bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stratospheric O3‐CO2 coupling in a photochemical‐radiative column model. I: Without chlorine chemistry
Authors: Groves K. S. , Tuck A. F. 
Published: February 2007

AbstractA column model coupling photochemistry and radiative transfer has been used to examine the relationship between carbon dioxide and ozone amounts in the stratosphere in a chlorine‐free atmosphere. The annually averaged ozone column density increases by about 10% as the CO2 volume mixing ratio is increased from 250 to 700ppmv. These increases result from cooling of the upper stratosphere by up to 20 K over this range. The phase of the seasonal variation of ozone in the upper stratosphere is correctly reproduced, with the annual maximum occurring at the time of minimum temperature rather than at the time of maximum insolation.
Airborne and ground‐based studies of thunderstorms in the vicinity of Langmuir Laboratory
Authors: Christian H. , Holmes C. R. , Bullock J. W. , Gaskell W. , Illingworth A. J. , Latham J. 
Published: February 2007

AbstractFlights through the central regions of thunderstorms were made over New Mexico on 6 and 15 August 1977 with the ONR/NMIMT Schweitzer aeroplane which carried equipment designed to measure all three components of the electric field, and the charge, Q, and diameter, d, of individual precipitation elements. On the earlier day, information was also obtained with: a rain‐gauge network surrounding Langmuir Laboratory; a 3 cm radar; an acoustic system for locating lightning channels; a ground‐based field‐change meter.The first cell on 6 August produced precipitation at the ground but no lightning. Vertical fields, Ex, of up to about 50kVm−1 and precipitation charge densities ρ of up to −0.5 C km−3 were recorded within the cloud. The second cell, which grew as the first one decayed, produced 7 lightning strokes in 9 minutes during which time the radar revealed vigorous vertical growth in a narrow zone containing precipitation.Thunder reconstructions showed the acoustic sources for the first flash of this cell to be very near the top of the cloud at an altitude of 10 km a.s.1. The subsequent flashes produced acoustic signals from progressively lower in the cloud. When the radar echo reached its maximum height lightning activity ceased. Ex values of up to about 50kVm−1 and pp values of down to −1 Ckm−3 were measured. ρp was consistently negative, individual charges being less than ±40 pC. Q values were within the inductive limit for a thundercloud at breakdown but no systematic relation between Q and d was found.Six penetrations were made through the thundercloud of 15 August, which produced only two lightning strokes. The Ex records were indicative of a (±) dipole located near the cloud top, at around –13°C. Fields of up to about 100kVm−1 and ρp values (positive and negative) of around 5Ckm−3 were measured. Q values of up to ±250 pC were recorded, with charges around ±50 pC being commonly found. No systematic Q‐d relation was revealed, and smaller precipitation particles frequently carried charges (positive or negative) in excess of the inductive limit.On both days estimated precipitation rates were of order 10mmh−1 and on most occasions the pilot reported precipitation particles to be either ‘ice’ or ‘mixed liquid water and ice’.
A model to derive precipitation patterns and vertical velocities in large‐scale rain systems
Authors: Ryan B. F. 
Published: February 2007

AbstractA simple model is proposed that enables a prediction to be made of precipitation patterns and vertical velocities from single‐station serial ascents. Micro physical processes are parametrized by dividing the liquid water generated by the model into cloud and rain water. The ice phase is not explicitly modelled. Rainfall is predicted reasonably well when the cloud cover is extensive and convection is not dominant. Calculations show that the precipitation developed by the model is not strongly dependent on changes in the microphysical parametrization.
Stratospheric transport by stationary planetary waves ‐ the importance of chemical processes
Authors: Pyle J. A. , Rogers C. F. 
Published: February 2007

