bluuebunny/crossref_metadata_2025_split huggingface dataset:
The analysis of umkehr observations of stratospheric ozone by a ‘Maximum Entropy’ method
Authors: Read P. L. 
Published: February 2007

AbstractAn application is described of the ‘Maximum Entropy’ (ME) principle to the analysis of umkehr observations of atmospheric ozone. The method is shown to produce results which are comparable with more conventional analyses, and which show a marginally higher correlation with simultaneous ozonesonde measurements than the standard evaluation method. Differences between conventional and ME solutions are attributable to the low intrinsic information content of umkehr observations, and the use of climatological information in addition to observational data in the standard method of analysis. This additional information may also be included in ME solutions, reducing the systematic errors of the simple ME solutions, but possibly degrading that part of the information content of the solution which is due to the observations. Some further meteorological applications of the method are discussed.
Diurnal variation of pressure‐heights in the Eastern Atlantic (GATE)
Authors: Riehl H. , Haurwitz B. 
Published: February 2007

AbstractAt first, the daily variation of pressure‐heights in the troposphere and low stratosphere is determined with observations from GATE. Resulting values are compared with those obtained in the Caribbean in the 1940's. One finds the semi‐diurnal cycle well maintained up to 500mb in both samples, as well as the transition to a single asymmetric wave in the high troposphere and low stratosphere. The amplitude is much reduced in GATE, suggesting that the temperature corrections applied in the Caribbean were too small. Nevertheless, the range of 60m at 100mb still corresponds to the mean latitudinal pressure‐height difference over 20° latitude across the GATE area in the Northern Hemisphere summer.The 24‐ and 12‐hourly oscillations of the standard pressure surfaces have been determined by harmonic analysis up to 100mb, the highest level for which pressure‐height data were available. The results are given in Table 3 and they show more precisely than Fig. 1 the vertical distribution of the first and second harmonics and the transition from a daily pressure variation with two maxima and minima to one where only one predominant maximum and one predominant minimum appears each day.
Planetary wave modelling of the Middle Atmosphere: The importance of travelling wave components
Authors: Austin John 
Published: February 2007

AbstractA linerized stationary planetary wave model is applied to mean data for a chosen quiescent winter month (December 1979). Comparison with observations from the Stratosperic Sounding Unit on board NOAA‐6 shows that both the amplitude and height of propagation of wavenumber one are significantly underpredicted. This behaviour is not substantially modified by extension to more sophisticated model formulation and representation of dissipative processes. It is shown that the response to forcing varies appreciably with travelling wave frequency, even at periods greater than one month and it is suggested that this sensitivity is a significant limitation on the applicability of stationary wave models based only on time mean behaviour.
A two‐dimensional numerical study of horizontal roll vortices in an inversion capped planetary boundary layer
Authors: Mason P. J. , Sykes R. I. 
Published: February 2007

AbstractThe dynamics of large‐scale horizontal roll vortices in an inversion‐capped planetary boundary layer subject to surface heating are investigated by means of a numerical model. The rolls are assumed to be twodimensional and calculated explicity, while small scale turbulence is parametrized using a buoyancy‐dependent mixing length hypothesis. The assumptions of the model are based upon atmospheric observations which show the occurrence of large eddies highly elongated in a direction close to that of the geosstrophic wind and a partitioning of turbulence energy between these large eddies and smaller scales. The model produces realistic turbulence statistics and provides information on the sensitivity to various assumptions and parameters. Apart from the generation of internal gravity waves in the stable region above the boundary layer the results are insensitive to the details of the parametization. The internal gravity wave generation is sensitive to most parameterss and in particular to the roll orientation.
A diffusive model of the turbulent mixing of dry and cloudy air
Authors: Baker M. B. , Latham J. 
Published: February 2007

