Showing papers on "Precipitation published in 1989"

Precipitation Patterns Associated with the High Index Phase of the Southern Oscillation

Abstract: The relationships are examined between precipitation and the high index phase of the Southern Oscillation (SO) for 19 regions of the globe which have documented low SO index-precipitation relationships (Ropelewski and Halpert 1986, 1987). The study reveals that 15 of these regions also show evidence of characteristic precipitation anomalies during the high index phase of the SO. In each of the regions, the high SO index-precipitation relationships show the opposite sign of those documented for the low index. These precipitation relationships were consistent, holding for over 70% of the high SO index years, and statistically significant. In particular, the high index phase of the SO is associated with enhanced precipitation for the monsoons of India and northern Australia as well as for the rainy seasons in northeastern South America and southeastern Africa. High SO index precipitation was found to be less than median in the central Pacific, Minicoy-Sri Lanka, eastern equatorial Africa, the Gulf o...

The Effect of Eurasian Snow Cover on Regional and Global Climate Variations

Abstract: The sensitivity of the global climate system to interannual variability of he Eurasian snow cover has been investigated with numerical models. It was found that heavier than normal Eurasian snow cover in spring leads to a “poor” monsoon over Southeast Asia thereby verifying an idea over 100 years old. The poor monsoon was characterized by reduced rainfall over India and Burma, reduced wind stress over the Indian Ocean, lower than normal temperatures on the Asian land mass and in the overlying atmospheric column, reduced tropical jet, increased soil moisture, and other features associated with poor monsoons. Lighter than normal snow cover led to a “good” monsoon with atmospheric anomalies like those described above but of opposite sign. Remote responses from the snow field perturbation include readjustment of the Northern Hemispheric mass field in midlatitude, an equatorially symmetric response of the tropical geopotential height and temperature field and weak, but significant, perturbations in the surface wind stress and heat flux in the tropical Pacific. The physics responsible for the regional response involves all elements of both the surface heat budget and heat budget of the full atmospheric column. In essence, the snow, soil and atmospheric moisture all act to keep the land and overlying atmospheric column colder than normal during a heavy snow simulation thus reducing the land–ocean temperature contrast needed to initiate the monsoon. The remote responses are driven by heating anomalies associated with both large scale air-sea interactions and precipitation events. The model winds from the heavy snow experiment were used to drive an ocean model. The SST field in that model developed a weak El Nino in the equatorial Pacific. A coupled ocean-atmosphere model simulation perturbed only by anomalous Eurasian snow cover was also run and it developed a much stranger El Nino in the Pacific. The coupled system clearly amplified the wind stress anomaly associated with the poor monsoon. These results show the important role of an evolving (not specified) sea surface temperature in numerical experiments and the real climate system. Our general results also demonstrate the importance of land processes in global climate dynamics and their possible role as one of the factors that could trigger ENSO events.

The "greenhouse" effect and climate change

Abstract: The presence of radiatively active gases in the Earth's atmosphere (water vapor, carbon dioxide, and ozone) raises its global mean surface temperature by 30 K, making our planet habitable by life as we know it. There has been an increase in carbon dioxide and other trace gases since the Industrial Revolution, largely as a result of man's activities, increasing the radiative heating of the troposphere and surface by about 2 W m -2. This heating is likely to be enhanced by resulting changes in water vapor, snow and sea ice, and cloud. The associated equilibrium temperature rise is estimated to be between 1 and 2 K, there being uncertainties in the strength of climate feedbacks, particularly those due to cloud. The large thermal inertia of the oceans will slow the rate of warming, so that the expected temperature rise will be smaller than the equilibrium rise. This increases the uncertainty in the expected warming to date, with estimates ranging from less than 0.5 K to over 1 K. The observed increase of 0.5 K since 1900 is consistent with the lower range of these estimates, but the variability in the observed record is such that one cannot necessarily conclude that the observed temperature change is due to increases in trace gases. The prediction of changes in temperature over the next 50 years depends on assumptions concerning future changes in trace gas concentrations, the sensitivity of climate, and the effective thermal inertia of the oceans. On the basis of our current understanding a further warming of at least 1 K seems likely. Numerical models of climate indicate that the changes will not be uniform, nor will they be confined to temperature. The simulated warming is largest in high latitudes in winter and smallest over sea ice in summer, with little seasonal variation in the tropics. Annual mean precipitation and runoff increase in high latitudes, and most simulations indicate a drier land surface in northern mid-latitudes in summer. The agreement between different models is much better for temperature than for changes in the hydrological cycle. Priorities for future research include developing an improved representation of cloud in numerical models, obtaining a better understanding of vertical mixing in the deep ocean, and determining the inherent variability of the ocean-atmosphere system. Progress in these areas should enable detection of a man-made "greenhouse" warming within the next two decades.

