bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐dimensional model studies of methyl chloroform in the troposphere
Authors: Derwent R. G. , Eggleton A. E. J. 
Published: July 2010

AbstractThe tropospheric measurements, atmospheric release rates, and OH reaction rates for methyl chloroform are consistent with present estimates of the tropospheric OH distribution and a methyl chloroform lifetime of about 5 years. Reaction with OH radicals is found to be the major atmospheric removal process for this species. Although excellent agreement is obtained in the northern hemisphere, recent southern hemisphere observations have indicated a much more rapid growth than can be accounted for by model calculations. A comparison of the two‐dimensional model with simpler formulations such as global, hemispheric or one‐dimensional models, shows that the simpler models may not adequately represent tropospheric transport and removal by OH radicals.
An analysis of wave height records for the N.E. Atlantic
Authors: Jardine T. P. , Latham F. R. 
Published: July 2010

AbstractThe analysis of records, for the period 1962‐1975, reveals that the wave height observations exhibit a seasonal variation in both the average value and the standard deviation. Examination of the seasonally adjusted wave heights indicates that these values may be approximately described by first order autoregressive time series models. the validity of these models is checked using statistical tests, comparing short‐term forecasts of wave heights with actual observations and by simulating observations and examining the frequency and duration of storms and calm periods. Methods of improving the models for wave height are examined.
On the proper employment of evaporation pans and atmometers in estimating potential transpiration
Authors: Thom A. S. , Thony J.‐L. , Vauclin M. 
Published: July 2010

AbstractTo investigate the feasibility of estimating Penman's potential transpiration (Erp) without recourse to sophisticated instrumentation, the rates of evaporation from a Class‐A pan and from a Piche atmometer exposed within a thermometer screen were analysed in detail using continuous micrometeorological measurements taken on the same site. Evaporimeter and other associated manual measurements were made not only on a routine daily basis but also on certain days from hour to hour. the latter measurements were of particular help in interpreting physically the behaviour of both evaporimeters.It is shown:
that the evaporation from the Piche was closely proportional to the (complete) second term in Penman's (Erp) equation;
that evaporation from the Class‐A pan was adequately described by a combination‐type equation including an effective psychrometric constant γp = 2.1 γ (where γ = 0‐66mb(°C)−1, near sea level) and the wind function fp(u) = 0.12(1 + 1.35 u) mmd−1(mb)−1;
that the deduced daily (24 h) net radiation absorbed by the pan was consistently 31% larger than that on the short, green (but unirrigated) grass covering the site;
by applying (iii), that close to 8.5% of rainfall was lost by splashout from the pan, and
that on applying (iv), wet‐day values of pan evaporation lost much of their supposedly inaccurate and paradoxical nature.

The franework for the general application of conclusions (i) and (iii) in generating a synthetic series of values of Erp is introduced and discussed.
Some effects of convection on geostrophic flow
Authors: Manton M. J. 
Published: July 2010

AbstractConvection in the lower troposphere produces a deficit in the local surface pressure caused by heating of the air in the well‐mixed convection layer. Variations in the surface heat flux can therefore induce horizontal pressure gradients in the convection layer. These pressure gradients can in turn lead to significant geostrophic flows, such as cyclonic ‘heat lows’ in the vicinity of local maxima in the surface heat flux. Turbulent mixing causes the motion in the convection layer to generate vertical velocities, which lead to some geostrophic flow being generated in the middle troposphere above the convection layer.
A sudden warming in the middle atmosphere of the southern hemisphere
Authors: Al‐Ajmi D. N. , Harwood R. S. , Miles T. 
Published: July 2010

