bluuebunny/crossref_metadata_2025_split huggingface dataset:
North Pacific Climate Response to Freshwater Forcing in the Subarctic North Atlantic: Oceanic and Atmospheric Pathways
Authors: Okumura Yuko M. , Deser Clara , Hu Aixue , Timmermann Axel , Xie Shang-Ping 
Published: September 2008

Abstract
Sudden changes of the Atlantic meridional overturning circulation (AMOC) are believed to have caused large, abrupt climate changes over many parts of the globe during the last glacial and deglacial period. This study investigates the mechanisms by which a large freshwater input to the subarctic North Atlantic and an attendant rapid weakening of the AMOC influence North Pacific climate by analyzing four different ocean–atmosphere coupled general circulation models (GCMs) under present-day or preindustrial boundary conditions. When the coupled GCMs are forced with a 1-Sv (Sv ≡ 106 m3 s−1) freshwater flux anomaly in the subarctic North Atlantic, the AMOC nearly shuts down and the North Atlantic cools significantly. The South Atlantic warms slightly, shifting the Atlantic intertropical convergence zone southward. In addition to this Atlantic ocean–atmosphere response, all of the models exhibit cooling of the North Pacific, especially along the oceanic frontal zone, consistent with paleoclimate reconstructions. The models also show deepening of the wintertime Aleutian low.
Detailed analysis of one coupled GCM identifies both oceanic and atmospheric pathways from the Atlantic to the North Pacific. The oceanic teleconnection contributes a large part of the North Pacific cooling: the freshwater input to the North Atlantic raises sea level in the Arctic Ocean and reverses the Bering Strait throughflow, transporting colder, fresher water from the Arctic Ocean into the North Pacific. When the Bering Strait is closed, the cooling is greatly reduced, while the Aleutian low response is enhanced. Tropical SST anomalies in both the Atlantic and Pacific are found to be important for the equivalent barotropic response of the Aleutian low during boreal winter. The atmospheric bridge from the tropical North Atlantic is particularly important and quite sensitive to the mean state, which is poorly simulated in many coupled GCMs. The enhanced Aleutian low, in turn, cools the North Pacific by increasing surface heat fluxes and southward Ekman transport. The closure of the Bering Strait during the last glacial period suggests that the atmospheric bridge from the tropics and air–sea interaction in the North Pacific played a crucial role in the AMOC–North Pacific teleconnection.
Temperature and Melt Modeling on the Prince of Wales Ice Field, Canadian High Arctic
Authors: Marshall Shawn J. , Sharp Martin J. 
Published: September 2008

AbstractNear-surface temperature variability and net annual mass balance were monitored from May 2001 to April 2003 in a network of 25 sites on the Prince of Wales Ice Field, Ellesmere Island, Canada. The observational array spanned an area of 180 km by 120 km and ranged from 130 to 2010 m in altitude. Hourly, daily, and monthly average temperatures from the spatial array provide a record of mesoscale temperature variability on the ice field. The authors examine seasonal variations in the variance of monthly and daily temperature: free parameters in positive-degree-day melt models that are presently in use for modeling of glacier mass balance. An analysis of parameter space reveals that daily and seasonal temperature variability are suppressed in summer months (over a melting snow–ice surface), an effect that is important to include in melt modeling. In addition, average annual vertical gradients in near-surface temperature were −3.7°C km−1 in the 2-yr record, steepening to −4.4°C km−1 in the summer months. These gradients are less than the adiabatic lapse rates that are commonly adopted for extrapolation of sea level temperature to higher altitudes, with significant implications for modeling of snow and ice melt. Mass balance simulations for the ice field illustrate the sensitivity of melt models to different lapse rate and temperature parameterizations.
Statistical Evaluation of Combined Daily Gauge Observations and Rainfall Satellite Estimates over Continental South America
Authors: Vila Daniel A. , de Goncalves Luis Gustavo G. , Toll David L. , Rozante Jose Roberto 
Published: September 2008