Simulation of the regional climatic impact of Amazon deforestation

Abstract: THE Amazon basin contains about half of Earth's Tropical forest1. Population pressure and subsequent demands for crop production, timber and firewood have led to rapid deforestation. Quantitative estimates of the rate of deforestation from analysis of Landsat observations indicate that rates are increasing exponentially in many regions2,3, but the precise figures are not known4. Removal of the protection provided by natural cover can lead to soil erosion, disturbance of the ecosystem and reduction in species diversity5. Here we report results from a three-year simulation, using a general circulation model, in which we replace Amazon tropical forest and savannah with pasture. The simulated local climate response was dominated by a weakened hydrological cycle, with less precipitation and evaporation and an increase in surface temperature. The reductions in precipitation and evaporation were mostly caused by changes in surface roughness and albedo: decreased roughness dominated the reduction in evaporation (and the increase in temperature), whereas the increased albedo was the main cause of a decrease in the moisture flux convergence (measured as the difference between precipitation and evaporation) contributing to the decrease in precipitation.

Surface water resources of South Africa

Abstract: Water is arguably South Africa's most precious natural resource. Research and investigations have shown that groundwater resources in South Africa are relatively meagre. South Africa's major water supplies are and will probably always be derived mainly from surface resources. South Africa's climate is semi-arid with an average rainfall of 475 mm/a, compared with 735 mm for the USA and 860 mm for the world as a whole.1 In South Africa about nine per cent of the precipitation, ie 43 mm or about 52.109 m3/a, reaches the river systems as runoff. The economically exploitable proportion of this is estimated at 34.109 m3/a, ie 67 per cent of the total. It is predicted that all of this will be fully exploited by the year 2020.2

Precipitation fluctuations over global land areas since the late 1800's

Abstract: An analysis of southern hemisphere land precipitation records for the last 100 years indicates an increase in mean annual precipitation since the 1940's, with positive anomalies, compared to the 1921–1960 reference period, occurring during approximately the last 15 years in all seasons except southern summer (December–February). There is little or no temporal correlation with corresponding precipitation indices for the northern hemisphere (Bradley et al., 1987a). Furthermore, while trends in the northern hemisphere temperate regions were opposite those in the northern tropical areas, in the southern hemisphere both zones exhibit similar trends. The change toward higher precipitation in middle latitudes begins about 10 years earlier in the northern than in the southern hemisphere (in the 1940's versus the 1950's, respectively). For the northern hemisphere, the overall linear trend from 1890 to 1986 is not significantly different from zero. However, a decline is evident since the 1950's, primarily due to lower rainfall amounts south of about 30°N. Globally, the trend is toward higher values in annual and seasonal precipitation, except for the boreal summer season (June–August). Most of the observed increases, however, took place from about 1940 to the mid-1950's, after which time the record has displayed little overall trend, instead exhibiting decade-long fluctuations. The observations are only broadly consistent with zonally averaged profiles of precipitation changes derived from general circulation model (GCM) simulations of climate using doubled atmospheric CO2 concentrations, although we note that there is considerable variability in precipitation response from one model to another. One possible discrepancy occurs in the northern hemisphere tropics, where most GCMs indicate relatively little change in precipitation in response to CO2 doubling (Gutowski et al., 1988), whereas in the past couple of decades there has been a major decline in rainfall in this region. The overall increase in southern hemisphere precipitation is consistent with marine observations for the tropics and extratropical southern latitudes, which show an increase in sea surface temperature of about 0.3°C since the mid-1970's and an increase in surface wind speed of between 0.4 and 0.8 m/s since 1950. The potential increase in evaporation could have contributed to the observed rainfall trends. We note, however, that precipitation in tropical land areas is strongly influenced by the phases of the El Nino/Southern Oscillation (ENSO), being generally lower during warm events and higher during the opposite cold phase. The effects of the strong ENSO warm events of 1982–1983 and around 1940 are clearly evident in the global record, as are precipitation peaks during cold years, such as 1974–1975 and 1954–1956.

