bluuebunny/crossref_metadata_2025_split huggingface dataset:
Information-Based Skill Scores for Probabilistic Forecasts
Authors: Ahrens Bodo , Walser André 
Published: January 2008

AbstractThe information content, that is, the predictive capability, of a forecast system is often quantified with skill scores. This paper introduces two ranked mutual information skill (RMIS) scores, RMISO and RMISY, for the evaluation of probabilistic forecasts. These scores are based on the concept of mutual information of random variables as developed in information theory. Like the ranked probability skill score (RPSS)—another and often applied skill score—the new scores compare cumulative probabilities for multiple event thresholds. The RMISO quantifies the fraction of information in the observational data that is explained by the forecasts. The RMISY quantifies the amount of useful information in the forecasts. Like the RPSS, the new scores are biased, but they can be debiased with a simple and robust method. This and additional promising characteristics of the scores are discussed with ensemble forecast assessment experiments.
A Diagnostic Case Study of Mei-yu Frontogenesis and Development of Wavelike Frontal Disturbances in the Subtropical Environment
Authors: Chen George Tai-Jen , Wang Chung-Chieh , Chang Sau-Wa 
Published: January 2008

Abstract
During 6–7 June 2003, a mei-yu front over southern China, with active mesoscale convective systems (MCSs) along it and to its south, intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1.7 × 10−4 s−1 and a low-level jet (LLJ) of 22.5 m s−1 at 850 hPa. Moreover, both the mass and wind fields and convection developed a wavelike structure at meso-α scale along the front. Using mainly gridded analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF), the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity (PV) inversion.
Results indicate that this mei-yu front was characterized by strong horizontal shear and moderate temperature gradient, and its development was not baroclinic in nature. The initiation of a wavelike structure along the frontal shear zone was consistent with barotropic instability. The growth of mesoscale frontal disturbances (cyclogenesis) was a result of the nonlinear mechanism similar to the conditional instability of the second kind (CISK) in which the frontal PV centers and cumulus convection reinforce each other through a positive feedback process.
As the MCSs were both intense and persistent, the latent heating was highly efficient and caused significant enhancement of the mei-yu frontal system, even at latitudes below 25°N. The vorticity budget analysis indicates that the front was maintained mainly by a stretching effect, while its gradual eastward extension and slow southward migration were linked to horizontal advection and a tilting effect, respectively. Induced by the MCSs, the transverse circulation south of the front was exceptionally strong, and the LLJ developed within its lower branch of northward-directed ageostrophic flow through Coriolis torque.
Effects of Terrain Heights and Sizes on Island-Scale Circulations and Rainfall for the Island of Hawaii during HaRP
Authors: Yang Yang , Chen Yi-Leng 
Published: January 2008

AbstractIslands in Hawaii have different sizes and terrain heights with notable differences in climate and weather. In this study, the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) land surface model (LSM) is used to conduct numerical simulations for the island of Hawaii with different model terrain heights and sizes during the diurnal cycle for the Hawaiian Rainband Project (HaRP) period. In addition to island blocking and orographic lifting, terrain heights also affect the land surface thermal forcing throughout the diurnal cycle by the variations of orographic clouds during the day and by the variations of the longwave radiation heat loss at night. The simulated rainfall distributions and amounts throughout the diurnal cycle are closely related to rising motions caused by nonlinear interactions among island blocking, orographic lifting, and land surface processes. Besides the terrain/mountain height, island size is another factor that affects rainfall production and distribution in Hawaii, because island size affects orographic lifting, surface forcing, and the advection time scale for an air parcel to reach the mountaintop. The heavy rainfall maximum on the mountaintop of the island of Kauai is due to its suitable height and size. This study confirms that the evening rainfall maximum along the western Kona leeside coast is caused by the convergence between the westerly return flow and the offshore flow. For a lower model terrain, the westerly return flow is weaker; as a result, there are smaller evening rainfall amounts.
Quasi-Biweekly Oscillation of the Convection around Sumatra and Low-Level Tropical Circulation in Boreal Spring
Authors: Wen Min , Zhang Renhe 
Published: January 2008

