Storm Of Cycle Research Articles

THE MAP ROOM: One Hundred Inches in One Hundred Hours

rom 22–27 November 2001, two complex Intermountain storm systems produced 108 inches of snow at Alta ski area in the Wasatch Mountains of northern Utah (Fig. 1; Steenburgh 2003). Since 100 in. fell in 100 h, local news media coined the phrases “100 inches in 100 hours” and “Hundred-Inch Storm Cycle” to describe the event (a storm cycle is a period where multiple winter storms occur in rapid succession). The storm cycle was the largest at Alta since 1991, provided a boost for preparations for the 2002 Winter Olympics, and produced substantial lowland precipitation. Salt Lake City International Airport (SLC) observed 1.27 in. of rain on 22 November, a record for a calendar day in that month, while during colder periods, up to 33 in. of snow fell in the Salt Lake City metropolitan area. The event provided an excellent example of the complex evolution of Intermountain winter storms, with storm stages delineated by the passage of large-scale weather features and their accompanying changes in stability and precipitation processes. Contrasts between mountain and lowland precipitation varied from stage to stage and storm to storm, illustrating the limitations of applying climatological precipitation–altitude relationships for short-range quantitative precipitation forecasting. The first storm system moved through Utah from 0600 UTC 22 to 0700 UTC 24 November, producing 50 in. of snow at Alta. Time–height sections for SLC, created from hourly National Centers for Environmental Prediction (NCEP) Rapid Update Cycle (RUC2) analyses, showed an intrusion of low-θe air aloft several hours ahead of a surface-based cold front (Fig. 2). Widespread valley rain and mountain snow ONE HUNDRED INCHES IN ONE HUNDRED HOURS The Complex Evolution of an Intermountain Winter Storm Cycle

One Hundred Inches in One Hundred Hours: Evolution of a Wasatch Mountain Winter Storm Cycle

Synoptic, orographic, and lake-effect precipitation processes during a major winter storm cycle over the Wasatch Mountains of northern Utah are examined using radar imagery, high-density surface data, and precipitation observations from Alta Ski Area [2600–3200 m above mean sea level (MSL)] and nearby Salt Lake City International Airport (1288 m MSL). The storm cycle, which occurred from 22 to 27 November 2001, included two distinct storm systems that produced 108 in. (274 cm) of snow at Alta Ski Area, including 100 in. (254 cm) during a 100-h period. Each storm system featured an intrusion of low equivalent potential temperature (θe) air aloft, well in advance of a surface-based cold front. Prefrontal precipitation became increasingly convective as low-θe air aloft moved over northern Utah, while cold frontal passage was accompanied by a convective line and a stratiform precipitation region. Postfrontal destabilization led to orographic and lake-effect snowshowers that produced two-thirds of the observed snow water equivalent at Alta. Storm stages were defined based on the passage of the above features and their accompanying changes in stability and precipitation processes. Contrasts between mountain and lowland precipitation varied dramatically from stage to stage and storm to storm, and frequently deviated from climatology, which features a nearly fourfold increase in precipitation between Salt Lake City and Alta. Based on the two storms, as well as other studies, a schematic diagram is presented that summarizes the evolution of Intermountain West snowstorms featuring an intrusion of low-θe air aloft ahead of a surface cold front. Implications for short-range quantitative precipitation forecasting and seasonal-to-annual hydrometeorological prediction are discussed.

Storm‐time distortion of the inner magnetosphere: How severe can it get?