Intraseasonal Periodicities in Indian Rainfall

Abstract: Spectral analysis of a 70-year (1901–70) record of daily precipitation from 3700 stations in the country of India is carried out to search for periodicities on subseasonal time scales during the summer monsoon. Two statistically significant spectral peaks are found. A 40–50 day spectral peak corresponding to the Madden-Julian Oscillation is found over most of the portion of India south of 23°N. The phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula. Ten to 12 days later the precipitation peaks simultaneously all along the coast west of the Western Ghats and along a line running across India between 20° and 25°N. The precipitation maximum then spreads slowly northward and loses significance. Cross-spectral analysis shows strong coherence between the precipitation patterns and wind oscillations. The zonal wind oscillations at 850 and 200 mb am about 180 degrees out-of-phase equatorward of about 20°N, but in-pha...

Simulation of Precipitation by Weather-Type Analysis

Abstract: A new approach that uses weather-type analysis as a basis for stochastic precipitation modeling was developed and tested for Philadelphia, Pennsylvania. The weather types permit the identification of weather conditions associated with varying frequencies, intensities, and amounts of precipitation. Weather-type frequencies were used to stochastically simulate precipitation for Philadelphia and to produce estimates that statistically match observed precipitation. A new method that applies climatic-change scenarios to weather-type frequencies to simulate future precipitation was developed.

Glaciochemical Investigations as a Tool for Determining the Spatial and Seasonal Variation of Snow Accumulation in the Central Karakoram, Northern Pakistan

Abstract: Between 70 and 80% of the total annual run-off from the Upper Indus Basin originates from heavy snowfall and glacierized basins at elevations greater than 3500 m a.s.l. However, very little is known concerning the mountainous headwaters of the Indus. This is especially true with respect to the amount of snowfall in the major source area, the high Karakoram. Recent studies of high-altitude alpine glaciers indicate that geochemical dating techniques can accurately and confidently identify seasonal and annual stratigraphy within snow pits and ice cores, and thus can be used to determine the seasonal and annual rate of snow accumulation. In addition, chemical records can usually be employed to determine sources of precipitation. Six snow pits, each 5–10 m deep, were investigated in the accumulation zones of the Biafo and Khurdopin Glacier basins. Both accumulation zones are characterized by broad, open basins separated by steep, narrow ridges in which direct precipitation is the dominant form of nourishment. Seasonal stratigraphy is delineated through an analysis of the seasonal variation in the chemical and physical characteristics of the snow-pack. Annual snow accumulation in the Biafo Glacier basin ranges from 0.9 to 1.9 m water equivalent; maximum accumulation occurs in the elevation band 4900–5400 m a.s.l. Roughly one-third of this snow accumulation occurs during the summer.

