bluuebunny/crossref_metadata_2025 huggingface dataset:
A GCM study of climate change in response to the 11‐year solar cycle
Authors: Haigh Joanna D.
Published: February 2007

A general‐circulation model (GCM) is used to investigate the impact of the 11‐year solar‐activity cycle on the climate of the lower atmosphere. Solar forcing is represented by changes in both incident irradiance and stratospheric ozone concentrations. Experiments are carried out with realistic and factor‐ten enhanced solar irradiance changes and with ozone changes based on two‐dimensional photochemical model results and loosely based on Total Ozone Mapping Spectrometer ozone column data. A pattern of response, consistent across all the experiments, is found in which the tropical Hadley cells weaken and broaden, and the sub‐tropical jets and mid‐latitude Ferrel cells move polewards. This causes sub‐tropical warming and a characteristic vertical banding of mid‐latitudes temperature changes in both the summer and winter hemispheres. the GCM results suggest that the precise response of the atmosphere depends on the magnitude and distribution of the ozone changes. This is confirmed by use of an equal‐area model of the tropical Hadley cells in which the input radiative equilibrium‐temperature anomalies are determined from the downward irradiance (both solar and long wave) at the tropopause as calculated in the GCM. As both the magnitude of the solar irradiance change and, more particularly, the latitude‐height structure of solar‐induced ozone changes over the 11‐year cycle are not yet well established, the GCM study may well underestimate the solar effects.
Electrodynamic trapping and manipulation of ice crystals
Authors: Swanson Brian D. , Bacon Neil J. , Davis E. James , Baker Marcia B.
Published: February 2007

We have developed a double‐ring double‐disk electrodynamic balance with humidity control provided by an internal thermal diffusion chamber to study several atmospherically important processes involving 10‐200 μm ice particles. the balance constants needed to quantify the particle size and mass were determined by a three‐dimensional relaxation‐method calculation of the non‐axisymmetric electric fields, and by experimental measurement of the onset of particle stability using polystyrene latex microspheres of known size and mass. We have levitated frost particles of various shapes and sizes under a range of atmospherically relevant temperature and humidity conditions. the measured mass changes during growth and sublimation are consistent with predictions based on vapour and thermal diffusion to equivalent spheres. the electrodynamic balance is shown to be a useful tool for exploring single particle growth and sublimation rates, and for measuring their light‐scattering characteristics.
Effects of cloud‐droplet spectra on the average surface‐temperature of ice accreted on fixed cylindrical collectors
Authors: Avila E. E. , Castellano N. E. , Saunders C. P. R.
Published: February 2007

An experimental study of the heat balance of a stationary cylindrical collector accreting supercooled water droplets has shown a new dependence on the sizes of the water droplets in the laboratory cloud. In a study in 1967, MacKlin and Payne related the steady‐state heat‐release during accretion to the heat loss by convection and conduction; their equation involved a numerical factor χ for which they assumed a value of 0.28. the present study has shown that χ is a function of the droplet spectrum with values around 0.5 at a velocity of 4 m s‐1 for a mean volume‐weighted droplet‐diameter of 18 μm, and that χ approaches 0.3 for droplets greater than 30 μm diameter. the results have importance to the surface temperatures of riming graupel pellets and hailstones in convective storms which, in the presence of small water‐droplets, will be heated to a smaller degree than has been assumed in current models of hailstone growth. Furthermore, the effect of droplet size may influence ice‐crystal multiplication and charge transfer in convective clouds, both of which are highly temperature dependent.
An investigation into convectively generated potential‐vorticity anomalies using a mass‐forcing model
Authors: Gray M. E. B.
Published: February 2007

A mass‐forcing model is used to investigate how the potential‐vorticity (PV) anomalies, formed as a response to changes in the mass field due to convection in a rotating, stratified fluid, are dependent upon the horizontal distribution of the vertical mass transfer.

It is found that when the mass is concentrated within a single convective plume a stronger PV anomaly results than when an equivalent total mass is distributed about an ensemble of plumes. When the ensemble is well separated the resultant balanced energy is approximately proportional to the sum of each plume's convected mass to the five‐thirds. As the separation of the ensemble is reduced below that of a Rossby radius the ensemble behaves more like a single system. However, as the PV anomalies interact they coalesce and energy lost in this coalescence process, plus the entrainment of environmental PV, results in less balanced energy than predicted from the above quantitative relationship.

