bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for glutamatergic mechanisms in the vagal sensory pathway initiating cardiorespiratory reflexes in the shorthorn sculpinMyoxocephalus scorpius
Authors: Sundin L. , Turesson J. , Taylor E. W.
Published: January 2003

Glutamate is a major neurotransmitter of chemoreceptor and baroreceptor afferent pathways in mammals and therefore plays a central role in the development of cardiorespiratory reflexes. In fish, the gills are the major sites of these receptors, and, consequently, the terminal field (sensory area)of their afferents (glossopharyngus and vagus) in the medulla must be an important site for the integration of chemoreceptor and baroreceptor signals. This investigation explored whether fish have glutamatergic mechanisms in the vagal sensory area (Xs) that could be involved in the generation of cardiorespiratory reflexes.

The locations of the vagal sensory and motor (Xm) areas in the medulla were established by the orthograde and retrograde axonal transport of the neural tract tracer Fast Blue following its injection into the ganglion nodosum. Glutamate was then microinjected into identified sites within the Xs in an attempt to mimic chemoreceptor- and baroreceptor-induced reflexes commonly observed in fish. By necessity, the brain injections were performed on anaesthetised animals that were fixed by `eye bars' in a recirculating water system. Blood pressure and heart rate were measured using an arterial cannula positioned in the afferent branchial artery of the 3rd gill arch, and ventilation was measured by impedance probes sutured onto the operculum.

Unilateral injection of glutamate (40-100 nl, 10 mmol l-1) into the Xs caused marked cardiorespiratory changes. Injection (0.1-0.3 mm deep) in different rostrocaudal, medial-lateral positions induced a bradycardia, either increased or decreased blood pressure, ventilation frequency and amplitude and, sometimes, an initial apnea. Often these responses occurred simultaneously in various different combinations but, occasionally, they appeared singly, suggesting specific projections into the Xs for each cardiorespiratory variable and local determination of the modality of the response. Response patterns related to chemoreceptor reflex activation were predominantly located rostral of obex, whereas patterns related to baroreceptor reflex activation were more caudal, around obex.

The glutamate-induced bradycardia was N-methyl-D-aspartate (NMDA)receptor dependent and atropine sensitive. Taken together, our data provide evidence that glutamate is a putative player in the central integration of chemoreceptor and baroreceptor information in fish.
Ontogeny of feeding function in the gray short-tailed opossumMonodelphis domestica: empirical support for the constrained model of jaw biomechanics
Authors: Thompson Elicia N. , Biknevicius Audrone R. , German Rebecca Z.
Published: January 2003

The constrained model of masticatory function enables specific predictions of bite force potentials in skulls of differing craniodental configurations. In this study, empirical support for the constrained model is provided using maximum voluntary bite force data along Region I and II of the jaws of gray short-tailed opossums Monodelphis domestica. Then, growth series of M. domestica are used to assess how bite force potential changes with growth by evaluating craniodental changes using longitudinal sets of dorsoventral radiographs and by assessing maximal bite force potential at the Region I-II boundary of the jaw in juveniles (aged 70-80 days) and adults. Our findings show that, while juveniles and adults alike enclose at least three molariform teeth within Region II (the area of highest bite force potential along the jaw), age-dependent elongation of the masticatory muscle resultant lever arm and narrowing of the palate relative to jaw length especially enhance the mechanical advantage of the adductor muscle resultant in adults. While maximal bite forces at the Region I-II boundary are absolutely greater in adults, these bite forces scale isometrically with body mass, which suggests that mass-specific forces exerted by jaw adductor muscles of larger(adult) opossums are disproportionately smaller than those exerted by smaller(juvenile) opossums.
Cardiovascular responses to hypoxia and anaemia in the toadBufo marinus
Authors: Andersen Johnnie B. , Hedrick Michael S. , Wang Tobias
Published: January 2003

Amphibians exhibit cardiorespiratory responses to hypoxia and, although several oxygen-sensitive chemoreceptor sites have been identified, the specific oxygen stimulus that triggers these responses remains controversial. This study investigates whether the cardiovascular response to oxygen shortage correlates with decreased oxygen partial pressure of arterial blood(PaO2) or reduced oxygen concentration([O2]) in toads. Toads, equipped with blood flow probes and an arterial catheter, were exposed to graded hypoxia [fraction of oxygen in the inspired air (FIO2)=0.21, 0.15, 0.10, 0.07 and 0.05] before and after reductions in arterial [O2] by isovolemic anaemia that reduced haematocrit by approximately 50%. Toads responded to hypoxia by increasing heart rate (fH) and pulmocutaneous blood flow(Q̇pc) and reducing the net cardiac right-to-left-shunt. When arterial [O2] was reduced by anaemia, the toads exhibited a similar cardiovascular response to that observed in hypoxia. While arterial CO2 partial pressure(PaCO2) decreased significantly during hypoxia,indicative of increased alveolar ventilation, anaemia did not alter PaCO2). This suggests that reductions in[O2] mediate cardiovascular adjustments, while ventilatory responses are caused by reduced PaO2.
norpAanditprmutants reveal roles for phospholipase C and inositol (1,4,5)- trisphosphate receptor inDrosophila melanogasterrenal function
Authors: Pollock Valerie P. , Radford Jonathan C. , Pyne Susan , Hasan Gaiti , Dow Julian A. T. , Davies Shireen-A.
Published: January 2003

