Showing papers on "Precipitation published in 1983"

The Mesoscale and Microscale Structure and Organization of Clouds and Precipitation in Midlatitude Cyclones. VIII: A Model for the “Seeder-Feeder” Process in Warm-Frontal Rainbands

Abstract: Previous field studies have indicated that warm-frontal rainbands form when ice particles from a “seeder” cloud grow as they fall through a lower-level “feeder” cloud. In this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a “seeder-feeder” type situation. The model is applied to two types of warm-frontal rainbands. In the first (Type 1 situation) the vertical air motions are typical of those associated with slow, widespread lifting in the vicinity of warm fronts. In the second (Type 2 situation) the vertical air motions are stronger, and more characteristic of the mesoscale. The model simulations show that in the Type 1 situations the growth of the “seed” ice crystals within the feeder zone is due to vapor deposition. The feeder zone in this case is slightly sub-saturated with respect to water due to the presence of the seed crystals. In regions where the feeder zone is not “seeded” from aloft, snow cryst...

Measurement of weak organic acidity in precipitation from remote areas of the world

Abstract: The Global Precipitation Chemistry Project collects precipitation by event to determine the composition of precipitation and processes that control it in five remote regions Ion balances based on major inorganic species revealed consistent anion deficits at certain sites This and other evidence suggested that weak organic acids contributed to free acidity Accurate and precise techniques were developed to measure organic anions and total acidity in precipitation Twelve samples from a remote site were analyzed for major organic and inorganic chemical constituents Formic and acetic acids were found in all aliquots which had been treated with a biocide The disappearance of these acids from untreated aliquots corresponded to a proportionate decrease in free acidity Weak organic acids contributed 64% of free acidity and 63% of total acidity to precipitation during part of the 1981–1982 wet season at Katherine, Australia Unmeasured proton donors contributed 21% of total acidity during the period

The 1982–83 climate anomaly in the equatorial Pacific

Abstract: Disastrous climatic events, such as the Australian–Indonesian drought and the severe flooding in South America, which occurred in the equatorial Pacific in 1982/83 are part of a pattern which can be followed in unprecedented detail using satellite data. The evolution of wind, precipitation and surface temperature fields during this remarkable example of atmosphere–ocean interaction are described in this article. Models can relate the main features of the sea-surface temperature, sea level and surface current patterns to the winds, and relate wind to precipitation (atmospheric heating) patterns. The precipitation field shows a close relationship with surface temperature, but this is less well understood.

Some Spatial Characteristics of Drought Duration in the United States

Abstract: By using the Palmer Drought Severity Index (PDSI) as calculated from state averages of temperature and precipitation and from numerous single station analyses, it has been demonstrated that droughts (as defined by the PDSI) persist longer in the interior of the United States than in areas farther east or west. The question arises whether this is merely an artifact of the PDSI calculations, or whether there is actually more persistence of abnormally dry (wet) weather in the interior. The sensitivity of the PDSI was tested in relation to changes of derived and prescribed parameters included in the PDSI calculations in order to determine their effect on the spatial characteristics of drought duration. The sensitivity tests indicated a negligible effect. Contingency tables which use the PDSI as the predictor for the following one-month, six-month and 12-month precipitation anomalies (and also anomalies of precipitation minus potential evapotranspiration) however, are generally characterized by signif...

Late Glacial Climate History from Ice Cores

Abstract: Ice cores contain information on climatic variations and their causes. Recent results obtained on the new deep ice core drilled in 1981 at Dye 3, South Greenland, in the frame of the US-Danish-Swiss Greenland Ice Sheet Program are: Comparison of the δ 180 variations in the Greenland ice cores with those in European lake carbonate exhibits strong similarities and provides time marks (13,000, 11,000, 10,000 B.P.) for the Late-Glacial section of the ice cores; CO2 concentration measurements in the occluded air indicate low (180–200 ppm) CO2 concentrations 30,000 to 15,000 B.P. and an increase to ca. 300 ppm around 13,000 B.P.,. The CO2 increase might reflect a change in the ocean circulation at the end of the last glaciation and could have contributed to the establishment of the Holocene environmental conditions; 10Be concentration measurements on samples covering the last 50,000 yaers show a correlation with δ 180, low δ 180 values corresponding to high 10Be concentrations (atoms per g of ice). Probably this mainly reflects changes in the rate of precipitation in the northern hemisphere.

