bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Simple Multicloud Parameterization for Convectively Coupled Tropical Waves. Part II: Nonlinear Simulations
Authors: Khouider Boualem , Majda Andrew J. 
Published: February 2007

Abstract
Observations in the Tropics point to the important role of three cloud types, congestus, stratiform, and deep convective clouds, besides ubiquitous shallow boundary layer clouds for both the climatology and large-scale organized anomalies such as convectively coupled Kelvin waves, two-day waves, and the Madden–Julian oscillation. Recently, the authors have developed a systematic model convective parameterization highlighting the dynamic role of the three cloud types through two baroclinic modes of vertical structure: a deep convective heating mode and a second mode with lower troposphere heating and cooling corresponding respectively to congestus and stratiform clouds. The model includes both a systematic moisture equation where the lower troposphere moisture increases through detrainment of shallow cumulus clouds, evaporation of stratiform rain, and moisture convergence and decreases through deep convective precipitation and also a nonlinear switch that favors either deep or congestus convection depending on whether the lower middle troposphere is moist or dry. Here these model convective parameterizations are applied to a 40 000-km periodic equatorial ring without rotation, with a background sea surface temperature (SST) gradient and realistic radiative cooling mimicking a tropical warm pool. Both the emerging “Walker cell” climatology and the convectively coupled wave fluctuations are analyzed here while various parameters in the model are varied. The model exhibits weak congestus moisture coupled waves outside the warm pool in a turbulent bath that intermittently amplify in the warm pool generating convectively coupled moist gravity wave trains propagating at speeds ranging from 15 to 20 m s−1 over the warm pool, while retaining a classical Walker cell in the mean climatology. The envelope of the deep convective events in these convectively coupled wave trains often exhibits large-scale organization with a slower propagation speed of 3–5 m s−1 over the warm pool and adjacent region. Occasional much rarer intermittent deep convection also occurs outside the warm pool. The realistic parameter regimes in the multicloud model are identified as those with linearized growth rates for large scale instabilities roughly in the range of 0.5 K day−1.
Effects of Diurnal Variations on Tropical Equilibrium States: A Two-Dimensional Cloud-Resolving Modeling Study
Authors: Gao Shouting , Zhou Yushu , Li Xiaofan 
Published: February 2007

Abstract
Effects of diurnal variations on tropical heat and water vapor equilibrium states are investigated based on hourly data from two-dimensional cloud-resolving simulations. The model is integrated for 40 days and the simulations reach equilibrium states in all experiments. The simulation with a time-invariant solar zenith angle produces a colder and drier equilibrium state than does the simulation with a diurnally varied solar zenith angle. The simulation with a diurnally varied sea surface temperature generates a colder equilibrium state than does the simulation with a time-invariant sea surface temperature. Mass-weighted mean temperature and precipitable water budgets are analyzed to explain the thermodynamic differences. The simulation with the time-invariant solar zenith angle produces less solar heating, more condensation, and consumes more moisture than the simulation with the diurnally varied solar zenith angle. The simulation with the diurnally varied sea surface temperature produces a colder temperature through less latent heating and more IR cooling than the simulation with the time-invariant sea surface temperature.
Interacting Mountain Waves and Boundary Layers
Authors: Smith Ronald B. 
Published: February 2007

Abstract
Linear hydrostatic 3D mountain wave theory is extended to include a thin frictional boundary layer (BL), parameterized using two characteristic relaxation times for wind adjustment. The character of the BL is described using a “compliance coefficient,” defined as the ratio of BL thickness change to imposed pressure. In this formulation the simplest model that captures the two-way interaction between mountain waves and the boundary layer is sought. The slower BL wind speed amplifies the wind response and shifts it upstream so that the wind maxima occur in regions of favorable pressure gradient, not at points of minimum pressure. Variations in BL thickness reduce the mountain wave amplitude. The BL effect is sensitive to the wind profile convexity. The boundary layer improves the linear theory description of windy peaks. Low-level flow splitting is enhanced and wave breaking aloft is reduced. The BL also decreases the amount of upslope orographic precipitation. The wave momentum flux reduction by the BL is greater than the pressure drag reduction, indicating that part of the pressure drag is taken from BL momentum.
A General Method for Conserving Energy and Potential Enstrophy in Shallow-Water Models
Authors: Salmon Rick 
Published: February 2007

