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This study examines the characteristics of a large number of extreme rain events over the eastern two-thirds of the United States. Over a 5-yr period, 184 events are identified where the 24-h precipitation total at one or more stations exceeds the 50-yr recurrence amount for that location. Over the entire region of study, these events are most common in July. In the northern United States, extreme rain events are confined almost exclusively to the warm season; in the southern part of the country, these events are distributed more evenly throughout the year. National composite radar reflectivity data are used to classify each event as a mesoscale convective system (MCS), a synoptic system, or a tropical system, and then to classify the MCS and synoptic events into subclassifications based on their organizational structures. This analysis shows that 66% of all the events and 74% of the warm-season events are associated with MCSs; nearly all of the cool-season events are caused by storms with strong synoptic forcing. Similarly, nearly all of the extreme rain events in the northern part of the country are caused by MCSs; synoptic and tropical systems play a larger role in the South and East. MCS-related events are found to most commonly begin at around 1800 local standard time (LST), produce their peak rainfall between 2100 and 2300 LST, and dissipate or move out of the affected area by 0300 LST. [ABSTRACT FROM AUTHOR]

A quasi balance with respect to parcel buoyancy at cloud base between destabilizing processes and convection is imposed as a constraint on convective cloud-base mass flux in a modified version of the Kain–Fritsch cumulus parameterization. Supporting evidence is presented for this treatment, showing a cloud-base quasi balance (CBQ) on a time scale of approximately 1–3 h in explicit simulations of deep convection over the U.S. Great Plains and over the tropical Pacific Ocean with the Naval Research Laboratory’s Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS). With the exception of the smaller of two convective events in the Great Plains simulation, a CBQ is still observed upon restriction of the data analysis to instances where the available buoyant energy (ABE) exceeds a threshold value of 1000 J kg-1. This observation is consistent with the view that feedbacks between convection and cloud-base parcel buoyancy can control the rate of convection on shorter time scales than those associated with the elimination of buoyant energy and supports the addition of a CBQ constraint to the Kain–Fritsch mass-flux closure. Tests of the modified Kain–Fritsch scheme in single-column-model simulations based on the explicit three-dimensional simulations show a significant improvement in the representation of the main convective episodes, with a greater amount of convective rainfall. The performance of the scheme in COAMPS precipitation forecast experiments over the continental United States is also investigated. Improvements are obtained with the modified scheme in skill scores for middle to high rainfall rates. [ABSTRACT FROM AUTHOR]

Wet deposition (WD), throughfall (TF) and stemflow (SF) measurements undertaken in a deciduous forest show 85% of the WD liquid flux is observed as TF and approximately 2% as SF. TF and SF were observed to be enriched in base cations and accordingly had an average pH of 6.1 and 5.9, respectively relative to a WD pH of 5.1. The seasonal variability of TF pH below the deciduous canopies was more pronounced than that of WD though both exhibited a growing season maximum, and there is evidence that the seasonal variability of TF pH below the pines is inverted relative to the deciduous canopies likely due to enhanced dust capture and buffering by calcium carbonate. TF ion concentrations differed significantly between deciduous and pine canopies during the growing season, and there is some evidence that variation in sky view factor of 0.18–0.22 is sufficient to manifest statistically differing TF composition below sugar maples. The total atmospheric flux of inorganic nitrogen to the forest is approximately 14–18 kg-N ha−1 yr−1 with approximately half taken up by the canopy. Associated experiments designed to quantify uncertainties in the nutrient fluxes included laboratory tests of the Aerochem automated wet-dry sampler. These experiments indicate the delay in initiating sample collection is less than half a minute for rainfall rates above 1 cm h−1, but may increase substantially for lower precipitation rates. [ABSTRACT FROM AUTHOR]

Diurnal variations in the climatological large-scale summertime hydrologic cycle over the southwestern United States are examined using surface and upper-air observations along with regional model output. Rainfall rates are greatest during the daytime, but the hydrologic balance that supports this rainfall changes as the day progresses. During the late morning and early afternoon, the area-averaged rainfall is balanced predominantly by evapotranspiration augmented by low-level moisture convergence; moisture from these two sources is redistributed via eddy diffusion, resulting in an overall moistening of the atmosphere and a divergence of moisture aloft. During the late afternoon, vertical redistribution via eddy diffusion weakens considerably, although precipitation continues at approximately the same rate because of drying aloft, which also supports continued large-scale divergence of moisture at these levels. This large-scale divergence aloft persists at all times of day, suggesting that for the domain as a whole, precipitation is dependent upon low-level moisture sources. At finer scales, these balances are modified principally by the presence of moisture convergence/divergence centered on the elevated regions of the domain, suggesting that local balances may be more complex than the area-average balances described here. [ABSTRACT FROM AUTHOR]

Technology for the 14- and 35-GHz Second-Generation Precipitation Radar (PR-2) is currently being developed by the National Aeronautics and Space Administration Jet Propulsion Laboratory to support the development of future spaceborne radar missions. PR-2 will rely on high-performance onboard processing techniques in order to improve the observation capabilities (swath width, spatial resolution, and precision) of a low-earth orbiting rainfall radar. Using field-programmable gate arrays (FPGAs), we have developed a prototype spaceborne processor and controller module that will support advanced capabilities in the PR-2 such as autotargeting of rain and compression of rainfall science data. In this paper, we describe the new technology components designed for the onboard processor, including an FPGA-based 40 × 109 op/s pulse-compression receiver/filter with a range sidelobe performance of -72 dB, and an adaptive scanning controller which yields a six-fold increase in the number of radar looks over areas of precipitation. [ABSTRACT FROM AUTHOR]

The authors demonstrate that much can be learned about the performance of a numerical weather prediction (NWP) model by examining the temporal modes of its simulated rainfall. Observations from the Weather Surveillance Radar-1988 Doppler (WSR-88D) network are used to evaluate the rainfall frequency, and its diurnal and semidiurnal modes, in simulations made by a preliminary version of the Weather Research and Forecasting (WRF) model for the conterminous United States during the summer of 2003. Simulations and observations were broadly similar in the normalized amplitudes of their diurnal and semidiurnal modes, but not in the modes' phases, and not in overall frequency of rain. Simulated rain fell too early, and light rain was too frequent. The model also did not produce the distinct, nocturnal maximum in rainfall frequency that is integral to the hydrologic cycle of the Great Plains. The authors provide evidence that there were regional and phenomenological dependencies to the WRF model's performance. [ABSTRACT FROM AUTHOR]

