P. Dias - Academia.edu (original) (raw)

Papers by P. Dias

Journal of the Atmospheric Sciences

Here the theory of global nonhydrostatic normal modes has been further developed with the analysi... more Here the theory of global nonhydrostatic normal modes has been further developed with the analysis of both linear and weakly nonlinear energetics of inertia–acoustic (IA) and inertia–gravity (IG) modes. These energetics are analyzed in the context of a shallow global nonhydrostatic model governing finite-amplitude perturbations around a resting, hydrostatic, and isothermal background state. For the linear case, the energy as a function of the zonal wavenumber of the IA and IG modes is analyzed, and the nonhydrostatic effect of vertical acceleration on the IG waves is highlighted. For the nonlinear energetics analysis, the reduced equations of a single resonant wave triad interaction are obtained by using a pseudoenergy orthogonality relation. Integration of the triad equations for a resonance involving a short harmonic of an IG wave, a planetary-scale IA mode, and a short IA wave mode shows that an IG mode can allow two IA modes to exchange energy in specific resonant triads. These ...

Climate Dynamics

A 21-yr climatology of Easterly Waves Disturbances (EWDs) over the Tropical South Atlantic (TSA) ... more A 21-yr climatology of Easterly Waves Disturbances (EWDs) over the Tropical South Atlantic (TSA) has been examined using data from the European Centers for Medium-Range Weather Forecasting (ECMWF) interim reanalysis (ERAI) and satellite data. This includes the frequency distribution of EWDs and their interannual variability. The largescale environment associated with EWDs has been investigated for the coastal region of Northeast Brazil (NEB) for the rainy (April-August) season using a composite analysis. EWDs were first identified in ERAI, resulting in 518 observed cases. These were found to show notable interannual variability with around 16-40 episodes each year and with an average lifetime of 4-6 days. Of the identified EWDs, 97% reached the coast of NEB, of which 64% were convective in nature and 14% moved across the NEB region and reached the Amazon. The annual occurrence of EWDs seems to be lower (higher) during El Niño (La Niña). The monthly occurrence of EWDs shows higher activity in the rainy season. EWDs originate in association with five types of system: cold fronts, convective clusters from the west coast of Africa, Intertropical Convergence Zone and Tropical Upper Tropospheric Cyclonic Vortices. The composite analysis indicates strong relative vorticity (RV) and divergence anomalies at low levels, as well as in the vertical profiles of relative humidity and vertical velocity (omega). The precipitation composites show that the EWDs propagate between the TSA and NEB and contribute at least 60% of the total rainfall over the east coast of NEB throughout the rainy season.

In this work, a restructuring of the calls of the direct model solver was carried out to remove r... more In this work, a restructuring of the calls of the direct model solver was carried out to remove redundant executions of the symbolic and numerical factorization stages present in the original implementation of the chemistry module from BRAMS regional numerical weather prediction. In the case study chosen, this change resulted in a gain of approximately 37.5% on average of the chemistry iteration serial time.

Climate responses to volcanic eruptions include changes in the distribution of temperature and pr... more Climate responses to volcanic eruptions include changes in the distribution of temperature and precipitation such as those associated with El Niño Southern Oscillation (ENSO). Recent studies suggest an ENSO-positive phase after a volcanic eruption. In the Atlantic Basin, a similar mode of variability is referred as the Atlantic Niño, which is related to precipitation variability in West Africa and South America. Both ENSO and Atlantic Niño are characterized in the tropics by conjoined fluctuations in sea surface temperature (SST), zonal winds, and thermocline depth. Here, we examine possible responses of the Tropical Atlantic to last millennium volcanic forcing via SST, zonal winds, and thermocline changes. We used simulation results from the National Center for Atmospheric Research Community Earth System Model Last Millennium Ensemble single-forcing experiment ranging from 850 to 1850 C.E. Our results show an SST cooling in the Tropical Atlantic during the post-eruption year accompanied by differences in the Atlantic Niño associated feedback. However, we found no significant deviations in zonal winds and thermocline depth related to the volcanic forcing in the first 10 years after the eruption. Changes in South America and Africa monsoon precipitation regimes related to the volcanic forcing were detected, as well as in the Intertropical Convergence Zone position and associated precipitation. These precipitation responses derive primarily from Southern and Tropical volcanic eruptions and occur predominantly during the austral summer and autumn of the post-eruption year.

