Showing papers on "Precipitation published in 1973"

Distribution and Peculiarity of Mediterranean Ecosystems

Abstract: The lands of mediterranean scrub or chaparral climate and the ecosystems that have developed in them must be defined in climatic terms. If we attempt to focus on the characteristic core of a mediterranean scrub or chaparral climate three terms stand out, two involving precipitation and one temperature. The most distinctive term involves the concentration of rainfall in the winter half year, November through April in the northern hemisphere and May through October in the southern. Although at a large number of stations, especially in California and Chile, 80 or even 90% of the precipitation occurs in winter, so large a proportion rarely obtains around the Mediterranean Basin itself. The value of at least sixty five percent of the year’s precipitation occurring in the winter half year seems, on the basis of examining a considerable number of station records, to form a satisfactory boundary. Winter rainfall, because of lower evaporation, is more effective in sustaining plant growth than is warm season precipitation; nonetheless, in this climatic region all but favorably located phreatophytic vegetation is subject to drought stress in summer.

Statistical Properties of Precipitation Patterns

Abstract: Space and time autocorrelation functions are defined for the precipitation process on a horizontal plane. An optical device was designed and used to measure these functions as well as the mean, the mean square, and the variance of the rainfall rate for a time sequence of precipitation patterns of a widespread convective storm. The input data were radar PPI records stored on film in which the transmittance was adjusted to be proportional to rainfall rate.

Precipitation Modification By Major Urban Areas

Abstract: Historical weather records at eight American urban areas of varying size, type, and climate were studied for indications of inadvertent precipitation modification. The six largest cities all had experienced warm seasonal rainfall increases of 9 to 17% during the 1955–70 period. The increases in the Midwest cities occurred largely with cold frontal systems, but in the coastal cities they were largely during air mass (non-frontal) conditions. The Midwest increases also were found to occur as enhancement, not initiation, of moderate to heavy rain days. Significant increases in summer thunder-day frequencies (13 to 41%,) and hail-day frequencies (90 to 450%) were found at the six largest cities, and the increases occurred largely in the morning hours. The typical locations of maxima in the Midwest cities were thunder over and near the city, and rain and hail 25 to 55 km downwind. The maxima of all events in coastal cities were in or near the city. Overall, the results suggest that urban precipitation...

Variations in mean annual sediment yield as a function of mean annual precipitation

Abstract: Statistical analysis of available data; no simple relationship between annual precipitation and sediment yield

The structure of rainbands within a mid-latitude depression

Abstract: A case study is presented of a winter depression over the British Isles in which extensive banded structure was observed within precipitation ahead of the surface warm front. Measurements of the mesoscale airflow and precipitation structure of the rainbands were made using a variety of radar techniques together with multiple radiosonde and aircraft observations. The measurements were made over the sea to avoid the confusing effects of topography. The dominant rainbands were oriented parallel to the surface cold front and were typically 100 km wide. They moved with a velocity faster than the underlying warm front. For the most part the bands were characterized by clusters of weak small-scale convective cells due to the release of potential instability produced where tongues of relatively dry air of low θw in the middle troposphere overran low-level moist air undergoing slantwise ascent above the warm frontal zone. Although there was the usual large-scale, and thermally-direct, circulation associated with the active warm front, the air which ascended as small-scale convection within the rainbands entered a region of weak cold frontal baroclinicity, whereupon it participated in a thermally direct circulation of its own. This led to each rainband having a rearward-sloping anvil cloud canopy characterized by ascending air with colder drier air descending beneath. Precipitation falling from the canopy evaporated within the underlying drier air thereby probably intensifying the descending branch of the circulation. Very large ageostrophic winds were measured in association with these circulations. The important ingredient responsible for the convective nature of the rainbands appears to have been the incursion of tongues of relatively dry air of low θw in the middle troposphere above the moist warm-sector air in a region where the resulting instability could be realized by large-scale ascent. Although the potential instability was very weak in the present case, the origin of the rainbands appears to have been similar to that of pre-frontal squall lines. The intensity of the convection within rainbands depends on the stability but the very existence of any precipitation in the first place depends on other dynamical factors leading to widespread ascent.

