bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transcriptional Profiling of the Chick Pineal Gland, a Photoreceptive Circadian Oscillator and Pacemaker
Authors: Bailey Michael J. , Beremand Phillip D. , Hammer Rick , Bell-Pedersen Deborah , Thomas Terry L. , Cassone Vincent M. 
Published: July 2003

AbstractThe avian pineal gland contains both circadian oscillators and photoreceptors to produce rhythms in biosynthesis of the hormone melatonin in vivo and in vitro. The molecular mechanisms for melatonin biosynthesis are largely understood, but the mechanisms driving the rhythm itself or the photoreceptive processes that entrain the rhythm are unknown. We have produced cDNA microarrays of pineal gland transcripts under light-dark and constant darkness conditions. Rhythmic transcripts were classified according to function, representing diverse functional groups, including phototransduction pathways, transcription/translation factors, ion channel proteins, cell signaling molecules, and immune function genes. These were also organized relative to time of day mRNA abundance in light-dark and constant darkness. The transcriptional profile of the chick pineal gland reveals a more complex form of gene regulation than one might expect from a gland whose sole apparent function is the rhythmic biosynthesis of melatonin. The mRNAs encoding melatonin biosynthesis are rhythmic as are many orthologs of mammalian “clock genes.” However, the oscillation of phototransductive, immune, stress response, hormone binding, and other important processes in the transcriptome of the pineal gland, raises new questions regarding the role of the pineal gland in circadian rhythm generation, organization, and avian physiology.
The Spectrum and Term System of S VII
Authors: Christer Jupén  , Lars Engström  
Published: July 2003

The spectrum of six times ionized sulphur, S VII, has been investigated in the wavelength region 200–4000 Å by means of the beam-foil and laser-produced plasma techniques. The analysis comprises 219 lines of which 105 are newly identified. The present work establishes 123 2s22p5nlenergy levels of which 66 are new. The level energies are determined with an internal consistency of better than 20 cm-1. The observed level structure has been investigated by means of parametric calculations. The center-of-gravity ionization energy of the 2s22p52P limit has been determined to 2 269 410±60 cm-1. Of the identified 3s-3p and 3p-3d lines 27 are present in the solar coronal spectrum recorded by the SUMER instrument onboard the SOHO satellite. The present work adds 2 new solar identifications and improved wavelengths of some other solar coronal lines.
Tropospheric–stratospheric coupling: Extratropical synoptic systems in the lower stratosphere
Authors: Canziani Pablo O. , Legnani Walter E. 
Published: July 2003

AbstractSynoptic‐scale disturbances, existing in the lower stratosphere of middle to high southern latitudes and linked to tropospheric synoptic systems, are reviewed. Geopotential and wind fields show that synoptic‐scale perturbations exist in the re‐analysis products of the US National Center for Environmental Prediction, at least up to the 50 hPa level. A spatial spectral approach is used to demonstrate the existence of sizeable, episodic synoptic‐scale perturbations throughout the lower stratosphere. The extension of synoptic systems from the troposphere into the lower stratosphere at high and mid latitudes, during early spring is discussed, using two case‐studies. The background conditions given by the mean zonal flow, modulated by planetary‐scale waves, appear to provide the limiting conditions for such penetration, which would have been theoretically impossible if the zonal mean flow alone were considered. The results are discussed under a simple generalization of the Charney–Drazin limits to wave propagation. Copyright © 2003 Royal Meteorological Society.
A probabilistic description of convective mass fluxes and its relationship to extreme‐value theory
Authors: Naveau P. , Moncrieff M. W. 
Published: July 2003