Abstract
The quasi-biweekly oscillation (QBWO) of the tropical convection around Sumatra and its relation to the low-level circulation over the tropical Indian Ocean in boreal spring is investigated. From March to May, the convection over northern Sumatra increases continuously and oscillates with a pronounced period of 10–20 days. Time-lag cross correlations among the QBWOs of the convection, the apparent heat source, and winds in the lower troposphere reveal a possible mechanism of QBWO maintenance. In the strongest phase of the QBWO of the convection around Sumatra, there is an anomalous convective heating symmetric about the equator. The atmospheric Rossby wave response to the heating produces twin cyclones straddling the equator in the west of the convection area. The development of the twin cyclones induces an anomalous southerly north of the equator and a northerly south of the equator at 850 hPa, giving rise to the divergence of the low-level wind field, which weakens the convection around Sumatra. The weakening of the convection leads to the negative phase of convection. In the weakest phase, the Rossby wave response to the anomalous convective cooling produces twin anticyclones symmetric about the equator, resulting in the convergence of the low-level winds and, in turn, enhancing the convection around Sumatra. Consequently, the feedbacks among convection, the Rossby wave response, and the associated wind field at the lower troposphere may be important maintenance mechanisms of the tropical QBWO. The appearance of a tropical westerly is a crucial index of the Asian summer monsoon onset. In the northern equatorial region, the westerly first occurs just to the west of Sumatra, and then extends westward in boreal spring. The westerly around the equator associated with the Rossby wave response to the convective heating of the QBWO of the convection around Sumatra displays a notable intraseasonal feature, which may play an important role in modulating the process of the Asian summer monsoon onset.
Evaluation of a Nonlocal Quasi-Phase Observation Operator in Assimilation of CHAMP Radio Occultation Refractivity with WRF
Authors: Liu Hui , Anderson Jeffrey , Kuo Ying-Hwa , Snyder Chris , Caya Alain 
Published: January 2008

Abstract
A nonlocal quasi-phase radio occultation (RO) observation operator is evaluated in the assimilation of Challenging Minisatellite Payload (CHAMP) radio occultation refractivity using a Weather Research and Forecasting (WRF) ensemble data assimilation system at 50-km resolution. The nonlocal operator calculates the quasi phase through integration of the model refractivity along the observed ray paths. As a comparison, a local refractivity operator that calculates the model refractivity at the observed ray perigee points is also evaluated. The assimilation is done over North America during January 2003 in two different situations: in conjunction with dense, high-quality radiosonde observations and with only satellite cloud drift wind observations. Analyses of temperature and water vapor with the RO refractivity assimilated using the local and nonlocal operator are verified against nearby withheld radiosonde observations. The bias and RMS errors of the analyses of water vapor and temperature using the nonlocal operator are significantly reduced compared with those using the local operator in the troposphere when the only additional observations are satellite cloud drift winds. The reduction of the bias and RMS errors is reduced when radiosonde observations are assimilated.
Numerical Simulations of the Role of Land Surface Conditions in the Evolution and Structure of Summertime Thunderstorms over a Flat Highland
Authors: Yamada Hiroyuki 
Published: January 2008

