bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the influence of different radiation parametrizations on model‐generated radiation fields
Authors: Morcrette Jean Jacques , Geleyn Jean Francois 
Published: July 2010

AbstractRadiation fields for 10‐day forecasts with the operational ECMWF model using three different radiation schemes are presented. Simultaneous measurements of the radiation budget at the top of the atmosphere derived from TIROS‐N AVHRR data are compared with the computed budgets. Initial values of the radiation fields computed by the three schemes are compared and large intrinsic differences are found. Discrepancies in the heating rate profiles are located in the stratosphere and in the tropical lower layers. Land‐sea contrasts in the maps of outgoing longwave fluxes, related to differences in cloudiness, vary from one scheme to another, and are usually smaller than those derived from satellite measurements. Over the 10‐day period of integration, all three schemes lead to similar changes in the cloud fields, with a decrease over the ITCZ and an increase at high latitudes. This effect can be related to deficiencies in the hydrological cycle of the global model. Despite relatively large differences between the initial values of the radiation fields, compensating mechanisms are such that the computed fields, averaged over the 10 days, show smaller deviations from the observed fields.
Solar tides in the middle atmosphere. I: Description of satellite observations and comparison with theoretical calculations at equinox
Authors: Brownscombe J. L. , Nash J. , Vaughan G. , Rogers C. F. 
Published: July 2010

AbstractIn recent years several refinements have been made in the numerical computation of solar atmospheric tides between 30 and 60 km. Although comparisons have been made with winds observed by rockets it has not been possible until now to test these predictions against a globally extensive set of observations. In this paper we describe techniques for obtaining such observations from measurements made by the stratospheric sounding units (SSU) on the TIROS‐N series of satellites. These unique data are compared with calculations of the radiance variations expected from the SSU based on classical tidal theory at equinox.
The production and dispersal of marine aerosol
Authors: Exton H. J. , Latham J. , Park P. M. , Perry S. J. , Smith M. H. , Allan R. R. 
Published: July 2010

AbstractThis paper describes an extensive series of aerosol experiments conducted from a coastal site on the island of South Uist in the Outer Hebrides. Measurements at this site are shown to be reasonably representative of open ocean conditions. Aerosol size distributions (0.08 < radius, r, < 23.5 m̈m) and basic meteorological parameters were measured under both continental and maritime conditions. In all cases wind speed was found to have a dominant effect on aerosol characteristics; the volumetric loading, V(m̈m3 cm−3), increased rapidly with wind speed U(ms−1) according to ln(V) = bU + A, where, for the larger aerosol b ≈ 0.2 sm−1 and A ≈ 4. the size distributions could be principally divided into two ranges at r ≈ 0.5 m̈m, the lower corresponding to long‐range aerosol and the higher to particles produced locally, by bubble bursting at the sea surface. Results of the S. Uist experiments are compared with each other and with those of other workers.Other findings include a general but not exclusive insensitivity of aerosol characteristics to the range of relative humidity experienced at S. Uist; a decrease of aerosol concentrations, n, with altitude; and an inverse relationship between n and mixing height.
Ozone photochemistry in the antarctic stratosphere in summer
Authors: Farman J. C. , Murgatroyd R. J. , Silnickas A. M. , Thrush B. A. 
Published: July 2010

AbstractOzone photochemistry over Antarctica in summer has been examined using a 1‐D model. With diffusive transport alone, the predicted ozone decay rates from the December (summer) solstice to the March (autumn) equinox were found greatly to exceed observed rates. In order to obtain broad agreement between calculated and observed ozone amounts, it was necessary to include the effects of a slow downward mean velocity. the velocities used, a few tens of metres per day, are compatible with a Lagrangian mean circulation pattern derived from thermodynamic considerations and from GCMs.The rates of change of ozone amounts computed for 75°S decrease abruptly following the change from continuous to interrupted photolysis when the sun first sets (in mid‐February) after the long polar day of midsummer. In the polar day regime, N2O5 concentrations are depressed strongly, and CIONO2 concentrations moderately, relative to those in regions subjected to diurnal interruption of photolysis. the effects on the diurnal variations of ozone and other minor constituents are described.
A model study of some aspects of soil hydrology relevant to climatic modelling
Authors: Hunt B. G. 
Published: July 2010