Flash flood and debris flow reports from Storm Data and the U.S. Geological Survey (USGS) are used to investigate the relationship between hazardous hydrological responses, convective rainfall, and cloud-to-ground (CG) lightning flash parameters. Basins burned by the Coal Seam and Missionary Ridge wildfires during the summer of 2002 in western Colorado were selected as primary study areas. The North American monsoon (NAM) air mass played a pivotal role in providing low-level moisture over much of Colorado during each of the 12 hydrological events identified. Surface θe values as high as 354 K were calculated over western Colorado in a composite analysis that also saw a θe ridge through 500 hPa extending northward into Nebraska and southern South Dakota. Storm-total CG flashes were as high as 718, and the median flash total for the population of events was 256. Mean 5-min CG flash intensity for the events was 18.1 flashes. The mean rainfall intensity associated with the 12 hydrological events was 10.5 mm h-1, and average storm-total rainfall was 14.2 mm. Continuous CG flash sequences (one or more flashes per sequential 5-min interval) were significantly correlated with rainfall intensity, total rainfall, and rainfall duration for events generating postwildfire flash floods and debris flows. Operational utility may be derived from the observation of the mean lag time from the first recorded CG flash in a 7850-km2 study area to the peak rainfall intensity, and the mean lag time from peak CG flash rate to peak rainfall at the hydrological event location. The mean lag times for the 12 events in the study were 165 and 41 min, respectively. [ABSTRACT FROM AUTHOR]

The use of radar-based precipitation is investigated for possible improvement of spatially lumped continuous hydrologic modeling in two subbasins of the Cumberland River basin in Middle Tennessee. Hydrologic predictions of streamflow at the outlets of the subbasins are obtained using HEC-HMS and two precipitation inputs, Stage III radar-derived and gauge-only data. Model performance with each precipitation input is assessed by comparing predicted and measured streamflow at each subbasin outlet and calculating streamflow volume bias, root mean square difference, mean normalized peak error, and mean peak timing error. The results indicate that the Stage III precipitation suffers from systematic underestimation at both the point and subbasin scales and cannot be completely offset by model recalibration. Simulations driven by both the Stage III and gauge-only data periodically failed to reproduce observed flood peaks in both subbasins. But Stage III simulations are generally less accurate in prediction of streamflow volume as compared to gauge-only simulations and, although comparable to the gauge-only simulations in predicting the magnitude and time to peak, offer no apparent improvement in predicting these quantities either. [ABSTRACT FROM AUTHOR]

A hierarchical Bayesian strategy for modeling annual U.S. hurricane counts from the period 1851–2000 is illustrated. The approach is based on a separation of the reliable twentieth-century records from the less precise nineteenth-century records and makes use of Poisson regression. The work extends a recent climatological analysis of U.S. hurricanes by including predictors (covariates) in the form of indices for the El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). Model integration is achieved through a Markov chain Monte Carlo algorithm. A Bayesian strategy that uses only hurricane counts from the twentieth century together with noninformative priors compares favorably to a traditional (frequentist) approach and confirms a statistical relationship between climate patterns and coastal hurricane activity. Coinciding La Niña and negative NAO conditions significantly increase the probability of a U.S. hurricane. Hurricane counts from the nineteenth century are bootstrapped to obtain informative priors on the model parameters. The earlier records, though less reliable, allow for a more precise description of U.S. hurricane activity. This translates to a greater certainty in the authors' belief about the effects of ENSO and NAO on coastal hurricane activity. Similar conclusions are drawn when annual U.S. hurricane counts are disaggregated into regional counts. Contingent on the availability of values for the covariates, the models can be used to make predictive inferences about the hurricane season. [ABSTRACT FROM AUTHOR]

have responded with critical comments as to whether urbanization-enhanced precipitation is maximized in the south-southeast of Atlanta, Georgia, as was recently documented byThe reply herein offers both general and specific responses to the issues raised by [ABSTRACT FROM AUTHOR]

Traditional stormwater management does not mitigate groundwater depletion resulting from groundwater pumping and reduction in recharge. Infiltration practices, such as rain gardens, offer a potentially effective approach for addressing groundwater depletion. A rain garden is a landscaped garden in a shallow depression that receives the stormwater from nearby impervious surfaces, focusing recharge. We have developed a numerical model that can be applied in rain garden design and evaluation. Water flow through the rain garden soil is modeled over three layers: a root zone, a middle storage layer of high conductivity, and a subsoil lower layer. To continuously simulate recharge, runoff, and evapotranspiration, the model couples the Richards Equation with a surface water balance. The model was applied to the climate of southern Wisconsin. Simulation results show that very high recharge rates are possible during the non-snowfall season. (The model does not handle snowmelt.) A rain garden with an area of about 10-20% of the contributing impervious area maximizes groundwater recharge. Increasing the depression depth increases recharge and saturation times, affecting plant survival. Rain garden feasibility also depends on the subsoil hydraulic conductivity. [ABSTRACT FROM AUTHOR]

A method for the objective evaluation of short-term, nonrandomized operational convective cloud-seeding projects on a floating-target-area basis has been developed and tested in the context of the operational cloud-seeding projects of Texas. The computer-based method makes use of the Next-Generation Radar (NEXRAD) mosaic radar data to define fields of circular (25-km radius) floating-target analysis units with lifetimes from the first echo to the disappearance of all echoes and then superimposes the track and seeding actions of the project seeder aircraft onto the unit fields to define seeded (S) and nonseeded (NS) analysis units. Objective criteria (quantified herein) are used to identify “control” (C) matches for each of the seed units from the archive of NS units. To minimize potential contamination by seeding, no matching is allowed for any control unit if its perimeter came within 25 km of the perimeter of a seed unit during its lifetime. The methodology was used to evaluate seeding effects in the High Plains Underground Water Conservation District (HP) and Edwards Aquifer Authority (EA) programs during the 1999, 2000, and 2001 (EA only) seasons. Objective unit matches were selected from within and outside each operational target within 12, 6, 3, and 2 h of the time on a given day that seeding of a particular unit took place. These were done to determine whether selection biases and the diurnal convective cycle confounded the results. Matches were also drawn from within and outside each target using the entire archive of days on which seeding was done. Although the results of all analyses are subjected to statistical testing, the resulting probability (P) values were used solely to determine the relative strength of the various findings. In the absence of treatment, randomization P values cannot be used as proof of seeding efficacy. The apparent effect of seeding in both programs was large—even after determining the effect of selection biases and the diurnal convective cycle. The most conservative and credible estimates of seeding effects were obtained from control matches drawn from outside the operational target within 2 h of the time that each unit was seeded initially. Under these circumstances, the percentage increase exceeds 50% and the volumetric increment was greater than 3000 acre-feet (3700 kt) per unit with strong P-value support (i.e., <0.0001) in both the HP and EA programs. This is in good agreement with the apparent percentage effects of seeding for the randomized Texas and Thailand cloud-seeding programs, which were 43% and 48%–92%, respectively. The results and their P-value support after partitioning gave even stronger indications of positive seeding effects. Although the results of these and other analyses described herein make a strong case for enhanced rainfall by the operational seeding programs, such programs must not be viewed as substitutes for randomized seeding efforts that are conducted in conjunction with realistic cloud modeling and are followed by replication, preferably by independent groups for maximum credibility. [ABSTRACT FROM AUTHOR]

