bluuebunny/crossref_metadata_2025 huggingface dataset:
Normal-Mode Analysis of a Baroclinic Wave-Mean Oscillation
Authors: Wolfe Christopher L. , Samelson Roger M.
Published: November 2006

The stability of a time-periodic baroclinic wave-mean oscillation in a high-dimensional two-layer quasigeostrophic spectral model is examined by computing a full set of time-dependent normal modes (Floquet vectors) for the oscillation. The model has 72 × 62 horizontal resolution and there are 8928 Floquet vectors in the complete set. The Floquet vectors fall into two classes that have direct physical interpretations: wave-dynamical (WD) modes and damped-advective (DA) modes. The WD modes (which include two neutral modes related to continuous symmetries of the underlying system) have large scales and can efficiently exchange energy and vorticity with the basic flow; thus, the dynamics of the WD modes reflects the dynamics of the wave-mean oscillation. These modes are analogous to the normal modes of steady parallel flow. On the other hand, the DA modes have fine scales and dynamics that reduce, to first order, to damped advection of the potential vorticity by the basic flow. While individual WD modes have immediate physical interpretations as discrete normal modes, the DA modes are best viewed, in sum, as a generalized solution to the damped advection problem. The asymptotic stability of the time-periodic basic flow is determined by a small number of discrete WD modes and, thus, the number of independent initial disturbances, which may destabilize the basic flow, is likewise small. Comparison of the Floquet exponent spectrum of the wave-mean oscillation to the Lyapunov exponent spectrum of a nearby aperiodic trajectory suggests that this result will still be obtained when the restriction to time periodicity is relaxed.
Potential Vorticity Diagnosis of a Simulated Hurricane. Part II: Quasi-Balanced Contributions to Forced Secondary Circulations
Authors: Zhang Da-Lin , Kieu Chanh Q.
Published: November 2006

Although the forced secondary circulations (FSCs) associated with hurricane-like vortices have been previously examined, understanding is still limited to idealized, axisymmetric flows and forcing functions. In this study, the individual contributions of latent heating, frictional, and dry dynamical processes to the FSCs of a hurricane vortex are separated in order to examine how a hurricane can intensify against the destructive action of vertical shear and how a warm-cored eye forms. This is achieved by applying a potential vorticity (PV) inversion and quasi-balanced omega equations system to a cloud-resolving simulation of Hurricane Andrew (1992) during its mature stage with the finest grid size of 6 km.

It is shown that the latent heating FSC, tilting outward with height, acts to oppose the shear-forced vertical tilt of the storm, and part of the upward mass fluxes near the top of the eyewall is detrained inward, causing the convergence aloft and subsidence warming in the hurricane eye. The friction FSC is similar to that of the Ekman pumping with its peak upward motion occurring near the top of the planetary boundary layer (PBL) in the eye. About 40% of the PBL convergence is related to surface friction and the rest to latent heating in the eyewall.

In contrast, the dry dynamical forcing is determined by vertical shear and system-relative flow. When an axisymmetric balanced vortex is subjected to westerly shear, a deep countershear FSC appears across the inner-core region with the rising (sinking) motion downshear (upshear) and easterly sheared horizontal flows in the vertical. The shear FSC is shown to reduce the destructive roles of the large-scale shear imposed, as much as 40%, including its forced vertical tilt. Moreover, the shear FSC intensity is near-linearly proportional to the shear magnitude, and the wavenumber-1 vertical motion asymmetry can be considered as the integrated effects of the shear FSCs from all the tropospheric layers. The shear FSC can be attributed to the Laplacian of thermal advection and the temporal and spatial variations of centrifugal force in the quasi-balanced omega equation, and confirms the previous finding of the development of wavenumber-1 cloud asymmetries in hurricanes.

Hurricane eye dynamics are presented by synthesizing the latent heating FSC with previous studies. The authors propose to separate the eye formation from maintenance processes. The upper-level inward mass detrainment forces the subsidence warming (and the formation of an eye), the surface pressure fall, and increased rotation in the eyewall. This increased rotation will induce an additional vertical pressure gradient force to balance the net buoyancy generated by the subsidence warming for the maintenance of the hurricane eye. In this sense, the negative vertical shear in tangential wind in the eyewall should be considered as being forced by the subsidence warming, and maintained by the rotation in the eyewall.
Generation and Trapping of Gravity Waves from Convection with Comparison to Parameterization
Authors: Alexander M. Joan , Richter Jadwiga H(Beres) , Sutherland Bruce R.
Published: November 2006

