bluuebunny/crossref_metadata_2025_split huggingface dataset:
Is There a Statistical Connection between Stratospheric Sudden Warming and Tropospheric Blocking Events?
Authors: Taguchi Masakazu 
Published: April 2008

Abstract
This paper presents statistical analyses of possible associations between major stratospheric sudden warming (SSW) and tropospheric blocking events in the Northern Hemisphere (NH) with 49 yr of NCEP–NCAR reanalysis data from 1957/58 to 2005/06. Using a random shuffling or “bootstrap” method, these analyses explore two hypotheses claiming that blocking events occur preferentially and last longer in association with SSWs (pre- and post-SSW periods are considered separately). In the shuffling method, the defined SSWs are randomly redistributed to evaluate the statistical significance of linked cases in the original data. The author’s analyses generally do not support either hypothesis for the pre- or post-SSW period when treating the SSW events all together, suggesting that such associations are not dominant modes of coupling.
A Lagrangian Spectral Parameterization of Gravity Wave Drag Induced by Cumulus Convection
Authors: Song In-Sun , Chun Hye-Yeong 
Published: April 2008

Abstract
A Lagrangian spectral parameterization of gravity wave drag (GWD) induced by cumulus convection (GWDC) is developed based on ray theory and several assumptions and implemented into the NCAR Whole Atmosphere Community Climate Model. The Lagrangian parameterization calculates explicitly gravity wave (GW) propagation that has been treated too simply in existing column-based parameterizations. For comparison with column-based parameterization, a hydrostatic and Boussinesq version of the Lagrangian parameterization is used in the present study. One-day convective GW-packet trajectories demonstrate that the Lagrangian parameterization calculates reasonably the GW-packet propagation, and GW packets propagate upward along curved paths determined by Doppler shifting and the variation of stability. The GW trajectories show that the horizontal extent of GW propagation can be as large as 20° as GWs approach critical levels. Comparison with column-based parameterization through one-month simulations indicates that the magnitude of GWDC is much increased due mainly to the vertical convergence of GW packets in the lower stratosphere and equatorial troposphere with the Lagrangian parameterization. However, this increase in GWDC is found to be essentially dependent on the horizontal propagation characteristics of GWs. In climate simulations, it is found that the easterly flow in the equatorial stratosphere and mesospheric subtropical jet are improved through the Lagrangian parameterization. With the Lagrangian parameterization, interannual variability is significantly enhanced in the equatorial lower stratosphere and exhibits a structure related to the onset of the westerly phase of the stratospheric quasi-biennial oscillations. Finally, limitations of the current Lagrangian parameterization and required improvements are noted.
Using Singular Value Decomposition to Parameterize State-Dependent Model Errors
Authors: Danforth Christopher M. , Kalnay Eugenia 
Published: April 2008

Abstract
The purpose of the present study is to use a new method of empirical model error correction, developed by Danforth et al. in 2007, based on estimating the systematic component of the nonperiodic errors linearly dependent on the anomalous state. The method uses singular value decomposition (SVD) to generate a basis of model errors and states. It requires only a time series of errors to estimate covariances and uses negligible additional computation during a forecast integration. As a result, it should be suitable for operational use at a relatively small computational expense.
The method is tested with the Lorenz ’96 coupled system as the truth and an uncoupled version of the same system as a model. The authors demonstrate that the SVD method explains a significant component of the effect that the model’s unresolved state has on the resolved state and shows that the results are better than those obtained with Leith’s empirical correction operator. The improvement is attributed to the fact that the SVD truncation effectively reduces sampling errors. Forecast improvements of up to 1000% are seen when compared with the original model. The improvements come at the expense of weakening ensemble spread.
Why Precipitation Is Mostly Concentrated over Islands in the Maritime Continent
Authors: Qian Jian-Hua 
Published: April 2008