AbstractThe vertical flux of mass by atmospheric convection, and convective cloud systems in particular, is a key quantity used in parametrization schemes for numerical weather‐prediction models and climate models. The concept of formulating mass fluxes in terms of statistical quantities is discussed and a probabilistic description of the upward mass fluxes, based on extreme‐value theory, is presented. This approach is illustrated by a statistical analysis of two‐dimensional, numerical realizations of two regimes of tropical convection, namely squall lines and non‐squall clusters. Our statistical model allows these distinct cloud systems, which play a key role in determining the shape of the mass‐flux profile, to be efficiently integrated. Also taken into account is the distinction between mesoscale and convective components of the mass flux. Copyright © 2003 Royal Meteorological Society.
Nonlinear singular spectrum analysis of the tropical stratospheric wind
Authors: Hsieh William W. , Hamilton Kevin 
Published: July 2003

AbstractThe neural‐network‐based nonlinear singular spectrum analysis (NLSSA) is applied to the zonal winds in the 70–10 hPa region (roughly 20–30 km altitude) measured at near‐equatorial stations during 1956–2000. The data are pre‐filtered by the linear singular spectrum analysis (SSA), with the leading eight SSA principal components (PCs) used as inputs for the NLSSA. The NLSSA fits a curve to the data in the eight‐dimensional PC space. This NLSSA curve, when projected onto the two‐dimensional plane spanned by any two PCs, shows the relation between the two SSA PCs. As different SSA modes are associated with different time‐scales, the relations found by the NLSSA reveal the time‐scales between which there are interactions—interactions between the dominant quasi‐biennial oscillation (QBO) time‐scale of about 28 months and the first harmonic at 14 months, and between 28 months and 12 months are found. The anharmonic nature of the QBO is well represented by the NLSSA mode 1, but not by individual SSA modes. The NLSSA is also applied to the time series of the zonal‐wind acceleration. Copyright © 2003 Royal Meteorological Society.
A feedback mechanism between soil‐moisture distribution and storm tracks
Authors: Pal Jeremy S. , Eltahir Elfatih A. B. 
Published: July 2003

AbstractHow the distribution of soil moisture impacts the location and persistence of the storm track and the resulting distribution of precipitation is investigated. Particular attention is given to North America where an extensive series of numerical experiments using a regional climate model are performed to investigate these issues. The findings suggest that soil‐moisture distribution has a pronounced impact on the large‐scale dynamics via a meridional displacement of the storm track. The displacement tends to enhance the local soil moisture–rainfall feedback over the region of the anomaly. The initial feedback is induced by the local effects of soil moisture on the boundary‐layer energy budget and then propagated to the large‐scale through modifications to the geopotential heights. Because of soil moisture's impact on the large‐scale dynamics, a local soil‐moisture anomaly can induce both flood‐ and drought‐like conditions in surrounding regions. Experiments with a dry anomaly applied either over the upper Midwest or Great Plains display a northward shift in the storm track. This shift tends to result in drought‐like conditions in the region of the anomaly and both flood‐ and drought‐like conditions in surrounding regions. Anomalous wetting in the Southwest impacts the distribution of precipitation not only locally, but also over most of the United States; drought‐like conditions are simulated to the north and east of the anomaly region while flood‐like conditions are simulated locally and eastward. Overall, the impacts of soil‐moisture distribution on the large‐scale dynamics and the location and intensity of the storm track play a significant role in determining summer rainfall distribution. Soil‐moisture anomalies over relatively small regions can induce floods and droughts not only locally, but also over remote regions. Copyright © 2003 Royal Meteorological Society.
Characteristics of mixed‐phase clouds. II: A climatology from ground‐based lidar
Authors: Hogan R. J. , Illingworth A. J. , O'connor E. J. , Baptista J. P. V. Poiares 
Published: July 2003