AbstractThis paper presents a case study of a wave‐mean flow interaction, or minor warming, near the southern hemisphere stratopause for 15‐30 July 1974. the analysis is based mainly on data from the selective chopper radiometer carried by Nimbus 5.A deceleration of the zonal mean wind of 70 m s‐1 from 20 to 25 July is observed in middle latitudes at 0.5 mb, with an acceleration further south. the polar vortex is, however, not disrupted.Eliassen‐Palm cross‐sections are presented for the event and a good correlation found between the E‐P flux convergence and the deceleration. the channelling of the E‐P fluxes from the tropopause to the convergent region is in broad agreement with the distribution of refractive index but there is a region of E‐P flux divergence at high levels in polar latitudes suggesting a source of wave activity there.The residual circulation is calculated both from the momentum budget and from an omega equation, both methods diagnosing a region of modest equatorward flow near the region of E‐P flux divergence embedded in the stronger poleward flow elsewhere.Maps of potential vorticity on the isentropic surface of 0 = 1640 K are presented and the evolving pattern related to zonal mean and isobaric descriptions. the event is shown to be associated with an incursion of low latitude air into middle latitudes with a corresponding irreversible mixing of potential vorticity reminiscent of the ‘wave breaking’ in northern hemisphere events reported by McIntyre and Palmer (J. At. Ter. Ph., 46, 825), but of much smaller amplitude.
Size spectra of ice particles in frontal clouds: Correlations between spectrum shape and cloud conditions
Authors: Herzegh Paul H. , Hobbs Peter V. 
Published: July 2010

AbstractIce particle size spectra measured by optical particle size spectrometers during airborne sampling of clouds associated with several frontal precipitation systems in the Pacific Northwest are presented and discussed. In the majority of the spectra measured, the concentration densities of particles <2 mm in diameter deviated significantly below or above the exponential curve fitting larger diameters (we term these sub‐exponential and super‐exponential spectra, respectively). Sub‐exponential spectra were found to be dominant in regions of weak stratiform cloud, where liquid water was scarce. Super‐exponential spectra were dominant in convective regions between the ‐1 and ‐9°C levels, where supercooled liquid water was present in amounts up to 0.2 gm‐3. Exponential spectra were dominant in convective regions at the ‐11 °C level and above.Microphysical processes as well as shear‐induced particle size sorting were found to play a role in the development of spectrum shapes. Depletion of small particles due to aggregation appears to have been an important cause of sub‐exponential spectra. Secondary ice crystal production appears to have been responsible for the formation of super‐exponential spectra. the role of particle size was largely to broaden the range of spectrum shapes present, rather than to promote the dominance of a particular spectrum type.The impact of spectrum deviations on the relationship between radar reflectivity factor and snowfall rate, though observable, is found to be small with respect to other sources of error often found in radar estimates of snowfall.
Statistical forecasting of tropical cyclone movement in the australian region
Authors: Keenan T. D. 
Published: July 2010

AbstractThe forecasting of tropical cyclone motion in the Australian region was investigated by various statistical approaches which included a synoptic forcing. Both forward stepwise regression and empirical orthogonal function methods were tested using analysis data to represent the synoptic flow. the stepwise regression approach proved superior although both schemes exhibited more skill than previous Australian objective aids and the present operational forecasts. Experiments conducted with the perfect prognosis approach did not lead to any significant improvements due to the limited skill of the numerical prognoses in tropical regions.
Structure of a cold front over the ocean
Authors: Bond Nicholas A. , Fleagle Robert G. 
Published: July 2010

AbstractThe kinematic and thermodynamic structure of a strong cold front over the Gulf of Alaska has been determined using aircraft, dropsonde, and radiosonde data obtained during the Storm Transfer and Response Experiment. Synoptic‐scale analysis using the Sawyer‐Eliassen secondary circulation equation shows that friction and diabatic heating, as well as the geostrophic forcing, are important in accounting for the secondary circulation at the front. A fine‐scale analysis, with horizontal resolution of 700m and vertical resolution of 100 m, shows strong relative inflow of warm boundary layer air toward the front from the east and a weaker inflow of cold air from the west. Updraught velocities of greater than 6 m s−1 over a 2 km width were measured at 875 mb near the leading edge of the front. the frontogenetical effects of confluence, turbulent mixing, and tilting of isentropic surfaces are evaluated in the region of the front and compared with the results of previous studies. the high resolution of the thermodynamic fields provides new data for comparison with high resolution numerical models.
A shallow water intercomparison of three numerical wave prediction models (Swim)
Authors: Group Swim , Bouws E. , Ephraums J. J. , Ewing J. A. , Francis P. E. , Gunther H. , Janssen P. A. E. M. , Komen G. J. , Rosenthal W. , De Voogt W. J. P. 
Published: July 2010

