bluuebunny/crossref_metadata_2025_split huggingface dataset:
Climate Sensitivity via a Nonparametric Fluctuation–Dissipation Theorem
Authors: Cooper Fenwick C. , Haynes Peter H. 
Published: January 2011

Abstract
The fluctuation–dissipation theorem (FDT) has been suggested as a method of calculating the response of the climate system to a small change in an external parameter. The simplest form of the FDT assumes that the probability density function of the unforced system is Gaussian and most applications of the FDT have made a quasi-Gaussian assumption. However, whether or not the climate system is close to Gaussian remains open to debate, and non-Gaussianity may limit the usefulness of predictions of quasi-Gaussian forms of the FDT. Here we describe an implementation of the full non-Gaussian form of the FDT. The principle of the quasi-Gaussian FDT is retained in that the response to forcing is predicted using only information available from observations of the unforced system, but in the non-Gaussian case this information must be used to estimate aspects of the probability density function of the unforced system. Since this estimate is implemented using the methods of nonparametric statistics, the new form is referred to herein as a “nonparametric FDT.” Application is demonstrated to a sequence of simple models including a stochastic version of the three-component Lorenz model. The authors show that the nonparametric FDT gives accurate predictions in cases where the quasi-Gaussian FDT fails. Practical application of the nonparametric FDT may require optimization of the method set out here for higher-dimensional systems.
An Idealized Cloud-Resolving Framework for the Study of Midlatitude Diurnal Convection over Land
Authors: Schlemmer Linda , Hohenegger Cathy , Schmidli Jürg , Bretherton Christopher S. , Schär Christoph 
Published: January 2011

Abstract
This paper introduces an idealized cloud-resolving modeling (CRM) framework for the study of midlatitude diurnal convection over land. The framework is used to study the feedbacks among soil, boundary layer, and diurnal convection. It includes a setup with explicit convection and a full set of parameterizations. Predicted variables are constantly relaxed toward prescribed atmospheric profiles and soil conditions. The relaxation is weak in the lower troposphere and upper soil to allow the development of a realistic diurnal planetary boundary layer. The model is run to its own equilibrium (30 days).
The framework is able to produce a realistic timing of the diurnal cycle of convection. It also confirms the development of deeper convection in a more unstably stratified atmosphere.
With this relaxation method, the simulated “diurnal equilibrium convection” determines the humidity profile of the lower atmosphere, and the simulation becomes insensitive to the reference humidity profile. However, if a faster relaxation time is used in the lower troposphere, the convection and rainfall become much more sensitive to the reference humidity, consistent with previous studies.
Toward a Physical Characterization of Raindrop Collision Outcome Regimes
Authors: Testik F. Y. , Barros A. P. , Bliven L. F. 
Published: January 2011

Abstract
A comprehensive raindrop collision outcome regime diagram that delineates the physical conditions associated with the outcome regimes (i.e., bounce, coalescence, and different breakup types) of binary raindrop collisions is proposed. The proposed diagram builds on a theoretical regime diagram defined in the phase space of collision Weber numbers We and the drop diameter ratio p by including critical angle of impact considerations. In this study, the theoretical regime diagram is first evaluated against a comprehensive dataset for drop collision experiments representative of raindrop collisions in nature. Subsequently, the theoretical regime diagram is modified to explicitly describe the dominant regimes of raindrop interactions in (We, p) by delineating the physical conditions necessary for the occurrence of distinct types of collision-induced breakup (neck/filament, sheet, disk, and crown breakups) based on critical angle of impact consideration. Crown breakup is a subtype of disk breakup for lower collision kinetic energy that presents distinctive morphology. Finally, the experimental results are analyzed in the context of the comprehensive collision regime diagram, and conditional probabilities that can be used in the parameterization of breakup kernels in stochastic models of raindrop dynamics are provided.
Climatic Effects on Lake Basins. Part I: Modeling Tropical Lake Levels
Authors: Ricko Martina , Carton James A. , Birkett Charon 
Published: January 2011

Abstract
The availability of satellite estimates of rainfall and lake levels offers exciting new opportunities to estimate the hydrologic properties of lake systems. Combined with simple basin models, connections to climatic variations can then be explored with a focus on a future ability to predict changes in storage volume for water resources or natural hazards concerns. This study examines the capability of a simple basin model to estimate variations in water level for 12 tropical lakes and reservoirs during a 16-yr remotely sensed observation period (1992–2007). The model is constructed with two empirical parameters: effective catchment to lake area ratio and time delay between freshwater flux and lake level response. Rainfall datasets, one reanalysis and two satellite-based observational products, and two radar-altimetry-derived lake level datasets are explored and cross checked. Good agreement is observed between the two lake level datasets with the lowest correlations occurring for the two small lakes Kainji and Tana (0.87 and 0.89). Fitting observations to the simple basin model provides a set of delay times between rainfall and level rise ranging up to 105 days and effective catchment to lake ratios ranging between 2 and 27. For 9 of 12 lakes and reservoirs the observational rainfall products provide a better fit to observed lake levels than the reanalysis rainfall product. But for most of the records any of the rainfall products provide reasonable lake level estimates, a result which opens up the possibility of using rainfall to create seasonal forecasts of future lake levels and hindcasts of past lake levels. The limitations of the observation sets and the two-parameter model are discussed.
Vegetation Dynamics Enhancing Long-Term Climate Variability Confirmed by Two Models
Authors: Delire Christine , de Noblet-Ducoudré Nathalie , Sima Adriana , Gouirand Isabelle 
Published: January 2011