AbstractIn part I it was demonstrated that supercooled liquid‐water clouds can occur in the form of thin but radiatively significant layers that are distinctive in lidar imagery due to their high backscatter coefficient. In this paper, 18 months of near‐continuous lidar data from two midlatitude locations are analysed to estimate the frequency of occurrence of such clouds as a function of temperature. An algorithm is developed that uses the integrated backscatter to identify liquid‐water clouds with a visible optical depth of greater than 0.7 (i.e. those that scatter more than half of the incident radiation), and is found to compare favourably with microwave‐radiometer measurements of liquid‐water path. From data taken with a lidar pointing at 5° from zenith, the frequency of supercooled liquid‐water layers over Chilbolton in southern England is found to fall steadily with temperature; 27% of clouds between −5°C and −10°C are found to contain significant liquid water, falling to only 6% of clouds observed between −25°C and −30°C. The horizontal extent of the layers typically ranges between 20 and 70 km. When the lidar is pointed directly at zenith, specular reflection by horizontally aligned plate crystals is found to bias the statistics between −10°C and −20°C. The importance of supercooled liquid‐water clouds in the radiation budget is reduced when thick ice clouds are present above them, so we then use simultaneous cloud radar data to estimate the optical depth of any cloud above. It is found that around 30% of supercooled liquid‐water clouds with temperatures between 0°C and −20°C have ice above with a visible optical depth in excess of 0.5, falling to 10% between −20°C and −30°C. Given the substantial optical depth of the supercooled water itself, we conclude that in the majority of cases when supercooled water is present, it will dominate the radiative properties of the cloud profile. Finally, we compare the occurrence of supercooled‐liquid clouds with the amounts found in the models of the UK Met Office and the European Centre for Medium‐Range Weather Forecasts (ECMWF). Both models are found to produce too much supercooled liquid at warmer temperatures and too little at colder temperatures (with virtually none being simulated below −20°C), although the occurrence of supercooled cloud is far higher in the ECMWF model than the Met Office model. The observations in this paper are limited to one climatic zone but the forthcoming spaceborne lidars will be able to extend these comparisons to the whole globe. Copyright © 2003 Royal Meteorological Society.
Predictability study of the observed and simulated European climate using linear regression
Authors: Blender Richard , Luksch Ute , Fraedrich Klaus , Raible Christoph C. 
Published: July 2003

AbstractMonthly mean temperature anomalies in the regions England, Germany and Scandinavia are predicted by linear regression. Two predictors are selected from monthly mean teleconnection indices, North Atlantic sea surface temperatures (SSTs) projected on the first three empirical orthogonal functions (EOFs), and European climate variables (temperature, sea level pressure, and precipitation) averaged in the three predictand regions. The predictors are chosen separately for each month according to their correlation with the predictand. Observations from 1870–1999 and data from a 600‐year integration with the coupled atmosphere– ocean general‐circulation model ECHAM/HOPE are used to assess and compare the forecast skill. The skill is measured by the anomaly correlation coefficient (ACC) and the explained variance (EV).For a one‐month lead time the ACC for observations is up to 0:6 (EV≈35%) for February–March and August–September in the three regions. The skill for the simulated data is lower (maximum values at ACC≈0:5,EV≈25%) and its seasonal dependence differs from that of the observations. Main predictors are the preceding temperatures in the predictand region. Using segments of the simulated data the spread of skill is estimated as 0.1 in ACC (10% in EV).For lead times up to one year there is a small ACC (0.3–0.4) in the observations for England (spring and late summer), and Scandinavia (August–September), but none in Germany. The observed two‐month mean England temperature in spring and late summer can be predicted with six months' lead time for 1971–96 with 1870–1969 as a training set, selecting the first two North Atlantic SST EOF coefficients as predictors. A leave‐two‐out cross‐validation in 1870–1999 shows a distinct reduction of skill. In simulated data, the skill beyond one month is negligible compared with the observations. Copyright © 2003 Royal Meteorological Society.
Comparing mass‐consistent atmospheric moisture budgets on an irregular grid: An Arctic example
Authors: Göber M. , Hagenbrock R. , Ament F. , Hense A. 
Published: July 2003