First results are presented of an effort to model the storm‐time distortion of the magnetic field in the inner magnetosphere using space magnetometer data. Strong geomagnetic storms are relatively rare events, represented by only a small fraction of the data used in the derivation of existing empirical geomagnetic field models. Hence using those models for the mapping of the storm‐time magnetosphere is at most an extrapolation based on trends, obtained from quiet and moderately disturbed data. To overcome that limitation, a set of data was created, containing only clear‐cut events with Dst ≤ −65 nT, with the goal to derive models of the inner and near geomagnetic field (R < 15 RE), representing strongly disturbed geomagnetic configurations and their evolution during the storm cycle. The final data set included about 143,000 records with 5‐min average B‐vectors, covering 37 major storms between 1996 and 2000. Most of the data came from GOES‐8, ‐9, ‐10, Polar, and Geotail spacecraft, and two storms in February–March of 1998 were also partially covered by the data of Equator‐S. In all cases, only those storms were selected for which concurrent solar wind and IMF data were available for the entire duration of the event. Interplanetary medium data were provided by Wind, ACE, and, to a lesser extent, by IMP 8 and Geotail. The inner magnetospheric field was represented using the newly developed T01 model [Tsyganenko, 2002a, 2002b], with a duskside partial ring current with variable amplitude and scale size, an essential part of the storm‐time current system. The modeling revealed an enormous distortion and dawn‐dusk asymmetry of the inner magnetosphere during the peak of the storm main phase, caused by the combined effect of the symmetric and partial ring currents, cross‐tail current, and Birkeland currents. We found that during storms with Dst < −250 nT the tail‐like deformation of the nightside field penetrates so close to Earth that the quasi‐dipolar approximation breaks down at distances as small as 3–4 RE. This finding yields a quantitative answer to the question of why the auroras expand to unusually low latitudes during extremely strong storms. It also may provide a natural explanation for the observed impulsive injections and energizations of charged particles on the innermost L‐shells. Finally, it questions the validity of using the dipole or quasi‐dipole approximation in numerical simulations of severe storms in the inner magnetosphere.

Evolution of snow slope stability during storms

The evolution of snow slope stability during storms is investigated using simple models to calculate the shear strength of a buried layer (from its density) and the imposed shear stress (from the weight of the overburden). There is a competition between the rate of loading from new snowfall and the rate of strengthening of buried layers. In theory, unstable conditions will occur when the stability index Σ z ( t) (the ratio of the shear strength of a buried weak layer at depth z to the shear stress imposed by the overburden) approaches 1.0. A related index of practical interest is the expected time to failure t f( t) (the time when Σ z ( t) will become critical if the current conditions continue). The model is tested using measurements and observations of avalanche activity during three storm cycles at Snoqualmie Pass in the Washington Cascades. In two cases, the avalanche activity was high while in the other, few avalanches released. t f ( t) proved to be a better discriminator between stable and unstable conditions than Σ z ( t). This is because it contains information about both the magnitude and the present trend of Σ z ( t). Even if Σ z ( t) is close to critical, if it is not decreasing then slopes will remain stable. Results indicate the model may prove useful for forecasting avalanches during storms. The model is suitable for operational use because the required input (hourly measurements of precipitation, air temperature and new snow density) is routinely measured at many study sites.

Development of a prograding carbonate wedge during sea level fall: Lower Pleistocene of Rhodes, Greece

A Lower Pleistocene carbonate platform is described from north‐east Rhodes, Greece. It comprises a succession of warm temperate calcarenites (the Cape Arkhangelos calcarenite facies group) developed in a steep‐sided coastal basin. The depositional setting for the sediments is a carbonate wedge developed within a larger‐scale forced regression. Deposition began with aggradation of storm‐dominated lower and upper shoreface deposits. Later, the development of a prograding platform produced giant clinoform foresets. A marked alternation of cross‐bedded and bioturbated clinoforms indicates seasonal transport of carbonate material off the platform. Periodically, the platform edge has been deeply scoured by exceptional storms, after which further deposition repaired the platform margin, and progradation resumed. More than 20 such major storm cycles are preserved. Applying sequence stratigraphy to this succession leads to two different possible interpretations: one with a lowstand systems tract and one with a forced regressive systems tract, depending on the scale of view. The implications of this are discussed. The present example shows clearly that the application of sequence stratigraphic models to real carbonate sequences requires careful consideration of scale and context before interpretations are made.

Superposed epoch analysis applied to large-amplitude travelling convection vortices

Abstract. For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period.Key words. Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)

Superposed epoch analysis applied to large-amplitude travelling convection vortices

For the six months from 1 October 1993 to 1 April 1994 the recordings of the IMAGE magnetometer network have been surveyed in a search for large-amplitude travelling convection vortices (TCVs). The restriction to large amplitudes (>100 nT) was chosen to ensure a proper detection of evens also during times of high activity. Readings of all stations of the northern half of the IMAGE network were employed to check the consistency of the ground signature with the notation of a dual-vortex structure moving in an azimuthal direction. Applying these stringent selection criteria we detected a total of 19 clear TCV events. The statistical properties of our selection resemble the expected characteristics of large-amplitude TCVs. New and unexpected results emerged from the superposed epoch analysis. TCVs tend to form during quiet intervals embedded in moderately active periods. The occurrence of events is not randomly distributed but rather shows a clustering around a few days. These clusters recur once or twice every 27 days. Within a storm cycle they show up five to seven days after the commencement. With regard to solar wind conditions, we see the events occurring in the middle of the IMF sector structure. Large-amplitude TCVs seem to require certain conditions to make solar wind transients 'geoeffective', which have the tendency to recur with the solar rotation period.Key words. Ionosphere (Aural ionosphere; Ionosphere- magnetosphere interactions) · Magnetospheric Physics (current system)