AbstractThe shallow-water equations may be posed in the form df /dt = {F, H, Z}, where H is the energy, Z is the potential enstrophy, and the Nambu bracket {F, H, Z} is completely antisymmetric in its three arguments. This makes it very easy to construct numerical models that conserve analogs of the energy and potential enstrophy; one need only discretize the Nambu bracket in such a way that the antisymmetry property is maintained. Using this strategy, this paper derives explicit finite-difference approximations to the shallow-water equations that conserve mass, circulation, energy, and potential enstrophy on a regular square grid and on an unstructured triangular mesh. The latter includes the regular hexagonal grid as a special case.
Potential Vorticity as Meridional Coordinate
Authors: Stan Cristiana , Randall David A. 
Published: February 2007

Abstract
The dynamical equations of atmospheric flow are written using potential vorticity as the meridional coordinate and potential temperature as the vertical coordinate. Within this system, the atmosphere is divided into undulating tubes bounded by isentropic and constant potential vorticity surfaces, and, under adiabatic and frictionless conditions, the air moves through the tubes without penetrating through the walls.
Spectral Properties of One-Dimensional Diffusive Systems Subject to Stochastic Forcing
Authors: Liu H-L. 
Published: February 2007

AbstractThe vertical wavenumber and frequency spectra of horizontal wind and temperature in stochastically driven systems with diffusion, either due to uniform background eddy and molecular transport, or due to adjustment processes associated with shear or convective instability, are studied. Because of the dominating role of vertical transport in a stratified fluid, one-dimensional Langevin-type equations could be ascribed to such systems in the vertical direction. The linear equation with uniform diffusion is solved explicitly, and the spectra follow power-law distributions if the stochastic force is Gaussian. The nonlinear equations with gradient (either shear or lapse rate) dependent diffusion coefficients are shown to support scale invariance, and the power-law indices of the spectra are determined from dynamic renormalization group (DRG) analysis under rather general conditions. The exact power-law indices vary with the spectrum of the stochastic force and the nonlinearity of the systems. If the wavenumber spectrum of the force is moderately red (between k0 and k−2), the spectral indices of horizontal wind and temperature and the range of their variability are in general agreement with those inferred from wind and temperature measurements. The indices in both linear and nonlinear cases are confirmed by numerical simulations. This theory may suggest an alternative explanation to the universal vertical wavenumber and frequency spectra and their variability. By relating the universal spectra to systems characterized by stochastic forcing and background diffusion or diffusive adjustment due to shear or convective instability, which are ubiquitous in a stratified fluid, the difficulty to associate the time- and location-independent spectral features directly with the highly time- and location-dependent gravity waves or wave-breaking events is avoided. If such systems are suggestive of the real atmosphere, there is a need to be cautious in making assumptions regarding gravity waves solely based on the universal spectra when analyzing and interpreting wind and temperature observations.
Cloud Activating Properties of Aerosol Observed during CELTIC
Authors: Stroud Craig A. , Nenes Athanasios , Jimenez Jose L. , DeCarlo Peter F. , Huffman J. Alex , Bruintjes Roelof , Nemitz Eiko , Delia Alice E. , Toohey Darin W. , Guenther Alex B. , Nandi Sreela 
Published: February 2007