Mutants of norpA, encoding phospholipase Cβ (PLCβ), and itpr, encoding inositol (1,4,5)-trisphosphate receptor(IP3R), both attenuate response to diuretic peptides of Drosophila melanogaster renal (Malpighian) tubules. Intact tubules from norpA mutants severely reduced diuresis stimulated by the principal cell- and stellate cell-specific neuropeptides, CAP2b and Drosophila leucokinin (Drosokinin), respectively, suggesting a role for PLCβ in both these cell types. Measurement of IP3production in wild-type tubules and in Drosokinin-receptor-transfected S2 cells stimulated with CAP2b and Drosokinin, respectively, confirmed that both neuropeptides elevate IP3 levels.

In itpr hypomorphs, basal IP3 levels are lower,although CAP2b-stimulated IP3 levels are not significantly reduced compared with wild type. However,CAP2b-stimulated fluid transport is significantly reduced in itpr alleles. Rescue of the itpr90B.0 allele with wild-type itpr restores CAP2b-stimulated fluid transport levels to wild type. Drosokinin-stimulated fluid transport is also reduced in homozygous and heteroallelic itpr mutants.

Measurements of cytosolic calcium levels in intact tubules of wild-type and itpr mutants using targeted expression of the calcium reporter,aequorin, show that mutations in itpr attenuated both CAP2b- and Drosokinin-stimulated calcium responses. The reductions in calcium signals are associated with corresponding reductions in fluid transport rates.

Thus, we describe a role for norpA and itpr in renal epithelia and show that both CAP2b and Drosokinin are PLCβ-dependent, IP3-mobilising neuropeptides in Drosophila. IP3R contributes to the calcium signalling cascades initiated by these peptides in both principal and stellate cells.
Feeding mechanisms in carp: crossflow filtration, palatal protrusions and flow reversals
Authors: Callan W. Todd , Sanderson S. Laurie
Published: January 2003

It has been hypothesized that, when engulfing food mixed with inorganic particles during benthic feeding, cyprinid fish use protrusions of tissue from the palatal organ to retain the food particles while the inorganic particles are expelled from the opercular slits. In crossflow filtration, the particle suspension is pumped parallel to the filter surface as filtrate exits through the filter pores, causing the suspension to become more concentrated as it travels downstream along the filter. We used high-speed video endoscopy to determine whether carp Cyprinus carpio use crossflow filtration and/or palatal protrusions during benthic feeding. We found that carp use crossflow filtration to concentrate small food particles in the pharyngeal cavity while expelling small dense inorganic particles through the opercular slits and via spits. Our results suggest that, during feeding on small food particles, palatal protrusions serve a localized chemosensory function rather than a mechanical particle-sorting function. However, palatal protrusions did retain large food particles while large inorganic particles were spit anteriorly from the mouth. We also investigated whether flow is continuous and unidirectional during suspension feeding in carp. As reported previously for ventilation in hedgehog skates and for certain industrial crossflow filtration applications, we observed that flow is pulsatile and bidirectional during feeding. These results have implications for hydrodynamic models of crossflow filtration in suspension-feeding fishes.
Comparative analysis of nitric oxide and SALMFamide neuropeptides as general muscle relaxants in starfish
Authors: Melarange Richard , Elphick Maurice R.
Published: January 2003

Previous studies have established that the gaseous signalling molecule nitric oxide (NO) and the SALMFamide neuropeptides S1 and S2 cause cardiac stomach relaxation in the starfish Asterias rubens. Here we show that S1, S2 and the NO donor SNAP also cause relaxation of two other preparations from Asterias — tube feet and the apical muscle of the body wall. The rank order of effectiveness as muscle relaxants when tested at a concentration of 10 μmol l-1 was SNAP>S2>S1 for both tube feet and apical muscle whereas for cardiac stomach it was S2>S1>SNAP. Significantly, these data indicate that NO and SALMFamide neuropeptides function as general muscle relaxants in starfish but vary in their relative importance in different organ systems.

The molecular mechanisms by which NO and SALMFamides cause muscle relaxation in starfish are not known, but previous pharmacological studies on the cardiac stomach using the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazol[4,3-a]quinoxalin-1-one (ODQ) indicate that the cyclic nucleotide second messenger cGMP may mediate effects of NO. Consistent with this hypothesis, here we report that ODQ also causes partial inhibition of the relaxing effect of SNAP on tube foot and apical muscle preparations. To further investigate the involvement of cyclic nucleotides as mediators of the effects of NO and SALMFamides on starfish muscle, we have measured both cGMP and cAMP in cardiac stomach and in apical muscle after treatment with S1, S2 or SNAP. However, no significant changes in cyclic nucleotide content were observed compared with controls. Further experiments were performed on apical muscle tissue in the presence of the cyclic-nucleotide-phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), a drug that also causes cardiac stomach relaxation in starfish. Treatment with IBMX caused a 2-3-fold increase above basal levels for cGMP and cAMP, but co-treatment with IBMX and S1 or S2 or SNAP resulted in no significant further increase above the level observed with IBMX alone. We conclude from these data that the relaxing action of NO on starfish muscle may be mediated by both cGMP-dependent and cGMP-independent pathways. However, the mechanisms by which SALMFamides cause muscle relaxation in starfish remain unknown and, although our results do not rule out the involvement of cGMP or cAMP, other signalling pathways may now need to be investigated.
Dynamical aspects of the life cycle of the winter storm ‘Lothar’ (24–26 December 1999)
Authors: Wernli Heini , Dirren Sebastien , Liniger Mark A. , Zillig Matthias
Published: January 2003