AbstractThree operational shallow water wave models are intercompared for two artificial experiments and verified for a severe storm hindcast, with the objectives of further understanding the effects of the parametrization of shallow water wave processes in numerical models.The models used are the HYPAS (Max‐Planck Institute) and GONO (KNMI) coupled‐hybrid models, and the BMO (Meteorological Office) coupled‐discrete model which are all briefly described. In the first case, depth‐dependent fetch‐limited wave growth in a steady wind is examined. In the second case a steady onshore wind is specified over an idealized constant slope coastal shelf, and the stationary wave spectra at various depths are intercompared. For the third case the wind fields for the North Sea storms of 18‐26 November 1981 were accurately reconstructed and used by each model in its operational configuration to produce a wave hindcast for this period.In case 1 the GONO and BMO models exhibit similar behaviour in the evolution of energy and peak frequency, whereas HYPAS displays less depth attenuation and little variation in peak frequency. In case 2 the energy values at different shelf depths are approximately as predicted in case 1 for HYPAS though rather higher for BMO and GONO. However, GONO and HYPAS show little change in peak frequency with depth here whereas BMO wave spectra become double‐peaked with a wind‐sea peak migrating to higher frequencies in shallower waters. In case 3, the hindcasts, all models produce qualitatively similar results. the time series of wave height and period agree well with measurements, BMO and HYPAS predicting correct energy levels except at storm peaks and GONO generally overpredicting both at lower energy levels and in a duration‐limited strong wind case. the r.m.s. error in wave height at the southern shallow water verification site is 0.5 m for all models, and varies between 0.9 m (GONO) and 1.5m (HYPAS) at the northern deep water site. Some wave spectra are presented and the directional relaxation of wind‐sea in each model is illustrated.The results of cases 1 and 2 are readily explained by the formulation of shallow water processes adopted in each model, but it is difficult to isolate and identify these mechanisms in the measured or modelied spectra from the hindcast. It is suggested that future studies involving detailed verification and intercomparison of wave models should be confined to more carefully designed wave‐measuring experiments so that less ambiguous results are obtained.
A comparison of a numerical model of radiation fog with detailed observations
Authors: Turton J. D. , Brown R. 
Published: July 2010

AbstractA one‐dimensional numerical model designed to study the formation and growth of radiation fog is described. the realism of the model in simulating the formation of fog is assessed by critical comparisons with detailed observations made on two nights. the comparisons show that the model is unable to reproduce the very light winds which occur near the surface in stable conditions. As a consequence the formation of radiation fog is inhibited in the model unless the afternoon relative humidity is very high. It is suggested that the discrepancy is caused by the use of a turbulence formulation tuned to match observations over an ideally flat site. the influence of turbulence, radiative cooling, advection and frost deposition on the formation of fog during the two nights is also discussed.
On the derivation of the divergent flow from the rotational flow: The χ problem
Authors: Sardeshmukh Prashant D. , Hoskins Brian J. 
Published: July 2010

AbstractThe vertical component of the vorticity equation in pressure coordinates involves only the divergent and rotational components of the horizontal motion. Taking the dominant rotational component as specified, the equation may be considered as an equation for the velocity potential, χ, of the divergent motion. Solving this χ problem yields a divergence pattern which is dynamically consistent with the generally much better observed rotational flow (provided, of course, that the vorticity dynamics is represented correctly). A simple way of doing this is described, and applied to seasonally averaged and instantaneous winds analysed at the European Centre for Medium Range Weather Forecasts (ECMWF). In view of the delicate nature of the vorticity balance, a comparison of δ, the horizontal divergence obtained in this manner, with D, derived directly from the analysed winds, provides a stringent test for the data assimilation system.For seasonal averages, D̃ based on an inviscid vorticity equation in the upper troposphere is generally found to agree well with D, even in the deep tropics. However, some features achieve a more interesting and believable structure than in the analyses. Allowing for a vorticity sink in regions of strong organized convection changes this estimate of δ only slightly, well within the range of observational uncertainty, and not always in the sense of improving the agreement with D. It is therefore possible that on the large scale, ‘cumulus friction’ is only important in areas of strong convection, and if so, is not large enough to be determined unambiguously from existing data sets.Solution of the χ problem at a particular initial time requires an additional piece of information, the vorticity tendency, which could be obtained operationally using a suitable backward time‐differencing scheme. This contrasts with the use of the usual balance procedures, which require a knowledge of the less readily accessible diabatic heating rate.
The albedo of broken cloud fields
Authors: Kite Anne 
Published: July 2010

