bluuebunny/crossref_metadata_2025_split huggingface dataset:
Forcing a Distributed Glacier Mass Balance Model with the Regional Climate Model REMO. Part I: Climate Model Evaluation
Authors: Kotlarski Sven , Paul Frank , Jacob Daniela 
Published: July 2009

Abstract
A coupling interface between the regional climate model REMO and a distributed glacier mass balance model is presented in a series of two papers. The first part describes and evaluates the reanalysis-driven regional climate simulation that is used to force a mass balance model for two glaciers of the Swiss mass balance network. The detailed validation of near-surface air temperature, precipitation, and global radiation for the European Alps shows that the basic spatial and temporal patterns of all three parameters are reproduced by REMO. Compared to the Climatic Research Unit (CRU) dataset, the Alpine mean temperature is underestimated by 0.34°C. Annual precipitation shows a positive bias of 17% (30%) with respect to the uncorrected gridded ALP-IMP (CRU) dataset. A number of important and systematic model biases arise in high-elevation regions, namely, a negative temperature bias in winter, a bias of seasonal precipitation (positive or negative, depending on gridbox altitude and season), and an underestimation of springtime and overestimation of summertime global radiation. These can be expected to have a strong effect on the simulated glacier mass balance. It is recommended to account for these shortcomings by applying correction procedures before using the RCM output for subsequent mass balance modeling. Despite the obvious model deficiencies in high-elevation regions, the new interface broadens the scope of application of glacier mass balance models and will allow for a straightforward assessment of future climate change impacts.
Interdecadal Variations of Meridional Winds in the South China Sea and Their Relationship with Summer Climate in China*
Authors: Li Chunhui , Li Tim , Liang Jianyin , Gu Dejun , Lin Ailan , Zheng Bin 
Published: July 2009

Abstract
Analysis of the NCEP and 40-yr ECMWF Re-Analysis (ERA-40) data and the Xisha Island station observation indicates that the low-level meridional wind (LLMW) over the South China Sea (SCS) experienced an interdecadal variation since the late 1970s. The LLMW change is associated with the reduction of tropospheric temperature in midlatitude East Asia. A mechanism is put forward to explain the triggering and maintenance of the tropospheric cooling. The enhanced convective heating over the southern South China Sea results in a meridional vertical overturning circulation, with anomalous descending motion appearing over continental East Asia. The anomalous descending motion reduces the local humidity through both anomalous low-level divergence and dry vertical advection. The decrease of the local tropospheric humidity leads to the enhanced outgoing longwave radiation into space and thus cold temperature anomalies. The decrease of the temperature and thickness leads to anomalous low (high) pressure and convergent (divergent) flows at upper (lower) levels. This further enhances the descending motion and leads to a positive feedback loop.
The fall in tropospheric temperature over continental East Asia reduces the land–sea thermal contrast and leads to the weakening of cross-equatorial flows and the LLMW over SCS. A further diagnosis indicates that the LLMW is closely linked to the summer precipitation and temperature variations in China on interdecadal time scales. A weakening of the LLMW after 1976 is associated with a “−, +, −” meridional rainfall pattern, with less rain in Guangdong Province and north China but more rain in the Yangtze and Huaihe River basins and northeast China, and a “+, −, +” temperature pattern, with increased (decreased) surface temperature in the south and north (central) China.
Objective Classification of Tropical Mesoscale Convective Systems
Authors: Pope Mick , Jakob Christian , Reeder Michael J. 
Published: July 2009

