bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spectrophone measurements of the absorption of solar radiation by aerosol
Authors: Foot J. S. 
Published: February 2007

AbstractAbsorption of the direct solar beam was measured using an instrument based on the spectrophone. The method is described and results obtained from filtered and unfiltered air samples are presented. This enabled the aerosol's contribution to the absorption to be determined. Comparison of this absorption was made with the local visibility: with a visibility of 10km the heating rates observed were typically 0.2K day−1, increasing to 0.5K day−1 when smoke made a major contribution to the aerosol.
Phase‐lagged wave‐CISK
Authors: Davies H. C. 
Published: February 2007

AbstractThe conventional formulation of the wave‐CISK mechanism involves a quasi‐equilibrium assumption whereby the instantaneous large‐scale diabatic heating that is induced by cloud‐scale motions is assumed to be related to the instantaneous distribution of the large‐scale flow, and in particular to the low‐level moisture convergence of the large‐scale flow. Thus in this context the deep convective clouds of the tropical atmosphere are viewed as instantaneous processors of the large‐scale moisture supply.Herein a conventional, inviscid wave‐CISK model is developed and an examination undertaken of the properties of the analytically determined solutions. The quasi‐equilibrium assumption is then discarded by incorporating into the CISK model's formulation a simple time‐dependent model of the dynamics of a cumulus cloud ensemble. The latter model has a finite adjustment time (TR) to changes in the large‐scale forcing field. Hence the apparent diabatic heat source experienced by the large‐scale fields becomes a function of the time history of that same forcing field.Neutral solutions of the refined wave‐CISK model are derived as functions of the diabatic heating amplitude and the adjustment time. These solutions illustrate the frequency‐selective stabilizing effect of the hypothesized cloud‐scale dynamics. Again, the marginally unstable waves of the refined model are shown to exhibit properties that overcome some of the debilitating features of conventional wave‐CISK. These solutions also reproduce some of the observed features of tropical wave motions. In particular, for Tr ∼ 12 h and with a physically reasonable value of the cumulus diabatic heating amplitude, it is shown that all the inertia‐gravity modes are stable, and that the most unstable Kelvin wave, mixed Rossby‐gravity wave and Rossby (n = 1 and n = 2) waves have finite preferred spatial length scales corresponding respectively to zonal wavenumbers (m) of 2, 4, 6 and 8. The periods of these four waves correspond approximately to 10, 4/1/2 12/1/2 and 15 days but the growth rates are comparatively small. The agreement with tropical wave data is not unreasonable when allowance is made for the Doppler shift of the Rossby waves.Also the vertical structures of these preferred modes are different: the Kelvin and mixed Rossby‐gravity waves are associated respectively with the shortest and longest vertical wavelengths, and the meridional wind field of the Rossby wave (n = 1) has a maximum in both the upper and lower troposphere. The degree of mutual compensation in the model solutions between diabatic heating due to cumulus clouds and cooling due to large‐scale ascent is not as strong as that observed in the atmosphere.
Measurements of boundary layer structure and development over SE England using aircraft and tethered balloon instrumentation
Authors: Moores W. H. , Caughey S. J. , Readings C. J. , Milford J. R. , Mansfield D. A. , Abdulla S. , Guymer T. H. , Johnston W. B. 
Published: February 2007

AbstractDuring August 1974 the Co‐operative Atmospheric Boundary Layer Experiment (CABLE) took place in which several experimental groups combined resources to study spatial and temporal characteristics of the convective atmospheric boundary layer over a fairly uniform area of SE England. The results presented concentrate on the four‐day period 19–22 August. Mesoscale variations in boundary layer development and the influence of synoptic scale features on boundary layer structure are described and discussed. Profiles of sensible heat flux, obtained by several independent methods, are examined in some detail and are shown to imply significant heating due to absorption of solar radiation.
A note on momentum transfer above very rough surfaces
Authors: Mulhearn P. J. 
Published: February 2007

AbstractData from wind tunnel experiments on the deviations from unity of the non‐dimensional velocity gradient, ΦM = (kz/u*)(δU/δz), close to very rough surfaces are reviewed and compared with field data discussed by J. R. Garratt. It is found for z/z0 < 102 that ΦM < 1 in field data and > 1 in the wind tunnel experiments. This difference is discussed tentatively in terms of roughness element flexibility and porosity.
Baroclinic instability governed by the modified quasi‐geostrophic equations
Authors: White A. A. , Gadian A. M. 
Published: February 2007