AbstractA considerable international effort is being made to improve all aspects of the physical processes represented in numerical models of climate. This particular paper is concerned with one of those aspects, namely the manner in which soil hydrology is included in such models and how it affects climate. For this purpose a 1‐dimensional radiative‐convective model has been coupled with various soil hydrology formulations. This simple approach has the combined advantages of permitting a self‐consistent energetic evaluation of the impact of the moisture content of the soil, and of providing a very economical means for investigating the model's response to perturbations in selected variables. Three soil hydrology parametrizations suitable for use in climatic models were compared, and their individual characteristics illustrated. A method devised by J. W. Deardorff was judged to be superior and was therefore used in the subsequent experiments. These experiments were designed to clarify the role of soil moisture and its variability on the model's surface temperature and surface heat fluxes. the approach adopted permitted individual responses to be followed in great detail, and highlighted the potential role of the model for assisting in the design and subsequent analysis of appropriate experiments using climatic models. Importantly, the results illustrate the limitations of current formulations for surface hydrology used in climatic models, and the need for better parametrizations to be developed.
Modification of turbulence characteristics in flow over hills
Authors: Zeman Otto , Jensen Niels Otto 
Published: July 2010

AbstractA new model has been developed to investigate turbulence in flows over two‐dimensional hills: the von Mises transformation was applied in mean momentum equations, and turbulence equations (second‐order‐closure type) were solved in a coordinate system aligned with streamlines; the hill perturbation pressure was calculated by means of potential flow theory. the model predictions were compared with some experimental results from the Askervien Hill project with good agreement. It was found that apart from rapid distortion the curvature of streamlines has an important dynamical effect on turbulence. the curvature effect is shown to be particularly pronounced in the vicinity of the inner layer height on the hill top, where it attenuates turbulence. Overall, the salient features of the hill top turbulence profile were successfully explained by analysing the turbulence conservation equations in streamline coordinates.
The two‐dimensional dynamics of West African squall lines
Authors: Dudhia J. , Moncrieff M. W. , So D. W. K. 
Published: July 2010

AbstractThe two‐dimensional dynamics of multicell and unicell squall lines are examined using a numerical model. Both types feature a convective jump updraught with extensive, deep, rearward‐extending anvils. the multicell case contains travelling convection cells and is unsteady but persistent, whereas the unicell case is quasi‐steady.In the multicell case, an extensive density current is produced by the evaporation and drag of rain falling from a succession of convection cells which travel rearwards relative to the density current head. the circulation within the density current is complex and consists of three mutually interactive branches: a rotor, a cold downdraught, and a subsidence region.In the unicell case, a density current is not produced and the updraught is forced by a propagating wave of elevation, generated as an interaction between the updraught, water loading and evaporation in a very localized area.The squall line structure is compared with other models and it is shown that certain propagating two‐dimensional tropical and mid‐latitude squall lines are dynamically similar, their detailed structure being controlled by the inflow wind profile.The multicell case is compared with a quasi‐two‐dimensional West African squall line which occurred on 22 June 1981 during the Convection Profonde Tropicale (COPT 81) experiment performed in the northern part of the Ivory Coast. Good agreement is found between the model and the observations, and hence the dynamics of the observed squall line is quantified. the unicell case, in which a density current and conventional downdraughts are absent, has yet to be identified in atmospheric observations.
An analytic model of the heat‐induced tropical circulation in the presence of a mean wind
Authors: Phlips P. J. , Gill A. E. 
Published: July 2010

AbstractA linear analytic model of the response of the tropical troposphere‐in the presence of a uniform zonal mean wind‐to an isolated region of deep heating is presented. the O(1) components of the response are the long Kelvin and planetary waves. as found in earlier work by Matsuno, Gill, and others. the behaviour of these modes is a function of a non‐dimensional parameter which combines the damping time, the wave speed, the mean wind speed, and the length of the heating region. It is interpreted as the ratio of the heating region length to the wave decay distance. When this ratio is small the response consists of long waves propagating away from the heating region. But when it is large, disturbances are locally determined at each longitude, and the dynamics are those of two‐dimensional Hadley circulations.In a westerly mean wind one also finds short stationary mixed and planetary waves downstream of the heating region. Their amplitude is small compared with the long waves, and proportional to U/LAH2 for small U, where U is the mean wind speed and LH the length of the heating region. In easterly mean winds the short stationary waves are replaced by inertial boundary layers at the edges of the heating region.
A Sequential Estimation Approach to Cloud‐Clearing For Satellite Temperature Sounding
Authors: Eyre J. R. , Watts P. D. 
Published: July 2010

AbstractTemperature sounding of the troposphere using satellite‐borne infrared radiometers is complicated by the effects of clouds on the measured radiances. If accurate products are to be obtained these effects must first be detected and, if possible, corrections must be made for them in the retrieval procedures. This is normally done by converting the measured radiances to the ‘clear‐column’ values which would be observed from the same atmospheric profile in the absence of cloud—a process known as ‘cloud‐clearing’.In this paper a review of cloud‐clearing methods is presented. Then a new approach to cloud‐clearing, based on the principles of optimal estimation, is developed and applied to data from HIRS (the High‐resolution Infrared Radiation Sounder) on the TIROS‐N/NOAA satellite series.Preliminary estimates of clear‐column radiances and their expected errors are obtained at each HIRS spot by one of a number of methods, depending on the cloud characteristics. the properties of horizontal consistency expected in the clear‐column radiance field are then employed to improve the initial estimates using a sequential estimation procedure. This scheme is intended for implementation in the Local Area Sounding System of the Meteorological Office, which provides satellite soundings of high horizontal resolution for use in operational weather forecasting. Details of the new scheme, and of the old scheme which it replaces, are given. the improvements in clear‐column radiances are demonstrated by comparing the products of the old and new schemes with clear‐column radiances derived from coincident data of AVHRR (the Advanced Very High Resolution Radiometer).
Some Comments On the Concept of Thermal Forcing
Authors: Shutts G. J. 
Published: July 2010