Meiobenthic communities of the Santa Maria Basin on the California continental shelf

The Santa Maria Basin encompasses the bulk of the continental shelf off the central coast of California. Meiofauna communities on this shelf are very abundant. The average density of metazoa plus protozoans to a sediment depth of 10 cm was 4040 per 10 cm 2. Metazoan meiofauna were restricted to the surface sediments, where 84% were found in the top 4 cm. Over a 3-year period the average density within the top 4 cm of sediment was 1910 per 10 cm 2 in water depths of 90–410 m. At a depth of 565 m the density was much lower, 218 per 10 cm 2. The decrease in density correlated with a decrease in dissolved oxygen with depth. The percent of fine sediments and total organic carbon (TOC) content increased with water depth, therefore clay and carbon content were inversely correlated with density. There appears to be a seasonal cycle of increasing densities in the autumn and winter and decreasing densities in the summer. This cycle could be related to the seasonal cycle of storms and upwelling, which contribute energy to the benthos. The community structure of harpacticoid copepods was very complex. There were 115 species among 371 samples, and about 100 were undescribed species. Community structure was homogeneous between 90 and 410 m, but very different at 565 m. These changes correlated with changes in depth and sediment texture. Harpacticoid diversity also decreased with water depth. A suite of three factors; decreasing oxygen concentration and sediment grain size, and increasing TOC content; correlated with decreasing population density with water depth and with decreasing latitude across the basin.

Equilibrium slopes and cross-shore velocity asymmetries in a storm-dominated, barred nearshore system

The near-bed (0.10 m elevation), horizontal velocities were measured across a two-barred, lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low-order moments of the velocity field. Large cross-shore velocity asymmetries indicated: 1. (1) Spatially extensive and temporally persistent offshore mean flows (up to 0.18 m s −1 across the landward slope of the linear outer bar) reflecting an undertow driven by a wave-induced setup. 2. (2) An onshore directed skewness opposing the mean flow, of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar. Extensive sediment reactivation with near-zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state (volumetrically) over the storm cycle. Uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar. However, time integration of the near-bed velocity field at this location indicated an offshore net flux of water, while sedimentary structures indicated bedform migration (and thus at least bedload) almost uniformly onshore when ripples and megaripples were present. The sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near-bed velocity vector, but requires knowledge of the time-varying, instantaneous sediment transport vector. Onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period. Low-frequency oscillations were only significant close to the shoreline, but may have influenced the development of a sinuous three-dimensional inner bar form as it migrated onshore.

Is holocene storm-generated stratification in Florida Bay a reflection of solar storm cycles?

A descriptive analysis of surficial sediments of Crane Key (Florida Bay) showed that the sediments consist of storm layers (winter storm and hurricane deposits) and algal laminated sediments. Storm layers are riddled with the following types of cavities: gas escape vugs; dissolution vugs; burrows; rootholes and cryptalgal vugs. Structures and sediment types are arranged into a 15 cm thick thickening-upward, storm-generated sequence which formed in approximately 100 yr under a deepening trend. Periodograms of sea-level variations match the frequency distribution of strong intensity storms which occurred in south Florida since the beginning of this century. The calculated recurrence time of strong storms ( 10±3 yr ) and the time interval of formation of the sequence ( 100±25 yr ) are probably a response of climatic parameters to short-period (11-yr) and longer-period (90–110 yr) cycles of solar activity. Comparison with the ancient record shows analogous dm-thick storm-generated sequences probably linked to solar cycles and 10 2 yr sea-level rises.