Rainfall-generated floods in the Arctic are rare and seldom documented. The authors were fortunate in July 1999 to monitor such a flood on the Upper Kuparuk River in response to a 50-h duration rainfall event that produced a watershed average in excess of 80 mm. Atmospheric conditions prevailed that allowed moist air to move northward over areas of little or no vertical relief from the North Pacific Ocean to the Arctic Ocean. Cyclogenesis occurred along the quasi-stationary front separating maritime and continental air masses along the arctic coast. This low-pressure system propagated southward (inland) over the 142-km[sup 2] headwater basin of the Kuparuk River in the northern foothills of the Brooks Range; a treeless area underlain by continuous permafrost. This research catchment was instrumented with a stream gauging station, two major and six minor meteorological stations, for a total of eight shielded rain gauges. The peak instantaneous flow was estimated at 100 m[sup 3] s[sup -1] and was about 3 times greater than any previously measured flood peak. Historically in the Arctic, annual peak floods occur following snowmelt when the snowpack that has accumulated for 8–9 months typically melts in 7–14 days. The shallow active layer, that surficial layer that freezes and thaws each year over the continuous permafrost, has limited subsurface storage when only thawed to a depth of 40 cm (at the time of the flood). Typically for this area, the ratio of runoff volume to snowmelt volume is near 0.67 or greater and the ratio for cumulative summer runoff and rainfall averages around 0.5 or greater. For the storm discussed here the runoff ratio was 0.73. These high runoff ratios are due to the role of permafrost limiting the potential subsurface storage and the steep slopes of this headwater basin. [ABSTRACT FROM AUTHOR]

Details an analysis of high-resolution wind and reflectivity data collected by a mobile, W-band Doppler radar. Near-surface life history of a tornado in a supercell in north-central Nebraska on June 5, 1999; Description of the formation of the tornado vortex near the ground from a sequence of vector scans ranging from 30-second interval prior to tornadogenesis to 10-15-second intervals during much of the lifetime of the tornado.

The precipitation efficiencies for mesoscale convective systems (MCS) over the central United States are calculated. During July–September 2000 and June–September 2001, 24 MCS for which sufficient data were available occurred over or near Missouri. Precipitable water fields from the hourly Rapid Update Cycle (RUC) and radar-derived precipitation grids are used to calculate the precipitation efficiency. Geostationary Operational Environmental Satellite soundings and RUC winds are used to assess the pre-MCS environment. Statistical analysis reveals that precipitation efficiency has a relatively strong positive correlation with the relative humidity in the layer between the surface and the lifting condensation level; significant negative correlations are found between the precipitation efficiency and both the convective inhibition and the environmental wind shear. The latter, inverse relationship between shear and precipitation efficiency supports the findings of previous investigators. [ABSTRACT FROM AUTHOR]

Flash floods are among the most devastating natural weather hazards in the United States, causing an average of more than 225 deaths and $4 billion in property damage annually. As a result, prediction of flash floods in an accurate and timely fashion is one of the most important challenges in weather prediction. Data from geostationary and polar-orbiting satellites are significant sources of information for the diagnosis and prediction of heavy precipitation and flash floods. Geostationary satellites are especially important for their unique ability simultaneously to observe the atmosphere and its cloud cover from the global scale down to the storm scale at high resolution in both time (every 15 min) and space (1–4 km). This capability makes geostationary satellite data ideally suited for estimating and predicting heavy precipitation, especially during flash-flood events. Presented in this paper are current and future efforts in the National Environmental Satellite, Data, and Information Service that support National Weather Service River Forecast Centers and Weather Forecast Offices during extreme-precipitation events. [ABSTRACT FROM AUTHOR]

A detailed intercomparison was performed for the period January 1998–June 1999 of three different sets of rainfall observations over the watershed covered by the National Weather Service Arkansas–Red Basin River Forecast Center (ABRFC). The rainfall datasets were 1) hourly 4-km-resolution ABRFC-produced P1 estimates, 2) 15-min 2-km resolution NOWrad estimates produced and marketed by Weather Services International Corporation (WSI), and 3) conventional hourly rain gauge observations available from the operational observing network. Precipitation estimates from the three products were compared at monthly, daily, and hourly timescales for the Arkansas–Red River basin and the Illinois River basin. Results indicate that the P1 products had a higher correlation and smaller bias relative to rain gauges than did the WSI products. The fact that the P1 estimates are bias corrected using gauges themselves makes an independent assessment difficult. WSI monthly accumulations seemed to overestimate (underestimate) total rainfall relative to gauges during the warm (cold) season. WSI and P1 estimates had very good agreement overall with correlation coefficients of daily accumulations generally greater than 0.7. The P1 hourly estimates were characterized by a large proportion of extremely light rainfall rates (less than 2 mm h[sup -1] ). This is likely due to the P1 bias correction algorithm's use of sparse gauge data during low-level stratiform precipitation events. Finally, analyses of mean areal precipitation, fractional coverage, and storm total rainfall for the Illinois River basin demonstrate the potential impact of these rainfall products on hydrologic models that use these precipitation estimates as meteorological forcing. [ABSTRACT FROM AUTHOR]

The uncertainty of rainfall estimated from averages of discrete samples collected by a satellite is assessed using a multiyear radar dataset covering a large portion of the United States. The sampling-related uncertainty of rainfall estimates is evaluated for all combinations of 100-, 200-, and 500-km space domains; 1-, 5-, and 30-day rainfall accumulations; and regular sampling time intervals of 1, 3, 6, 8, and 12 h. These extensive analyses are combined to characterize the sampling uncertainty as a function of space and time domain, sampling frequency, and rainfall characteristics by means of a simple scaling law. Moreover, it is shown that both parametric and nonparametric statistical techniques of estimating the sampling uncertainty produce comparable results. Sampling uncertainty estimates, however, do depend on the choice of technique for obtaining them. They can also vary considerably from case to case, reflecting the great variability of natural rainfall, and should therefore be expressed in probabilistic terms. Rainfall calibration errors are shown to affect comparison of results obtained by studies based on data from different climate regions and/or observation platforms. [ABSTRACT FROM AUTHOR]