Variations in the global water budget

Abstract: TECHNIQUES OF MEASUREMENT AND ANALYSIS: I, ATMOSPHERIC PROCESSES.- The atmospheric branch of the hydrological cycle and climate.- The atmospheric water vapour budget over Europe.- Remote sensing of atmospheric water content from satellites.- Comparison of water vapour data from Monex-79 and the Tiros-N satellite.- Atmospheric water distributions determined by the Seasat multi-channel microwave radiometer.- Variations of deuterium and oxygen-18 in continental precipitation and groundwater, and their causes.- TECHNIQUES OF MEASUREMENT AND ANALYSIS: II. SURFACE PROCESSES.- Monthly and areal patterns of mean global precipitation.- Comparison of rainfall rates derived from radar and Nimbus 5 microwave observations in the tropical Atlantic.- Evaporation models in the global water budget.- The use of long-term river level and discharge records in the study of climatic variations in the Federal Republic of Germany.- Plant and soil water storage in Arctic and boreal forest ecosystems.- Recent fluctuations of Alpine glaciers and their meteorological causes 1880-1980.- Radiometric chronology of some Himalayan glaciers.- SECULAR VARIABILITY: INTERACTIONS AND TELECONNECTIONS.- Recent rainfall fluctuations in Africa - Inter-hemispheric teleconnections.- Droughts and floods over India in summer monsoon seasons 1871-1980.- The heavy rainfall in China in 1980 and a comparison with earlier extremes.- Variability of rainfall over northern Australia.- Moisture variations associated with El Nino events.- Surges of tropical Pacific rainfall and tele-connections with extratropical circulation patterns.- Antarctic sea ice variations 1973-1980.- LONG-TERM CHANGES.- Late-glacial circulation over central North America revealed by aeolian features.- Fluctuations in closed-basin lakes as an indicator of post atmospheric circulation patterns.- Present-day and early-Holocene evaporation of Lake Chad.- Marine shorelines in estuaries as palaeoprecipi-tation indicators.- Monsoon rains of the late Pleistocene and early Holocene Patterns, intensity and possible causes of changes.- Sea-level control of ice sheet disintegration.- A climate feedback mechanism involving oceanic upwelling, atmospheric CO2 and water vapour.- Illusions and problems in water-budget synthesis.- MODELLING AND PREDICTION.- The hydrological cycle as simulated by an atmospheric general circulation model.- Effects of soil moisture anomalies over Europe in summer.- Some simulation model results of the effect of vegetation change on the near-surface hydro-climate.- The concept of runoff in the global water budget.

The seasonal response of a general circulation model to changes in CO2 and sea temperatures

Abstract: The seasonal response of an atmospheric general circulation model to changes in atmospheric carbon dioxide concentrations and sea surface temperatures is discussed. The model has five layers and a quasi-uniform 330km horizontal grid. Sea surface temperatures, sea ice extents, and zonally mean cloud amounts are prescribed from climatology, so that feedbacks between these variables and the rest of the model are ignored. Soil moisture, snow depth and boundary layer height are modelled explicitly, and both diurnal and seasonal variations of solar zenith angle are included. Two experiments are carried out, and compared with a three-year control integration. In each case, the model's response varies with season and location. In the first experiment the effect of increasing atmospheric carbon dioxide concentrations with prescribed present day sea surface temperatures is examined. The model's troposphere becomes warmer, thereby increasing the low level static stability over the ocean and reducing evaporation and precipitation. The warming is larger over land than over the oceans. In summer, this results in an increase in precipitation along the eastern coasts of continents. In the second experiment, the sea surface temperatures are increased by 2 K and the carbon dioxide concentration is doubled. The land surface temperature rises by 3 K. Evaporation increases markedly over the oceans. Precipitation increases in the main regions of atmospheric convergence and decreases in some regions of the subtropics. The magnitude of the model's response is shown to be reasonably consistent with that found in other three-dimensional climate models.

