sedimentation; their upper fine layer contracts more quickly than the rest and the pieces break away from the soil beneath. I took some such fragile, soft crumbs and burned them under small bonfires, about 1/2 m high and 70 cm 96 which were fed wood for about 4 hours. We obtained hard, dish-like crumbs which could be broken by hand only with difficulty. These crumbs have a Mohr hardness between 3 and 5, a waterabsorbing capacity between 8 and 25%, and a modulus of rupture between 30 and 60 kg/cm 2. Modern data on burned fire clay range from 50 to 220 kg/cm 2. I propose that dish-like pieces burned accidentally in bonfires may have given to prehistoric man the idea that ceramic dishes can be made by moulding certain clays by hand and burning

Origins of some massive pyritic ore deposits of western Europe

Abstract: The geologic environments of formation of three types of massive, pyritic, largely stratiform orebodies of western Europe are compared. The largest concentration of such ores, the pyrite belt of Spain and Portugal, seems to have resulted from volcanic-hydrothermal precipitation on the sea floor largely in or adjacent to quartz keratophyre eruptive centers. The smaller deposits of northwestern Germany, important for their content of zinc and lead and with abundant barite, are in pelites close to reef limestones. They apparently are shallow-water accumulations, largely organically precipitated. The third and economically least important pyritic ores are those of southern Tuscany. The original sulfide accumulations appear to have formed in stagnant deep-water basins associated with calcium sulfate evaporites. The Triassic ores of Tuscany have been strongly modified and mobilized during a near-surface thermal event accompanied by a few intrusions during the Pliocene.

A Numerical Model of Precipitation from Seeded and Unseeded Cold Orographic Clouds.

Abstract: This paper describes a numerical model of ice-phase precipitation from orographic clouds which includes the effects of seeding with artificial ice nuclei. The model describes the events which take place when a layer of moist air of near-neutral stability, overlain by a more stable dry layer, flows over a mountain ridge. A two-dimensional, steady-state model of the flow in the vertical plane normal to the ridge furnishes a field of the flow streamlines along which microphysical processes are followed. The cloud physics model describes the formation of the supercooled cloud, the formation of ice particles from both natural and artificial ice nuclei, and the growth and precipitation of ice particles. Growth by both vapor deposition and riming are included. Artificial ice nuclei are released from a localized source at ground level. A simple Fickian diffusion process is used to describe the vertical transport of nuclei to the cold upper region of the cloud.The model calculates the rate of precipitatio...

A Comparison of Canadian and United States Standard Methods of Measuring Precipitation.

Abstract: Methods of measuring precipitation vary from country to country. Consequently, the comparability of precipitation data along international borders is questionable. The present paper compares 5 years of precipitation data at Windsor, Ontario, using the standard Canadian and United States methods of measuring precipitation. Monthly rain amounts are very similar, but substantial differences exist in snow measurement. The Canadian method appears to overestimate precipitation from snowfall.

Rebound limits on charge separation by falling precipitation

Abstract: Neglect of the angle dependence of rebound probabilities for cloud droplets colliding with hail pellets has led to an overestimate of the amounts of charge that can be separated with the Elster-Geitel mechanism. Application of the wind tunnel results obtained by Aufdermaur and Johnson suggests that the actual amounts of charge transferred may be less than 20% that assumed by ignoring the angle dependence. Observations of the charges carried by hail and rain particles within the bases of thunderclouds support these lower estimates and raise questions about the adequacy of the precipitation processes in explanations of thundercloud electrification.

Temperature effects on Great Lakes water balance studies

Abstract: . Beginning of month water temperature profiles are estimated for each lake. These water temperature profiles along with surface water temperatures are used to determine the effects of thermal expansion and contraction of water on the net basin supply values obtained from water balance studies using end of month lake levels. It is demonstrated that net basin supply values (equivalent to precipitation on the lake minus the evaporation from the lake plus the runoff into the lake) obtained from water balance studies without accounting for the thermal expansion and contraction of water may be in error by as much as 100 percent during some months for each lake.