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Recent Refereed Journal Articles

Ashley, W. A., Mote, T. L. and M. L. Bentley, 2005: On the episodic nature of derechos.
International Journal of Climatology, 25, 1915-1932. Abstract

Bentley, M. L. and J. A. Stallins, 2005: Climatology of cloud-to-ground lightning in Georgia, USA, 1992-2003. International Journal of Climatology, 25, 1979-1996. Abstract

Bentley, M. L., and S. L. Horstmeyer, 2004: Thailand - Living with Heat. Weatherwise, 57, 1, 16-20.

Bentley, M. L. and J. Sparks, 2003: A 15-year climatology of derecho producing mesoscale convective systems over the Central and Eastern United States. Climate Research, 24, 129-139. Abstract

Bentley, Mace L., Michael Buban, Stonie Cooper, 2002: A Multiscale Observational Case Study of the Development of an Isolated High Plains Tornadic Supercell. Weather and Forecasting: Vol. 17, No. 6, pp. 1268-1276. Abstract

Bentley, Mace L., Thomas L. Mote, Paporn Thebpanya, 2002: Using Landsat to Identify Thunderstorm Damage in Agricultural Regions. Bulletin of the American Meteorological Society: Vol. 83, No. 3, pp. 363-376. Abstract

Grundstein, Andrew J., Mace L. Bentley, 2001: A Growing-Season Hydroclimatology, Focusing on Soil Moisture Deficits, for the Ohio Valley Region. Journal of Hydrometeorology: Vol. 2, No. 4, pp. 345-355. Abstract

Bentley, M. L., Mote, T. L. and S. F.Byrd, 2000: A synoptic climatology of derecho producing mesoscale convective systems (DMCSs) in the Northern Plains. International Journal of Climatology, 20, 1329-1349. Abstract

Bentley, M.L. and T.L. Mote, 2000: Synoptic Environments Associated with Cool Season Derecho Producing Mesoscale Convective Systems (DMCSs). Physical Geography, 21, 1, 21-37. Abstract

Bentley, M.L., S.F. Byrd and T.L. Mote, 1999: North Central Great Plains Derecho Producing Mesoscale Convective Systems (DMCSs): A Forecasting Primer. NOAA Technical Service Publication, National Weather Service Central Region Headquarters, TSP-08. 12 pages.

Bentley, M.L. and T.L. Mote, 1998: A Climatology of Derecho Producing Mesoscale Convective Systems 1986 - 1995, Part I: Temporal and Spatial Distribution. The Bulletin of the American Meteorological Society, 79, 11, 2527-2540. Abstract

Bentley, M.L. and S.R. Cooper, 1997: The 8 and 9 July 1993 Nebraska Derecho: An Observational Study and Comparison to the Climatology of Related Mesoscale Convective Systems. Weather and Forecasting, 12, 3,
673-683. Abstract

Mote, M.L., D. Gamble, S.J. Underwood, and M.L. Bentley, 1997: Synoptic-scale Features Common to Heavy Snowstorms in the Southeast U.S. Weather and Forecasting, 12, 1, 5-23. Abstract

Bentley, M.L., 1995: Synoptic Conditions Favorable for the Formation of the 15 July 1995 Southeastern Canada/northeastern United States Derecho Event. National Weather Digest, 21, 2, 28-36.

Recent Research Grants:
National Science Foundation, Geography and Regional Science, “Changes in the frequency of extreme warm season surface dewpoints in the Midwestern U.S.: Implications for weather-related hazards.” Accepted for funding in January 2004, for period from 2004-2006. Co-P.I. with David Changnon and Tony Stallins.

Committee for the Improvement of Undergraduate Education, Northern Illinois University, Visual Explanations: Enhancing Introductory Meteorology Instruction through Computer Graphics, 2004 Summary

National Science Foundation, Collaborative Research: A Complex Controls on the Distribution of Lightning Characteristics and Property Damage in an Urbanized Region, with Stallins, J.A., 2003-2006 Summary
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Recent Refereed Journal Articles

Ashley, W. A., Mote, T. L. and M. L. Bentley, 2005: On the episodic nature of derechos.
International Journal of Climatology, 25, 1915-1932.