Abstract
This paper describes a comprehensive assessment of a new high-resolution, gauge–satellite-based analysis of daily precipitation over continental South America during 2004. This methodology is based on a combination of additive and multiplicative bias correction schemes to get the lowest bias when compared with the observed values (rain gauges). Intercomparisons and cross-validation tests have been carried out between independent rain gauges and different merging techniques. This validation process was done for the control algorithm [Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis real-time algorithm] and five different merging schemes: additive bias correction; ratio bias correction; TRMM Multisatellite Precipitation Analysis, research version; and the combined scheme proposed in this paper. These methodologies were tested for different months belonging to different seasons and for different network densities. All compared, merging schemes produce better results than the control algorithm; however, when finer temporal (daily) and spatial scale (regional networks) gauge datasets are included in the analysis, the improvement is remarkable. The combined scheme consistently presents the best performance among the five techniques tested in this paper. This is also true when a degraded daily gauge network is used instead of a full dataset. This technique appears to be a suitable tool to produce real-time, high-resolution, gauge- and satellite-based analyses of daily precipitation over land in regional domains.
Modeling the Response of Canopy Stomatal Conductance to Humidity
Authors: Wang Shusen , Yang Yan , Trishchenko Alexander P. , Barr Alan G. , Black T. A. , McCaughey Harry 
Published: September 2008

Abstract
Humidity of air is a key environmental variable in controlling the stomatal conductance (g) of plant leaves. The stomatal conductance–humidity relationships employed in the Ball–Woodrow–Berry (BWB) model and the Leuning model have been widely used in the last decade. Results of independent evaluations of the two models vary greatly. In this study, the authors develop a new diagnostic parameter that is based on canopy water vapor and CO2 fluxes to assess the response of canopy g to humidity. Using eddy-covariance flux measurements at three boreal forest sites in Canada, they critically examine the performance of the BWB and the Leuning models. The results show that the BWB model, which employs a linear relationship between g and relative humidity (hs), leads to large underestimates of g when the air is wet. The Leuning model, which employs a nonlinear function of water vapor pressure deficit (Ds), reduced this bias, but it still could not adequately capture the significant increase of g under the wet conditions. New models are proposed to improve the prediction of canopy g to humidity. The best performance was obtained by the model that employs a power function of Ds, followed by the model that employs a power function of relative humidity deficit (1 − hs). The results also indicate that models based on water vapor pressure deficit generally performed better than those based on relative humidity. This is consistent with the hypothesis that the stomatal aperture responds to leaf water loss because water vapor pressure deficit rather than relative humidity directly affects the transpiration rate of canopy leaves.
The Surface Circulation of the Caribbean Sea and the Gulf of Mexico as Inferred from Satellite Altimetry
Authors: Alvera-Azcárate Aida , Barth Alexander , Weisberg Robert H. 
Published: September 2008

Abstract
The surface circulation of the Caribbean Sea and Gulf of Mexico is studied using 13 years of satellite altimetry data. Variability in the Caribbean Sea is evident over several time scales. At the annual scale, sea surface height (SSH) varies mainly by a seasonal steric effect. Interannually, a longer cycle affects the SSH slope across the current and hence the intensity of the Caribbean Current. This cycle is found to be related to changes in the wind intensity, the wind stress curl, and El Niño–Southern Oscillation. At shorter time scales, eddies and meanders are observed in the Caribbean Current, and their propagation speed is explained by baroclinic instabilities under the combined effect of vertical shear and the β effect. Then the Loop Current (LC) is considered, focusing on the anticyclonic eddies shed by it and the intrusion of the LC into the Gulf of Mexico through time. Twelve of the 21 anticyclonic eddies observed to detach from the LC are shed from July to September, suggesting a seasonality in the timing of these events. Also, a relation is found between the intrusion of the LC into the Gulf of Mexico and the size of the eddies shed from it: larger intrusions trigger smaller eddies. A series of extreme LC intrusions into the Gulf of Mexico, when the LC is observed as far as 92°W, are described. The analyses herein suggest that the frequency of such events has increased in recent years, with only one event occurring in 1993 versus three from 2002 to 2006. Transport through the Straits of Florida appears to decrease during these extreme intrusions.
Northward Penetration of Antarctic Intermediate Water off Northwest Africa
Authors: Machín F. , Pelegrí J. L. 
Published: September 2008