Further experiments show that the final PV anomalies show only a little sensitivity to the horizontal scale of the mass transfer, and it is argued that the final balanced energy is primarily a function of the convected mass. However, when the local intensity of the mass transfer is high, such as when the mass is forced through smaller scales, there is a much stronger fast manifold response in the form of inertia‐gravity waves. This complements other studies which argue that convective heating on scales less than a Rossby radius will mostly excite inertia‐gravity waves, whilst when on scales greater than a Rossby radius will strengthen the balanced flow.
The effect of the cloud‐droplet spectrum on electrical‐charge transfer during individual ice‐ice collisions
Authors: Avila E. E. , Pereyra R. G. , Varela G. G. Aguirre , Caranti G. M.
Published: February 2007

Experiments were conducted with a wind tunnel in a cold room, in order to investigate the influence of the cloud‐droplet spectrum on the charges transferred when individual ice spheres collided with a fixed artificial graupel pellet growing by riming. the experiments were carried out with ice spheres of about 100 μm in diameter, impact velocities around 4 m s−1, temperatures between −10°C and −30°C and effective water contents representative of real clouds. Two different cloud‐droplet spectra were used. One had more than 30% of the droplets with sizes greater than 13 μm, and the other had more than 50% of the droplets greater than that. the new results show that the size distribution of the droplets is very important to the sign of electric charge transferred. the target graupel charged positively over all the temperature range covered when the smaller‐droplet spectrum was used, but negatively at temperatures below −18°C for the larger‐droplet spectrum. These results show the importance of droplet sizes to thunderstorm charging.
Role of salient potential‐vorticity elements in an event of frontal‐wave cyclogenesis
Authors: Fehlmann René , Davies Huw C.
Published: February 2007

Extratropical cyclogenesis is usually accompanied by both an upper‐level trough and a surface front with its cloud‐diabatic accoutrements. In the present study these distinctive structures are interpreted as salient elements of the atmosphere's potential vorticity (PV) distribution, and their role examined for one particular event of frontal‐wave cyclogenesis.

The strategy adopted is a form of diagnosis by PV dismemberment. It entails adopting a ‘successful’ forecast with a limited‐area model as a surrogate for the actual event, and then performing a sequence of simulations with modified initial conditions that correspond in each case to the removal of one (or more) of the salient PV elements. This approach provides an assessment of the relative significance of the individual elements, permits an insightful comparison of various extant theories of cyclogenesis, and pinpoints the particular PV elements influencing the event's predictability.

It is shown that the replication of the simulated cyclone requires an adequate representation both of specific fine‐scale PV features at tropopause levels and of the diabatically maintained low‐level pre‐frontal PV band. Thus, a tenable theory of cyclogenesis that incorporates this not atypical event should both recognize and help clarify the dependence of cyclogenesis upon the relative locations, movement, scales and structures of the aforementioned salient PV elements.
Least action principle for a general, non‐hydrostatic, compressible, acoustically non‐filtered pressure‐coordinate model
Authors: Rõõm Rein
Published: February 2007

The least action principle is described for general (non‐hydrostatic, compressible, acoustically non‐filtered) pressure‐coordinate equations of atmospheric dynamics (Rõõm 1989), which represents a generalization of the Least Action Principle, first developed for the pressure‐coordinate representation of atmospheric dynamics by Salmon and Smith (1994).
Large‐eddy simulations of neutrally stratified flow over surfaces with spatially varying roughness length
Authors: Hobson J. M. , Wood N. , Brown A. R.
Published: February 2007

Large‐eddy simulations of neutrally stratified flow over a homogeneous surface (with constant roughness length) are used to help determine the requirements for a credible large‐eddy simulation of similar flow over a heterogeneous surface (with varying roughness length). It transpires that particular attention must be paid to simulating the unperturbed mean profiles correctly and to using appropriately high grid resolution. Results from heterogeneous large‐eddy simulations are then compared with those obtained using a first‐order mixing‐length closure model. Finally, the implications of the results for the validity of the effective‐roughness‐length parametrizations that are used in many numerical weather prediction models are considered.
Ensemble simulations of eurasian snow‐depth anomalies and their influence on the summer Asian monsoon
Authors: Ferranti L. , Molteni F.
Published: February 2007

The effect of springtime surface conditions over Eurasia on the monsoon circulation is addressed by using several simulations with the model used by the European Centre for Medium‐Range Weather Forecasts (ECMWF). the simulations have been specially designed to investigate whether the Eurasian snow‐anomaly is a passive response to the tropical forcing, implying that the ultimate relationship exists only between the El Niño/Southern Oscillation (ENSO) and the monsoon as suggested by previous studies, or plays an active independent role in the monsoon modulation. Preliminary results suggest that the Eurasian snow depth is probabilistically predictable, and that it does influence the seasonal‐mean monsoon independently of the ENSO phase. Therefore, proper observations and simulations of the Eurasian snow field can provide an additional and independent contribution to monsoon prediction.
A case‐study of a partially cloudy boundary layer
Authors: Price Jeremy D.
Published: February 2007

A case‐study of a partially cloudy boundary layer consisting of cumulus and stratocumulus is presented, and the main dynamical processes responsible for its evolution are identified. Measurements were made with the UK Meteorological Office tethered‐balloon facility which was located in Hampshire, southern England, during the Doppler Radar Observation Project, September 1998.

Results show that fair weather cumulus formed during the morning of the third and quickly overdeveloped into patches of stratocumulus. A characteristic of this day was a relatively weak capping inversion which allowed a significant amount of encroachment/entrainment to occur. Between 1100 and 1400 GMT this was calculated at 153 kg m−2. The ratio of entrapment to encroachment was found to be 0.6.