AbstractA model is presented of the turbulent mixing between a shere of droplet‐free air (saturated or under‐saturated) and a spherical volume of cloud within which it is embedded. The rates of equalization of super‐saturation, temperature and liquid water are examined as functions of the turbulent energy dissipation rate, the dimensions of the interacting volumes, the drop‐size distribution in the cloud and other parameters. Spectral changes resulting from the mixing conform closely with those predicted by the recent inhomogeneous or dilution‐only descriptions of mixing (Baker et al. 1980; Telford and Chai 1980).It is shown that spectral changes observed during entainment into shallow cumulus, stratocumulus and cap clouds are good agreement with those predicted on the basis of this diffusive model.Calculations of mixing in the presence of an updraught yield size‐distributions (including bimodal spectra) similar to those oberved in natural clouds.Calculations of mixing during descent from cloud‐top suggest that regions of substantial under‐saturation may exist in the deep interiors of clouds which are entraining environmental air at their summits. Crude estimates of the degree of lateral spreading produced by turbulence as this descent proceeds indicates that significant horizontal structure in the water properties may exist throughout a substantial fraction of the cloud‐depth.
On the droplet distribution near the base of cumulus clouds
Authors: Manton M. J. , Warner J. 
Published: February 2007

AbstractLateral entrainment in cumulus clouds is usually assumed to occur continuously as a cloud parcel rises. Computations of the droplet distribution using that assumption are compared with those in which entrainment occurs intermittently, and little difference is found. The width of the droplet distribution is shown to increase as the relative humidity of the entrained air is reduced. The inclusion of the effects of molecular accommodation at the surface of droplets also leads to substantial broadening of the droplet distribution.
Kinematic and thermal structures of two surges of flow in the Northern Mozambique Channel Area
Authors: Rao Gandikota V. , Haney James L. 
Published: February 2007

AbstractTwo atmospheric surges near the northern Mozambique Channel were explored by NCAR's Electra aircraft on 17 June 1977 and 3 July 1977 during MONSOON–77 field experiment. The surges were probed from Nairobi eastwards to the coast and then south from 1°S to 8°S along 41°E. Offshore the former day was characterized by deep south‐south‐easterlies and south‐easterlies, squalls, and rain and the latter day by shallow south‐south‐easterlies overlain by south‐westerlies and fair weather cumulus.Vertical structures of u, v, T and q for both days are discussed. Early on the disturbed day southerlies reached their maximum over land at 880 mb on a cross‐section approximately along 2°S. By noon diurnal heating reduced the overland winds, resulting in an apparent ocean‐ward shift of the jet axis. On the undisturbed day the southerly maximum was over the ocean near the coast.On both days two southerly maxima were found on longitudinal coross‐sections along 41°E: an elevated and stronger maximum near the equator; a depressed and weaker one near 8°S. On the disturbed day the equatorial maximum was located in the south‐south‐easterlies and on the undisturbed day was sandwiched between south‐south‐easterlies in the low levels and south‐south‐westerlies at 770 mb. The southern maximum was from south‐south‐east on both days.During these two periods meridional mass fluxes from two stations, Port Elizabeth and Dar‐es‐Salaam, were computed. They showed that the latter station lags the former by as much as four days; however, its meridional mass flux is double the former.
The seasonal response of a general circulation model to changes in CO2 and sea temperatures
Authors: Mitchell John F. B. 
Published: February 2007