Dynamical aspects of the life cycle of the winter storm ‘Lothar’ (24–26 December 1999) are investigated with the aid of the European Centre for Medium‐Range Weather Forecasts analysis data and mesoscale model simulations. Neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds, but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event. The analysis and interpretation is primarily based upon the evolution of the lower‐ and upper‐level potential vorticity (PV) field complemented by three‐dimensional trajectory calculations.

‘Lothar’ originated in the western Atlantic and travelled as a shallow low‐level cyclone of moderate intensity towards Europe. This translation took place below and slightly to the south of a very intense upper‐level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low‐level PV anomaly (not unlike the concept of a ‘diabatic Rossby wave’). No significant PV anomalies were evident at the tropopause level during this early phase of the life cycle. The surface cyclone intensified rapidly when the shallow cyclone approached the jet‐stream axis. The circulation induced by the diabatically produced low‐tropospheric PV anomaly on steeply sloping isentropic surfaces that transect the intense upper‐level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold. This stratospheric PV anomaly virtually merged with the diabatically produced ephemeral PV feature to form a vertically aligned tower of positive PV at the time of maximum storm intensity. A sensitivity study with a dry adiabatic hindcast simulation shows no PV‐tower configuration (and only a very weak surface development) and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid ‘bottom‐up’ intensification of ‘Lothar’.

A comparison of the anomalously high Atlantic sea surface temperatures in December 1999 with the water‐vapour source regions for the latent‐heat release that accompanied the rapid intensification phase of ‘Lothar’ shows a close relationship. This is of importance when discussing the possible implications of climate variability and change on the development of North Atlantic winter storms. Copyright © 2002 Royal Meteorological Society
Idealized numerical simulations of shallow föhn
Authors: Zängl G.
Published: January 2003

Idealized numerical simulations are performed in order to get a deeper dynamical understanding of the so‐called shallow föhn. This is a southerly gap flow which sometimes occurs in north–south oriented Alpine valleys under approximately westerly synoptic‐scale flow conditions. Observations indicate that shallow föhn is primarily driven by a hydrostatic pressure difference between relatively cold air to the south of the Alps and warmer air to the north. A recent study suggested that the meridional pressure gradient associated with geostrophically balanced westerly wind also has the potential to induce significant shallow föhn. While this study is restricted to an infinitely long mountain ridge with a gap, various isolated ridges are considered in the present work.

It is found that replacing the infinite ridge by an isolated one leads to fundamental changes in the behaviour of the gap flow if surface friction is excluded and the large‐scale flow is taken to be uniform westerly. While strong southerly gap flow is found for the infinite ridge, weak northerly gap flow prevails for the isolated mountains. This is primarily because flow splitting and Coriolis effects yield—in the parameter range relevant for the Alps—strong anticyclonic flow around an isolated mountain. Due to ageostrophy, this anticyclonic flow is associated with a northerly flow component towards the northern side of the mountain, piling up some air there and compensating for or even reversing the geostrophic pressure gradient across the mountain. From that it follows that the mere presence of a geostrophic pressure gradient is not sufficient to induce shallow föhn. Surface friction yields a southerly flow component in the boundary layer and reinforces the pressure gradient across the mountain. Therefore, friction supports southerly gap flow and reduces the differences between infinite and isolated ridges. However, additional simulations with an arc‐shaped mountain similar to the real Alps indicate a further reduction of the tendency towards southerly gap flow. This is due to a weak lee cyclone which forms to the east of the arc and reduces the cross‐Alpine pressure gradient. A southerly component in the large‐scale flow appears to be necessary to obtain southerly gap flow for the arc‐shaped mountain. In this case, potentially cold low‐level air is piled up on the southern side of the Alps, and a hydrostatic pressure difference across the Alps is established in accordance with observations. Copyright © 2002 Royal Meteorological Society
Properties of embedded convection in warm‐frontal mixed‐phase cloud from aircraft and polarimetric radar
Authors: Hogan R. J. , Field P. R. , Illingworth A. J. , Cotton R. J. , Choularton T. W.
Published: January 2003