A Theoretical Study of the Flow of Air and Fallout of Solid Precipitation Over Mountainous Terrain: Part II. Microphysics

Abstract: Expressions are derived for the horizontal and vertical components of the wind, the temperature, and the mass of water vapor condensed when air flows over a long mountainous ridge. The growth of solid precipitation particles in the orographic clouds by deposition from the vapor phase, riming and aggregation are considered. The trajectories of these precipitation particles are then computed from their fallspeeds and the airflow model. The model is used to investigate the effects of the microstructure of clouds on the growth and fallout of solid precipitation over the Cascade Mountains. It is shown that, under suitable conditions, increases in the concentration of ice particles in the clouds from about 1 to 100 liter−1 can cause the solid precipitation to be carried farther downwind and over the Cascade crest, so that snowfall is deposited on the eastern rather than the western slopes of the mountains.

Structure and Functional Response of Ecosystems in the Mediterranean Climate of Australia

Abstract: The mediterranean-type climate of Australia, with wet winter periods alternating with dry summer periods, is confined to the south-west corner of Western Australia, the southern portion of South Australia, and the western half of Victoria. To the north it grades into the semi-arid zone of the interior of Australia; in the east, it merges with areas receiving increasing amounts of summer rainfall. Within this zone, annual precipitation varies from 250 to 1,500 mm with 5–15% of this precipitation falling during the summer months, December to February. This small incidence of summer rainfall appears to have enabled certain growth patterns atypical of most mediterranean regions of the world to persist in the southern Australian vegetation.

Estimating the precipitation climate

Abstract: A method has been developed for estimating climatic expectancies of flood or drought from the mean and variance of a precipitation record An interrelationship between the distributions of amounts from the various observing periods, eg, hourly, daily, monthly, is demonstrated, so that any one of these records may be used to estimate the others The method is based on the cube root normal distribution of precipitation and on an observed tendency for the distribution lines to be parallel Graphs and tables are provided as an aid to making these estimates The relationship between monthly, daily, and so forth amounts must be derived in some manner from the frequency spectrum of precipitation rates This spectrum is shown to have the same profile as the theoretical spectrum for atmospheric pressure; thus the E(f) ∼ f−5/3 spectrum of kinetic energy regulates the relationship between precipitation distributions

Precipitation patterns of central Elburz

Abstract: This study is based on the 10-years homogeneous precipitation datas of 19 stations during 1960–1969. The geographical distribution of annual precipitation shows a general decrease from west to east and from north to south, with a zone of more than 1600 mm centrad at Bandar Pahlavi. The rainfall regime of Caspian costal plains, comprises a principal maximum in autumn, a second maximum in March and a minimum in May or July. The regime of southern central Elburz is semi Mediterranean type. The mean annual precipitation increases with altitude in southern slopes of Elburz and decreases with altitude in the northern parts of the region. The precipitation variability was studied by the coefficient of variation. In the coastal plains of the Caspian Sea, the coefficient of variation has a constant value of about 18 and is independent of mean annual precipitation. In the southern region of Elburz, this coefficient is much larger (varies from 27 to 83) and decreases with the increasing mean of annual precipitaiton. The correlation coefficients between monthly rainfall of any two stations of each sides of Elburz are generally high and significant, but they are not significant between one station from northern and the other from southern slope. This demonstrates that the precipitation in both sides of central Elburz are from different origins. The mechanism of the intense rainfalls in south west of the Caspian Sea (Bandar Pahlavi) probably consists of a advection of Siberian cold air mass through the Caspian Sea, because of which the stability of air decreases and its specific humidity increases. Caspian maritime air mass, from one side, and the Continental air of central Iran, from the other side, contact at the Mouth of the Sefid Rood valley (Bandar Pahlavi region) and cause the intensive rains.

Comparison Between Ice Age and Present General Circulations

Abstract: Small reductions of tropical sea surface temperatures during ice ages are associated with substantial reductions in latent heat release and in the temperature of the upper tropical troposphere. Numerical simulations confirm that this reduced the mean baroclinicity during ice age winters and presumably the atmospheric heat transport from low to high latitudes. The computed wind driven ocean circulation was also weaker. Local heat balance considerations suggest that ice age cloud cover over the tropical oceans was more extensive inl spite of reduced evaporation and precipitation. The same deduction is suggested by analytical arguments about atmospheric convection.