Abstract
Measurements of aerosol size distribution, chemical composition, and cloud condensation nuclei (CCN) concentration were performed during the Chemical Emission, Loss, Transformation, and Interactions with Canopies (CELTIC) field program at Duke Forest in North Carolina. A kinetic model of the cloud activation of ambient aerosol in the chamber of the CCN instrument was used to perform an aerosol–CCN closure study. This study advances prior investigations by employing a novel fitting algorithm that was used to integrate scanning mobility particle sizer (SMPS) measurements of aerosol number size distribution and aerosol mass spectrometer (AMS) measurements of the mass size distribution for sulfate, nitrate, ammonium, and organics into a single, coherent description of the ambient aerosol in the size range critical to aerosol activation (around 100-nm diameter). Three lognormal aerosol size modes, each with a unique internally mixed composition, were used as input into the kinetic model. For the two smaller size modes, which control CCN number concentration, organic aerosol mass fractions for the defined cases were between 58% and 77%. This study is also unique in that the water vapor accommodation coefficient was estimated based on comparing the initial timing for CCN activation in the instrument chamber with the activation predicted by the kinetic model. The kinetic model overestimated measured CCN concentrations, especially under polluted conditions. Prior studies have attributed a positive model bias to an incomplete understanding of the aerosol composition, especially the role of organics in the activation process. This study shows that including measured organic mass fractions with an assumed organic aerosol speciation profile (pinic acid, fulvic acid, and levoglucosan) and an assumed organic aerosol solubility of 0.02 kg kg−1 still resulted in a significant model positive bias for polluted case study periods. The slope and y intercept for the CCN predicted versus CCN observed regression was found to be 1.9 and −180 cm−3, respectively. The overprediction generally does not exceed uncertainty limits but is indicative that a bias exists in the measurements or application of model. From this study, uncertainties in the particle number and mass size distributions as the cause for the model bias can be ruled out. The authors are also confident that the model is including the effects of growth kinetics on predicted activated number. However, one cannot rule out uncertainties associated with poorly characterized CCN measurement biases, uncertainties in assumed organic solubility, and uncertainties in aerosol mixing state. Sensitivity simulations suggest that assuming either an insoluble organic fraction or external aerosol mixing were both sufficient to reconcile the model bias.
Closures for Ensemble-Mean Linear Dynamics with Stochastic Basic Flows
Authors: Jin F-F. , Lin L. 
Published: February 2007

Abstract
This paper demonstrates the validity of a second-order closure for the ensemble-mean dynamics using the approach of direct numerical ensemble simulations of a linear barotropic model with stochastic basic flows. For various configurations of the stochastic basic flow and external forcing, the deterministic solutions under the second-order closure capture, with remarkable accuracy, the ensemble means and the associated eddy covariance fields of forced responses simulated by a 500-member numerical ensemble. Thus, the second-order closure is found to be adequate for describing the ensemble-mean linear dynamics with stochastic basic flows. Moreover, simple analytical solutions based on the second-order closure also demonstrate that the stochastic component of a superrotational basic flow not only damps the ensemble-mean Rossby waves, but also enhances their eastward propagation. Various examples of ensemble-mean solutions all show the important role played by the stochastic synoptic eddy component of the basic flow in determining the ensemble-mean responses to external forcing. This study supports the notion that linear frameworks of ensemble-mean dynamics under second-order closure are useful tools for describing and understanding the dynamics of the synoptic eddy and the low-frequency flow (SELF) feedback and extratropical atmospheric low-frequency variability.
Characteristics of the Atlantic Storm-Track Eddy Activity and Its Relation with the North Atlantic Oscillation
Authors: Rivière G. , Orlanski I. 
Published: February 2007

