Showing papers on "Precipitation published in 1970"

Numerical Simulation of the Life History of a Hailstorm

Abstract: A two-dimensional, time-dependent cloud model has been used to simulate the evolution of hail cells and hailstorms. The model has been under development for several years tested on a few days of real data, and gives reasonable predictions of the convective characteristics and essential precipitation processes for both severe and nonsevere convection days. Hydrodynamic equations for. deep convection are integrated over a 20 km square grid with 200 m spacing between grid points. Cloud formation and precipitation processes employing bulk water techniques are simulated in the model. Autoconversion and accretion are used to transform cloud water to rain. Precipitating ice (hail) is formed by the freezing of rain and through an approximation to the Bergeron-Findeisen process to transform cloud liquid to precipitating ice. Accretion of cloud water by rain, and accretion of cloud water, cloud ice and rain by hail are modeled. Wet and dry growth of hail and the shedding of rain from hail are simulated. Cl...

The classification of snow metamorphism

Abstract: A new classification of snow on the ground is based on the major physical processes involved in the metamorphism of a snow cover. The major divisions are based on (I) the mechanical damage to snow crystals during precipitation, (II) the transport of water vapor at constant temperature because of surface-energy differences, (III) the transport of water vapor along a thermal gradient, and (IV) firnification because of melting and refreezing, and pressure consolidation.

Tropical Circulation in a Time-Integration of a Global Model of the Atmosphere

Abstract: An analysis is made of the structure and energetics of the tropical circulation which emerged from a numerical time integration of a global circulation model with realistic orography. Near the earth's surface, the general features of the time mean flow field and the location of the inter-tropical convergence zone of the model compare favorably with those of the actual atmosphere. Along the convergence zone or shear line, disturbances with a characteristic scale of 2000–3000 km develop and cause heavy precipitation. They tend to develop in the geographical areas where the formation of actual tropical storms is most probable. In the upper troposphere of the model tropics, disturbances with planetary scale develop and are responsible for the maximum of eddy kinetic energy there. In general, both the kinetic energy of the tropical cyclones and that of the planetary-scale disturbances in the model tropics are chiefly maintained by the conversion of available potential energy generated by the heat of c...

Lead and other metal ions in United States precipitation

Abstract: ATMOSPHERIC PRECIPITATION SAMPLES COLLECTED BY A NATIONWIDE NETWORK OF 32 STATIONS THROUGHOUT THE UNITED STATES WERE ANALYZED FOR LEAD, ZINC, COPPER, IRON, MANGANESE AND NICKLE BY ATOMIC ABSORPTION. VALUES FOR EACH STATION, AVERAGED OVER APPROXIMATELY SIX MONTHS DURING 1966 AND 1967, INDICATE HUMAN ACTIVITY AS THE PRIMARY SOURCE OF THESE MATERIALS IN ATMOSPHERIC PRECIPITATION. THE STUDY REVEALS THAT THE NORTHWEST PORTION OF THE U.S. IS CONSPICUOUSLY LOW IN CONTAMINATION; THE NORTHEAST IS RELATIVELY HIGH; AND THE SOUTHWEST AND SOUTHEAST VARY FROM LOW TO MODERATE, DEPENDING ON THE METAL. THE CONCENTRATION OF LEAD IN PRECIPITATION WAS FOUND TO BE CORRELATED WITH THE AMOUNT OF GASOLINE CONSUMED IN THE AREA IN WHICH THE SAMPLE WAS COLLECTED. THE OVERALL MEAN CONCENTRATIONS OF THE METALS IN PRECIPITATION ARE COMPARED WITH ANALOGOUS VALUES IN SURFACE WATER SUPPLIES. /AUTHOR/