Convectively generated windstorms occur over broad temporal and spatial scales; however, one of the larger-scale and most intense of these windstorms has been given the name 'derecho'. This study illustrates the
tendency for derecho-producing mesoscale convective systems to group together across the United States * forming a derecho series. The derecho series is recognized as any succession of derechos that develop
within a similar synoptic environment with no more than 72 h separating individual events. A derecho dataset for the period 1994 * 2003 was assembled to investigate the groupings of these extremely damaging
convective wind events. Results indicate that over 62% of the derechos in the dataset were members of a derecho series. On average, nearly six series affected the United States annually. Most derecho series consisted of two or three events; though, 14 series during the period of record contained four or more events. Two separate series involved nine derechos within a period of nine days. Analyses reveal that derecho
series largely frequent regions of the Midwest, Ohio Valley, and the south * central Great Plains during May, June, and July. Results suggest that once a derecho occurred during May, June, or July, there was a 58%
chance that this event was the first of a series of two or more, and about a 46% chance that this was the first of a derecho series consisting of three or more events. The derecho series climatology reveals that forecasters in regions frequented by derechos should be prepared for the probable regeneration of a derecho-producing convective system after an initial event occurs.
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Bentley, M. L. and J. A. Stallins, 2005: Climatology of cloud-to-ground lightning in Georgia, USA, 1992-2003. International Journal of Climatology, 25, 1979-1996.

A 12-year climatology of lightning cloud-to-ground flash activity for Georgia revealed the existence of three primary regions of high lightning activity: the area surrounding the Atlanta Metropolitan Statistical Area, east-central Georgia along the fall line, and along the Atlantic coast. Over 8.2 million ground flashes were identified
during the climatology. July was the most active lightning month and December was the least active. Annual, seasonal, and diurnal distributions of cloud-to-ground flashes were also examined. These patterns illustrated the interacting effects of land cover, topography, and convective instability in enhancing lightning activity throughout Georgia. A synoptic analysis of the ten highest lightning days during the summer and winter revealed the importance of frontal boundaries in organizing convection and high lightning activity during both seasons. The prominence of convective instability during the summer and strong dynamical forcing in the winter was also found to lead to outbreaks of high lightning activity.
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Bentley, M. L. and J. Sparks, 2003: A 15-year climatology of derecho producing mesoscale
convective systems over the Central and Eastern United States. Climate Research, 24, 129-139.

A 15-year (1986 - 2000) climatology of derecho producing mesoscale convective systems (DMCSs) is presented in order to better delineate their spatial and temporal patterns. Several significant results emerged from the analysis including the development of the northwest flow corridor as the dominant derecho activity region in the climatology.

Results suggest that as the sample size of DMCSs increases (230 events), the prominent derecho activity corridors across the eastern United States become located in the northern Plains through the Ohio Valley with a secondary maximum in the southern Plains. Evidence further suggests that climatological factors strongly control the distribution of derechos. For example, an anomalously strong 500 hPa height gradient existed coincident with the northern U.S. derecho activity corridor. Another aspect of derecho development is related to the temporal distribution. Evidence suggests that derecho systems tend to occur in groups or “families”, with several events occurring within several days. The synoptic environment also appears to be responsible for activating these corridors and providing an environment conducive to DMCS grouping.
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On 21 May 1995, a strong tornado developed with an isolated supercell in southwestern Nebraska. Large-scale conditions were not supportive of a tornadic thunderstorm outbreak; however, evidence suggests significant mesoscale enhancements produced a local environment favorable for strong tornado formation. This case study illustrates the importance of "situation awareness" and illustrates how mesoscale enhancements must be anticipated by forecasters in order to properly assess rapidly changing atmospheric conditions.
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During 12 and 18 August 1999, severe thunderstorms produced damaging winds and hail that caused an estimated $50 million in damage to agriculture in west-central Illinois. Landsat-7 imagery was obtained to determine the areal extent of damage and produce a crop damage dollar estimate. The normalized difference vegetation index (NDVI) was calculated for images taken "before" and "after" the severe thunderstorm events in order to examine the changes in NDVI, or vegetation vigor. A differenced image was also produced by subtracting the NDVI of the two images.

Landsat-7 data was found to be useful for identifying the areal extent of severe thunderstorm damage in west-central Illinois. In comparing the detection of damage produced by high winds and hail, it was found that hail damage was considerably easier to identify. This is due to the fact that large hail typically destroys the crops while high winds blow over corn plants that can remain rooted and survive.

