bluuebunny/crossref_metadata_2025_split huggingface dataset:
Overview of the field phase of the fronts and Atlantic Storm‐Track EXperiment (FASTEX) project
Authors: Joly Alain , Browning Keith A. , Bessemoulin Pierre , Cammas Jean‐Pierre , Caniaux Guy , Chalon Jean‐Pierre , Clough Sidney A. , Dirks Richard , Emanuel Kerry A. , Eymard Laurence , Gall Robert , Hewson Tim D. , Hildebrand Peter H. , Jorgensen Dave , Lalaurette François , Langland Rolf H. , Lemaǐtre Yvon , Mascart Patrick , Moore James A. , Persson P. Olag. , Roux Frank , Shapiro Melvyn A. , Snyder Chris , Toth Zoltan , Wakimoto Roger M. 
Published: February 2007

AbstractThe field phase of the Fronts and Atlantic Storm‐Track Experiment (FASTEX) project took place between 5 January and 27 February 1997 with the deployment of a unique set of observing facilities across the North Atlantic. the major objective was to document the life cycle of a representative set of mid‐latitude cyclones. Other objectives were to test the practical feasibility of ‘adaptive’ observations with a view to improving the prediction of these same cyclones and to document the internal structure of the associated cloud systems using combined airborne Doppler radars and dropsondes. Another goal of FASTEX was to measure air‐sea exchange parameters under conditions of strong winds with high seas.These objectives were successfully achieved. Intensive Observation Periods were conducted on 19 occasions. High‐resolution vertical profiles through the same cyclones at three different stages of their life cycle have been obtained on more than 10 occasions. the calculation of critical areas where further observations were needed to limit the growth of forecast error, was undertaken using different techniques, and flights were planned and executed in these areas in time to achieve this. Combined dropsonde and Doppler radar observations of cloud systems are available for 10 cases. A unique air‐sea turbulent exchange dataset has been obtained.
Forecast skill of the ECMWF model using targeted observations during FASTEX
Authors: Montani A. , Thorpe A. J. , Buizza R. , Undén P. 
Published: February 2007

AbstractThe impact of targeted observations on forecast accuracy is investigated for five case‐studies of cyclogenesis during the Fronts and Atlantic Storm‐Track EXperiment (FASTEX). Calculations of localized singular vectors (SVs) have been made using the European Centre for Medium‐Range Weather Forecasts (ECMWF) forecasting model to find the sensitive regions for each case‐study. Two sets of analyses have been prepared: a ‘control’ set consisting of analyses in which all the FASTEX data have been removed from the operational analysis, and a ‘perturbed’ set obtained by adding to the control the data from the dropsondes deployed in regions highlighted as sensitive by SVs. Analysis and forecast differences have been compared with the structure of the SVs as they evolve during the forecast. Model integrations, starting from the two different analyses, have been performed. the impact of the dropsonde data on the forecast skill has been assessed on the basis of both subjective and objective scores. Re‐runs of the model from perturbed analyses almost always give better objective scores than those starting from the control analyses. the impact is more evident if the verification area coincides with the regions over which the SVs have been optimized. In this case, short‐range prediction errors (up to day 2) are reduced on average by 15%, with a maximum error reduction of about 37%.
Targeting observations with the quasi‐inverse linear and adjoint NCEP global models: Performance during FASTEX
Authors: Pu Zhao‐Xia , Kalnay Eugenia 
Published: February 2007

AbstractThis note gives a brief summary of the targeting results obtained with both adjoint and quasi‐inverse linear NCEP global spectral models during the Fronts and Atlantic Storm‐Track EXperiment (FASTEX). Questions concerning the feasibility of the methods and related issues about targeting observations are briefly discussed.
Dynamical Characterization of the FASTEX cyclogenesis cases
Authors: Baehr Christophe , Pouponneau Béatrice , Ayrault Franck , Joly Alain 
Published: February 2007