Conditioning stochastic daily precipitation models on total monthly precipitation

Abstract: Chain-dependent stochastic daily precipitation models are fit to dry, near-normal, and wet subsets of monthly total precipitation data, using category definitions consistent with the 30-day forecasts issued by the Climate Analysis Center of the National Oceanic and Atmospheric Administration. The resulting models are compared to those derived unconditionally from entire data records. It is found that for the 10 selected North American stations investigated, the unconditional models produce distributions of total monthly precipitation having too few dry and wet months as compared to the observations, while appropriate probability mixtures of the three conditional models can accurately reproduce the climatological distributions of total monthly precipitation. Application of the conditional precipitation models to generation of daily data consistent with certain longer-term aspects of the observations is also illustrated.

The climate of niwot ridge, front range, colorado, u.s.a.

Abstract: The climate of Niwot Ridge is described using monthly and annual mean temperatures and monthly and annual total precipitation values for the period 1951 to 1985 and comparable precipitation values for the nearby Silver Lake station from 1915. Summary statistics and water budget values are presented. Time series analysis indicates abnormally low temperatures in the early 1980s and an overall downward trend in temperature. Autoregressive moving average forecasting models and spectral analysis hint at some cyclicity in the data series of annual values of both temperature and precipitation. Silver Lake annual precipitation data show only a slight downward trend when the extremely high value for the year of 1921 is excluded. Implications of these changes for the alpine tundra ecosystem are briefly discussed.

The impact of decadal fluctuations in mean precipitation and temperature on runoff: a sensitivity study over the United States

Abstract: The nature of climate variability is such that decadal fluctuations in average temperature (up to 1 °C annually or 2 °C seasonally) and precipitation (approximately 10% annually), have occurred in most areas of the United States during the modern climate record (the last 60 years). The impact of these fluctuations on runoff was investigated, using data from 82 streams across the United States that had minimal human interference in natural flows. The effects of recent temperature fluctuations on streamflow are minimal, but the impact of relatively small fluctuations in precipitation (about 10%) are often amplified by a factor of two or more, depending on basin and climate characteristics. This result is particularly significant with respect to predicted changes in temperature due to the greenhouse effect. It appears that without reliable predictions of precipitation changes across drainage basins, little confidence can be placed in hypothesized effects of the warming on annual runoff.

Hydrologic effects of climate change in the delaware rwer basin1

Abstract: The Thornthwaite water balance and combinations of temperature and precipitation changes representing climate change were used to estimate changes in seasonal soil-moisture and runoff in the Delaware River basin. Winter warming may cause a greater proportion of precipitation in the northern part of the basin to fall as rain, which may increase winter runoff and decrease spring and summer runoff. Estimates of total annual runoff indicate that a 5 percent increase in precipitation would be needed to counteract runoff decreases resulting from a warming of 2C; a 15 percent increase for a warming of 4C. A warming of 2 to 4C, without precipitation increases, may cause a 9 to 25 percent decrease in runoff. The general circulation model derived changes in annual runoff ranged from {minus}39 to +9 percent. Results generally agree with those obtained in studies elsewhere. The changes in runoff agree in direction but differ in magnitude. In this humid temperate climate, where precipitation is evenly distributed over the year, decreases in snow accumulation in the northern part of the basin and increases in evapotranspiration throughout the basin could change the timing of runoff and significantly reduce total annual water availability unless precipitation were to increase concurrently.

Haze Particle Nucleation Simulations in Cirrus Clouds, and Applications for Numerical and Lidar Studies

Abstract: A one-dimensional cloud microphysical model is applied to exploring the basic conditions under which ice crystal nucleation, from the homogeneous freezing of ammonium sulfate haze particles, can occur in cirrus clouds at temperatures ≲ −35°C. Cirrus generating regions maintained by uniform updrafts of 0.1–0.25 m s−1, and an idealized ice crystal precipitation mechanism dependent on vertical wind shear are treated in the model. The findings indicate that ice crystals are generated in a pulse-like fashion as a result of water vapor competition effects from ice crystals nucleated within an updraft, followed by precipitation. Water saturation is not required for ice crystal nucleation at ≲ −35°C, and the relative humidities required at decreasing temperatures gradually decrease. The temperature dependency of the relative humidities associated with ice production does not depend significantly on model inputs, suggesting that cirrus cloud processes follow an adjusted pseudoadiabat, which produces ice m...