Some parameterizations of gravity wave mean flow forcing in global circulation models (GCMs) add realism by describing wave generation by tropospheric convection. Because the convection in GCMs is itself a parameterized process, these convectively generated wave parameterizations necessarily use many simplifying assumptions. In this work, the authors use a realistic simulation of wave generation by convection described in previous work, which was validated by observations from the Darwin Area Wave Experiment (DAWEX), to test these assumptions and to suggest some possible improvements to the parameterizations. In particular, the authors find that wave trapping in the troposphere significantly modifies the spectrum of vertically propagating waves entering the stratosphere above convective wave sources, and offer a linear method for computing wave transmission and reflection effects on the spectrum suitable for inclusion in the parameterizations. The wave fluxes originate from both a time-varying heating mechanism and an obstacle effect mechanism acting in the simulation. Methods for including both mechanisms in the parameterizations are described. Waves emanating from the obstacle effect remain very sensitive to the depth of penetration of latent heating cells into an overlying shear zone, which will continue to make it difficult to accurately parameterize in a GCM where the convective cells are not resolved.
Internal Variability of the Winter Stratosphere. Part I: Time-Independent Forcing
Authors: Scott R. K. , Polvani L. M.
Published: November 2006

This paper examines the nature and robustness of internal stratospheric variability, namely the variability resulting from the internal dynamics of the stratosphere itself, as opposed to that forced by external sources such as the natural variability of the free troposphere. Internal stratospheric variability arises from the competing actions of radiative forcing, which under perpetual winter conditions strengthens the polar vortex, and planetary wave breaking, which weakens it. The results from a stratosphere-only model demonstrate that strong internal stratospheric variability, consisting of repeated sudden warming-type events, exists over a wide range of realistic radiative and wave forcing conditions, and is largely independent of other physical and numerical parameters. In particular, the coherent form of the variability persists as the number of degrees of freedom is increased, and is therefore not an artifact of severe model truncation. Various diagnostics, including three-dimensional representations of the potential vorticity, illustrate that the variability is determined by the vertical structure of the vortex and the extent to which upward wave propagation is favored or inhibited. In this paper, the variability arising from purely internal stratosphere dynamics is isolated by specifying thermal and wave forcings that are completely time independent. In a second paper, the authors investigate the relative importance of internal and external variability by considering time-dependent wave forcing as a simple representation of tropospheric variability.
The Role of Stationary Waves in the Maintenance of the Northern Annular Mode as Deduced from Model Experiments
Authors: Körnich Heiner , Schmitz Gerhard , Becker Erich
Published: November 2006

The influence of stationary waves on the maintenance of the tropospheric annular mode (AM) is examined in a simple global circulation model with perpetual January conditions. The presented model experiments vary in the configurations of stationary wave forcing by orography and land–sea heating contrasts. All simulations display an AM-like pattern in the lower troposphere. The zonal momentum budget shows that the feedback between eddies with periods less than 10 days and the zonal-mean zonal wind is generally the dominating process that maintains the AM. The kinetic energy of the high-frequency eddies depends on the stationary wave forcing, where orographic forcing reduces and thermal forcing enhances it. The AMs in the model experiments differ in the superposed anomalous stationary waves and in the strength of the zonally symmetric component. If only orographic stationary wave forcing is taken into account, the mountain torque decelerates the barotropic wind anomaly, and thus acts to weaken the AM. However, the combined forcing of orography and land–sea heating contrasts produces a feedback between the anomalous stationary waves and the AM that compensates for the mountain torque. The different behavior of the model experiments results from the fact that only the thermal forcing changes the character of the anomalous stationary waves from external Rossby waves for orographic forcing alone to vertically propagating waves that enable the feedback process through wave–mean flow interaction. Only with this feedback, which is shown to be due to linear zonal–eddy coupling, does the model display a strong AM with centers of action over the oceans. The main conclusions are that this process is necessary to simulate a realistic northern AM, and that it distinguishes the northern from the southern AM.
Electrification and Lightning in an Idealized Boundary-Crossing Supercell Simulation of 2 June 1995*
Authors: Fierro Alexandre O. , Gilmore Matthew S. , Mansell Edward R. , Wicker Louis J. , Straka Jerry M.
Published: November 2006

A nonhydrostatic cloud model with electrification and lightning processes was utilized to investigate how simulated supercell thunderstorms respond when they move into environments favorable for storm intensification. One model simulation was initialized with an idealized horizontally varying environment, characteristic of that observed across an outflow boundary in the west Texas Panhandle on 2 June 1995 with larger convective available potential energy (CAPE) and wind shear on the boundary’s cool side. That simulation was compared with a control simulation initialized without the boundary. The simulated right-moving supercell rapidly increased in updraft strength and volume, low-level rotation, radar reflectivity, and 40-dBZ echo-top height as it crossed the boundary, whereas the supercell that did not cross the boundary failed to intensify. For the same kinematic and microphysical evolution and the same inductive charging parameterization, four noninductive (NI) charging parameterizations were tested. In all four cases, there was a general tendency for the charge regions to be lofted higher within the updraft after crossing the boundary. Once the precipitation regions between the main storm and a secondary storm started merging farther on the cool side of the boundary, a gradual deepening and strengthening of the lowest charge regions occurred with relatively large increases in hail and graupel volume, charging rates, charge volume, charge density, and intracloud and cloud-to-ground (CG) flash rates. The negative charge present on graupel within the downdraft appeared to have a common origin via strong NI charging within the midlevel updraft in all four NI cases. Positive channels were more consistent in coming closer to the ground with time compared to negative channels within this graupel and hail-filled downdraft (four of four cases). Those NI schemes that also set up a positive dipole (three of four cases) or inverted tripole (two of four cases) above the downdraft had downward-propagating positive channels that reached ground as positive CG (+CG) flashes. The best overall performance relative to the 2 June 1995 CG lightning observations occurred within one of the rime-accretion-rate-based schemes and the Gardiner scheme as parameterized by Ziegler.
Model and Observational Analysis of the Northeast U.S. Regional Climate and Its Relationship to the PNA and NAO Patterns during Early Winter
Authors: Notaro M. , Wang W-C. , Gong W.
Published: November 2006

