bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solar heating of the oceans—diurnal, seasonal and meridional variation
Authors: Woods J. D. , Barkmann W. , Horch A. 
Published: February 2007

AbstractSolar heating is an important factor in modelling the upper boundary layer of the ocean. It influences not only the temperature, but also the depth of the mixed layer and must be taken into account in circulation dynamics. The study reported in this paper was designed to reveal the principal features of the global climatology of solar heating in the ocean, with such applications in mind. The meridional, seasonal and diurnal variations of the vertical distribution of solar heating inside the ocean, expressed in terms of I(z), the rate of heat accumulation below depth z, and †(z) = (1/c). dzI(z), the rate of temperature rise, are calculated for given values of cloud cover and seawater turbidity (expressed in terms of Jerlov's water types) using a model that incorporates a new parametrization of I(z)/I(0), which is shown to be more accurate than previous versions. At present there exist no reliable global climatologies of cloud cover and seawater turbidity, so the values of the corresponding parameters are held constant in each computation, which is then repeated using parameter sets covering the full ranges from clear to overcast sky, clear to turbid ocean water. It is found that uncertainty in cloud cover is more important in the mixed layer, and uncertainty in seawater turbidity is more important below. The results presented in this paper are mainly concerned with solar heating below the mixed layer. It is calculated that the annual temperature rise can exceed 1 K and the annual heat accumulation can exceed 100 MJ/m2 below the mixed layer in the tropics. At higher latitudes solar heating produces similar heating rates in summer, but the stored heat is extracted locally in winter when the mixed layer depth exceeds the maximum depth of solar heating, defined here by a daily temperature rise of 1 mK or a heat flux of 86.4 KJ/m2d (=1 W/m2). The sensitivity of the seasonal and meridional variations of the maximum depth of solar heating to cloud cover and seawater turbidity is investigated. The actual change of temperature due to solar heating in the seasonal thermocline at Ocean Weather Station ‘C’ is calculated using Bunker's monthly mean cloud cover and Jerlov's seawater turbidity. Extension of such calculations to the whole of the World Ocean must await the publication of global climatologies of cloud cover and seawater turbidity, which are expected to be derived from satellite observations during the next decade.A solar heating climatology is a prerequisite for computation of the thermal response of the ocean to CO2 pollution of the atmosphere. The implications of the results obtained from the present study are discussed. An early rise in tropical sea surface temperature seems likely, but exact prediction will be hindered by uncertainty in the turbidity of the tropical ocean.
The dynamics of stratocumulus: Aircraft observations and comparisons with a mixed layer model
Authors: Nicholls S. 
Published: February 2007

AbstractResults are presented from a detailed case study of daytime stratocumulus over the North Sea using an instrumented aircraft. The measurements include turbulence fluctuation data, radiation fluxes and droplet spectra and were made both in and out of cloud. The mean structure is discussed and a diagnostic, one‐dimensional, mixed layer model is formulated to predict the variation of turbulent fluxes with height and to assess the sensitivity of these solutions to various physical processes. These predictions are compared with observations enabling the effectiveness of some widely used model assumptions to be tested.Water transport by gravitational settling is found to be important throughout the depth of the cloud. Mixing within the cloud is driven by convection generated primarily by radiative effects: strong cooling from cloud top with warming beneath although the net heating of the cloud layer is close to zero. Turbulent kinetic energy is exported downwards via negatively buoyant elements from the zone of intense cooling near cloud top into the body of the cloud. This appears to be achieved by the combined action of the turbulent transport and velocity‐pressure correlation terms in the turbulent kinetic energy balance equation which are therefore important in maintaining mixing in the lower part of the cloud.The cloud and sub‐cloud layers are found to be decoupled, i.e. they appear as two separated mixed layers. Reasons for this are examined and some further consequences for cloud evolution are investigated. In the particular case studied, potential instability could be generated in the lower layer leading to low‐level cumulus formation. These rise into the stratocumulus layer thereby reconnecting the two previously separated regions. The implications for stratiform cloud modelling are discussed and some recommendations for future work made.
Atmospheric flow over a succession of nearly two‐dimensional ridges and valleys
Authors: Mason P. J. , King J. C. 
Published: February 2007

AbstractObservations of neutral static stability flow in a nearly two‐dimensional valley are presented. Upstream and downstream of the valley are a succession of similar ridges and valleys. The valley sides have a slope of about 32° to the horizontal and when the wind is nearly perpendicular to the valley there is a marked flow separation.The observations of mean flow and turbulence are compared with numerical simulations of flow over periodic two‐dimensional ridges and valleys.
Random walk modelling of diffusion in inhomogeneous turbulence
Authors: Thomson D. J. 
Published: February 2007