Abstract
Numerical simulations of summertime thunderstorms over a flat highland (4700 m MSL), assuming the central Tibetan Plateau, were conducted with the use of a cloud-resolving nonhydrostatic model. This study was aimed at clarifying the role of land surface conditions, such as soil moisture and vegetation activity, in the evolution and structure of airmass thunderstorms over the plateau. Two simulations with cyclic lateral boundaries and different surfaces of a dry or wet land were initialized using a unique vertical atmospheric profile at dawn. These initial conditions assume the real atmospheric conditions in two periods of the 1998 summer monsoon, which are characterized by a dry or wet surface. The results of the two experiments were used to examine the contrasting features between the two experiments arising from the different surface conditions. The simulations reproduced differences in the convective structure, the conditions of the subcloud layer, and the evaporation rate of precipitation within this layer. These resulted from different surface-heating processes and were supported by the observational evidence clarified in a previous study. Moreover, the simulations also reproduced the cell broadening occurring in both the boundary and cloud layers and different precipitation processes dependent on the updraft strength. The evidence was partly supported by additional analyses of observational data. This study, therefore, demonstrates a significant effect of the plateau surface upon the cloud evolution and the precipitation process.
Parameterization of Strong Stratospheric Inertia–Gravity Waves Forced by Poleward-Breaking Rossby Waves
Authors: Zülicke Christoph , Peters Dieter 
Published: January 2008

Abstract
The link between poleward-breaking Rossby waves and stratospheric inertia–gravity waves is examined. With a visual inspection of Ertel’s potential vorticity maps based on ECMWF analyses it was found that Rossby wave–breaking events occurred over northern Europe in about 40% of the winter days in 1999–2003. The majority of them were breaking poleward downstream. A total of 10 field campaigns were performed in the winters of 1999–2002 at Kühlungsborn, Germany (54°N, 12°E). They are related to such events and can be considered as representative for poleward-breaking Rossby waves. Inertia–gravity wave properties are diagnosed from radiosonde observations. They appeared to be shallower, slower, and stronger than the climatological mean for the north German lowlands. Hence, Rossby wave–breaking events are linked with strong stratospheric inertia–gravity wave activity. A novel parameterization of inertia–gravity wave generation and propagation is proposed. The stratospheric inertia–gravity wave action in the 16–20-km height range was parameterized with the synoptic-scale cross-stream ageostrophic wind, which accounts for imbalances in the upper-tropospheric jet streak. This empirical relationship is supported with quasigeostrophic theory. Effects of damping and critical level absorption are taken into account with Wentzel–Kramers–Brillouin theory. For verification of the parameterization with homogeneous meteorological fields in space and time, the 10 field campaigns were hindcasted with the nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. About 80% of the variance in inertia–gravity wave action was found to be explained. For the 10 campaigns a close link was found between the poleward-breaking Rossby waves and the strong stratospheric inertia–gravity waves. The role of the polar vortex was twofold: first, it forced the poleward-oriented Rossby waves to break downstream and to form strong tropospheric jet streaks generating inertia–gravity waves. Second, the strong winds in the stratosphere favored the upward propagation of the inertia–gravity waves. The proposed new parameterization of inertia–gravity wave generation and propagation was validated and can be used to deduce mesoscale wave intensity from synoptic flow characteristics during poleward Rossby wave–breaking events.
A Three-Dimensional Anelastic Model Based on the Vorticity Equation
Authors: Jung Joon-Hee , Arakawa Akio 
Published: January 2008

Abstract
A three-dimensional anelastic model has been developed using the vorticity equation, in which the pressure gradient force is eliminated. The prognostic variables of the model dynamics are the horizontal components of vorticity at all heights and the vertical component of vorticity and the horizontally uniform part of the horizontal velocity at a selected height. To implement the anelastic approximation, vertical velocity is diagnostically determined from the predicted horizontal components of vorticity by solving an elliptic equation. This procedure replaces solving the elliptic equation for pressure in anelastic models based on the momentum equation. Discretization of the advection terms uses an upstream-weighted partially third-order scheme. When time is continuous, the solution of this scheme is quadratically bounded. As an application of the model, interactions between convection and its environment with vertical shear are studied without and with model physics from the viewpoint of vorticity dynamics, that is, the deceleration/acceleration process of the basic flow in particular. The authors point out that the process is purely three-dimensional, especially when the convection is relatively localized, involving the twisting terms and the horizontal as well as vertical transports of vorticity. Finally, it is emphasized that parameterization of cumulus friction is a resolution-dependent problem of vorticity dynamics associated with cumulus convection.
Scale-Selective Verification of Rainfall Accumulations from High-Resolution Forecasts of Convective Events
Authors: Roberts Nigel M. , Lean Humphrey W. 
Published: January 2008