AbstractResults are presented for the baroclinic instability of zonal flows on a β‐plane according to the modified quasi‐geostrophic equations (which retain a non‐Doppler term in the rigid horizontal boundary condition).Numerical techniques, with up to 180 interior levels, are used. In the absence of a β‐effect the instability of the longer waves is fairly sensitive to the non‐Doppler term, the more so if static compressibility is neglected. A realistic β‐effect markedly reduces this sensitivity: the weakly unstable long waves are essentially internal mode phenomena and are consequently little affected by the non‐Doppler term. It is confirmed that the stable external mode Rossby waves, where they exist, are radically altered when the term is included..
Some aspects of turbulence structure through the depth of the convective boundary layer
Authors: Caughey S. J. , Palmer S. G. 
Published: February 2007

AbstractResults from a series of boundary layer measurements carried out at Ashchurch, Worcestershire during July 1976 are combined with those from the 1973 Minnesota experiment. This data set provides a more complete description of the behaviour of some turbulence statistics through the depth of the convective boundary layer and into the stable air of the free atmosphere. Although the two experimental regions differ quite markedly topographically, the two sets of data are found to merge together quite well in the middle of the boundary layer and do not reveal any systematic differences that might be attributable to surface effects. The vertical profiles of turbulence statistics are compared, where possible, with other results from numerical models and laboratory experiments.
On the net forces produced by surface‐mounted obstacles
Authors: Mason P. J. , Sykes R. I. 
Published: February 2007

AbstractNumerical calculations of the forces involved in Ekman layer flow past three‐dimensional topography are presented. The forces are obtained from finite‐difference solutions of the Navier‐Stokes equations. The results confirm expectations from earlier two‐dimensional work that many flows produce no significant change in total momentum transfer between the fluid and the surface. Only flows generating some form of trailing vortex system appear capable of changing the total force on the lower boundary. The effects of Ekman boundary layer instabilities, and their interaction with topography, are also discussed.
Empirical orthogonal functions of 500 mb height in the northern hemisphere determined from a large data sample
Authors: Rinne Juhani , Karhila Vesa 
Published: February 2007

AbstractHorizontal empirical orthogonal functions (EOFs) were determined from a sample of 11 876 500 mb analyses given at 1404 gridpoints covering the northern hemisphere north of 20°N. Due to computer restrictions a joining method had to be applied. The set of 175 EOFs determined explains 99.5% of the total variance in the dependent sample and 99.6 to 99.7% in the independent samples.
Truncation of the EOF series representing 500 mb heights
Authors: Rinne Juhani , Järvenoja Simo 
Published: February 2007

AbstractThe representativeness of different sets of EOFs describing 500 mb heights over the northern hemisphere north of 20° is discussed. Some criteria for truncating series given in EOFs are introduced. A case study is presented to find out how well charts constructed with the aid of EOFs represent the original synoptic analysis.In the EOF series, about 160, 130 and 120 terms are needed when applying functions based on analyses from one year, 4 years and 20 years, respectively. Thus the degrees of freedom of the EOF series are cut down to one tenth of those in the corresponding gridpoint presentation (1404 points). From the error variance of the analyses, assumed to be 1.5% of the total sample variance, 0.5 percentage units are included in the EOF series, while the remaining 1.0% is rejected into the residual. The true information lost when truncating the EOF series is 0.5% of the total variance.The EOFs are stable; functions based on data from 1946 work reasonably well in independent data from 1965.
Conditional symmetric instability ‐ a possible explanation for frontal rainbands
Authors: Bennetts D. A. , Hoskins B. J. 
Published: February 2007

AbstractIn order to study the possible importance of symmetric baroclinic instability in the formation of frontal rainbands, the existing theory is reviewed and the inclusion of the effects of latent heat release attempted. When an atmosphere is rendered symmetrically unstable by latent heat release, it may be said to be conditionally symmetrically unstable. Simple numerical experiments support the extended theory and describe the structure of the finite amplitude cells. These exhibit conditional gravitational instability in preferred linear regions. It is shown that such a gravitational destabilization is possible only when a wet bulb potential vorticity is initially negative. This latter is a necessary and possibly sufficient condition for ‘conditional symmetric instability’ (CSI). Limited comparison with observed frontal rainbands lends some support to the hypothesis that CSI can be a dominant formative mechanism, though more sophisticated numerical modelling and observational studies are required.
Growth and disappearance of evaporation fog during the transformation of a cold air mass
Authors: Wessels H. R. A. 
Published: February 2007

AbstractEvaporation fog (sea smoke, steam fog) occurs during the advection of cold air over warm water. Current knowledge of the structure of unstable surface layers is used to predict the height of the fog patches as a function of the meteorological conditions. A possible application is the estimation of an increase of fog frequency due to discharge of cooling water.An inversion‐capped mixed layer model is developed, which describes the transformation of the temperature and humidity characteristics of the cold air mass. The results agree with the observation that evaporation fog is usually restricted to coastal waters.
The numerical modelling of storm surges in the Bay of Bengal
Authors: Johns B. , Ali M. Anwar 
Published: February 2007