Abstract
A cluster analysis is applied to the mesoscale convective systems (MCSs) that developed in northern Australia and the surrounding oceans during six wet seasons (September–April) from 1995/96 to 2000/01. During this period, 13 585 MCSs were identified and tracked using an infrared channel (IR1) on the Japanese Meteorological Agency Geostationary Meteorological Satellite 5 (GMS5). Based on the lifetimes of the MCSs, the area covered by cloud, the expansion rate of the cloud, the minimum cloud-top temperature, and their zonal direction of propagation, the MCSs are grouped objectively into four classes. One of the strengths of the analysis is that it objectively condenses a large dataset into a small number of classes, each with its own physical characteristics.
MCSs in class 1 (short) are relatively short lived, with 95% having lifetimes less than 5 h, and they are found most frequently over the oceans during the early and late parts of the wet season. MCSs in classes 2 and 3 [long and intermediate west (Int-West)] are longer lived and propagate to the west, developing over continental northwest Australia in deep easterly flow during breaks in the monsoon. These two classes are distinguished principally by their lifetime, with 95% of MCSs in the long class having lifetimes exceeding 4 h. Class 4 (Int-East) comprises MCSs that form over the subtropical latitudes of eastern Australia and in the deep westerly flow over northern parts of the continent during the monsoon and active phases of the MJO.
Joint Spatiotemporal Variability of Global Sea Surface Temperatures and Global Palmer Drought Severity Index Values
Authors: Apipattanavis Somkiat , McCabe Gregory J. , Rajagopalan Balaji , Gangopadhyay Subhrendu 
Published: July 2009

Abstract
Dominant modes of individual and joint variability in global sea surface temperatures (SST) and global Palmer drought severity index (PDSI) values for the twentieth century are identified through a multivariate frequency domain singular value decomposition. This analysis indicates that a secular trend and variability related to the El Niño–Southern Oscillation (ENSO) are the dominant modes of variance shared among the global datasets. For the SST data the secular trend corresponds to a positive trend in Indian Ocean and South Atlantic SSTs, and a negative trend in North Pacific and North Atlantic SSTs. The ENSO reconstruction shows a strong signal in the tropical Pacific, North Pacific, and Indian Ocean regions. For the PDSI data, the secular trend reconstruction shows high amplitudes over central Africa including the Sahel, whereas the regions with strong ENSO amplitudes in PDSI are the southwestern and northwestern United States, South Africa, northeastern Brazil, central Africa, the Indian subcontinent, and Australia. An additional significant frequency, multidecadal variability, is identified for the Northern Hemisphere. This multidecadal frequency appears to be related to the Atlantic multidecadal oscillation (AMO). The multidecadal frequency is statistically significant in the Northern Hemisphere SST data, but is statistically nonsignificant in the PDSI data.
Parameterization of Shortwave and Longwave Radiative Properties of Ice Clouds for Use in Climate Models
Authors: Hong Gang , Yang Ping , Baum Bryan A. , Heymsfield Andrew J. , Xu Kuan-Man 
Published: July 2009

AbstractClimate modeling and prediction require that the parameterization of the radiative effects of ice clouds be as accurate as possible. The radiative properties of ice clouds are highly sensitive to the single-scattering properties of ice particles and ice cloud microphysical properties such as particle habits and size distributions. In this study, parameterizations for shortwave (SW) and longwave (LW) radiative properties of ice clouds are developed for three existing schemes using ice cloud microphysical properties obtained from five field campaigns and broadband-averaged single-scattering properties of nonspherical ice particles as functions of the effective particle size De (defined as 1.5 times the ratio of total volume to total projected area), which include hexagonal solid columns and hollow columns, hexagonal plates, six-branch bullet rosettes, aggregates, and droxtals.A combination of the discrete ordinates radiative transfer model and a line-by-line model is used to simulate ice cloud radiative forcing (CRF) at both the surface and the top of the atmosphere (TOA) for the three redeveloped parameterization schemes. The differences in CRF for different parameterization schemes are in the range of −5 to 5 W m−2. In general, the large differences in SW and total CRF occur for thick ice clouds, whereas the large differences in LW CRF occur for ice clouds with small ice particles (De less than 20 μm). The redeveloped parameterization schemes are then applied to the radiative transfer models used for climate models. The ice cloud optical and microphysical properties from the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product over a granule and the collocated atmospheric profiles from the Atmospheric Infrared Sounder (AIRS) product are input into these radiative transfer models to compare the differences in CRF between the redeveloped and existing parameterization schemes. Although differences between these schemes are small in the LW CRF, the differences in the SW CRF are quite large.
Air–Sea Heat Exchanges Characteristic of a Prominent Midlatitude Oceanic Front in the South Indian Ocean as Simulated in a High-Resolution Coupled GCM
Authors: Nonaka Masami , Nakamura Hisashi , Taguchi Bunmei , Komori Nobumasa , Kuwano-Yoshida Akira , Takaya Koutarou 
Published: July 2009