AbstractA Monte Carlo model of short‐wave radiative transfer in a broken cloud field is described. Output from the model is presented and the effect of cloud shape and depth, droplet absorption and water vapour absorption on the effective fractional cloud cover, Ne, is investigated. Inhomogeneities are introduced into the cloud field in the form of a variable cloud width and a cloud optical depth which is dependent upon cloud cover. It is shown that these inhomogeneities lead to much better agreement between the modelled values of Ne and experimental values derived from data collected with the Meteorological Research Flight Hercules. the conclusion is that Ne is a nonlinear function of the fractional cloud cover, N, which may be approximated by the relationship Ne = N2.
Large‐Scale Circulation Departures Related to Wet Episodes In North‐East Brazil
Authors: Sikdar Dhirendra N. , Elsner James B. 
Published: July 2010

AbstractThis study examines the large‐scale tropical environment of north‐east Brazil during its 1979 rainy season. Data were primarily from the First GARP Global Experiment (FGGE). Results show that in the mean NE Brazil is south of the intertropical trough zone (ITZ) and north‐west of the South Atlantic high. This pattern results in a westward low‐level flow over the region. Immediately over NE Brazil, middle‐level subsidence and low‐level moisture divergence dominate, producing a mean local environment which is unfavourable for precipitation. During wet episodes cloudiness departures show a more active ITZ over the equatorial Atlantic. Strong sea level pressure departures are found in the vicinity of the subtropical highs indicating short period fluctuations in the Hadley cell. Locally, weaker middle‐level subsidence and weaker moisture divergence during wet episodes allow for increased convection.
Modelling the Quasi‐Equilibrium Dynamics of the Atmosphere
Authors: Cullen M. J. P. , Norbury J. , Purser R. J. , Shutts G. J. 
Published: July 2010

AbstractThe prime need in forecasting atmospheric motions is to predict the synoptic pattern accurately, and to fill in as much mesoscale detail on it as possible. the problem is difficult because the atmospheric fields contain almost discontinuous structures such as fronts and inversions, and the large‐scale flow may separate around mountains. This paper demonstrates that such phenomena may be described as quasi‐equilibrium structures where the fluid remains close to a minimum energy state. This minimum is shown to correspond to geostrophic and hydrostatic balance, and the implied quasi‐equilibrium evolution to correspond to the Lagrangian form of the geostrophic momentum equations. Examples of flows that can be treated include boundary layers separating at surface fronts and mountain blocking with associated drag. By including diabatic effects, the inland penetration of sea breezes can also be studied. the quasi‐equilibrium idea can be applied globally, but describes only a limited subset of tropical motions.Primitive equation models attempt to produce these structures by relying on explicit geostrophic adjustment. This paper presents evidence that this is not always adequate, especially when the structures contain discontinuities. Implicit algorithms are described which may be more effective.
A Comparison of the Impact of an Envelope Orography and of A Parametrization of Orographic Gravity‐Wave Drag On Model Simulations
Authors: Slingo A. , Pearson D. W. 
Published: July 2010