AbstractA numerical model is developed for the simulation of surges generated by a tropical cyclone in the Bay of Bengal. The analysis area extends from approximately 11°N to 22°N and, in the northeastern sector of the Bay, includes a representation of the Ganges‐Brahmaputra‐Meghna river system in Bangladesh. The extent of the analysis area allows three days of the surge‐generating capacity of a cyclone originating in the southern Indian Ocean to be recorded before landfall at the Bangladesh coast. The incorporation of the river system permits a potentially deep inland penetration of surges originating in the Bay. The model is non‐linear and this allows a determination of the interactive effect between surge and the astronomical tide. Numerical experiments are described that relate to the change in surge response resulting from a change in the cyclone track during the 24 hours preceding landfall. An account is given of the interaction between surge and tide in the Bay and the river system.
Stratospheric O3‐CO2 coupling in a photochemical‐radiative column model. II: With chlorine chemistry
Authors: Groves K. S. , Tuck A. F. 
Published: February 2007

AbstractIt is shown that the inclusion of a chlorine chemistry mechanism, necessitated by present abundances of methyl chloride and carbon tetrachloride, reduces the modelled natural stratospheric ozone above about 25 km by 20 to 40% compared with part I, resulting in substantial agreement with observations. The effects of simultaneous increases in the atmospheric mixing ratios of carbon dioxide and chlorofluoromethanes (CFMs) are investigated. It is found that there is alleviation of the CFM‐induced ozone reductions attributable to increased CO2, and that the effects of the two perturbations upon ozone column density are not quite linearly additive. The net effect on ozone column density consists of larger percentage decreases in the upper stratosphere almost compensated by smaller percentage increases in the lower stratosphere, where most of the ozone is resident.
Volcanic eruptions and long‐term temperature records: An empirical search for cause and effect
Authors: Taylor Billie L. , Gal‐Chen Tzvi , Schneider Stephen H. 
Published: February 2007

AbstractThe ‘superposed epoch’ analysis method of compositing temperatures is employed to aid in the search for evidence of a drop in surface temperature due to large volcanic dust veils. The temperature records examined have been chosen from the archives at the National Center for Atmospheric Research according to the length and completeness of the record. Various groupings of the data stations are used as data bases and the strength of the ‘volcanic signal’ determined in the different cases. A seasonal (winter‐summer) investigation of the signal is also conducted. A significant dip in temperature can be found within a few years after the major eruption dates in most of the dust veil temperature superpositions, whereas the noise appears to vary randomly from superposition to superposition. The evidence points to a stronger, but less statistically significant, response to the effects of large volcanic dust veils in higher latitudes, although a definite conconclusion requires, among other things, a larger and more representative data base. The seasonal investigation reveals a stronger summer signal in the majority of cases.
Redistribution of scalars during upper ocean frontogenesis: A numerical model
Authors: Macvean M. K. , Woods J. D. 
Published: February 2007

AbstractA two‐dimensional frontogenesis model forced by a barotropic horizontal deformation field has been developed. Turbulent mixing is neglected and the long‐front flow is assumed geostrophic. The horizontal gradients at the surface become infinite after 3–4 days, assuming a deformation rate of 10−5s−1. In reality we expect turbulent mixing to prevent the final collapse to a singularity. The inclination of cross‐front streamlines to isopycnals decreases rapidly below the surface; the horizontal density gradients do not therefore increase rapidly there. However, such flow can effectively increase the horizontal gradients of passive scalars (we consider temperature here) whose isopleths are inclined to the isopycnals. In a typical example the isotherm pattern makes a front appear to be an order of magnitude thinner and to penetrate much deeper than does the isopycnal pattern. The isotherm patterns produced vary markedly with the initial inclination of isopycnals and isotherms.
Laboratory studies of riming, and its relation to ice splinter production
Authors: Choularton T. W. , Griggs D. J. , Humood B. Y. , Latham J. 
Published: February 2007

AbstractExperiments have shown that if a supercooled drop is accreted on to a rimer in such a way that it lands on an already frozen smaller droplet then it may develop a protuberance as it freezes, presumably because the heat loss is fairly symmetrical. These protuberances were found in the temperature range –3 to –8°C, and their probability of production reached a maximum at –5 to –6°C of 1 for every 20 drops accreted. The protuberances tended to have a larger aspect ratio and to be longer relative to the drop diameter at lower temperatures. All these effects were found to be independent of speed of collection over the range 1.5 to 3ms−1. Due to the strong parallelism between the conditions required for protuberance production and ice splinter ejection during riming we suggest that the splinters are a result of explosive fragmentation of about 1% of the protuberances formed. This idea is supported by some experimental evidence.
The dynamical behaviour of a two‐dimensional model of the stratosphere
Authors: Harwood R. S. , Pyle J. A. 
Published: February 2007