Sources of Sahel Precipitation for Simulated Drought and Rainy Seasons

Abstract: The sources of sub-Saharan precipitation are studied using diagnostic procedures integrated into the code of the GISS climate model. Water vapor evaporating from defined source region is “tagged,” allowing the determination of the relative contributions of each evaporative source to the simulated July rainfall in the Sahel. Two June–July simulations are studied to compare the moisture sources, moisture convergence patterns and the spatial variations of precipitation for rainy and drought conditions. Results for this eau study indicate that patterns of moisture convergence and divergence over northern Africa had a stronger influence on model rainfall over the sub-Sahara than did evaporation rates over the adjacent oceans or moisture advection from ocean to continent. While local continental evaporation contributed significant amounts of water to sahelian precipitation in the “rainy” simulation, moisture from the Indian Ocean did not precipitate over the Sahel in either case.

Mesoγ-Scale Distribution of Orographic Precipitation: Numerical Study and Comparison with Precipitation Derived from Radar Measurements

Abstract: On the assumption that moisture convergence due to mechanical uplifting approximately equals the orographic precipitation, the mesoγ-scale rainfall distributions over mountainous regions in Israel are investigated. The simulated distributions are compared to rainfall observations both from raingages and from radar reflectivities. The mean error in the predicted rainfall on scale of 2 km was ±8.4% for mean annual normals and 15%–20% for three case studies. It is suggest that orographic rainfall on the small mesoscale is highly predictable with the adiabatic assumption that the uplifting is determined by V·ΔZs, where V is the horizontal wind encountering the mountain and Zs, is the topographic elevation. It is also illustrated that the climatological observed rainfall distribution could be complemented by the model at locations where sufficient observations were not available. By comparison of the model simulation with the radar-derived rainfall, the considerable effect that a change in the wind di...

Large-scale precipitation and outgoing longwave radiation from INSAT-1B during the 1986 southwest monsoon season

Abstract: Areally averaged precipitation and broadband outgoing longwave radiation (OLR) have been estimated from infrared window channel observations from INSAT-1B, the Indian geostationary satellite, for the period June–September 1986. The estimation techniques used were identical with those contained in previously published work using GOES (for precipitation) and NOAA (for OLR) satellite data. The fields of estimated monthly mean precipitation and OLR are quite similar, with regions of low flux corresponding to arm of heavy precipitation. Two bands of heavy rainfall were found, one near the equator, possibly associated with the Intertropical Convergence Zone, and another extending northwestward from Indonesia through the Bay of Bengal and over India. This latter feature exhibited a pronounced southeastward retreat during the course of the season. The rainfall estimates are reasonably consistent in both distribution and magnitude over India with climatological mean fields derived from rain gauge measurem...

The effect of parameterized ice microphysics on the simulation of vortex circulation with a mesoscale hydrostatic model

Abstract: It has been proposed that ice microphysics, particularly the melting effect, can play an important role in the generation of mesoscale structure and evolution of convective weather systems and associated stratiform rainfall. In this paper, parameterized cloud ice and snow crystals are incorporated into an explicit (grid-resolved) convective scheme as prognostic variables and tested using an observed mesovortex on a grid resolution of 25 km. With the inclusion of ice microphysics parameterization, the resolvable-scale precipitation begins to develop nearly 1 h earlier and undergoes a more rapid acceleration. Meanwhile, the resulting maximum upward motion and locally accumulated rainfall are significantly larger than that without ice microphysics. However, the model produced a relatively weak mesovortex circulation with the maximum cyclonic vorticity located more than 50 mb higher when the ice microphysics is incorporated. It is found that the freezing and sublimation provide a positive forcing for the rapid development of the mid-tropospheric warm-core vortex circulation, while the melting tends to destroy the concentration of cyclonic vorticity in the lower levels. In particular, intercomparisons among all sensitivity experiments so far performed reveal that the melting effect can be of equal importance to those of the hydrostatic water loading and evaporative cooling in retarding the development of the CISK-like instability and in reducing the intensity of the mesovortex. The results indicate that the vertical distribution of diabatic heating may be more important than the total heating in determining the strength of mesovortices, when the melting effect is considered. DOI: 10.1111/j.1600-0870.1989.tb00371.x

