bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Cold Front of 15 April 1994 over the Central United States. Part I: Observations
Authors: Demoz B. B. , Starr D. O’C. , Evans K. D. , Lare A. R. , Whiteman D. N. , Schwemmer G. , Ferrare R. A. , Goldsmith J. E. M. , Bisson S. E. 
Published: June 2005

AbstractDetailed observations of the interactions of a cold front and a dryline over the central United States that led to dramatic undulations in the boundary layer, including an undular bore, are investigated using high-resolution water vapor mixing ratio profiles measured by Raman lidars. The lidar-derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold-frontal system. An elevated, well-mixed, and deep midtropospheric layer, as well as a sharp transition (between 5- and 6-km altitude) to a drier region aloft, was observed. The moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted. The enhanced precipitable water vapor and roll clouds, the undulations associated with the bore, the strong vertical circulation and mixing that led to the increase in the depth of the low-level moist layer, and the subsequent lifting of this moist layer by the cold-frontal surface, as well as the feeder flow behind the cold front, are clearly indicated.A synthesis of the Raman lidar–measured water vapor mixing ratio profiles, satellite, radiometer, tower, and Oklahoma Mesonet data indicated that the undular bore was triggered by the approaching cold front and propagated south-southeastward. The observed and calculated bore speeds were in reasonable agreement. Wave-ducting analysis showed that favorable wave-trapping mechanisms existed; a low-level stable layer capped by an inversion, a well-mixed midtropospheric layer, and wind curvature from a low-level jet were found.
The Development and Structure of an Oceanic Squall-Line System during the South China Sea Monsoon Experiment
Authors: Wang Jian-Jian , Carey Lawrence D. 
Published: June 2005

Abstract
A primary goal of the South China Sea Monsoon Experiment (SCSMEX), a major field campaign of the Tropical Rainfall Measuring Mission (TRMM), is to define the initiation, structure, evolution, and dynamics of precipitation processes associated with the onset of the South China Sea (SCS) summer monsoon. In this study, dual-Doppler and dual-polarimetric radar analysis techniques are used to investigate the development and structure of a squall-line system observed on 24 May 1998. The focus is the linkage between the airflow and the microphysical fields through the system.
The squall-line system, including three distinct lines, persisted from 1200 UTC 24 May to the following day. A detailed study was performed on the structure of the second and most intense line, lasting for over 10 h. Compared to tropical squall lines observed in other regions, this narrow squall-line system had some interesting features including 1) maximum reflectivity as high as 55 dBZ; 2) relatively little stratiform rainfall that preceded instead of trailed the convective line; and 3) a broad vertical velocity maximum in the rear part of the system, rather than a narrow ribbon of vertical velocity maximum near the leading edge.
Polarimetric radar–inferred microphysical (e.g., hydrometeor type, amount, and size) and rainfall properties are placed in the context of the mesoscale morphology and dual-Doppler-derived kinematics for this squall-line system. A comparison is made between results from this study for SCSMEX and the previous studies for the TRMM Large-Scale Biosphere–Atmosphere experiment (LBA). It was found that precipitation over the SCS monsoon region during the summer monsoon onset was similar to the precipitation over the Amazon monsoon region during the westerly regime of the TRMM–LBA, which has previously been found to be closer to typical conditions over tropical oceans. Both of these cases showed lower rain rates and rainwater contents, smaller raindrops, and significantly lower ice water contents between 5 and 8 km than the precipitation over the Amazon during the easterly regime of the TRMM–LBA with more tropical continental characteristics.
Centrifuging of Hydrometeors and Debris in Tornadoes: Radar-Reflectivity Patterns and Wind-Measurement Errors
Authors: Dowell David C. , Alexander Curtis R. , Wurman Joshua M. , Wicker Louis J. 
Published: June 2005

AbstractHigh-resolution Doppler radar observations of tornadoes reveal a distinctive tornado-scale signature with the following properties: a reflectivity minimum aloft inside the tornado core (described previously as an “eye”), a high-reflectivity tube aloft that is slightly wider than the tornado core, and a tapering of this high-reflectivity tube near the ground. The results of simple one-dimensional and two-dimensional models demonstrate how these characteristics develop. Important processes in the models include centrifugal ejection of hydrometeors and/or debris by the rotating flow and recycling of some objects by the near-surface inflow and updraft.Doppler radars sample the motion of objects within the tornado rather than the actual airflow. Since objects move at different speeds and along different trajectories than the air, error is introduced into kinematic analyses of tornadoes based on radar observations. In a steady, axisymmetric tornado, objects move outward relative to the air and move more slowly than the air in the tangential direction; in addition, the vertical air-relative speed of an object is less than it is in still air. The differences between air motion and object motion are greater for objects with greater characteristic fall speeds (i.e., larger, denser objects) and can have magnitudes of tens of meters per second. Estimates of these differences for specified object and tornado characteristics can be obtained from an approximation of the one-dimensional model.Doppler On Wheels observations of the 30 May 1998 Spencer, South Dakota, tornado demonstrate how the apparent tornado structure can change when the radar-scatterer type changes. When the Spencer tornado entered the town and started lofting debris, changes occurred in the Doppler velocity and reflectivity fields that are consistent with an increase in mean scatterer size.
The Extratropical Transition of Tropical Cyclone Lili (1996) and Its Crucial Contribution to a Moderate Extratropical Development
Authors: Agustí-Panareda Anna , Gray Suzanne L. , Craig George C. , Thorncroft Chris 
Published: June 2005