AbstractThe use of random walk techniques in diffusion modelling has been very successful when the turbulence is not too inhomogeneous. In this paper the difficulties associated with inhomogeneous turbulence are investigated, and a random walk model is developed which ensures the correct steady state distribution of particles in phase space. The model requires the generation of random numbers from non‐Gaussian distributions, and this makes the model difficult to apply in cases of severe inhomogeneity. An alternative model is presented which overcomes this problem in cases where the velocity distribution is Gaussian.
An observational study of the structure of stratiform cloud sheets: Part II. Entrainment
Authors: Nicholls S. , Turton J. D. 
Published: February 2007

AbstractThe structure near the top of stratocumulus clouds is investigated with the aid of aircraft data to determine possible processes influencing entrainment. An expression is derived to predict the buoyancy fluctuations which can be produced by mixing at the interface due to evaporative cooling, and the relative influence of cooling by radiation and by evaporation near cloud top is discussed. It is argued that the effects of evaporative cooling are not properly considered in current assessments of the stability of inversions to entrainment. A method for taking this into account in a more realistic manner is proposed.Entrainment rates derived directly from aircraft flux measurements are compared with various prediction methods. These include the predictions from four entrainment models. These predictions are found to vary widely for a given set of conditions but are generally smaller than the observationally derived values. Some of the consequences of underestimating entrainment and various other shortcomings of the models which are exposed by the comparisons are also discussed.
Alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization
Authors: Palmer T. N. , Shutts G. J. , Swinbank R. 
Published: February 2007

AbstractSystematic westerly biases in the northern hemisphere wintertime flow of the Meteorological Office 15‐layer operational model and 11‐layer general circulation model are described. Evidence that the failure to parametrize subgrid‐scale orographic gravity wave drag may account for such biases is presented. This evidence is taken from aircraft studies, surface pressure drag measurements, and studies of the zonally averaged momentum budget. A parametrization scheme is described in which the surface stress is proportional to the near‐surface wind speed and static stability, and to the variance of subgrid‐scale orography. The stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear. A Richardson‐number‐dependent wave breaking formulation is devised, and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability. It is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere.Results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere, warms polar regions by adiabatic descent, and decelerates the mean westerlies in the troposphere.The influence of the parametrization scheme on integrations of the 11‐layer model is described, and found to be generally beneficial.In a discussion of the reasons why this problem has only recently emerged, it is suggested that the satisfactory northern hemisphere winter circulations of previous, coarser general circulation models were due to a compensation implied by underestimating both the surface drag, and the horizontal flux of momentum by explicitly resolved large‐scale eddies.
Concerning the effect of surface drag on the circulation of a baroclinic planetary atmosphere
Authors: James I. N. , Gray L. J. 
Published: February 2007

AbstractExtended runs of a multi‐level spectral numerical model of atmospheric flow on a hemisphere have been used to investigate the effect of surface drag variations on the nature of the time‐averaged flow. It is shown that the most drastic effect of reducing the surface drag is to permit strong horizontal, barotropic shears in the zonal mean flow, which inhibit baroclinic instability. This superficially paradoxical result is implicit in many earlier calculations, most clearly in the lifecycle description of nonlinear baroclinic instability, but appears not to be widely appreciated. The kinetic energy spectra are interpreted in terms of the wavenumber of the most baroclinically unstable normal modes KR, the Rhines blocking wavenumber Kβ, and a limiting wavenumber based on surface drag KD. The changes in KR and the smaller changes in Kβ as drag is reduced account satisfactorily for the changes found in the kinetic energy spectra.
The impact of ensemble forecasts on predictability
Authors: Murphy J. M. 
Published: February 2007