AbstractWe present a method to minimize the effects of different resolution and mass imbalance when comparing atmospheric energy and water budgets from different datasets. Sizeable differences between re‐analysis‐ and radiosonde‐based atmospheric budgets had been found in earlier studies and it had been suspected that the different resolutions of the datasets strongly contributes to these discrepancies. Furthermore, most studies so far had used mass‐imbalanced wind fields, which can lead to serious errors. We balance the wind field by using a variational modification algorithm combined with a finite‐element discretization which allows the use of data on a grid defined by the radiosonde network. This method permits the computation of flux divergences in integral form and gives a consistent numerical method to get a mass‐balanced wind field with minimum modifications.Applying this method to Arctic radiosonde and re‐analysis data on the same grid leads to a better agreement with respect to the horizontal distribution and the mean annual cycle of the moisture flux convergence. The constraint of mass balance on the wind field leads to a greatly reduced and more realistic variability in space and time. However, a systematic difference of about 20% remains between the estimate based on a re‐analysis dataset sampled only on the coarse grid of the radiosonde network and an estimate based on the use of the full, fine grid of the re‐analysis. These systematic differences can be significantly reduced by creating a simulated radiosonde dataset from the re‐analysis with doubled resolution. We undertake an extensive analysis of the uncertainty of the estimates originating from the choices made in the specification of the algorithm. Based solely on radiosonde data, which are likely to result in a low bias, we estimate the net water gain of the Arctic atmosphere as 164 ± 10 mm yr−1 (0.45 ± 0.03 mm d−1) for 1979–93. Copyright © 2003 Royal Meteorological Society.
Forcing singular vectors and other sensitive model structures
Authors: Barkmeijer J. , Iversen T. , Palmer T. N. 
Published: July 2003

AbstractModel tendency perturbations can, like analysis perturbations, be an effective way to influence forecasts. In this paper, optimal model tendency perturbations, or forcing singular vectors, are computed with diabatic linear and adjoint T42L40 versions of the European Centre for Medium‐Range Weather Forecasts' forecast model. During the forecast time, the spatial pattern of the tendency perturbation does not vary and the response at optimization time (48 hours) is measured in terms of total energy. Their properties are compared with those of initial singular vectors, and differences, such as larger horizontal scale and location, are discussed. Sensitivity calculations are also performed, whereby a cost function measuring the 2‐day forecast error is minimized by only allowing tendency perturbations. For a given number of minimization steps, this approach yields larger cost‐function reductions than the sensitivity calculation using only analysis perturbations. Nonlinear forecasts using only one type of perturbation confirm an improved performance in the case of tendency perturbations. For a summer experiment a substantial reduction of the systematic error is shown in the case of forcing sensitivity. Copyright © 2003 Royal Meteorological Society.
Linking boundary‐layer variability with convection: A case‐study from JET2000
Authors: Taylor C. M. , Ellis R. J. , Parker D. J. , Burton R. R. , Thorncroft C. D. 
Published: July 2003

AbstractThe properties of the planetary boundary layer (PBL) are crucial for understanding convection and dynamics in the tropical atmosphere. In semi‐arid regions, there are strong links between the PBL and soil moisture. This study demonstrates the link between PBL characteristics and antecedent rainfall via soil moisture variability on length‐scales from 10 to 100 km. Spatial variability of the PBL in the west African Sahel is explored using observations from an aircraft for one day in the wet season, as part of the JET2000 experiment. Meteosat and surface station data provide information about rainfall patterns during the previous days.The aircraft transect crossed several well‐defined bands of low surface temperature and albedo, as determined by the satellite imagery. These bands indicate high soil moisture beneath the paths of recent storms. Observed atmospheric properties are closely linked to the surface gradients. Above moist soils, the PBL tends to be shallower, cooler, moister and less turbulent than in adjacent dry areas. The study shows that the characteristic large‐scale gradients of temperature and humidity across the Sahel are concentrated in zones defined by recent rainfall.Evidence is presented which is consistent with a positive feedback at the storm‐scale between deep convection and soil moisture. Atmospheric profiles indicate that soil moisture plays an important role in determining the stability of the atmosphere to subsequent convection. It was found that in a region of low surface moisture covering 80000 km2, cold‐cloud systems did not occur in the 48 hours following the flight. By contrast, mesoscale convective systems were observed in adjacent regions with wetter soils. Copyright © 2003 Royal Meteorological Society.
Horizontal and temporal variability of mountain waves over Mont Blanc
Authors: Smith S. A. , Broad A. S. 
Published: July 2003

