RSS 1.0Brockport Earth Sciences Faculty Publications
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Sedge/Grass Meadow Restoration on Former Agricultural Lands along a Lake Ontario Drowned-River-Mouth TributaryRestoration of sedge/grass meadow habitat was implemented on former agricultural lands adjacent to a Lake Ontario drowned-river-mouth tributary at an elevation that historically supports this community type. Four hectares of land were disked in spring and seeded with diverse wetland mixes containing sedges, grasses, and forbs, with additional Calamagrostis canadensis (bluejoint) and Carex stricta (upright sedge) seeds added. Seedling plugs of C. canadensis and C. stricta were also planted. Mowing at a height of 45 cm to control tall, invasive annual weeds prior to seed-set was conducted as an adaptive management practice. Three years after implementation, C. canadensis and C. stricta were not found, but seeded Carex vulpinoidea (fox sedge) was dominant, and seeded Carex lupulina (hop sedge) and Carex lurida (shallow sedge) were also present. Most invasive annuals were rare, but canopies created by larger perennials may pose future problems. Although a greenhouse seed-bank emergence study was conducted, field sampling suggested that plants growing on adjacent lands were a better predictor of future plant communities, with select seeded species serving as a secondary predictor. Failure of some sedges to survive after seeding likely was not related to stratification or diurnal temperature range. However, inadequate soil moisture related to soil type and a second-year drought likely played a role, as might loss of viability of seeds during storage. Future efforts on similar lands might use fresh Carex seeds broadcast in autumn for over-winter stratification, and specially developed seed mixes could focus on species that established at the site and native species found nearby, while avoiding some potential problem species.
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INTEGRATING WEIGHTED FLOW ACCUMULATION AND AERIAL PHOTOGRAPHY FOR DESCRIBING OVERLAND FLOW PATHS: A CASE STUDY IN WESTERN NEW YORKField measurements of overland runoff and aerial photographs were analyzed in Black Creek watershed (western New York State), to determine if a topographically based loading model could be used to identify overland flow paths in order to rank stream segments for prioritization for nutrient remediation. Discharge and phosphorous concentration were measured at twelve sites to compute the frequency of overland flow, approximate volume of overland flow and flux of phosphorous at each site. Using these metrics, sites were ranked according to their phosphorous contribution to the stream network. Although a nonparametric correlation of observed and modeled rankings suggests that flow accumulation did an inadequate job of ranking the sites, valuable management information on hydrologic connectivity was acquired by identifying where the model did not perform well. An analysis of the model showed that the performance of the weighted flow accumulation model was due primarily to its inaccuracy in estimating contributing area. The field and aerial assessments suggest that subtle anthropogenic changes to topography and hydrography, which altered surface flow paths, were the primary cause of this inaccuracy. These changes were not represented at the resolution of the USGS 10-meter DEM used in the model, either because the landscape modification took place after the source material for the DEM was created or the resolution was too low. In descending order of importance, topographic alterations include road and driveway berms, drainage ditches, stream straightening and stream squaring. One other modification type, tile drains, was important for changing the catchment area of overland flows. These features have an enormous impact on surface flow paths in the study area and were found to be important in controlling hydrologic 'connectivity' to the stream network. Identifying where these features impact surface flow paths is critical information in Best Management Practice (BMP) prioritization. Although the flow accumulation model did not accurately assess overland flow paths well enough to rank stream segments sufficiently for buffer prioritization, useful information was gleaned by overlaying the results of the model on aerial photographs and conducting field assessments. The ease with which this model approach can be carried out, requiring no calibration and needing spatial data that are available in practically all areas, make it a very effective tool for watershed planning. The study underscores the importance that anthropogenic alterations of the landscape have on hydrology and the need for better digital elevation products that represent these features.
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The Role of Sublimational Cooling in a Late-Season Midwestern Snow EventAnalysis is provided of a surprise late-season snow event over eastern Missouri and western Illinois. While snow totals failed to exceed 15 cm (6 in.) at any single location, the system was noteworthy because of the poor performance of public, private, and media forecasts in anticipating the event. Using observed data and a successful simulation with a mesoscale numerical model, the event is scrutinized to determine the forcing mechanisms for the precipitation over a small area. A region of enhanced frontogenesis is diagnosed over the region both in the observed data as well as the model output. That the precipitation fell as snow is shown to be the result of a dry layer of air between the surface and the cloud base that saturated and cooled due largely to snow sublimation–evaporation in just a few hours to permit the fall of snow uninhibited from the cloud base to the ground.