The relationship between the large-scale circulation and regional climate of the northeast United States is investigated for early winter using observational data and the State University of New York at Albany regional climate model. Simulated patterns of temperature, precipitation, and atmospheric circulation compare well with observations, despite a cold, dry bias. Ten December runs are analyzed to investigate the impact of the Pacific–North American (PNA) pattern on temperature, precipitation, clouds, and circulation features. During a positive PNA pattern, the simulated and observed eastern U.S. jet shifts to the southeast, coinciding with cold, dry conditions in the Northeast. This shift and intensification of the upper-level jet stream during a positive PNA pattern coincides with a greater frequency of cyclones and anticyclones along a distinct southwest–northeast track. Despite increased cyclone activity, total wintertime precipitation is below normal during a positive PNA pattern because of enhanced stability and subsidence over land, along with lower-atmospheric moisture content. Lower surface air temperatures during a positive PNA pattern result in enhanced simulated cloud cover over the Great Lakes and Atlantic Ocean due to increased thermal contrast and fluxes of sensible and latent heat, and a reduction in clouds over land. Interactions between the PNA and North Atlantic Oscillation (NAO) patterns impact the Northeast winter climate. Observed frontal passages through New York are most abundant during a negative PNA and positive NAO pattern, with a zonal upper-level jet positioned over New York. A positive PNA pattern is frequently characterized by an earlier observed Great Lakes ice season, while the greatest lake-effect snowfall occurs during a positive PNA and negative NAO pattern. The NAO pattern has the largest impact on northeast U.S. temperatures and the eastern U.S. upper-level jet during a positive PNA pattern.
Transition of the Rainfall Characteristics Related to the Moistening of the Land Surface over the Central Tibetan Plateau during the Summer of 1998
Authors: Yamada Hiroyuki , Uyeda Hiroshi
Published: November 2006

This paper describes a transition of rainfall characteristics related to the moistening of the land surface over the central Tibetan Plateau. This transition was observed three weeks after the onset of the summer rainy season of 1998. The objective is to clarify the potential of the plateau surface to modify the characteristics of monsoon rainfall. Summer rain events were first separated according to large-scale conditions into three types: one with a near-surface heat low and a Tibetan upper high, one with a near-surface low associated with a midlatitude trough, and one without a near-surface low. The first type was studied in further detail because of its intraseasonal variability in the rainfall amount (from 2.8 mm day−1 in June to 5.7 mm day−1 in August). The smaller amounts of the diurnal rain in June than July are related to the evaporation of precipitation within a drier and deeper subcloud layer. The moistening of this layer was related to the increase in the soil moisture and activation of vegetation. These results suggest a significant impact of the plateau surface upon the modification of the rainfall characteristics. This impact is the largest under the condition with a near-surface heat low forming due to strong solar heating.
Probabilistic Quantitative Precipitation Forecasts Based on Reforecast Analogs: Theory and Application
Authors: Hamill Thomas M. , Whitaker Jeffrey S.
Published: November 2006

A general theory is proposed for the statistical correction of weather forecasts based on observed analogs. An estimate is sought for the probability density function (pdf) of the observed state, given today’s numerical forecast. Assume that an infinite set of reforecasts (hindcasts) and associated observations are available and that the climate is stable. Assume that it is possible to find a set of past model forecast states that are nearly identical to the current forecast state. With the dates of these past forecasts, the asymptotically correct probabilistic forecast can be formed from the distribution of observed states on those dates.

Unfortunately, this general theory of analogs is not useful for estimating the global pdf with a limited set of reforecasts, for the chance of finding even one effectively identical forecast analog in that limited set is vanishingly small, and the climate is not stable. Nonetheless, approximations can be made to this theory to make it useful for statistically correcting weather forecasts. For instance, when estimating the state in a local region, choose the dates of analogs based on a pattern match of the local weather forecast; with a few decades of reforecasts, there are usually many close analogs.