Additionally, county estimates of dollar losses in crops were produced and compare favorably with estimates contained in Storm Data. Findings suggest, however, that Storm Data reports are inadequate for attempting to determine the areal extent of damage due to the difficulties in drive-by, ground-based estimation. Storm Data is primarily useful for locating the general area and extent of storm damage when reports and loss estimates were able to be obtained by the local National Weather Service Office.
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A hydroclimatology, or description of long-term means and interannual variation, that focuses on soil moisture deficits was constructed for the period of 1895-1998 for a six-state region composing the Ohio Valley. The term "deficit" is considered from an agricultural point of view whereby moisture-induced crop stress is a combination of insufficient precipitation and soil moisture. Of particular concern are deficits that occur during the growing season (May-September) when vegetation is most susceptible to moisture-induced stress. Evidence suggests that there is considerable temporal variability but no long-term trend toward either wetter or drier conditions in the Ohio Valley. The pattern of growing-season deficit is characterized by multiyear and multidecadal cycles of wet and dry periods. Decreases in precipitation during years with anomalously large growing-season deficits, however, are associated more with the reduced frequency of precipitation events than with any changes in intensity. These variations in precipitation frequency and the conditions conducive to droughts are intimately linked with large-scale atmospheric conditions, including the low-level and upper-level flow patterns.
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Synoptic-scale environments favorable for producing derechos, or widespread convectively induced windstorms, in the North-Central Plains are examined with the goal of providing pattern-recognition/diagnosis techniques. Fifteen derechos were identified across the North-Central Plains region during 1986-1995. The synoptic environment at the initiation, midpoint, and decay of each derecho was then evaluated using surface, upperair and NCAR/NCEP reanalysis datasets. Results suggest that the synoptic environment is critical in maintaining derecho producing mesoscale convective systems (DMCSs). The synoptic environment in place downstream of the MCS initiation region determines the movement and potential strength of the system. Circulation around surface low pressure increased the instability gradient and maximized leading edge convergence in the initiation region of nearly all events regardless of DMCS location or movement. Other commonalities in the environments of these events include: the presence of a weak thermal boundary, high convective instability, and a layer of dry low to mid-troposheric air. Of the two corridors sampled, northeastward moving derechos tend to initiate east of synopticscale troughs while southeastward moving derechos form on the northeast periphery of a synoptic-scale ridge. Other differences between these two DMCS events are also discussed.
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Bentley, M.L. and T.L. Mote, 2000: Synoptic Environments Associated with Cool Season Derecho Producing Mesoscale Convective Systems (DMCSs). Physical Geography, 21, 1, 21-37.

Synoptic-scale environments favorable for producing derechos in the cool season (September through February) are examined with the goal of providing useful techniques for identifying commonalities within derecho corridors. Fourteen derechos were identified from two activity corridors located in the southeastern United States and Atlantic seaboard regions between 1986 and 1995. The synoptic environment at the initiation and midpoint of each derecho was then evaluated using surface, upper-air, and the NCAR/NCEP reanalysis data sets. Models are provided in order to illustrate the synoptic-scale environment and to assist meteorologists in recognizing conditions favorable for cool-season derecho formation. Marginal instability and strong synoptic-scale forcing characterized the environments of events in both corridors. The overall synoptic patterns associated with cool-season derecho-producing mesoscale convective systems (DMCSs) resembled environments found with cool-season tornado episodes. Recognition of key elements in this environment could lead to improvements in cool-season severe weather prediction.
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In 1888, Iowa weather researcher Gustavus Hinrichs gave widespread convectively induced windstorms the name “derecho”. Refinements to this definition have evolved after numerous investigations of these systems; however, to date, a derecho climatology has not been conducted.

This investigation examines spatial and temporal aspects of derechos and their associated mesoscale convective systems that occurred from 1986 to 1995. The spatial distribution of derechos revealed four activity corridors during the summer, five during the spring, and two during the cool season. Evidence suggests that the primary warm season derecho corridor is located in the southern Great Plains. During the cool season, derecho activity was found to occur in the southeast states and along the Atlantic seaboard. Temporally, derechos are primarily late evening or overnight events during the warm season and are more evenly distributed throughout the day during the cool season.
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This study addresses a particularly damaging derecho that occurred on 8 and 9 July 1993. This progressive, warm season derecho organized in northeastern Colorado and swept through Nebraska and Kansas before dissipating in western Iowa. Records indicate this was one of the costliest single storms in Nebraska’s history.