AbstractA series of diagnostics based on the automatic tracking of cyclones is applied to the 25 life cycles captured during the field phase of the Fronts and Atlantic Storm‐Track Experiment (FASTEX). the tracking enables the various cases to be set into a common frame of reference that moves with the system. Time‐filtering is used to further separate the events into a basic‐state and perturbations. Information is obtained on environmental properties such as strain or baroclinicity.Combining these diagnostics, it is shown that instability mechanisms based on the existence of potential vorticity strips or the control of these instabilities by deformation may be involved in the initial genesis of a number of cases, but do not seem to characterize specific types nor to determine a systematic behaviour.On the other hand, it is shown that rapid‐deepening phases leading Eastern Atlantic systems to their maximum amplitude happen suddenly and at the same time as crossing the jet stream even in the absence of a clear additional upper‐level feature. For cold‐air systems, development results from meeting a diffluent zone. This is unlike the American east‐coast systems that are associated with jet exit/entrance complex.Another remarkable feature is the generation of a frontal wave as a result of the parent vorticity maximum being apparently stretched and split. This has occurred in 25% of cases.A number of other properties of the FASTEX cases are shown, such as several occurrences of large phase changes in sharp contrast to the idea of phase locking.
Surface fluxes in the North Atlantic current during CATCH/FASTEX
Authors: Eymard L. , Caniaux G. , Dupuis H. , Prieur L. , Giordani H. , Troadec R. , Bessemoulin P. , Lachaud G. , Bouhours G. , Bourras D. , Guérin C. , Le Borgne P. , Brisson A. , Marsouin A. 
Published: February 2007

AbstractCATCH (Couplage avec l'Atmosphère en Conditions Hivernales) was the oceanic component of FASTEX (Fronts and Atlantic Storm‐Track Experiment). It took place in January and February 1997, in the Newfoundland Basin near 47°N, 40°W, a region characterized by the presence of the warm North Atlantic Current and cold surrounding waters. CATCH was devoted to the study of the parametrization of surface turbulent fluxes in strong winds and changing directions, the surface‐flux variability related to the passage of atmospheric fronts and the influence on fluxes of the strong sea surface temperature gradients associated with the North Atlantic Current. This paper presents first results of ship data analysis. A large range of wind and stratification conditions were experienced: 5% of measured winds were higher than 20 m s‐1; 30% of unstable stratification (air‐sea temperature differences lower than −5 °C) and 30% of very dry conditions (air‐sea moisture differences lower than −2.5 g kg−1) were sampled. Surface turbulent heat and momentum fluxes were obtained using the inertial‐dissipative method from which a bulk algorithm was derived. A significant increase of latent‐heat and momentum‐transfer coefficients with increasing wind is obtained. This parametrization is compared to others published using the CATCH dataset. For high winds and unstable stratifications, differences between schemes reach 200 W m−2 for latent‐heat flux values of 600 W m−2. Radiative and turbulent ship‐measured fluxes are compared with modelled fluxes from the European Centre for Medium‐Range Forecasts (ECMWF) along the ship's trajectory: each component of the net heat budget is higher in the ECMWF model, consequently the heat loss of the ocean is 35% higher in the model. Finally, the effect of sea surface temperature fronts on surface turbulent fluxes is analysed by evaluating the contribution of the various terms in the flux variations, showing a significant impact of the surface temperature change in all unperturbed cases.
The evolution of the tropical western Pacific atmosphere‐ocean system following the arrival of a dry intrusion
Authors: Parsons David B. , Redelsperger Jean‐Luc , Yoneyama Kunio 
Published: February 2007