Data analysis, together with a simple model, shows that encroachment/entrainment of warm air into the upper pan of the boundary layer significantly increased the stability there and caused a reduction in the cloud area. The data were used to assess the UK Meteorological Office cloud parametrization, and show that during the middle of the day cloud amount was underestimated.
Observed winter cyclone tracks in the northern hemisphere in re‐analysed ECMWF data
Authors: Sickmöller Michaela , Blender Richard , Fraedrich Klaus
Published: February 2007

The observed cyclone activity in the northern‐hemisphere winter (DJF) is investigated in 1979‐97 European Centre for Medium‐Range Weather Forecasts re‐analyses. The cyclone trajectories are determined automatically by a next‐neighbour search of minima identified in the 1000 hPa geopotential‐height field (z1000). These are compared with the traditional storm track, defined by the root mean square of the band‐pass filtered 500 hPa geopotential‐height anomaly. The analysis covers the North Atlantic and North Pacific basins. The trend of the cyclone density (distribution) is similar to that of the storm track in the North Atlantic, but opposite in the North Pacific. In the Atlantic, the total number of cyclones with low central z1000 increases, due to the northward shift towards lower regional climatological pressure, whereas the number of cyclones with large gradients decreases. In the Pacific, the number of intense (weak) cyclones with large (low) gradients increases (decreases).

The cyclone‐track variability is investigated by a cluster analysts of the relative cyclone trajectories. The three centroids corresponding to north‐eastward and zonally propagating cyclones and nearly stationary ones are very similar in both ocean basins. The winter‐mean cluster occupation numbers of the two propagating cyclone clusters are positively correlated with one another in the Atlantic, and negatively in the Pacific. The three Atlantic cyclone clusters can be linked to particular aspects of the central European climate.

The cyclonic activity can be related to teleconnection patterns which are dominant during northern hemisphere winter. During high North Atlantic Oscillation index winters (deeper Icelandic lows), the Atlantic cyclone density shifts northward and is associated with more stationary cyclones. During El Niño warm‐event winters, the Pacific cyclone density is shifted northward and their propagation is oriented more zonally as in high Pacific/North American index phases (deeper Aleutian lows). In the North Atlantic propagating cyclones occur less and stationary ones more frequently in El Nino winters. The correlations between the north‐east ward propagating cyclones in the Pacific and the north‐eastward and zonally propagating ones in the Atlantic suggest an interaction between the two storm tracks.
Combined use of sensitivity information and observations to improve meteorological forecasts: A feasibility study applied to the 'Christmas storm' case
Authors: Hello Gwenaëlle , Lalaurette Frančcois , Thépaut Jean‐Noël
Published: February 2007

An analysis correction method is presented that uses directly the sensitivity information coming from gradient fields at initial time to perform an alternative forecast. The method consists in imposing, at initial time, a 'sensitive' structure to the perturbation which is first computed by adjoint tools. The tuning of the perturbation amplitude is obtained by reducing the distance to the observations at the locations where the sensitive structure is of significant amplitude.

The method is tested on a severe meteorological event which was operationally badly forecast even at very short ranges. Several sets of homogeneous observations are considered and the method proves its efficiency for part of them.
Observations of tropical convection events using Indian MST radar: First results
Authors: Jain A. R. , Rao Y. Jaya , Patra A. K. , Rao P. B. , Viswanathan G. , Subramanian S. K.
Published: February 2007

Mesoscale convective events, associated with severe weather, play a significant role in troposphere‐stratosphere coupling processes. Deep convection occurs very often at tropical latitudes. The convection events result in the transport of energy from the lower troposphere to the upper troposphere and stratosphere, and may also affect global circulation. In the Indian tropical region, meteorological convection events are a common occurrence during the months of May to December. In the present study, very‐high‐frequency radar located at Gadanki (13.45°N, 79.18°E), a tropical station in India, is used to make observations of winds, turbulence and stable‐layer structures, during the passage of convective events over the radar site under different synoptic situations.

Radar observations of vertical velocity show enhanced up and down draughts during the passage of convection events. Height and time cross‐sections of radar‐observed signal‐to‐noise ratio clearly show distinct regions of enhanced signal intensity, indicating height and time Structures of enhanced atmospheric turbulence associated with the convection. It is also noted that stable‐layer structures associated with the tropical tropopause are not well defined during the passage of convection. This suggests ‘weakening’ of stable‐layer structures during the convective activity. The present observations also show enhanced mass flux, both in upward and downward directions, through the tropopause, indicating mass exchange between troposphere and stratosphere during the period of convective activity.
Decadal precipitation variability over Europe and its relation with surface atmospheric circulation and sea surface temperature
Authors: Rimbu Norel , Treut Hervf Le , Janicot Serge , Boroneant Constanta , Laurent Carine
Published: February 2007

The relationships between decadal (>5‐year period) observed winter precipitation (PP) variability over Europe and atmospheric circulation and sea surface temperature (SST) during the period 1950–1995 are investigated. More than 48% of the decadal precipitation variability is described by two modes: a meridional dipolar pattern (high PP over northern Europe and low over southern Europe, the Mediterranean and most of central Europe) explaining about 32% of the variance, and an alternating pattern in latitude over Europe (high in central Europe and low in far north‐western Europe and the Mediterranean) explaining about 16% of the variance. The first mode is strongly related to the North Atlantic Oscillation.