Several approximate analog techniques are then tested for their ability to skillfully calibrate probabilistic forecasts of 24-h precipitation amount. A 25-yr set of reforecasts from a reduced-resolution global forecast model is used. The analog techniques find past ensemble-mean forecasts in a local region that are similar to today’s ensemble-mean forecasts in that region. Probabilistic forecasts are formed from the analyzed weather on the dates of the past analogs. All of the analog techniques provide dramatic improvements in the Brier skill score relative to basing probabilities on the raw ensemble counts or the counts corrected for bias. However, the analog techniques did not produce guidance that was much more skillful than that produced by a logistic regression technique. Among the analog techniques tested, it was determined that small improvements to the baseline analog technique that matches ensemble-mean precipitation forecasts are possible. Forecast skill can be improved slightly by matching the ranks of the mean forecasts rather than the raw mean forecasts by using highly localized search regions for shorter-term forecasts and larger search regions for longer forecasts, by matching precipitable water in addition to precipitation amount, and by spatially smoothing the probabilities.
Low-Level Convergence Lines over Northeastern Australia. Part II: Southerly Disturbances
Authors: Smith Roger K. , Reeder Michael J. , May Peter , Richter Harald
Published: November 2006

Observations of northward-moving borelike convergence lines over the southern part of the Gulf of Carpentaria region of northern Australia are described. Eleven such disturbances were documented during the 45-day period of the 2002 Gulf Lines Experiment. Of these, six were classified as major and five as minor, depending on their coherence throughout the region. The mean synoptic conditions leading to the two types of events were found to differ. The data for the events provide further insight into the structure and origin of borelike disturbances in the region. Two of the major events, those of 28–29 September and 9 October, are particularly noteworthy. The first of these had a clear double-change structure at all surface stations in the southeastern gulf region with an undular borelike wave preceding and separating from an airmass change in the form of a dryline. It is probably one of the best documented cases of its type. The second, which was documented in unprecedented detail by an instrumented research aircraft, consisted of three separate disturbances: one moving from the southeast, one from the south, and one from the northeast, all of which collided over the gulf. It is believed that the aircraft measurements are the first of their kind anywhere in the world. The aircraft made two long low-level transects through the disturbances and a higher-level transect where they were colliding. Various soundings were also made. The aircraft data showed clearly the undular borelike nature of the southeasterly disturbance. Measured vertical velocities in the waves were as high as 3 m s−1 at a mean altitude of about 230 m. Vertical velocities as high as 5 m s−1 were measured in the region of the collision at an altitude of about 1 km. The longevity of the bores is not explained by the vertical structure of the Scorer parameter, which indicates a leaky waveguide.
Inner-Loop Stopping Criteria for Incremental Four-Dimensional Variational Data Assimilation
Authors: Lawless A. S. , Nichols N. K.
Published: November 2006

Incremental four-dimensional variational data assimilation is a method that solves the assimilation problem by minimizing a sequence of approximate “inner-loop” functions. In any implementation of such a scheme a decision must be made as to how accurately to solve each of the inner minimization problems. In this paper recently developed theory is applied to derive a new stopping criterion for the inner-loop minimizations, which guarantees convergence of the outer loops. This new criterion is shown to give improved convergence compared with other commonly used inner-loop stopping criteria.
High-Resolution Dual-Doppler Analyses of the 29 May 2001 Kress, Texas, Cyclic Supercell
Authors: Beck Jeffrey R. , Schroeder John L. , Wurman Joshua M.
Published: November 2006

On 29 May 2001, Doppler on Wheels radars collected data on a supercell near Kress, Texas. The supercellular storm, cyclic in nature, produced multiple mesocyclones throughout its lifetime. Dual-Doppler syntheses were conducted using a grid spacing of 100 m, resulting in the highest-resolution observational analysis of a cyclic supercell to date. In addition, collection of data from ground-based radar allowed for the analysis of near-ground features irresolvable with airborne radar, providing another advantage over previous studies. The syntheses revealed a number of evolving low-level mesocyclones over the observation period of 900 s. While nontornadic during the synthesis period, the supercell exhibited evidence of strong (vertical vorticity greater than 10−2 s−1) low-level circulation with classic cyclic structure and multiple tornadoes beginning 3600 s later. A comparison between the current results, conceptual models, and previous lower-resolution analyses is presented. A striking similarity exists between the cyclic evolution of the Kress storm during the synthesis time period and other previous cyclic conceptual models. However, differences did exist between the Kress storm and previously studied tornadic storms. Analysis showed that the rear-flank downdraft provided the only surface boundary associated with low-level mesocyclogenesis. Other characteristics, including forward-flank gust front structure and the orientation of low-level horizontal vorticity, also differed. In addition, there was a general lack of surface convergence associated with the forward-flank reflectivity gradient, yet convergence associated with the forward-flank gust front increased with height. Finally, a large component of crosswise horizontal vorticity was found to exist throughout the supercell environment, within both the inflow and outflow. Incorporating these differences, an attempt was made to identify possible mechanisms responsible for the lack of tornadogenesis during the synthesis time period.
Influence of the Subtropical Andes on Baroclinic Disturbances: A Cold Front Case Study
Authors: Seluchi Marcelo E. , Garreaud RenéD. , Norte Federico A. , Saulo A. Celeste
Published: November 2006