AbstractThe transport of reactive trace gases by stationary planetary scale waves has been investigated with the aid of Matsuno's stationary planetary wave model (1970) and the linear eddy equation derived from the tracer continuity equation. It is shown that, for stationary fluxes, K‐theory fields, as introduced by Reed and German (1965), may be defined. These become matrix fields when photochemical coupling effects are considered. The eddy flux of a particular trace gas is related to the gradients of the mean concentrations of the other chemically coupled trace gases, as well as to the gradients of its own mean concentration. In the special case of a chemically inert tracer our treatment indicates Kyy = Kxx = 0 and Kyx = – Kxy in contradiction to the results obtained by Reed and German (1965) but in agreement with recent results of Clark and Rogers (1978) and Matsuno (1980). The consequences of photochemical coupling effects for eddy fluxes are investigated quantitatively for two simple chemical schemes involving the pairs O3 and NOx, and NO and NO2. These effects are shown to be significant especially for NO and NO2 whose photochemical time‐constants are short. Furthermore, even in regions of the atmosphere where coupling effects become small, such as the lower stratosphere for O3 and NOx, the uncoupled K‐fields are quite different for various species indicating a source of error in current 1‐ and 2‐dimensional photochemical models. The relative importance of dynamical and chemical contributions to the uncoupled K‐fields is dependent on the characteristic time‐scales for photochemical and zonal advection processes. The relation of our work to a Lagrangian description of the transport process is discussed.
Dynamical models of two‐dimensional downdraughts
Authors: Thorpe A. J. , Miller M. J. , Moncrieff M. W. 
Published: February 2007

AbstractObservational and numerical model data have indicated the crucial role of the downdraught in the motion, structure and regeneration of severe storms. This paper considers downdraught dynamics in two dimensions, using both a numerical and an analytical model. In the numerical model the downdraught is produced and maintained by a constant heat sink. The adjustment of an ambient inflow, and the resultant downdraught and potential regeneration of storm cells, is simulated.To elucidate physical principles, steady analytical models are also described in which a simple parametrization of downdraught thermodynamics is used. Two distinct types of individual draught dynamics, labelled symmetric and jump, have been identified allowing a qualitative description of six dynamically consistent updraughts and downdraughts. In particular, a cold symmetric downdraught and a cold jumptype updraught are analysed, the former having negative, the latter positive outflow shear. These analytical solutions agree well with steady states developed by the numerical model.The numerical model is also used to describe the propagation of downstream and upstream gust fronts, and these results are in good agreement with atmospheric and tank data.
A laboratory model of an atmospheric mesofront
Authors: Simpson J. E. , Britter R. E. 
Published: February 2007

AbstractConsideration is given to the leading edge of a well‐defined flow of dense air without significant condensation, such as occurs at a thunderstorm outflow or a sea‐breeze front. Explanation of the front is proposed in terms of a gravity (density) current formed by the denser air. Observations of such flows are related both to laboratory gravity current heads in which head, tail and calm wind conditions are simulated and to a simple, theoretical gravity current model based primarily on a momentum balance. Good agreement is found between the atmosphere, laboratory and analytical results.The mean flow in the gravity current behind the head is greater than the velocity of the head, a result of mixing between the two fluids. This mixing nearly all occurs at the leading edge of the current. The excess height of the head of the gravity current is interpreted as the mixing region at the leading edge, and this mixed fluid lays down a stable layer above the following gravity current. In the laboratory the effect of a headwind is to flatten the profile of the raised head at the front and to reduce its rate of advance by about three‐fifths of the value of the opposing flow.
The influence of entrainment on the evolution of cloud droplet spectra: I. A model of inhomogeneous mixing
Authors: Baker M. B. , Corbin R. G. , Latham J. 
Published: February 2007

AbstractIn this, the first of two related papers, we present calculations of the growth of a population of condensate droplets rising above cloud base within small cumuli which are entraining undersaturated environmental air. It is assumed, on the basis of dimensional arguments and laboratory experiments on entrainment, conducted within a cloud droplet evolution tunnel, that this mixing process is inhomogeneous.In the extreme situation to which the calculations apply undersaturated air is entrained in a stream, or in blobs, and some droplets of all sizes are completely removed from the condensate spectrum by evaporation, while others do not change in size. This is equivalent to assuming that the time constant for turbulent mixing (ττ) is large relative to that for droplet evaporation (τr), and is thus the antithesis to the homogeneous model utilized by other workers, which assumes implicitly that ττ/τr = 0.The calculations based on the extreme inhomogeneous model produce spectral shapes which agree well with those reported in cumulus by Warner (1969a) and indicate that a small proportion of the droplets can grow several times faster through the condensate spectrum than classical theory predicts.
Destruction of ozone at the earth's surface
Authors: Galbally I. E. , Roy C. R. 
Published: February 2007