Pollutant transfer in upland regions by occult precipitation

Abstract: Pathways for the transfer of pollutants from the atmosphere to vegetation by gaseous absorption (dry deposition) and in rain (wet deposition) have been studied extensively. Here we quantify deposition by a third pathway, that which occurs when vegetation exposed in wind-driven cloud intercepts water drops which are not collected efficiently in standard rain gauges1. From measurements of the chemical content and rate of this ‘occult precipitation’2 at Great Dun Fell, Cumbria in the United Kingdom, we make preliminary estimates of the deposition of several elements. We tentatively conclude that the inclusion of the occult deposition pathway in assessing annual chemical deposition in areas prone to low cloud could increase wet deposition estimates by up to 20% from values recorded in conventional rainfall chemistry gauges alone.

On the Formation of Continental Polar Air

Abstract: This research investigates the transformation of maritime polar air into continental polar air in the Arctic during winter. The evolution of the vertical profiles of temperature and humidity is simulated using a one-dimensional model. The following physical processes are examined 1) surface enthalpy flux; 2) infrared radiative cooling due to emission by CO2, water vapor, water droplets, and ice crystals; 3) gravitational setting of the condensed water, 4) turbulent mixing, and 5) subsidence. The modeled formation of continental polar air is dominated by the radiative cooling due to emission by ice crystals and water droplets. The model reproduces the formation of low-level clouds that are frequently observed in these cold air masses, and also the phenomenon of “cloudless” ice crystal precipitation. The model requires two weeks for the formation of fully-developed continental polar air, although after only four days of cooling the air has acquired most of the air mass properties. The rate of cooli...

Comparison of weather station snowfall with winter snow accumulation in high arctic basins

Abstract: Most water balance studies in the High Arctic indicate that the weather stations underestimate annual precipitation, but the magnitude of such error is unknown. Based on up to seven years of field measurements, this study provides a comparison of snowfall at weather stations with the winter snow accumulation in their nearby drainage basins. Snowfall is the major form of precipitation in the polar region for nine months every year. Without vegetation, snowdrift is controlled by the local terrain. By establishing the snow characteristics for different terrain types, total basin snow storage can be obtained by areally weighting the snow cover for various terrain units in the basin. Such a method was successfully employed to compute total winter snowfall in the drainage basins near Resolute, Eureka and Mould Bay. Results show that the basins had 130 to 300per cent more snow than the weather stations recorded. Using revised snowfall values that are reinforced by Koerner's snow core measurements from i...

The relation between air mass trajectories and the water isotope composition of rain in the Mediterranean Sea area

Abstract: The isotopic composition of rainwater near Nahariya, Israel, was measured in 12 individual storms during the winter months of 1980/1981. Rains most depleted in the heavy stable isotopes and enriched in tritium are associated with air masses which come from North East Europe and have a short, intense interaction with the East Mediterranean Sea. Storms most enriched in 18O and D and depleted in tritium are associated with air masses which come from the Atlantic Ocean and enter the Mediterranean Sea on its western part, travelling along the North African Coast, sometimes with a southerly shift. A relatively high correlation coefficient was found between the stable isotopic content of precipitation and the 800 mb temperature.

Central Arctic Ocean Sediment Texture: A Key to Ice Transport Mechanisms

Abstract: The perennial Arctic Ocean ice-cover consists of sea ice and glacial ice. Sea ice is most common today but at times during the Late Cenozoic, glacial ice has been extremely abundant. Both sea ice and glacial ice can transport a significant sediment load. The mode of incorporation of sediment into the two ice types is quite different. Sea ice can trap atmospheric dust that accumulates during times of precipitation. In addition, silt and clay mobilized by wave action during autumnal storms in shallow shelf areas, may be incorporated into sea ice as it begins to form. This fine-grained component can be transported from the shelf to the central Arctic Ocean. Coarser sediment may be plucked from beach areas by shore-fast ice but probably is dropped before significant transport.