AbstractRecent studies using TOGA COARE data have found that extremely dry air from middle‐latitude waves frequently intrudes into the equatorial troposphere over the western Pacific. Using sounding data taken during the COARE, the magnitude of the advection of water vapour for one event is calculated, and it is estimated that the lime for the atmosphere to recover to moist conditions was ∼ 10‐20 days. From the magnitude of the drying and from the frequency of these events, it is proposed that dry intrusions must be a major contributor to the tropospheric moisture budget over the region during the COARE, making it difficult for the atmosphere to reach a radiative‐convective equilibrium, intrusions, instead, can help to recharge the tropical atmosphere by decreasing convective activity and, thus, driving the atmosphere toward unusually large values of convective available potential energy. A variety of atmospheric and oceanic measurements are also used to study the recovery process in detail. A conceptual model is proposed based on this work and previous investigations. As in past studies, the recovery of the atmosphere to moist conditions is accomplished through detrainment from convective clouds that began to form soon after the arrival of the dry air mass and slowly deepen in height as the recovery progresses. Previous investigators concluded that the entrainment of dry air into convective ceils is generally the factor that tends to suppress convective activity and limits the height of any convection that does develop under these adverse conditions. The idea that entrainment limits convective activity is consistent with the commonly held perception that the western Pacific is a region where there is little inhibition to deep convection and, when inhibition does occur, it can be removed by surface fluxes within hours. In contrast, it is found that convective inhibition can be large enough to suppress convection following dry intrusions, and that the diurnal variation in rainfall is due partly to modulations in convective inhibition. The modulations in convective inhibition are, in turn, caused by diurnal variations in the vertical profiles of radiation, in surface fluxes, and perhaps in large‐scale subsidence, leading to a minimum in convective inhibition during the late afternoon. In contrast, studies of this type of convection have generally emphasized diurnal variations in the surface fluxes, and often ignored convective inhibition and diurnal variations in atmospheric radiative heating.
Variational cloud‐clearing with TOVS data
Authors: Joiner J. , Rokke L. 
Published: February 2007

AbstractA number of studies have shown that the use of passive microwave and infrared satellite observations in data assimilation systems can increase forecast skill. Considerable effort has been expended over the past two decades, particularly with the TIROS Operational Vertical Sounder (TOVS), to achieve this result. The positive impact on forecast skill is a result of more rigorous treatment of quality control, improvements in systematic error correction schemes, and advances in data assimilation systems. Yet, there Still remains potential for improving the use of satellite data, particularly cloud‐contaminated observations, in data assimilation. Here, we use a one‐dimensional variational framework (1DVAR) as a first step towards improving the treatment of cloudy data by cloud‐clearing. Cloud‐clearing is a procedure that removes cloud radiative effects through comparison of partly cloudy adjacent pixels. The JDVAR approach simultaneously extracts cloud‐clearing parameters and information about the atmospheric and surface state from microwave and infrared observations. The variational framework ensures that the state estimate is consistent with all available measurements. The 1DVAR cloud‐clearing approach can also be extended to three or four dimensions (3DVAR, 4DVAR). Our TOVS cloud‐clearing implementation allows for complex cloud structures, including multiple cloud layers with wavelength‐dependent radiative properties. We present preliminary results of our 1DVAR cloud‐clearing implementation with TOVS. The results suggest that there is useful information in the cloud‐cleared data.
Propagation mechanisms for the Madden‐Julian Oscillation
Authors: Matthews Adrian J. 
Published: February 2007