Abstract
The development of NWP models with grid spacing down to ∼1 km should produce more realistic forecasts of convective storms. However, greater realism does not necessarily mean more accurate precipitation forecasts. The rapid growth of errors on small scales in conjunction with preexisting errors on larger scales may limit the usefulness of such models. The purpose of this paper is to examine whether improved model resolution alone is able to produce more skillful precipitation forecasts on useful scales, and how the skill varies with spatial scale. A verification method will be described in which skill is determined from a comparison of rainfall forecasts with radar using fractional coverage over different sized areas. The Met Office Unified Model was run with grid spacings of 12, 4, and 1 km for 10 days in which convection occurred during the summers of 2003 and 2004. All forecasts were run from 12-km initial states for a clean comparison. The results show that the 1-km model was the most skillful over all but the smallest scales (approximately &lt;10–15 km). A measure of acceptable skill was defined; this was attained by the 1-km model at scales around 40–70 km, some 10–20 km less than that of the 12-km model. The biggest improvement occurred for heavier, more localized rain, despite it being more difficult to predict. The 4-km model did not improve much on the 12-km model because of the difficulties of representing convection at that resolution, which was accentuated by the spinup from 12-km fields.
Ensemble Simulation of the Lightning Flash Variability in a 3D Cloud Model with Parameterizations of Cloud Electrification and Lightning Flashes
Authors: Pinty Jean-Pierre , Barthe Christelle 
Published: January 2008

Abstract
A series of ensemble simulations were performed to study the statistics of flash characteristics produced by an electrification and lightning scheme in the cloud-resolving model Méso-NH. Here, the electrical variability of two storms—one supercellular and one multicellular—results from a random triggering location of the flashes and from a branching algorithm that describes the flash path. The study shows that the electrical model is able to generate several estimates of the total flash number for an identical evolution of the dynamics and microphysics of each storm in the 120 ensemble members. The variability of the flash number spans over three standard deviations taken from the ensemble mean. The simulations produce regularly shaped distributions of flash internal parameters (i.e., number of segments and branching levels per flash). The ensemble simulation shows that the model is stable and self-regulatory as suggested by the limited overshoot on the maximum electric field time series. An application to the production of nitrogen oxides indicates that the two storms produce 200 ± 150 mol of NO per flash on average.
Accounting for Autocorrelation in Detecting Mean Shifts in Climate Data Series Using the Penalized Maximal t or F Test
Authors: Wang Xiaolan L. 
Published: January 2008

Abstract
This study proposes an empirical approach to account for lag-1 autocorrelation in detecting mean shifts in time series of white or red (first-order autoregressive) Gaussian noise using the penalized maximal t test or the penalized maximal F test. This empirical approach is embedded in a stepwise testing algorithm, so that the new algorithms can be used to detect single or multiple changepoints in a time series. The detection power of the new algorithms is analyzed through Monte Carlo simulations. It has been shown that the new algorithms work very well and fast in detecting single or multiple changepoints. Examples of their application to real climate data series (surface pressure and wind speed) are presented. An open-source software package (in R and FORTRAN) for implementing the algorithms, along with a user manual, has been developed and made available online free of charge.
Estimation of Global Ground Heat Flux
Authors: Bennett William B. , Wang Jingfeng , Bras Rafael L. 
Published: January 2008