Bulletin of the American Meteorological Society

Journal of the Atmospheric Sciences

In the present study a simplified multiscale atmosphere–ocean coupled model for the tropical inte... more In the present study a simplified multiscale atmosphere–ocean coupled model for the tropical interactions among synoptic, intraseasonal, and interannual scales is developed. Two nonlinear equatorial β-plane shallow-water equations are considered: one for the ocean and the other for the atmosphere. The nonlinear terms are the intrinsic advective nonlinearity and the air–sea coupling fluxes. To mimic the main differences between the fast atmosphere and the slow ocean, suitable anisotropic multispace/multitime scalings are applied, yielding a balanced synoptic–intraseasonal–interannual–El Niño (SInEN) regime. In this distinguished balanced regime, the synoptic scale is the fastest atmospheric time scale, the intraseasonal scale is the intermediate air–sea coupling time scale (common to both fluid flows), and El Niño refers to the slowest interannual ocean time scale. The asymptotic SInEN equations reveal that the slow wave amplitude evolution depends on both types of nonlinearities. An...

Geoscientific Model Development Discussions, 2016

We present a new version of the Brazilian developments on the Regional Atmospheric Modeling Syste... more We present a new version of the Brazilian developments on the Regional Atmospheric Modeling System where different previous versions for weather, chemistry and carbon cycle were unified in a single integrated software system. The new version also has a new set of state-of-the-art physical parameterizations and greater computational parallel and memory usage efficiency. Together with the description of the main features are examples of the quality of the transport scheme for scalars, radiative fluxes on surface and model simulation of rainfall systems over South America in different spatial resolutions using a scale-aware convective parameterization. Besides, the simulation of the diurnal cycle of the convection and carbon dioxide concentration over the Amazon Basin, as well as carbon dioxide fluxes from biogenic processes over a large portion of South America are shown. Atmospheric chemistry examples present model performance in simulating near-surface carbon monoxide and ozone in A...

We present a methodology to reconstruct vertical profiles of chlorophyll-a pigment concentration ... more We present a methodology to reconstruct vertical profiles of chlorophyll-a pigment concentration in open-ocean waters based on radiance values at different depths. The inverse problem is formulated here as an optimization problem and iteratively solved by an Ant Colony System (ACS) meta-heuristic. An objective function is given by the square difference between computed and experimental radiances at each iteration. The Laplace transform discrete ordinate (LTSN) method is used to solve the radiative transfer equation (direct problem) in order to compute the radiances. In a first approach, this methodology was not able to reconstruct profiles with two or more peaks of chlorophyll-a concentration. This result can be partially explained by the relatively low number of sampling points (11 points), that limits the geometric resolution of the vertical profile to be reconstructed. Alternatively, we propose the reconstruction vertical profile using a higher geometric resolution, lower than one meter, in order to evaluate the ability of identifying any peak in chlorophyll-a concentration. A hybrid methodology is adopted: initially, the original inverse ACS methodology is employed to retrieve a high resolution profile (81 points), and then this result is used as an initial guess for the deterministic method of optimization Levenberg-Marquardt to refine the profile.

Meteorology and Atmospheric Physics, 2006

This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the... more This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of Sã ao Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O 3 , CO and PM 10 concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components (U, V and W). The threedimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at 00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of 0.5 N, S, E and W of the MASP (¼ 23 33 0 S, ' ¼ 46 45 0 W), that last endpoint being centered in the MASP. To analyze cluster trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast, southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated from the same quadrant were classified as ''core'' days. Core day concentrations of CO, O 3 and PM 10 during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis of backtrajectory clusters in the MASP suggests a transport to ambient air of O 3 precursors and O 3 from the northeast region, which is associated with agricultural activities involving biomass burning.

