bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adjusted NOAA outgoing long‐wave and net solar irradiances
Authors: Weare Bryan C. , Soong Albert 
Published: February 2007

AbstractThe outgoing long‐wave (OLR) and net solar (NSR) radiation at the top of the atmosphere, derived from the NOAA series satellites, are compared with those measured by the wide‐field‐of‐view Earth Radiation Budget (ERB) radiometers aboard Nimbus 7. For selected months between 1979 and 1983 important regional differences are found for both the OLR and NSR between the ERB observations and the NOAA, which have been spatially smoothed to approximate the resolution of the former. Knowledge of the systematic differences is utilized to derive linear regression equations, which adjust the smoothed NOAA data to match as well as possible the ERB measurements. These adjustment equations reduce the mean squared difference between the NOAA and ERB data for independent samples, not used in the statistical model development, by approximately 50% for both OLR and NSR. the adjustment equations are applied to the 2.5° NOAA data for June 1974 through May 1988. Long‐term zonal averages of the annual and monthly radiation budget at the top of the atmosphere are displayed and discussed. the adjusted data budgets are much more realistic than those derived from unadjusted data and suggest physical features not clearly evident in the previously published analyses based upon lower resolution data.
Baroclinic adjustment in a zonally varying flow
Authors: Mole Nils , James Ian N. 
Published: February 2007

AbstractIn agreement with previous published results, based on a 2‐layer model measure of baroclinicity, the extratropical northern hemisphere zonal mean atmosphere is found to be close to marginal stability in both winter and summer of the FGGE year. In winter, however, considerable zonal variations are present. Results of some numerical model runs, with both zonally symmetric and varying thermal forcing, are presented, and it is found that for sufficiently short forcing time scales a state close to marginal stability, and a storm‐tracklike region, can be produced. Large steady eddies do not seem to result so readily from the thermal forcing. Time‐lagged correlations provide evidence of forcing of the high frequency (periods less than 10 days) eddy heat flux by the baroclinicity, and it is suggested that the low frequency eddy heat flux may be a result of a nonlinear cascade from the baroclinic scales.
Some measurements of turbulence over an antarctic ice shelf
Authors: King J. C. 
Published: February 2007

AbstractProfiles of wind speed, temperature and turbulent fluxes of heat and momentum in the lowest 32 m have been measured at a station on an antarctic ice shelf. During the antarctic winter the surface layer often shows strong static stability, with temperature gradients as large as 1 Km−1 in the lowest few metres. the surface inversion is destroyed during periods of high wind speed but the wind profile shows significant deviation from the expected logarithmic form under such conditions. Measurements of stress at 5 m indicate that the roughness length of the snow surface is about lO−4 m.At 5 m height, the variations of the dimensionless wind shear, ϕm, and potential temperature gradient, ϕT, agree with previously determined forms of the Monin‐Obukhov similarity functions. Above 5 m, the behaviour of ϕm and ϕT is only qualitatively similar and surface‐layer similarity theory does not provide a good description of the profiles.Turbulence length scales have been deduced from vertical velocity power spectra. Under near‐neutral conditions, the ratio of turbulence length scale to measurement height is observed to decrease with increasing height of measurement. This observation is consistent with the variation of turbulence length scale with height implied by the measurements of ϕm. It is suggested that the stability of the overlying atmosphere restricts the depth of the turbulent boundary layer and hence the length scales of turbulence within this layer. Increasing stability causes a decrease of turbulence length scales at all levels.The ratios of turbulence kinetic energy to stress and temperature variance to heat flux are examined. Measurements are somewhat scattered, but the distribution of values varies little with height or stability. the form of the distribution suggests that large‐scale motions, possibly internal gravity waves, may be playing an important role in boundary‐layer processes.
Frontogenesis at the boundary between air‐masses of different potential vorticity
Authors: Thorpe Alan J. 
Published: February 2007

AbstractTheoretical models of frontogenesis using the semi‐geostrophic approximation have imagined the process to occur between air‐masses whose only difference is their respective surface potential temperature. This is equivalent to assuming the Ertel potential vorticity (PV) to be constant in the troposphere and that there is a horizontal temperature gradient at the surface. For many cases this is a good approximation and furthermore the constraint on the dynamics of such uniform PV is a fundamental one. In some locations and synoptic situations, however, the air‐masses not only have a different surface potential temperature but also have significantly different static stability. In this case the PV, as well as the boundary potential temperature, has a horizontal variation. Here we take the variation in PV to be entirely due to the static stability, holding f constant, although in reality there is a contribution due to the variation of f with latitude. Examples of this type of frontogenesis are coastal fronts, where the air over the ocean has a different stability to that over the land, some mesoscale polar vortices which form at the ice margin, and cold fronts with polar air moving southwards over a warmer ocean giving enhanced convection and hence lower stability.Results are presented from a two‐dimensional semi‐geostrophic model of frontogenesis between two rigid horizontal surfaces to illustrate the effects of variations in PV. In many cases the conclusions can be deduced from the geometrical aspects of the problem. If the cold air‐mass has the larger stability the frontogenesis at the lower boundary proceeds at an increased rate compared to that at the upper boundary. Indeed it is possible for a particular stability difference between the air‐masses to eliminate the upper frontogenesis completely, producing a purely lower tropospheric phenomenon. the geometrically converse conclusions apply if the cold air‐mass has the smaller stability. the results also allow the role of the mean value of the PV or stability of the two air‐masses to be described.
Investigation of systematic errors by relaxation experiments
Authors: Klinker E. 
Published: February 2007