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Extracting Spatiotemporal Objects From Raster Data To Represent Physical Features and Analyze Related ProcessesNumerous ground-based, airborne, and orbiting platforms provide remotely-sensed data of remarkable spatial resolution at short time intervals. However, this spatiotemporal data is most valuable if it can be processed into information, thereby creating meaning. We live in a world of objects: cars, buildings, farms, etc. On a stormy day, we don’t see millions of cubes of atmosphere; we see a thunderstorm ‘object’. Temporally, we don’t see the properties of those individual cubes changing, we see the thunderstorm as a whole evolving and moving. There is a need to represent the bulky, raw spatiotemporal data from remote sensors as a small number of relevant spatiotemporal objects, thereby matching the human brain’s perception of the world. This presentation reveals an efficient algorithm and system to extract the objects/features from raster-formatted remotely-sensed data. The system makes use of the Python object-oriented programming language, SciPy/NumPy for matrix manipulation and scientific computation, and export/import to the GeoJSON standard geographic object data format. The example presented will show how thunderstorms can be identified and characterized in a spatiotemporal continuum using a Python program to process raster data from NOAA’s High-Resolution Rapid Refresh v2 (HRRRv2) data stream.
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Evidence of Secular Changes in Rainfall Data from the Tropical Western and Central Pacific over a 20-year PeriodRainfall data from the tropical western and central Pacific over the period from 1971 to 1990 show both decadal and interannual variability. A statistically significant secular trend may be used to model the overall rainfall variability. However, locally weighted regression analysis reveals that this increasing trend stalls in the early 1980' s, and reverses its course by the year 1990. Decomposition of individual rainfall time series into low frequency, seasonal, and irregular components facilitates the isolation of the time varying annual cycle and the elucidation of the interannual signal. Strong or prolonged warm EI Nino-Southern Oscillation events dominate the interannual variability during the study period. The decadal scale variation in the annual cycle is so systematic, in fact, there is approximately a 20% reduction in its amplitude between 1971 and 1982. In addition, the long-term change in the seasonal component appears to modulate the much shorter-term interannual signal.
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Feedback relations and causal orders between sea surface temperature and convection within the western Pacific warm poolAnalysis of time series of standardized anomalies of sea surface temperature and outgoing longwave radiation from the western Pacific warm pool revealed two distinct modes of atmosphere-ocean interaction. A statistically binding positive feedback relationship between convection and ocean temperature exists over the equatorial region surrounding the international date line. Here, the contemporaneous feedback between the/se two variables is not statistically significant. A causal order from the ocean temperature to outgoing longwave radiation is detected in a region of the Southwest Pacific, where ocean patches with temperatures greater than or equal to 29.75° C form most frequently. Dynamical implications associated with the aforementioned feedback relationship and causal order are illustrated by estimating the impact of a sudden transient LTJ.crease in convection on future values of sea surface temperature and vice versa.
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Initiation of an Elevated Mesoscale Convective System Associated with Heavy RainfallA mesoscale convective system (MCS) developed during the morning hours of 6 June 1993 and moved across northern and central Missouri, resulting in a narrow swath of excessive rainfall (.150 mm). The MCS developed well north of a surface warm front above a cool, stable boundary layer and moved east-southeast across the state. Although some features of the synoptic environment agree with the frontal flash flood composite model, predicting the elevated thunderstorms that composed the MCS posed a unique forecasting challenge. This paper first describes the diagnostic parameters of the prestorm environment that would have been helpful to predict the initiation of the MCS and the resultant locally excessive precipitation. Attention is then drawn to the MCS itself via IR satellite and WSR-88D imagery. Finally, the similarities and differences of this episode to previous studies of flash flooding and elevated thunderstorms are noted, and a summary of key parameters useful in the anticipation of this type of convection and associated heavy rainfall are offered.
