Earth Sciences Commons^™

Preservation And Erosion Of Theropod Tracks In Eolian Deposits: Examples From The Middle Jurassic Entrada Sandstone, Utah, U.S.A., Jesper Milán, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

The Middle Jurassic Entrada Sandstone, exposed near the town of Escalante, southern Utah, consists of large-scale cross-bedded eolian deposits that are interbedded with horizontally laminated sand sheets and thin sets of eolian cross-strata, representing periods with a moister climate. The flat-bedded units contain numerous tracks and trackways from small to large-sized theropod dinosaurs. These tracks are today exposed in several distinct erosional states, allowing detailed studies of track and undertrack formation in eolian deposits. Tracks that originally were emplaced on sloping surfaces show, in their present-day erosional state, a morphology distinct from those originally emplaced on horizontal surfaces. Further, the …

Dinosaur Tectonics: A Structural Analysis Of Theropod Undertracks With A Reconstruction Of Theropod Walking Dynamics, Ole Graversen, Jesper Milán, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

A dinosaur trackway in the Middle Jurassic eolian Entrada Sandstone of southern Utah, U.S.A., exposes three undertracks that we have modeled as isolated tectonic regimes showing the development of fold-thrust ramp systems induced by the dinosaur’s feet. The faulted and folded sequence is comparable to crustal-scale tectonics associated with plate tectonics and foreland fold-thrust belts. A structural analysis of the dinosaur tracks shows the timing and direction of the forces exercised on the substrate by the animal’s foot during the stride. Based on the structural analysis, we establish a scenario for foot movements and weight distribution in the feet. During …

Quantitative Analysis Of The Calcareous Nannofossil Assemblages From Ciros-1, Victoria Land Basin, Antarctica, David K. Watkins

Department of Earth and Atmospheric Sciences: Faculty Publications

The lower portion of the CIROS-1 core (McMurdo Sound, Antarctica) has been cited as evidence for Late Eocene continental glaciation on Antarctica. A reassessment of this age determination is warranted in the face of mounting evidence from multiple proxies that continental glaciation was initiated by rapid ice-growth during the earliest Oligocene. Examination of calcareous nannofossil assemblages from this section confirmed very low fossil abundance, low species richness, and the presence of reworked taxa. A minimum of 37% of the total species richness in the section comprises reworked forms, including Late Cretaceous and latest Paleocene to Middle Eocene species. Quantitative analysis …

Evaluation Of The Streambed Leakage Concept In Analytical Models Using Data From Three Pumping Tests, Sefan J. Kollet, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Two-dimensional analytical models of pumping induced drawdown and stream depletion account for the streambed properties and stream geometry. Using data from three pumping tests performed under various hydrologic conditions, the following hypotheses were tested: (1) a partially penetrating stream at a certain distance from the pumping well can be represented by the streambed leakage term in the analytical models; (2) in the streambed leakage term, the streambed conductance coefficient λ=(WK′)/m′ accounts for the average stream width W, the streambed thickness m′, and hydraulic conductivity K′. The first hypothesis was tested by comparing results from tests under flow and no-flow stream …

Stream Network Characteristics Used To Infer The Distribution Of Fold Types In The Zagros Simply Folded Belt, Iran, Caroline M. Burberry, John W. Cosgrove, Jian Guo Liu

Department of Earth and Atmospheric Sciences: Faculty Publications

Progressive deformation at a convergent margin (the Zagros Simply Folded Belt) was analysed using satellite images, digital elevation models, contour maps and artificially generated stream networks. Two end-member fold types (fault-bend folds and detachment folds) interact with streams flowing from the High Zagros Mountains into the Persian Gulf. Growing folds divert streams and create wind or water gaps in characteristic patterns which are related to the uplift histories of the two fold types. Additionally, the symmetry of minor channels reflects the inherent symmetry of the folds. The distribution of fold types is shown for the region N27°- N30°, E50°-E54° at …

Modeling Annual Extreme Precipitation In China Using The Generalized Extreme Value Distribution, Song Feng, Saralees Nadarajah, Qi Hu