AbstractThe systematic errors of the ECMWF forecast model have been investigated by relaxing forecasts towards analyses in selected regions. This method proved to be a useful tool to study the initial error growth in a certain region and the subsequent error propagation.The forecast fields in the tropics were relaxed towards the analysis by adding a contribution proportional to the current forecast error to the tendencies of temperature and momentum. From the comparison of control forecasts with tropically relaxed forecasts it was possible to separate large errors generated in the extra‐tropics from comparatively small errors penetrating from the tropics into the extra‐tropics.Relaxation in the major mountain regions showed different results for the Rocky Mountains and the Himalayas. the errors originating from the Rocky Mountains are substantial contributors to errors of both transient eddies and stationary eddies. the baroclinic waves in the Atlantic storm track are weakened and the stationary eddies develop a wave‐train‐like error pattern which is typical for many operational forecasts in the winter season.The errors in the Pacific are much less dependent on errors from the mountainous region. the error structure of the transient and stationary eddies, as revealed from experiments in which the Asian mountains are excluded or included from the relaxation, shows little similarity to operational forecast errors.
Extended‐range predictions with ecmwf models: Interannual variability in operational model integrations
Authors: Palmer T. N. , Branković Č. , Molteni F. , Tibaldi S. 
Published: February 2007

AbstractA set of 30‐day integrations made with the operational ECMWF model over a period of three and a half years (from 1985 to 1988) is studied. the impact of model reformulations during this period on the climate drift of the model is assessed, and the level of extended‐range forecast skill achieved by the operational model is studied.Diagnostics of zonal average 30‐day mean wind and temperature error show a systematic reduction in the extratropics over three years. It is argued that these improvements are consistent with the changes in model formulation. Eddy fluxes of heat and momentum, and levels of eddy kinetic energy are similarly improved. We also show that the ability to simulate blocking activity in the extended range has improved substantially over the three winters.From maps showing the ratio of systematic to total error it is concluded that, by the final winter, the middle‐latitude extended‐range error is almost entirely associated with random errors. This is supported by the growth of the dispersion, or spread, between forecasts initialized 24 hours apart. In particular, for the extended winter 1987/88, it is shown that the asymptotic level of (internal) spread is comparable with the asymptotic level of (external) skill. By contrast, in the tropics, the total error is dominated by the systematic error for all years.Despite improvements to the model, extended‐range forecast skill is modest. Skill has been measured in a spatially‐filtered three‐dimensional phase space, spanned by rotated EOF (empirical orthogonal function) coefficients of 500 mb height, which contain the principal weather regimes in the atmosphere. On average the skill scores are consistent with those of other major centres studying dynamical extended‐range prediction. In particular there is evidence of skill to day 15 and possibly to day 20 in middle latitudes. Beyond day 20 skill is marginal. We demonstrate that in the winter sample of operational‐model forecasts, skill is correlated with the observed value of the first rotated EOF, which can be described as a global version of the Pacific/North American mode.By contrast, the ability to predict monthly mean fields in the tropics depends primarily on a knowledge of the boundary forcing, including sea surface temperature. It is shown that some aspects of the interannual variations in the summer monsoon circulation can be predicted, in particular the tropical easterly jet anomalies, African rainfall, and, to a much lesser extent, Indian monsoon rainfall.
Travelling waves in Nimbus‐7 SBUV ozone measurements: Observations and theory
Authors: Prata A. J. 
Published: February 2007

AbstractObservations of travelling waves in the ozone measurements made by the Solar Backscatter Ultraviolet (SBUV) instrument on board the Nimbus‐7 satellite are presented. In one month's data for January 1979 evidence for a westward travelling 5‐day wave and an equatorially trapped eastward travelling Kelvin wave of 7‐day period is found. These modes arise through the coupling of ozone with the temperature perturbation field: their structure depends on the mean zonal wind, the mean zonal ozone and the photochemistry of ozone. It is shown that the structure of these waves can be described reasonably well by a simple theory involving only the latitudinal variation of the important physical processes. the waves are shown to reach highest amplitudes in the transition region between about 3 mb and 1 mb and it is speculated that they may contribute to the transport of ozone by wave interaction in the stratosphere. Some data are also presented showing wave‐induced effects on the temperature dependence of ozone in the stratosphere.
The maximum entropy production principle in climate models: Application to the faint young sun paradox
Authors: Gerard Jean‐Claude , Delcourt Dominique , Francois Louis M. 
Published: February 2007