AbstractAircraft observations of mountain waves over Mont Blanc during the 2 November 1999 Mesoscale Alpine Programme (MAP) case‐study are analysed. The present paper focuses on the horizontal and temporal variability of the wave field and its momentum fluxes. Results from the first Met Office Unified Model new‐dynamics simulation of a real mountain‐wave case are presented. The wave field and its fluxes are reproduced reasonably well considering the complexity of the problem.The wave momentum fluxes are observed to be extremely variable, which is surprising considering the stationarity of the wave field, although some variation is observed in the vertical‐velocity magnitude. The flux variability may result from the increasing midtropospheric wind shear with time. The simulated wind fields are used to investigate the horizontal variability in the wave field. The along‐track wave momentum flux is affected only slightly by a 2 km change in the position of the transect relative to Mont Blanc due to its displacement from the centre of the wave. More important in this particular case is the effect of the averaging length on the flux profile due to the limited downstream extent of the wave field, with large fluxes observed immediately over Mont Blanc. However, the position of the transect affects the apparent extent of the wave field and the magnitude of the variation in the cross‐wind component. © Crown copyright 2003.
Solar radiative transfer for stratiform clouds with horizontal variations in liquid‐water path and droplet effective radius
Authors: Räisänen Petri , Isaac George A. , Barker Howard W. , Gultepe Ismail 
Published: July 2003

AbstractEffects of horizontal variations in liquid‐water path (LWP) and droplet effective radius (re) on solar radiative‐transfer properties of stratiform clouds are addressed. To this end, a broadband Monte Carlo solar radiation code and in situ aircraft observations of cloud properties collected in the Radiation, Aerosol and Cloud Experiment are used. The experiments confirm that the radiative impact of cloud horizontal inhomogeneity is dominated by variations in LWP, which make cloud short‐wave albedo smaller than that for a corresponding plane‐parallel horizontally homogeneous cloud. When horizontal variations in re are accounted for, however, the impact due to horizontal variations in LWP is usually reduced. When re and LWP are highly correlated, as is typically the case, the impact on albedo due to LWP variations alone can be reduced easily by 30% when variations in re are included. Uncertainty factors involved in the calculations are also discussed. Copyright © 2003 Royal Meteorological Society.
Impact of temperature and humidity variability on cloud cover assessed using aircraft data
Authors: Tompkins A. M. 
Published: July 2003

AbstractAircraft thermodynamic measurements taken in liquid‐water clouds over the North American Great Plains are analysed to assess the relative importance of temperature and humidity fluctuations for cloud cover. It is found that the effect of temperature variability is roughly half that of humidity. Thus, although the representation of humidity variability in models is the primary task, the parametrization of temperature perturbations is also desirable. This aim would be easier if temperature and humidity fluctuations were correlated, since a diagnostic parametrization may then be possible. Examination of the data reveals that the majority of events show a negative correlation, in agreement with previous observations. Moreover, the cloud cover error is significantly smaller in the cases where temperature and humidity perturbations are uncorrelated for two reasons. Firstly, the de‐correlation is likely to be the result of a faster dissipation time‐scale for temperature fluctuations, which also reduces their magnitude and thus importance. Secondly, it is shown that there is a significant cancellation of cloud cover errors when no correlation between temperature and humidity exists. A simple estimate of the temperature/humidity correlation is made assuming vertical adiabatic motion is the only source of horizontal fluctuations, and it is found to produce a close fit to the data in some instances, mostly when the magnitude of the temperature fluctuations is larger, as predicted. In summary, the analysis implies that a simple diagnostic parametrization for temperature fluctuations may be helpful and indeed possible. Copyright © 2003 Royal Meteorological Society.