bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the occurrence of cloud streets over Northern Germany
Authors: Müller D. , Etling D. , Kottmeier Ch. , Roth R. 
Published: July 2010

AbstractCloud‐street observations over northern Germany are analysed with respect to wind and temperature profiles obtained from routine radiosonde stations in the area. In nearly all cases the wind profiles on cloudstreet days were characterized by an inflection point in the cross‐wind component with unstable stratification of the boundary layer. the height of the inflection point was found to be related to the convection height on those days, which may suggest the importance of both inflection point and convective instability for explanation of cloud‐street development.
Some observations of turbulence structure in stable layers
Authors: Hunt J. C. R. , Kaimal J. C. , Gaynor J. E. 
Published: July 2010

AbstractThree days of measurements in stable conditions (Monin‐Obukhov length L between 15 and 300 m) at the Boulder Atmospheric Observatory tower are presented. Winds came off the Rocky Mountains on two days and off the plains on the other day. Vertical profiles of the mean horizontal velocity and Brunt‐Väisälä frequency N, and the standard deviation of the vertical component, ow, fluxes, spectra, cospectra, quadspectra, correlations and length scales are examined in this study. the measurements indicate that wave motion was present on all occasions, but which varied in strength, from weak to strong. New theoretical arguments are tested, which suggest that where the Richardson number is less than one, the velocity gradient dU/dz rather than N determines the integral scales Lx(w) of the vertical velocity fluctuations, i.e. Lx(w) ≃ ow/(dU/dz). But theory also suggests that it is not this scale, but the larger buoyancy scale ow/N that determines the temperature variance and thermal diffusivity. On this basis, dimensionless parameters are developed for plotting the measurements of temperature variance and thermal diffusivity. They are found to be in reasonably good agreement with other observations and with theory, even though the relative strength of wave motion to turbulence varied considerably. Low frequency wave motion appeared to be associated with significant heat flux, a possibility that has been excluded or overlooked in some previous studies.
The global atmospheric angular momentum balance inferred from analyses made during the fgge
Authors: Swinbank By R. 
Published: July 2010

AbstractUsing analyses made during the First GARP Global Experiment (FGGE), a study has been made of the angular momentum budget of the atmosphere. the time evolution of atmospheric angular momentum has been compared with the calculated torques acting upon it. This comparison has shown for the first time that the mountain torque is the main contributor to the short‐term variation in the global atmospheric angular momentum. the variation of the torques as functions of latitude has also been compared with the total torque implied by the meridional transport of angular momentum by the atmosphere. the torques calculated agree qualitatively with the angular momentum transport, but there are some significant differences in magnitude; some possible reasons for these differences are discussed in the light of results from a general circulation model and from a second set of analyses made during the FGGE.
The derivation of hydrogen‐containing radical concentrations from satellite data sets
Authors: Pyle J. A. , Zavody A. M. 
Published: July 2010

AbstractData from the LIMS and SAMS instruments on Nimbus 7 are used to derive zonal‐mean OH fields from 85°N to 64°s for November 1978 to May 1979. Two methods are used. One relies on the establishment of a photochemical steady state between NO2 and HNO3. In the second method OH is calculated from its sources and sinks. There is substantially good agreement between the two methods. Areas of discrepancy can be explained. Indeed, some differences should be expected if present photochemical theory is correct.
A fast method for calculating scale‐dependent photochemical acceleration in dynamical models of the stratosphere
Authors: Haigh J. D. 
Published: July 2010

AbstractIt is shown that photochemical acceleration of the thermal relaxation rate in the stratosphere may be expressed as a matrix multiplication between a square matrix, which may be calculated for quite general conditions, and a vector representing the deviation of temperature from an equilibrium profile. Such a matrix is presented and its form discussed. Use of this matrix allows for temperature perturbations of any vertical scale and thus provides an accurate, as well as fast, method for calculating photochemical acceleration suitable for use in numerical models of stratospheric dynamics. the inclusion of the ozone 9.6 m̈m band into the heating rate calculations is shown to reduce the photochemical relaxation rate in the upper stratosphere.
The effect of mechanical forcing on the formation of a mesoscale vortex
Authors: Wu Guo‐Xiong , Chen Shou‐Jun 
Published: July 2010