AbstractSeveral hundred new measurements of the surface resistance to ozone uptake of grass, soil, sand, fresh water, sea water and snow are presented. Grass and soil show, in agreement with previous work, a daytime surface resistance of median value 100 sm−1. The first direct evidence is presented of a nocturnal increase in surface resistance for grass and soil, with night‐time values of surface resistance of about 300 sm−1. The surface resistances of sea water and snow are considerably larger, about 1000 to 2000 sm−1. A representative global ozone destruction rate for the earth's surface is derived using the above information and other published ozone data. Allowance is made for the latitudinal variation of the different types of surface, their various ozone destruction constants, the latitudinal and diurnal variation of ozone in the surface air and the diurnal variation of eddy transfer near the earth's surface. The global average ozone destruction rate is estimated to be in the range 2 to 6 × 1029 molecules s−1 (0.5 to 1.5 × 1012kg yr−1). This range extends to slightly higher values than previous estimates. The ratio of ozone destruction rate between the southern and northern hemispheres is about 2:3. The implications for the tropospheric ozone cycle are discussed.
Surface influence upon vertical profiles in the atmospheric near‐surface layer
Authors: Garratt J. R. 
Published: February 2007

AbstractObservations from two towers situated in flat, tree‐covered terrain (z0 lying between 0.4 and 0.9 m) have been used to investigate the
flux‐profile relations in the height range z/z0 from 5 to 85, where z is the height above the zero‐plane displacement. The analysis confirms a lower height limit (at z = z*) to the validity of the Monin and Obukhov functions ϕM, H(z/L) in unstable conditions and, by implication, of the logarithmic wind law in neutral conditions. We find z*/z0 ≃ 35 and 150 for wind at the denser and less dense (lower z0) surfaces, whilst for temperature z*/z0 ≃ 100.The level z* corresponds with the top of the transition layer, within which it is assumed the profiles depend additionally upon a length scale zs, related to surface wake generation. On the assumption that z* α zs, modification of the profiles in the transition layer is then described through a function ø(z/z*) whose explicit form is derived from length‐scale considerations in a region of wake‐shear interaction. The observed non‐dimensional profiles ϕ° are well represented byϕ° ≃ 0.5ϕ(z/L)exp(0.7z/z*)Both for wind and temperature. For wind at both surfaces, the depth z* is approximately constant in unstable conditions and equal to 3δ, δ being the tree spacing. We tentatively conclude that δ is the relevant surface length scale zs characterizing the wake field and depth of penetration z*.
The influence of entrainment on the evolution of cloud droplet spectra: II. Field experiments at Great Dun Fell
Authors: Blyth A. M. , Choularton T. W. , Fullarton G. , Latham J. , Mill C. S. , Smith M. H. , Stromberg I. M. 
Published: February 2007

AbstractMeasurements have been made of the liquid water content and droplet‐size distributions within clouds enveloping the summit of Great Dun Fell, Cumbria. These covered extensive periods and a variety of meteorological situations.It was found that in highly stable atmospheric conditions cap clouds contain narrow drop‐size distributions and near adiabatic liquid water content. In less stable conditions mixing with the cloud environment was found to have a substantial effect on the microphysical properties of the cloud.In the cases studied the admixture of undersaturated air was found to produce a substantially subadiabatic liquid water content and the spectral shape experienced broadening in a way more consistent with the extreme inhomogeneous model of mixing described in Paper I* than with the classical treatment. In particular, it was found that a small number of large drops experience a greatly enhanced growth rate.In a particular study, it was observed that the interaction of the cap cloud with a pre‐existing strato‐cumulus deck produced a broad drop‐size distribution and an enhanced liquid water content.
An analysis of the large‐scale features of the upper troposphere and the stratosphere in a global, three‐dimensional, general circulation model
Authors: O'neill A. , Newson R. L. , Murgatroyd R. J. 
Published: February 2007