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Tropical Wind Stress from Time-Averaged WindsOceanwide direct measurement of the surface wind stress is impracticable; instead, the wind stress must be parameterized in terms of individual shipboard wind reports. The number of ship observations, however, are insufficient over the tropical oceans for an adequate analysis of the wind stress. A method is developed to take advantage of the monthly mean wind field which can be determined by meshing several sources of data with the ship observations. It is shown that a single empirical correction factor can be used to estimate the surface pseudostress from monthly mean winds for all months throughout the oceanic tropics.
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The Environment of Warm-Season Elevated Thunderstorms Associated with Heavy Rainfall Over the Central United StatesTwenty-one warm-season heavy-rainfall events in the central United States produced by mesoscale convective systems (MCSs) that developed above and north of a surface boundary are examined to define the environmental conditions and physical processes associated with these phenomena. Storm-relative composites of numerous kinematic and thermodynamic fields are computed by centering on the heavy-rain-producing region of the parent elevated MCS. Results reveal that the heavy-rain region of elevated MCSs is located on average about 160 km north of a quasi-stationary frontal zone, in a region of low-level moisture convergence that is elongated westward on the cool side of the boundary. The MCS is located within the left-exit region of a south-southwesterly lowlevel jet (LLJ) and the right-entrance region of an upper-level jet positioned well north of the MCS site. The LLJ is directed toward a divergence maximum at 250 hPa that is coincident with the MCS site. Near-surface winds are light and from the southeast within a boundary layer that is statically stable and cool. Winds veer considerably with height (about 1408) from 850 to 250 hPa, a layer associated with warm-air advection. The MCS is located in a maximum of positive equivalent potential temperature ue advection, moisture convergence, and positive thermal advection at 850 hPa. Composite fields at 500 hPa show that the MCS forms in a region of weak anticyclonic curvature in the height field with marginal positive vorticity advection. Even though surfacebased stability fields indicate stable low-level air, there is a layer of convectively unstable air with maximumu e CAPE values of more than 1000 J kg21 in the vicinity of the MCS site and higher values upstream. Maximumu e convective inhibition (CIN) values over the MCS centroid site are small (less than 40 J kg21) while to the south convection is limited by large values of CIN (greater than 60 J kg21). Surface-to-500-hPa composite average relative humidity values are about 70%, and composite precipitable water values average about 3.18 cm (1.25 in.). The representativeness of the composite analysis is also examined. Last, a schematic conceptual model based upon the composite fields is presented that depicts the typical environment favorable for the development of elevated thunderstorms that lead to heavy rainfall.
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An examination of the 4 March 1999 blizzard© Copyright 2001 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyright@ametsoc.org.
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Evaluating Elevated Convection with the Downdraft Convective InhibitionA method for evaluating the penetration of a stable layer by an elevated convective downdraft is discussed. Some controversy exists on the community’s ability to define truly elevated convection from surface-based convection. By comparing the downdraft convective inhibition (DCIN) to the downdraft convective available potential energy (DCAPE), we determine that downdraft penetration potential is progressively enabled as the DCIN is progressively smaller than the DCAPE; inversely as DCIN increases over DCAPE, so does the likelihood of purely elevated convection. Serial vertical soundings and accompanying analyses are provided to support this finding.
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Assessing Upper Tropospheric Jet Streak Proximity Using the Rossby Radius of DeformationThe Rossby radius of deformation is a parameter that describes the relative role of buoyant and inertial forces for atmospheric phenomena in a flow regime. It will be demonstrated that it can also be used to determine whether or not forcing for vertical motions in the region between upper level tropospheric jet streaks overlaps or interacts. Using predefined points in the entrance and exit regions of neighboring upper level jet streaks, the distance between them is calculated for each event. If they are closer than twice the Rossby radius of deformation, the resulting region affected by both streaks is termed the Rossby Radius of Deformation Overlap Zone (RRDOZ). Plan-view and cross-sectional analysis shows that ageostrophic transverse circulations within the RRDOZ led to enhanced upward vertical velocities as predicted in prior research. Lastly, a short-term climatology for overlap events in North America is derived, and these are classified according to three proposed archetypes.