AbstractFor the atmosphere below approximately 60 km the dynamical behaviour of the zonal mean circulation model described by Harwood and Pyle (1975, 1977) is discussed in detail and compared with observations. The major features of the observed extra‐tropical circulation are reproduced by the model, although the principal jets are overestimated. Equatorial temperatures are representative but horizontal temperature gradients are too large, in keeping with the excess wind speed.The roles played in forcing the mean meridional circulation by the diabatic heating and the eddy fluxes of angular momentum and heat are considered.The temperature structure of the summer stratopause is discussed in detail; the model results indicate that this region is in radiative equilibrium to a good approximation.The model has been used to investigate stratospheric ozone and in this paper the sensitivity of the ozone distribution to a number of the model variables is discussed. Reasonable changes in the specified eddy diffusion coefficients and momentum fluxes can alter the total ozone column by around 10%. For small changes (∼ a few tenths K d−1) in the radiative heating of the lower stratosphere even larger changes in the ozone amount are found in the model. The net radiative heating in the lower stratosphere is difficult to calculate. The implication of these sensitivity experiments for pollution perturbation calculations is stressed. Unless all feedback processes are included calculations of pollution‐induced changes in ozone of around 10% must be regarded with caution.
Charge transfer accompanying the splashing of supercooled raindrops on hailstones
Authors: Latham J. , Warwicker R. 
Published: February 2007

AbstractMeasurements have been made of the charge transfer accompanying the splashing of a supercooled water drop, of raindrop dimensions, onto a simulated hailstone. The important variables were: temperature of drop and hailstone (–4°C to –20°C); impact velocity (1 to 4ms−1); impact parameter (0 to ±1); drop composition (pure water; NaCl and (NH4)2CO3 solution; CO2‐saturated water; water containing detergent); and surface structure of the hailstone.It was found that the hailstone always acquired a positive charge, of magnitude invariably less than 200 fC, and usually around 20 fC. These values are much less than those measured by other workers (in experiments where the drops were not significantly supercooled), and are far too small to be of significance in thunderstorm electrification.When these experiments were performed in the presence of an electric field substantial charges (up to 300 fC m V−1) were measured, but their sign was such as to dissipate the field.
Three‐dimensional lee waves
Authors: Marthinsen T. 
Published: February 2007

AbstractLinear wave theory is used to find the stationary, trapped lee waves behind an isolated mountain. The lower atmosphere is approximated by a three‐layer model with Brunt‐Väisälä frequency and wind velocity constant in each layer. The Fourier‐integrals are solved by a uniformly valid asymptotic expansion and also by numerical methods.The wave pattern is found to be strongly dependent on the atmospheric stratification. The way the waves change when the parameters describing the atmosphere and the shape of the mountain vary, is studied. Further, the results predicted by the theory are compared with waves observed on satellite photographs. It is found that the observed wave patterns are described well by the linear theory, and there is good agreement between observed and computed wavelengths.
Numerical experiments on the inland penetration of the sea breeze
Authors: Physick W. L. 
Published: February 2007

AbstractA two‐dimensional primitive‐equation model is used to investigate various aspects of the sea‐breeze phenomenon. The influence of soil moisture content is examined by varying the Bowen ratio of the underlying land surface. This is equivalent to controlling the magnitude of the sensible heat flux at the ground since the diurnal variation of net radiation minus ground heat flux is approximately the same in all cases. It is found that the inland penetration rate of the sea breeze varies significantly with the degree of soil moisture. The model predicts a significant slowing of the frontal advance around midday for the case of ‘relatively weak’ sensible heating over the land, as well as reproducing the frontal acceleration observed in late afternoon for all cases. The sea‐breeze circulation detaches itself from the coastline around sunset and moves rapidly inland with diminishing magnitude and this aspect is discussed in relation to observations in the south of England.An attempt is made to model the southern England sea breeze of 14 June 1973. Various experiments are discussed, including one in which different values of Bowen ratio are specified ahead of and behind the front. Fairly good agreement is found, although it is not possible to reproduce all features of the inland penetration curve for that day.Some implications of these experiments for the production of daily forecasts by mesoscale models are briefly discussed.
Thermal radiation in Arctic stratus clouds
Authors: Herman G. F. 
Published: February 2007

AbstractInfrared radiative properties of Arctic stratus clouds in the 10.1 to 12.7μm wavelength region are determined from a series of aircraft measurements. The average emissivity of the clouds when scattering is neglected is unity for cloud depths greater than 350m. Under the assumption that the cloud layers are homogeneous the cloud droplet volume absorption coefficient is estimated as 17±5km−1. Several mass absorption coefficients are estimated for several assumed liquid water distributions. It is also concluded that the cloud reflectance is not larger than 2(£5%).