Heat and Moisture Budgets of Tropical Mesoscale Anvil Clouds

Abstract: An analysis of the heat and moisture budgets of tropical mesoscale anvil clouds has been carried out. Mesoscale anvils, defined as widespread (∼100 km) cloud systems extending from near the freezing level to the high troposphere, are characterized by light, stratiform precipitation. These cloud features, which are preceded by and generally merged with cumulonimbus clouds, are prevalent throughout the tropics and summertime midlatitudes and may account for an important fraction of the total tropical rainfall. Sounding data from the December 1978 field phase of the International Winter Monsoon Experiment (Winter MONEX) are used to determine heat and moisture (Q1t and Q2) budgets for a number of mesoscale anvil cloud systems. The composite heating (Q1) profile shows a warming peak in the upper troposphere near 350 hPa or 8–9 km that can be attributed to condensation and freezing in the anvil and a cooling peak in the lower troposphere near 700 hPa or 3 km due to rainfall evaporation and melting. The...

Monthly and Areal Patterns of Mean Global Precipitation

Abstract: After summarizing the history of the cartographic representation of global and continental-scale precipitation, and demonstrating in so doing the gradual refinements used in deducing annual and seasonal variations of rainfall over large areas, a presentation is made of a gridding technique for evaluating precipitation over the continents and the oceans based on the subdivision of the Earth’s surface into nearly 2600 sectors and data obtained prior to 1965. The results of this analysis, comprising the record of the monthly meridional distribution of rainfall, and maps of mean precipitation — variously ordered to show the monthly and annual variations in respect to latitudinal zones as well as land and sea surfaces, are presented and described.

Hail Growth in an Oklahoma Multicell Storm

Abstract: Hail growth in an Oklahoma multicellular storm is studied using a numerical model of hailstone growth and decay and dual-Doppler derived wind fields. Hail was collected at the time of the Doppler radar data collection which provided input for computation of the modeled trajectories. A unique feature of this investigation is the subsequent comparison of model hail trajectories with deuterium derived trajectories obtained from the hail samples. Formation of large hail is found to be almost entirely due to injection of embryos into the major storm updraft from the upwind side, with subsequent growth occurring during repeated vertical excursions through the prime growth layer between 7 and 8 km. Primary embryo source regions are a feeder cell and the precipitation debris region between the feeder and main cells. Qualitative comparisons between observed and modeled hailstones falling near the collection site reveal strong similarities, particularly with respect to ambient temperature during ice format...

The composition of Western Atlantic precipitation using shipboard collectors

Abstract: Techniques have been developed for the collection of rain on board ships. Chemical and meteorological analysis of rain events shows that rain can be collected for major ions on board ships in a contamination-free manner by using collectors on the windward side of the ship. The results also support the conclusion of dickells et al. (1982) that rain associated with North American air masses has elevated levels of SO4 =*, NO3-, and H +, while rain associated with eastern Atlantic air masses has background values.

The influence of annual precipitation, topography, and vegetative cover on soil moisture and summer drought in southern California.

Abstract: The influence of annual precipitation and vegetation cover on soil moisture and on the length of the summer drought was estimated quantitatively using 9 years of soil moisture data collected at Echo Valley in southern California The measurements support the conclusions that in the semi-arid mediterranean climate a soil drought will occur regardless of vegetation cover and annual precipitation, but the length of the drought is greatly dependent on soil depth and rockiness Evergreen species which can survive this drought tend to accentuate the drought, especially in deep soil levels, by developing a canopy with a large transpiring surface

Atmospheric EHF window transparencies near 35, 90, 140 and 220 GHz

Abstract: Transparency of the four atmospheric extremely high frequency (EHF) window ranges located around 35, 90, 140, and 220 GHz is obscured by precipitation (rain, wet snow), by suspended particles (fog, cloud, haze, dust), and by water vapor An assessment is made of the quantitative picture (ie, models versus experiments and theory), upon which estimations for general radio path behavior can be based Useful models are provided for calculating attenuation based upon measurable meteorological variables: rain rate, liquid water content, humidity, temperature, and pressure Information currently available is not yet complete enough to provide accurate predictions under all climatological conditions Emphasis is on recent advances in formulating the physical basis for modeling transparency and on a discussion of some of the principal remaining uncertainties

Variations of Deuterium and Oxygen-18 in Continental Precipitation and Groundwater, and Their Causes