Abstract
High-resolution observations and regional climate model simulations reveal that precipitation over the Maritime Continent is mostly concentrated over islands. Analysis of the diurnal cycles of precipitation and winds indicates that this is predominantly caused by sea-breeze convergence over islands, reinforced by mountain–valley winds and further amplified by the cumulus merger processes. Comparison of a regional climate model control simulation to a flat-island run and an all-ocean run demonstrates that the underrepresentation of islands and terrain in the Maritime Continent weakens the atmospheric disturbance associated with the diurnal cycle, and hence underestimates precipitation. The implication of these regional modeling results is that systematic errors in coarse-resolution global circulation models probably result from insufficient representation of land–sea breezes associated with the complex topography in the Maritime Continent. It is found that precipitation in the Maritime Continent, simulated by a global model, is indeed smaller than observed. The simulated upper-atmospheric velocity potential, which represents large-scale tropospheric heating, was substantially displaced eastward compared to observations. Possible approaches toward solving this problem are suggested.
Rapid Filamentation Zone in a Numerically Simulated Tropical Cyclone*
Authors: Wang Yuqing 
Published: April 2008

Abstract
In a recent study, Rozoff et al. proposed a possible mechanism to explain the formation and maintenance of the weak-echo annulus (or moat) outside of the primary eyewall of a tropical cyclone observed in radar images. By this mechanism, the moat is determined to be a region of the strain-dominated flow outside of the radius of maximum wind in which essentially all fields are filamented and deep convection is hypothesized to be highly distorted and even suppressed. This strain-dominated region is defined as the rapid filamentation zone wherein the filamentation time is shorter than the overturning time of deep convection. An attempt has been made in this study to test the hypothesis in a full-physics tropical cyclone model under idealized conditions and to extend the concept to the study of the inner-core dynamics of tropical cyclones. The foci of this paper are the evolution of the rapid filamentation zone during the storm intensification, the potential roles of rapid filamentation in the organization of inner spiral rainbands, and the damping of high azimuthal wavenumber asymmetries in the tropical cyclone inner core.
The presented results show that instead of suppressing deep convection, the strain flow in the rapid filamentation zone outside the elevated potential vorticity core provides a favorable environment for the organized inner spiral rainbands, which generally have time scales of several hours, much longer than the typical overturning time scale of individual convective clouds. Although the moat in the simulated tropical cyclone is located in the rapid filamentation zone, it is mainly controlled by the subsidence associated with the overturning flow from eyewall convection and downdrafts from the anvil stratiform precipitation outside of the eyewall. It is thus suggested that rapid filamentation is likely to play a secondary role in the formation of the moat in tropical cyclones. Although the deformation field is determined primarily by the structure of the tropical cyclone, it can have a considerable effect on the evolution of the storm. Because of strong straining deformation, asymmetries with azimuthal wavenumber &gt;4 are found to be damped effectively in the rapid filamentation zone. The filamentation time thus provides a quantitative measure of the stabilization and axisymmetrization of high-wavenumber asymmetries in the inner core by shearing deformation and filamentation.
Large-Eddy Simulations and Observations of Atmospheric Marine Boundary Layers above Nonequilibrium Surface Waves
Authors: Sullivan Peter P. , Edson James B. , Hristov Tihomir , McWilliams James C. 
Published: April 2008

Abstract
Winds and waves in marine boundary layers are often in an unsettled state when fast-running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields. A large-eddy simulation (LES) model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low-wind/fast-wave regime. It is used to simulate idealized situations with wind following and opposing fast-propagating waves (swell), and stationary bumps. LES predicts momentum transfer from the ocean to the atmosphere for wind following swell, and this can greatly modify the turbulence production mechanism in the marine surface layer. In certain circumstances the generation of a low-level jet reduces the mean shear between the surface layer and the PBL top, resulting in a near collapse of turbulence in the PBL. When light winds oppose the propagating swell, turbulence levels increase over the depth of the boundary layer and the surface drag increases by a factor of 4 compared to a flat surface. The mean wind profile, turbulence variances, and vertical momentum flux are then dependent on the state of the wave field. The LES results are compared with measurements from the Coupled Boundary Layers Air–Sea Transfer (CBLAST) field campaign. A quadrant analysis of the momentum flux from CBLAST verifies a wave age dependence predicted by the LES solutions. The measured bulk drag coefficient CD then depends on wind speed and wave state. In situations with light wind following swell, CD is approximately 50% lower than values obtained from standard bulk parameterizations that have no sea state dependence. In extreme cases with light wind and persistent swell, CD &lt; 0.
Arctic Mixed-Phase Clouds Simulated by a Cloud-Resolving Model: Comparison with ARM Observations and Sensitivity to Microphysics Parameterizations
Authors: Luo Yali , Xu Kuan-Man , Morrison Hugh , McFarquhar Greg 
Published: April 2008