Abstract
An integration of a high-resolution coupled general circulation model whose ocean component is eddy permitting and thus able to reproduce a sharp gradient in sea surface temperature (SST) is analyzed to investigate air–sea heat exchanges characteristic of the midlatitude oceanic frontal zone. The focus of this paper is placed on a prominent SST front in the south Indian Ocean, which is collocated with the core of the Southern Hemisphere storm track. Time-mean distribution of sensible heat flux is characterized by a distinct cross-frontal contrast. It is upward and downward on the warmer and cooler flanks, respectively, of the SST front, acting to maintain the sharp gradient of surface air temperature (SAT) that is important for preconditioning the environment for the recurrent development of storms and thereby anchoring the storm track. Induced by cross-frontal advection of cold (warm) air associated with migratory atmospheric disturbances, the surface flux is highly variable with intermittent enhancement of the upward (downward) flux predominantly on the warmer (cooler) flank of the front. Indeed, several intermittent events of cold (warm) air advection, whose total duration accounts for only 21% (19%) of the entire analysis period, contribute to as much as 60% (44%) of the total amount of sensible heat flux during the analysis period on the warmer (cooler) flank. This antisymmetric behavior yields the sharp cross-frontal gradient in the time-mean flux. Since the flux intensity is strongly influenced by local magnitude of the SST–SAT difference that tends to increase with the SST gradient, the concentration of the flux variance to the frontal zone and cross-frontal contrasts in the mean and skewness of the flux all become stronger during the spinup of the SST front. Synoptically, the enhanced sensible heat flux near the SST front can restore SAT toward the underlying SST effectively with a time scale of a day, to maintain a frontal SAT gradient against the relaxing effect of atmospheric disturbances. The restoration effect of the differential surface heating at the SST front, augmented by the surface latent heating concentrated on the warm side of the front, represents a key process through which the atmospheric baroclinicity and ultimately the storm track are linked to the underlying ocean.
A Study of the Free Tropospheric Humidity Interannual Variability Using Meteosat Data and an Advection–Condensation Transport Model
Authors: Brogniez Hélène , Roca Rémy , Picon Laurence 
Published: July 2009

Abstract
Water vapor in the midtroposphere is an important element for the earth radiation budget. Despite its importance, the relative humidity in the free troposphere is not very well documented, mainly because of the difficulties associated with its measurements. A new long-term archive of free tropospheric humidity (FTH) derived from the water vapor channel of the Meteosat satellite from 1983 to 2005 is introduced. Special attention is dedicated to the long-term homogeneity and the definition of the retrieval layer. It is shown to complement the existing databases and is used to establish the climatology of FTH. Interannual variability is then evaluated for each season by using a normalized interannual standard deviation. This normalization approach reveals the importance of the relative variability of the dry areas to the moist regions. In consequence, emphasis is on the driest area of the region. Focusing on composites of the moist and dry seasons of the time series, the authors demonstrate that the 500-hPa relative humidity field, reconstructed using an idealized Lagrangian model, is a good proxy for the FTH variability there. The analysis of the origin of the air mass, using the back trajectory model, points out that lateral mixing between the deep tropics and extratropical latitudes takes place over this area, as advocated in previous theoretical studies. Systematic estimation of this large-scale mixing shows that, indeed, a significant part of the interannual variability of the free tropospheric humidity in this subtropical region stems from the amount of mixing of air originating from the deep tropics versus extratropical latitudes. The importance of this mechanism in the general understanding of the FTH distribution and variability is then discussed.
El Niño–Induced Tropical Droughts in Climate Change Projections
Authors: Coelho Caio A. S. , Goddard Lisa 
Published: July 2009