AbstractThe influence of mechanical forcing on the formation of a mesoscale vortex which occurred over the eastern flank of the Qinghai‐Tibetan Plateau (QTP) is investigated by running a series of numerical experiments. Different orography schemes are tested. It is shown that there are three branches of air flow converging towards the vortex: the northerlies associated with the middle latitude westerly currents, the southerlies with the lowlevel monsoon jet, and the easterlies with the west Pacific subtropical high. These flows are very sensitive to mechanical forcing and play very important roles in the formation and location of the vortex.The model with either the mean or the envelope orography is shown to be capable of predicting the formation of the vortex and the associated torrential rain. However, its location is not predicted precisely. A modified orography, simulating the ‘step’ structure of the eastern flank of the QTP, is then used in an attempt to improve the prediction. Results from this experiment suggest that the weakening of some of the steep slopes of the large‐scale orography in a numerical model, due to excessive smoothing of mountain height and expanding of mountain area, is responsible for the inaccuracy in the forecast of such synoptic systems. Therefore further improvements in the orography scheme are discussed.
Observations of intermittent cumulus convection in the boundary layer
Authors: Brümmer Burghard , Wendel Melchior 
Published: July 2010

AbstractDuring the 1978 JASIN experiment radiosonde and tethered balloon measurements were performed from the R. V. Meteor. On 1 September, two cloud layers (cumulus below stratocumulus) were observed below an inversion at about 900m. Such a boundary layer situation occurred relatively often during the experiment. Cumulus clouds were not present all the time but alternately appeared and disappeared. When they occurred on 1 September, a relatively large vertical shear (about 0.006 s−1) together with an inflection point in the profile of the wind component normal to the mean wind direction was observed in the cumulus cloud layer. the airsea temperature difference was small (δT = −0.5 K) and there was a relatively large dynamical contribution to cloud generation. This may suggest the idea of an interaction between large‐scale processes generating a favourable mean wind shear profile and dynamically forced convection.Significant vertical transport of heat and momentum in the cloud layer occurred only in connection with cumulus clouds. Although in parts of some clouds the transports were locally as large as several 100W m−2 and 1N m−2, there were only a few events with such large excursions so that the transports averaged over the whole field of cumulus clouds were small.The relative air flow in and around active cumulus clouds was characterized by updraughts within the cloud and downdraughts at the cloud edges. the thermodynamic properties of updraughts and downdraughts are discussed.
Diffusion of gaussian puffs
Authors: Mikkelsen T. , Larsen S. E. , Pécseli H. L. 
Published: July 2010

AbstractA formula for the relative diffusion of a puff is proposed in which the rate of growth is related to common, one‐dimensional velocity spectra obtainable, for instance, from direct measurements in the atmosphere. Often, an equation of this type is in demand for modelling of instant or short‐term release of potentially harmful gases or smoke, for example, in connection with a puff diffusion model.A simple expression like Taylor's equation for single‐particle diffusion is not obtainable in general for relative diffusion. Therefore, the present approach is based on a kinematic‐statistical model in which a Gaussian approximation has been applied to the relative displacement process of the fluid particles. This is along lines suggested previously, where the expansion of a Gaussian puff has been related to the kinematic energy spectrum in three‐dimensional, isotropic turbulence. Here, however, we attempt to relate the growth rate directly to the one‐dimensional velocity spectra (or their corresponding correlations) most commonly available in the atmosphere. In particular, this is of value for the surface layer, where diffusions in the horizontal and vertical directions are different (anisotropy) due to the presence of the ground.Experimental evaluation is based on a series of smoke release experiments carried out in the surface layer over homogeneous terrain in Denmark. Solutions of the puff growth rate equation with the measured correlations are found to compare well with the experimental data of cross‐wind relative diffusion over the limited scale of the experiments.
A comparative study of southern hemisphere blocking during the global weather experiment
Authors: Lejenäs Harald 
Published: July 2010

