bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessment of wind‐stress errors using bias corrected ocean data assimilation
Authors: Huddleston M. R. , Bell M. J. , Martin M. J. , Nichols N. K. 
Published: May 2004

AbstractCurrent seasonal forecasting methods make extensive use of wind‐stress products and ocean thermal profile observations to produce ocean analyses for retrospective forecasts. The combination of inaccurate wind‐stress forcing and relatively accurate ocean thermal profile observations can have significant detrimental impacts on the analysis in equatorial regions as it leads to an imbalance between the zonal pressure gradient and wind stress. Model integrations have been performed to assess various wind‐stress products using a Pacific region ocean general‐circulation model in three assimilation modes. The assimilation of thermal profile data has been shown to impact negatively on the zonal and vertical current structure. A bias correction scheme has been used to illustrate how these errors can be mitigated. The method used to correct for these systematic errors allows for the errors to evolve in time and space. The strength of the equatorial undercurrent is brought to a realistic level, but the scheme does reduce its variability. The European Remote Sensing satellite scatterometer wind products have been used to illustrate the methodology and comparisons have been drawn with several other wind‐stress products. © Royal Meteorological Society, 2004. Contributions by M. R. Huddleston, M. J. Bell and M. J. Martin are Crown copyright.
A simplified bi‐dimensional variational analysis of soil moisture from screen‐level observations in a mesoscale numerical weather‐prediction model
Authors: Balsamo G. , Bouyssel F. , Noilhan J. 
Published: May 2004

AbstractThe analysis of soil moisture for the initialization of a mesoscale numerical weather‐prediction (NWP) model is considered subject to operational constraints, both in terms of computational cost and data availability. A variational technique is used to analyse the soil moisture by assimilating screen‐level observations of temperature and relative humidity. We consider a simplified bi‐dimensional (z and t) variational approach (simplified 2D‐VAR), where the estimate of the observation operator is obtained from extra integration(s) of the numerical model. The fundamental assumptions of the method are first evaluated: linearity of the observation operator, horizontal decoupling between grid points, and truncation of the control variable space (variable decoupling), that allow the simplified 2D formalism. Thus, the variational method is applied at each grid point separately and the gain matrix is computed from finite differences given the small dimension involved. The 2D‐VAR technique keeps count of the full physics of the model, so the corrections applied to the control variable are adapted to the current meteorological conditions and the grid‐point characteristics (texture and vegetation), as well as to the previous soil state. The linear estimate of the observation operator is studied in detail to optimize its evaluation. The validation of the method is shown with simulated observations, and the assimilation of real observations is performed with different time‐windows. A sequential assimilation cycle on a 6‐hour time‐window allows the comparison with the optimum interpolation technique, while a 24‐hour window is considered to extend the temporal consistency of the assimilated observations in the analysis. Results from the performed analyses with the simplified 2D‐VAR method show a good retrieval of soil moisture, and a comparison with other initialization methods is also provided. Copyright © 2004 Royal Meteorological Society.
The response time of a convective cloud ensemble to a change in forcing
Authors: Cohen Brenda G. , Craig George C. 
Published: May 2004

AbstractIn this paper, the timescale of the convective mass‐flux response to step‐function changes in external forcing conditions is measured directly using idealized cloud‐resolving model simulations of unorganized convection in radiative–convective equilibrium. Many parametrization schemes require an estimate of this response time in the form of a fixed adjustment timescale, but the physical mechanism which sets its value is currently unknown. These experiments confirm the existence of a unique timescale, for given initial forcing conditions, of the order of one hour. The hypothesized role of gravity waves in effecting the convective adjustment is tested by changing the mean cloud spacing of the initial state. This reveals a linear dependence of the response time on the cloud spacing, in agreement with the theory. Meanwhile, similar experiments to investigate the sensitivity of the timescale to changes in gravity‐wave speed reveal a remarkable robustness of the average wave speed over a range of stratifications and tropospheric depths. Copyright © 2004 Royal Meteorological Society.
The effect of overlying absorbing aerosol layers on remote sensing retrievals of cloud effective radius and cloud optical depth
Authors: Haywood Jim M. , Osborne Simon R. , Abel Steven J. 
Published: May 2004