Atmospheric Environment, 2005

An in-line simplified photochemical module was coupled with RAMS, an atmopsheric mesoscale model,... more An in-line simplified photochemical module was coupled with RAMS, an atmopsheric mesoscale model, to produce an operational forecast of ozone and other constituent concentration for the Metropolitan Area of Sa˜o Paulo (MASP), Brazil. Comparisons between surface pollutants concentrations data, provided by automatic network stations for air quality monitoring and modeled values, show good agreement, with correlation coefficients greater than 0.7 for all stations considered. Mean values over all analyzed stations have an index of agreement higher than 0.8. An important feature observed during the simulations was the ability of the model to simulate nocturnal concentrations of ozone over MASP which are usually observed as a result of transport of this pollutant from other regions and from higher levels of the atmosphere, representing the close coupling between the micro scale process and the chemical reactions, although these nocturnal maximums are overestimated by the model in some cases. The computational efficiency of the model shows that it can be considered for operational procedures with relatively small PC-based clusters and used as a tool for emission control strategies by environmental agencies concerned with the improvement of air quality.

In this work, a new theoretical mechanism is presented in which equatorial Rossby and inertio-gra... more In this work, a new theoretical mechanism is presented in which equatorial Rossby and inertio-gravity wave modes may interact with each other through resonance with the diurnal cycle of tropical deep convection. We have adopted the two-layer incompressible equatorial primitive equations forced by a parametric heating that roughly represents deep convection activity in the tropical atmosphere. The heat source was parametrized in the simplest way according to the hypothesis that it is proportional to the lower-troposphere moisture convergence, with the background moisture state function mimicking the structure of the ITCZ. In this context, we have investigated the possibility of resonant interaction between equatorially trapped Rossby and inertio-gravity modes through the diurnal cycle of the background moisture state function. The reduced dynamics of a single resonant duo shows that when this diurnal variation is considered, a Rossby wave mode can undergo significant amplitude modulations when interacting with an inertio-gravity wave mode, which is not possible in the context of the resonant triad non-linear interaction. Therefore, the results suggest that the diurnal variation of the ITCZ can be a possible dynamical mechanism that leads the Rossby waves to be significantly affected by high frequency modes.

The dynamics of convectively coupled equatorial waves (CCEWs) is analyzed in an idealized model o... more The dynamics of convectively coupled equatorial waves (CCEWs) is analyzed in an idealized model of the large-scale atmospheric circulation. The model is composed of a linear rotating shallow-water system with a variable equivalent height, or equivalent gravity wave speed, which varies in space. This model is based on the hypothesis that moist convection acts to remove convective instability, therefore modulating the equivalent height of a shallow-water system. Asymptotic solutions are derived in the case of a small perturbation around a constant coefficient, which is assumed to be a mean moist equivalent height derived from satellite observations. The first-order solutions correspond to the free normal modes of the linear shallow-water system and the second-order flow is derived solving a perturbation eigenvalue problem. The asymptotic solutions are documented in the case of a zonally varying equivalent height and for wavenumbers and frequencies that are consistent with observations of CCEWs. This analysis shows that the dynamics of the secondary divergence and its impact on the full divergence varies mode by mode. For instance, for a negative equivalent height anomaly, which is interpreted as a moister background, the secondary divergence is nearly in phase with the primary divergence in the case of Kelvin waves-in contrast to mixed Rossby-gravity waves where the secondary divergence acts to attenuate the primary divergence. While highly idealized, the modeled waves share some features with observations, providing a mechanism for the relationship between CCEWs phase speed, amplitude, and horizontal structure.