Abstract
Single-layer mixed-phase stratiform (MPS) Arctic clouds, which formed under conditions of large surface heat flux combined with general subsidence during a subperiod of the Atmospheric Radiation Measurement (ARM) Program’s Mixed-Phase Arctic Cloud Experiment (MPACE), are simulated with a cloud-resolving model (CRM). The CRM is implemented with either an advanced two-moment [Morrison et al. (MCK)] or a commonly used one-moment [Lin et al. (LFO)] bulk microphysics scheme and a state-of-the-art radiative transfer scheme.
The MCK simulation, which uses the two-moment scheme and observed aerosol size distribution and ice nulei (IN) number concentration, reproduces the magnitudes and vertical structures of cloud liquid water content (LWC), total ice water content (IWC), and number concentration and effective radius of cloud droplets as suggested by the MPACE observations. The simulation underestimates ice crystal number concentrations by an order of magnitude and overestimates effective radius of ice crystals by a factor of 2–3. The LFO experiment, which uses the one-moment scheme, produces values of liquid water path (LWP) and ice plus snow water path (ISWP) that were about 30% and 4 times, respectively, those produced by MCK. The vertical profile of IWC exhibits a bimodal distribution in contrast to the constant distribution of IWC produced in MCK and observations.
A sensitivity test that uses the same ice–water saturation adjustment scheme as in LFO produces cloud properties that are more similar to the LFO simulation than MCK. The mean value of the intercept parameter of snow size spectra (N0s) from MCK is one order of magnitude smaller than that assumed in LFO. A sensitivity test that prescribes the larger LFO N0s results in 20% less LWP and 5 times larger snow water path than that in MCK. When an exponential ice size distribution replaces the gamma size distribution in MCK, the ISWP decreases by 70% but the LWP increases by 7% versus that in the MCK. Increasing the IN number concentration from the observed value of 0.16 to 3.2 L−1 forces the MPS clouds to become glaciated and dissipate, but the simulated ice number concentration agrees initially with the observations better. Physical explanations for these quantitative differences are provided. It is further shown that the differences between the LFO and MCK results are larger than those due to the estimated uncertainties in the prescribed surface fluxes. Additional observations and simulations of a variety of cases are required to further narrow down uncertainties in the microphysics schemes.
Vertical Motions in Arctic Mixed-Phase Stratiform Clouds
Authors: Shupe Matthew D. , Kollias Pavlos , Persson P. Ola G. , McFarquhar Greg M. 
Published: April 2008

Abstract
The characteristics of Arctic mixed-phase stratiform clouds and their relation to vertical air motions are examined using ground-based observations during the Mixed-Phase Arctic Cloud Experiment (MPACE) in Barrow, Alaska, during fall 2004. The cloud macrophysical, microphysical, and dynamical properties are derived from a suite of active and passive remote sensors. Low-level, single-layer, mixed-phase stratiform clouds are typically topped by a 400–700-m-deep liquid water layer from which ice crystals precipitate. These clouds are strongly dominated (85% by mass) by liquid water. On average, an in-cloud updraft of 0.4 m s−1 sustains the clouds, although cloud-scale circulations lead to a variability of up to ±2 m s−1 from the average. Dominant scales-of-variability in both vertical air motions and cloud microphysical properties retrieved by this analysis occur at 0.5–10-km wavelengths. In updrafts, both cloud liquid and ice mass grow, although the net liquid mass growth is usually largest. Between updrafts, nearly all ice falls out and/or sublimates while the cloud liquid diminishes but does not completely evaporate. The persistence of liquid water throughout these cloud cycles suggests that ice-forming nuclei, and thus ice crystal, concentrations must be limited and that water vapor is plentiful. These details are brought together within the context of a conceptual model relating cloud-scale dynamics and microphysics.
Characteristics of Summer Airflow over the Antarctic Peninsula in Response to Recent Strengthening of Westerly Circumpolar Winds
Authors: Orr Andrew , Marshall Gareth J. , Hunt Julian C. R. , Sommeria Joel , Wang Chang-Gui , van Lipzig Nicole P. M. , Cresswell Doug , King John C. 
Published: April 2008