AbstractTwo types of partially absorbing aerosol are included in calculations that are based on intensive aircraft observations: biomass burning aerosol characterized during the Southern AFricAn Regional science Initiative (SAFARI 2000) and mineral dust aerosol characterized during the SaHAran Dust Experiment (SHADE). Measurements during SAFARI 2000 reveal that the biomass burning aerosol layer is advected over the South Atlantic ocean at elevated altitudes above the marine boundary layer which is capped by semi‐permanent stratocumulus cloud sheets. Similarly, the mineral dust is measured at elevated altitudes during SHADE resulting in transport above cloud for distances of several thousands of kilometres. We perform theoretical calculations of the effect of these partially absorbing aerosol layers on satellite retrievals of cloud effective radius and cloud optical depth, and show that, in these cases, retrievals of cloud optical depth or liquid water path are likely to be subject to systematic low biases. The theoretical calculations suggest that the cloud effective radius may be subject to a significant low bias for Moderate resolution Imaging Spectrometer (MODIS) retrievals that rely on the 0.86 and 1.63 µm radiance pair for an overlying aerosol layer of either biomass burning aerosol or mineral dust. Conversely, the cloud effective radius may be subject to a significant high bias for Advanced Very High Resolution Radiometer or MODIS retrievals that rely on the 0.63 and 3.7 µm radiance pair for an overlying aerosol layer of mineral dust. Analysis of 1 km resolution MODIS data for the SAFARI 2000 period suggests that the effective radius derived from the 0.86 and 1.63 µm radiance pair is, indeed, subject to a low bias in the presence of overlying biomass burning aerosol. These results show the difficulties associated with remote sensing retrievals, which must be kept in mind when attempting to assess any potential indirect effect. © Crown copyright 2004.
The capability of 4D‐Var systems to assimilate cloud‐affected satellite infrared radiances
Authors: Chevallier Fr'ed'eric , Lopez Philippe , Tompkins Adrian M. , Janisková Marta , Moreau Emmanuel 
Published: May 2004

AbstractFour‐dimensional variational (4D‐Var) assimilation schemes assume the linearity of their forward model in the vicinity of prior information and usually do not properly handle variables that have finer temporal and spatial scales in the real world than in the forward model. Hence cloud‐affected satellite infrared radiances are discarded from numerical weather‐prediction 4D‐Var systems, despite the critical need of observations within the cloudy regions. This paper suggests the reappraisal of that choice, subject to achieving improvements in the numerical simulation of cloudiness.A new observation operator, that computes cloud‐affected infrared radiances from 4D‐Var control variables, namely atmospheric temperature, humidity, ozone, surface temperature and surface pressure, is presented. The vertical distributions of cloud cover and of cloud condensate are diagnosed in the operator itself. The goal of this paper is to assess the feasibility of using it to assimilate cloud‐affected infrared radiances, such as those from the narrow‐band Advanced Infrared Sounder on‐board the Aqua platform or those from the broad‐band Meteosat Visible and Infrared Imager. It is shown that there is a potential benefit in assimilating directly in 4D‐Var some of the upper‐tropospheric channels at 4.5, 6.3 and 14.3 µm in the presence of clouds, for instance the 6.3 µm channel on board all the geostationary satellites. The approach is illustrated with one‐dimensional variational retrievals collocated with radiosonde observations. © Royal Meteorological Society, 2004.
Variational retrieval of temperature and humidity profiles using rain rates versus microwave brightness temperatures
Authors: Moreau Emmanuel , Lopez Philippe , Bauer Peter , Tompkins Adrian M. , Janisková Marta , Chevallier Frédéric 
Published: May 2004