AbstractArguments are given to support the notion that the thermally‐forced component of large‐scale motion is not simply that associated with pre‐specified diabatic heat sources as expressed in the classical models of thermal forcing. the concept of thermal equilibration, as an idealized response in models with a Newtonian diabatic heating process, is introduced and is argued to be relevant to real and numerically simulated atmospheric circulation. Equilibration is possible when Newtonian forcing is compatible with a nonlinear free mode flow pattern. the general question of the possible importance of equilibration and nonlinear free mode structures in the atmosphere is raised.
Tropical‐wide teleconnection and oscillation. I: Teleconnection indices and type I/type II states
Authors: Navarra A. , Ward M. N. , Miyakoda K. 
Published: July 2010

AbstractThe tropical oscillation of the ENSO‐monsoon (El Niño Southern Oscillation‐Asian monsoons) system is studied based on 34‐year simulations of an atmospheric general‐circulation model with specified sea surface temperature (SST), together with some observed data for the same period. In particular, two indices are studied: the first is the generalized index of Indian monsoon rainfall (IMR), and the other is an index by which the interaction/non‐interaction between the ENSO and the Indian monsoon system is assessed.In order to examine the validity of the first index, the Indian subcontinent and the near‐equatorial western Pacific were selected as two key locations. They correspond, approximately, to the dominant regions in the first empirical orthogonal function of precipitation, for boreal summer and winter, respectively. These two regions form the western rim of a ‘horseshoe’ teleconnection pattern in their respective seasons. the time coefficients of empirical orthogonal function mode 1 in the two seasons are taken as the key indices which are referred to as the Tropical‐wide Oscillation Index (TOI).Having defined the spatial patterns in both seasons, the lead‐lag teleconnection structure associated with the ENSO‐monsoon system is studied; the result is that the TOI for boreal summer is more useful than the TOI for boreal winter for identifying the lead‐lag nature of the ENSO‐monsoon. the new index is then related to traditional indices like the IMR and the Southern Oscillation Index, but proves to be a more comprehensive index for lead‐lag correlations with key variables, while the latter, the TOI for winter, has no precursory signal for the Indian monsoon for the following summer.The second index is the Walker circulation Index (WAI), which represents the eastward/westward shift of the updraught region of the Walker circulation. It is proposed that the WAI can usefully distinguish between years when the ENSO‐monsoon oscillation operates (type I) and years when it does not (type II). If the SST in the key region has a climatologically close‐to‐normal condition, the state of the coupled equatorial system is in type II. On the other hand, if the deviation from climatology is large, the tropical‐wide oscillation will continue to be active; these years are type I. Elimination of the type II years from the data significantly enhances the time‐lagged correlations between the TOI and some key variables, such as SST. As a result, the biennial oscillation becomes clearer.
Analysis of the CEPEX ozone data using a 3D chemistry‐meteorology model
Authors: Lawrence Mark G. , Crutzen Paul J. , Rasch Philip J. 
Published: July 2010