Abstract
The transition that a tropical cyclone experiences as it moves into the extratropical environment (known as extratropical transition) can result in the decay or intensification of a baroclinic cyclone. The extratropical transition (ET) of Tropical Cyclone Lili (1996) in the North Atlantic resulted in a moderate extratropical development of a baroclinic cyclone. The impact of Lili in the extratropical development that occurred during its ET is investigated. Numerical experiments are performed using potential vorticity inversion and the Met Office Unified Model to forecast the extratropical development with and without the tropical cyclone in the initial conditions. In contrast with other case studies in the literature, Lili is shown to play a crucial role during its ET in the development of a baroclinic cyclone that occurred in the same region. A hypothesis of the possible scenarios of ET is presented that links the case-to-case variability of ET case studies in the literature with a classification of the life cycles of baroclinic cyclones.
Radar Observations of the Diurnally Forced Offshore Convective Lines along the Southeastern Coast of Taiwan
Authors: Yu Cheng-Ku , Jou Ben Jong-Dao 
Published: June 2005

Abstract
This study documents offshore convective lines along the southeastern coast of Taiwan, a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the Taiwan mei-yu season. Doppler radar and surface observations were gathered from a specially chosen period (11–15 May 1998) when the offshore convective lines were active off the southeastern coast of Taiwan. These observations were used to show the basic character, structure, and possible formative processes of offshore convective lines. The synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly/south-southeasterly winds in the boundary layer with southwesterlies/westerlies aloft. Examination of radar data during the study period indicates that the lines generally occurred ∼10–30 km offshore and were characterized by an elongated narrow zone (∼5–10 km wide) of heavy precipitation. The lines were oriented roughly parallel to the coastline and generally did not move significantly. The intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night.
Detailed analyses of an event on 14–15 May 1998 further show the important physical link between the offshore flow and the development of the line. The offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow. Particularly, a very narrow zone (∼2 km) of low-level heavy precipitation (40–45 dBZ) coincided with regions of strong updrafts and convergence, where the prevailing southerly onshore flow encountered the cool offshore flow nearshore. This offshore flow–induced convergence, given a stable thermodynamic condition in the lowest ∼1 km in the inflow region, was a crucial low-level forcing that provided lifting to trigger moist deep convection in this case. The line’s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line. No consistent upshear tilt of updrafts throughout the storm layer was observed, which is consistent with the presence of a strong westerly shear in the line’s environment. Both of these observations explain a relatively strong (weak) modification of low-level onshore (offshore) flow by precipitation. Additionally, a combination of surface and Doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0.7 m s−1 and possessed a frontal character with notable discontinuities in near-surface wind and temperature (instead of pressure and dewpoint temperature).
Southerly Surges on Submonthly Time Scales over the Eastern Indian Ocean during the Southern Hemisphere Winter
Authors: Fukutomi Yoshiki , Yasunari Tetsuzo 
Published: June 2005

Abstract
Meridional wind surges from the extratropics into the Tropics strongly regulate tropical convective activity. This paper confirms that extratropical forcing manifested as a meridional surge does modulate the tropical atmosphere over the eastern Indian Ocean, and it describes the tropical–extratropical connection in the region.
Surges in the lower atmosphere on submonthly (6–25 days) time scales over the eastern Indian Ocean were examined in tandem with associated tropical convection and large-scale atmospheric fields during the Southern Hemisphere (SH) winter (June–August). Data used in this study are NCEP-2 reanalyses and daily NOAA/Climate Diagnostics Center (CDC) outgoing longwave radiation (OLR) data for 23 yr, from 1979 to 2001. A low-level surge index was calculated using the 850-hPa meridional wind component (υ) averaged over a region where sub–monthly scale υ variance shows a local maximum (17.5°–2.5°S, 87.5°–97.5°E). The surge index defines 62 different surge events. Composites of various components were generated based on the index to define relationships between surge events and large-scale fields.
Low-level southerly surges over the eastern Indian Ocean originate from midlatitude Rossby waves with strong baroclinic development in the entrance region of a subtropical jet core off Australia’s west coast. Strengthened low-level wind surges cause cross-equatorial flow stretching from the subtropical eastern Indian Ocean to the southern Bay of Bengal. Surges are accompanied by the advection of cold, dry air from midlatitudes into the Tropics. A cold and dry front develops at the leading surge edge during the surge period. Two to four days later, as the surge peaks, negative OLR anomalies develop near the key region. The OLR anomalies indicate a local blow up of convection over the tropical eastern Indian Ocean. Convection reflects increased instability in the surge region, which is caused by low-level dry air advection and near-surface moistening that is forced by enhanced sea surface evaporation associated with the surge. The southerly surge on submonthly time scales is an important bridge linking the Tropics and midlatitudes over the Indian Ocean.
A Spatial Two-Dimensional Discrete Filter for Limited-Area-Model Evaluation Purposes
Authors: Feser Frauke , von Storch Hans 
Published: June 2005