AbstractAn estimate of the mean effect of ensemble‐averaging on forecast skill, under idealized ‘perfect model’ conditions, is obtained from a set of eight independent 50‐day winter ensemble forecast experiments made with a hemispheric version of the Meteorological Office (UKMO) 5‐level general circulation model. Each ensemble forecast consisted of seven individual integrations. Initial conditions for these were obtained by adding spatially correlated perturbations to a given wintertime analysis, and a further integration created in the same manner was used to represent nature, giving the perfect model approach.The ensemble‐mean forecast shows a clear improvement in amplitude and phase skill compared with individual forecasts, the period of significant predictability for daily fields being increased by 50%. The improvement in skill is consistent with simple theoretical estimates based on the perfect model assumption. These calculations are used to deduce how ensemble‐mean forecast skill should vary with the size of ensemble. The superiority of the ensemble‐mean is maintained when forecasts are spatially smoothed or time‐averaged.The spread of an ensemble distribution can in principle give an a priori indication of forecast skill. A moderate level of correlation between ensemble spread and the forecast skill of the ensemble‐mean is found on the hemispheric scale.The extent to which the potential benefits of ensemble forecasting may be achieved in reality depends on the model's practical forecast skill. Since the practical skill of the 5‐level model is rather low, an ensemble‐mean forecast is on average no better than an individual forecast up to the normal limit of deterministic predictability. However, in four experiments where the individual forecasts show skill beyond this point, the ensemble‐mean forecast does give increased skill.Spatial variations in both the practical and perfect model skills of an ensemble‐mean anomaly field are found to be related to corresponding variations in the statistical significance of the anomaly field. For example, the average perfect model skill, in regions where the ensemble‐mean anomaly is significantly different from zero, exceeds the full field skill in all experiments for forecast days 1–15, and in all but two cases for days 16–30.
Detailed description of deformation‐induced semi‐geostrophic frontogenesis
Authors: Davies H. C. , Muller J. C. 
Published: February 2007

AbstractA variant of the classical deformation‐induced surface frontogenesis problem is studied in the semigeostrophic limit. The particular flow system examined is the response of a baroclinic, semi‐infinite, stratified, uniform potential vorticity atmosphere to an imposed deformation flow field.This flow system permits the derivation of: a class of simple analytical solutions in geostrophic space; an explicit functional solution of the Sawyer‐Eliassen ageostrophic circulation equation; and a self‐contained nonlinear equation in real space for the surface development of the along‐front wind component.The derived relationships are utilized to examine various frontogenetic aspects of this model system. These include the time scale of frontal development, the co‐occurrence of different frontal types, the slope and movement of frontal features, the structure and strength of the ageostrophic circulation, and the degree of validity of the semi‐geostrophic approximation.
Measurements of the size dependence of cloud droplet deposition at a hill site
Authors: Gallagher M. W. , Choularton T. W. , Morse A. P. , Fowler D. 
Published: February 2007

AbstractMeasurements have been made of the deposition of cloud droplets and dissolved chemical species to moorland vegetation. Measurements of liquid water fluxes have been made by the gradient technique using Knollenberg FSS probes and by a weighing lysimeter. Deposition velocities for cloud liquid water in the range 0.1 to 0.24 g m −3 at a height of 1.0m were close to those for momentum. The FSS probes enabled the determination of deposition velocities as a function of droplet size. It was found that the deposition velocity increased with droplet radius from 2.5 μm to 6.5 μm radius. Between 6.5 and 12.5 μm radius, deposition velocities exceeded those for momentum, but decreased sharply between 12.5 and 15.5 μm.In periods of thin cloud (〈0.1 g m −3〉), evaporation from the surface occurred despite continued deposition.
Numerical models of the raingauge exposure problem, field experiments and an improved collector design
Authors: Folland C. K. 
Published: February 2007

AbstractA new design of conventional raingauge is proposed that minimizes the most important source of systematic error in point rainfall measurements: that due to the interaction of the wind with the gauge (the ‘raingauge exposure’ problem). Basic physical principles, numerical simulations and extensive field trials in England and Denmark are also used to provide a consistent quantitative description of the wind‐induced errors of conventional cylindrical gauges.It is shown that an inverted conical collector with a large semi‐vertical angle may provide the basis of an adequate solution of the raingauge exposure problem. The need to minimize outsplash demands that the collector should have a fairly large diameter and take the form of a flat champagne glass. A small diameter flat champagne glass collector has been tested for over 31/2 years against a standard 5′’ cylindrical gauge, a 5′ pit gauge and an inverted conical gauge at the Institute of Hydrology, Wallingford. The insensitivity of the losses of the ‘flat champagne glass’‐shaped collector to wind speed at low rates of rainfall is confirmed, as well as the need for a larger collector diameter to minimize outsplash. A combination of a ‘steep champagne glass’ gauge and a ‘flat champagne glass’ gauge might lead to even better estimates of rainfall in high winds, notably on ships, and could provide a low‐cost approach to improving snowfall measurements on land.
The annual cycle of oceanic heat storage and oceanic meridional heat transport
Authors: Hsiung Jane , Newell Reginald E. , Houghtby Thomas 
Published: February 2007