A canonical correlation analysis between regional precipitation and sea‐level pressure fields shows that a PP pattern similar to the first decadal PP mode is associated with a north‐westerly circulation anomaly pattern while a PP pattern similar to the second decadal PP mode is associated with a monopolar circulation anomaly pattern over most parts of Europe.

The correlation map between the time series of expansion coefficients of the first PP mode and sea surface temperature emphasizes a global pattern which resembles the linear trend coefficients pattern of SST for the analysed period. The second PP mode is associated with an SST anomaly pattern similar to that of the SST anomalies characterizing ‘decadal El Niňo Southern Oscillation’ SST pattern.

Composite maps of global 500 mb geopotential height based on the time series of expansion coefficients of PP modes emphasize global patterns compatible with SST patterns. After removing the linear trend from the data, the first PP pattern remains almost unchanged but it emphasizes mainly regional connections. The second spatial pattern of the second PP mode and its connections are not affected significantly by removing the trend.
A study of probability distributions of boundary‐layer humidity and associated errors in parametrized cloud‐fraction
Authors: Price Jeremy D.
Published: February 2007

Observations of boundary‐layer‐humidity probability‐distributions made with the Meteorological Office tethered‐balloon facility have been derived from nine representative days between 1996 and 1999. Measurements include those made at several heights simultaneously. Four types of distribution have been defined, including skewed and multimodal types. These have been analysed on scales relevant to sub‐grid parametrizations. Four distribution functions have been fitted to the observations and their accuracy in predicting cloud fraction assessed. It was found that a standard beta‐type distribution gave the best representation of the observed humidity‐distribution. In addition, it was found that for grid scales greater than about 5 km, advection plays a significant role in determining the form of the humidity distribution, and that this must be accounted for in any parametrizations. The cloud‐fraction error arising from errors in the mean total specific‐humidity and saturation specific‐humidity is also discussed. That from the former is found to be relatively large.
Residual cumulus parametrization
Authors: Yano Jun‐Ichi
Published: February 2007

A novel approach to the parametrization of convective heating‐moistening is proposed. It is observationally known that convective heating is balanced overall by adiabatic cooling due to the resolved‐scale upward motion (large‐scale forcing) during the convective situations, with a corresponding balance also found in the moisture budget. A parametrization may be tuned to satisfy this first‐order balance. However, a small difference between these two terms defines the actual temporal evolution of the temperature and the moisture fields. Hence, the errors due to the cumulus parametrization are often the same order of magnitude as the temporal change itself, in spite of this first‐order tuning. In the present paper, it is proposed that this small ‘residual’ difference be directly represented by a cumulus parametrization. This idea is pursued by adopting a simple Newtonian relaxation formulation in the same spirit as the Betts‐Miller cumulus parametrization. Both the relaxation time‐scale and the reference profile are defined by the optimal fitting of convective‐forcing data diagnosed over the Intensive Flux Array domain during the TOGA‐COARE period for both the total and the residual convective heating parametrizations. Performance of these two types of parametrizations under this optimization is compared using single‐column model experiments.
The O3N2O relation from balloon‐borne observations as a measure of Arctic ozone loss in 1991/92
Authors: Müller Rolf , McKenna Daniel S. , Schmidt Ulrich , Engel Andreas , Proffitt Michael H.
Published: February 2007

We analyse balloon‐borne measurements of ozone (O3) and nitrous oxide (N2O) in the Arctic, obtained during the European Arctic Stratospheric Ozone Experiment campaign in winter and early spring 1991/92. Using N2O as a long‐lived tracer, we identify chemical ozone depletion in the Arctic vortex in the presence of ozone variations caused by dynamical effects. Substantial chemical ozone loss of about 25% locally over the height range of 15‐21 km, corresponding to the potential‐temperature range of 400‐550 K, is deduced for late winter. Mixing processes can be ruled out as the major cause of the observed anomaly in the O3‐N2O relation by considering the concurrently measured chloroflurocarbon‐11‐N2O relation. The chemical ozone loss derived from the balloon‐borne measurements is in agreement with the loss derived, following the same methodology, from satellite (Halogen Occultation Experiment) vortex observations. Consistent with the dynamical development of the polar vortex and with the observed chlorine activation, the major fraction of the ozone decline occurred before February 1992. The reduced ozone levels persisted over the lifetime of the polar vortex until late March 1992.
Explicit simulation of cumulus ensembles with the GATE phase III data: Budgets of a composite easterly wave
Authors: Xu Kuan‐Man , Randall David A.
Published: February 2007