Abstract
A two-dimensional discrete spatial filter was developed. It serves as a means to classify meteorological fields on a limited-area grid according to their spatial dimensions by filtering certain wavenumber ranges. Thereby it performs an isotropic spatial-scale separation of the atmospheric fields. A general algorithm was developed, which allows the construction of a filter that closely approximates a specific isotropic response function. The filter is simple in the construction and easy to apply while giving reasonable results. The method allows for considerable flexibility in choosing this specific response. This way, low-, band-, and high-pass filters are obtained. Examples show an effective scale separation of atmospheric fields on limited-area grids that can be used for process studies, model evaluation, or comparisons.
Atlantic Hurricane Season of 2003
Authors: Lawrence Miles B. , Avila Lixion A. , Beven John L. , Franklin James L. , Pasch Richard J. , Stewart Stacy R. 
Published: June 2005

Abstract
The 2003 Atlantic hurricane season is described. The season was very active, with 16 tropical storms, 7 of which became hurricanes. There were 49 deaths directly attributed to this year’s tropical cyclones.
Linearization of a Simple Moist Convection Scheme for Large-Scale NWP Models
Authors: Mahfouf Jean-François 
Published: June 2005

Abstract
A simple Kuo-type convection scheme with an improved closure based on moist enthalpy accession (Kuo symmetric) has been linearized for the tangent-linear (TL) and adjoint (AD) versions of the Global Environmental Multiscale (GEM) model. The nonlinear scheme exhibits a reasonable behavior in terms of heating and moistening rates when evaluated in stand-alone mode over a set of deep convective profiles. A preliminary evaluation of a straightforward linearization in the global TL model has revealed the existence of noise that leads to an unacceptable solution after 12 h of integration. By neglecting several terms in the linearization (detrainment rate and cloud properties), the temporal evolution of humidity analysis increments is improved by including this simplified linearized convection scheme in the TL model. The behavior of the linearized scheme has also been compared favorably to the linearized version of the European Centre for Medium-Range Weather Forecasts (ECMWF) mass-flux convection scheme. When examining the validity of the TL approximation for surface precipitation, it appears that linearization errors are large for both stratiform and convective rainfall (rms errors are about twice the mean absolute perturbed precipitation). These errors are not reduced when considering accumulated rain rates instead of instantaneous quantities. However, the occurrence of “on–off” processes is reduced by a temporal integration of rain. This could make the variational assimilation of accumulated precipitation rates easier. Finally, errors coming from internal nonlinearities are slightly larger than those produced by discontinuities. This confirms the interest for improving the linearity of nonlinear convection schemes for applications in variational contexts.
Moist Dynamics and Orographic Precipitation in Northern and Central California during the New Year’s Flood of 1997
Authors: Galewsky Joseph , Sobel Adam 
Published: June 2005

Abstract
The dynamics of moist orographic flows during the January 1997 floods in northern and central California are investigated using numerical simulations computed with the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Early in the event (31 December 1996–1 January 1997), the low-level winds offshore of California’s central coast were blocked by the topography of the Santa Lucia Range, and the low-level winds in the Central Valley were blocked by the topography of the central Sierra Nevada Range. In contrast, moisture-laden winds along the northern Coast Ranges and the northern Sierra Nevada flowed over topographic barriers. As the core of humid air migrated to the south over 24 h, the low-level barrier jets weakened as the atmospheric stability decreased, bringing heavy rainfall to the central and southern Sierra Nevada at the end of the event. The heavy precipitation during this event was largely controlled by the interaction of the flow with topography, with little contribution from non–topographically forced dynamical uplift. Latent heating was essential for lowering the effective stability of the flow and allowing the winds to flow over mountainous terrain, particularly in the northern Coast Ranges, and for enhancing the low-level jet and associated moisture transport. The horizontal distribution of static stability played a key role in the event by setting up a complex combination of flow-over and flow-around regimes that enhanced uplift in the northern Sierra Nevada during the period of heaviest rainfall.
Relative Humidity over the West Florida Continental Shelf
Authors: Virmani J. I. , Weisberg R. H. 
Published: June 2005