Department of Earth and Atmospheric Sciences: Faculty Publications

Extreme precipitation events are the major causes of severe floods in China. In this study, four time series of daily, 2-day, 5-day, and 10-day annual maximum precipitation from 1951 to 2000 at 651 weather stations in China were analyzed. The generalized extreme value (GEV) distribution was used, to model the annual extreme precipitation events at each station. The GEV distribution was also modified to explore the linear temporal trends in the extreme events. The results showed that more than 12% of the stations have significant (p-value < 0.10) linear trends. Decreasing trends are mainly observed in northern China, and increasing trends are observed in the Yangtze River basin and northwestern China. The return periods of extreme participation have changed stations with significant temporal trends. The 50-year event observed in parts of the Yangtze River basin, and northwestern China during the 1951-60, has become a more frequent 25-year event in the 1990s. The spatial distribution of the return levels of the 651 stations are closely related to the climatic mean precipitation, and are influenced by the East Asian summer monsoon system (return levels are measures of extremity – for example, a 10 year return level is the value that can be expected to be exceeded on average once in every 10 years). The return period of extreme precipitation, that caused the 1998 severe floods in the Yangtze River basin, was also evaluated from a probabilistic perspective.

Lithostratigraphy Of The Late Early Permian (Kungurian) Wandrawandian Siltstone, New South Wales: Record Of Glaciation?, S. G. Thomas, Christopher R. Fielding, Tracy D. Frank

Department of Earth and Atmospheric Sciences: Faculty Publications

The late Early Permian (273–271 Ma) Wandrawandian Siltstone in the southern Sydney Basin of New South Wales represents a marine highstand that can be correlated over 2000 km. A mainly fine-grained terrigenous clastic succession, the Wandrawandian Siltstone contains evidence for cold, possibly glacial conditions based on the presence of outsized clasts and glendonites, mineral pseudomorphs after ikaite, a mineral that forms in cold (0–7°C) marine sediments. A lithostratigraphic and facies analysis of the unit was conducted, based on extensive coastal outcrops and continuous drill-cores. Eight facies associations were identified: (i) siltstone; (ii) siltstone with minor interbedded sandstone; (iii) interbedded tabular …

Polarimetric Signatures And Microphysical Processes In Tornadic Southern And High Plains Classic Supercells, Matthew S. Van Den Broeke

Department of Earth and Atmospheric Sciences: Faculty Publications

Preliminary schematics of polarimetric signatures are developed for classic, tornadic supercells at low, mid, and upper levels for the Southern and High Plains. Schematics are developed for pre-tornado, tornado, and tornado demise times from a small collection of cases, most of which were cyclically tornadic. Characteristic signatures and patterns are identified for reflectivity factor (Z_HH), differential reflectivity (Z_DR), correlation coefficient (ρ_hv), specific differential phase (K_DP), and linear depolarization ratio (LDR_VH), and signatures likely related to the tornado lifecycle are discussed.

Additionally, observed changes in four polarimetric variables (Z_HH, …

Spatial And Temporal Variation In Cores From Lake Titicaca, Bolivia/Peru During The Last 13,000 Years, Sherilyn C. Fritz, P. A. Baker, P. Tapia, J. Garland

Department of Earth and Atmospheric Sciences: Faculty Publications

We compared the stratigraphy of sediment cores that span the last 13,000 yrs from three sites in the main basin of Lake Titicaca, Boliva/Peru as indicators of regional paleoclimate. The cores show similar patterns of change after ~6,400 calendar yrs before present (cal yr BP) but differ before that time. Site NE98-PC2, which is near the Rio Illave and its delta, shows differences in diatom species composition and in calcium carbonate concentrations relative to cores from the other two sites, particularly during times of inferred high precipitation. In contrast, the carbon isotopic stratigraphy of the three sites is relatively similar. …

Cold Climate In The Eastern Australian Mid- To Late Permian May Reflect Cold Upwelling Waters, Andrew T. Jones, Tracy D. Frank, Christopher R. Fielding

Department of Earth and Atmospheric Sciences: Faculty Publications

A suite of ice-rafted dropstones and glendonites throughout the Permian succession of eastern Australia indicates the cold climate associated with the late Paleozoic ice age persisted longest in this part of Gondwana. Paradoxically, these cold climate indicators are preserved in transgressive and highstand facies and formed at mid to high latitudes at a time when paleofloral and sedimentological data suggest equable onshore environments during the intervening lowstands and temperate conditions at the pole. These apparent inconsistencies suggest that eastern Australia was anomalously cold in the context of post-Sakmarian Gondwanan climates, and the distribution of sedimentary indicators could indicate localized cooling …