AbstractSouthern hemisphere blocking during the Global Weather Experiment has been studied. Two different data sets, and two different methods to identify blocking have been used. One data set consists of maps analysed at the Australian Bureau of Meteorology and the other of FGGE level III‐b data. the results show that one method, which tends to emphasize blocks accompanied by cut‐off lows, is more sensitive to data accuracy than the other, which is based on a count of persistent positive anomalies exceeding a certain threshold value.
Convective heating and precipitation estimates for the tropical South Pacific during fgge, 10‐18 january 1979
Authors: Miller Bernard L. , Vincent Dayton G. 
Published: July 2010

AbstractA modified version of ECMWF analyses is used to compute heat and moisture budgets during part of FGGE SOP‐1 (10‐18 January 1979) for an area which contains the South Pacific convergence zone (SPCZ). Precipitation estimates are derived as residuals and compared with those derived from a GOES IR satellite technique.The 12‐hour precipitation rates derived from the heat budget appear to be reasonably accurate, whereas those obtained from the moisture budget contain some error due to the contribution from the local rate of change term. Moreover, the heat budget estimates are generally in good agreement with the IR estimates. the axis of maximum precipitation derived from the heat budget is aligned well with the lowest values of outgoing long‐wave radiation (OLR), which represent high, cold cloud tops resulting from deep cumulus convection.As expected, the vertical advection term is found to be the dominant term in the heat budget which, together with radiative cooling, indicates an approximate balance between adiabatic cooling and diabatic heating. the vertical profiles of convective heating obtained from the heat budget are compared with those derived by other investigators using similar methods for other geographical regions. the present profiles, which show maximum heating near 500 mb, are more comparable to those for the western North Pacific than to those in the eastern Atlantic.
On systematic errors in satellite sounding products and their climatological mean values
Authors: Eyre J. R. 
Published: July 2010

AbstractEstimates of atmospheric parameters derived from passive measurements of thermal radiation made by satellite‐borne radiometers have rather subtle error characteristics. Moreover, they are sensitive to the ‘first guess’ of the atmospheric state which is used, either explicitly or implicitly, in the inversion process. A proper understanding of these characteristics is desirable when using such data in climate studies or in numerical weather prediction.Relations describing the error structure of individual retrievals are derived and developed to describe the error characteristics of mean values of retrieved products as typically required in climate studies. It is shown that systematic retrieval errors will occur if the first guess used in the inversion is systematically different from the true atmospheric state. the errors are quantified for one particular inversion method‐a scheme designed to retrieve atmospheric temperature and humidity profiles and surface temperature from TOVS (TIROS‐N Operational Vertical Sounder) data. In this case the biases in retrieved surface temperature are small (but not necessarily negligible). However, for less directly observable quantities such as surface air temperature and surface relative humidity, the problem is acute.Potential methods for correcting retrieved parameters for such biases, in retrospect, using an improved first guess are discussed. They rely on information concerning the first guess applied in the inversion being available to the user of the retrieval products. This has important implications for the design of operational systems to process, disseminate and archive satellite sounding data.
On the interpretation of the eliassen‐palm flux divergence
Authors: Andrews David G. 
Published: July 2010

AbstractNew expressions are presented for the wave‐activity density and the non‐conservative source of wave activity in the small amplitude Eliassen‐Palm theorem for the primitive equations in log(pressure) and isentropic coordinates. These expressions involve Ertel's potential vorticity, and include versions that are of Eulerian form.The theoretical results are used as a basis for investigating the interpretation of the Eliassen‐Palm flux divergence in terms of physical wave properties. Implications for modelling and observational studies of planetary waves are discussed and connections with stability theory and the definition of orthogonality of normal modes are mentioned.
Photochemical model comparisons with lims observations in a stratospheric trajectory coordinate system
Authors: Austin J. , Pallister R. C. , Pyle J. A. , Tucks A. F. , Zavody A. M. 
Published: July 2010