AbstractThis paper assesses the performance of two different approaches for the retrieval of temperature and humidity profiles from the satellite passive microwave measurements of the Tropical Rainfall Measuring Mission (TRMM) and of the Special Sensor Microwave Imager in rainy areas. Both methods are based on a one‐dimensional variational retrieval (1D‐Var) approach. The input to the first one is rainfall rates estimated by a standard retrieval algorithm from the raw brightness temperatures. In the second technique, 1D‐Var directly uses the brightness temperatures. The retrieval experiments utilize new simplified physical parametrizations of convection and large‐scale condensation specially designed for variational assimilation as well as a microwave radiative‐transfer model.Several tropical and midlatitude meteorological situations are studied. In all cases, it is found that both 1D‐Var approaches are able to converge satisfactorily and produce consistent temperature and specific‐humidity increments. However, the convergence of 1D‐Var retrievals on surface rainfall rates, and to a lesser extent of 1D‐Var retrievals on brightness temperatures, is reduced when precipitation in the background is produced through convection and not by large‐scale processes. The results of the two 1D‐Var methods are then compared in brightness temperature and rainfall rate space and are validated against independent observations from the precipitation radar on‐board the TRMM. Finally, the sensitivity of the 1D‐Var retrievals to the specification of observation‐error statistics is studied. Copyright © 2004 Royal Meteorological Society.
The dynamics of idealized katabatic flow over a moderate slope and ice shelf
Authors: Renfrew Ian A. 
Published: May 2004

AbstractA non‐hydrostatic numerical weather prediction model has been employed to simulate idealized katabatic flows over a moderate slope and adjoining ice shelf. The topography of Coats Land and the adjoining Brunt Ice Shelf, Antarctica, has been used; this is typical of much of the Antarctic coastline. The Regional Atmospheric Modeling System Version 4.3 has been adapted for simulations over compacted snow, most notably through changes to the multi‐layer soil model. The simulations are initialized using clear‐sky conditions and at rest. On the slope, a shallow katabatic flow develops, the winds becoming approximately steady on the slope by ∼12 h. The peak downslope winds are about 7 m s−1 at 30 m above the snow surface. The katabatic flow depth ranges from 50 to 100 m down the slope. Over the ice shelf the katabatic flow peters out, while a pool of cold air develops, primarily through sensible‐heat loss into the surface and partially balancing the net radiative‐heat loss to space. Near‐surface and sounding data from the model simulations compare well with archetypal and typical katabatic flow observations, especially after some tuning of the model's turbulence parametrization.An analysis of the downslope flow dynamics shows the buoyancy force is generally balanced by the inertial force, except towards the foot of the slope where it is balanced by upslope forces related to gradients in the potential‐temperature deficit and katabatic‐layer height, caused by the pool of cold air over the ice shelf. Over time, the cooling of the ice shelf boundary layer leads to an apparent retreat of the katabatic flow from the ice shelf and some way up the slope. The dynamical analysis explains the surface climatology observed, such that the persistent katabatic winds of Coats Land rarely reach the Brunt Ice Shelf. The simulated katabatic flow moves from ‘shooting’ to ‘tranquil’ towards the foot of the slope. This transition acts to trigger a train of internal gravity waves which propagate energy upwards away from the katabatic flow jump. Previous studies have also found shooting to tranquil katabatic flow transitions, so to generalize these findings would suggest that internal gravity‐wave generation is ubiquitous around much of coastal Antarctica and Greenland. Copyright © 2004 Royal Meteorological Society.
On the withdrawal of the Indian summer monsoon
Authors: Syroka Joanna , Toumi Ralf 
Published: May 2004

