bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for a Rapid Global Climate Shift across the Late 1960s
Authors: Baines Peter G. , Folland Chris K. 
Published: June 2007

Abstract
It is shown that a number of important characteristics of the global atmospheric circulation and climate changed in a near-monotonic fashion over the decade, or less, centered on the late 1960s. These changes were largest or commonest in tropical regions, the Southern Hemisphere, and the Atlantic sector of the Northern Hemisphere. Some, such as the decrease in rainfall in the African Sahel, are well known. Others appear to be new, but their combined extent is global and dynamical linkages between them are evident. The list of affected variables includes patterns of SST; tropical rainfall in the African Sahel and Sudan, the Amazon basin, and northeast Brazil; pressure and SST in the tropical North Atlantic and the west and central Pacific; various branches of the southern Hadley circulation and the southern subtropical jet stream; the summer North Atlantic Oscillation; south Greenland temperature; the Southern Hemisphere storm track; and, quite likely, the Antarctic sea ice boundary. These changes are often strongest in the June–August season; changes are also seen in December–February but are generally smaller. In Greenland, annual mean temperature seems to be affected strongly, reflecting similar changes in SST throughout the year in the higher latitudes of the North Atlantic. Possible causes for these coordinated changes are briefly evaluated. The most likely candidates appear to be a likely reduction in the northward oceanic heat flux associated with the North Atlantic thermohaline circulation in the 1950s to 1970s, which was nearly in phase with a rapid increase in anthropogenic aerosol emissions during the 1950s and 1960s, particularly over Europe and North America.
A Bayesian Assessment of Climate Change Using Multimodel Ensembles. Part II: Regional and Seasonal Mean Surface Temperatures
Authors: Min Seung-Ki , Hense Andreas 
Published: June 2007

Abstract
A Bayesian approach is applied to the observed regional and seasonal surface air temperature (SAT) changes using single-model ensembles (SMEs) with the ECHO-G model and multimodel ensembles (MMEs) of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) simulations. Bayesian decision classifies observations into the most probable scenario out of six available scenarios: control (CTL), natural forcing (N), anthropogenic forcing (ANTHRO), greenhouse gas (G), sulfate aerosols (S), and natural plus anthropogenic forcing (ALL). Space–time vectors of the detection variable are constructed for six continental regions (North America, South America, Asia, Africa, Australia, and Europe) by combining temporal components of SATs (expressed as Legendre coefficients) from two or three subregions of each continental region.
Bayesian decision results show that over most of the regions observed SATs are classified into ALL or ANTHRO scenarios for the whole twentieth century and its second half. Natural forcing and ALL scenarios are decided during the first half of the twentieth century, but only in the low-latitude region (Africa and South America), which might be related to response patterns to solar forcing. Overall seasonal decisions follow annual results, but there are notable seasonal dependences that differ between regions. A comparison of SME and MME results demonstrates that the Bayesian decisions for regional-scale SATs are largely robust to intermodel uncertainties as well as prior probability and temporal scales, as found in the global results.
Intraseasonal Convective Perturbations Related to the Seasonal March of the Indo-Pacific Monsoons
Authors: Bellenger H. , Duvel J. P. 
Published: June 2007