Upper Flow Regime Sheets, Lenses And Scour Fills: Extending The Range Of Architectural Elements For Fluvial Sediment Bodies, Christopher R. Fielding

Department of Earth and Atmospheric Sciences: Faculty Publications

Fluvial strata dominated internally by sedimentary structures of interpreted upper flow regime origin are moderately common in the rock record, yet their abundance is not appreciated and many examples may go unnoticed. A spectrum of sedimentary structures is recognised, all of which occur over a wide range of scale: 1. cross-bedding with humpback, sigmoidal and ultimately low-angle cross-sectional foreset geometries (interpreted as recording the transition from dune to upper plane bed bedform stability field), 2. planar/flat lamination with parting lineation, characteristic of the upper plane bed phase, 3. flat and low-angle lamination with minor convex-upward elements, characteristic of the transition …

Large Wind Shift On The Great Plains During The Medieval Warm Period, Venkataramana Sridhar, David B. Loope, James B. Swinehart, Joseph A. Mason, Robert J. Oglesby, Clinton M. Rowe

Department of Earth and Atmospheric Sciences: Faculty Publications

Spring-summer winds from the south move moist air from the Gulf of Mexico to the Great Plains. Rainfall in the growing season sustains prairie grasses that keep large dunes in the Nebraska Sand Hills immobile. Longitudinal dunes built during the Medieval Warm Period (800 to 1000 years before the present) record the last major period of sand mobility. These dunes are oriented NW-SE and are composed of cross-strata with bipolar dip directions. The trend and structure of the dunes record a drought that was initiated and sustained by a historically unprecedented shift of spring-summer atmospheric circulation over the Plains: Moist …

Geomorphic Impact And Rapid Subsequent Recovery From The 1996 Skeióarársandur Jökulhlaup, Iceland, Measured With Multi-Year Airborne Lidar, Laurence C. Smith, Yongwei Sheng, Francis J. Magilligan, Norman D. Smith, Basil Gomez, Leal A. K. Mertes, William B. Krabill, James B. Garvin

Department of Earth and Atmospheric Sciences: Faculty Publications

The November 1996 jökulhlaup that burst from the Vatnajökull ice cap onto Skeiðarársandur was the highest-magnitude flood ever measured on the largest active glacial outwash plain (sandur). Centimeter-scale elevation transects, measured from repeat-pass airborne laser altimetry missions flown in 1996 (pre-flood), 1997, and 2001, show that sediment deposition exceeded erosion across the central Skeiðarársandur and established an average net elevation gain of +22 cm for the event. Net elevation gains of +29 and +24 cm occurred in braided channels of the Gígjukvísl and Skeiðará rivers, respectively. Nearly half of these gains, however, were removed within 4 years, and the two …

Coupling Between Primary Terrestrial Succession And The Trophic Development Of Lakes At Glacier Bay, D. R. Engstrom, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

We use sediment cores from lakes in Glacier Bay National Park to examine the relationship between successional changes in catchment vegetation and trends in water-column nitrogen (a limiting nutrient) and lake primary production. Terrestrial succession at Glacier Bay follows several different pathways, with older sites in the lower bay being colonized directly by spruce (Picea) and by-passing a prolonged alder (Alnus) stage that characterizes younger upper-bay sites. Sediment cores from three sites spanning this successional gradient demonstrate that the variability in trophic development among lakes is a consequence of the establishment and duration of N-fixing alder …

Physical And Chemical Predictors Of Diatom Dissolution In Freshwater And Saline Lake Sediments In North America And West Greenland, David B. Ryves, Richard W. Battarbee, Stephen Juggins, Sherilyn C. Fritz, N. John Anderson

Department of Earth and Atmospheric Sciences: Faculty Publications

Diatom dissolution in surface sediment samples from two regional lake datasets in the Northern Great Plains (NGP; n = 64) and West Greenland (n = 40) is assessed using a morphological approach categorizing valves during routine diatom analysis. Two dissolution indices are derived to parameterize diatom dissolution, and, when compared between two analysts in a blind test, show good correspondence and are closely correlated to diatom fragmentation. We explore the relationships between hydrochemical and physical lake parameters (including meromixis) on dissolution within both lake regions using multivariate methods and modeled with logistic regression. Salinity is the sole significant predictor …