AbstractThe global climatology of monthly heat storage and heat transport are presented using data from the Master Oceanographic Observations Data Set for the period 1949–1980. Heat storage and the rate of heat storage change are calculated for the Pacific, Atlantic and Indian Oceans. Heat transports on a monthly basis are calculated using surface energy flux data from a previous study together with the computed heat storage change. There is a large annual cycle in heat storage change at almost all latitudes with the largest amplitude in latitudes where the western boundary currents dominate. There is also a considerable annual cycle in the heat transport estimates. The heat transport in the Atlantic is northward most of the year except in January when there is significant southward transport. The largest northward transport is found at 5°N during March with a magnitude of about 2.0PW (1 PW =1015W). In the Pacific Ocean, northward transport dominates north of 20°N with a maximum of about 1.5PW at 25°N in July‐September. South of 20°N, there is significant southward transport in July through September with a maximum of 1.5PW at 10°S in August. Overall, the largest northward transport in the Pacific is about 2.1 PW in March at 10°N. Heat transport in the Indian Ocean is mostly southward with a maximum of about 2.5 PW in May at 20°S except for a small northward transport in January‐February north of 5°S. Although the uncertainties involved with the transport estimates are large, the transport values presented here compare rather well with direct estimates and with model results.
Droplet accretion during rime growth and the formation of secondary ice crystals
Authors: Dong Ya Yi , Hallett John 
Published: February 2007

AbstractLaboratory experiments have been performed to study rime growth and its relation to secondary ice crystal production (the Hallett‐Mossop process). The rime was grown in a wind tunnel on a fixed vertical fibre 0.5 mm in diameter. The range of conditions extended from −1.0°C to −13°C in temperature, from 20cms−1 to 200cms−1 in air speed, and liquid water content up to 1.5 gm−3. The droplet size distributions were 5 to 25 μm and 8 to 50 μm, peaking at diameters of 9 and 22 μm respectively. Under conditions favourable for secondary ice production, the accreting droplets spread out on the ice surface; individual frozen droplets formed only at the lower temperatures. A separate experiment showed that supercooled water droplets froze as cones on a flat surface above −10.°C. At temperatures between −1. and −4.°C the spreading ratio of supercooled droplets on the basal surface of ice was less than on other faces, with lower molecular packing density. It is hypothesized that spreading takes place in a quasi‐liquid layer which is thinner on the basal surface. Splinter formation by pressure build‐up inside individual frozen droplets is therefore unlikely to be responsible for shatter; a new model is suggested in which thermal gradients give stresses leading to an ice crack at about − 5°C.
A comparison of incoming solar radiation at marine and continental stations
Authors: Dobson Fred W. , Smith Stuart D. 
Published: February 2007

AbstractIn modelling solar radiation from surface weather observations, different approaches have been successful with marine and with land‐based data. We apply a simple model to a marine and a mid‐latitude continental station to illustrate systematic differences in the dependence of the insolation on solar elevation, cloud, and season. Relative to the continental station, the marine station has less insolation at low solar elevations, particularly in winter, but more insolation at high solar elevations. Two mechanisms are discussed to explain these differences.
Inversion of cloudy satellite sounding radiances by nonlinear optimal estimation. I: Theory and simulation for TOVS
Authors: Eyre J. R. 
Published: February 2007

AbstractA new approach is proposed for inverting satellite sounding data for use in numerical weather prediction (NWP). It may be considered in two ways: either as a retrieval scheme which uses a forecast profile as a background or ‘first guess’ and the covariance of forecast error as a constraint in order to produce retrieved profiles compatible with the subsequent NWP analysis; or as a module within a NWP analysis scheme to perform the vertical analysis of satellite radiances at the observation points (i.e. to project the information in the radiances on to the NWP analysis levels in the vertical). The new scheme performs an inversion of the radiances to retrieve simultaneously the temperature and humidity profiles, the surface temperature and microwave emissivity, and the cloud‐top pressure and amount. It employs an iterative method which finds the maximum probability solution to a nonlinear retrieval/analysis problem. It operates on ‘raw’, potentially cloud‐affected radiances and thus bypasses the separate pre‐processing and cloud‐clearing stages necessary in many retrieval schemes. The technique is a fully ‘physical’ method, involving calculations for each profile of corresponding radiances (and of derivatives of radiance with respect to profile parameters). It is also a ‘statistical’ method, since it uses the covariance of forecast error as a constraint.The paper develops the theory of the new approach and examines its convergence properties and inherent quality control characteristics. The application of the scheme to data from the TIROS Operational Vertical Sounder (TOVS) is then discussed. The theoretical error characteristics of the scheme are investigated, and the results of retrievals from simulated TOVS radiances are presented. The theoretical advantages of retrieving cloud parameters simultaneously with other variables are demonstrated, in terms of both the temperature retrieval accuracies in cloudy conditions and the skill with which the cloud parameters themselves may be obtained.