Abstract
In this article, historical and climatological datasets are used to investigate the seasonal northward propagation of Antarctic Intermediate Waters (AAIW) along the eastern margin of the North Atlantic subtropical gyre. A cluster analysis for data north of 26°N shows the presence of a substantial number of hydrographic stations with AAIW characteristics that stretch northeast along the African slope. This water mass extends north during fall, as shown both through the comparison of actual and climatological data, and by applying a mixing analysis to normal-to-shore seasonal sections at both 28.5° and 32°N. The mixing analysis is further used with several fall cruises between 32° and 36°N, and shows that at these latitudes the core of AAIW propagates along the 27.5 isoneutral with contributions that reach as much as 50% at 32.5°N. An idealized Sverdrup-type model is used in combination with climatological hydrographic and wind data to examine what forces this eastern boundary propagation. It is found that column stretching, initiated in the tropical North Atlantic, is the dominant term in the vorticity balance of the AAIW stratum, capable of sustaining a winter–spring–summer northward transport of about 3–4 Sv (1 Sv ≡ 106 m3 s−1) that reaches as far north as the Canary Archipelago (28°N). In fall, this transport may continue beyond 28°N, sustained by a near-slope meridional stretching of this water stratum. AAIW probably fades away in the northeastern region as the result of several processes, specially enhanced double diffusion with surrounding waters and interaction with Mediterranean water lenses.
The South China Sea Throughflow Retrieved from Climatological Data*
Authors: Yaremchuk Max , McCreary Julian , Yu Zuojun , Furue Ryo 
Published: September 2008

Abstract
The salinity distribution in the South China Sea (SCS) has a pronounced subsurface maximum from 150–220 m throughout the year. This feature can only be maintained by the existence of a mean flow through the SCS, consisting of a net inflow of salty North Pacific tropical water through the Luzon Strait and outflow through the Mindoro, Karimata, and Taiwan Straits. Using an inverse modeling approach, the authors show that the magnitude and space–time variations of the SCS thermohaline structure, particularly for the salinity maximum, allow a quantitative estimate of the SCS throughflow and its distribution among the three outflow straits. Results from the inversion are compared with available observations and output from a 50-yr simulation of a highly resolved ocean general circulation model.
The annual-mean Luzon Strait transport is found to be 2.4 ± 0.6 Sv (Sv ≡ 106 m3 s−1). This inflow is balanced by the outflows from the Karimata (0.3 ± 0.5 Sv), Mindoro (1.5 ± 0.4), and Taiwan (0.6 ± 0.5 Sv) Straits. Results of the inversion suggest that the Karimata transport tends to be overestimated in numerical models. The Mindoro Strait provides the only passage from the SCS deeper than 100 m, and half of the SCS throughflow (1.2 ± 0.3 Sv) exits the basin below 100 m in the Mindoro Strait, a result that is consistent with a climatological run of a 0.1° global ocean general circulation model.
Transport in an Idealized Three-Gyre System with Application to the Adriatic Sea
Authors: Rypina Irina I. , Brown Michael G. , Koçak Huseyin 
Published: September 2008