Abstract
El Niño brings widespread drought (i.e., precipitation deficit) to the tropics. Stronger or more frequent El Niño events in the future and/or their intersection with local changes in the mean climate toward a future with reduced precipitation would exacerbate drought risk in highly vulnerable tropical areas. Projected changes in El Niño characteristics and associated teleconnections are investigated between the twentieth and twenty-first centuries. For climate change models that reproduce realistic oceanic variability of the El Niño–Southern Oscillation (ENSO) phenomenon, results suggest no robust changes in the strength or frequency of El Niño events. These models exhibit realistic patterns, magnitude, and spatial extent of El Niño–induced drought patterns in the twentieth century, and the teleconnections are not projected to change in the twenty-first century, although a possible slight reduction in the spatial extent of droughts is indicated over the tropics as a whole. All model groups investigated show similar changes in mean precipitation for the end of the twenty-first century, with increased precipitation projected between 10°S and 10°N, independent of the ability of the models to replicate ENSO variability. These results suggest separability between climate change and ENSO-like climate variability in the tropics. As El Niño–induced precipitation drought patterns are not projected to change, the observed twentieth-century variability is used in combination with model-projected changes in mean precipitation for assessing year-to-year drought risk in the twenty-first century. Results suggest more locally consistent changes in regional drought risk among models with good fidelity in reproducing ENSO variability.
Quantifying the Consequences of the Ill-Defined Nature of Neutral Surfaces
Authors: Klocker Andreas , McDougall Trevor J. 
Published: July 2009

Abstract
In the absence of diapycnal mixing processes, fluid parcels move in directions along which they do not encounter buoyant forces. These directions define the local neutral tangent plane. Because of the nonlinear nature of the equation of state of seawater, these neutral tangent planes cannot be connected globally to form a well-defined surface in three-dimensional space; that is, continuous “neutral surfaces” do not exist. This inability to form well-defined neutral surfaces implies that neutral trajectories are helical. Consequently, even in the absence of diapycnal mixing processes, fluid trajectories penetrate through any “density” surface. This process amounts to an extra mechanism that achieves mean vertical advection through any continuous surface such as surfaces of constant potential density or neutral density. That is, the helical nature of neutral trajectories causes this additional diasurface velocity. A water-mass analysis performed with respect to continuous density surfaces will have part of its diapycnal advection due to this diasurface advection process. Hence, this additional diasurface advection should be accounted for when attributing observed water-mass changes to mixing processes. Here, the authors quantify this component of the total diasurface velocity and show that locally it can be the same order of magnitude as diasurface velocities produced by other mixing processes, particularly in the Southern Ocean. The magnitude of this diasurface advection is proportional to the ocean’s neutral helicity, which is observed to be quite small in today’s ocean. The authors also use a perturbation experiment to show that the ocean rapidly readjusts to its present state of small neutral helicity, even if perturbed significantly. Additionally, the authors show how seasonal (rather than spatial) changes in the ocean’s hydrography can generate a similar vertical advection process. This process is described here for the first time; although the vertical advection due to this process is small, it helps to understand water-mass transformation on density surfaces.
Coherence Resonance in a Double-Gyre Model of the Kuroshio Extension
Authors: Pierini Stefano 
Published: July 2009