AbstractResults are presented from extended annual‐cycle integrations of the Meteorological Office 11‐layer atmospheric general circulation model. an 8‐year control integration produces a good simulation in the southern hemisphere in both summer and winter and also in the northern hemisphere in summer. In northern winter, however, there is excessive westerly near‐surface flow polewards of about 40°N. It is argued that this indicates a lack of orographic forcing of the flow by the major mountain ranges. Two solutions which have been proposed for this problem are investigated. the first is envelope orography and the second is a parametrization of the effects of orographic gravity‐wave drag. Each was included separately in 3 1/2 year integrations in parallel with the control. Both produce substantial changes in the model's climatology, but envelope orography does not improve the westerly problem over the European area and it also degrades the summer circulation. the gravity‐wave drag scheme, however, gives results which in general are in very good agreement with the observations in both hemispheres and seasons. Comparison of the zonally averaged torques from the three experiments demonstrates that with envelope orography the northern hemisphere near‐surface westerlies are reduced because of a dramatic increase in the mountain pressure torque. In the experiment with the gravity‐wave scheme, however, the reduction is due to the gravity‐wave drag and the mountain torque is similar in magnitude to that in the control. A study of the variability of the 500mb height fields on synoptic timescales demonstrates the improvement in the positions of the northern hemisphere storm tracks in this integration. Some remaining errors in the simulations are identified, particularly in the stratosphere. Finally, it is argued that despite these results it may be too early to come to a final conclusion as to the role of gravity‐wave drag in the general circulation and also as to the relative importance of dynamical and radiative processes in the polar winter stratosphere.
A Numerical Simulation of Quasi‐Stationary Tropical Convective Bands
Authors: Dudhia J. , Moncrieff M. W. 
Published: July 2010

AbstractA method of imposing large‐scale ascent on a three‐dimensional numerical model is introduced and this is shown to be crucial in maintaining the quasi‐stationary convective bands observed in GATE. the effects of ascent on the overall convective development are to enhance updraughts and particularly to maintain the development of new convection cells. the magnitutude of the forcing is varied to show the sensitivity of growth on convergence.A quasi‐stationary convective band, aligned approximately parallel to the low‐level wind shear, is simulated in an initial environment defined from soundings obtained from the GATE ships Researcher and Oceanographer on 3 September 1974; the organization is therefore quite distinct from that of fast‐moving squall lines aligned at right angles to the shear. the simulated convective system has marked dynamical similarity to the observed bands; these consisted of a number of cumulonimbus cells with new cells developing on the eastern end of the hand with deeper cells to the west. the cells generally travel along the line.The large shear due to the strong low‐level jet is crucial in influencing the band development and orientation. the dynamical structure of the convective band is investigated by a trajectory analysis, which indicates an organized three‐dimensional structure.The transports of heat, moisture and momentum are calculated, and a quasi‐balance between large‐scale ascent and cloud‐induced descent on a time scale of a few hours is shown to exist. Apparent heat sources and moisture sinks are calculated and these have a bi‐modal vertical structure, in general agreement with those in observed tropical cloud clusters.
On the Two‐Dimensional Steady Upshear‐Sloping Convection
Authors: Xu Qin , Chang Lang‐Ping 
Published: July 2010

AbstractA 2‐D inviscid steering‐level model due to M. W. Moncrieff is reexamined both analytically and numerically. It is found that the thermal effects on the distribution of energy and vorticity play opposite roles in determining the interface slope, with the former being dominant. By separating the two effects, a useful insight is obtained into how the interface is controlled by the internal flow regime. Consequently, a mixed jump and steering‐level model is proposed, in which the returning updraught and downdraught are separated by adjacent jump updraught and downdraught. By solving for the internal flow, upshear‐sloping convection is obtained in the mixed model. Numerical results indicate that the inferface slope increases towards the vertical, or even becomes downshear‐sloping, as (i) the jump outflow becomes shallow, (ii) the lifting condensation level (LCL) becomes low, and/or (iii) the Richardson number (proportional to the ratio between convective available potential energy and kinetic energy in the inflow) increases (except for the cases where the jump outflow is very deep and LCL is very high). These features are discussed in connection with the recent results of A. J. Thorpe et al., and the observed differences between tropical propagating squall lines and mid‐latitude steering‐level‐type squall lines.