Abstract
Motivated by observations of surface drifters in the Adriatic Sea, transport in a three-gyre system is studied with the aid of dynamical systems techniques. Particular attention is paid to the issue of intergyre transport. The velocity field is assumed to be two-dimensional and incompressible and composed of a steady three-gyre background flow on which a time-dependent perturbation is superimposed. Two systems of this type are considered: 1) an observationally motivated, analytically prescribed model consisting of a steady background on which a multiperiodic time-dependent perturbation is superimposed, and 2) an observationally based model of the Adriatic Sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time-dependent altimetry-based perturbation velocity field is superimposed. It is shown that for a small perturbation to the steady three-gyre background, two of the gyres exchange no fluid with the third gyre. When the perturbation strength exceeds a certain threshold, transport between all three gyres occurs. This behavior is described theoretically, illustrated using the analytic model and shown to be consistent with the observationally based model of the Adriatic. The relevance of the work presented to more complicated multiple-gyre problems is discussed.
Observed Interannual Variability of the Florida Current: Wind Forcing and the North Atlantic Oscillation
Authors: DiNezio Pedro N. , Gramer Lewis J. , Johns William E. , Meinen Christopher S. , Baringer Molly O. 
Published: September 2008

AbstractThe role of wind stress curl (WSC) forcing in the observed interannual variability of the Florida Current (FC) transport is investigated. Evidence is provided for baroclinic adjustment as a physical mechanism linking interannual changes in WSC forcing and changes in the circulation of the North Atlantic subtropical gyre. A continuous monthly time series of FC transport is constructed using daily transports estimated from undersea telephone cables near 27°N in the Straits of Florida. This 25-yr-long time series is linearly regressed against interannual WSC variability derived from the NCEP–NCAR reanalysis. The results indicate that a substantial fraction of the FC transport variability at 3–12-yr periods is explained by low-frequency WSC variations. A lagged regression analysis is performed to explore hypothetical adjustment times of the wind-driven circulation. The estimated lag times are at least 2 times faster than those predicted by linear beta-plane planetary wave theory. Possible reasons for this discrepancy are discussed within the context of recent observational and theoretical developments. The results are then linked with earlier findings of a low-frequency anticorrelation between FC transport and the North Atlantic Oscillation (NAO) index, showing that this relationship could result from the positive (negative) WSC anomalies that develop between 20° and 30°N in the western North Atlantic during high (low) NAO phases. Ultimately, the observed role of wind forcing on the interannual variability of the FC could represent a benchmark for current efforts to monitor and predict the North Atlantic circulation.
Three-Dimensional Wind Retrieval: Application of MUSCAT to Dual-Doppler Lidar
Authors: Drechsel Susanne , Mayr Georg J. , Chong Michel , Weissmann Martin , Dörnbrack Andreas , Calhoun Ronald 
Published: September 2008

Abstract
During the field campaign of the Terrain-induced Rotor Experiment (T-REX) in the spring of 2006, Doppler lidar measurements were taken in the complex terrain of the Californian Owens Valley for six weeks. While fast three-dimensional (3D) wind analysis from measured radial wind components is well established for dual weather radars, only the feasibility was shown for dual-Doppler lidars. A computationally inexpensive, variational analysis method developed for multiple-Doppler radar measurements over complex terrain was applied. The general flow pattern of the 19 derived 3D wind fields is slightly smoothed in time and space because of lidar scan duration and analysis algorithm. The comparison of extracted wind profiles to profiles from radiosondes and wind profiler reveals differences of wind speed and direction of less than 1.1 m s−1 and 3°, on average, with standard deviations not exceeding 2.7 m s−1 and 27°, respectively. Standard velocity–azimuth display (VAD) retrieval method provided higher vertical resolution than the dual-Doppler retrieval, but no horizontal structure of the flow field. The authors suggest a simple way to obtain a good first guess for a dual-lidar scan strategy geared toward 3D wind retrieval that minimizes scan duration and maximizes spatial coverage.
Simulation of Significant Wave Height by Neural Networks and Its Application to Extreme Wave Analysis
Authors: Aminzadeh-Gohari A. , Bahai H. , Bazargan H. 
Published: September 2008