AbstractTwo different coupled climate–vegetation models, the Community Climate Model version 3 coupled to the Integrated Biosphere Simulator (CCM3–IBIS) and the Laboratoire de Météorologie Dynamique’s climate model coupled to the Organizing Carbon and Hydrology in Dynamic Ecosystems model (LMDz–ORCHIDEE), are used to study the effects of vegetation dynamics on climate variability. Two sets of simulations of the preindustrial climate are performed using fixed climatological sea surface temperatures: one set taking into account vegetation cover dynamics and the other keeping the vegetation cover fixed. Spectral analysis of the simulated precipitation and temperature over land shows that for both models the interactions between vegetation dynamics and the atmosphere enhance the low-frequency variability of the biosphere–atmosphere system at time scales ranging from a few years to a century. Despite differences in the magnitude of the signal between the two models, this confirms that vegetation dynamics introduces a long-term memory into the climate system by slowly modifying the physical characteristics of the land surface (albedo, roughness evapotranspiration).Unrealistic modeled feedbacks between the vegetation and the atmosphere would cast doubts on this result. The simulated feedback processes in the models used in this work are compared to the observed using a recently developed statistical approach. The models simulate feedbacks of the right sign and order of magnitude over large regions of the globe: positive temperature feedback in the mid- to high latitudes, negative feedback in semiarid regions, and positive precipitation feedback in semiarid regions. The models disagree in the tropics, where there is no statistical significance in the observations. The realistic modeled vegetation–atmosphere feedback gives us confidence that the vegetation dynamics enhancement of the long-term climate variability is not a model artifact.
Controls on Arctic Sea Ice from First-Year and Multiyear Ice Survivability
Authors: Armour Kyle C. , Bitz Cecilia M. , Thompson LuAnne , Hunke Elizabeth C. 
Published: January 2011

Abstract
Recent observations of Arctic sea ice show that the decrease in summer ice cover over the last few decades has occurred in conjunction with a significant loss of multiyear ice. The transition to an Arctic that is populated by thinner, first-year sea ice has important implications for future trends in area and volume. Here, a reduced model for Arctic sea ice is developed. This model is used to investigate how the survivability of first-year and multiyear ice controls the mean state, variability, and trends in ice area and volume. A hindcast with a global dynamic–thermodynamic sea ice model that traces first-year and multiyear ice is used to estimate the survivability of each ice type. These estimates of survivability, in concert with the reduced model, yield persistence time scales of September area and volume anomalies and the characteristics of the sensitivity of sea ice to climate forcing that compare well with a fully coupled climate model. The September area is found to be nearly in equilibrium with climate forcing at all times, and therefore the observed decline in summer sea ice cover is a clear indication of a changing climate. Keeping an account of first-year and multiyear ice area within global climate models offers a powerful way to evaluate those models with observations, and could help to constrain projections of sea ice decline in a warming climate.
Testing for Deterministic Trends in Global Sea Surface Temperature
Authors: Barbosa Susana M. 
Published: January 2011

AbstractLong-term variability in global sea surface temperature (SST) is often quantified by the slope from a linear regression fit. Attention is then focused on assessing the statistical significance of the derived slope parameter, but the adequacy of the linear model itself, and the inherent assumption of a deterministic linear trend, is seldom tested. Here, a parametric statistical test is applied to test the hypothesis of a linear deterministic trend in global sea surface temperature. The results show that a linear slope is not adequate for describing the long-term variability of sea surface temperature over most of the earth’s surface. This does not mean that sea surface temperature is not increasing, rather that the increase should not be characterized by the slope from a linear fit. Therefore, describing the long-term variability of sea surface temperature by implicitly assuming a deterministic linear trend can give misleading results, particularly in terms of uncertainty, since the actual increase could be considerably larger than the one predicted by a deterministic linear model.
Climate Feedbacks in Response to Changes in Obliquity
Authors: Mantsis Damianos F. , Clement Amy C. , Broccoli Anthony J. , Erb Michael P. 
Published: January 2011