Results are presented from a case‐study in which the macrophysical and microphysical characteristics of a warm‐frontal mixed‐phase cloud were investigated using simultaneous aircraft and polarimetric‐radar measurements. A region of embedded convection was located and sampled at various stages of its ascent through the cloud from −5° to −11°, and evidence is presented that it was triggered by Kelvin–Helmholtz instability near the melting layer. High concentrations of small crystals were observed in and above narrow convective turrets, around 1 km across, that contained supercooled liquid‐water droplets with an effective diameter of 24 µm and riming ice particles. The area surrounding the turrets was found to contain pristine columns, and was strikingly visible to the radar as a broad plume of high differential reflectivity ZDR (around 3 dB), contrasting with the 0–0.5 dB range usually found in ice clouds. The columns observed in situ had axial ratios of around 5:1, in close agreement with the values predicted theoretically from ZDR assuming horizontal alignment of the crystals. We argue that the high concentrations of small ice crystals (up to 103 l−1) observed in this case were splinters produced via the Hallett–Mossop mechanism in the riming process, and these then grew rapidly by deposition in the water‐saturated environment into pristine columns. Later in the ascent the picture was complicated by the presence of a fallstreak containing large, low‐ZDR aggregates which appeared to rapidly accrete the columns. A number of plumes of high ZDR were observed by the radar on the same day, each of which persisted for at least half an hour. In the vicinity of cloud top −15°, the regions of high ZDR tended to spread out horizontally, and attain values as high as 7 dB. At these temperatures plates and dendrites are known to grow, so these ZDR observations are in good agreement with our theoretical finding that columns alone cannot produce values of ZDR greater than 4 dB, no matter how extreme their axial ratios, whereas planar crystals can attain values up to 10 dB. Embedded convection could clearly be important in determining the distribution of ice and liquid water in frontal clouds, which affects both cloud glaciation and the radiation budget, and is important for aircraft icing. Copyright © 2002 Royal Meteorological Society
Cloud‐top striations above ana‐cold frontal circulations
Authors: Browning K. A. , Wang C.‐G.
Published: January 2003

Satellite images occasionally show regular arrays of cloud‐top striations within mesoscale cloud features associated with vigorous ana‐cold frontal circulations. Observational case‐studies with a variety of types of radar are presented to show that the striations are due to bands of upright upper‐level convective cells. These convective cells form at the top of the rearward‐sloping‐ascent part of a transverse frontal circulation which, in one of the cases studied, had a multi‐layered structure fed in turn by upright line convection lifting air from the boundary layer. This coexistence and interdependence of upright and slantwise forms of convection may not in itself be uncommon; what is less usual in these results is the way in which the upper‐level convection is manifested as bands, or striations, orientated roughly parallel to the wind shear at cloud‐top level but almost perpendicular to the strong thermal‐wind shear in the underlying frontal zone—a behaviour that may be specific to vigorous ana‐cold frontal systems. The striations have a large wavelength (30 to 55 km) but we are unaware of any simple dynamical mechanism that can account for the convection being organized on this scale. The striations are regarded as an important indicator of accompanying adverse weather. Earlier studies have suggested that such striations are associated with rapid cyclogenesis and surface gusts. One of the cases presented here falls into this category; the other, more detailed, case‐study is notable for the rainfall associated with the vigorous frontal circulations. Copyright © 2002 Royal Meteorological Society
Effects of in‐cloud nucleation and turbulence on droplet spectrum formation in cumulus clouds
Authors: PINSKY M. B. , Khain A. P.
Published: January 2003

Drop spectrum evolution is investigated using a moving mass grid microphysical cloud parcel model containing 2000 mass bins and allowing turbulent effects on droplet collisions. Utilization of precise methods of diffusion and collision drop growth eliminates any artificial droplet spectrum broadening. Simulation of continental, intermediate and maritime clouds is conducted using different concentrations of cloud condensation nuclei and different vertical velocities at the cloud base.

An increase of the collision kernel in turbulent surroundings is found to be an important factor in the acceleration of large droplet and raindrop formation. Droplet spectrum formation was found to be affected by three stages of in‐cloud droplets' nucleation: (a) nucleation near the cloud base, forming the primary mode of the droplet spectrum; (b) nucleation within a parcel, where supersaturation exceeds its maximum at the cloud base, this type of nucleation forming the secondary spectral mode; and (c) nucleation within the zone of intensive collisions, when a rapid decrease in drop concentration leads to an increase in supersaturation.

It is shown that the secondary mode in the droplet spectrum contributes significantly to raindrop formation, therefore the absence of the secondary mode (the single‐mode spectrum) can reduce or even inhibit formation of raindrops.