A Technique for Computing Vertical Transports by Precipitating Cumuli

Abstract: A method is described for calculating cumulus-scale vertical transports of mass, sensible heat and hori-zontal momentum from detailed measurements of precipitation. The basic premises are that the amount of lifting in a cumulus cell is related to the precipitation which it produces and that the temperature excess and entrainment are reflected in its vertical development. The amount of cellular precipitation may be obtained from quantitative radar data or high-resolution rain gauge records, the cell depths from radar and radiosonde data. The mass of air transported upward within the cells is computed from the conservation of water given the amount of cellular precipitation. A relationship between measured cellular rain and condensate within cumulus cells is based on available empirical information. Entrainment rate and the shape of the mass transport curve as a function of height are specified in a manner consistent with physical considerations, experimental evidence, and one-dimensional dynamic m...

Estimating Rainfall in Regions of Active Convection

Abstract: An attempt to estimate rainfall in convectively active regions using Kuo's parameterization scheme has been made. The precipitation in this model is given by P = lQ1/Δt, where P is the precipitation per unit time, l the fraction of a synoptic area covered by deep active convection, Q1 the mount of condensation heating according to moist adiabatic ascent, and Δt a time parameter related to the precipitating lifetime of the convective elements. Investigation of the above equation when P, l and Q1 were available indicated that an appropriate time parameter was 30 min and that the main contribution to the precipitation comes from the l parameter. A case is presented where l is obtained from satellite observations. The resulting precipitation estimate appears quite reasonable. The potential for estimating precipitation over the tropical means is pointed out.

A study of the acidity in the precipitation in Southwestern Norway

Abstract: Using 6-hourly samples of precipitation at Lista, the influence of local and remote sources of acid precipitation in Southwestern Norway is discussed. The distribution of pH values for different wind directions indicates that the acidity in this area is hardly caused by local sources. A study of the trajectories of the rainbearing airmasses shows that the highest acidity in Southwestern Norway occurs in airmasses passing over the major industrial areas in Central Europe and the United Kingdom. DOI: 10.1111/j.2153-3490.1973.tb00613.x

Deforestation effects on soil moisture, streamflow, and water balance in the central Appalachians

Abstract: Soil moisture, precipitation, and streamflow were measured on three watersheds in West Virginia, two deforested and one forested. Water content of barren soil always exceeded that of forest soil throughout the growing season and especially in dry weather. Streamflow increased 10 inches annually on the watersheds that were cleared, most of the increase occurring between July and October. Higher soil moisture was accompanied by large instantaneous peak flows during small storms in the growing season but this peak effect was minor in large stoms and in all storms during the dormant season. With precipitation, streamflow, interception losses, and soil-moisture change estimated to comparable levels of precision, the water balance equation was solved for transpiration with sufiicient sensitivity to demonstrate the effects of tree leaf growth. After tree leaves were fully grown, calculated evaporative losses from the forested watershed somewhat exceeded potential rates as long as unmeasured runoff (leakage) was disre arded. With all components of the water balance quantified, including leakage, estimated soil-moisture loss by transpiration was at rates close to potential. Estimated leakage seemed consistent with observed stream behavior.

Monitoring snow water equivalent by using natural soil radioactivity

Abstract: The attenuation by snow cover of natural gamma radiation emitted from the soil serves as an excellent index to the water equivalent of the snow cover. A small portable gamma ray detector was installed on a boom about 2 meters above the ground at the National Oceanic and Atmospheric Administration-Agricultural Research Service (ARS) cooperative snow study site at the ARS Sleepers River watershed near Danville, Vermont, for the 1970–1971 snow season. Comparison of gamma ray count rates with snow measurements taken at the site indicates that the small unshielded gage could be used to measure snow water equivalent (range 5–40 cm) with a standard error of 1.5 cm without preliminary editing of gamma ray count rates. A major source of this error was the deposition of radioactive aerosols on the snow surface by precipitation. The deviation of gamma ray count rates due to precipitation events is short-lived, and a simple editing procedure on the count rate time trace reduced the snow season standard error to 1.1 cm. The edited count rate yielded 6% error in the 5- to 13-cm water equivalent range, decreasing to 4% in the 25- to 40-cm water equivalent range. This measurement method could be extremely valuable in providing unmanned measurement of snow water equivalents at remote locations.