Abstract
The feedbacks involved in the response of climate to a reduction of Earth’s obliquity are investigated in the GFDL Climate Model version 2.1 (CM2.1). A reduction in obliquity increases the meridional gradient of the annual mean insolation, causing a strengthening of the atmospheric and ocean circulation that transports more heat poleward. The heat transport does not balance the direct obliquity forcing completely, and additional local radiative fluxes are required to explain the change in the equilibrium energy budget. The surface temperature generally increases at low latitudes and decreases at high latitudes following the change in the insolation. However, in some areas, the sign of the temperature change is opposite of the forcing, indicating the strong influence of feedbacks. These feedbacks are also responsible for a decrease in the global mean temperature despite that the change in the global mean insolation is close to zero. The processes responsible for these changes are increases in the ice fraction at high latitudes and the global cloud fraction—both of which reduce the absorbed solar radiation. A reduction in the global greenhouse trapping, due to changes in the distribution of the water vapor content of the atmosphere as well as a change in the lapse rate, has an additional cooling effect. Among these feedbacks, clouds and the lapse rate have the larger contribution, with water vapor and surface albedo having a smaller effect. The implications of the findings presented here for interpretation of obliquity cycles in the paleoclimate record are discussed.
Equatorward Pathways of Solomon Sea Water Masses and Their Modifications
Authors: Melet Angélique , Verron Jacques , Gourdeau Lionel , Koch-Larrouy Ariane 
Published: January 2011

Abstract
The Solomon Sea is a key region of the southwest Pacific Ocean, connecting the thermocline subtropics to the equator via western boundary currents (WBCs). Modifications to water masses are thought to occur in this region because of the significant mixing induced by internal tides, eddies, and the WBCs. Despite their potential influence on the equatorial Pacific thermocline temperature and salinity and their related impact on the low-frequency modulation of El Niño–Southern Oscillation, modifications to water masses in the Solomon Sea have never been analyzed to our knowledge. A high-resolution model incorporating a tidal mixing parameterization was implemented to depict and analyze water mass modifications and the Solomon Sea pathways to the equator in a Lagrangian quantitative framework. The main routes from the Solomon Sea to the equatorial Pacific occur through the Vitiaz and Solomon straits, in the thermocline and intermediate layers, and mainly originate from the Solomon Sea south inflow and from the Solomon Strait itself. Water mass modifications in the model are characterized by a reduction of the vertical temperature and salinity gradients over the water column: the high salinity of upper thermocline water [Subtropical Mode Water (STMW)] is eroded and exported toward surface and deeper layers, whereas a downward heat transfer occurs over the water column. Consequently, the thermocline water temperature is cooled by 0.15°–0.3°C from the Solomon Sea inflows to the equatorward outflows. This temperature modification could weaken the STMW anomalies advected by the subtropical cell and thereby diminish the potential influence of these anomalies on the tropical climate. The Solomon Sea water mass modifications can be partially explained (≈60%) by strong diapycnal mixing in the Solomon Sea. As for STMW, about a third of this mixing is due to tidal mixing.
Vertical Moistening by AMMA Mesoscale Convective Systems
Authors: Scialom G. , Lemaître Y. 
Published: January 2011

Abstract
The apparent heat source Q1 and the apparent moisture sink Q2 are crucial parameters for precipitating systems studies because they allow for the evaluation of their contribution in water and energy transport and infer some of the mechanisms that are responsible for their evolution along their lifetime. In this paper, a new approach is proposed to estimate Q2 budgets from radar observations within precipitating areas at the scale of the measurements, that is, either convective scale or mesoscale, depending on the selected retrieval zone. This approach relies upon a new analysis of the radar reflectivity based on the concept of the traditional velocity–azimuth display (VAD) analysis. From the following five steps, Q2 is deduced from velocity and reflectivity fields: (i) mixing ratio retrieval using empirical relations, (ii) radial wind analysis using the VAD analysis, (iii) radar reflectivity analysis using a new analysis called reflectivity–azimuth display (RAD), (iv) retrieval of mixing ratio derivatives, and (v) Q2 retrieval.
The originality and the main interest of the present approach with respect to previous studies rely on the fact it uses radar data alone and is based on a relatively low-cost analysis, allowing future systematic application on large datasets.
In the present paper, this analysis is described and its robustness is evaluated and illustrated on three cases observed during the African Monsoon Multidisciplinary Analyses (AMMA) special observing period (SOP) field experiment (15 June–15 September) by means of the Recherche sur les Orages et Nuages par un Système Associé de Radars Doppler (RONSARD) radar.
Results are analyzed in terms of the convective or stratiform character of observed precipitation.
Study of the Far Wake of a Large Ship
Authors: Gilman M. , Soloviev A. , Graber H. 
Published: January 2011