The Andes Cordillera produces a significant disruption to the structure and evolution of the weather systems that cross South America. In particular, cold fronts tend to be “channeled” to the north immediately to the east of the Andes, fostering the advance of cold air incursions (cold surges) well into subtropical, and sometimes tropical, latitudes. In contrast, active cold fronts hardly reach subtropical latitudes along the western side of the Andes (Pacific sea border). Instead, as a cold front moves equatorward along the east side of the Andes, a marked low-level warming tends to appear along the west side of the subtropical Andes, leading to the formation of a mesoscale coastal low (or trough) in this region. To further understand the processes that lead to a contrasting evolution of the cold front at each side of the Andes, a typical frontal passage is studied in this work, using synoptic observations and a regional model [Eta–Centro de Previsão de Tempo e Estudos Climáticos (CPTEC)] simulation.

The passage of the postfrontal anticyclone over southern South America produces a poleward-pointing pressure gradient and, hence, geostrophic easterly flow at low levels. The tall and steep mountains block the flow, leading to a very small zonal wind component close to the slopes. Convergence (divergence) of the zonal flow to the east (west) of the subtropical Andes is largely compensated for by upward (downward) motion, and the associated cooling (warming) over this region. The weak zonal wind component near the Andes also breaks down the geostrophic balance over this region, giving rise to an acceleration of the southerly winds (i.e., along-barrier flow) and the consequent increase in cold advection. Therefore, to the east of the subtropical Andes both horizontal and vertical advection cool the lower troposphere, fostering the equatorward propagation of the cold front. To the west of the Andes, horizontal advection is largely offset by the strong warming associated with the enhanced subsidence over that region hindering the advance of the cold front into subtropical latitudes.
The Structure and Evolution of Hurricane Elena (1985). Part II: Convective Asymmetries and Evidence for Vortex Rossby Waves
Authors: Corbosiero Kristen L. , Molinari John , Aiyyer Anantha R. , Black Michael L.
Published: November 2006

A portable data recorder attached to the Weather Surveillance Radar-1957 (WSR-57) in Apalachicola, Florida, collected 313 radar scans of the reflectivity structure within 150 km of the center of Hurricane Elena (in 1985) between 1310 and 2130 UTC 1 September. This high temporal and spatial (750 m) resolution dataset was used to examine the evolution of the symmetric and asymmetric precipitation structure in Elena as the storm rapidly strengthened and attained maximum intensity. Fourier decomposition of the reflectivity data into azimuthal wavenumbers revealed that the power in the symmetric (wavenumber 0) component dominated the reflectivity pattern at all times and all radii by at least a factor of 2. The wavenumber 1 asymmetry accounted for less than 20% of the power in the reflectivity field on average and was found to be forced by the environmental vertical wind shear.

The small-amplitude wavenumber 2 asymmetry in the core was associated with the appearance and rotation of an elliptical eyewall. This structure was visible for nearly 2 h and was noted to rotate cyclonically at a speed equal to half of the local tangential wind. Outside of the eyewall, individual peaks in the power in wavenumber 2 were associated with repeated instances of cyclonically rotating, outward-propagating inner spiral rainbands. Four separate convective bands were identified with an average azimuthal velocity of 25 m s−1, or ∼68% of the local tangential wind speed, and an outward radial velocity of 5.2 m s−1. The azimuthal propagation speeds of the elliptical eyewall and inner spiral rainbands were consistent with vortex Rossby wave theory.

The elliptical eyewall and inner spiral rainbands were seen only in the 6-h period prior to peak intensity, when rapid spinup of the vortex had produced an annular vorticity profile, similar to those that have been shown to support barotropic instability. The appearance of an elliptical eyewall was consistent with the breakdown of eyewall vorticity into mesovortices, asymmetric mixing between the eye and eyewall, and a slowing of the intensification rate. The inner spiral rainbands might have arisen from high eyewall vorticity ejected from the core during the mixing process. Alternatively, because the bands were noted to emanate from the vertical shear-forced deep convection in the northern eyewall, they could have formed through the axisymmetrization of the asymmetric diabatically generated eyewall vorticity.
Seasonal Predictability and Spatial Coherence of Rainfall Characteristics in the Tropical Setting of Senegal
Authors: Moron Vincent , Robertson Andrew W. , Ward M. Neil
Published: November 2006