Abstract
The seasonal evolution of the 20–90-day intraseasonal variability (ISV) of the convection in the Indo-Pacific region presents intriguing features related to monsoon dynamics: (i) a sharp ISV maximum in May for the southern Bay of Bengal and in June for the eastern Arabian Sea, (ii) a maximum ISV over the west Pacific in July–September when the ISV over the northern Indian Ocean is weaker, (iii) a persistent ISV north of Australia from December to March, and (iv) a weak ISV over continental regions. The source of these behaviors is investigated from time series of satellite observations, meteorological reanalysis, and from an ocean mixed layer depth (MLD) climatology. For the northern Indian Ocean, sharp ISV maxima in May and June, when the MLD is still small (∼20–30 m), are related to an abrupt surface cooling associated with the setting of the monsoon low-level jet. The ISV of the convection is smaller over these regions during July–September when the MLD is deepened (∼60–70 m) by the monsoon low-level wind forcing. At this time, the low-level wind is weak over the west Pacific, the MLD is small, and the amplitude of the ISV remains large. North of Australia, and also over the south equatorial Indian Ocean, there is no particular reinforcement of the ISV near the onset. A weak low-level jet and a small MLD prevail during the whole monsoon season in good agreement with a more uniform ISV. These results support the hypothesis that a moderately shallow (∼20–30 m) ocean mixed layer is important for maintaining locally the ISV of the convection, when the conditions (e.g., SST, large-scale circulation) for such an ISV to exist are satisfied. The seasonal variability of the MLD, related in part to the monsoon low-level jet variability over the tropical oceans, thus gives a link between the seasonal march of monsoon circulations and the seasonal evolution of the ISV of the convection. This has implications for a better understanding of the origin of the ISV and for the predictability of its amplitude, especially near the monsoon onset date.
Diagnosing Summertime Mesoscale Vertical Motion: Implications for Atmospheric Data Assimilation
Authors: Pagé Christian , Fillion Luc , Zwack Peter 
Published: June 2007

Abstract
Balance omega equations have recently been used to try to improve the characterization of balance in variational data assimilation schemes for numerical weather prediction (NWP). Results from Fisher and Fillion et al. indicate that a quasigeostrophic omega equation can be used adequately in the definition of the control variable to represent synoptic-scale balanced vertical motion. For high-resolution limited-area data assimilation and forecasting (1–10-km horizontal resolution), such a diagnostic equation for vertical motion needs to be revisited. Using a state-of-the-art NWP forecast model at 2.5-km horizontal resolution, these issues are examined. Starting from a complete diagnostic partial differential equation for omega, the rhs forcing terms were computed from model-generated fields. These include the streamfunction, temperature, and physical time tendencies of temperature in gridpoint space. To accurately compute one term of second-order importance (i.e., the ageostrophic vorticity tendency forcing term), a special procedure was used. With this procedure it is shown that Charney’s balance equation brings significant information in order to deduce the geostrophic time tendency term. Under these conditions, results show that for phenomena of length scales of 15–100 km over convective regions, a diagnostic equation can capture the major part of the model-generated vertical motion. The limitations of the digital filter initialization approach when used as in Fillion et al. with a cutoff period reduced to 1 h are also illustrated. The potential usefulness of this study for mesoscale atmospheric data assimilation is briefly discussed.
Spurious Grid-Scale Precipitation in the North American Regional Reanalysis
Authors: West Gregory L. , Steenburgh W. James , Cheng William Y. Y. 
Published: June 2007

Abstract
Spurious grid-scale precipitation (SGSP) occurs in many mesoscale numerical weather prediction models when the simulated atmosphere becomes convectively unstable and the convective parameterization fails to relieve the instability. Case studies presented in this paper illustrate that SGSP events are also found in the North American Regional Reanalysis (NARR) and are accompanied by excessive maxima in grid-scale precipitation, vertical velocity, moisture variables (e.g., relative humidity and precipitable water), mid- and upper-level equivalent potential temperature, and mid- and upper-level absolute vorticity. SGSP events in environments favorable for high-based convection can also feature low-level cold pools and sea level pressure maxima. Prior to 2003, retrospectively generated NARR analyses feature an average of approximately 370 SGSP events annually. Beginning in 2003, however, NARR analyses are generated in near–real time by the Regional Climate Data Assimilation System (R-CDAS), which is identical to the retrospective NARR analysis system except for the input precipitation and ice cover datasets. Analyses produced by the R-CDAS feature a substantially larger number of SGSP events with more than 4000 occurring in the original 2003 analyses. An oceanic precipitation data processing error, which resulted in a reprocessing of NARR analyses from 2003 to 2005, only partially explains this increase since the reprocessed analyses still produce approximately 2000 SGSP events annually. These results suggest that many NARR SGSP events are not produced by shortcomings in the underlying Eta Model, but by the specification of anomalous latent heating when there is a strong mismatch between modeled and assimilated precipitation. NARR users should ensure that they are using the reprocessed NARR analyses from 2003 to 2005 and consider the possible influence of SGSP on their findings, particularly after the transition to the R-CDAS.
Statistical Differences of Quasigeostrophic Variables, Stability, and Moisture Profiles in North American Storm Tracks
Authors: Mercer Andrew E. , Richman Michael B. 
Published: June 2007