We discuss the performances of a set of four microwave water vapor radiometers operating in the 20-30-GHz band during a field experiment, with an emphasis on calibration and achievable accuracy. The field experiment was conducted at the Department of Energy's Atmospheric Radiation Measurement Program's field site in north central Oklahoma, and was focused on clear-sky water vapor measurements by both radiometers and radiosondes. A comparison between two published radiometric tip curve calibration procedures is presented, and these procedures are applied to measurements from two nearly identical instruments placed a few meters apart. Using the instantaneous tip cal method of the Environmental Technology Laboratory, the brightness temperature measurements for the two identical instruments differed by less than 0.2 K over a 24-h period. Results from reference load cryogenic tests and brightness temperature cross comparisons have shown differences within 0.7 K. In addition, we compare radiometric measurements with calculations of brightness temperature based on the Rosenkranz absorption model and radiosonde observations. During the experiment, both Vaisala-type RS80 and RS90 humidity sensors were used. Our comparisons demonstrate the improvements achieved by the new Valsala RS90 sensors in atmospheric humidity profiling, which reduce or eliminate the "dry bias" problem. [ABSTRACT FROM AUTHOR]

The article presents reports from the technical committees of the Acoustical Society of America for the period 2000 to 2003. The technical committees are Acoustical Oceanography, Architectural Acoustics, Animal Bioacoustics, Biomedical Ultrasound and Bioresponse to Vibration, Engineering Acoustics, Musical Acoustics, Physical Acoustics, Psychological and Physiological Acoustics, Signal Processing Acoustics and Speech Communication.

Presents a study that documented estimates of synthetic dimensionless cumulative hyetographs for storms known to produce substantial runoff in small watersheds in Texas. Data used; Definition of dimensionless triangular hyetograph model in terms of rainfall intensity; Estimation of triangular hyetograph parameters.

Runoff data were analyzed from the semihumid 21.2 km2 Goodwin Creek Experimental Watershed (GCEW) in northern Mississippi to examine watershed response over a range of scales. Runoff is monitored at the GCEW outlet and in 13 subcatchments, ranging in area from 0.06 to 17.6 km2. Previous data-based studies have shown that simple scaling theory fails to describe scaling of flood quantiles in large watersheds, and there is a fundamental change in scaling behavior in semihumid watersheds at an area of approximately 100 km2. It has been found that flood quantiles in nearly all subbasins in the GCEW are self-similar as described by simple scaling theory. It has also been found that expected values of peak flows during single runoff events are described by a power law function of catchment area. The primary reasons why flood quantiles are self-similar on Goodwin Creek are that precipitation is relatively uniform over the basin; peak discharges in smaller catchments are highly correlated with rainfall rates; nearly the entire watershed regularly contributes to runoff and; the groundwater table plays little role in runoff production. [ABSTRACT FROM AUTHOR]

On 19-20 June 1979 a cyclone moved through the central United States. This cyclone contained a squall line associated with a cold front aloft (CFA), which caused significant damage. The fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) was used to diagnose the role of the cold pool in the maintenance of the squall line. A control simulation with "full physics" was run, at 18- and 3.6-km grid spacing. Both simulations produced a squall line that was similar in location, orientation, and speed to the observed squall line, and displayed several characteristics that differed from the "leading line-trailing stratiform" paradigm for midlatitude squall lines. Sensitivity test simulations were run for both grid spacings, with diabatic cooling due to evaporation and melting of precipitation withheld to prevent the formation of a cold pool. These simulations produced a squall line similar to that in the control simulation, in terms of the location, orientation, and movement of the squall line. The simulations showed that the CFA provided the primary lifting responsible for the maintenance and movement of the simulated squall line by means of the hydrostatic surface pressure pattern it induced. The cold pool did not play a critical role in the maintenance of the simulated CFA squall line, but it did retard the progression of the synoptic-scale trough that trailed the simulated squall line, thereby increasing the forward tilt of the Pacific cold front. [ABSTRACT FROM AUTHOR]

Data from the Tropical Rainfall Measuring Mission (TRMM) satellite's precipitation radar (PR) were employed to identify warm-season rainfall (1998-2000) patterns around Atlanta, Georgia; Montgomery, Alabama; Nashville, Tennessee; and San Antonio, Waco, and Dallas, Texas. Results reveal an average increase of about 28% in monthly rainfall rates within 30-60 km downwind of the metropolis, with a modest increase of 5.6% over the metropolis. Portions of the downwind area exhibit increases as high as 51%. The percentage changes are relative to an upwind control area. It was also found that maximum rainfall rates in the downwind impact area exceeded the mean value in the upwind control area by 48%-116%. The maximum value was generally found at an average distance of 39 km from the edge of the urban center or 64 km from the center of the city. Results are consistent with the Metropolitan Meteorological Experiment (METROMEX) studies of St. Louis, Missouri, almost two decades ago and with more recent studies near Atlanta. The study establishes the possibility of utilizing satellite-based rainfall estimates for examining rainfall modification by urban areas on global scales and over longer time periods. Such research has implications for weather forecasting, urban planning, water resource management, and understanding human impact on the environment and climate. [ABSTRACT FROM AUTHOR]

The California Landfalling Jets Experiment (CALJET) was carried out during the winter of 1997/98, in part to study orographic rainfall in California's coastal mountains using coastal wind profilers. This observational study statistically links hourly rainfall rates observed by tipping-bucket rain gauges in California's quasi-linear coastal mountains to the hourly averaged upslope component of the flow measured by coastal wind profilers immediately upstream. Vertical profiles of the linear correlation coefficient of upslope flow versus rain rate are calculated on a case-by-case basis, for all cases containing a low-level jet (LLJ), and for the winter season of 1997/98. These correlation coefficient profiles show a direct relationship between the magnitude of the upslope flow impacting the coast and the magnitude of the rain rate in the downstream coastal mountains. Maximum correlation coefficients are as large as 0.94 in some individual cases, 0.75 for a composite of LLJ cases, and 0.70 for the winter season. Using three locations with differing coastal terrain characteristics, it is found that the layer of upslope flow that optimally modulates orographic rainfall is near mountaintop, that is, about 1 km above mean sea level for California's coastal ranges. This height also corresponds to the mean altitude of landfalling LLJs observed by the coastal profilers. The correlation coefficient in this layer is largest when the rain rates are used from the coastal mountain sites rather than from the coastal sites, thus further highlighting the physical connection between upslope flow and orographic rainfall in the coastal mountains. The presence of shallow, terrain-blocked flow modulates the correlation coefficient profiles below mountaintop, such that the low-level flow at the coast is poorly correlated with rain rates observed in the coastal mountains. However, cases without significant blocking retain relatively large correlation coefficient values below mountaintop... [ABSTRACT FROM AUTHOR]