AbstractCurrent theories of stellar evolution imply that the solar luminosity was 25‐30% less than at present during early phases of the Earth's history. the response of the global annual climate to changes of the solar input is examined using the maximum entropy production (MEP) principle and a zonal energy balance model including ice‐albedo feedback. It is shown that this formulation reproduces satisfactorily the present meridional heat flux and latitudinal temperature distributions. It is found that the model predicts that the efficiency of the meridional heat transport decreases for low values of the solar constant. Consequently, if the solar irradiance is lowered, a progressive development of the polar caps and a decrease of the global surface temperature are obtained without major irreversibility in the system. A comparison with a similar model including diffusive heat transport formalism shows that the value of the critical solar luminosity causing a global glaciation is decreased when the meridional heat fluxes are determined by the MEP principle.
On the generation and propagation of the southern African coastal low
Authors: Reason C. J. C. , Jury M. R. 
Published: February 2007

AbstractThe time‐height variability of the lower marine atmosphere during the eastwards propagation of coastal lows around the coast of southern Africa is presented. These coastal lows are shallow, mesoscale disturbances that are trapped vertically by a strong subsidence inversion and horizontally, through Coriolis effects, against the steep escarpment that fringes the subcontinent. Prior to the event, warm offshore flow descending off this escarpment at about the inversion level provides an input of buoyancy which, together with the cyclonic vorticity acquired during the descent, acts to generate a coastal low rather than a high.Analysis of the data shows that coastal lows are characterized by a marked lowering of the inversion level, a switch in the direction of the winds below the inversion and a drop in the near‐surface temperature, which are all consistent with the hypothesis that the coastal low is an internal Kelvin wave propagating in the marine layer. Good agreement between the observed propagation speed of the coastal low and the theoretical phase speed of such a wave reinforces this hypothesis.A model of the vertical buoyancy advection into the marine atmosphere that results from the warm offshore flow is presented. It is illustrated that an internal Kelvin wave, in the form of a coastal low, results from this buoyancy advection.Comparisons are made between coastal‐low dynamics and those characteristics of other mesoscale, coastally‐trapped disturbances which propagate in the marine layers of California and south‐eastern Australia.
Dynamical aspects of the october storm, 1987: A study of a successful fine‐mesh simulation
Authors: Shutts G. J. 
Published: February 2007

AbstractA diagnostic study of a successful numerical simulation of the October storm 1987 is described. This good, non‐operational forecast was obtained using the Meteorological Office's fine‐mesh model run from a revised analysis at 00 GMT on 15 October 1987. the Meteorological Office's mesoscale model was also run using initial conditions at 12 GMT 15 October obtained by interpolating the above fine‐mesh forecast fields to examine the benefits of very high horizontal resolution (15km grid length).Diagnostic maps and cross‐sections derived are used to address two scientific issues:
the role of weak moist slantwise stability (or, alternatively, positive slantwise convective potential energy)
the dynamical significance of the striking cloud structure (the cloud head) seen in the satellite imagery early in the storm's life.
It appears that the baroclinic zone, in which the storm develops, is highly receptive to forcing by an upper trough and the warm boundary‐layer air just ahead of the main surface front is characterized by substantial slantwise convective available energy. the cloud head is identified with a region of intense slantwise ascent in the warm air just above the main frontal zone. Its great meridional extent is associated with the upper tropospheric outflow and horizontal spreading of air which has recently undergone rapid slantwise ascent. the low‐level temperature field exhibits, throughout the development period, a remarkable shape‐preserving thermal ridge of considerable intensity. the sensitivity of the forecast to the removal of surface energy fluxes and latent heat of condensation are investigated separately. It is found that on the timescale of the simulation, surface energy fluxes have negligible impact on the explosive development. On the other hand, the contribution of latent‐heat release to the development appears to dominate the dry baroclinic instability process.
On the parametric representation of the tropospheric thermodynamic structure for mid‐latitude convective situations
Authors: Binder Peter 
Published: February 2007