Diagenesis of sabkha-related, sulphate nodules in the early Proterozoic Gordon Lake formation, Ontario, Canada

Unusually old (c. 2.4 Ga) loosely-packed anhydrite nodules and replacement nodules of gypsum, quartz and jasper are well preserved in transgressive marine siliciclastic sabkha sediment of the Huronian Gordon Lake Formation. There is no evidence of a gypsum precursor. The nodules are commonest in mud chip breccia at the base of sandstone, siltstone and mudstone upward-fining storm cycles. Anhydrite nodules are composed of a mosaic of blocky crystals. An earlier lath form is preserved in silicified outer rims. Its texture is similar to that of Recent displacive sabkha anhydrite nodules. Siliceous nodules are composed of megaquartz, some calcite-cored, or of jasper. Megaquartz is normally anhedral with strongly undulose (flamboyant) extinction. Crystals may be columnar or crudely spheroidal. Some megaquartz crystals are lath-shaped with the oblique extinction of lutecite. Rarer euhedral megaquartz in calcite nodule cores may have simple extinction but was probably not formed by cavity filling. Megaquartz crystals and anhydrite inclusions may preserve the texture of pre-existing early anhydrite laths. Smaller “jasper” nodules are composed of hematite-bearing fibrous fine-grained quartz, that is coarser than true jasper. Fibrous structure in this jasper may have oblique, length fast or length slow extinction, suggestive of recrystallization after lutecite, length fast and length slow chalcedony. True chert and chalcedony (<20μ) are absent. The jasper of the smaller nodules may contain ghost laths, after anhydrite? and scattered anhydrite and carbonate crystals. The jasper of larger nodules is granular. The jasper nodules contain rare gypsum crystals as well as anhydrite crystals which have been replaced to varied degrees by pseudomorphous quartz mosaics and carbonate rhombs. Some jasper nodules have an outer rim of megaquartz with anhydrite inclusions and associated carbonate. Some larger jasper nodules may have been formed in subaqueous sediments. Some weakly-silicified anhydrite nodules have been hydrated to gypsum nodules that are connected with subhorizontal gypsum veinlets. The hydration postdates silicification and conversion of anhydrite laths to blocky anhydrite. The veinlets, probably related to late unroofing, are a possible access route for water of hydration. They are later than host-rock lithification and calcite formation in the anhydrite nodules. Where the Gordon Lake Formation is metamorphosed megaquartz replacement nodules can be recognized by inclusions of anhydrite and interstitial calcite patches. These nodules are a useful indicator of vanished evaporites in such rocks. If the evaporite nodules of the Gordon Lake Formation, and the replaced evaporites of the Kona Dolomite of Michigan and the Peribonca Formation of Quebec are stratigraphically equivalent they indicate a cupriferous sabkha with an original extent of at least 1400 km.

Cincinnatian Series--Model for Cyclic and Episodic Deposition of Carbonates and Shales on a Storm-Dominated Ramp: ABSTRACT

End_Page 311------------------------------Upper Ordovician (Cincinnatian) strata in Ohio, Indiana, and Kentucky were deposited as cyclic sequences. Three types of cycles are represented: thin, graded storm cycles, moderately thick megacycles (carbonate to shale sequences), and thick shoaling-upward cycles (shale-rich, grainstone-poor facies that grade upward into shale-poor, grainstone-rich facies). Cincinnatian strata were deposited on a gently sloping, shallow-marine carbonate ramp. Sedimentation was episodic; periods of in-situ carbonate accumulation were frequently interrupted by storm events. Tropical storms affected sedimentation and benthic ecology in seven ways by: (1) eroding sediments; (2) transporting allochthonous clays and silts onto a carbonate ramp; (3) winnowing, transporting, and redistributing carbonate sediments; (4) generating downslope gravity flows; (5) mixing benthic fauna from different communities; (6) periodically interrupting the process of community succession; and (7) creating favorable conditions for the evolution and success of opportunistic species. Because of the excellent preservation of episodic storm events and their influence on sedimentation and paleoecology, the Cincinnatian Series is recognized as an example of an ancient storm-dominated, carbonate ramp. The following characteristics are diagnostic of storm domination in the rock record: (1) abundant storm sequences occur in all facies; (2) storm sequences are variable; (3) inner shelf facies have thin, discontinuous bedding; (4) rudites dominate in inner shelf facies; (5) fine grainstones are concentrated in outer-shelf facies; (6) textural inversions are common; (7) carbonate rock types are widely variable; (8) storm-generated structures occur in all facies; (9) in-situ faunal communities are rare; and (10) most beds contain a mixture of fossil-preservational states.End_of_Article - Last_Page 312------------