AbstractThe Madden‐Julian Oscillation (MJO) is examined using 20‐years of outgoing long‐wave radiation and National Centers for Environmental Prediction/National Center for Atmospheric Research re‐analysis data. Two mechanisms for the eastward propagation and regeneration of the convective anomalies are suggested.The first is a local mechanism operating over the warm‐pool region. At the phase of the MJO with a dipole structure to the convection anomalies, there is enhanced tropical convection over the eastern Indian Ocean and reduced convection over the western Pacific. Over the equatorial western Indian Ocean, the equatorial Rossby wave response to the west of the enhanced convection includes a region of anomalous surface divergence associated with the anomalous surface westerlies and pressure ridge. This lends to suppress ascent in the boundary layer and shuts off the deep convection, eventually leading to a convective anomaly of the opposite sign. Over the Indonesian sector, the equatorial Kelvin wave response to the east of the enhanced convection includes a region of anomalous surface convergence into the anomalous equatorial surface easterlies and pressure trough, which will tend to favour convection in this region. The Indonesian sector is also influenced by an equatorial Rossby wave response (of opposite sign) to the west of die reduced convection over the western Pacific, which also has a region of anomalous surface convergence associated with its anomalous equatorial surface easterlies and pressure trough. Hence, convective anomalies of either sign tend to erode themselves from the west and initiate a convective anomaly of opposite sign via their equatorial Rossby wave response, and expand to the east via their equatorial Kelvin wave response.The second mechanism is global, involving an anomaly completing a circuit of the equator. Enhanced convection over the tropical western Pacific excites a negative mean‐sea‐level pressure (m.s.l.p.) anomaly which radiates rapidly eastward as a dry equatorial Kelvin wave at approximately 35 m s−1 over the eastern Pacific. It is blocked by the orographic barrier of the Andes and Central America for several days before propagating through the gap at Panama. After rapidly propagating as a dry equatorial Kelvin wave over the Atlantic, the m.s.l.p. anomaly is delayed further by the East African Highlands before it reaches the Indian Ocean and coincides with the development of enhanced convection at the start of the next MJO cycle.
Ice particle habits in stratiform clouds
Authors: Korolev A. , Isaac G. A. , Hallett J. 
Published: February 2007

AbstractIce crystals in clouds in the atmosphere have shapes that relate to their density, terminal fall velocity, growth rate and radiative properties. In calculations for climate‐change predictions, forecasting of precipitation, and remote‐sensing retrievals, idealized crystal shapes such as columns, needles, plates and dendrites are often assumed. The objective of this work is to study the frequency of occurrence of different habits of ice particles in natural clouds from aircraft observations. Images of cloud particles were measured by a PMS Optical Array Probe‐2DC at 25 μm resolution installed on the National Research Council Convair‐580. The processing of particle images was conducted with a newly developed algorithm for pattern recognition. Data were collected during four field projects in the Canadian and US Arctic over the North Atlantic near Newfoundland, and over the Great Lakes. Approximately 5 × 106 images of cloud particles having a size larger than 125 μm were analysed. The cloud particles were classified into four categories; spheres, irregulars, needles/columns and dendrites. The habit classification of particles was done for three different size ranges: > 125 μm, >250 μm. and >500 μm. The frequency of occurrence of different habits was found for each 5 degC temperature interval in the range −45°C < T < 0°C. It was concluded that the majority of ice particles in natural clouds were of irregular shape. The frequency of occurrence of irregular ice decreases with increasing particle size. On average, the concentration of particles larger than 125 μm was approximately constant down to −35°C, whereas the concentration of particles larger than 500 μm decreased at temperatures below −15°C. Since the data were collected in different climatic zones within many cloud lypes. and covered a significant cloud path length (3.6 × 104 km), the conclusions are applicable to most stratiform clouds containing ice.
Upper‐level barotropic growth as a precursor to cyclogenesis during FASTEX
Authors: Kucharski Fred , Thorpe Alan J. 
Published: February 2007

AbstractDuring the Fronts and Atlantic Storm‐Track Experiment (FASTEX) two large‐scale cyclones (in intensive observation periods 11 and 17) developed in the North Atlantic. These can be classified, in their initial phase, as Petterssen Type B cyclones. Initiation of the cyclones follows transient upper‐level barotropic growth, caused by a pre‐existing upper‐level trough approaching a jet associated with a strong baroclinic zone. The cyclones later developed further due to baroclinic energy conversion. A favourable orientation of the trough relative to the baroclinic zone ('horizontal tilt against the shear) is crucial for this transient barotropic growth. This scenario is therefore proposed as a general dynamical mechanism leading to Type B cyclogenesis.
Accounting for overlap of fractional cloud in infrared radiation
Authors: Li J. 
Published: February 2007