Abstract: Spatial and temporal variations in the deuterium- and 18O-content of precipitation are caused by isotope fractionation resulting from evaporation and condensation processes during circulation of atmospheric water vapour. During these phase transitions, the isotope-labelled water molecules are preferentially transferred into the liquid phase. Water loss by moist adiabatic cooling of air masses therefore leads to progressive isotopic depletion, which is described by a Rayleigh condensation formula. Application of this formula to the moist adiabatic ascent of discrete air masses yields exponential vertical profiles of the moisture and its D- and 18O-content assuming a constant relative humidity and a mean temperature lapse rate of −6°C km−1. These isotope profiles agree fairly well with observed profiles in tropospheric water vapour. The spatial variation of D and 18O in precipitation and groundwater across Europe and North America can also be described by a simple Rayleigh condensation model, which links the local isotope data with the parameters of the vertically-integrated water vapour flux. This model uses as input data monthly means of local temperature, relative humidity, precipitation and evapotranspiration. The model also yields an estimate of the variation of the isotope content of local precipitation with temperature. A one-year record of D and 18O in daily mean values of water vapour at Heidelberg shows the seasonal variation already known from monthly mean precipitation data and successfully simulated by the model. Superimposed on this seasonal pattern are strong short-term variations with a dominant periodicity of 22 days. This periodicity seems to be related to the phase velocity of long waves in the free atmosphere, which steer the water vapour transport in the lower troposphere.

Correction of Measured Precipitation in the Alps Using the Water Equivalent of New Snow

Abstract: The Hellmann heated siphon pluviograph with wind shield shows 56 % less winter precipitation than measured on a snow board at an altitude of 2,540 m a.s.l. For the Swiss heated tipping bucket gauge and the storage gauge precipitation was 31 % less. A relationship between the deficit and wind speed was only found for the storage gauge. The effect of the parameter of snowfall structure, defined as the portion of snowfall on days with temperature lower than -8°C, is small. The results can be used to make a preliminary adjustment of precipitation sums at Alpine gauge sites where wind speeds and temperature can be assessed.

Supercooled Liquid Water and Ice Crystal Distributions Within Sierra Nevada Winter Storms.

Abstract: Cloud physics data measured by aircraft during two successive winter field seasons (1978–79 and 1979–80) of the Sierra Cooperative Pilot Project operating over the Sierra Nevada Range have been examined in order to determine the distributions of supercooled liquid water and ice crystals. Results indicate that convective clouds provide the greatest likelihood of significant supercooled water. The Sierra barrier appears to optimize these conditions 40 to 90 km upwind of the crest within pockets of horizontal extent up to 64 km, although these conditions were greatly reduced at temperatures less than −10°C. The dominance of liquid water content over ice crystal concentration was maximized 7–10 h after the 700 mb trough passage. Area-wide and banded clouds, which make up the remaining precipitation events, showed only small amounts of supercooled water and general abundance of ice crystals. The largest liquid water contents were observed at the greatest temperatures, usually 0° to −5°C. Such climatol...

Precipitation in the central amazon basin : -the isotopic composition of rain and atmospheric moisture at belem and manaus

Abstract: In order to improve the understanding of the water in the Amazon Basin, samples of rain and moisture were collected daily at Belem and Manaus from August 78 to January 80 All isotope data are presented The most depleted values, sometimes lower than — 10‰ in δ18O at Belem or Manaus, were encountered during the rainy season (January-April) Possible causes of the seasonal differences in tne isotope pattern are discussed

Anomalies in temperature and rainfall during warm Arctic seasons

Abstract: The regional patterns of change of temperature and rainfall that might accompany a global warming due to increased carbon dioxide can be studied by experiments with theoretical models of the climate system, by reconstructing the climates of past warm epochs, and by determining the anomalies of temperature and precipitation that prevailed during years or seasons when the Arctic region was unusually warm. The current study pursues the last course, making use of the northern hemisphere meteorological data record for the period 1931–1978. Hemispheric maps of anomalies of both temperature and precipitation are presented for the 10 warmest Arctic seasons and years, and for differences between the 5 warmest and 5 coldest consecutive Arctic winters. Wintertime anomalies are generally greatest and dominate in determining the annual averages. The hemispheric temperature anomalies for these data sets are similar to those determined earlier by the first author (Williams, 1980) using 1900–1969 data, but the precipitation anomalies (for North America alone) show more variation, partly due to the method of computing the anomalies.