This study examines space–time characteristics of seasonal rainfall predictability in a tropical region by analyzing observed data and model simulations over Senegal. Predictability is analyzed in terms of the spatial coherence of observed interannual variability at the station scale, and within-ensemble coherence of general circulation model (GCM) simulations with observed sea surface temperatures (SSTs) prescribed. Seasonal mean rainfall anomalies are decomposed in terms of daily rainfall frequency and daily mean intensity. The observed spatial coherence is computed from a 13-station network of daily rainfall during the July–September season 1961–98 in terms of (i) interannual variability of a standardized anomaly index (i.e., the average of the normalized anomalies of each station), (ii) the external variance (i.e., the fraction of common variance among stations), and (iii) the number of spatiotemporal degrees of freedom. Spatial coherence of interannual anomalies across stations is found to be much stronger for seasonal rainfall amount and daily occurrence frequency, compared with daily mean intensity of rainfall. Combinatorial analysis of the station observations suggests that, for occurrence and seasonal amount, the empirical number of spatial degrees of freedom is largely insensitive to the number of stations considered, and is between 3 and 4 for Senegal. For daily mean intensity, by contrast, each station is found to convey almost independent information, and the number of degrees of freedom would be expected to increase for a denser network of stations. The GCM estimates of potential predictability and skill associated with the SST forcing are found to be remarkably consistent with those inferred from the observed spatial coherence: there is a moderate-to-strong skill at reproducing the interannual variations of seasonal amounts and rainfall occurrence, whereas the skill is weak for the mean intensity of rainfall. Over Senegal during July–September, it is concluded that (i) regional-scale seasonal amount and rainfall occurrence frequency are predictable from SSTs, (ii) daily mean intensity of rainfall is spatially incoherent and largely unpredictable at the regional scale, and (iii) point-score estimates of seasonal rainfall predictability and skill are subject to large sampling variability.
Principal Component Analysis of the Summertime Winds over the Gulf of California: A Gulf Surge Index
Authors: Bordoni Simona , Stevens Bjorn
Published: November 2006

A principal component analysis of the summertime near-surface Quick Scatterometer (QuikSCAT) winds is used to identify the leading mode of synoptic-scale variability of the low-level flow along the Gulf of California during the North American monsoon season. A gulf surge mode emerges from this analysis as the leading EOF, with the corresponding principal component time series interpretable as an objective index for gulf surge occurrence. This index is used as a reference time series for regression analysis and compositing meteorological fields of interest, to explore the relationship between gulf surges and precipitation over the core and marginal regions of the monsoon, as well as the manifestation of these transient events in the large-scale circulation. It is found that, although seemingly mesoscale features confined over the Gulf of California, gulf surges are intimately linked to patterns of large-scale variability of the eastern Pacific ITCZ and greatly contribute to the definition of the northward extent of the monsoonal rains.
Topographic Effects on a Wintertime Cold Front in Taiwan
Authors: Chien Fang-Ching , Kuo Ying-Hwa
Published: November 2006

This paper describes an observational and numerical study of an intense wintertime cold front that occurred in Taiwan on 8 January 1996. The front was associated with rope clouds at the leading edge, and a broad area of stratiform clouds behind. The front was blocked by the Central Mountain Range of Taiwan and divided into two sections on each side of the mountain range. As the cold air moved southward along the east coast, the increasing westward Coriolis force induced a landward acceleration. After the cold air piled up against the mountains, a coastal pressure ridge developed. The cold air damming yielded a geostrophic balance between the westward Coriolis force and the eastward component of the pressure gradient force in the x direction, and a southward acceleration in the y direction mainly caused by the southward pressure gradient force component. Over the Taiwan Strait, southward pressure gradient forces increased when the low-level stable cold air was confined over the Taiwan Strait, leading to a southward acceleration of the cold air. The formation of a windward ridge off the northwest coast of Taiwan contributed to a large southward acceleration, resulting in the development of a coastal jet. Over the Taiwan Strait, the cold air moved southward the fastest due to the channeling effect. The air parcels along the east coast of Taiwan experienced a downgradient acceleration from the cold air damming and advanced at a slower speed. Those traveling over the western plains and the nearshore coast advanced at the slowest speed. Two sensitivity runs, one without Taiwan’s topography (flat land only) and the other without Taiwan’s landmass, demonstrated the influences of Taiwan’s terrain and water–land contrast on the airflow. The run with no surface fluxes showed that the ocean modified the low-level cold air by supplying surface heat and moisture fluxes. This weakened the front, reduced low-level stability, and increased forced shallow convection (formation of rope clouds) at the leading edge.
An Assessment of ECMWF and NCEP–NCAR Reanalyses in the Southern Hemisphere at the End of the Presatellite Era: Results from the EOLE Experiment (1971–72)
Authors: Hertzog Albert , Basdevant Claude , Vial François
Published: November 2006