AbstractA stratospheric photochemical model with 32 species and 77 reactions has been integrated along stratospheric air parcel trajectories for both disturbed and quiescent periods in early 1979. the model has fully time‐dependent photodissociation coefficients, allows for scattering and albedo effects and the solar zenith angle is accurately computed. the trajectories were calculated from satellite data using a radiative scheme to compute the vertical displacements of the air parcels relative to isentropic surfaces θ0. The model results are compared with LIMS observations of NO2, HNO3, H2O and O3 at points of near coincidence along trajectories at five levels θ0 = 500 K (∼20km); 650 K (∼25km); 850 K (∼30km); 1100 K (∼35km); and 1400 K (∼40km). JPL‐85 data for rate coefficients were used as standard.At the upper two levels the amounts of chlorine and methane in the model were found to have an important effect on the results. Using SAMS CH4 and typical but not locally observed mixing ratios of chlorine, agreement between the model and LIMS O3 data could not be obtained using JPL‐85 rate coefficients. This ozone discrepancy could be essentially removed by using the CODATA‐82 rate coefficient data. Large variations in NO2 during the course of a day were successfully modelled at θ0 = 650K, 850K and 1100K. Disagreement between observations and calculations was found for HNO3 at θ0 = 850K and 1100K in the standard case, but agreement could be obtained at θ0 = 850K using CODATA‐82 rates. Sensitivity tests were performed in which molecular oxygen absorption cross‐sections and certain key rate coefficients were varied, among them those for the O + HO2, OH + NO2 + M, NO + O3 and O + O3 reactions. Variations in O3, NO2 and HNO3 during substantial meridional excursions were reproduced by the photochemical model for trajectories where these molecules were expected to be chemically responsive on a time scale of less than 10 days. In other cases, they acted as tracers.
Solar ultraviolet‐B radiation under cloudless skies
Authors: Webb A. R. , Steven M. D. 
Published: July 2010

AbstractSolar ultraviolet‐B (UVB) irradiance IB (300‐316 nm) and visible radiation IV (300‐700 nm) were measured at Sutton Bonington in the Midlands. On clear days the ratio of irradiance in the two wavebands, IB/IV, plotted against the cosine of the solar zenith angle gave a series of straight lines of the form IB/IV = x + y cos z. the gradients of the lines, y, were consistent from day to day whereas the intercepts, x, changed. Applying a theoretical treatment of aerosol scattering to obtain a theoretical value of IB/IV showed the gradient y to depend only on factors which are constant for Rayleigh scattering, whereas x is a function of other atmospheric variables, including ozone, which change from day to day. A similar procedure for the ratio of UVB to the full solar waveband IF (300‐3000 nm) produced straight lines of the form IB/IF = x′ + y′ cos z on clear days, but both x′ and y′ varied from day to day, possibly because of changes in absorption by water vapour in the infrared region of the spectrum.
Convection waves: Observations of gravity wave systems over convectively active boundary layers
Authors: Kuettner Joachim P. , Hildebrand Peter A. , Clark Terry L. 
Published: July 2010