Abstract
The derivation of the long-term statistical distribution of significant wave heights (Hss) is discussed in this paper. The distribution parameters are estimated using artificial neural networks (ANNs) trained with the help of a simulated annealing algorithm and operated in an autoregressive mode. The ANNs were utilized in estimating the parameters of a conditional probability distribution related to a desired Hs given its preceding Hss, approximated by a proposed distribution called the hepta-parameter spline. The performance function during training was based on the likelihood function of the statistical method of maximum likelihood estimation (MLE). Given the observed dataset, the most probable weights and biases of the neural networks were determined in such a way that the performance function was optimized. The distribution could be used in the simulation and forecasting of Hss. This paper also presents an extreme wave analysis using the simulated Hss. The extreme analysis conducted in this study using the maxima method offers an alternative approach, avoiding the unrealistic hypothesis that annual Hss are identically distributed, as is conventionally assumed when using the Fisher–Tippet theorem.
Parameterization of PBL Processes in an Atmospheric General Circulation Model: Description and Preliminary Assessment
Authors: Konor Celal S. , Boezio Gabriel Cazes , Mechoso Carlos R. , Arakawa Akio 
Published: September 2008

Abstract
This paper presents the basic features of a newly developed planetary boundary layer (PBL) parameterization, and the performance assessment of a version of the University of California, Los Angeles (UCLA), Atmospheric General Circulation Model (AGCM) to which the parameterization is incorporated. The UCLA AGCM traditionally uses a framework in which a sigma-type vertical coordinate for the PBL shares a coordinate surface with the free atmosphere at the PBL top. This framework facilitates an explicit representation of processes concentrated near the PBL top, which is crucially important especially for predicting PBL clouds. In the new framework, multiple layers are introduced between the PBL top and earth’s surface, allowing for predictions of the vertical profiles of potential temperature, total water mixing ratio, and horizontal winds within the PBL. The vertically integrated “bulk” turbulent kinetic energy (TKE) is also predicted for the PBL. The PBL-top mass entrainment is determined through an equation including the effects of TKE and the radiative and evaporative cooling processes concentrated near the PBL top. The surface fluxes are determined from an aerodynamic formula in which the velocity scale depends both on the square root of TKE and the grid-scale PBL velocity at the lowermost model layer. The turbulent fluxes within the PBL are determined through an approach that includes the effects of both large convective and small diffusive eddies. AGCM simulations with the new formulation of PBL are analyzed with a focus on the seasonal and diurnal variations. The simulated seasonal cycle of stratocumulus over the eastern oceans is realistic, as are the diurnal cycles of the PBL depth and precipitation over land. The simulated fluxes of latent heat, momentum, and shortwave radiation at the ocean surface and baroclinic activity in the middle latitudes show significant improvements over the previous versions of the AGCM based on the single-layer PBL.
Multipeak Raindrop Size Distribution Observed by UHF/VHF Wind Profilers during the Passage of a Mesoscale Convective System
Authors: Radhakrishna B. , Rao T. Narayana 
Published: September 2008

Abstract
The Indian Mesosphere–Stratosphere–Troposphere radar (IMSTR), Lower Atmospheric Wind Profiler (LAWP), and Joss–Waldvogel (JW) disdrometer measurements during the passage of two distinctly different (in terms of total rain and rainfall rate) convective storms are utilized to understand the nature and origin of the multipeak raindrop size distribution (MRDSD). Important issues, such as the preferential stage and height at which bi- or multimodal rain distribution occurs in a mesoscale convective system (MCS) are addressed. For both of the storms, the MRDSD is observed during the transition period from convection to stratiform rain. The pattern and variation of the MRDSD during this period is strikingly similar in both of the storms. The MRDSD is first observed above the freezing level in the presence of heavy riming. The subsequent spectra have shown bimodal distribution below the freezing level, and the bimodality is attributed to the coexistence of ice and supercooled droplets. Interestingly, the bimodal distribution has not varied much with altitude when it is produced because of the coexistence of ice and supercooled droplets. The MRDSD is also observed at few range gates and for a short duration. Such a type of MRDSD is seen during the transition period between decaying and intensifying rain.