Oceanic rainfall off the Pacific Northwest Coast

Abstract: Rainfall within 55 km of the northwest coast of the United States was measured from a buoy and estimated from weather reports at lightships. Results show that precipitation at sea was only about one half to one third of that found at coastal land stations. Rainfall typically occurs both at sea and on shore on the same days but for fewer hours at sea. The relative amount at sea seems to vary with the type of atmospheric system producing the rainfall.

The Full-Glacial Climate of the Southern High Plains, West Texas

Abstract: During the last full-glacial on the Southern High Plains of West Texas, the combined amount of precipitation and runoff into the small closed lake basins probably exceeded the present amount by at least 50%: minimum Pleistocene precipitation, based on the present local runoff of 3 inches, was approximately 29 inches; thus, West Texas was subjected to a pluvial climate in the classical sense during the last full-glacial. Pleistocene precipitation could have been less than the present rate and yet sustained the permanent Pleistocene pluvial lakes only if runoff averaged 35% of the precipitation rate. Such a high runoff-to-precipitation ratio occurs only with frequent intense storm activity.

Precipitation at ocean weather stations in the north Pacific

Abstract: Determination of precipitation at ocean weather stations in the North Pacific reveals much less annual rain than previous estimates, except in the northwestern part of the ocean, as well as a stronger north-south gradient. Seasonal distributions were about as shown on most charts except for the northwest Pacific. The amounts and isohyetal patterns at sea are quite different from those at coastal land stations.

Source and Budget of Sulfate in Precipitation From Central Alberta, Canada

Abstract: Rain, hail, and snow samples collected in central Alberta have been analyzed for sulfate and chloride content using a conductometric titration method. The mean values of sulfate concentration in rain and hail collected in the region of sulfur extraction gas plants were 2.7 mg/l and 2.9 mg/l respectively.The mean value of the sulfate content of a large number of hail samples collected from one severe storm well removed from a major SO/sub 2/ source was only 0.6 mg/l. Several snow samples collected in Alberta and southern British Columbia had a mean sulfate content of less than 0.5 mg/l. These results are discussed in terms of the efficiency with which s02 is removed from the atmosphere by the different precipitation processes. The results strongly suggest that most of the sulfate found in central Alberta precipitation is of local industrial origin. By comparing the sulfate deposition in precipitation around one isolated gas plant with the known SO/sub 2/ emission rate, a local atmospheric sulfur budget is derived. This budget indicates that the summertime convective storms are a very efficient mechanism for removing the SO/sub 2/ from the atmosphere, with between 32 and 46% of the sulfur emitted as SO/sub 2/ arriving atmore » the ground as sulfate sulfur within a radius of 25 miles of the source. In contrast snow is a very inefficient removal mechanism, since in winter less than 2% of the sulfur emission is deposited in the snowfall near the source.« less

Paleohydrologic Implications of Some Pluvial Lakes in Northwestern New South Wales, Australia

Abstract: Some internally draining lakes in northwestern New South Wales, Australia, are contained in structural basins but owe their lack of external outlets to arid climate. Former high lake shorelines are defined in part by precipitated crusts or by deltas. Radiocarbon dating, although as yet less than satisfactory, suggests that the high lake stands occurred not later than about 14,500 B.P. They may eventually be correlated with lacustrine episodes that, elsewhere in inland New South Wales, occurred in the range 23,500 to 15,500 B.P. Whether or not the lakes under discussion existed at the time of maximum cold is uncertain; but they were indubitably associated with low paleotemperatures. Reconstruction of former temperatures involves little or no controversy. Use of paleotemperatures to reconstruct former evaporation rates produces results that stand up well to checking. Manipulation of the equilibrium equations for closed lakes produces precipitation equations that involve evaporation, area ratio between lake and rest of basin, and evapotranspiration. Empirical studies and some paleohydrologic work supply values or ranges of evapotranspiration and basin loss. Even in the lowest observed or estimated range of evapotranspiration, the precipitation equations indicate former precipitation about 50 percent greater than that of today. Calculation of evapotranspiration rates for former conditions of radiation and temperature and for a range of sunshine incidence, and entry of these rates into the precipitation equations, show that very low values of sunshine incidence would be required to drive calculated precipitation down to, or below, today9s levels. That is to say, any hypothesis that the former high lake stands were associated with reduced precipitation demands inordinately low rates of evapotranspiration, plus a combination of reduced precipitation with inordinately high cloudiness.