Waves, currents, sediment flux and morphological response in a barred nearshore system

A shore-normal array of seven, bi-directional electromagnetic flowmeters and nine surface piercing, continuous resistance wave staffs were deployed across a multiple barred nearshore at Wendake Beach, Georgian Bay, Canada, and monitored for a complete storm cycle. Time-integrated estimates of total (ITVF) and net (INVF) sediment volume flux together with bed elevation changes were determined using depth-of-activity rods. The three bars, ranging in height from 0.10 to 0.40 m accreted during the storm (0.03 m), and the troughs were scoured (0.05 m). Sediment reactivation depths reached 0.14 m and 12% of the nearshore control volume was mobilized. However, the INVF value for the storm was less than 1% of the control volume revealing a near balance in sediment volume in the bar system. Landward migration of the inner, crescentic and second, sinuous bars occurred in association with an alongshore migration of the bar form itself; the outermost, straight, shore-parallel bar remained fixed in location. The surf zone was highly dissipative throughout the storm ( ϵ = 3.8 × 10 2–192 × 10 2) and the wave spectrum was dominated by energy at the incident frequency. Spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave, respectively. The former spectral peak was within the 95% confidence band for the spectrum while the latter contributed not more than 10% to the total energy in the surface elevation spectrum even near the shoreline. During the storm wave height exceeded 2 m ( H s) and periods reached 5 s ( T p k): orbital velocities exceeded 0.5 m s −1 ( u rm s) and were above the threshold of motion for the medium-to-fine sands throughout the storm. Shore-parallel flows in excess of 0.4 m s −1 were recorded with maxima in the troughs and minima just landward of the bar crest. The rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore-normal velocity field. These hydrodynamic parameters represent “steady” flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period. Increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential (erosion); decreases in these values spatially cause a decreasing net transport potential and thus deposition. These transport potentials are increased or decreased through the gravity potential induced by the local bed slope. Shore-parallel flow was important in explaining sediment flux and morphological change where orbital velocities, mean flows and flow asymmetries were at a minimum.

An analysis of the potential of Wind Energy Conversion Systems

Wind Energy Conversion Systems (WECS) are solar systems because the sun drives the atmospheric circulation. About 20 TW of wind energy flows poleward annually, over land in temperate latitudes, in the 500 m deep atmospheric boundary layer. An average 500 GW of electricity could be generated by massive exploitation of the U.S. Great Plains wind field. There are, however, large fluctuations in available wind power. There are frequent 20% variations in annual supply; annual periodicity brings most wind power during the spring; there are storm cycles; and there is a diurnal cycle. Gusts and turbulence also require filtering to meet normal power requirements. Several schemes are evolving to tame this erratic wind power supply. Modern technology is refining horizontal-axis turbines of a wide size range. Progress is also being made toward producing an economical vertical-axis turbine. Standards for turbine performance evaluation and installation site selection are now being developed. Yet it will be a few years before proven systems can significantly affect national energy supplies. Eventually, mass-produced WECS may cost $1000 per installed, rated kW, but the wind does not often flow at turbine-rated speed. With some storage or filtering, problems with wind variability may be overcome. Then WECS electricity production may be as economical as other electric generators. No serious hazards or environmental impacts should slow WECS development.

Simulation Model for Storm Cycles and Beach Erosion on Lake Michigan

A mathematical simulation model is used to study the relations among storm cycles, beach erosion, and nearshore bar migration. The model is based on Fourier analysis of weather and wave data collected on Lake Michigan during the summers of 1969 and 1970. In the simulation of coastal processes, barometric pressure is used as the independent variable with longshore current velocity computed as the first derivative and breaker height as a filtered version of the second derivative of barometric pressure. The simulated curves are used to compute wave and longshore current energy for each storm cycle and poststorm recovery. Daily profiles across the nearshore area provide data for topographic maps and maps of erosion and deposition. For simulation, the nearshore area is broken down into five components including beach, foreshore, plunge zone, trough, and bar. A gently sloping linear plus quadratic surface is used to represent the barless topography, with bars and troughs generated by normal curves. Bar distance is computed as a function of wave energy and bottom slope. Position of the bar and trough along the shore is determined by wave and longshore current energy. Simulated maps are produced for each storm cycle and poststorm recovery.