AbstractThe ozone (O3) data collected during the Central Equatorial Pacific Experiment (CEPEX) are analysed with the aid of the 3D global photochemistry model MATCH‐MPIC (Model of Atmospheric Transport and Chemistry‐Max‐Planck‐Institute for Chemistry version). This study focuses on using MATCH‐MPIC to address three specific questions: (1) are the individual CEPEX O3 soundings, in particular the extremely low O3 levels occasionally observed in the upper troposphere (UT), reproducible by a state‐of‐the‐art global photochemical model driven with analysed meteorological data from the same time period as the measurements (March 1993): (2) are the CEPEX O3 data likely to be representative of the mean state of the regional atmosphere, or do they instead indicate the degree of variability in this region of the atmosphere; and (3) what causes the UT O3 minima? It is found that MATCH‐MPIC is not able to reproduce the soundings obtained during CEPEX on an individual basis; however, the model does reproduce some of the key features present in the observations, such as UT minima and mid‐tropospheric maxima similar to those observed during CEPEX. the UT O3 minima computed by the model are mainly due to convective pumping of low‐O3 marine boundary‐layer air, as is demonstrated by comparison with the results of a run in which convective transport of O3 is suppressed. the UT O3 minima simulated by MATCH‐MPIC (with O3 between 5 and 10 nmol mol‐1) are less intense than those observed (with O3 < 5 nmol mol‐1), even at relatively high model spatial and temporal resolution, and with a convection scheme that would be expected to readily produce UT O3 minima via intense pumping of low‐O3 marine boundary‐layer air directly into the UT convective outflow regions. This may indicate that additional photochemical loss processes are involved, either in situ in the UT or, in particular, near the surface in the convective inflow regions. where the model tends to overestimate the observed O3 levels. In addition, although a significant temporal variability for O3 in this region is computed, it is still less than indicated by the observations in the UT. This high degree of variability implies that individual O3 soundings will often differ considerably from the mean over a longer period. For instance, 20‐50% less O3 in the UT during the CEPEX period is computed with MATCH‐MPIC than the average for March. Thus, the CEPEX expedition was perhaps fortunate in encountering extreme conditions which produced extensive UT O3 minima. which have helped to demonstrate one end of the large degree of variability of O3 in the tropical troposphere.
A self‐sustaining climate mode in the tropical atlantic, 1995–97: Observations and modelling
Authors: Handoh Itsuki C. , Bigg Grant R. 
Published: July 2010

AbstractAn anomalous climatic event in the tropical Atlantic, starting in autumn 1995 and continuing into the autumn of 1997, is investigated. Using remotely sensed datasets and a reduced‐gravity model, it is shown that this event contained both a warm and a cold phase, each of roughly 12 months duration. The propagating signal within each phase is identified in the sea surface height and temperature signatures as both equatorial and off‐equatorial waves in the ocean, with coupling to atmospheric convection. The strength, geographical pattern and timing of the anomalous period is consistent with it being the first observed example of a coupled mode of interaction between the ocean and atmosphere found in two previous coupled ocean‐atmosphere models of the tropics. This interpretation means that the two‐phased climate event, which we will call the Equatorial Atlantic Oscillation (EAO), was associated with purely internal atmospheric and oceanographic variability within the Atlantic basin and hence was independent of the Pacific climate. It can also be inferred, from long‐term monthly sea surface temperature and sea‐level pressure datasets, that there were potentially several previous EAO events during the past century.
Review of atmospheric turbulence over cities
Authors: Roth M. 
Published: July 2010

AbstractThis paper provides a comprehensive, critical review of turbulence observations over cities. More than fifty studies are analysed with their experimental conditions summarized in an appendix. The main results are based on 14 high‐quality experiments which met criteria based on stringent experimental requirements. The observations are presented as non‐dimensional statistics to facilitate comparison between urban studies and work conducted over other rough, inhomogeneous surfaces. Wake production associated with bluff bodies, and the inhomogeneous distribution of sources and sinks of scalars, result in a roughness sub‐layer which for the studies reviewed extends to about 2.5 to 3 times the height of the buildings. It is shown that within this region the basis of several traditional micrometeorological approaches to describe the turbulent exchange is in doubt. There are strong similarities to flow over plant canopies, and many of the turbulence characteristics can be interpreted in the framework of a plane mixing layer. Future field observations should concentrate on the turbulent exchange near the top and within the urban canopy as well as within the urban boundary layer.
Linear instability of broad baroclinic zones
Authors: Juckes M. N. 
Published: July 2010

AbstractBaroclinic energy conversions play a central role in mid‐latitude synoptic‐scale dynamics, drawing energy from the meridional temperature gradient and feeding it into the eddy dynamics. The physical mechanisms underlying these conversions can be investigated through the theory of small‐amplitude instabilities growing on a steady basic state. In a recent study the author analysed the instability associated with a boundary temperature transition concentrated in a narrow front. This paper looks at the complementary problem of a broad baroclinic zone. The solution is applicable both to the Eady model and to the Phillips two‐level quasi‐geostrophic model. The reduction in the growth rate relative to an infinitely broad, homogeneous baroclinic mne is inversely proportional to the width of the baroclinic zone, as found in previous studies. The constant of proportionality is expressed in a simplified and more general form, related to the derivative with respect to zonal wave number of the complex phase speed of the homogeneous problem. If the flow is purely baroclinic the maximum growth rate is reduced compared with that of a homogeneous, infinitely broad frontal zone by a factor 1 ‐ (2kmaxr)‐1. where kmax is the wave number of the most unstable mode of the homogeneous problem and r is the width of the baroclonic zone. The width, r, is defined in terms of the second meridional derivative of the boundary temperature gradient evaluated at the maximum of the latter. Results in the literature give consistent, though less general, expressions for the growth rate, but various predictions for the structure of the waves. The numerical solutions show that as the jet width is reduced a new type of mode appears in which critical lines at the lid (tropopause) play an important role.