The outbreak of tornadoes from the Mississippi River to just east of the Appalachian Mountains on 2–5 April 1974 is analyzed using conventional techniques and the Pennsylvania State University–National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5). The MM5 was run for 48 h using the NCEP–NCAR reanalysis dataset for initial conditions. It is suggested that the first damaging squall line within the storm of 2–5 April 1974 (herein referred to as the Super Outbreak storm) was initiated by updrafts associated with an undular bore. The bore resulted from the forward advance of a Pacific cold front into a stable air mass. The second major squall line within the Super Outbreak storm, which produced the strongest and most numerous tornadoes, was directly connected with the lifting associated with a cold front aloft. This second squall line was located along the farthest forward protrusion of a Pacific cold front as it occluded with a lee trough/dryline. An important factor in the formation of this occluded structure was the diabatic effects of evaporative cooling ahead of the Pacific cold front and daytime surface heating behind the Pacific cold front. These effects combined to lessen the horizontal temperature gradient across the cold front within the boundary layer. Although daytime surface heating and evaporative cooling are considered to be essential ingredients in the formation and maintenance of organized convection, the MM5 produced a strong squall line along the leading edge of the Pacific cold front even with the effects of surface heating and evaporational cooling removed from the model simulations. [ABSTRACT FROM AUTHOR]

A computer application and national geospatial database have been developed to support the calculation of flooding flow (Q f ) and threshold runoff across the conterminous United States and Alaska. Flooding flow is the flow required to cause a stream to slightly overflow its bank and cause damage. Threshold runoff @L#, defined as the depth of runoff required to cause flooding, is computed as flooding flow divided by the unit hydrograph peak flow. A key assumption in this work is that the two-year return flood (Q 2 ) is a useful surrogate for flooding flow. The application described here computes flood magnitude estimates for selected return periods Q 2 , Q 5 , Q 10 , etc.! using regression equations published by the U.S. Geological Survey for each of 210 hydrologic regions. The application delineates basin boundaries and computes all basin parameters required for the flood frequency calculations. The geographic information system database that supports these calculations contains terrain data @digital elevation models DEMs! and DEM derivatives#, reference data, and 89 additional data layers related to climate, soils, geology, and land use. Initial results indicate that there are some practical limitations associated with using Q 2 regression equations to estimate flooding flow. [ABSTRACT FROM AUTHOR]

Efforts to validate the Tropical Rainfall Measuring Mission (TRMM) space-based rainfall products have encountered many difficulties and challenges. Of particular concern is the quality of the ground-based radar products—the main tool for validation analysis. This issue is addressed by analyzing the uncertainty in the maps of rain rate provided by the ground-validation radar. To look closely at factors that contribute to the uncertain performance of the radar products, this study uses high-quality rainfall observations from several surface sensors deployed during the Texas and Florida Underflights (TEFLUN-B) field experiment in central Florida during the summer of 1998. A statistical analysis of the radar estimates is performed by comparison with a high-density rain gauge cluster. The approach followed in the current analysis accounts for the recognized effect of rainfall's spatial variability in order to assess its contribution to radar differences from independent reference observations. The study provides uncertainty quantification of the radar estimates based on classification into light and heavy rain types. The methodology and the reported results should help in future studies that use radar-rainfall products to validate the various TRMM products, or in any other relevant hydrological applications. [ABSTRACT FROM AUTHOR]

The early histories of radar echo and polarization differential reflectivity (Z[sub DR] ) from growing cumulus clouds observed in Florida with a 10-cm-wavelength radar are reported in detail. Raindrops 1 to several millimeters in diameter are present at about cloud-base level in most cases as soon as any identifiable precipitation echo is seen within cloud (distinct from Bragg scattering and echo from cloud droplets). This is in most cases by the time of the first 10-dBZ radar echo aloft. The very early occurrence of large drops is consistent with origination directly from coalescence on ultragiant aerosol. However, they appear to exist so early and so low in the clouds as to be unexpected if the cumulus were single, vigorous thermals. The explanation may lie in the presence of a more gradual, very early cloud stage that is generally not observed in any detail. Simultaneous Z[sub e] and Z[sub DR] measurements in the early stages of developing, warm cumulus will provide a powerful test of understanding the onset of drop growth by coalescence. [ABSTRACT FROM AUTHOR]

Provides information on a network-based telemetry architecture developed by the Woods Hole Oceanographic Institution (WHOI) for the Martha's Vineyard Coastal Observatory. List of nearshore field studies of the WHOI; System description; Power system of the observatory; Background on networked data telemetry.

KMSX, near Missoula, Montana, is one of the Weather Surveillance Radars-1988 Doppler (WSR-88Ds) that are located on the top of a mountain. Because all WSR-88Ds employ scanning strategies that were developed for flatland radars, mountaintop radars send signals well above the populated valleys and terrain surrounding the radars. Forecasters who use mountaintop WSR-88Ds are at a distinct disadvantage in not being able to detect crucial weather phenomena near the earth's surface. The use of negative elevation angles has been proposed as a solution to this problem. This type of radar operation poses no public radiation hazard, because the microwave radiation exposure level is about two orders of magnitude below the acceptable guideline near the radar and rapidly decreases with increasing distance. The feasibility of KMSX using negative elevation angles is simulated using several different weather situations. The simulations show the potential for improved detections of lowaltitude weather conditions in the surrounding valleys and improved estimates of precipitation amounts throughout the coverage area. For example, using the lowest elevation angle (+0.5°) of the current WSR-88D scanning strategies, simulated rainfall rates detected in the valleys progressively decrease from about 80% of the surface value near the radar to only 1% of the surface value at 220 km. However, using an elevation angle of -0.8°, simulated rainfall rates detected at all ranges out to 220 km are about 80%-95% of the surface values. [ABSTRACT FROM AUTHOR]