Abstract
This study focuses on feedbacks of the high-frequency eddy activity onto the quasi-stationary circulation, particularly with regard to the North Atlantic Oscillation (NAO). The methodology consists of analyzing NCEP–NCAR reanalysis data and sensitivity runs from a high-resolution nonhydrostatic regional model. Consistent with recent studies, results show that the jet displacement characteristic of the NAO phenomenon depends strongly on the dynamics of the synoptic-scale waves and the way they break. Positive and negative phases of the NAO are closely related to anticyclonic and cyclonic wave breaking, respectively. Indeed, the high-frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the NAO index over the Atlantic. The peak of the momentum flux signal precedes that of the NAO by a few days suggesting that wave breaking is triggering NAO events. Two examples illustrate the significant impact of single storms, in particular those occurring in the east coast of the United States. The wave breaking at the end of their life cycle can suddenly change the NAO index in few days, and as the return to equilibrium takes generally a longer time, it can even affect the sign of the NAO during an entire month.
An important issue determining the NAO phase is related to upstream effects. By considering a domain extending from the eastern Pacific to western Europe and by forcing the regional model with real data at the western boundary, sensitivity runs show that the right sign of the NAO index can be recovered. It indicates that waves coming from the eastern Pacific are crucial for determining the NAO phase. According to their spatial scales and frequencies when they reach the Atlantic domain, they can break one way or another and push the Atlantic jet equatorward or poleward. Synoptic waves with periods between 5 and 12 days break anticyclonically whereas those with periods between 2 and 5 days break both anticyclonically and cyclonically with a predominance for cyclonic wave breaking. Another crucial factor concerns surface effects. Cyclonic wave breaking in the upper levels is strongly connected with an explosive cyclonic development at the surface accompanied by strong surface moisture fluxes whereas such an explosive growth is not present in the anticyclonic wave breaking case. Finally, it is proposed that these results are not only useful for explaining the intraseasonal variations of the NAO but would serve also as a basis for understanding its interannual and interdecadal variations.
Evolution, Structure, Cloud Microphysical, and Surface Rainfall Processes of Monsoon Convection during the South China Sea Monsoon Experiment
Authors: Wang Jian-Jian , Li Xiaofan , Carey Lawrence D. 
Published: February 2007

Abstract
A two-dimensional cloud-resolving simulation is combined with dual-Doppler and polarimetric radar analysis to study the evolution, dynamic structure, cloud microphysics, and rainfall processes of monsoon convection observed during the South China Sea (SCS) summer monsoon onset.
Overall, the model simulations show many similarities to the radar observations. The rainband associated with the convection remains at a very stable position throughout its life cycle in the northern SCS. The reflectivity pattern exhibits a straight upward structure with little tilt. The positions of the convective, transition, and stratiform regions produced by the model are consistent with the observations. The major difference from the observations is that the model tends to overestimate the magnitude of updraft. As a result, the maximum reflectivity generated by the model appears at an elevated altitude.
The surface rainfall processes and associated thermodynamic, dynamic, and cloud microphysical processes are examined by the model in terms of surface rainfall, temperature and moisture perturbations, circulations, and cloud microphysical budget. At the preformation and dissipating stages, although local vapor change and vapor convergence terms are the major contributors in determining rain rate, they cancel each other out and cause little rain. The vapor convergence/divergence is closely related to the lower-tropospheric updraft/subsidence during the early/late stages of the convection. During the formation and mature phases, vapor convergence term is in control of the rainfall processes. Meanwhile, water microphysical processes are dominant in these stages. The active vapor condensation process causes a large amount of raindrops through the collection of cloud water by raindrops. Ice microphysical processes including riming are negligible up to the mature phase but are dominant during the weakening stage. Cloud source/sink terms make some contributions to the rain rate at the formation and weakening stages, while the role of surface evaporation term is negligible throughout the life cycle of the convection.
Observations of Stably Stratified Shear-Driven Atmospheric Turbulence at Low and High Richardson Numbers
Authors: Mauritsen Thorsten , Svensson Gunilla 
Published: February 2007

Abstract
Stably stratified shear-driven turbulence is analyzed using the gradient Richardson number, Ri, as the stability parameter. The method overcomes the statistical problems associated with the widely used Monin–Obukhov stability parameter. The results of the Ri-based scaling confirm the presence of three regimes: the weakly and the very stable regimes and the transition in between them. In the weakly stable regime, fluxes scale in proportion with variance, while in the very stable regime, stress and scalar fluxes behave differently. At large Ri, the velocity field becomes highly anisotropic and the turbulent potential energy becomes approximately equal to half of the turbulent kinetic energy. It appears that even in the strongly stable regime, beyond what is known as the critical gradient Richardson number, turbulent motions are present.
Coastal Wind Jets Flowing into the Tsushima Strait and Their Effect on Wind-Wave Development
Authors: Isoguchi Osamu , Kawamura Hiroshi 
Published: February 2007