The mass, heat and moisture budgets of a composite easterly wave over the eastern tropical Atlantic are analysed from simulations of a convection‐resolving model (CRM). The large‐scale data from the GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment (GATE) phase III are used to drive the CRM simulations. The simulated, composite easterly wave is reasonably comparable with the observed, except for the lack of shallow convection embedded in the simulated easterly waves. The mesoscale stratiform precipitation processes are found to be an inseparable component of cumulus convection embedded in the easterly waves. Their main differences from convective processes are twofold: (1) the distinct vertical structures of the budget components due to mesoscale updraughts and downdraughts, and (2) the phase lags relative to the convective processes in the temporal evolution of the easterly waves. Thus, theoretical studies should include both convective and mesoscale stratiform precipitation processes in order to further understanding of diabatic processes in the dynamics of the easterly waves and possibly other waves in the tropics. In addition, the budget analysis presented in this study also provides some details for improving parametrizations of cumulus convection.
A review on the use of the adjoint method in four‐dimensional atmospheric‐chemistry data assimilation
Authors: Wang K.‐Y. , Lary D. J. , Shallcross D. E. , Hall S. M. , Pyle J. A.
Published: February 2007

In this paper we review a theoretical formulation of the adjoint method to be used in four‐dimensional (4D) chemistry data assimilation. The goal of the chemistry data assimilation is to combine an atmospheric‐chemistry model and actual observations to produce the best estimate of the chemistry of the atmosphere. The observational dataset collected during the past decades is an unprecedented expansion of our knowledge of the atmosphere. The exploitation of these data is the best way to advance our understanding of atmospheric chemistry, and to develop chemistry models for chemistry‐climate prediction. The assimilation focuses on estimating the state of the chemistry in a chemically and dynamically consistent manner (if the model allows online interactions between chemistry and dynamics). In so doing, we can: produce simultaneous and chemically consistent estimates of all species (including model parameters), observed and unobserved; fill in data voids; test the photochemical theories used in the chemistry models. In this paper, the Hilbert space is first formulated from the geometric structure of the Banach space, followed by the development of the adjoint operator in Hilbert space. The principle of the adjoint method is described, followed by two examples which show the relationship of the gradient of the cost function with respect to the output vector and the gradient of the cost function with respect to the input vector. Applications to chemistry data assimilation are presented for both continuous and discrete cases. The 4D data variational adjoint method is then tested in the assimilation of stratospheric chemistry using a simple catalytic ozone‐destruction mechanism, and the test results indicate that the performance of the assimilation method is good.
FASTEX IOP 18: A very deep tropopause fold. II: Quasi‐geostrophic omega diagnoses
Authors: Donnadille Jérǒme , Cammas Jean‐Pierre , Mascart Patrick , Lambert Dominique
Published: February 2007

A set of two companion papers is dedicated to the documentation of the life cycle of a very deep tropopause fold (820 hPa) during the Intensive Observing Period 18 of the Fronts and Atlantic Storm‐Track EXperiment (FASTEX). In this second part, diagnoses of vertical motion using a Q‐vector partitioning in the natural coordinate system that follows the geostrophic wind are analysed. The partitioning allows the evaluation of vertical motions associated with forcing mechanisms such as confluence and diffluence, thermal advection by the horizontal geostrophic shear (shear advection) and curvature of the flow. The synoptic situation involves the formation of an intense upper‐level jet streak when an Arctic trough and a southern ridge move into phase with each other. Results assessed in the course of the tropopause‐fold life cycle show that subsiding vertical motions associated with each of the forcing mechanisms (confluence, shear advection and curvature) overlap on the cyclonic‐shear side of the entrance region of the jet streak. It is shown that an additional effect of shear advection over the confluence, a necessary ingredient for the development of deep tropopause folds in two‐dimensional contexts, takes place in the present case‐study. However, the forcing mechanisms that contribute mostly to subsiding vertical motions over the warm side of the upper‐level frontal zone (i.e. with a maximum frontogenetic effect) are, in order of importance, the shear advection and the curvature.
Water's two height scales: The moist adiabat and the radiative troposphere
Authors: Mapes Brian E.
Published: February 2007

The temperature structure of the tropical troposphere resembles a moist adiabat, with a lapse‐rate transition toward dry adiabatic where water becomes scarce at an altitude Hma ∼ 8 km (350 hPa). Infrared emission by water vapour cools a deeper layer, extending up to Hrad ∼ 14 km (160 hPa). Five consequences of these unequal heights are reviewed.

1. Upper‐tropospheric relative humidity is often low, highly variable, and bimodal, due to the rapidity of drying by radiative subsidence.

2. Large‐scale divergent circulations (e.g. equatorial v wind) exhibit a two‐celled vertical structure, with an elevated convergence layer near 8‐10 km in the rising branch.

3. The dominant deep convective heating process changes from latent heating at low levels to eddy heat‐flux convergence in the upper troposphere. This requires a substantial updraught‐environment temperature difference, which leads to large entrainment near Hma, yielding stratiform anvil clouds which also contribute radiative heating.

4. The rising branches of deep (∼Hrad) vertical circulations export more heat than they import as moisture, so that large‐scale tropical dynamics can be characterized by a ‘gross moist stability’.