A unique wintertime storm occurred on 12 February 1992 during the Stormscale Operational and Research Meteorology-Fronts Experiment Systems Test (STORM-FEST) field project. This storm consisted of a narrow east-west-oriented snow swath (max 20-cm snow depth) with an extensive area of freezing rain to the south. The event was well observed by various networks and systems. Included in these systems were about twice the normal sounding sites, which released rawinsondes every 3 h, single- and dual-Doppler capabilities, and NCAR King Air and Wyoming King Air aircraft. Four aspects of the storm were investigated: the temporal evolution of the low-level jet, the vertical stability of various layers, the development of isothermal layers, and the dynamical effects resulting from melting. The freezing rain related to this storm was a result of an overrunning situation, and the snow swath was produced from conditional symmetric instability with respect to the ice process in the overrunning cloud layer. The warm frontal layer was dynamically unstable in terms of the Richardson number and contained some shearinduced gravity waves. A convective boundary layer was present near the surface. A low-level jet was present at the top of the convective boundary layer and along the snow-freezing rain interface. Isothermal layers developed just below the bright band as a result of diabatic cooling because of melting. The diabatic process of melting appears to have enhanced the speed of the low-level jet and triggered and focused the release of the thermodynamic instability so that an enhanced precipitation rate occurred over the snow-freezing rain interface. [ABSTRACT FROM AUTHOR]

Evaluates long-term changes in soil physical conditions and hydraulic properties after eight years under different groundcover management systems in New York State. Pre- and post-emergence applications of herbicide; Volumetric soil water content; Soil porosity.

Introduces the automated flood-warning decision-support system (FW-DSS) that increases flood warning lead time for Sacramento County, California. Description of the FW-DSS; Components of a local flood warning system; Forecasting program capabilities.

Reflectivity factors and rainfall rates found from Level II WSR-88D data for the National Weather Service (NWS) radar in Greer, South Carolina (KGSP), are compared with similar parameters found from disdrometer data collected at the Clemson Atmospheric Research Laboratory. These comparisons are used to determine experimentally the sensitivity of rainfall amounts found from the WSR-88D data to variations in the parameters A and b of the Z–R law (Z = AR[sup b] ) that is used in analysis of the data. Analyses of data for nine storms in upstate South Carolina are described. These nine cases encompass a variety of rainfall types including stratiform rain, airmass thunderstorms, and strong cold front convective activity. It is found, after correction of the radar reflectivity factors for obvious calibration offset, that the rainfall depths found by radar are in good agreement with those found from the disdrometer when the NWS default values of A and b (A = 300, b = 1.4) are used. If the values of A and b found from an empirical Z–R analysis of the disdrometer data are used, then, as expected, the agreement is even better. It is important to recognize that this good agreement was obtained only after adjustment of the radar-measured reflectivity factors for calibration offset. A similar analysis is also described for one other storm but with the addition of rain gauge data from locations in upstate South Carolina, which are remote from the Clemson laboratory and where there are no collocated disdrometers. The radar data are used to determine rainfall amounts for each of the rain gauge locations as well as for the Clemson laboratory. It is found that the agreement between radar-measured rainfall amounts and those found from the rain gauges is very good, even when the default values of A and b are used. Again, this agreement is obtained only after correction of the radar data for the calibration offset found from comparison of the radar reflectivity fa... [ABSTRACT FROM AUTHOR]

ABSTRACT This study used the atmospheric Fifth-Generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (MM5) and the University of Washington Distributed Hydrology-Soil-Vegetation Model (DHSVM) for the simulation of a complex rain-on-snow flood event that occurred from 28 December 1996 to 3 January 1997 on the 1560-km[sup 2] Snoqualmie River watershed in western Washington. Three control simulations were created with MM5 applied at 36-, 12-, and 4-km horizontal spacing and DHSVM at a horizontal spacing of 100 m. Results showed that the accuracy of the atmospheric fields increased with higher horizontal resolution, although underforecasting of precipitation was evident for all three resolutions. Simulated river flows captured 67% (36 km), 75% (12 kin), and 72% (4 km) of the total flow and 52% (36 km), 58% (12 kin), and 62% (4 km) of the event peak flow. Several sensitivity simulations of the modeling system (4-km spacing only) were conducted to improve on the control simulations. Adjusting the MM5 precipitation using observations led to a streamflow forecast that captured 90% of the total flow. Reduction of the model high-wind speed bias improved the simulated snowmelt, although the resulting effects on streamflow were relatively small. A sensitivity experiment that included the precipitation from an intense rainband that was not captured by MM5 revealed the importance of this high-intensity, short-lived feature; simulated streamflow from this experiment captured 93% of the total flow and over 82% of the peak flow, with a 4-h timing error. A final set of sensitivity simulations, using both a higher- and... [ABSTRACT FROM AUTHOR]

Precipitation forecasts from the Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) are verified for the 1997-98 and 1998-99 cool seasons over the Pacific Northwest. The MM5 precipitation at 36-, 12-, and 4-km horizontal resolution is compared with over 250 NOAA cooperative observer, snow telemetry (SNOTEL), avalanche, and National Weather Service sites in order to evaluate the effects of increasing horizontal resolution and to document spatial variations in model skill. A noticeable improvement in bias, equitable threat, and root-mean-square (rms) error scores occurs as hori-zontal resolution is increased from 36- to 12-km resolution; however, going from 12- to 4-km resolution im-provements in skill are restricted to the heavy precipitation events (>5.08 cm in 24 h). For light to moderate precipitation events, both the 12- and 4-km domains have significant overprediction over the upper windward slopes of the higher terrain. In contrast, for heavy precipitation events there is no widespread overprediction, and all resolutions underpredict precipitation in the lowlands and major gaps in the Cascades. The cool-season undercatchment for selected storage gauges (non-SNOTEL) are estimated using collocated wind, temperature, and precipitation data with undercatchment regression relationships. The undercatchment generally ranges from 25%-40% for exposed high-elevation sites (>1500 m), 15%-20% within major gaps in the Cascades (˜1000 m), to 5%-15% in the lowlands. Undercatch corrections mitigate but do not eliminate the 4-km overprediction problem at low to moderate thresholds. Since synoptic forecast errors preferentially penalize high-resolution forecasts, less accurate large-scale fore-casts are eliminated by setting strict criteria for the 850-mb wind errors at the Quilayutte, Washington, and Salem, Oregon, soundings sites. For all horizontal resolutions there is a significant increase in... [ABSTRACT FROM AUTHOR]