Air motion and precipitation growth at a cold front

Abstract: A case study of a cold front has shown that, although appreciable ascent occurred over a deep layer, practically all precipitation growth was associated with the ascent of air which originated within the friction layer ahead of the front. Doppler radar observations showed that the ascent was accomplished in two phases; first through near-vertical line convection to between 1 and 3 km at the surface cold front, and thence through shallow-slope convection of the same air to between 3 and 6 km. The line convection was 2-dimensional rather than cellular and occurred in the absence of appreciable hydrostatic instability. Horizontal convergence at low levels was very intense (10−2 s−1 averaged over 500 m vertically and horizontally), so that despite the shallowness of the line convection, the updraught attained a rising speed of 8 m s−1 which was sufficient to generate hail and thunder. The subsequent slope convection produced a period of moderate precipitation behind the surface cold front, and was associated with a pronounced transverse circulation, with strong gradients of velocity separating the weak downdraughts in (and beneath) the sloping frontal zone from the overlying updraught. The overall efficiency of precipitation production was high, 60 per cent of the water vapour flux in the rising air reaching the ground as precipitation.

Sampling Errors in Measurement of Mean Precipitation

Abstract: Data from two dense networks of raingages in Illinois were used to obtain estimates of sampling errors in the measurement of areal mean precipitation on areas of 50–550 mi2 with investigations being made of storm, monthly, and seasonal precipitation. Storm data were grouped also according to season, precipitation type, and synoptic storm type to evaluate the relation between these factors and the sampling error. Storm sampling error was then related to areal mean precipitation, storm duration, area, and gage density within each data grouping. Several transformations of the above parameters were tested and results indicated a slight superiority for logarithms, followed by cube roots, square roots, and a logarithm-square root combination of the parameters. For a given sampling error, the gage density needed in warm season storms was 2–3 times greater than that required in the colder part of the year. Air mass storms required the greatest sampling density among synoptic storm types. Unstable types o...

Distinguishing seasonal recharge to groundwater by deuterium analysis in southern Arizona

Abstract: ABsRAcr. The Tucson Groundwater Basin in southern Arizona covers an area in excess of 600 square miles and contains fill that averages more than 1,000 feet thick. The apparent age of ground­ water as determined by C-14 analyses ranges from zero (near recharg.. -as) to about 6,000 years. Average annual precipitation is about I I inches, slightly more than half of which occurs during the summer as convective storms and most of the remainder during the winter as frontal storms. Summer moisture mostly originates in the Gulf of Mexico and winter moisture mostly comes from the Pacific Ocean. All streams in the basin are intermittent. Our current research attempts to estimate the relative importance of winter versus summer precipitation in recharging the Basin by studing the distribution of deuterium in rainfall, snowmelt, stream flow and groundwater. Seventeen summer -forms in 1968 show a weighted average deuterium value of -4.2 percent (relative to SMOW', and 14 winter storms in 1968-69 show a weighted average value of -6.1 percent. Two groundwater samples from wells near a recharge area show -6.6 and -6.3 percent values. Two other %.,.llsin widely separated parts of the valley, tapping much older water, show values of - 5.8 percent each. The deuterium values for most snowfall and snowmelt in the sur­ rounding mountains range from about - 6 to - 11 percent. The greater isotopic similarity between winter precipitation and groundwater gives strong reason to iuspect that winter runoff is the dominant factor in producing recharge to the Basin. A program is planned to provide sufficient data for a more precise statistical analysis of this hypothesis. It is hoped that an analysis of deute­ rium distribution in groundwater combined with C-14 ages, will provide a means for detecting past climatic changes.

A circularly symmetric primitive equation model of tropical cyclone development containing an explicit water vapor cycle

Abstract: The tropical cyclone model described in previous reports is extended to include an explicit water vapor cycle. Results of experiments that examine effects due to initial humidity conditions, radial resolution, and the finite-difference scheme are discussed. Growth to the mature stage is more rapid in the moist environment, but peak intensity is not strongly affected by the initial moisture content. Rainfall rates are quite reasonable, and nonconvective precipitation is found to be a significant proportion of the total rainfall, in agreement with recent empirical results. Experiments with upstream differencing yield more realistic solutions than do experiments with centered differences. This surprising result is discussed in detail.