5. Divergent motions with a vertical wavelength ∼8 km, corresponding to Kelvin or gravity wave speeds of ∼15 m s−1, are excited by simple (e.g. uniform) heating profiles extending through the lapse‐rate change near Hma.
The zonal drift associated with time‐dependent particle motion on the earth
Authors: Paldor Nathan
Published: February 2007

The zonal drift associated with the time‐dependent particle velocity on the rotating earth, such as the inertial motion–westward in midlatitudes and eastward in the tropics–is shown to result from the conservation of angular momentum. This finding follows from a transformation of Newton's second law of motion on the earth into a dynamical system where the angular momentum is a system variable, a procedure similar to that used in the description of a spinning top's dynamics. In near‐geostrophic zonal motion (i.e. time‐dependent motion in the presence of a fixed meridional pressure gradient), where the angular momentum is conserved, and for angular momentum that is below a threshold value, the dynamical system possesses two elliptic points located off the equator. The fixed points of the dynamical system correspond to the steady, geostrophic, zonal motion so the time‐dependent velocity of the small‐amplitude motion (when the latitudinal particle excursion is not too large) deviates only slightly from the geostrophic velocity. The explicit expressions derived for the drift near the elliptic points imply that in near‐geostrophic, eastward (westward) motion in midlatitudes the geostrophic, steady, speed provides an overestimate (underestimate) of the temporally averaged drift. This difference between the steady motion and the average of the periodic motion characterizes nonlinear systems. At large values of the angular momentum a single elliptic point exists on the equator and the drift is directed eastwards. This drift, too, can be quantified near the fixed point associated with a fixed zonal velocity on the equator, where the Coriolis force vanishes.

At large oscillation amplitude in midlatitudes, when the oscillation encompasses a large latitude band and the instantaneous velocity deviates significantly from the geostrophic velocity, the zonal drift is strongly affected by the presence of a hyperbolic point at the equator. Explicit expressions for the zonal drift are not available in this case, but numerical results show that the effect of this nonlinearity is to greatly enhance the westward drift in midlatitudes compared with the small‐amplitude case.
Conditional symmetric instability, frontogenetic forcing and rain‐band organization
Authors: Lemaǐtre Y. , Scialom G. , Protat A.
Published: February 2007

The mesoscale organization and the thermodynamic structures of cloud bands and rain bands observed on 9 January 1988 during the seventh Intensive Observation Period of the European field experiment project FRONTS 87 are investigated using both radiosounding measurements and dual Doppler‐radar data.

The combined role of the conditional symmetric instability (CSI) and of the frontogenetic forcing in this banded organization is quantitatively assessed. It is shown that the observations are in agreement with the subsequent scenario, cloud bands initiated by the large‐scale forcing in the presence of a weakly CSI unstable atmosphere evolve rapidly into CSI rolls. The detailed thermodynamics within one of these rain bands is shown to be in very good agreement with the ones predicted by the CSI theory. A different dynamic behaviour between the cloud bands and the rain bands is, however, shown. Some additional role is suspected to be played by microphysics processes, in particular by snow evaporation, in the reinforcement of CSI ascending motions.
Radiative influences on the structure and lifetime of cirrus clouds
Authors: Dobbie Steven , Jonas Peter
Published: February 2007

Our goal in this work is to determine the role of radiation in cirrus clouds. How it impacts the formation and evolution of cloud structure, whether or not it initiates convective instability, and what effect it has on the lifetime of these clouds. In this study, we simulate cirrus clouds using the Met Office large‐eddy simulation model with a broad‐band solar and infrared ice‐specific radiation scheme.

We find that radiation can have quite an effect on cirrus clouds. Results for runs with and without radiation show many dramatic differences. In general, radiatively influenced clouds are observed to be much more dynamic and inhomogeneous. The radiation is observed to strongly enhance cellular structure within the cloud layer, and a Fourier analysis of the horizontal ice‐water path (IWP) shows that this cellular enhancement gives rise to inhomogeneity length‐scales roughly related to the thickness of the layer. The Fourier amplitudes for the radiative cases are usually two or three times larger in magnitude than the non‐radiative cases. The inhomogeneity length‐scales do appear in the non‐radiative cases but they are very weak. The radiatively driven clouds in these simulations often had horizontally averaged IWPs larger in magnitude by more than double compared to the non‐radiative cases once the radiation had taken effect, and the cloud lifetime was increased by between 30 minutes and 2 hours.