AbstractThe formulation of a 13–Ievel general circulation model of the troposphere and stratosphere is described and an account given of the climatology produced from an annual integration. Emphasis is placed on the interhemispheric differences in the stratosphere and the seasonal variability exhibited by its circulation. Overall, a realistic simulation of various features of the large‐scale tropospheric and stratospheric flow patterns was achieved, although a number of shortcomings are noted.The atmospheric state of the model is resolved into zonal mean and eddy components by Fourier analysis around latitude circles, while the latter are further divided into time‐averaged and transient modes. The structure of these aspects of the flow is described and the influence of the eddies on the mean flow in the stratosphere is discussed from a dynamical point of view by considering momentum and heat budgets. An attempt is made to identify the various factors governing the seasonal cycle of zonal mean wind and temperature in the stratosphere, and it is suggested that wave transience initiated in the troposphere may play a role in this respect, in addition to the evolving field of net radiative heating.The apparent success of the model in spontaneously generating events which resemble stratospheric sudden warmings is also reported.
A field study of nocturnal stratocumulus: I. Mean structure and budgets
Authors: Roach W. T. , Brown R. , Caughey S. J. , Crease B. A. , Slingo A. 
Published: February 2007

AbstractObservations of anticyclonic stratocumulus obtained with ground‐based and balloon‐borne equipment during the night of 19/20 November 1976 at Cardington, Bedford, UK, are described in relation to the synoptic situation.The mean structure of the atmosphere from ground to about 300m above cloud top is discussed. Of particular interest are the large temperature and humidity ‘jumps’ observed within a layer 1‐10m thick at cloud top, and the thermally stable surface layer about 200m thick in the presence of an overcast sky and surface wind speed of 3–4 ms−1. The mean liquid water content profile is accounted for in terms of turbulence theory, but the cause of observed large variations in total cloud water content is not identified.The locally steady conditions allowed estimates to be made of the local budgets of heat and water for the boundary layer (cloud top to ground) as a whole. In particular, the shape of the temperature inversion above cloud top allowed a quantitative estimate of cloud top entrainment rate to be made.Although the local water budget appears to be in approximate balance, only about one‐third of the radiative loss from cloud top is accounted for locally. It is not possible to account for this deficit in terms of the observations; it is suggested it could result in a downstream mean cooling of the boundary layer of about 0.5K per 100km.The observed dispersal of cloud downstream cannot be explained by the local budget deficit (which would tend to increase cloud). It is estimated that a local subsidence rate of 2–4cms−1 through the cloud would be required to disperse it on the observed time scale. Potential sources of evidence for this are discussed.
Lagrangian Monte Carlo simulation of the turbulent motion of a pair of particles
Authors: Sawford B. L. 
Published: February 2007

AbstractA new scheme for simulating the turbulent motion of a pair of particles is presented. Realistic and self‐consistent inter‐particle correlations are introduced at a fundamental level using a simple parametrization of the two‐particle Lagrangian velocity correlation function. For the simple case of stationary homogeneous turbulence in one‐dimension, the simulation procedure is in excellent agreement with exact theoretical results. Extension of the method to include more general circumstances is straightforward.
An economical method for computing the radiative energy transfer in circulation models
Authors: Hense A. , Raschke E. , Kerschgens M. 
Published: February 2007