AbstractThe seasonal response of an atmospheric general circulation model to changes in atmospheric carbon dioxide concentrations and sea surface temperatures is discussed. The model has five layers and a quasi‐uniform 330km horizontal grid. Sea surface temperatures, sea ice extents, and zonally mean cloud amounts are prescribed from climatology, so that feedbacks between these variables and the rest of the model are ignored. Soil moisture, snow depth and boundary layer height are modelled explicitly, and both diurnal and seasonal variations of solar zenith angle are included. Two experiments are carried out, and compared with a three‐year control integration. In each case, the model's response varies with season and location. In the first experiment the effect of increasing atmospheric carbon dioxide concentrations with prescribed present day sea surface temperatures is examined. The model's troposphere becomes warmer, thereby increasing the low level static stability over the ocean and reducing evaporation and precipitation. The warming is larger over land than over the oceans. In summer, this results in an increase in precipitation along the eastern coasts of continents. In the second experiment, the sea surface temperatures are increased by 2 K and the carbon dioxide concentration is doubled. The land surface temperature rises by 3 K. Evaporation increases markedly over the oceans. Precipitation increases in the main regions of atmospheric convergence and decreases in some regions of the subtropics. The magnitude of the model's response is shown to be reasonably consistent with that found in other three‐dimensional climate models.
Variations of zonal mean sea surface temperature and large‐scale air‐sea interaction
Authors: Chiu Long S. , Newell Reginald E. 
Published: February 2007

AbstractTwenty‐four years data of zonal mean sea surface temperature (SST) were assembled to examine the seasonal and nonseasonal variations of SST. Outside the tropics, annual and semi‐annual variations of SST dominate, accounting for over 90% of the variance. In the tropics, the nonseasonal variation of SST is dominated by low‐frequency variations with periods longer than 3 years in the Pacific. Variations with periods of 24–32 months account for more than 10% of the variance in the tropical Atlantic from 25 £N to 10 £S and in the equatorial Pacific from 0–10 £S. An empirical orthogonal function (EOF) analysis showed that the major global pattern of zonal mean SST variations is dominated by variations in the equatorial eastern Pacific which precede zonal mean SST variations elsewhere. The time series of this EOF is found to be correlated with an index of the Southern Oscillation. The maximum correlation coefficient is −0£61, with the index leading by 2 months. Finally, the relation between SST and tropical tropospheric temperature (TTT) is examined. SST variations in the Atlantic and in the Indian Ocean are almost contemporary with variations in TTT. Possible explanations for the 1–2 seasons lead time between SST and TTT as found in earlier studies are suggested.
Simulation of storm surges using a three‐dimensional numerical model: An application to the 1977 Andhra cyclone
Authors: Johns B. , Sinha P. C. , Dube S. K. , Mohanty U. C. , Rao A. D. 
Published: February 2007

AbstractA three‐dimensional numerical model is developed for the simulation of storm surges generated by tropical cyclones off the east coast of India. Experiments are performed using wind‐stress forcing data representative of the 1977 Andhra cyclone and the results are compared with earlier simulations using a depth‐averaged model. The three‐dimensional model incorporates a turbulence energy closure scheme and is fairly sophisticated in comparison with the depth‐averaged approach. Even with the apparently more refined treatment of the frictional processes, there is no substantial difference between simulations performed with the two models.
An accurate variation of the two‐step lax‐wendroff integration of horizontal advection
Authors: Collins William G. 
Published: February 2007

AbstractThe split technique is one method used to integrate the primitive equations of motion efficiently. The horizontal advection is commonly integrated by the two‐step Lax‐Wendroff scheme. Both Gadd and Carpenter have discussed the design of operators to give either accurate amplitude or phase speed. This paper extends their analysis to yield a method which has both accurate amplitude and phase speed.
Mountain torque and angular momentum in barotropic planetary flows: Equilibrium solutions
Authors: Sawford B. L. , Frederiksen J. S. 
Published: February 2007