To evaluate if radiation is causing convective instability, we derive and implement a radiation stability number, Rsn. For radiative instability to occur, Rsn must satisfy the condition 0 < Rsn < 1. We also present similar stability numbers for latent, and the combined radiation and latent processes. By evaluating these numbers throughout the domain during the simulation, we can determine when these diabatic processes will overcome the thermal stratification of the layer and induce convective instability. These processes are found frequently to induce instability for the radiative inclusive case. We find that radiative and latent instability usually occurs in updraught regions, and that latent heating initially enhances the development of the plumes prior to the radiation. We also find that the magnitude of the latent heating is also strongly coupled to the effects of radiation, since stronger cell structure induced by radiation results in stronger latent heating at cloud top and less precipitation at cloud base.
Proportionality of scales: An isotropy‐like property of geophysical fields
Authors: Tsyroulnikov Mikhail D.
Published: February 2007

For the majority of meteorological and oceanographic fields, large (small) scales in the horizontal tend to be associated with large (small) scales in the vertical. This property (‘proportionality of scales’, the PS property) is sometimes referred to as a kind of three‐dimensional isotropy. In this article, we try to clarify the relationship between the PS property and isotropy. It is found that the PS property and isotropy are not directly related to each other. The question of in what sense these two properties are related, is addressed. A pertinent continuous‐covariance model is proposed. The model is defined partially in spectral space (in the horizontal) and partially in physical space (in the vertical). A self‐similarity hypothesis for spectral vertical correlations is suggested and tested. Treating the vertical inhomogeneity of covariances in the model is discussed. The model's capability of describing empirical three‐dimensional covariances is demonstrated.
Level of nodes in increasing trees revisited
Authors: Panholzer Alois , Prodinger Helmut
Published: February 2007

Simply generated families of trees are described by the equation T(z) = ϕ(T(z)) for their generating function. If a tree has n nodes, we say that it is increasing if each node has a label ∈ { 1,…,n}, no label occurs twice, and whenever we proceed from the root to a leaf, the labels are increasing. This leads to the concept of simple families of increasing trees. Three such families are especially important: recursive trees, heap ordered trees, and binary increasing trees. They belong to the subclass of very simple families of increasing trees, which can be characterized in 3 different ways.

This paper contains results about these families as well as about polynomial families (the function ϕ(u) is just a polynomial). The random variable of interest is the level of the node (labelled) j, in random trees of size n ≥ j. For very simple families, this is independent of n, and the limiting distribution is Gaussian. For polynomial families, we can prove this as well for j,n → ∞ such that n − j is fixed. Additional results are also given. These results follow from the study of certain trivariate generating functions and Hwang's quasi power theorem. They unify and extend earlier results by Devroye, Mahmoud, and others. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2007
Signal transduction in the type I interferon system and viral countermeasures
Authors: Brzózka Krzysztof , Pfaller Christian , Conzelmann Karl‐Klaus
Published: February 2007

Type I interferons (IFN) including IFNα/β are cytokines of the immune system with critical functions in innate and adaptive immune response. Secreted IFN acts via JAK/STAT signaling pathways to direct a huge gene expression program, including antiviral, apoptotic, survival and immune genes. Only recently, the molecular patterns and their receptors as well as the connected signaling pathways leading to transcriptional activation of IFN genes have been elucidated. Ubiquitous cytosolic RNA helicases like RIG‐I which sense intracellular triphosphate RNAs and activate the IFN‐controlling transcription factors IRF3 and IRF7 seem to play a major role in antiviral defense and immunity. Recognition of extracellular nucleic acids by a subset of Toll‐like receptors in addition contributes to a generalized host IFN response. During co‐evolution with the host, viruses have learned to counteract every piece of the IFN network. Learning from viruses how to target the IFN system may lead us to novel strategies for therapeutic intervention.
Avian influenza virus signaling: implications for the disease severity of H5N1 infection
Authors: Lee Davy C. W. , Lau Allan S. Y.
Published: February 2007

The global outbreak of avian influenza virus infections in poultry and wild birds as well as the high mortality rate in patients infected with the viruses pose a worldwide alert to the risk of an emerging epidemic. Scientific data to date showed some strains of avian influenza viruses including H5N1 are capable of going through mutations to develop into a novel, pandemic strain of influenza virus. Recent research has advanced our knowledge of the biological behavior of the virus, its interactions with mammalian cells, downstream signal transduction pathways, and the antiviral immune responses. A better understanding of the virus‐activated signaling pathways will provide new clues to delineate the mechanisms underlying the pathogenesis of avian influenza virus infection. Here, we reviewed the contributions of human and avian influenza virus virulence factors including hemagglutinin HA, RNA polymerase, and nonstructural protein NS1. We next discussed the interaction of the viruses with cellular factors including Toll‐like receptor TLR, RIG‐I/MDA5, signaling kinases including PKR, MAPK and PI3K, and transcription factors NF‐κB and IRF. Finally, we commented on the role of apoptosis and caspase activation as important host defense mechanisms. Taken together, virus replication and its activated inflammation contribute to the severity of avian influenza infections.
Implementing a generic component‐based framework for telecontrol applications
Authors: Chimaris Avraam N. , Papadopoulos George A.
Published: February 2007

The rapid growth of telecontrol systems is one of the major trends in today's network‐oriented community. The implementation of generic frameworks, consisting of reusable components that can form the basis for the development of such systems, is a necessity. There is a plethora of associated applications that can be developed in a distributed environment, such as audio/video teleconferencing, groupware and collaborative computing environments, remote controlled services, etc. In this paper we design and implement a generic framework of components that can be used for the realization of telecontrol applications. This category of applications focuses primarily on the issues of managing distributed units on remote end‐systems. Such applications contain remote units and administrators that are connected and exchange data and control messages. We analyse the outlined architecture of our framework and the most important system operations. We also describe the communication protocol used in message exchanges between the constituent components. Finally, we illustrate the usefulness of our framework by presenting two applications that were created by extending the basic software infrastructure. Copyright © 2007 John Wiley & Sons, Ltd.
Efficient embedded code generation with multiple load/store instructions
Authors: Paek Yunheung , Ahn Minwook , Cho Doosan , Kim Taehwan
Published: February 2007