AbstractThe cloud‐matrix method for describing the mutual cloud‐coverage relationship between any two levels is systematically discussed. A general method is devised for calculating the effective cloud emissivity for maximum‐random overlap clouds. For several cloud configurations with extreme variation in fractional cloud amounts, the errors are generally very small (<5%). The radiative‐transfer process that corresponds to the random‐overlap cloud scheme is discussed. Compared with the purely random clouds scheme, the maximum‐random overlap scheme always produces a smaller cooling rate in the lower layers of a cloud block and a smaller downward flux. The difference in cooling rate can be about 3 K d−1 and the difference in the downward flux near the surface can be as large as 20 W m−2. The calculations show that the scheme of effective cloud emissivity commonly used in general‐circulation models could cause underestimation of cloud cooling rate. The clear‐sky and the cloudy‐sky radiation field can be obtained through a single calculation process but with different water‐vapour profiles. The results show that for the all‐sky case the separate treatment of the water‐vapour profile for clear and cloudy portions makes only a very small difference in the cooling rate and upward flux at the top of the atmosphere in comparison with the results of an averaged water‐vapour profile.
Atmosphere‐ocean thermal coupling in the North Atlantic: A positive feedback
Authors: Watanabe M. , Kimoto M. 
Published: February 2007

AbstractIn this article, it is examined whether a positive atmosphere‐ocean feedback is found over the North Atlantic through a series of general circulation model (GCM) experiments.A 60‐year integration of an atmospheric GCM (AGCM) coupled with a 50 m deep motionless ocean was conducted. The coupled run was compared with two uncoupled runs, one with prescribed mid‐latitude climato‐logical sea surface temperatures (SSTs) and the other with daily SSTs derived from the coupled experiment. The uncoupled atmosphere forces the slab ocean, to obtain SST responses in these runs. Consistent with previous studies, the coupled atmosphere‐ocean fields show interannual variances larger than those in the uncoupled runs, due to reduction in the local thermal damping.Patterns of maximum atmosphere‐ocean covariability show the North Atlantic Oscillation (NAO) and tripole SST anomalies both in the coupled and uncoupled fields, indicating a dominant role of the atmosphere in generating the SST anomalies. On the other hand, analyses of the temporal variability in the three runs suggest an active role of SST anomalies in determining the polarity of the air‐sea coupled variability longer than the interannual time‐scale. A combined analysis of forcing SST, upper‐air height, and the response SST anomalies in the uncoupled run identified that a patch of positive SST anomalies in the mid‐latitude band around 40°N effectively excite the positive phase of the NAO, which in turn reinforces the tripole SST anomalies. This relationship was further confirmed by a nine‐member ensemble AGCM experiment forced by the relevant SST anomalies. Since the forcing and response SST anomaly patterns bear some resemblance, these results manifest positive feedback at work in the coupled atmosphere‐ocean patterns. The processes responsible for this positive feedback were elaborated by a series of linear model experiments. The local thermal adjustment of the atmosphere to the SST anomalies results in increased precipitation over the Gulf Stream region. Associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east, which highly influences the southern part of the NAO. This stationary response in turn induces a northward deflection in the storm track activity, leading to an eddy vorticity feedback that tends to force the positive phase of the NAO.
Exploring natural and anthropogenic variation of climate
Authors: Manabe S. , Knutson T. R. , Stouffer R. J. , Delworth T. L. 
Published: February 2007

AbstractThis lecture discusses the low‐frequency variability of surface temperature using a coupled ocean‐atmosphere‐land‐surface model developed at the Geophysical Fluid Dynamics Laboratory/NOAA. Despite the highly idealized parametrization of various physical processes, the coupled model simulates reasonably well the variability of local and global mean surface temperature. The first half of the lecture explores the basic physical mechanisms responsible for the variability. The second half examines the trends of local surface temperature during the last half century in the context of decadal variability simulated by the coupled model.