AbstractThe withdrawal of the Indian summer monsoon (ISM) is defined in terms of 850 mb daily winds. The withdrawal of the ISM is found to be more variable than the onset. Most of the interannual variability of the total seasonal rainfall is dominated by the variability of the retreat phase. The withdrawal of the ISM follows a period of enhanced convective activity over the Indian subcontinent and is associated with a dry phase of the intraseasonal oscillation. The intraseasonal break dynamics have relatively more hemispheric symmetry than during the main monsoon season. The monthly persistence of interannual anomalies, the correlations with El Niño and remote upper‐level temperature signals of a Rossby type are all stronger during the withdrawal than in the summer months. These observations are found to be consistent with a mobile latent heat source migrating towards the west Pacific during the monsoon withdrawal. Copyright © 2004 Royal Meteorological Society.
UK tornado climatology and the development of simple prediction tools
Authors: Holden J. , Wright A. 
Published: May 2004

AbstractThe principle features of tornado climatology in the UK are presented based on the 5‐year period from January 1995. Just over one third of reported tornadoes occurred in the south‐east region of England, and most tornado activity took place during the spring and summer while the least activity occurred during autumn. This was different to the seasonal distribution for the period from 1960 to 1989 when autumn had the greatest number of tornadoes. The reported tornado distribution was shown to be significantly affected by topography and the density of potential observers. Of the ground‐based meteorological variables tested, air temperature was most closely related to tornado occurrence with a peak at 13°C. An equation incorporating air temperature, dew‐point temperature, wind speed and pressure was shown to predict a tornado day with an accuracy of 86.2%. The probability that a tornado would occur on a predicted day was 81.2%. The model was used to predict actual tornado occurrences across England, Wales and Scotland during the 5‐year study period, and it was estimated that just over five‐times as many tornadoes occurred than were reported. The model results suggest that the bias induced by population density was not greater than the combined influence of topography and spatial setting. This is important in the UK, because most tornadoes are reported in lowland areas which are heavily populated and it has been difficult until now to determine the extent to which tornado reports are biased by the density of potential observers. Copyright © 2004 Royal Meteorological Society.
Describing surface fluxes in katabatic flow on Breidamerkurjökull, Iceland
Authors: Parmhed O. , Oerlemans J. , Grisogono B. 
Published: May 2004

AbstractFor very stable boundary layers there is no well‐accepted theory today. In this study, an improved Prandtl model with varying diffusivity is applied to less than ideal conditions for pure katabatic flow pertaining to very stable boundary layers. We find that the improved Prandtl model adequately describes the usual and persistent katabatic glacier wind on Breidamerkurjökull. This is true even for flows with very different heights and strengths of the jet. A theoretical estimate of the katabatic jet height, based on temperature deficit and lapse rate, is verified. The calculated surface fluxes compare well with the measured turbulence parameters. A possible reason for the robustness of the katabatic jet (and other low‐level jets) is given in terms of the Scorer parameter. Copyright © 2004 Royal Meteorological Society.
Possible long‐term changes in stratospheric circulation: Evidence from total ozone measurements at the edge of the Antarctic vortex in early winter
Authors: Roscoe H. K. , Fowler C. L. , Shanklin J. D. , Hill J. G. T. 
Published: May 2004

AbstractMeasurements of total ozone in Antarctica during early winter show an increase, consistent with the observed descent of stratospheric air and the convergence that accompanies descent. Measurements in the vortex edge region at Faraday (65°S) show that the rate of increase has on average doubled between the 1960s and the 1990s. We speculate that this increase in rate of ozone change is caused by an increase in convergence. If so, it suggests that the strength of the Brewer–Dobson residual stratospheric circulation, which brings tropospheric air into the stratosphere with its accompanying chlorofluorocarbons and greenhouse gases, increased significantly. There is no obvious explanation for an increase in the circulation. Models predict that an ozone hole increases vortex strength, but only later in the spring. Models also predict that increased greenhouse gases increase the circulation, but the convergence did not increase gradually whereas greenhouse gases did. Some of the measurements in the 1990s are able to distinguish the different rates of increase of ozone in individual years, which show considerable variability, as expected following the eruption of Pinatubo. Copyright © 2004 Royal Meteorological Society.
Does work stress predict insomnia? A prospective study
Authors: Linton Steven J. 
Published: May 2004