A Numerical Model of Cumulus Dynamics and Microphysics.

Abstract: A one-dimensional, time-dependent numerical model of cumulus convection is presented. The model considers the processes of horizontal mixing, evaporation, precipitation generation and freezing, as well as the standard thermodynamic and dynamic processes in isolated cumuli. The initial calculations show that: 1) the vertical velocity and liquid water content undergo coupled damped oscillations in time; 2) the rate at which precipitation-sized drops are formed and grow by collection are not sensitive parameters in the amount of rain which falls from the clouds; 3) the amount of liquid water in the form of cloud droplets that must be present in the cloud before a few large drops can be developed is a crucial parameter in determining the amount of rain which falls from the clouds (the higher the threshold cloud liquid water content, the lower the ultimate rainfall amount); and 4) the freezing time and precise ice-nucleation temperature affect the amount of rain that falls from the cloud in a way ofte...

The soils of the central Namib desert with special consideration of the soils in the vicinity of Gobabeb

Abstract: In this study the most important soils of the central Namib are discussed after a brief preliminary discussion of the climate. Precipitation consists of rain and fog, resulting in sparse vegetation, and succulent in sheItered places. Grass appears only after sufficent rain has fallen.

Prediction of Abnormally Heavy Precipitation over the Equatorial Pacific Dry Zone

Abstract: A simple objective method for using the barometric pressure changes associated with the Southern Oscillation to predict abnormally heavy rainfall over the Pacific equatorial dry zone was applied to 79 years of Darwin sea-level pressure data and precipitation data for a large number of small islands in the equatorial Pacific. It appears that this method, based on a consideration of pressure changes from one year to the next, could provide a prediction one to eight months in advance of heavy precipitation over most of the central and western part of the zone with about 76% effectiveness. There also appears to be some degree of correlation between the amount of pressure departure and the extensiveness (in time and space) of this heavy rainfall. A check into those cases where an associated El Nino occurred indicated that the El Nino usually sets in a few to several months earlier than the heavy precipitation over the central and western equatorial Pacific dry zone and prior to the obvious Darwin pres...

On the Quantitative Determination of Precipitation by a Radar.

Abstract: : Measurements of radar reflectivity, rainfall rate and drop-size distribution were made for three classes of rain type: drizzle, uniform steady rain, and thunderstorms. Power-law relationships of the type a(R to the b power) where Z is radar reflectivity factor, R is rain intensity, and a and b are constants, were found for the three classes of rain. For the measurement of daily rainfall amounts exceeding 10 mm, these relationships produced a standard error of estimate of plus or minus 13%. For the same data, use of a single Z-R relation of all types of rain gave a standard error of plus or minus 28%. (Author)

Content of trace elements in precipitation

Abstract: Seventy-five combined monthly precipitation samples collected in 1968–1969 at stations in the north, northwest, and central regions of the European territory of the Soviet Union have been analyzed. Annually averaged maximum and minimum concentrations of manganese, nickel, lead, and iron in precipitation are given, as well as mean concentrations of the same elements during cold and warm periods for regions of the European territory of the USSR.

Rainfall Enhancement by Dynamic Cloud Modification: Massive silver iodide seeding causes rainfall increases from single clouds over southern Florida

Abstract: In summary, the following points are made: 1) There are essentially two approaches to seeding for rain inducement, static and dynamic. 2) The dynamic approach is effective in inducing growth and increasing precipitation from individually seeded convective clouds under specifiable conditions. 3) The static approach to seeding for precipitation increases is apparently not relevant to the summer cumuli of Florida and Missouri. 4) Regional seeding climatologies, including studies of natural freezing processes in convective clouds, should be completed before commencement of a seeding operation. 5) The results of a seeding operation are frequently better understood by stratification of the data, especially with respect to weather conditions. Precipitation increases from seeding are usually found under fair weather regimes with isolated showers, whereas decreases are often noted under naturally rainy conditions.