Abstract
This study investigates the use of a previously published algorithm for estimating ground heat flux (GHF) at the global scale. The method is based on an analytical solution of the diffusion equation for heat transfer in a soil layer and has been shown to be effective at the point scale. The algorithm has several advantageous properties: 1) it only needs a single-level input of surface (skin) temperature, 2) the time-mean GHF can be derived directly from time-mean skin temperature, 3) it has reduced sensitivity to the variability in soil thermal properties and moisture, 4) it does not requires snow depth, and 5) it is computationally effective. A global map of the necessary thermal inertia parameter is derived using reanalysis data as a function of soil type. These parameter estimates are comparable to values obtained from in situ observations. The new global GHF estimates are generally consistent with the reanalysis GHF output simulated using two-layer soil hydrology models. The authors argue that the new algorithm is more robust and trustworthy in regions where they differ. The proposed algorithm offers potential benefits for direct assimilation of observations of surface temperature as well as GHF into the reanalysis models at various time scales.
The Collapse of the Bering Strait Ice Dam and the Abrupt Temperature Rise in the Beginning of the Holocene
Authors: Sandal Cathrine , Nof Doron 
Published: January 2008

Abstract
This paper focuses on the abrupt increase in the oceanic and atmospheric temperature in the Northern Hemisphere at the beginning of the Holocene, approximately 11 000 yr before the present. De Boer and Nof hypothesized that, at that time, the Bering Strait (BS) opened up abruptly because of the breakup of an ice dam (by rising sea levels). It is proposed further here that this sudden opening caused an abrupt increase in the mean temperature of the Northern Hemisphere. An analytical, coupled ocean–atmosphere model is applied to the North Atlantic in an attempt to quantify the temperature change resulting from the opening of the BS. Heat, salt, and mass are all conserved within a box in the North Atlantic. A convection condition allows water to enter the deep layer and the island rule relates the wind field to the mass fluxes.
The conventional approach that the meridional overturning cell (MOC) was not operating during the Younger Dryas because of an overwhelming freshwater flux is adopted here. Opening the BS in the early Holocene allowed these freshwater anomalies to be flushed out into the Pacific, reviving convection and the transport of heat northward. Restarting convection with an open BS increases mean oceanic and atmospheric temperature by 3° and 23°C, respectively. These values are comparable to those found in both the Centre Européen de Recherche et d’Enseignement des Géosciences de l’Environnement (CEREGE) alkenone and Greenland Ice Sheet Project 2 (GISP 2) ice core records. Of course, restarting convection increases the temperature even with a closed BS, but in the closed BS case the oceanic increase is slightly higher (4°C instead of 3°C), whereas the atmospheric is much lower (17.5°C instead of 23°C). This is because, by requiring a continuous sea level around the Americas, an open BS allows the wind field to limit the amount of Southern Ocean water that enters the South Atlantic. This controlled volume flux (8 Sv) is considerably smaller than that allowed into the Atlantic in the no-wind control closed BS case (17 Sv).
A Population-Level Analysis: The Influence of Hospital Type on Trends in Use and Outcomes of Lower Extremity Angioplasty
Authors: Vogel Todd R. , Symons Rebbecca G. , Flum Dave R. 
Published: January 2008

Objective The use of infrainguinal percutaneous transluminal angioplasty (PTA) has increased, but patterns of use have not been well studied. Academic institutions (AIs) and nonacademic institutions (NAIs) may have developed different practice patterns and may have different associated outcomes. Methods A retrospective statewide population-based administrative database was evaluated for patients undergoing PTA (1997-2004). Results A total of 1718 patients underwent PTA for claudication (51.9%), rest pain (12.1%), and ulceration or gangrene (23.1%). The use of infrainguinal stents (62.4% vs 60.8%), elective procedures (76.3% vs 79.8%), in-hospital death (1.6% vs 2.2%), 30-day mortality (2.1% vs 3.3%), readmission rates (17.1% vs 15.9%), and reintervention rates after readmission (38.5% vs 42.9%) were similar between groups. Increased use of PTA was noted in AIs versus NAIs (239.5% vs 53.9%). AIs were significantly less likely to perform PTA for rest pain (7.5% vs 14.4%, P < .05). Conclusion AIs had a more recent increase in the use of PTA, but less often used PTA for patients with rest pain compared with NAIs. Both center types had higher than expected 30-day readmission and reintervention rates. Further understanding of the implementation and associated outcomes of PTA is required.