AbstractThe effect of stochastic winds on the intrinsic low-frequency variability of the Kuroshio Extension (KE) is analyzed through a double-gyre (DG) model forced by a steady climatological wind plus an idealized Ornstein–Uhlenbeck wind noise. A DG model of the KE bimodality, whose results compare well to altimeter data, is first shown to be an excitable system. In fact, the relaxation oscillation (forced by steady winds) with decadal time scale that describes the bimodality is recognized to be an internal mode of the system, which can be excited also in a dissipative parameter range (PR) in which it does not arise spontaneously, provided appropriate initial conditions are chosen. It is then shown that, if the additive wind noise is included in the forcing, the actual excitation of the relaxation oscillation in PR occurs if the noise is red with a decorrelation time greater than a minimum time scale ranging from 1 month to 1 year, depending on the dissipation. This behavior, known as “coherence resonance,” is likely to be paradigmatic of the low-frequency variability of western boundary current extensions of intrinsic origin, when it is in the form of relaxation oscillations resulting from a homoclinic bifurcation. General considerations concerning the interpretation of model results obtained within different parameter ranges are applied to this study.
A Methodology to Derive Radar Reflectivity–Liquid Equivalent Snow Rate Relations Using C-Band Radar and a 2D Video Disdrometer
Authors: Huang Gwo-Jong , Bringi V. N. , Cifelli Robert , Hudak David , Petersen W. A. 
Published: July 2009

Abstract
The objective of this work is to derive equivalent radar reflectivity factor–liquid equivalent snow rate (Ze–SR) power-law relations for snowfall using the C-band King City operational weather radar and a 2D video disdrometer (2DVD). The 2DVD provides two orthogonal views of each snow particle that falls through its 10 cm × 10 cm virtual sensor area. The “size” parameter used here for describing the size distribution is based on the “apparent” volume computed from the two images, and an equivolume spherical diameter Dapp is defined. The determination of fall speed is based on matching two images corresponding to the same particle as it falls through two light planes separated by a precalibrated separation distance. A new “rematching” algorithm was developed to improve the quality of the fall speed versus Dapp as compared with the original matching algorithm provided by the manufacturer.
The snow density is parameterized in the conventional power-law form , where α and β are assumed to be variable. To account for strong horizontal winds that tend to decrease the measured concentrations from the 2DVD, a third parameter γ is introduced. The methodology estimates the three parameters (α, β, and γ) by minimizing the difference between the radar-measured reflectivity and the equivalent reflectivity computed from the 2DVD in a least squares sense. The optimally determined values of α, β, and γ are used to estimate the SR and the coefficient and exponent of the Ze = a(SR)b relation. For validation, the accumulation from the SR is compared with the manually recorded accumulations from the double-fence international reference (DFIR) gauge. The data were collected during the Canadian Cloudsat Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Validation Project (C3VP) conducted in Ontario, Canada, during the 2006/07 winter season. A total of seven snow days were analyzed and the accumulation intercomparisons gave a fractional standard deviation of 26% and normalized bias 2.1%. The range of the a and b values for the seven days appear reasonable and similar to conventional Ze–R relations.
A Total Lightning Trending Algorithm to Identify Severe Thunderstorms
Authors: Gatlin Patrick N. , Goodman Steven J. 
Published: July 2009

Abstract
An algorithm that provides an early indication of impending severe weather from observed trends in thunderstorm total lightning flash rates has been developed. The algorithm framework has been tested on 20 thunderstorms, including 1 nonsevere storm, which occurred over the course of six separate days during the spring months of 2002 and 2003. The identified surges in lightning rate (or jumps) are compared against 110 documented severe weather events produced by these thunderstorms as they moved across portions of northern Alabama and southern Tennessee. Lightning jumps precede 90% of these severe weather events, with as much as a 27-min advance notification of impending severe weather on the ground. However, 37% of lightning jumps are not followed by severe weather reports. Various configurations of the algorithm are tested, and the highest critical success index attained is 0.49. Results suggest that this lightning jump algorithm may be a useful operational diagnostic tool for severe thunderstorm potential.