The process of atmospheric cooling due to melting precipitation is examined to evaluate its contribution to determining precipitation type. The 'melting effect' is typically of second-order importance compared to other processes that influence the lower-tropospheric air temperature and hence the type of precipitation that reaches the ground. In some cases, however, cooling due to melting snowflakes can emerge as the dominant agent of temperature change, occasionally surprising forecasters (and the public) by inducing an unexpected changeover from rain to heavy snow. One such case occurred on 3-4 February 1998 in east-central Tennessee and surrounding areas. Commonly applied considerations for predicting precipitation type had convinced forecasters that significant snowfall was not likely with this event. However, real-time observations and a postevent analysis by forecasters at the Storm Prediction Center led to the hypothesis that the melting effect must have provided the cooling necessary to allow widespread heavy snowfall. To test this hypothesis, the Pennsylvania State University-NCAR Mesoscale Model was used to generate a mesoscale-resolution, four-dimensional dataset for this event. Diagnostic analysis of the model output confirmed that cooling due to melting snowflakes was of a sufficient magnitude to account for the disparity between observed and forecasted lower-tropospheric temperatures in this case. A simple formula is derived to provide a 'rule of thumb' for anticipating the potential impact of the melting effect. In addition, guidelines are provided for identifying meteorological patterns that favor a predominance of the melting effect. [ABSTRACT FROM AUTHOR]

On 1 March 1997 violent tornadoes caused numerous fatalities and widespread damage across portions of central and eastern Arkansas and western Tennessee. In addition, the associated thunderstorms produced very heavy rainfall and flash flooding, with a few locations receiving up to 150 mm (6 in.) of rainfall in 3 h. The initial environment appeared favorable for strong tornadoes with unseasonably warm moist air at lower levels resulting in significant instability (convective available potential energy values between 1400 and 1800 J kg[sup -1]) where 0-2-km storm-relative helicities exceeded 300 m² s[sup -2] and the middle-tropospheric storm-relative flow was conducive for tornadic supercells. The most destructive tornadoes developed along a preexisting surface boundary where lower-tropospheric moisture convergence and frontogenesis were enhanced. Tornadoes and heaviest rainfall only ensue after upward motion associated with the direct circulation of an upper-tropospheric jet streak became collocated with lower-tropospheric upward forcing along the surface boundaries. From a flash flood perspective the event occurred in a hybrid mesohigh-synoptic heavy rain pattern as thunderstorms developed and moved along surface boundaries aligned nearly parallel to the mean wind. In addition, strong flow and associated moisture flux convergence in the lower troposphere favored the formation of cells to the southwest or upstream of the initial convection with thunderstorms, including a a tornadic supercell, traversing over the same area. The available moisture and ambient instability also supported both vigorous updrafts and high precipitation rates. [ABSTRACT FROM AUTHOR]

It has been hypothesized that the Solitario Canyon watershed, just west of Yucca Mountain, Nev., could provide a zone of focused ground-water recharge through its ephemeral-stream channels that might be an important factor in the performance of the potential repository for high-level radioactive waste. To examine this possibility, the KINEROS2 rainfall-runoff model was used to estimate the infiltration from surface runoff in each of 79 channel elements using a 100-year simulated rainfall sequence and two sets of saturated hydraulic conductivity KS values. The annual average estimated infiltration ranged from 0.18 to 0.57 mm/year (expressed as depth over the entire 10.7 km2 watershed). Evaporation and transpiration by vegetation near the channels were neglected, therefore these quantities of channel infiltration are not assumed to be ground-water recharge. The simulated rainfall intensities compared favorably with depth-duration-frequency curves for nearby stations. The simulated 100-year peak discharge rates for Solitario Canyon and for four subwatersheds exceeded the regionally estimated 100-year rates for the lowest values of KS and were slightly below those rates for the higher values of KS, suggesting the true value of peak discharge (and channel infiltration from surface runoff) is bounded by those obtained for the 100-year simulations. [ABSTRACT FROM AUTHOR]

Due to a number of hydrologic and meteorologic factors, Houston, Texas, is subject to major flooding problems. The National Weather Service's (NWS) WSR-88D radar (NEXRAD) was used to estimate the areal and spatial distribution of rainfall for three storms over the Brays Bayou watershed in Houston for hydrologic modeling purposes. Rainfall rates estimated from the NEXRAD radar compared favorably to the point rainfall measurements at the operating rain gauges in the watershed for the large October 1994 storm, but tended to overpredict the point rainfall measurements at the rain gauges for two smaller events. Using HEC-1, two model runs were made using the unadjusted NEXRAD-estimated rainfall rates and also using the rain gauge network, and the modeled outflow hydrographs were compared to the measured hydrograph for all three storms. The results from the radar proved to be as accurate, and in some cases more accurate, than the rain gauge model when predicting runoff volume, peak flow, and time of peak. Results from this research are being used to create a local flood warning system on the Brays Bayou watershed using real-time NEXRAD radar. [ABSTRACT FROM AUTHOR]

Estimates land surface microwave emissivity over the Atmospheric Radiation Measurement Program southern Great Plains site during October 1995. Use of atmospheric microwave radiative transfer model and Special Sensor Microwave Imager satellite observations and data; Retrieval of emissivities for clear and cloudy conditions; Factors affecting emissivities.

Focuses on governmental policies and regulations concerning global satellite communications systems in the United States. Trading provisions of the Telecommunication Pact of World Trade Organization; Protocol issues affecting satellite communications; Interoperability of satellite and terrestrial communications; Account on paper satellites.

Part I. Compares different techniques for the estimation and prediction of convective rainfall applied to the Buffalo Creek in Colorado from a convection-resolving dynamic model using radar and an automated algorithmic forecast system. Precipitation estimation for flash-flood prediction; Superiority of rainfall simulations to algorithmic system.

The diurnal cycle of airflow on the island of Hawaii and the structure of the low-level flow separation line between the island-induced offshore flow and incoming trade winds are reasonably well understood. This study examines the formation and organization of nocturnal and early morning offshore Hawaiian rainbands, the flow patterns associated with these rainbands, and their relationship to the flow separation line. This investigation uses the complete radar and aircraft dataset from the 1990 Hawaiian Rainband Project. The formation and evolution of nocturnal and early morning rainfall on the windward side of the island were found to be related to four major factors: (a) the existence or absence of trade wind cloud patches arriving from the northeast Pacific, (b) the effect of island blocking on the trade wind flow as it approaches the island, (c) the low-level convergence and thermal and moisture stratification near the flow separation line, and (d) the position of the flow separation line, controlled by both the Froude number and diabatic processes (nocturnal radiative cooling and evaporative cooling) occurring over the island. If trade wind cloud patches are absent over the ocean upstream of the island, rainbands normally will not form upstream of the flow separation line. Under normal Froude number conditions, if the ratio of the low-level trade wind speed to the Brunt–Väisälä frequency, U/N, is greater than the height of the level of free convection, rainbands will form offshore over the flow separation line. Otherwise, rainbands will not form at this location. When the Froude number is elevated (typically, strong trade wind cases) rainbands will form over the windward shore independent of this ratio. If trade wind cloud patches are present, which is the typical case, light rain normally falls far from the island. These rain regions are enhanced by the weak convergence associated with island blocking and are organized into... [ABSTRACT FROM AUTHOR]