In the present work we use an asymptotic approach to obtain the long wave equations. The shallow ... more In the present work we use an asymptotic approach to obtain the long wave equations. The shallow water equation is put as a function of an external parameter that is a measure of both the spatial scales anisotropy and the fast to slow time ratio. The values given to the external parameters are consistent with those computed using typical values of the perturbations in tropical dynamics. Asymptotically, the model converge toward the long wave model. Thus, it is possible to go toward the long wave approximation through intermediate realizable states. With this approach, the resonant nonlinear wave interactions are studied. To simplify, the reduced dynamics of a single resonant triad is used for some selected equatorial trios. It was verified by both theoretical and numerical results that the nonlinear energy exchange period increases smoothly as we move toward the long wave approach. The magnitude of the energy exchanges is also modified, but in this case depends on the particular triad used and also on the initial energy partition among the triad components. Some implications of the results for the tropical dynamics are disccussed. In particular, we discuss the implications of the results for El Niño and the Madden-Julian in connection with other scales of time and spatial variability.

This chapter is based on recent works from Atmosfera Massiva Research Group 1 on evaluating OLAM'... more This chapter is based on recent works from Atmosfera Massiva Research Group 1 on evaluating OLAM's performance and scalability in multi-core environments-single node and cluster. Large-scale simulations, as OLAM, need a high-throughput shared storage system so that the distributed instances can access their input data and store the execution results for later analysis. One characteristic of weather and climate forecast models is that data generated during the execution is stored on a large amount of small files. This has a large impact on the scalability of the system, especially when executing using parallel file systems: the large amount of metadata operations for opening and closing files, allied with small read and write operations, can transform the I/O subroutines in a significant bottleneck. General Purpose computation on Graphics Processing Units (GPGPU) is a trend that uses GPUs (Graphics Processing Units) for general-purpose computing. The modern GPUs' highly parallel structure makes them often more effective than general-purpose CPUs for a range of complex algorithms. GPUs are "many-core" processors, with hundreds of processing elements. In this chapter, we also present recent studies that evaluates a implementation of OLAM that uses GPUs to accelerate its computations. Therefore, this chapter presents an overview on OLAM's performance and scalability. We aim at exploiting all levels of parallelism in the architectures, and also at paying attention to important performance factors like I/O. The remainder of this chapter is structured as follows. Section 2 presents the Ocean-Land-Atmosphere Model, and Section 3 presents performance experiments and analysis. Related works are shown in Section 4. The last section closes the chapter with final remarks and future work.

One possible explanation for the relatively high signal of the mixed Rossby–gravity waves observe... more One possible explanation for the relatively high signal of the mixed Rossby–gravity waves observed in the tropical atmosphere is explored in this paper. This explanation is based on the nonlinear interactions among equatorial waves, and is made by adopting the nonlinear shallow water equations on the equatorial β plane. These equations are solved by a spectral method that uses the eigensolutions of the linear problem as the expansion basis. Numerical simulations are performed with a specified stationary mass source representative of the tropospheric heating associated with the typical convective activity over the Amazon Basin during the austral summer period. The numerical results show that the mixed Rossby–gravity waves are excited by a nonlinear mechanism in which the slow modes excited by the thermal forcing generate a quasigeostrophic basic state that supplies energy especially to the mixed Rossby–gravity waves with zonal wavenumbers 4 and 5, which have periods of the order of 4 days. The phase propagation of these unstable mixed modes leads to a periodic energy exchange between the mixed Rossby–gravity waves and the quasigeostrophic modes (Rossby and ultralong Kelvin modes). This regular nonlinear energy exchange implies a 4-day-cycle vacillation in the solution, which might be linked to the 4–6-day local oscillations in the dynamical field data throughout the Amazon region found in observational studies. Besides the importance of quasigeostrophic modes in the excitation of mixed Rossby–gravity waves, the numerical results also suggest that the predominance of the slow modes is crucial for maintaining the high signal of the unstable mixed modes, since these waves are strongly suppressed by the inclusion of the fast modes in the integration.