Abstract
Observed relative humidity variations on the coastal ocean of the West Florida Continental Shelf (WFS) are examined over the 5-yr period 1998–2003. Despite considerable daily variability within seasons, the monthly mean values are nearly constant at about 75%. Summertime specific humidity is twice that during winter, so high air temperatures are responsible for the low summer monthly mean relative humidities. Winter has the greatest relative humidity variability; values range from less than 50% to over 100% as extratropical fronts move over the WFS. Saturation (and fog) occurs as warm moist air passes over colder water. Two different sensors, mounted on multiple moorings, were used to make these observations. Monthly mean values from the Rotronics MP-100F are higher than the Hygrometrix 1020SHT. In addition to sensor differences, a contributing cause to this offset appears to be the locations chosen for sensor deployment. NCEP reanalysis climatology over the WFS and land-based coastal data both show an annual cycle in monthly mean relative humidity, with higher values in summer, suggesting that the reanalysis field is influenced by land. Air–sea fluxes over the WFS are sensitive to small spatial variability in the coastal ocean and atmosphere. The large grid spacing of the NCEP reanalysis does not capture this variability. The lack of coastal ocean data for assimilation biases the NCEP reanalysis fields toward land-based measurements. Increased spatial coverage via evolving Coastal Ocean Observing Systems should remedy this problem by providing required information for describing and understanding the complicated ocean–atmosphere interactions that occur on continental shelves.
Alignment Error Models and Ensemble-Based Data Assimilation
Authors: Lawson W. Gregory , Hansen James A. 
Published: June 2005

Abstract
The concept of alternative error models is suggested as a means to redefine estimation problems with non-Gaussian additive errors so that familiar and near-optimal Gaussian-based methods may still be applied successfully. The specific example of a mixed error model including both alignment errors and additive errors is examined. Using the specific form of a soliton, an analytical solution to the Korteweg–de Vries equation, the total (additive) errors of states following the mixed error model are demonstrably non-Gaussian for large enough alignment errors, and an ensemble of such states is handled poorly by a traditional ensemble Kalman filter, even if position observations are included. Consideration of the mixed error model itself naturally suggests a two-step approach to state estimation where the alignment errors are corrected first, followed by application of an estimation scheme to the remaining additive errors, the first step aimed at removing most of the non-Gaussianity so the second step can proceed successfully. Taking an ensemble approach for the soliton states in a perfect-model scenario, this two-step approach shows a great improvement over traditional methods in a wide range of observational densities, observing frequencies, and observational accuracies. In cases where the two-step approach is not successful, it is often attributable to the first step not having sufficiently removed the non-Gaussianity, indicating the problem strictly requires an estimation scheme that does not make Gaussian assumptions. However, in these cases a convenient approximation to the two-step approach is available, which trades obtaining a minimum variance estimate ensemble mean for more physically sound updates of the individual ensemble members.
Maximum Likelihood Ensemble Filter: Theoretical Aspects
Authors: Zupanski Milija 
Published: June 2005

Abstract
A new ensemble-based data assimilation method, named the maximum likelihood ensemble filter (MLEF), is presented. The analysis solution maximizes the likelihood of the posterior probability distribution, obtained by minimization of a cost function that depends on a general nonlinear observation operator. The MLEF belongs to the class of deterministic ensemble filters, since no perturbed observations are employed. As in variational and ensemble data assimilation methods, the cost function is derived using a Gaussian probability density function framework. Like other ensemble data assimilation algorithms, the MLEF produces an estimate of the analysis uncertainty (e.g., analysis error covariance). In addition to the common use of ensembles in calculation of the forecast error covariance, the ensembles in MLEF are exploited to efficiently calculate the Hessian preconditioning and the gradient of the cost function. A sufficient number of iterative minimization steps is 2–3, because of superior Hessian preconditioning. The MLEF method is well suited for use with highly nonlinear observation operators, for a small additional computational cost of minimization. The consistent treatment of nonlinear observation operators through optimization is an advantage of the MLEF over other ensemble data assimilation algorithms. The cost of MLEF is comparable to the cost of existing ensemble Kalman filter algorithms. The method is directly applicable to most complex forecast models and observation operators. In this paper, the MLEF method is applied to data assimilation with the one-dimensional Korteweg–de Vries–Burgers equation. The tested observation operator is quadratic, in order to make the assimilation problem more challenging. The results illustrate the stability of the MLEF performance, as well as the benefit of the cost function minimization. The improvement is noted in terms of the rms error, as well as the analysis error covariance. The statistics of innovation vectors (observation minus forecast) also indicate a stable performance of the MLEF algorithm. Additional experiments suggest the amplified benefit of targeted observations in ensemble data assimilation.