Abstract
Three common synoptic storm tracks observed throughout the United States are the Alberta Clipper, the Colorado cyclone, and the East Coast storm. Numerous studies have been performed on individual storm tracks analyzing quasigeostrophic dynamics, stability, and moisture profiles in each. This study evaluated storms in each track to help diagnose patterns and magnitudes of the aforementioned quantities, documenting how they compare from track to track. Six diagnostic variables were computed to facilitate the comparison of the storm tracks: differential geostrophic absolute vorticity advection, temperature advection, Q-vector divergence, mean layer specific humidity, low-level stability, and midlevel stability. A dataset was compiled, consisting of 101 Alberta Clippers, 165 Colorado cyclones, and 159 East Coast cyclones and mean fields were generated for this comparison. Maxima and minima of the 25th and 75th percentiles were generated to diagnose magnitudes and patterns of strong versus weak cyclones and measure their similarities and differences to the mean patterns. Alberta Clippers were found to show the weakest magnitude of quasigeostrophic variables, while East Coast storms had the strongest magnitudes. Alberta Clippers maintained the lowest moisture content through their life cycle as well. However, East Coast storms were the most stable of the three tracks. Typically, correlations between storm tracks were high; suggesting that storm evolution is similar between tracks, in terms of the patterns of diagnostic variables measured. However, significant magnitude differences in the quasigeostrophic variables distinguished the storms in each track.
Improvements in the Subgrid-Scale Representation of Moist Convection in a Cumulus Parameterization Scheme: The Single-Column Test and Its Impact on Seasonal Prediction
Authors: Byun Young-Hwa , Hong Song-You 
Published: June 2007

Abstract
This study describes a revised approach for the subgrid-scale convective properties of a moist convection scheme in a global model and evaluates its effects on a simulated model climate. The subgrid-scale convective processes tested in this study comprise three components: 1) the random selection of cloud top, 2) the inclusion of convective momentum transport, and 3) a revised large-scale destabilization effect considering synoptic-scale forcing in the cumulus convection scheme of the National Centers for Environmental Prediction medium-range forecast model. Each component in the scheme has been evaluated within a single-column model (SCM) framework forced by the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment data. The impact of the changes in the scheme on seasonal predictions has been examined for the boreal summers of 1996, 1997, and 1999. In the SCM simulations, an experiment that includes all the modifications reproduces the typical convective heating and drying feature. The simulated surface rainfall is in good agreement with the observed precipitation. Random selection of the cloud top effectively moistens and cools the upper troposphere, and it induces drying and warming below the cloud-top level due to the cloud–radiation feedback. However, the two other components in the revised scheme do not play a significant role in the SCM simulations. On the other hand, the role of each modification component in the scheme is significant in the ensemble seasonal simulations. The random selection process of the cloud top preferentially plays an important role in the adjustment of the thermodynamic profile in a manner similar to that in the SCM framework. The inclusion of convective momentum transport in the scheme weakens the meridional circulation. The revised large-scale destabilization process plays an important role in the modulation of the meridional circulation when this process is combined with other processes; on the other hand, this process does not induce significant changes in large-scale fields by itself. Consequently, the experiment that involves all the modifications shows a significant improvement in the seasonal precipitation, thereby highlighting the importance of nonlinear interaction between the physical processes in the model and the simulated climate.
Mesoscale Convective Vortices Observed during BAMEX. Part II: Influences on Secondary Deep Convection
Authors: Trier Stanley B. , Davis Christopher A. 
Published: June 2007