AbstractBased on the methodology of a two‐stream approximation (Kerschgenset al.1978) the transfer of radiative energy in model atmospheres can now be calculated with high economy and sufficient accuracy. In this model the number of spectral intervals has been minimized to four (solar spectrum) and six (infrared spectrum) for which new effective transmission functions have been computed, where standard aerosol profiles and absorption and scattering coefficients are incorporated. The concentrations of major atmospheric gases (water vapour, carbon dioxide, ozone), the cloud cover and cloud liquid water content of each layer can be changed freely. Thus this model could be used in any numerical circulation model.In the first part of this paper we discuss the basic principles of the method and results obtained for cloudless model atmospheres. The accuracy of computed flux densities is better than 5% and of flux divergences better than 20% in the worst cases.In the second part this method will be applied to total and partial cloud cover in each layer.
The addition of heat to a stratified airstream with application to the dynamics of orographic rain
Authors: Smith Ronald B. , Lin Yuh‐Lang 
Published: February 2007

AbstractThe response of a stratified airstream to combined thermal and orographic forcing is investigated theoretically using the linearized hydrostatic equations of motion. The magnitude of the heating aloft is computed from observed rainfall rates. The elevated heating is shown to produce vertically propagating waves whose amplitude, relative to the mountain waves, is determined by the parameter gQb/apTU‐2Nh (symbols Appendix I). For typical wind speeds and rainfall rates the thermally generated waves will equal or exceed the oro‐graphically generated waves. These waves produce large vertical variations in the wave momentum flux at the levels where heat is being added and alter, or even reverse, the mountain drag. In hydrostatic flow, the phase relationship between the heating rate and the induced vertical displacements is found, unexpectedly, to be negative. In the vicinity of the heating, air parcels are displaced downwards. This result can be explained by wave propagation ideas but not by parcel arguments. This helps to explain why mountain wave amplitudes are sometimes reduced in moist atmospheres. The broad heat‐induced descent may act to limit the amount of condensation‐precipitation occurring in a stable middle‐level orographic cloud. Other types of orographic precipitation involving embedded convection in stratus layers, low level feeder clouds, or deep cumulus convection may not be adversely effected by the neat‐induced descent.
The forcing of stationary wave motion by tropical diabatic heating
Authors: Simmons A. J. 
Published: February 2007

AbstractThe forcing of stationary wave motion by tropical diabatic heating is examined using idealized models. A steady, linear, primitive equation model is used to study both the extratropical and the tropical response to tropical forcing. In the former case an isolated region of heating may excite a wavetrain with a substantial poleward direction of propagation. The sensitivity of this response is discussed. The tropical response is largely in agreement with a simpler model proposed by Gill, but some significant modifications due to the presence of a zonal‐mean flow and more detailed vertical structure are found. Specifying the tropical forcing by means of a relaxation towards climatology results in a large extratropical response.Barotropic experiments are discussed in which an isolated tropical forcing is superimposed on a constant forcing which maintains a climatological basic flow with zonal variation. In these cases a large response is found in the North Pacific region, particularly when the forcing is located to the south of the region of strongest flow. Non‐linearity amplifies or damps this response depending on the sign of the forcing. Maintenance of a region of tropical westerly wind of limited zonal extent results in a substantial cross‐equatorial propagation.
Extremal principles for global climate models
Authors: Mobbs S. D. 
Published: February 2007

AbstractPaltridge has recently hypothesized that the mean global climate operates near a state of maximum entropy production. In this paper an attempt is made to justify this hypothesis by parametrizing the eddy heat fluxes in terms of eddy diffusivities and using the local potential method of Glansdorff and Prigogine. With eddy diffusivities independent of the temperature and its gradient a principle of minimum entropy production is in fact found. However, by using a more realistic parametrization, a quantity closely related to entropy production is found to be maximized. The relevance of this to global climate models is discussed.
An experiment on the initial conditions for a mesoscale forecast
Authors: Carpenter K. M. , Lowther L. R. 
Published: February 2007

AbstractA 6–h forecast starting at midday on a good sea breeze day has been repeated for seven different sets of initial conditions. The initial values for each field could either be given by an 8–h mesoscale forecast valid at 1200GMT or interpolated from a synoptic scale forecast valid at the same time. It was found that changing the initial temperature field had an important effect on the subsequent forecast, but the impact of changing the initial wind field was relatively small. Changing the initial surface pressures had no visible effect on any aspect of the subsequent forecast other than the forecast of surface pressure itself.