AbstractThe climatic‐mean‐value of the total zonal relative angular momentum of the atmosphere in topographically forced inviscid barotropic models on a sphere is examined using the methods of equilibrium statistical mechanics. Models incorporating wave–wave interactions as well as simplified systems in which only wave–zonal‐flow interactions are allowed are considered. It is shown analytically that for a given truncation the equilibrium state of the system does not depend on the presence of wave–wave interactions although the detailed evolution towards it does.We interpret our results in terms of a generalization of the properties of the equilibrium solutions for unforced barotropic flow. For realistic resolution (with truncation wavenumber ° 15) most flows evolve towards an equilibrium with westward angular momentum, and the solutions are strongly dependent on the initial conditions. An important exception is the case when the flow initially has westward angular momentum, when the equilibrium state remains close to the initial state regardless of resolution. An upper bound on the climatic‐mean‐value of the solid‐body rotation component of the flow is derived. In general, highly truncated systems are insensitive to the initial conditions and evolve towards a state in which the angular momentum is eastward and close to the upper bound.Reasonable rescating of the global topography used has little influence on the climatic‐mean angular momentum, but the case of no topography represents a singular limit in which angular momentum is conserved.
Dual channel satellite measurements of sea surface temperature
Authors: Barton I. J. 
Published: February 2007

AbstractResults from the 11.6γm channel on the Nimbus 5 selective chopper radiometer are presented that show ambiguity in the temperature deficit obtained for any tropical sea surface temperature (s.s.t.). The analysis indicates that to gain an accurate measurement of s.s.t. in the 10–13γm band further information on the water vapour content of the overlying atmosphere is required. A transmission model is used to show that for two channels a linear relation exists between the two apparent surface temperatures and simple algorithms are derived that give s.s.t.s with an accuracy better than 0.3K for vertically‐viewing satellite radiometers. Algorithms giving s.s.t. are derived for both dual wavelength and dual angle‐of‐view techniques and these are compared with those derived by other authors.
Observed inter‐relations between 10m winds, ocean whitecaps and marine aerosols
Authors: Monahan Edward C. , Fairall Christopher W. , Davidson Kenneth L. , Boyle Patricia Jones 
Published: February 2007

AbstractLow elevation aerosol spectra, ocean whitecap cover and 10m wind speeds measured during the 1978 JASIN experiment have been inter‐related and compared with previously published observations. The positive dependence of aerosol concentration upon whitecap cover was found to increase with droplet radius reflecting the expected higher correlation of the concentration of larger droplets, which have shorter effective residence time in the marine atmospheric boundary layer, with the immediate whitecap cover, which reflects the instantaneous rate of aerosol generation at the sea surface. The power‐law wind dependence, Uγ of the low elevation concentration of droplets larger than 8γm radius was determined to be similar to the wind dependence of whitecap cover, with γ values of 3.23 and 3.31 resulting from the respective application of the robust bi‐weight fitting technique. This observation is consonant with an aerosol generation model in which the instantaneous rate of production is simply proportional to the immediate whitecap cover.The large droplet end of the JASIN low elevation aerosol spectrum is seen to undergo a marked enhancement when the wind speed exceeds 10ms−1. This is a consequence of the onset at that speed of supplementary droplet production via the mechanical disruption of wave crests. The observed growth, with increasing wind speed, in the disparity in amplitude of near‐sea‐surface and near‐cloud‐base aerosol spectra is in part a consequence of the fact that the larger droplets, produced in relative abundance at the higher wind speeds, fall out before they can be mixed effectively through the boundary layer.
A wave prediction system for real‐time sea state forecasting
Authors: Golding B. 
Published: February 2007

AbstractThe considerable increase in requirements for sea state forecasts in recent years has led to development of a numerical wave forecasting system in the Meteorological Office. This is based on a wave prediction model which combines the advantages of the parametric technique in predicting a growing wind‐sea with those of a discrete spectral model in the swell regime. This is done using a discrete model by parametrizing the nonlinear interactions term in the energy balance equation in a way that reproduces the behaviour of the parametric model. The main difficulty with the method is in the separation of wind‐sea and swell required to do this. Propagation of wave energy is performed using an accurate form of the Lax‐Wendroff integration scheme. A two‐term representation of wave growth is used whilst dissipation is modelled by an explicit whitecapping mechanism. Shallow water effects are included by representations of shoaling, refraction and bottom friction. The operational numerical atmospheric model at the Meteorological Office provides the wind input. An extensive program of evaluation has shown that the results provide high quality guidance with 24‐hour forecasts of wave height having a r.m.s. error ranging from 0·6 m in the southern North Sea to 1·0 m east of the Shetlands.
Application of extreme value analysis to Weibull data
Authors: Carter D. J. T. , Challenor P. G. 
Published: February 2007