AbstractA large dataset of high-resolution photographic images of far wakes of a volunteer observing ship (Royal Caribbean’s Explorer of the Seas) has been acquired under various meteorological conditions and ship operation modes. This work presents the description of instrumentation, methodology, and the results of the experiment. Environmental and ship operation factors that affect appearance and geometric properties of ship wakes in photographic and satellite-based radar images have been analyzed. The photo imagery reveals an asymmetry of the wake depending on wind direction relative to the ship course. In addition, a good agreement between the averaged shape of the wakes measured from the photographic images and a few available satellite-based radar images of the wake of the same ship has been found.
Nonlinear Internal Wave Properties Estimated with Moored ADCP Measurements
Authors: Chang Ming-Huei , Lien Ren-Chieh , Yang Yiing Jang , Tang Tswen Yung 
Published: January 2011

Abstract
A method is developed to estimate nonlinear internal wave (NLIW) vertical displacement, propagation direction, and propagation speed from single moored acoustic Doppler current profiler (ADCP) velocity observations. The method is applied to three sets of bottom-mounted ADCP measurements taken on the continental slope in the South China Sea in 2006–07. NLIW vertical displacement is computed as the time integration of ADCP vertical velocity observations corrected with the vertical advection of the background flow by the NLIW. NLIW vertical currents displace the background horizontal current and shear by ~150 m. NLIW propagation direction is estimated as the principal direction of the wave-induced horizontal velocity vector, and propagation speed is estimated using the continuity equation in the direction of wave propagation, assuming the wave’s horizontal spatial structure and propagation speed remain constant as the NLIW passes the mooring, typically O(10 min). These NLIW properties are estimated simultaneously and iteratively using the ADCP velocity measurements, corrected for their beam-spreading effect. In most cases, estimates converge to within 3% after four iterations. The proposed method of extracting NLIW properties from velocity measurements is confirmed using NLIWs simulated by the fully nonlinear Dubreil–Jacotin–Long model. Estimates of propagation speed using the ADCP velocity measurements are also in good agreement with those calculated from NLIW arrival times at successive moorings. This study concludes that velocity measurements taken from a single moored ADCP can provide useful estimates of vertical displacement, propagation direction, and propagation speed of large-amplitude NLIWs.
A Space–Time Multiscale Analysis System: A Sequential Variational Analysis Approach
Authors: Xie Y. , Koch S. , McGinley J. , Albers S. , Bieringer P. E. , Wolfson M. , Chan M. 
Published: January 2011

Abstract
As new observation systems are developed and deployed, new and presumably more precise information is becoming available for weather forecasting and climate monitoring. To take advantage of these new observations, it is desirable to have schemes to accurately retrieve the information before statistical analyses are performed so that statistical computation can be more effectively used where it is needed most. The authors propose a sequential variational approach that possesses advantages of both a standard statistical analysis [such as with a three-dimensional variational data assimilation (3DVAR) or Kalman filter] and a traditional objective analysis (such as the Barnes analysis). The sequential variational analysis is multiscale, inhomogeneous, anisotropic, and temporally consistent, as shown by an idealized test case and observational datasets in this study. The real data cases include applications in two-dimensional and three-dimensional space and time for storm outflow boundary detection (surface application) and hurricane data assimilation (three-dimensional space application). Implemented using a multigrid technique, this sequential variational approach is a very efficient data assimilation method.
Adaptive Ensemble Covariance Localization in Ensemble 4D-VAR State Estimation
Authors: Bishop Craig H. , Hodyss Daniel 
Published: January 2011

Abstract
An adaptive ensemble covariance localization technique, previously used in “local” forms of the ensemble Kalman filter, is extended to a global ensemble four-dimensional variational data assimilation (4D-VAR) scheme. The purely adaptive part of the localization matrix considered is given by the element-wise square of the correlation matrix of a smoothed ensemble of streamfunction perturbations. It is found that these purely adaptive localization functions have spurious far-field correlations as large as 0.1 with a 128-member ensemble. To attenuate the spurious features of the purely adaptive localization functions, the authors multiply the adaptive localization functions with very broadscale nonadaptive localization functions. Using the Navy’s operational ensemble forecasting system, it is shown that the covariance localization functions obtained by this approach adapt to spatially anisotropic aspects of the flow, move with the flow, and are free of far-field spurious correlations. The scheme is made computationally feasible by (i) a method for inexpensively generating the square root of an adaptively localized global four-dimensional error covariance model in terms of products or modulations of smoothed ensemble perturbations with themselves and with raw ensemble perturbations, and (ii) utilizing algorithms that speed ensemble covariance localization when localization functions are separable, variable-type independent, and/or large scale. In spite of the apparently useful characteristics of adaptive localization, single analysis/forecast experiments assimilating 583 200 observations over both 6- and 12-h data assimilation windows failed to identify any significant difference in the quality of the analyses and forecasts obtained using nonadaptive localization from that obtained using adaptive localization.