Abstract
Summer near-surface temperatures over the northeast coast of the Antarctic Peninsula have increased by more than 2°C over the past 40 years, a temperature increase 3 times greater than that on the northwest coast. Recent analysis has shown a strong correlation between this striking warming trend and significant change in the summer Southern Hemisphere annular mode (SAM), which has resulted in greatly increased summer westerlies across the northern peninsula. It has been proposed that the strengthening westerlies have resulted in increased vertical deflection of relatively warm maritime air over the northern peninsula, contributing significantly to the observed warming and the recent collapse of northern sections of the Larsen Ice Shelf. In this study, laboratory and numerical modeling of airflow incident to the peninsula are employed to further understand this mechanism. It is shown that the effect of the strengthening westerlies has led to a distinct transition from a “blocked” regime to a “flow-over” regime, that is, confirmation of the proposed warming mechanism. The blocked regime is dominated by flow stagnation upstream (i.e., little vertical deflection) and consequent lateral deflection of flow along the western side of the peninsula. The flow-over regime is dominated by vertical deflection of mid/upper-level air over the peninsula, with strong downslope winds following closely to the leeward slope transporting this air (which warms adiabatically as it descends) to the near-surface of the northeast peninsula. The strong rotation typical of high latitudes considerably increases the flow over the peninsula, particularly strengthening it over the southern side (verified by aircraft measurements), suggesting that the warming trend is not solely confined to the northeast. Globally, flow regime transitions such as this may be responsible for other local climate variations.
Results of a prospective pilot trial on mobility after whole body vibration in children and adolescents with osteogenesis imperfecta
Authors: Semler Oliver , Fricke Oliver , Vezyroglou Katharina , Stark Christina , Stabrey Angelika , Schoenau Eckhard 
Published: April 2008

Objective: To evaluate the effect of whole body vibration on the mobility of long-term immobilized children and adolescents with a severe form of osteogenesis imperfecta. Osteogenesis imperfecta is a hereditary primary bone disorder with a prevalence from 1 in 10000 to 1 in 20000 births. Most of these children are suffering from long-term immobilization after recurrent fractures. Due to the immobilization they are affected by loss of muscle (sarcopenia) and secondary loss of bone mass. Subjects: Whole body vibration was applied to eight children and adolescents (osteogenesis imperfecta type 3, N=5; osteogenesis imperfecta type 4, N=3) over a period of six months. Interventions and results: Whole body vibration was applied by a vibrating platform (Galileo Systems) constructed on a tilting-table. Success of treatment was assessed by measuring alterations of the tilting-angle and evaluating the mobility (Brief Assessment of Motor Function). All individuals were characterized by improved muscle force documented by an increased tilting-angle (median = 35 degrees) or by an increase in ground reaction force (median at start=30.0 [N/kg] (14.48—134.21); median after six months = 146.0 [N/kg] (42.46—245.25). Conclusions: Whole body vibration may be a promising approach to improve mobility in children and adolescents severely affected with osteogenesis imperfecta.
Serial casting versus positioning for the treatment of elbow contractures in adults with traumatic brain injury: a randomized controlled trial
Authors: Moseley Anne M , Hassett Leanne M , Leung Joan , Clare Jennifer S , Herbert Robert D , Harvey Lisa A 
Published: April 2008