The contributions of diffusion and collision growth to drop spectrum formation are compared. Effective collisions are found to start when the effective radius attains about 15 µm. The level where the effective radius attains 15 µm can be considered as the level of the first radar echo. This height is shown to crucially depend on cloud dynamics (in particular, on the vertical velocity at the cloud base) and on the concentration of aerosol particles. Copyright © 2002 Royal Meteorological Society
A numerical model of the cloud‐topped marine boundary layer with explicit treatment of supersaturation–number concentration correlations
Authors: Svensson Gunilla , Seinfeld John H.
Published: January 2003

A numerical model of the cloud‐topped marine boundary layer is presented. The model, based on ensemble‐averaged conservation equations and containing detailed aerosol microphysics, differs from previous models in one major respect: the mean supersaturation–cloud drop number concentration correlation term, generally neglected in previous numerical mean cloud models, is parametrized using a traditional boundary‐layer flux‐gradient relationship. The present work highlights the importance of this correlation term and shows how a simple representation of this correlation can lead to dramatically different, and improved, simulations of cloud behaviour. Simulations are presented for a well‐studied marine boundary‐layer stratocumulus case. Inclusion of the supersaturation–cloud drop number concentration correlation leads to more physically realistic cloud drop spectra and cloud drop concentrations throughout the height of the cloud. Although the parametrization presented must be viewed as a first approximation, the crudeness of the approach should be seen as a justification and starting point for future work. Copyright © 2002 Royal Meteorological Society
Principal‐component analysis for raindrops and its application to the remote sensing of rain
Authors: Meagher Jonathan P. , Haddad Ziad S.
Published: January 2003

In the problem of inverting remote‐sensing measurements of rain, current representations of the raindrop size distribution suffer crucially from the expedient but unjustified and empirically ill‐fitting assumption that the distribution has a known closed‐form shape, whether log‐normal or Γ‐distributed. This paper proposes an approach to avoid such unfounded a priori assumptions entirely. The resulting representation of the rain is then used to derive ‘forward’ formulae for rain remote‐sensing algorithms. Copyright © 2002 Royal Meteorological Society
Use of an explicit model of the microphysics of precipitating stratiform cloud to test a bulk microphysics scheme
Authors: Cardwell J. R. , Choularton T. W. , Wilson D. , Kershaw R.
Published: January 2003

An explicit microphysical model is used to study the development of nimbostratus cloud. The model contains a simple representation of embedded convection. The results show that secondary ice processes can be important in determining the ice and liquid‐water contents of the cloud, especially when embedded convection is switched on. The results are used to test the bulk microphysical parametrization that is used in a state‐of‐the‐art climate model, by running the bulk scheme within the same dynamical framework as the explicit scheme. Compared with the explicit scheme, the bulk scheme overestimates the ice and underestimates the liquid‐water content compared with the explicit scheme. To parametrize the secondary ice processes effectively, the bulk scheme will require representation of small ice crystals. Copyright © 2002 Royal Meteorological Society
An intercomparison of cloud‐resolving models with the atmospheric radiation measurement summer 1997 intensive observation period data
Authors: Xu Kuan‐Man , Cederwall Richard T. , Donner Leo J. , Grabowski Wojciech W. , Guichard Françoise , Johnson Daniel E. , Khairoutdinov Marat , Krueger Steven K. , Petch Jon C. , Randall David A. , Seman Charles J. , Tao Wei‐Kuo , Wang Donghai , Cheng Xie Shao , Yio J. John , Zhang Ming‐Hua
Published: January 2003

This paper reports an intercomparison study of midlatitude continental cumulus convection simulated by eight two‐dimensional and two three‐dimensional cloud‐resolving models (CRMs), driven by observed large‐scale advective temperature and moisture tendencies, surface turbulent fluxes, and radiative‐heating profiles during three sub‐periods of the summer 1997 Intensive Observation Period of the US Department of Energy's Atmospheric Radiation Measurement (ARM) program. Each sub‐period includes two or three precipitation events of various intensities over a span of 4 or 5 days. The results can be summarized as follows.

CRMs can reasonably simulate midlatitude continental summer convection observed at the ARM Cloud and Radiation Testbed site in terms of the intensity of convective activity, and the temperature and specific‐humidity evolution. Delayed occurrences of the initial precipitation events are a common feature for all three sub‐cases among the models. Cloud mass fluxes, condensate mixing ratios and hydrometeor fractions produced by all CRMs are similar. Some of the simulated cloud properties such as cloud liquid‐water path and hydrometeor fraction are rather similar to available observations. All CRMs produce large downdraught mass fluxes with magnitudes similar to those of updraughts, in contrast to CRM results for tropical convection. Some inter‐model differences in cloud properties are likely to be related to those in the parametrizations of microphysical processes.

There is generally a good agreement between the CRMs and observations with CRMs being significantly better than single‐column models (SCMs), suggesting that current results are suitable for use in improving parametrizations in SCMs. However, improvements can still be made in the CRM simulations; these include the proper initialization of the CRMs and a more proper method of diagnosing cloud boundaries in model outputs for comparison with satellite and radar cloud observations. Copyright © 2002 Royal Meteorological Society
Aspects of the parametrization of organized convection: contrasting cloud‐resolving model and single‐column model realizations
Authors: Gregory D. , Guichard F.
Published: January 2003