Geochronology And Mammalian Biostratigraphy Of Middle And Upper Paleocene Continental Strata, Bighorn Basin, Wyoming, Ross Secord, Philip D. Gingerich, M. Elliot Smith, William C. Clyde, Peter Wilf, Brad S. Singer

Department of Earth and Atmospheric Sciences: Faculty Publications

The Bighorn Basin of northwestern Wyoming preserves one of the most complete records of middle Paleocene to lower Eocene continental biota. The geochronology of this important interval depends partly on numerical calibration of the geomagnetic polarity time scale (GPTS), but the middle and late Paleocene parts of the GPTS have been poorly constrained radioisotopically. A new volcanic ash from the northern Bighorn Basin provides the first radioisotopic age for upper middle Paleocene strata (upper Selandian) and is an important calibration point for the base of polarity Chron C26n and the Selandian-Thanetian stage boundary in the GPTS. Sanidine from the ash …

Modeling The Evolution Of Natural Organic Matter In The Environment With An Agent-Based Stochastic Approach, Xiaorong Xiang, Yingping Huang, Gregory Madey, Steve Cabaniss, Leilani Arthurs, Patricia Maurice

Department of Earth and Atmospheric Sciences: Faculty Publications

Natural organic matter (NOM) is ubiquitous in terrestrial and aquatic ecosystems, and it plays a crucial role in the evolution of soils, the transport of pollutants, and the global carbon cycle. NOM is a complex mixture of molecules and is thus heterogeneous in structure and composition. As NOM passes through an ecosystem, it is acted upon by a variety of processes, such as microbial degradation, adsorption to mineral surfaces, and photochemical reactions that can change its properties and reactivity. The evolution of NOM in space and time thus is an important research area in biology, geochemistry, ecology, soil science, and …

A 2200-Year Record Of Hydrologic Variability From Foy Lake, Montana, Usa, Inferred From Diatom And Geochemical Data, Lora R. Stevens, Jeffery R. Stone, Josh Campbell, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

A 2200-yr long, high-resolution (~5 yr) record of drought variability in northwest Montana is inferred from diatoms and δ¹⁸O values of bio-induced carbonate preserved in a varved lacustrine core from Foy Lake. A previously developed model of the diatom response to lake-level fluctuations is used to constrain estimates of paleolake levels derived from the diatom data. High-frequency (decadal) fluctuations in the de-trended δ¹⁸O record mirror variations in wet/dry cycles inferred from Banff tree-rings, demonstrating the sensitivity of the oxygen-isotope values to changes in regional moisture balance. Low frequency (multi-centennial) isotopic changes may be associated with shifts …

The Last 2000 Years In Northern Yellowstone National Park Based On Multiproxy Data From Crevice Lake, Cathy Whitlock, Sherilyn C. Fritz, Brandi Bracht, Lora Stevens, Mitchell Power

Department of Earth and Atmospheric Sciences: Faculty Publications

Pollen, charcoal, diatoms, stable-isotope, and geochemical records were analyzed in high-resolution in cores obtained from Crevice Lake, a varved-sediment lake in northern Yellowstone National Park. The objective was to reconstruct the vegetation, fire, and ecohydrologic history of the watershed for the period from AD 0-1917 and compare the results with the PDSI reconstructions of Cook et al. (2004). Pollen percentages and accumulation rates provide information on vegetation and flowering season conditions. Charcoal accumulation rates (CHAR) provide information on fire activity, including fire size or intensity and fire frequency. Diatoms disclose the nature of spring nutrient status, time of ice off, …

The Late Paleozoic Ice Age Revisited, Christopher R. Fielding, Tracy D. Frank, John L. Isbell

Department of Earth and Atmospheric Sciences: Faculty Publications

The late Paleozoic Gondwanan ice age (LPGIA), which spans the late Carboniferous through early Permian, marks Earth's last complete transition into, and out of,'icehouse' conditions, and corresponds to peaks in the diversity and extent of paleotropical 'wet' forests [Gastaldo et al, 1996].Studying the LPGIA therefore has the potential to provide valuable information for understanding the Earth's transition out of the current Cenozoic ice age.