Rainfall Intensity, the Weibull Distribution, and Estimation of Daily Surface Runoff

Abstract: A new method for estimating absorption and runoff at a point on the basis of total daily precipitation and the absorption capacity of the soil is proposed. The method is based on a statistical characterization of the variation of precipitation rates over the course of a day. Short-duration precipitation rates are modeled as Weibull random variates. Distribution parameters are estimated using maximum likehood methods by regarding precipitation from “dry” intervals as censored data.

Observational and Numerical Study of a Microburst Line-Producing Storm

Abstract: An analysis is performed on a microburst line-producing cloud that occurred near Denver, Colorado on 13 July 1982. The cloud line developed in an environment conducive to the production of low-reflectivity microbursts. Doppler radar analysis revealed strong convergence above cloud base into the region of downdraft 3.5 to 4.5 km above ground. Aircraft measurements detected light rain with graupel aloft in microburst downdrafts. A two-dimensional cloud model simulation captured many of the observed features of the cloud line structure and wind fields. In particular, both the development of multiple microbursts and the convergence aloft were well simulated. The formation of graupel/hail was important to the precipitation process in the model. The loading of rain and graupel and the cooling effect of rain evaporation and graupel melting were all important in microburst production—the graupel in the formative stages of the downdraft, and the rain in the further intensification of the downdraft and enh...

Enhancement of surface-atmosphere fluxes by desert-fringe vegetation through reduction of surface albedo and of soil heat flux

Abstract: Under the arid conditions prevailing at the end of the dry season in the western Negev/northern Sinai region, vegetation causes a sharp increase relative to bare soil in the daytime sensible heat flux from the surface to the atmosphere. Two mechanisms are involved: the increase in the surface absorptivity and a decrease in the surface heat flux. By increasing the sensible heat flux to the atmosphere through the albedo and the soil heat flux reductions, the desert-fringe vegetation increases the daytime convection and the growth of the planetary boundary layer. Removal of vegetation by overgrazing, by reducing the sensible heat flux, tends to reduce daytime convective precipitation, producing higher probabilities of drought conditions. This assessment of overgrazing is based on observations in the Sinai/Negev, where the soil albedo is high and where overgrazing produces an essential bare soil. Even if the assessment for the Sinai/Negev does not quantitatively apply throughout Africa, the current practice in many African countries of maintaining a large population of grazing animals, can contribute through the mesoscale mechanisms described to reduce daytime convective precipitation, perpetuating higher probabilities of drought. Time-of-day analysis of precipitation in Africa appears worthwhile, to better assess the role of the surface conditions in contributing to drought.

Monitoring the chemical climate of the Mt. Mitchell State Park for evaluation of its impact on forest decline