Cloud‐resolving model (CRM) simulations of organized tropical convection observed in the Tropical Ocean/Global Atmosphere Coupled Ocean–Atmosphere Response Experiment are used to evaluate versions of the European Centre for Medium‐Range Weather Forecasts convection and cloud schemes in single‐column model simulations. Emphasis is placed upon the ability of the convection scheme to represent ‘convective‐scale’ processes with typically mode‐1 heating structures through the troposphere, together with a cloud scheme representing the ‘stratiform (mesoscale) component’ with upper‐level heating and low‐level cooling due to the evaporation of precipitation. While diagnosis of convective and stratiform precipitation is sensitive to the sampling criteria applied to the CRM, vertical structures of the mass and heat budgets are robust. Using diagnostics from the CRM simulations as a guide, revisions to the convection and cloud schemes are suggested in order to enable the parametrization to represent the two scales. The study suggests that a mass‐flux convection scheme linked via detrainment to a prognostic treatment of cloud can represent organized convection, provided that the upward motion in the upper‐level stratiform cloud is considered. Copyright © 2002 Royal Meteorological Society
Some aspects of the improvement in skill of numerical weather prediction
Authors: Simmons A. J. , Hollingsworth A.
Published: January 2003

Recent verification statistics show a considerable improvement in the accuracy of forecasts from three global numerical weather prediction systems. The improvement amounts to about a 1‐day gain in predictability of mean‐sea‐level pressure and 500 hPa height over the last decade in the northern hemisphere, with a similar gain over the last 3 years in the southern hemisphere. Differences between the initial analyses from the three systems have been substantially reduced.

Detailed study of the European Centre for Medium‐Range Weather Forecasts verifications shows that identifiable improvements in the data assimilation, model and observing systems have significantly increased the accuracy of both short‐ and medium‐range forecasts, although interannual (flow‐dependent) variations in error‐growth characteristics complicate the picture. The implied r.m.s. error of 500 hPa height analyses has fallen well below the 10 m level typical of radiosonde measurement error. Intrinsic error‐doubling times, computed from the divergence of northern hemisphere forecasts started 1 day apart, exhibit a small overall reduction over the past 10 years at day two and beyond, and a much larger reduction at day one. Error‐doubling times for the southern hemisphere have become generally shorter and are now similar to those for the northern hemisphere. One‐day forecast errors have been reduced so much in the southern hemisphere that medium‐range forecasts for the region have become almost as skilful as those for the northern hemisphere.

The approach to saturation of forecast error beyond the 10‐day range has been examined for sets of 21‐day forecasts. When the systematic (sample‐mean) component of the error is subtracted, forecast errors and the differences between successive forecasts both appear to level out near the end of the 21‐day range at values close to the limit set by the natural level of variance of the atmosphere for the northern hemisphere. A number of features of the model 500 hPa height fields remain quite realistic at the three‐week range. The most obvious discrepancy in mean climate is in the Pacific/North‐American sector, and variance is too high in the southern hemisphere. Copyright © 2002 Royal Meteorological Society
On shallow‐water potential‐vorticity inversion by Rossby‐number expansions
Authors: Mohebalhojeh A. R.
Published: January 2003

For the f‐plane shallow water (SW) equations, the basic properties of formal Rossby‐number expansions and potential vorticity (PV) inversion by the implied asymptotic balance conditions are re‐examined. An indeterminacy inherent in conventional expansions beyond leading‐order geostrophic balance is highlighted. The indeterminacy gives us the freedom to define, in principle, infinite sets of ‘balance conditions’ relating inertia–gravity modes to Rossby modes. Examples discussed include balance conditions that are obtained when one of the variables, linearized PV, vorticity, or perturbation height is regarded purely as a leading‐order geostrophic quantity.

For the sake of conservation of global mass and boundary circulation, SW PV inversion is defined as one that employs the PV anomaly, i.e. the deviation of PV from its domain‐area average. SW PV inversion by means of various Rossby‐number balance conditions and the modified expansion procedure for the PV anomaly are presented. In the latter, called the ‘WBSV procedure’ in this paper, the PV anomaly is regarded purely as the leading‐order geostrophic quantity and the Rossby formula for SW PV anomalies is satisfied asymptotically. A modification of the WBSV procedure satisfying the exact SW equation for the PV anomaly is also presented.

Numerical results for these PV inversion procedures, accurate up to second order in Rossby number, are presented for two SW simulations involving weakly and strongly ageostrophic flows. Also presented are results from PV inversion using the δ–γ hierarchy of balance conditions, which sets the Nth‐order time derivatives of divergence and ageostrophic vorticity to zero. It is shown that the WBSV procedure incurs a significant loss of accuracy relative to both the δ–γ hierarchy and other asymptotic procedures like the one that regards the linearized PV as a leading‐order geostrophic quantity. The modified WBSV procedure shows little improvement. The inaccuracy of this procedure stems from a poor leading‐order solution for the balanced fields. Copyright © 2002 Royal Meteorological Society
Objective analysis combining observation errors in physical space and observation space
Authors: Schyberg Harald , Breivik Lars‐Anders
Published: January 2003

A generalization of the traditional observation‐error model in objective analysis is presented. It is suggested that for observations with nonlinear observation operators, the observation errors should be split up into one contribution in the measurement domain and one contribution in the domain of the model physical quantities interpolated to the measurement locations (physical space). In particular, errors of representativeness are better modelled in physical space. Analysis equations are derived for this generalized problem. The approach suggested has important applications in the assimilation of satellite observations. For special cases with a wide application this generalization does not introduce an inhibiting computational complexity. Copyright © 2002 Royal Meteorological Society
Wave breaking and critical levels for propagating inertio‐gravity waves in the lower stratosphere
Authors: Moldovan H. , Lott F. , Teitelbaum H.
Published: January 2003