AbstractIn the application of extreme value analysis it is usually assumed that the size of the samples from which the extreme values are obtained is sufficiently large for the asymptotic extreme value distribution to be used. The necessary sample size depends upon the population distribution and this is generally not known; but assuming a Weibull distribution, which is often fitted to wind speed and wave height data, it is shown that the rate of convergence is rapid and that the asymptotic distribution may be used for a sample size as small as ten. An ‘exponential approximation’ for the distribution of maxima is sometimes confused with the extreme value distribution. This approximate form is derived for the Weibull distribution and the essential difference between it and the asymptotic extreme value distribution is explained.
Upper stratospheric circulations in the two hemispheres observed by satellites
Authors: Hirota I. , Hirooka T. , Shiotani M. 
Published: February 2007

AbstractA global analysis is made of upper stratospheric circulations with the aid of Nimbus 5 and Tiros N satellite observations in order to make a comparison of characteristics between the northern hemisphere (NH) and the southern hemisphere (SH).It is shown that the reversal of north‐south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the SH winter, while the temperature gradient of the NH winter is variable because of the occurrence of sudden warmings. Consequently, due to the thermal wind relation, the polar night westerlies of the SH stratosphere are generally stronger than those of the NH stratosphere. In association with this difference, the activity of transient planetary waves of wavenumber 2 is striking in the SH, in contrast to the predominance of steady waves in the NH.Finally, the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discussed.
Reduction of systematic forecast errors in the ECMWF model through the introduction of an envelope orography
Authors: Wallace John M. , Tibaldi Stefano , Simmons Adrian J. 
Published: February 2007

AbstractDay 1 forecast errors in the ECMWF model geopotential height fields during wintertime show a distinctive and highly reproducible signature with negative biases over the major mountain barriers. These biases are largest on days when the 500mb flow over the mountains is strong and they tend to shift position from day to day so as to remain close to the region where the jet stream crosses the mountain barrier. These systematic errors evolve through the forecast interval until by day 10 they assume an equivalent barotropic structure which strongly resembles the upper‐level stationary wave pattern, but has the opposite sign, which indicates that the model does not have sufficient (presumably orographic) forcing to maintain the stationary waves.The time evolution of the systematic error pattern is investigated by means of a series of experiments with a barotropic model, in which the observed mean wintertime 300 mb flow is perturbed by a steady forcing derived from the day 1 forecast error pattern. The day 10 error patterns, as simulated by the barotropic model, bear a strong similarity to the observed ones. The forcing in the vicinity of the northern Rockies makes a particularly large contribution to the simulated day 10 error pattern whereas that in the Himalaya region appears to be relatively less important.The impact of an enhanced orography upon the climate of the ECMWF model is investigated by carrying out a pair of extended integrations out to 50 days. The control run is based on the conventional average‐type orography used for operational forecasting; the other run is based on an ‘envelope orography’ constructed by adding to the conventional, grid‐square averaged, orography an increment proportional to the standard deviation of the sub‐grid scale variance. Results for this one, rather short pair of integrations suggest that the envelope orography may be capable of yielding a more realistic simulation of the observed wintertime flow pattern, particularly with respect to features in the Pacific and western North American sectors. Certain aspects of the zonally averaged circulation are also more realistic in this envelope simulation.A series of 21 successive ten‐day forecast integrations has also been carried out with this envelope orography from February 1982 data. Results indicate that the introduction of the envelope orography results in a slight degradation of the short‐range forecasts together with a distinct improvement of the forecast beyond four days. The beneficial impact towards the end of the forecast interval appears to be large enough to increase the forecast usefulness by perhaps as much as half a day.