A recent two-day workshop brought together about 40 researchers from the various subdisciplines of the geosciences to (1) assess the current understanding of the timing, duration, and character of the LPGIA and how it influenced Earth's …

Pumping-Induced Drawdown And Stream Depletion In A Leaky Aquifer System, James J. Butler Jr., Xiaoyong Zhan, Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

The impact of ground water pumping on nearby streams is often estimated using analytic models of the interconnected stream-aquifer system. A common assumption of these models is that the pumped aquifer is underlain by an impermeable formation. A new semianalytic solution for drawdown and stream depletion has been developed that does not require this assumption. This solution shows that pumping-induced flow (leakage) through an underlying aquitard can be an important recharge mechanism in many stream-aquifer systems. The relative importance of this source of recharge increases with the distance between the pumping well and the stream. The distance at which leakage …

Diatom Paleolimnological Record Of Holocene Climatic And Environmental Change In The Altai Mountains, Siberia, Karlyn S. Westover, Sherilyn C. Fritz, Tatyana A. Blyakharchuk, Herbert E. Wright

Department of Earth and Atmospheric Sciences: Faculty Publications

The sedimentary diatom records of three shallow lakes in the Altai Mountains, southern Siberia, were examined to assess the nature and timing of Holocene environmental changes. Few paleoenvironmental records, especially reconstructions not based on pollen, have been reported from this region. The lakes differ in elevation, annual precipitation, and catchment vegetation. Diatom assemblages in all lakes were dominated for the entire period of record by small benthic species of Pseudostaurosira Williams & Round, Staurosira Ehrenberg, and Staurosirella Williams & Round. Planktonic taxa only occur in very low abundances (<5%). The most diverse diatom flora was found in Dzhangyskol, which is situated at the lowest elevation within a forested catchment. A lack of detailed information on the ecological preferences of the dominant taxa and the complexity of environmental drivers make direct interpretation of the diatom record difficult. However, other proxies suggest that dramatic shifts in dominance between Staurosira elliptica and Staurosirella pinnata in Grusha Ozero reflect millennial-scale variability …

Understanding Farmers’ Forecast Use From Their Beliefs, Values, Social Norms, And Perceived Obstacles*, Q. Steven Hu, Lisa M. Pytlikzillig, Gary D. Lynne, Alan Tomkins, William J. Waltman, Michael J. Hayes, Kenneth Hubbard, Ikrom Artikov, Stacey Hoffman, Donald A. Wilhite

Department of Earth and Atmospheric Sciences: Faculty Publications

Although the accuracy of weather and climate forecasts is continuously improving and new information retrieved from climate data is adding to the understanding of climate variation, use of the forecasts and climate information by farmers in farming decisions has changed little. This lack of change may result from knowledge barriers and psychological, social, and economic factors that undermine farmer motivation to use forecasts and climate information. According to the theory of planned behavior (TPB), the motivation to use forecasts may arise from personal attitudes, social norms, and perceived control or ability to use forecasts in specific decisions. These attributes are …

The Earth All Around Us: Selected Building Stone In Lincoln, Nebraska. A Walking Tour, William J. Wayne

Department of Earth and Atmospheric Sciences: Faculty Publications

Stone has been a primary building material for millennia. Cities, therefore, are treasure troves of earth materials. A wide variety of stones from many places are used for walls, as foundations to support entire buildings, as trim, and more recently as cladding (facing, an overlay). The Earth science teacher can find, in the limited space of an urban environment, a superb collection of stones with which to introduce students to these materials. The surfaces of stones on the outsides of buildings illustrate the durability and the vulnerability of each kind of stone to the local climate. And the history of …

Burrows Dug By Large Vertebrates Into Rain-Moistened Middle Jurassic Sand Dunes, David B. Loope

Department of Earth and Atmospheric Sciences: Faculty Publications

In south-central Utah, eolian cross-strata of the Escalante Member of the Entrada Sandstone contain inclined, cylindrical burrows up to 63 cm in diameter and 305 cm long. Of the 14 large tunnels located during this study, 12 descend from second- and third-order bounding surfaces that formed on the lee slopes of large dune ridges, well above the water table. The tunnels are inclined 15°–22°; one tunnel ends in an expanded chamber. Eolian cross-strata fill proximal portions of four of the tunnels and indicate that after abandonment, sand drifts migrated as much as a meter into the open shafts. Structureless sand …