This paper analyses and interprets the formation of mixed layers due to propagating inertio‐gravity waves observed during the Fronts and Atlantic Storm‐Track EXperiment. The data used are high‐vertical‐resolution soundings launched from different sites located in the North Atlantic sector. In agreement with other studies, attributing the origin of the inertio‐gravity waves to the adjustment of the jet stream near fronts, the largest waves observed are often located in the vicinity of and above frontal bands. The amplitude of these waves is large enough that they give rise to narrow mixed layers. By a detailed analysis of the waves' characteristics, we can distinguish whether such a mixing is favoured by the presence of an inertia‐critical level, where |Ω|=f, or results from wave‐induced convective instability occurring far from critical levels. Here, Ω is the wave intrinsic frequency and f is the Coriolis parameter. These observations highlight the importance of inertio‐gravity waves in the vertical exchanges that occur in the stratosphere. Copyright © 2002 Royal Meteorological Society
A semi‐empirical parametrization for total in situ specific humidity standard deviation derived from tethered balloon observations
Authors: Price Jeremy D.
Published: January 2003

A parametrization has been derived from tethered balloon observations made between ground level and 1.8 km to predict the standard deviation of in situ specific humidity. The algorithm has possible use in cloud prediction models which use a distribution function for the total specific humidity, allowing it to be continuously scaled in each model grid‐box. It consists of two parts designed to cope both with stable and convective regimes. The average error in predicted humidity standard deviations has been estimated by comparison with observations and found to be 0.038 g kg−1, which is an order of magnitude smaller than the observed variation in the quantity. Copyright © 2002 Royal Meteorological Society
Diagnostic and prognostic equations for the depth of the stably stratified Ekman boundary layer
Authors: Zilitinkevich Sergej , Baklanov Alexander , Rost Jutta , Smedman Ann‐sofi , Lykosov Vasiliy , Calanca Pierliugi
Published: January 2003

Refined diagnostic and prognostic equations for the depth of the stably stratified barotropic Ekman boundary later (SBL) are derived employing a recently developed non‐local formulation for the eddy viscosity. In well‐studied cases of the thoroughly neutral SBL, the nocturnal atmospheric SBL and the oceanic SBL dominantly affected by the static stability in the thermocline, the proposed diagnostic equation reduces to the Rossby–Montgomery, Zilitinkevich and Pollard–Rhines–Thompson equations, respectively. In its general form it is applicable to a range of regimes including long‐lived atmospheric SBLs affected by the near‐surface buoyancy flux and the static stability in the free atmosphere. Both diagnostic and prognostic SBL depth equations are validated against recent data from atmospheric measurements. Copyright © 2002 Royal Meteorological Society.
Density currents in shear flows: Effects of rigid lid and cold‐pool internal circulation, and application to squall line dynamics
Authors: Xue Ming
Published: January 2003

Idealized density current models that contain a rigid lid, developed in previous studies, are evaluated. It is shown, through numerical experiments, that a realistic stable layer placed at the level of the rigid lid acts very much like a rigid lid, in confining the environmental flow to the levels below and in controlling the behaviour of density currents that propagate in the flow. When this stable layer is replaced by a neutrally stable layer, the behaviour of the density current is very different. These results support the hypothesis that in the atmosphere, the tropopause or a tropospheric inversion layer acts much like a rigid lid in the idealized density current models, and the solutions of these models are applicable to organized quasi‐two‐dimensional convective systems such as squall lines in the atmosphere.

The effects of cold‐pool internal circulations on density current behaviour are also examined. When a single circulation is present initially inside the cold pool, the direction of circulation that gives rise to a smaller shear across the density interface leads to a smoother interface and a much more steady density current head. Large‐amplitude eddies develop along the interface when the direction of circulation is reversed. When two layers of shear are initially present inside the cold pool, the flow pattern inside the cold pool tends to be dominated by the circulation of the lower layer. In this case, the behaviour of the density interface and density current head depends on more than just the initial cross‐interface shear.

The overall flow pattern in the density current, in which the cold‐pool circulation contains rearward flows at the ground level, bears a close similarity to that found in mature squall line systems, as shown by comparisons with a simulated squall line. When the cold pool in a squall line is defined in terms of the equivalent potential temperature, the solutions of idealized density currents in sheared flows become more readily applicable to squall lines. Copyright © 2002 Royal Meteorological Society.
Two‐stream approximations revisited: A new improvement and tests with GCM data
Authors: Räisänen P.
Published: January 2003

Two‐stream approximations (TSAs) are employed for multiple‐scattering calculations in most solar radiation schemes used in atmospheric general‐circulation models (GCMs). Two issues related to TSAs are addressed. First, a simple extension of the two‐stream formalism is presented that allows different parametrizations for different factors, such as water clouds, ice clouds and aerosols. A ‘tuned two‐stream approximation’ that uses this extension is then developed. Second, the accuracy of the tuned TSA and selected other TSAs is quantified using a global GCM‐generated dataset (nearly 25000 atmospheric columns with clouds, aerosols and absorbing gases).