In a recent study, we discovered that many single load/store operations in embedded applications can be parallelized and thus encoded simultaneously in a single‐instruction multiple‐data instruction, called the multiple load/store (MLS) instruction. In this work, we investigate the problem of utilizing MLS instructions to produce optimized machine code, and propose an effective approach to the problem. Specifically, we formalize the MLS problem, that is, the problem of maximizing the use of MLS instructions with an unlimited register file size. Based on this analysis, we show that we can solve the problem efficiently by translating it into a variant of the problem finding a maximum weighted path cover in a dynamic weighted graph. To handle a more realistic case of the finite size of the register file, our solution is then extended to take into account the constraints of register sequencing in MLS instructions and the limited register resource available in the target processor. We demonstrate the effectiveness of our approach experimentally by using a set of benchmark programs. In summary, our approach can reduce the number of loads/stores by 13.3% on average, compared with the code generated from existing compilers. The total code size reduction is 3.6%. This code size reduction comes at almost no cost because the overall increase in compilation time as a result of our technique remains quite minimal. Copyright © 2007 John Wiley & Sons, Ltd.
An automatically‐tuned sorting library
Authors: Bida Eran , Toledo Sivan
Published: February 2007

We present ATSL, an automatically‐tuned sorting library. ATSL generates a sorting routine optimized to the target machine for a specific data type. ATSL finds a high‐performance sorting routine by searching an algorithmic space that we have defined. The search space includes basic sorting algorithms and automatically‐generated compositions of sorting algorithms. Performance measurements are used both for ranking candidate algorithms and for characterizing the behavior of candidates in specific settings (e.g. ranges of input sizes). These characterizations allow ATSL to generate hybrid algorithms that intelligently exploit the strengths of particular algorithms, such as high speed at specific input‐size ranges. Many sorting algorithms can be tuned using numeric parameters and ATSL searches these parameter spaces to find values that yield high performance on the target machine. The building blocks from which ATSL synthesizes sorting algorithms include adaptations of many of the most effective hand‐tuned sorting routines, including several that are tuned for cache efficiency. An extensive experimental evaluation shows that ATSL generates high‐performance codes that are well tuned for the target machine and data type. The experiments were conducted on six different machines, of several architectures, and with three different compilers. The algorithms that are generated are fast; in particular, they beat the hand‐tuned building blocks and the compiler's C++ built‐in sorting routine. The algorithms that ATSL generates on different machines and using different compilers are different from each other. Copyright © 2007 John Wiley & Sons, Ltd.
Recent progress in the manufacture of alkanesulfonates: Photosulfochlorination of single‐chain length (C12−C16) n‐alkanes using SO2Cl2 at high conversion rates in pure phase and in the presence of solvent
Authors: Assassi Naziha , Azira Hakima , Tazerouti Amel
Published: February 2007

Increasing concentration of sulfuryl chloride during the photosulfochlorination reaction under visible light shows that under these conditions n‐alkanes react at high conversion rates instead of the conversion rate of 15% reported in the literature. This photosulfochlorination with sulfuryl chloride leads to better and more interesting results compared with those of photosulfochlorination by gas mixture. Indeed, nearly total conversion of n‐alkanes, specifically n‐heptane, n‐dodecane, n‐tetradecane, and n‐hexadecane, occurred in pure phase, with a quantitative global yield, a sulfochlorination‐to‐chlorination molar ratio of about 1, and a relative reactivity of secondary to primary hydrogen of about 2.5, at a reaction temperature of 30°C and a reaction time of 120 min, using 2×10−2 mol L−1 of pyridine. Under these conditions, no polysulfochlorinated compounds are detected. These results are further improved using chlorobenzene as the solvent, instead of benzene. Indeed, the sulfochlorination of n‐heptane at a conversion rate of 80% in the presence of chlorobenzene leads also to a quantitative reaction yield, a higher RSO2Cl/RCl molar ratio, and, as expected, a high selectivity of secondary over primary hydrogen. Under these conditions, sulfochlorination of long‐chain n‐alkanes leads to the highest RSO2Cl/RCl molar ratio for n‐dodecane, n‐tetradecane, and n‐hexadecane belonging to detergent range, and the value of the molar ratio for these is between 1.45 and 1.7. The isomeric distribution of sulfochlorinated compounds obtained during sulfochlorination in the presence of solvent resembles that of secondary alkanesul‐fonates produced by sulfoxidation reaction, whereas that obtained in pure phase has a similar conversion rate, is rich in primary isomer, and thus is different from that of classic radical reactions such as photochlorination or photosulfochlorination with gas mixture.