A detailed analysis was conducted to determine which synoptic and mesoscale processes initiated, sustained, and dissipated the derecho. Research has provided insights into derecho environments and structure; however, observational studies using comprehensive datasets are necessary for comparative examinations.

This study presents several unique characteristics of the derecho-producing mesoscale convective system, including multiscale interactions and observational data with strong temporal relevance to the event. It is both the climatological and unique characteristics that are examined in this investigation.
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Mote, M.L., D. Gamble, S.J. Underwood, and M.L. Bentley, 1997: Synoptic-scale Features Common to Heavy Snowstorms in the Southeast U.S. Weather and Forecasting, 12, 1, 5-23.

Eighteen heavy snowstorms in the Southeast are examined to determine the synoptic-scale features common to these storms. Storm-relative composites in the temporal domain are created by assigning a “zero hour” to each storm based on the time of initial snowfall at Asheville, North Carolina. The composites indicate the importance of warm air advection (isentropic upglide) in producing upward motion within these storms. Of secondary importance in producing upward motion are the right entrance region of an upper-level jet streak, diabatic processes, and cyclogenetic lift. The composites also indicate that moisture is drawn off the Gulf of Mexico to feed these storms, while Atlantic moisture pools at low levels and may inhibit snowfall in the Piedmont region by limiting evaporative cooling. The surface cyclones, which deepen over the Atlantic near the Carolina coast, appear to play a small role in the development of Southeast snowstorms but often lead to heavy snowfall in the Northeast.
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Recent Research Grants:

National Science Foundation, Geography & Regional Science, “Changes in the Frequency of Extreme Warm Season Surface Dewpoints in the Midwestern U.S.: Implications for Weather-related Hazards,” with D. Changnon, 2004-2006

Land - atmosphere interactions in the Upper Midwest have been largely ignored even though it is a major agricultural region (i.e. corn and soybean) and is an area that experiences dangerous heat waves and frequent warm season thunderstorm development. Modeling studies suggest that land - atmosphere interactions in mid-continental locations are important for global induced climate changes and that even subtle land use changes may have important impacts on the occurrence of climate extremes. This study will develop a multi-decadal extreme dew point climatology, determine the temporal and spatial distribution of surface atmospheric moisture, and identify regions favorable to moisture pooling in the Upper Midwest. This will be achieved by integrating ground-based observations, high-resolution satellite data, and geographic information systems. These data and tools will allow the investigators to determine the role of land cover, vegetation (including agriculture), and topography in enhancing the spatial and temporal distributions of low-level atmospheric moisture.

Determining the spatial distribution of low-level atmospheric moisture and its source regions during the warm season will forward our understanding of patterns conducive to the development of thunderstorms and dangerous heat waves in the Upper Midwest. By detailing and mapping the evolution of warm season extreme dew point events, we will provide tools to forecasters and other researchers in mitigating the hazards associated with heat waves/heat stress conditions, derechos, and the combination of urban heat and high humidities. We will also inform emergency service agencies and the public of detailed regional risks associated with extreme dew point events.
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National Science Foundation, Collaborative Research: A Complex Controls on the Distribution of Lightning Characteristics and Property Damage in an Urbanized Region, with Stallins, J.A., 2003-2006

Lightning property damage is often less spectacular and more dispersed in time than other weather phenomena such as hurricanes or tornadoes. Consequently, lightning has been under recognized in its potential to generate large economic losses. Recent studies have found that heat generated from large urban areas may alter the local distribution of lightning strikes. However, little is known about the characteristics of this lightning and how surface properties and land-use trends influence its damage potential. Geographic studies of lightning property damage conducted to date cast lightning risk as linear and assume only one causal factor. For example, trends in lightning property damage can be attributed to background thunderstorm regime, a control imposed by the physical environment. Other studies emphasize that these loss trends are caused by an increasing societal sensitivity to thunderstorms. This investigation is unique in that the investigators simultaneously consider the physical environment and the societal template as interacting causal agents. The investigators will employ multivariate techniques, cartographic visualization, and remotely-sensed meteorological data in a geographic information systems framework to extend the knowledge of urban lightning hazards, a relatively undocumented environmental aspect of urban sprawl. The study region, Atlanta, GA, provides an ideal setting to investigate how these interactions shape lightning hazards. Recent studies have found that heat from downtown Atlanta can trigger thunderstorms in outlying counties. Evidence also suggests that densely populated suburban counties to the south and east of downtown Atlanta have high lightning strike densities approaching those along the northern Gulf Coast of Florida. The investigators will employ lightning strike data, insurance claims summaries, and spatial physiographic data to map lightning characteristics and to test hypotheses about the underlying controls of associated property damage. The investigators will also examine how the structure, location, and time of day of these thunderstorms correspond to lightning production and efficiency.