On 19 September 1996, a squall line stretching from Nebraska to Texas with intense embedded convection moved eastward across the Kansas–Oklahoma area, where special observations were taken as part of a Water Vapor Intensive Observing Period sponsored by the Atmospheric Radiation Measurement program. This provided a unique opportunity to test mesoscale data assimilation strategies for a strong convective event. In this study, a series of real-data assimilation experiments is performed using the MM5 four-dimensional variational data assimilation (4DVAR) system with a full physics adjoint. With a grid size of 20 km and 15 vertical layers, the MM5-4DVAR system successfully assimilated wind profiler, hourly rainfall, surface dewpoint, and ground-based GPS precipitable water vapor data. The MM5-4DVAR system was able to reproduce the observed rainfall in terms of precipitation pattern and amount, and substantially reduced the model errors when verified against independent observations. Additional data assimilation experiments were conducted to assess the relative importance of different types of mesoscale observations on the results of assimilation. In terms of the assimilation model’s ability to recover the vertical structure of moisture and in reproducing the rainfall pattern and amount, the wind profiler data have the maximum impact. The ground-based GPS data have a significant impact on the rainfall prediction, but have relatively small influence on the recovery of moisture structure. On the contrary, the surface dewpoint data are very useful for the recovery of the moisture structure, but have relatively small impact on rainfall prediction. The assimilation of rainfall data is very important in preserving the precipitation structure of the squall line. All the data are found to be useful in this mesoscale data assimilation experiment. Issues related to the assimilation time window, weighting of different types of observations, and the use of... [ABSTRACT FROM AUTHOR]

Heavy rainfall and flooding occurred on the Gulf Coastal Plain physiographic province of southeastern Texas in October 1994 and caused 22 deaths and more than $1 billion in damages. Record flooding occurred in the 1085 km[sup2] Spring Creek catchment, which received peak rainfall accumulations of more than 500 mm during a 12-hour period. Rainfall and flooding of greater magnitude occurred 100 km northeast of Spring Creek over Kickapoo Creek. The peak discharge of 2400 m[sup3] s[supminus1] in Kickapoo Creek at a drainage area of 148 km[sup2] places the event just below the Texas and United States envelope curve of peak discharge. Peak rainfall accumulations in Kickapoo Creek at time intervals from 15 minutes to 24 hours approached Texas and United States record values. The storms that resulted in flooding in Spring Creek and Kickapoo Creek were two components of one mesoscale convective system. The Spring Creek and Kickapoo Creek storms exhibited contrasts in storm structure, evolution, and motion that are of fundamental importance for extreme flood response of drainage basins. The Spring Creek storm produced near-record spatial cloud-to-ground lightning frequencies over Spring Creek and large, cold cloud tops. The Kickapoo Creek storm had a relatively low lightning frequency and a low echo centroid structure in radar reflectivity profiles. The envelope curve of flood peaks in Texas is defined by floods from the Edwards Plateau, which is separated from the Coastal Plain by the Balcones Escarpment. On 22 June 1997, flooding in Seco Creek, which is located in the Edwards Plateau 450 km southwest of Kickapoo Creek, resulted in a flood peak with a unit discharge comparable to that of the October 1994 Kickapoo Creek flood. The Seco Creek and Kickapoo Creek storms provide two contrasting examples of how storm structure, evolution, and motion can maximize flood peaks in a drainage basin. The storm properties that maximize flood peaks in Seco Creek and... [ABSTRACT FROM AUTHOR]

The effects of grid-cell size on surface runoff modeling using a distributed hydrologic model are examined. The raster-based hydrologic CASC2D model is applied to two watersheds in northern Mississippi. Observed streamflow for Goodwin Creek (21 km2) is used in calibrating the model's infiltration, runoff, and routing parameters. The results are extended to Hickahala-Senatobia (560 km2), which has similar physical characteristics. The applicability of CASC2D in simulating rainfall-runoff processes is tested using square grid-cell sizes ranging from 127 to 914 m. Event-based simulation results indicate that coarser grid-cell resolutions can be used in rainfall-runoff simulations as long as parameters are appropriately calibrated. It is demonstrated that the primary effect of increasing grid-cell size on simulation parameters is to require an increase in overland and channel roughness coefficients. The concept of a watershed time-to-equilibrium is used in evaluating the runoff response of overland and channel cells. At different grid-cell sizes, raster maps generated within a GRASS GIS environment provide information regarding the spatial distribution of drainage area, time-to-equilibrium, and equilibrium discharge on Goodwin Creek and Hickahala-Senatobia. It is shown that at increasing grid-cell size, the statistical distribution of drainage areas associated with overland cells is significantly increased, while the statistical distribution of drainage areas associated with channel cells is hardly affected by grid-cell size. It is also demonstrated that flow on overland cells is more sensitive to changes in grid-cell size than is channel flow. Since channel flow dominates the shape of the hydrograph in large watersheds, the results indicate that coarse grid sizes can be used for rainfall-runoff simulations on large watersheds. The results also indicate that coarser grid sizes will be more appropriate when simulating events of high intensity or of long duration. [ABSTRACT FROM AUTHOR]

The article discusses the rising environmental concern and awareness in both farm and nonfarm communities on the use of soil-applied herbicides following several contamination of groundwater due to herbicide leaching in the U.S. Herbicides are progressively important production tools of commercial citrus for the control of grasses and broadleaf weeds. In addition, leaching of chemicals including herbicides is a major concern due to the expected loss of the chemical, which then no longer gives the needed function.

The effect of beam blockage on rainfall estimates derived from radar reflectivity and specific propagation phase was evaluated from measurements of a convective rainfall event from the National Center for Atmospheric Research's S-band polarized (S-Pol) radar. This storm produced a flash flood in a mountainous watershed to the southwest of Denver, Colorado, and widespread rainfall over the plains. A beam blockage map of the region, based on a digital elevation model and characteristics of the S-Pol radiation pattern, was computed. Rain-rate estimates over both low and high beam-blockage areas were compared. Results supported the hypothesis that specific propagation phase-based quantitative precipitation estimates tend to be less influenced by terrain than reflectivity-based precipitation estimates are. [ABSTRACT FROM AUTHOR]