This article estimates the biases and standard deviations of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the 50-yr National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis (NN50) in the upper troposphere and lower stratosphere in 1971–72. These estimates are obtained by comparing the reanalyzed temperatures and winds with EOLE observations, a dataset collected during 480 superpressure-ballon flights in the Southern Hemisphere (SH). Dedicated algorithms have been developped to control the quality of this dataset and a stringent selection has been performed on the observations. None of the atmospheric centers has assimilated the EOLE dataset, which is therefore fully independent from the reanalyses. It is furthermore argued that the statistics obtained in this study at the end of the presatellite era may be representative of the reanalysis accuracy since 1957. The results of these comparisons indicate that NN50 tends to be a few degrees colder than the observations in the SH subpolar latitudes, while ERA-40 is less hit by this cold-pole issue. Both reanalyses, on the other hand, are found to be warmer than the observations by about 1 K in the subtropics. In contrast, the wind comparisons only exhibit nonsignificant or small reanalysis biases, even though the reanalyzed subtropical jet is slightly displaced equatorward with respect to the observations. The ability of reanalyses to capture the atmospheric synoptic-scale variability in the upper troposphere is assessed by computing the standard deviations of the reanalysis minus observation differences. The ERA-40 and NN50 standard deviations show a maximum (i.e., a poorer reanalysis accuracy) in the SH storm track. However, ERA-40 standard deviations are found to be much larger than NN50 standard deviations. The standard deviations also exhibit a marked decrease above the continents, stressing the heterogeneity of the atmospheric observation network during the presatellite era. Finally, in contrast with previous studies, the reanalysis accuracy does not appear to be better during summer than during winter.
Prediction of Near-Surface Variables at Independent Locations from a Bias-Corrected Ensemble Forecasting System
Authors: Yussouf Nusrat , Stensrud David J.
Published: November 2006

The ability of a multimodel short-range bias-corrected ensemble (BCE) forecasting system, created as part of NOAA’s New England High Resolution Temperature Program during the summer of 2004, to obtain accurate predictions of near-surface variables at independent locations within the model domain is explored. The original BCE approach produces bias-corrected forecasts only at National Weather Service (NWS) observing surface station locations. To extend this approach to obtain bias-corrected forecasts at any given location, an extended BCE technique is developed and applied to the independent observations provided by the Oklahoma Mesonet. First, a Cressman weighting scheme is used to interpolate the bias values of 2-m temperature, 2-m dewpoint temperature, and 10-m wind speeds calculated from the original BCE approach at the NWS observation station locations to the Oklahoma Mesonet locations. These bias values are then added to the raw numerical model forecasts bilinearly interpolated to this same specified location. This process is done for each forecast member within the ensemble and at each forecast time. It is found that the performance of the extended BCE is very competitive with the original BCE approach across the state of Oklahoma. Therefore, a simple postprocessing scheme like the extended BCE system can be used as part of an operational forecasting system to provide reasonably accurate predictions of near-surface variables at any location within the model domain.
The contested space of multinationals: Varieties of institutionalism, varieties of capitalism
Authors: Morgan Glenn , Kristensen Peer Hull
Published: November 2006

The article argues that institutionalist theory applied to multinationals focuses on the issue of ‘institutional duality’, that is, that within multinationals, actors are pressured to conform to the expectations of their home context whilst also being subjected to the transfer of practices from the home context of the MNC itself. This institutional duality leads to conflicts that can be labelled as forms of ‘micro-politics’. The head office managers transfer practices, people and resources to subsidiaries in order to maintain control and achieve their objectives. Local subsidiaries have differential capacities to resist these transfers or to develop them in their own interests depending on their institutional context. The article distinguishes institutional contexts that produce ‘Boy Scout’ subsidiaries, doing what they are told and consequently allowing locally distinctive capabilities to be undermined and those that produce ‘subversive strategists’ which look to deepen their connection with the local context not the MNC itself. These processes are exacerbated by the demands of capital markets which impose performance requirements on MNCs and lead to continuous organizational restructuring. Head offices become stronger in their attempts to impose standards in all their subsidiaries. The consequences of these processes are that except for a few pockets of ‘subversive strategists’, multinationals produce subsidiary ‘clones’ with little ability to leverage the specific assets which the institutional context provides. As it is the subversive strategists that are best placed to be innovative, the problem for the MNC is how to manage this tension.
Design and Spin Test of a Hybrid Composite Flywheel Rotor with a Split Type Hub
Authors: Ha Sung K. , Kim Myung H. , Han Sang C. , Sung Tae-Hyun
Published: November 2006

A study is conducted on lowering the radial tensile stresses and increasing the performance of the fiber wound composite flywheel rotor by applying pressure on the inner surface of the rotor using a split type hub that spreads in the radial direction due to the centrifugal force. A conventional solid or ring type hub in most cases produces tensile stresses within the rotor, possibly causing delamination and eventually lowering the maximum speed of the rotor. The relationship between the stresses of the rotor and the thickness of the hub is derived and applied to the single and hybrid rotors. A hybrid composite rotor of 180 mm inner diameter and 340 mm outer diameter is designed and fabricated, which reaches only the strength ratio of 0.58 at the maximum rotating speed of 40,000 rpm. A spin test was conducted to show the improved performance of the rotor with the split type hub by measuring the mechanical strains from the rotor. The radial and circumferential strains at four different locations are measured up to 30,000 rpm using a wireless telemetry system, and they are in good agreement with the analytical calculations. The rotor has survived a spin test of up to 40,000 rpm, which corresponds to the usable energy of at least 500 W h with the safety factor of 1.7.
How Do Organizations Allocate Rewards? The Predictive Validity of National Values, Economic and Organizational Factors Across Six Nations
Authors: Fischer Ronald , Smith Peter B. , Richey Brenda , Ferreira Maria Cristina , Assmar Eveline Maria Leal , Maes Jürgen , Stumpf Siegfried
Published: November 2006