AbstractThe thermodynamic structure related to mid‐latitude continental summer convection is investigated from a set of upper‐air soundings from a station in western Europe. In particular an examination is undertaken of the applicability to mid‐latitude situations of the convective adjustment scheme proposed by Betts (1986), which was based primarily on tropical data. It is shown that, given a proper set for the adjustable parameters derived from the observations, the deep‐convection reference profile of Betts characterizes well the convectively adjusted atmosphere of the extra‐tropical continental environment. In comparison with the reference profile determined by Betts and Miller (1986), the temperature structure derived from the present data‐set is found to be even more unstable below melting level. In addition the humidity profile exhibits some distinctive physical characteristics.
Three‐dimensional baroclinic instability and summertime frontogenesis in the Australian region
Authors: Reeder Michael J. , Keyser Daniel , Schmidt Brian D. 
Published: February 2007

AbstractThe structure of a mature three‐dimensional baroclinic wave and its attendant cold front is examined using an idealized numerical model with a simple parametrization of dry buoyant convection resulting from diurnal heating. Relative‐flow isentropic analyses of the numerical solution and of an observed Australian summertime frontal system are compared. It is shown that the model well represents the typical synoptic environment accompanying frontogenesis in the Australian region. A diagnosis of the three‐dimensional vertical circulation is obtained using a technique involving a vector streamfunction. The circulation in a cross‐sectional plane parallel with the low‐level temperature gradient is found to be highly two‐dimensional, with geostrophic confluence constituting the principal frontogenetical forcing at low levels, while at upper levels the frontogentical forcing is dominated by geostrophic horizontal shear. In a second cross‐section, taken zonally, the frontogenetic forcing is found to consist almost solely of geostrophic horizontal shear throughout the entire troposphere. However, in this case the circulation in the plane of cross‐section is found to be only qualitatively two‐dimensional, as a significant proportion of the low‐level postfrontal subsidence is associated with circulation normal to the cross‐section. It is shown that the frontal structure analysed is sensitive to the location of the chosen cross‐sectional plane, and that this in turn provides an explanation for the observed relative shallowness of Australian summertime fronts. The effects of diurnal heating are important but confined to the surface‐based mixed layer. With the addition of diurnal heating, the prefrontal updraught amplifies almost threefold and the frontal temperature contrast over the heated region approximately doubles. The diabatic forcing term in the well‐known Sawyer‐Eliassen equation is shown to be negligible. This suggests that the increased low‐level convergence is a reflection of the model's enhanced response to frontogenetic forcing in the presence of low static stability in the surface‐based well‐mixed layer. Finally, the numerical model solution is compared with a simpler two‐dimensional model specifically developed to study Australian summertime fronts.
A numerical study of tropical cyclone motion using a barotropic model. II: Motion in spatially‐varying large‐scale flows
Authors: Ulrich Wolfgang , Smith Roger K. 
Published: February 2007

AbstractThe motion of an initially symmetric vortex in a spatially‐varying large‐scale flow on a beta plane is investigated using a nondivergent, barotropic numerical model. The calculations extend those carried out for the case of zero basic flow in Part I. The large‐scale flows are provided by meridionally‐varying zonal flows, or single‐mode, stationary, finite‐amplitude planetary waves in a channel. Interest is focused on the evolution of vortex asymmetries and their role in determining vortex motion relative to the basic large‐scale flow.As in Part I, the calculations are used to assess averaging procedures for computing the environmental wind field of a tropical cyclone from observed wind data. It is shown that averaging over an annular region centred on the vortex is, in principle, more accurate when there is a basic flow, in comparison with the case of zero basic flow.
The Papal Front of 3 May 1987: A remarkable example of frontogenesis near the Alps
Authors: Volkert Hans , Weickmann Ludwig , Tafferner Arnold 
Published: February 2007

AbstractAll available, routinely collected surface data are used to document the development of the ‘Papal Front’, which crossed southern Germany on 3 May 1987 causing casualities and damage. Objective analyses on isentropic surfaces, initialized with the European aerological data, indicate that the development of the violent mesoscale front, which exhibited squall‐line characteristics, began when a distinct mid‐troposopheric anomaly of potential vorticity reached the north‐western rim of the Alpine arc. The forced uplift ahead of the associated shortwave trough combined with ageostrophic motions due to a jet streak at higher levels apparently provided a trigger for deep convection as was observed over the Alpine foreland. Numerical simulations with a dry hydrostatic model indicate the relative importance of the synoptic‐scale forcing and the Alpine orography for the generation of the ‘Papal Front’. A westerly ‘orographic jet’ over the foreland below crest height only develops in the simulation with full Alps and is corroborated by the few mountain wind observations that are available.A comparison with studies of frontal propagation along other mountain ranges reveals that the routine network in the Alpine region and its surroundings is at least of similar density, but so far hardly used for frontal case‐studies. It is concluded that a series of ‘routine‐data case‐studies’ could help to determine the variability of frontal progression along the Alps and, thus, provide guidance when assessing the significance of single events, particularly those sampled during special observation programmes.