In the tests with the GCM dataset, the Practical Improved Flux Method (PIFM) provided slightly better results than the delta‐Eddington approximation. Two recent modifications of delta‐Eddington yielded no, or only slight, improvement. For PIFM, the root‐mean‐square (r.m.s.) errors in top‐of‐the‐atmosphere (TOA) and surface net short‐wave fluxes and in total column absorption were 2.22, 3.09 and 2.98 W m−2, as compared with delta‐16‐stream discrete‐ordinate method results. For the tuned TSA, which was developed using the present dataset, the TOA and surface r.m.s. errors were 33% and 48% smaller than for PIFM, with substantially larger improvements at low solar elevations. The robustness of these results is tested in several sensitivity experiments in which the properties of the GCM dataset are modified systematically.

While typical delta‐TSAs performed, overall, fairly well, they all had a negative bias in atmospheric absorption and a positive bias in surface net short‐wave flux of ≈1 W m−2 in the global mean (including, also, night grid points). Furthermore, the absorption errors depended substantially on solar elevation. The reasons for these problems are discussed.

The tests with GCM data also confirmed that the delta‐four‐stream method is considerably more accurate than the TSAs, especially so for atmospheric absorption. Copyright © 2002 Royal Meteorological Society
A comparison of ensemble‐transform Kalman‐filter targeting guidance with ECMWF and NRL total‐energy singular‐vector guidance
Authors: Majumdar S. J. , Bishop C. H. , Buizza R. , Gelaro R.
Published: January 2003

Ongoing adaptive observing programmes strive to improve short‐ and medium‐range forecasts of winter weather over populated areas. Aircraft equipped with Global Positioning System (GPS) dropwindsondes are directed over ordinarily data‐sparse regions (oceans) to collect observations to enhance the subsequent operational analysis–forecast cycle. Two objective techniques that have been used to identify optimal ‘target regions’ are the ensemble‐transform Kalman filter (ET KF) and the singular‐vector technique. The similarities and differences between targeting guidance based on the ET KF and total‐energy singular vectors (TESVs) are assessed for ten cases during the North Pacific Experiment (NORPEX). TESVs are computed at the European Centre for Medium‐Range Weather Forecasts (ECMWF) and the Naval Research Laboratory (NRL) using their respective global models, and the ET KF uses 25 ECMWF ensemble perturbations.

Using measures based on (i) rankings of aircraft flight tracks and (ii) spatial similarities between targeting guidance maps, the main finding is that (a) the ET KF guidance is reasonably correlated with TESV guidance for at least seven of the ten NORPEX cases. Other findings include: (b) the ECMWF and NRL TESV targets sometimes differ significantly, (c) the ET KF and TESV guidance maps often display different optimal locations for targeting on smaller scales, but larger‐scale aspects are usually similar, (d) the ET KF generally identifies larger regions over which useful observations can be taken compared with the SV technique, and (e) regions that are deemed effective for targeting by both techniques often correspond to baroclinic zones.

The ET KF and SV techniques may identify similar regions for targeting if locations of large ensemble‐based analysis‐error variance coincide with areas where rapid perturbation growth occurs. On the other hand, they may identify different targeting locations for the following two reasons. First, the ET KF implicitly accounts for error correlation length‐scales in its predictions of forecast‐error variance reduction produced by any set of targeted observations. Hence, it can identify locations for targeted observations that are distant from the regions of high analysis sensitivity that are selected for targeting by the SV technique. Second, ET KF estimates of analysis‐error variance are constrained to a subspace of evolved ensemble perturbations and are, therefore, rank deficient. Copyright © 2002 Royal Meteorological Society
Some practical aspects of providing a diagnostic service for respiratory chain defects
Authors: Janssen A.J.M. , Smeitink J.A.M. , van den Heuvel L.P.
Published: January 2003

The oxidative phosphorylation system (OXPHOS) is organized into five multi-protein complexes, comprising four complexes (I-IV) of the respiratory chain and ATP synthase (complex V). OXPHOS has a vital role in cellular energy metabolism and ATP production. Enzyme analysis of individual OXPHOS complexes in a skeletal muscle biopsy remains the mainstay of the diagnostic process for patients suspected of mitochondrial cytopathy. Practical guidelines are presented to provide optimal conditions for performance of laboratory investigations and a reliable diagnosis. A fresh muscle biopsy is preferable to a frozen muscle sample because the overall capacity of the OXPHOS system can be measured in a fresh biopsy. In about 25% of patients referred for muscle biopsy to our centre, reduced substrate oxidation rates and ATP+creatine phosphate production rates were found without any defect in complexes I-V and the pyruvate dehydrogenase complex. Investigation of frozen muscle biopsy alone may lead to false-negative diagnoses in many patients. In some patients, it is necessary to investigate fibroblasts for prospective diagnostic purposes. An exact diagnosis of respiratory chain defects is a prerequisite for rational therapy and genetic counselling. Provided guidelines for specimen collection are followed, there are now reliable methods for identifying respiratory chain defects.