Differences in the reported use of reward allocation principles based on equity, equality, and need in work organizations in Germany, United Kingdom, New Zealand, the United States, and Brazil are investigated. Organization-level and nation-level predictors are used to explain reported differences. Organizational, macroeconomic, and Schwartz's nation-level value indices are all found to be significant predictors. Reliance on equity is predicted by organization-level variables and high nation-level mastery. Reliance on equality is only influenced by organization-level variables. Reliance on need is predicted by the unemployment rate and high nation-level embeddedness. The results indicate that reward allocation studies that focus solely on individual-level factors will fail to detect important sources of variance. The need to consider multiple levels of explanation in cross-cultural research is discussed.
The Contribution of Ethnic Minority Status to Adaptive Style: A Comparison of Mexican, Mexican American, and European American Children
Authors: Varela R. Enrique , Steele Ric G. , Benson Eric R.
Published: November 2006

Ethnic minority status and health minority status (i.e., presence of illness) may facilitate repressive adaptive style (RAS) in an additive fashion, and a “double stigma” hypothesis has been proposed to explain this additive effect. The authors compare RAS in European American, Mexican American, and Mexican children and examine the association of RAS to the traditional values of simpatia and collectivism. Results do not confirm the hypothesis that minority status contributes to RAS; however, collectivism is a significant predictor of defensiveness supporting a cultural hypothesis for RAS.
An Examination of the Relationship Between Commitments and Culture Among Five Cultural Groups of Israeli Teachers
Authors: Cohen Aaron
Published: November 2006

This study examines the relationship between commitment forms (organizational commitment, occupational commitment, job involvement, work involvement, and group commitment) and cultural values (individualism versus collectivism, power distance, uncertainty avoidance, and masculinity versus femininity). Five groups of Israeli teachers who are assumed to represent different cultural groups (secular Jews, orthodox Jews, kibbutz teachers, Druze, and Arabs) are examined. Of the 2,269 questionnaires that are distributed in 54 schools in northern Israel, 1,328 usable questionnaires are returned, a response rate of 59%. The findings, using MANCOVA and regression analysis, show the strong effect of culture on multiple commitments. First, the five cultural groups related to commitment forms even when cultural values are controlled. Second, all of the cultural values are related to forms of commitment, and they add to the variance already explained by the cultural groups. The findings and their implications for the continuation of research on commitment and culture are discussed.
Acculturation Orientations Toward Two Majority Groups: The Case of Palestinian Arab Christian Adolescents in Israel
Authors: Horenczyk Gabriel , Munayer Salim J.
Published: November 2006

This study employs an expanded conceptualization and methodology of acculturation orientations to examine the identity and acculturation patterns of Palestinian Arab Christian adolescents in Israel, who can be seen as a “double minority”—Arabs in the midst of the majority Jewish population and Christians within Israel's dominantly Muslim Arab society. We examined the acculturation attitudes of 281 Palestinian Arab Christian adolescents in Israel and their perceptions of the expectations held by majority peers regarding their preferred mode of acculturation vis-à-vis two majority groups: Israeli Jews and Muslim Arabs. Findings suggest that Palestinian Arab Christian adolescents in Israel wish to maintain their ingroup identity; however, they expressed more willingness to adopt elements of the Jewish society than did Muslim Arabs. They also feel stronger assimilation pressures coming from Israeli Jews. These results are explained primarily in terms of differences between the two majority groups in their control over valuable resources.
Article: What We Teach and What They Use: Teaching and Learning in Scientific and Technical Communication Programs and Beyond
Authors: Brady Ann
Published: November 2006

Over the past two decades, studies have examined how social contexts influence the composition and production of workplace documents. But much remains to be known about what happens when writers move from one social context to another—from the academy to the workplace, for instance. This article demonstrates that students in scientific and technical communication classrooms learn what they are taught about composing. They take this knowledge with them to the workplace, where they apply it, practically and theoretically, and improve their understanding of it with repeated use.
Approaches/Practices: Surviving the Design and Implementation of a Content-Management System: Do the Benefits Offset the Challenges?
Authors: Pennington Lori L.
Published: November 2006

Technical communicators should be prepared to take on challenges that are beyond their daily tasks. The author took on such a challenge when she was asked to develop and implement a company's content-management system. This article addresses the different phases of designing and implementing a unified content-management system. The article also offers suggestions for any content developer faced with developing and implementing a content-management system or for any technical communication instructor who wishes to learn more about this process to help meet the academic needs of upcoming content developers.