Urban weather hazards have recently been identified by the US Weather Research Program as a critically important area of research in consideration of the large economic liabilities embedded within densely-populated regions. By articulating the subtleties of lightning hazards, the investigators provide detail as to how to redistribute insurance risks and allocate emergency service resources in urbanized landscapes. Given predicted increases in lightning frequency under global warming, a baseline assessment of urban lightning hazards will be a valuable source of information for future investigations. By articulating the relationships among urban thunderstorm structure, distribution, and lightning production, contributions will also be made to the field of urban thunderstorm climatology. Finally, this investigation will extend the conceptual and methodological framework through which geographers study the complex interplay between human and natural systems.
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Presentations

Rose, L., Stallins, J. A., and M. L. Bentley, 2006: Delineating urban-enhanced lightning production: an approach using flash-defined thunderstorm tracks. Association of American Geographers Annual Meeting,
Chicago, IL, March.

Bentley, M. L., Stallins, J. A., and L. Rose, 2006: Urban lightning climatology and GIS: An analytical framework from the case study of Atlanta, Georgia, USA. European Geosciences Society 2006 General
Assembly, Vienna, Austria, April.

Bentley, M. L., Stallins, J. A., and L. Rose, 2005: The Extent of Urban-modified Cloud-to-ground Lightning Characteristics for Atlanta, Georgia (USA), 1992-2003. Asia-Oceania Geosciences Society 2nd Annual Meeting, Asia-Oceania Geosciences Society, Singapore, June.

Rose, L., Stallins, J. A., Bentley, M., and S. Lewers, 2005: The extent of urban-modified lightning production around Atlanta, Georgia. Association of American Geographers, 2005 Annual Meeting, Denver, CO, March.

Changnon, D., Sandstrom, M., Lauritsen, R., and M. L. Bentley, 2005: Increasing Midwestern dew points: Is this a result of changing agricultural practices? 16th Conference on Climate Variability and Change, American Meteorological Society, San Diego, CA, January.

Ashley, W. S., Mote, T. L., and M. L. Bentley, 2004: Derecho families. 22nd Conference on Severe Local Storms, American Meteorological Society, Hyannis, MA, October.

Graham, R., Bentley, M. L., Sparks, J. A., Dukesherer, B., and J. S. Evans, 2004: Lower Michigan MCS climatology: Trends, pattern types, and marine layer influences. 22nd Conference on Severe Local Storms, American Meteorological Society, Hyannis, MA, October.

Graham, R., and M. L. Bentley, 2004: Lower Michigan MCS Climatology: Trends, Pattern Types, and Marine Layer Impacts. 13th Great Lakes Conference on Operational Meteorology, National Weather Service, Buffalo, NY, August.

Bentley, M. L. and T. S. Stallins, 2004: A descriptive lightning climatology for Georgia, 1992-2002. International Conference on Storms, Australian Bureau of Meteorology, Brisbane, Australia, July.

Ashley, W. S. and M. L. Bentley, 2004: Long-lived, convectively generated high wind events in the United States: A climatology and assessment of hazards. International Conference on Storms, Australian Bureau of Meteorology, Brisbane, Australia, July.

Wassel, G. A., Ashley, W. S., Bentley, M. L., and T. L. Mote, 2004: On the episodic nature of long-lived, convectively generated high-wind events in the United States. Association of American Geographers, Centennial Meeting, Philadelphia, PA, March.

Bentley, M. L., Sparks, J., and R. Graham, 2003: The effect of Lake Michigan on the sustenance of mesoscale convective systems. Part I: Short-term climatology. Fall meeting, American Geophysical Union, San Francisco, CA, December.

Ashley, W. S., Bentley, M. L., and T. L. Mote, 2003: A preliminary investigation into derecho families. 28th Annual Meeting of the National Weather Association, Jacksonville, FL, October.

Bentley, M. L., Sparks, J., and R. Graham, 2003: The effect of the United States Great Lakes on the maintenance of mesoscale convective systems. AGU/EGU/EGS Joint Assembly, Nice, France, April.
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Mace Bentley