Abstract
Observations from the Bow Echo and Mesoscale Convective Vortex (MCV) Experiment are used to examine the role of the five mesoscale convective vortices described in Part I on heavy precipitation during the daytime heating cycle. Persistent widespread stratiform rain without deep convection occurs for two strong MCVs in conditionally stable environments with strong vertical shear. Two other MCVs in moderate-to-strong vertical shear have localized redevelopment of deep convection (termed secondary convection) on their downshear side, where conditional instability exists. The strongest of the five MCVs occurs in weak vertical shear and has widespread secondary convection, which is most intense on its conditionally unstable southeast periphery. The two MCVs with only localized secondary convection have well-defined mesoscale vertical motion couplets with downshear ascent and upshear descent above the planetary boundary layer (PBL). Although the amplitude is significantly greater, the kinematically derived vertical motion dipole resembles that implied by steady, vortex-relative isentropic flow, consistent with previous idealized (dry) simulations and diagnoses based on operational model analyses. In the other three cases with either widespread precipitation or weak environmental vertical shear, the kinematic and isentropic vertical motion patterns are poorly correlated. Vertical motions above the PBL provide a focus for secondary convection through adiabatic cooling downshear and adiabatic warming upshear of the MCV center. The MCVs occur within surface frontal zones with large temperature and moisture gradients across the environmental vertical shear vector (Part I). Thus, the effect of vertical motions on conditional instability is reinforced by horizontal advections of high equivalent potential temperature air downshear, and low equivalent potential temperature air upshear within the PBL. On average, the quadrant immediately right of downshear (typically southeast of the MCV center) best supports deep convection because of the juxtaposition of greatest mesoscale ascent, high equivalent potential temperature PBL air, and MCV-induced enhancement of the vertical shear.
Banded Convection Caused by Frontogenesis in a Conditionally, Symmetrically, and Inertially Unstable Environment
Authors: Schultz David M. , Knox John A. 
Published: June 2007

Abstract
Several east–west-oriented bands of clouds and light rain formed on 20 July 2005 over eastern Montana and the Dakotas. The cloud bands were spaced about 150 km apart, and the most intense band was about 20 km wide and 300 km long, featuring areas of maximum radar reflectivity factor of about 50 dBZ. The cloud bands formed poleward of an area of lower-tropospheric frontogenesis, where air of modest convective available potential energy was being lifted. During initiation and maintenance of the bands, mesoscale regions of dry symmetric and inertial instability were present in the region of the bands, suggesting a possible mechanism for the banding. Interpretation of the extant instabilities in the region of the bands was sensitive to the methodology to assess the instability. The release of these instabilities produced circulations with enough vertical motion to lift parcels to their lifting condensation level, resulting in the observed cloud bands. A high-resolution, numerical weather prediction model demonstrated that forecasting these types of events in such real-time models is possible, although the timing, evolution, and spacing of the bands were not faithfully reproduced. This case is compared to two previous cases in the literature where banded convection was associated with a combination of conditional, symmetric, and inertial instability.
Examining Two-Way Grid Nesting for Large Eddy Simulation of the PBL Using the WRF Model
Authors: Moeng C-H. , Dudhia Jimy , Klemp Joe , Sullivan Peter 
Published: June 2007