Abstract: During the last decade, a new type of forest decline has become increasingly apparent, especially at high elevations, in north America and western Europe. One of the causes for this decline could be anthropogenic air pollutants, the deposition of which is facilitated by natural causes at high elevations such as strong windfield, direct cloud capture by the forest canopy, high frequency of frosting and riming etc. At Mt. Mitchell, North Carolina (35°44′05″N, 82°17′15″W) which is the highest peak (2,038 m MSL) in the eastern United States, the decline of red spruce and Fraser fir forest is noticeable above the cloud-base which is frequently observed around 1585 m MSL. In order to quantitatively assess the chemical climate of Mt. Mitchell State Park, we erected a 16.5 m tall aluminium walk-up tower and instrumented it with an electronic weather station, cloud water collectors and ozone analyzers. Our observations during summer 1986 confirm that Mt. Mitchell has a high frequency of being immersed in clouds. During early morning hours, cloudiness is maximum in frequency and results in short duration cloud events ranging from 2-8 h. Although the average pH of precipitation was about 4.4, the pH of cloud water ranged between 2.2–5.4. Short-duration cloud events (8 h or less) were more acidic, in general, than the long duration ones during which the cloud water was most acidic at the onset and dissipative stages. Both types of event were characterized by highly variable liquid water content (LWC) which was lower for the short events. The pH of the cloud water was demonstrated to be a function of wind direction at the site. For the average wind direction of 210°, the pH was 3.4. During early summer episodes, neutralization of the acidic anions (SO‾‾ 4 and NO‾ 3 ) was not as effective as in the later summer episodes. During all cloud episodes, ozone concentration registered a dramatic decrease. The average minimum ozone concentration of about 63 ppb during the whole summer of 1986 was above the background level (50 ppb) in the United States. Diurnal ozone variation revealed a nocturnal maximum of about 75 ppb after sunset. This is contrary to conventional midday maximum in ozone concentration reported in the literature. Episodic excursions in ozone concentration equal to or exceeding 100 ppb level were found on 5 occasions. The maximum cloud water deposition rate, which is estimated using a micrometeorological model, is found to be 1.30 mm h -1 . Ionic deposition on the forest canopy is found to be similar to that reported for the Mt. Moosilauke (New Hampshire) forest. Ionic deposition due to direct cloud capture is found to be 2 to 5 times the deposition due to precipitation, and the evaporation associated with wind speeds as high as 15-18 m s -1 realized during some episodes is pointed out to be of great significance regarding the canopy exposure. DOI: 10.1111/j.1600-0889.1989.tb00128.x

Trace inorganic species in precipitation and their potential use in source apportionment studies

Abstract: Trace species in atmospheric particles have frequently been used to apportion pollutants in acid rain to their sources by comparing the relative concentrations of trace species at the source and receptor sites. Another approach is to use the trace species in precipitation directly in a source apportionment. This has rarely been done due to the paucity of data on trace species in precipitation and the unknown fractionation of the species during the scavenging process. A study was undertaken to analyze precipitation for a large number of trace species and to compare the concentrations with those in atmospheric particles. Precipitation was collected in Lenox, MA during the summer of 1984. Extreme measures were taken to avoid contamination during collection and analysis. Using five analytical methods, including the novel method of freeze-drying the precipitation followed by neutron-activation analysis, 31 species were analyzed in the rain. The trace concentrations measured in this study were lower than those found in earlier studies, where contamination was believed to be a problem. Concentrations of trace species in the precipitation were compared with those in atmospheric particles. A few species were enriched in precipitation relative to particles, including some large-particle species (Ca, Ti, Fe) and species with gaseous precursors (SO4, NO3, Br). Due to this enrichment, these species should be carefully considered before using them in source apportionment calculations. However, most species showed similar enrichments in precipitation and in atmospheric particles, suggesting that negligible fractionation had taken place during the scavenging process. These species could be used effectively in the future to apportion the pollutants in precipitation to their various sources.

Soil Temperature and Water Content, Seeding Depth, and Simulated Rainfall Effects on Winter Wheat Emergence

Abstract: (…) Median emergence time decreased by 1.3 d and emergence was more uniform for every degree increase in soil temperature in the 5 to 20 o C range. Median emergence time increased as soil water potential decreased from −0.20 to 1.5 MPa. However, simulation studies demonstrated that 9.3 mm of precipitation on a dry soil was adequate to establish winter wheat seeded less than 25 mm deep (…)