Objective: To compare the effects of serial casting with positioning for 1 hour per day for the treatment of elbow flexion contracture in adults with traumatic brain injury. Design: Pragmatic randomized controlled trial with concealed allocation and assessor blinding. Setting: Four brain injury rehabilitation units. Subjects: Twenty-six adults with elbow flexion contracture after traumatic brain injury participating in multidisciplinary inpatient rehabilitation. Interventions: Subjects were randomized to receive either serial casting or positioning for two weeks. In the subsequent four weeks subjects could be positioned for up to 1 hour/day. Main measures: Torque-controlled passive elbow extension was measured at baseline, post-intervention (two weeks), post-intervention plus one day, and at follow-up (four weeks post-intervention). Results: All 26 subjects completed the study. Post-intervention, serial casting reduced contracture by an average of 22 degrees (95% confidence interval (CI) 13 to 31; P <0.001) compared with the positioning group. One day later this effect had decreased to 11 degrees (95% CI 0 to 21 degrees; P= 0.052). The effect had almost completely disappeared at the four-week follow-up (mean 2 degrees, 95% CI -13 to 17; P= 0.782). Conclusions: Serial casting induces transient increases in range of motion. These effects are not maintained.
Can exercise limits prevent post-exertional malaise in chronic fatigue syndrome? An uncontrolled clinical trial
Authors: Nijs Jo , Almond Freya , De Becker Pascale , Truijen Steven , Paul Lorna 
Published: April 2008

Objective: It was hypothesized that the use of exercise limits prevents symptom increases and worsening of their health status following a walking exercise in people with chronic fatigue syndrome. Design: An uncontrolled clinical trial (semi-experimental design). Setting: Outpatient clinic of a university department. Subjects: Twenty-four patients with chronic fatigue syndrome. Interventions: Subjects undertook a walking test with the two concurrent exercise limits. Each subject walked at an intensity where the maximum heart rate was determined by heart rate corresponding to the respiratory exchange ratio = 1.0 derived from a previous submaximal exercise test and for a duration calculated from how long each patient felt they were able to walk. Main outcome measures: The Short Form 36 Health Survey or SF-36, the Chronic Fatigue Syndrome Symptom List, and the Chronic Fatigue Syndrome — Activities and Participation Questionnaire were filled in prior to, immediately after and 24 hours after exercise. Results: The fatigue increase observed immediately post-exercise (P= 0.006) returned to pre-exercise levels 24 hours post-exercise. The increase in pain observed immediately post-exercise was retained at 24 hours post-exercise (P=0.03). Fourteen of the 24 subjects experienced a clinically meaningful change in bodily pain (change of SF-36 bodily pain score ≥10); 6 indicated that the exercise bout had slightly worsened their health status, and 2 had a clinically meaningful decrease in vitality (change of SF-36 vitality score ≥20). There was no change in activity limitations/participation restrictions. Conclusion: It was shown that the use of exercise limits (limiting both the intensity and duration of exercise) prevents important health status changes following a walking exercise in people with chronic fatigue syndrome, but was unable to prevent short-term symptom increases.
Short- and long-term outcome of constraint-induced movement therapy after stroke: a randomized controlled feasibility trial
Authors: Dahl AE , Askim T. , Stock R. , Langørgen E. , Lydersen S. , Indredavik B. 
Published: April 2008

Objective: Constraint-induced movement therapy (CIMT) is a method to improve motor function in the upper extremity following stroke. The aim of this trial was to determine the effect and feasibility of CIMT compared with traditional rehabilitation in short and long term. Design: A randomized controlled trial. Setting: An inpatient rehabilitation clinic. Subjects: Thirty patients with unilateral hand impairment after stroke. Intervention: Six hours arm therapy for 10 consecutive weekdays, while using a restraining mitten on the unaffected hand. Main measures: The patients were assessed at baseline, post-treatment and at six-month follow-up using the Wolf Motor Function Test as primary outcome measure and the Motor Activity Log, Functional Independence Measure and Stroke Impact Scale as secondary measurements. Results: The CIMT group (n=18) showed a statistically significant shorter performance time (4.76 seconds versus 7.61 seconds, P= 0.030) and greater functional ability (3.85 versus 3.47, P= 0.037) than the control group (n=12) on the Wolf Motor Function Test at post-treatment assessment. There was a non-significant trend toward greater amount of use (2.47 versus 1.97, P= 0.097) and better quality of movement (2.45 versus 2.12, P=0.105) in the CIMT group according to the Motor Activity Log. No such differences were seen on Functional Independence Measure at the same time. At six-month follow-up the CIMT group maintained their improvement, but as the control group improved even more, there were no significant differences between the groups on any measurements. Conclusions: CIMT seems to be an effective and feasible method to improve motor function in the short term, but no long-term effect was found.