Coupling Between Primary Terrestrial Succession And The Trophic Development Of Lakes At Glacier Bay, Alaska, D. R. Engstrom, Sherilyn C. Fritz

Department of Earth and Atmospheric Sciences: Faculty Publications

The natural eutrophication of lakes is still an accepted concept in limnology, arising as it does from the earliest efforts to classify lakes and place them in an evolutionary sequence. Recent studies of newly formed lakes at Glacier Bay, Alaska, only partially support this idea, and suggest more variable trends in lake trophic development which are under local (catchment-level) control. Here we use sediment cores from several lakes in Glacier Bay National Park to examine the relationship between successional changes in catchment vegetation and trends in water-column nitrogen (a limiting nutrient) and lake primary production. Terrestrial succession at Glacier Bay …

Isopiestic Measurement Of The Osmotic Coefficients Of Aqueous {Xh2So4 + (1−X)Fe2(So4)3} Solutions At 298.15 And 323.15 K, Mariano Velazquez-Rivera, Donald Palmer, Richard Kettler

Department of Earth and Atmospheric Sciences: Faculty Publications

This study measures the osmotic coefficients of {xH₂SO₄ +(1−x)Fe₂ (SO₄)₃}(aq) solutions at 298.15 and 323.15 K that have ionic strengths as great as 19.3 mol•kg^-1, using the isopiestic method. Experiments utilized both aqueous NaCl and H₂SO₄ as reference solutions. Equilibrium values of the osmotic coefficient obtained using the two different reference solutions were in satisfactory internal agreement. The solutions follow generally the Zdanovskii empirical linear relationship and yield values of a_w for the Fe₂ (SO₄)₃–H₂O binary system at 298.15 …

Reconstructing Sea-Level Change From The Internal Architecture Of Stromatolite Reefs: An Example From The Mesoproterozoic Sulky Formation, Dismal Lakes Group, Arctic Canada, L C. Kah, Julie K. Bartley, Tracy D. Frank, Timothy W. Lyons

Department of Earth and Atmospheric Sciences: Faculty Publications

The Mesoproterozoic Dismal Lakes Group, arctic Canada, contains a relatively thin, yet regionally extensive stromatolitic reef complex that developed subtidally during a major transgression, shoaled to sea level, and was overlain by intertidal to supratidal carbonate and evaporite strata. The September Lake reef complex exhibits a complex internal architecture that records the interaction between stromatolite growth and changes in accommodation space derived from both higher order (4th- or 5th-order, parasequence-scale) changes in sea level and the variable bathymetry of the sea floor. Reef growth, which was initiated during three sea-level cycles, records progressive marine transgression over depositional lows that were …

Reply To Comment By Sushil K. Singh On "A Concept Of Maximum Stream Depletion Rate For Leaky Aquifers In Alluvial Valleys", Vitaly A. Zlotnik

Department of Earth and Atmospheric Sciences: Faculty Publications

Vitaly A. Zlotnik's reply to the comment by Sushil K. Singh on Zlotnik's "A concept of maximum stream depletion rate for leaky aquifers in alluvial valleys."

Cloud-To-Ground Lightning Production In Strongly Forced, Low-Instability Convective Lines Associated With Damaging Wind, Matthew S. Van Den Broeke, David M. Schultz, Robert H. Johns, Jeffry S. Evans, John E. Hales

Department of Earth and Atmospheric Sciences: Faculty Publications

During 9–11 November 1998 and 9–10 March 2002, two similar convective lines moved across the central and eastern United States. Both convective lines initiated over the southern plains along strong surface-based cold fronts in moderately unstable environments. Both lines were initially associated with cloud-to-ground (CG) lightning, as detected by the National Lightning Detection Network, and both events met the criteria to be classified as derechos, producing swaths of widespread damaging wind. After moving into areas of marginal, if any, instability over the upper Midwest, CG lightning production ceased or nearly ceased, although the damaging winds continued. The 9 March 2002 …