Abstract
Coastal wind jets that flow into the Tsushima Strait, Japan, and their effects on wind waves are investigated using synthetic aperture radar (SAR) images and altimeter-derived wind and waves. The coastal wind jets appear in 7 of 28 SAR-derived wind fields under the conditions of ambient southeasterly winds. Atmospheric conditions corresponding to the appearance of the coastal wind jets are examined by a high-resolution atmospheric community model, which indicates that stratified flows are influenced by the land topography and then pass through the strait forming low-level jet flows. Sensitivity experiments reveal that easterly to southerly stratified flows are a necessary condition for a jet’s formation and the degree of its enhancement is mostly controlled by the Froude number of the upstream flows. Atmospheric conditions in which the SAR observed the coastal jets meet the model-derived necessary conditions, which corroborate the validity of the model simulation and the jet’s formation mechanism. Next, the authors present a case study concerning effects of the coastal jets on wind-wave development by using altimeter-derived wind speed and significant wave height (SWH). Both profiles show similar convex spatial distribution within the wind jet range. The nondimensional SWH and fetch indicate agreements with the empirical fetch graph formula, suggesting that the wind waves are locally developed by the coastal jet. Through investigation of ship-based climatological data, it is found that the coastal jets occur frequently in midsummer due to prevailing southeasterly flows, which is accounted for by the seasonal evolution of the Asian summer monsoon.
The Role of Averaging for Improving Sea Surface Salinity Retrieval from the Soil Moisture and Ocean Salinity (SMOS) Satellite and Impact of Auxiliary Data
Authors: Philipps Sabine , Boone Christine , Obligis Estelle 
Published: February 2007

Abstract
Soil Moisture and Ocean Salinity (SMOS) was chosen as the European Space Agency’s second Earth Explorer Opportunity mission. One of the objectives is to retrieve sea surface salinity (SSS) from measured brightness temperatures (TBs) at L band with a precision of 0.2 practical salinity units (psu) with averages taken over 200 km by 200 km areas and 10 days [as suggested in the requirements of the Global Ocean Data Assimilation Experiment (GODAE)]. The retrieval is performed here by an inverse model and additional information of auxiliary SSS, sea surface temperature (SST), and wind speed (W). A sensitivity study is done to observe the influence of the TBs and auxiliary data on the SSS retrieval. The key role of TB and W accuracy on SSS retrieval is verified. Retrieval is then done over the Atlantic for two cases. In case A, auxiliary data are simulated from two model outputs by adding white noise. The more realistic case B uses independent databases for reference and auxiliary ocean parameters. For these cases, the RMS error of retrieved SSS on pixel scale is around 1 psu (1.2 for case B). Averaging over GODAE scales reduces the SSS error by a factor of 12 (4 for case B). The weaker error reduction in case B is most likely due to the correlation of errors in auxiliary data. This study shows that SSS retrieval will be very sensitive to errors on auxiliary data. Specific efforts should be devoted to improving the quality of auxiliary data.
Sampling Errors in the Measurement of Rainfall Parameters Using the Precipitation Occurrence Sensor System (POSS)
Authors: Sheppard B. E. 
Published: February 2007

Abstract
The Precipitation Occurrence Sensor System (POSS) is a small Doppler radar originally designed by the Meteorological Service of Canada (MSC) to report the occurrence, type, and intensity of precipitation in automated observing stations. It is also used for real-time estimation of raindrop size distributions (DSDs). From the DSD, various rainfall parameters can be calculated and relationships established, such as between the radar reflectivity factor (Z) and the rainfall rate (R). Earlier work presented first-order estimates of the sampling errors for some POSS rainfall parameter estimates. This work combines a Monte Carlo simulation and “inverse problem” analysis to better estimate errors due to the specific sampling problems of this disdrometer type. The uncertainties are necessary to determine the statistical significance of differences between DSD estimates by the POSS and other collocated disdrometers, or between POSS measurements in different climatologies. Additionally, confidence limits can be assigned to regression coefficients for rainfall parameter relationships determined from POSS estimates. An example is given of the uncertainties in the coefficients of measured Z–R relationships.