Problems of vertical and horizontal arrangement in the high mountains of the extreme arid zone (central sahara)

Abstract: Three geomorphological-ecological altitude stages in the mountains of the extreme arid zone are described: glacial or nival forms, solifluction or "periglacial appearances," and the problem of the upper tree line. The present altitude levels are not thermally dependent in the alpine, Mediterranean, or fully tropical sense, but are primarily influenced by availability of moisture. They are not comparable with high mountains of other climatic zones and are subject to their own laws. In the fully arid mountain areas of the tropics an extratropical thermal seasonal climate clashes with a tropical monsoon precipitation distribution.

Seasonal and annual precipitation efficiency in Canada

Abstract: Precipitation efficiency is the percentage of the total water vapor over an area that falls to the surface as measurable precipitation on an average day This variable focuses attention on the dynamic mechanisms that produce different precipitation patterns in different areas The concept of precipitation efficiency is discussed and its seasonal and annual values are mapped for several Canadian stations Maximum seasonal values occur in winter for all of the country National highs are found on the West Coast and along the St Lawrence Lowland, a result of the cyclonic activity in these regions

Inadvertent Weather and Precipitation Modification by Urbanization

Abstract: Urban-industrial complexes produce measurable inadvertent modification of all weather conditions and specifically significant increases in the precipitation conditions of interest to hydrologists and urban planners. In, and immediately downwind of, major urban areas the annual precipitation may be increased from 5–30%, the annual thunderstorm frequency is increased 15–30%, the heavy (2-in.) daily rainstorm frequencies are increased by 20–40%. Increases in local runoff may be from 15–20%. Local crop yields may be increased 2–10% by this rain modification.

Precipitation characteristics during the Venezuela rainy season

Abstract: An extensive program of observations designed to determine the structure of tropical mesoscale rain areas over land and their relation to synoptic envelopes was carried out during the rainy season of 1969 (June to September) in eastern Venezuela. The frequency distribution of precipitation in the area seen by radar (radius 100 km), as given by the average of 30 stations, was highly skewed: 14 per cent of the days in the experiment delivered half of the precipitation; 80 per cent could be attributed to rain episodes related to mobile synoptic systems. On the hourly basis, 0·45 per cent of all hours (or 10 hours) produced half of the precipitation. Daily precipitation in the radar circle was not correlated with radar echo height but markedly with echo area. Heavy rainfall occurs when a few very large clouds appear. A cloud distribution in terms of area and rain productiveness was determined for rainy and for dry days. Rain productivity increases with cloud area; however, since the number of clouds also decreases as their size increases, water yield to the ground is almost independent of cloud scale. No clear difference in the 200 mb flow could be found between cloud ensemble. On rainy days the temperature is lower and the specific humidity higher than on dry days confirming that cold-core precipitation takes place also over Venezuela. A mean ascending velocity appears to exist in and out of clouds in the convection cores, but could not be found prior to onset of afternoon convection.

Secular Climatic Fluctuations In Southwestern Colorado

Abstract: Precipitation and temperature data since records began in southwestern Colorado are analyzed on a seasonal basis. Interstation correlations for recent years indicate that the region responds fairly uniformly to seasonal variations in precipitation, but this was not true earlier this century when precipitation variability was higher. Changes in the dependence of precipitation on elevation are also shown. Annual precipitation totals were low about 1860, 1900, 1930–35 and 1950–55. Mean annual temperatures appear to have fallen from about 1867 to about 1930 when the trend reversed. Overall, the climate of southwestern Colorado in the 1860s appears to have been warmer and at least as dry as current normals.