Abstract
The performance of two-way nesting for large eddy simulation (LES) of PBL turbulence is investigated using the Weather Research and Forecasting model framework. A pair of LES-within-LES experiments are performed where a finer-grid LES covering a smaller horizontal domain is nested inside a coarser-grid LES covering a larger horizontal domain. Both LESs are driven under the same environmental conditions, allowed to interact with each other, and expected to behave the same statistically. The first experiment of the free-convective PBL reveals a mean temperature bias between the two LES domains, which generates a nonzero mean vertical velocity in the nest domain while the mean vertical velocity averaged over the outer domain remains zero. The problem occurs when the horizontal extent of the nest domain is too small to capture an adequate sample of energy-containing eddies; this problem can be alleviated using a nest domain that is at least 5 times the PBL depth in both x and y. The second experiment of the neutral PBL exposes a bias in the prediction of the surface stress between the two LES domains, which is found due to the grid dependence of the Smagorinsky-type subgrid-scale (SGS) model. A new two-part SGS model is developed to solve this problem.
Visual Servoing for Nonholonomically Constrained Three Degree of Freedom Kinematic Systems
Authors: Lopes Gabriel A. D. , Koditschek Daniel E. 
Published: June 2007

This paper addresses problems of robot navigation with nonholonomic motion constraints and perceptual cues arising from onboard visual servoing in partially engineered environments. A general hybrid procedure is proposed that adapts to the constrained motion setting the standard feedback controller arising from a navigation function in the fully actuated case. This is accomplished by switching back and forth between moving “down” and “across” the associated gradient field toward the stable manifold it induces in the constrained dynamics. Guaranteed to avoid obstacles in all cases, conditions are provided under which the new procedure brings initial configurations to within an arbitrarily small neighborhood of the goal. Simulation results are given for a sample of visual servoing problems with a few different perceptual models. The empirical effectiveness of the proposed algorithm is documented by reporting results of its application to outdoor autonomous visual registration experiments with the robot RHex guided by engineered beacons.
Compartmentalised expression of Delta-like 1 in epithelial somites is required for the formation of intervertebral joints
Authors: Teppner Ingeborg , Becker Sonja , de Angelis Martin Hrabé , Gossler Achim , Beckers Johannes 
Published: June 2007

Abstract

Background
Expression of the mouse Delta-like 1 (Dll1) gene in the presomitic mesoderm and in the caudal halves of somites of the developing embryo is required for the formation of epithelial somites and for the maintenance of caudal somite identity, respectively. The rostro-caudal polarity of somites is initiated early on within the presomitic mesoderm in nascent somites. Here we have investigated the requirement of restricted Dll1 expression in caudal somite compartments for the maintenance of rostro-caudal somite polarity and the morphogenesis of the axial skeleton. We did this by overexpressing a functional copy of the Dll1 gene throughout the paraxial mesoderm, in particular in anterior somite compartments, during somitogenesis in transgenic mice.

Results
Epithelial somites were generated normally and appeared histologically normal in embryos of two independent Dll1 over-expressing transgenic lines. Gene expression analyses of rostro-caudal marker genes suggested that over-expression of Dll1 without restriction to caudal compartments was not sufficient to confer caudal identity to rostral somite halves in transgenic embryos. Nevertheless, Dll1 over-expression caused dysmorphologies of the axial skeleton, in particular, in morphological structures that derive from the articular joint forming compartment of vertebrae. Accordingly, transgenic animals exhibited missing or reduced intervertebral discs, rostral and caudal articular processes as well as costal heads of ribs. In addition, the midline of the vertebral column did not develop normally. Transgenic mice had open neural arches and split vertebral bodies with ectopic pseudo-growth plates. Endochondral bone formation and ossification in the developing vertebrae were delayed.

Conclusion
The mice overexpressing Dll1 exhibit skeletal dysmorphologies that are also evident in several mutant mice with defects in somite compartmentalisation. The Dll1 transgenic mice demonstrate that vertebral dysmorphologies such as bony fusions of vertebrae and midline vertebral defects can occur without apparent changes in somitic rostro-caudal marker gene expression. Also, we demonstrate that the over-expression of the Dll1 gene in rostral epithelial somites is not sufficient to confer caudal identity to rostral compartments. Our data suggest that the restricted Dll1 expression in caudal epithelial somites may be particularly required for the proper development of the intervertebral joint forming compartment.