The distribution of mean monthly precipitable water vapor and annual precipitation efficiency in Nigeria

Abstract: Precipitable water vapor was calculated for Nigeria using a combination of surface and upper air data and mean monthly maps have been drawn. Annual maps of precipitable water vapor and precipitation efficiency have also been included.

Possible Effects of Precipitation Modification on Stream Channel Geometry and Sediment Yield

Abstract: Stream channel geometry data were collected on 18 small watersheds in the West and sediment yield data were obtained for 673 small watersheds across the United States. Regression analysis was used to test what effects precipitation modification might have on these watershed parameters. No consistent changes of stream channel geometry between watershed areas were obtained, but the results indicated that the stream channel at a given location would adjust significantly in response to increases in precipitation (amounting to 14% annually). This response would probably initiate increased stream channel erosion. Sediment yield will increase substantially in semiarid regions with increasing precipitation until about 27 inches mean annual precipitation; at this point vegetation growth as a result of increased precipitation will begin to reduce sediment yield. Significant changes in stream channel geometry and sediment yield may result in sufficient economic damage to nullify many of the beneficial effects of weather modification.

The effect of wind on the precipitation distribution over a hillock

Abstract: An account is given of precipitation measurements on a hillock carried out during June-November 1959 by means of a very dense network of gauges. It was found that the precipitation distribution in the area on a single rainfall could vary considerably owing to the wind conditions. The cause of this phenomenon seems to lie in the aerodynamical conditions around the hillock. When choosing sites for precipitation measurements such aerodynamic effects should be realized.

Short term variations of a glacier-fed river

Abstract: The main factors determining the short term variations of the river Thjorsa in Iceland are rainfall and the melting of snow and glaciers Time dependent spectral analysis was applied to investigate seasonal variations in the second order properties of the variations of Thjorsa and their relationships with temperature and precipitation In late summer a linear model of Thjorsa and the temperature and precipitation at the meteorological station at Haell provides a good fit of the observations Because of non-linear effects connected with snow melting linear models are less appropriate during the winter although they can still explain a significant proportion of the variations of Thjorsa The most important information for predictions a few days ahead are past values of the river itself Some improvement can be achieved by also taking meteorological observations into account DOI: 101111/j2153-34901970tb00500x

Land Breezes And Rainfall on the Natal Coast

Abstract: The diurnal rainfall at Durban shows highest rainfall frequencies and totals at 2100 with sharp decreases thereafter. A high proportion of this nocturnal precipitation is of low intensity producing less than 1.0 mm/hr. It is suggested that the light nocturnal showers over the coast are produced by undercutting of moist sea air by the cool land breeze. The showers cease with, the arrival of the mountain-plain wind from the interior and subsequent deepening of the cool air layer.

Summer fallow soil water losses on intermountain dryland and its effect on cropping winter wheat.

Abstract: Intermountain drylands lose water from the root zone during the summer of fallow even though they receive a monthly average of 3.1 cm of precipitation. Soil water content in the 7.5- to 15-cm seed zone at the end of summer fallow was related to soil water content at the time tillage was initiated in the spring. Fall soil water content was not appreciably affected by variations in summer rainfall. Adequate soil water for winter wheat (Triticum aestivum L. em Thell) emergence was best assured by initiating summer fallow tillage when the water content in the 7.5- to 15-cm layer was relatively high, rather than depending on summer rain to rewet this layer.

The Effects of Forests on Precipitation

Abstract: Debate has continued for many years as to the influence of the forest on the amount of precipitation falling in the vicinity of the forest itself as well as over wide regions. Evidence for such an influence is reviewed with reference to measurement of rainfall within the forest and moistening of the atmosphere by forest transpiration. Much of this evidence is circumstantial, some of which is based only on casual observation. Meteorological factors such as orographic effect, condensation and freezing nuclei, and vapor content of the atmosphere are discussed. This evidence, while based on analyses of the physical system, is not conclusive or completely satisfying either. The conclusion reached is that the maximum effect that may reasonably be attributed to the forest is a five per cent increase in precipitation, and this only in particular circumstances.