Objectives: The aim of this study was to investigate the one‐year development of self‐reported sleep problems in workers with no sleep problem at baseline, and to evaluate the role of work stress in the etiology of a new episode.Design: A prospective design was employed.Methods: A total of 816 employees with no sleeping problems during the past three months completed a baseline questionnaire concerning their general health, working hours and working conditions. One year later they were contacted again to ascertain whether they were experiencing problems sleeping.Results: At the follow‐up, the three‐month point prevalence of self‐reported sleep problems for this population was 14.3%. While controlling for age and gender, it was found that irregular working hours and general health were not significantly related to the development of a new episode of sleeping problems. However, stress in the form of a ‘poor’ psychosocial work environment increased the risk of a new episode by more than twofold (odds ratio 2:15). The attributable fraction suggested that eliminating stress could prevent 53% of the cases.Conclusion: In a population of employees with no reported sleeping problems, 14.3% developed a sleeping problem during the coming year. Even when controlling for possible confounders, stress in the form of a ‘poor’ psychosocial work environment doubled the risk of developing a sleep problem.
Positivity in illness: Self‐delusion or existential growth?
Authors: Sodergren S.C. , Hyland M.E. , Crawford A. , Partridge M.R. 
Published: May 2004

Objectives: This study investigated the relationship between a measure of positivity in illness, the Silver Lining Questionnaire (SLQ), and measures of personality and spirituality/religious beliefs as a way of determining whether positivity in illness is a delusion or existential growth.Method: This is a cross‐sectional study comparing response to the SLQ, to the Eysenck Personality Questionnaire (EPQ‐R), breathlessness, illness type, and spiritual and religious beliefs in a final total sample of 194 respiratory outpatients.Results: The SLQ was associated positively with extraversion (r = .16, p< .05), unrelated to neuroticism (r = .11, n.s.) and repression (r = .10, n.s.) and was positively associated with spiritual and religious beliefs, F(2; 187) = 7.12, p < 001, as predicted by the existential growth but not the delusion interpretation. There was no relationship between positivity and age, r(194) = .09, n.s., or between positivity and gender t(192) = −1.27, n.s., and nor were there relationships with type of illness, F(4, 188) = 2.17, n.s., or breathlessness, F (5, 173) = 0.42, n.s.Conclusions: The results suggest that positivity in illness is associated with existential growth, though the cross‐sectional nature of the study precludes a conclusion of causal direction. The non‐significant correlation between the SLQ and neuroticism is in the opposite direction predicted by the delusion explanation, but the non‐significant relationship between the SLQ and repression is in the predicted direction. We cannot rule out the possibility that some positivity is delusion.
The impact of personal and social comparison information about health risk
Authors: French David P. , Sutton Stephen R. , Marteau Theresa M. , Kinmonth Ann Louise 
Published: May 2004

Objectives: To examine the emotional and cognitive impact of personal and social comparison information about health risk.Methods: A total of 970 adults responded to vignettes describing risk presentation scenarios that varied in terms of having (a) a ‘real world’ analogue (cardiac event) versus no such analogue (a fictitious pancreatic disease) condition, (b) high versus low levels of personal risk, and (c) no comparison group information given, comparison group risk higher or lower than own risk.Results: For both the cardiac and pancreatic disease vignettes, respondents' emotional responses and estimates of their own risk were influenced by both personal and social comparison risk information. The cardiac event vignettes produced larger effects than the pancreatic disease vignettes. Unfavourable social comparison information had no discernible impact, relative to not providing any social comparison information. Favourable social comparison information resulted in greater reassurance, less worry, and perceptions of lower susceptibility. Lower personal risk generally produced similar effects, relative to higher personal risk.Conclusions: In contrast to previous theory and research in this area, we found that both personal and (favourable) social comparison risk information have emotional and cognitive consequences. We hypothesize that the perceived clarity of the information may account for the different patterns of findings in the literature.