AbstractWidespread gravity wave systems have been found to exist over convectively active boundary layers (CBLs) in the presence of vertical wind shear. In contrast to mountain waves, these ‘convection waves’ occur over flat terrain and are ubiquitous over fields of shallow fair weather cumuli or clear air thermals. They extend vertically to at least 9km a.m.s.l., probably to the tropopause. First discovered by glider pilots as ‘thermal waves’, they have now been systematically investigated by research aircraft during the NCAR Convection Wave Project, which also incorporates an effort in numerical simulation. the flight results are reported in this paper, while the numerical simulations are described in a companion paper.Typical wavelengths of convection waves were found to range from 5 to 15 km, (average 9 km) and typical vertical motion amplitudes from ± 1 to ± 3 m s−1. In all cases vertical wind shear exceeded 3×10−3s−1. Under these conditions cloud tops were measured to move with relative velocities of 8 to 10 m s−1 against their environment, hence they present an obstacle to the surrounding airflow. the analogy to mountainous obstacles launching gravity waves into the atmosphere is suggestive and borne out by the aforementioned numerical simulations, which describe this process step by step.The interaction between the CBL and the overlying stable layers is studied by spectral and cross‐spectral analysis of aircraft data including coherence and phase relations between wave motions and cloud population underneath. Consideration is given to other potential sources of the observed gravity waves. At this stage the conclusions of our pilot study may be considered tentative. Some implications for further research are also discussed.
Polarization radar studies of precipitation development in convective storms
Authors: Illingworth A. J. , Goddard J. W. F. , Cherry S. M. 
Published: July 2010

AbstractRadar observations of the differential reflectivity (ZDR) of developing convective clouds are presented. This parameter provides a measure of a mean hydrometeor shape, and when analysed in conjunction with the conventional reflectivity (Z), it gives an indication of whether the precipitation is ice or liquid water; for rain it enables an estimate of raindrop size and concentration to be made. the results suggest that some isolated echoes which subsequently develop into large cumulonimbus clouds initially have very small concentrations of large (diameter greater than 4 mm) supercooled raindrops, a very different size distribution from that normally observed in mature convective clouds. an alternative explanation in terms of an even lower population of much larger ice particles in wet growth is technically possible but does not seem physically realistic.
Data Assimilation: the 1984/85 Revisions of the Ecmwf Mass and Wind Analysis
Authors: Shaw D. B. , Lönnberg P. , Hollingsworth A. , Undén P. 
Published: July 2010

AbstractA comprehensive evaluation of the ECMWF operational data assimilation system has been made, based largely on statistics of its performance over a long period of time. the evaluation has identified many deficiencies, covering such aspects of the analysis as the optimum interpolation statistics, the data selection algorithms, and the quality control criteria applied within the analysis.The observation and forecast error variances were seriously in error in the stratosphere and in the tropics. A more faithful model of the forecast error spectrum is provided by the Bessel function expansion than by the Gaussian model. the vertical structure of the height error is assumed to be composed of two components: a ‘barotropic’ part related to a horizontally constant mode and a ‘baroclinic’ structure for the horizontally varying modes. the wind field errors also have a large‐scale component. the extratropical vertical correlation remained similar to the earlier correlations, but the tropical height and wind structures changed dramatically.Reasonable rejection limits were defined from the distributions of the observation departures from the first guess, as were observation errors for satellite and aircraft wind reports and Australian pseudo‐observations.A comprehensive and homogeneous data selection algorithm has been devised. However, it has been found necessary to exclude land surface wind reports from the analysis process as the wind departures from a first‐guess field commonly contradict the surface pressure departures due to difficulties in generating a reasonable 10 m first‐guess wind. the omission of surface winds alleviated the data selection problem in data‐dense regions.The representation of the vertical correlations was changed to a continuous representation in the vertical which enabled a multivariate interpolation from data on standard pressure levels directly to model coordinates. the earlier procedure used a multivariate interpolation to constant pressure surfaces in the model grid, followed by a univariate interpolation to model surfaces in the vertical.The results of these improvements, in a series of tests covering in total some 30 days of assimilations, are also described. In summary they yield an analysis and a subsequent first guess which are in closer agreement with observations. the analysis scheme yields more balanced fields in the sense that the subsequent initialization produces more modest changes. the major impact on forecasts, in particular in the short range, is also judged to be positive.These improvements have been incorporated in the ECMWF operational data assimilation system. They have also been incorporated in the reassimilation of the final FGGE level IIb data set at ECMWF.