Resonant interactions among equatorial waves in the presence of a diurnally varying heat source a... more Resonant interactions among equatorial waves in the presence of a diurnally varying heat source are studied in the context of the diabatic version of the equatorial β-plane primitive equations for a motionless, hydrostatic, horizontally homogeneous and stably stratified background atmosphere. The heat source is assumed to be periodic in time and of small amplitude [i.e., O(ε)] and is prescribed to roughly represent the typical heating associated with deep convection in the tropical atmosphere. In this context, using the asymptotic method of multiple time scales, the free linear Rossby, Kelvin, mixed Rossby–gravity, and inertio-gravity waves, as well as their vertical structures, are obtained as leading-order solutions. These waves are shown to interact resonantly in a triad configuration at the O(ε) approximation, and the dynamics of these interactions have been studied in the presence of the forcing. It is shown that for the planetary-scale wave resonant triads composed of two first baroclinic equatorially trapped waves and one barotropic Rossby mode, the spectrum of the thermal forcing is such that only one of the triad components is resonant with the heat source. As a result, to illustrate the role of the diurnal forcing in these interactions in a simplified fashion, two kinds of triads have been analyzed. The first one refers to triads composed of a k = 0 first baroclinic geostrophic mode, which is resonant with the stationary component of the diurnal heat source, and two dispersive modes, namely, a mixed Rossby–gravity wave and a barotropic Rossby mode. The other class corresponds to triads composed of two first baroclinic inertio-gravity waves in which the highest-frequency wave resonates with a transient harmonic of the forcing. The integration of the asymptotic reduced equations for these selected resonant triads shows that the stationary component of the diurnal heat source acts as an “accelerator” for the energy exchanges between the two dispersive waves through the excitation of the catalyst geostrophic mode. On the other hand, since in the second class of triads the mode that resonates with the forcing is the most energetically active member because of the energy constraints imposed by the triad dynamics, the results show that the convective forcing in this case is responsible for a longer time scale modulation in the resonant interactions, generating a period doubling in the energy exchanges. The results suggest that the diurnal variation of tropical convection might play an important role in generating low-frequency fluctuations in the atmospheric circulation through resonant nonlinear interactions.

In this paper we explore some dynamical features on the non-linear interactions among equatorial ... more In this paper we explore some dynamical features on the non-linear interactions among equatorial waves. The shallowwater equation model with the equatorial β-plane approximation is used for this purpose. The Galerkin method is applied to the governing equations with the basis functions given by the eigensolutions of the linear problem. From the phase space expansion of two particular integrals of motion of the system, quadratic to lowest order, some constraints are obtained which the coupling coefficients must satisfy in order to ensure the invariance of such integrals. From the numerical evaluation of the coupling coefficients, these constraints are used to determine the possible resonant triads among equatorial waves. Numerical integrations of the resonant three-wave problem show that the energy of the waves in a resonant triad evolves periodically in time, with the period and amplitude of the energy oscillations dependent on the magnitude of the initial amplitudes of the waves and the way in which the initial energy is distributed among the triad components. The high-frequency modes are found to be energetically more active than the low-frequency modes. The latter tend to act as 'catalytic' components in a resonant triad. Integrations of the problem of two resonant triads coupled by a single mode point out the importance of gravity waves in the intertriad energy exchanges, suggesting the significance of these modes in the redistribution of energy throughout the atmospheric motion spectrum. The results also show that the intertriad energy exchanges provided by the highest frequency mode of two triads occur in a longer timescale than the intratriad interactions. Therefore, these results also suggest the importance of the high-frequency modes in the generation of the low-frequency variability (intraseasonal and even longer term) of the atmospheric flow.

Meteorology and Atmospheric …, 1986

Journal of the Atmospheric Sciences

Here the theory of global nonhydrostatic normal modes has been further developed with the analysi... more Here the theory of global nonhydrostatic normal modes has been further developed with the analysis of both linear and weakly nonlinear energetics of inertia–acoustic (IA) and inertia–gravity (IG) modes. These energetics are analyzed in the context of a shallow global nonhydrostatic model governing finite-amplitude perturbations around a resting, hydrostatic, and isothermal background state. For the linear case, the energy as a function of the zonal wavenumber of the IA and IG modes is analyzed, and the nonhydrostatic effect of vertical acceleration on the IG waves is highlighted. For the nonlinear energetics analysis, the reduced equations of a single resonant wave triad interaction are obtained by using a pseudoenergy orthogonality relation. Integration of the triad equations for a resonance involving a short harmonic of an IG wave, a planetary-scale IA mode, and a short IA wave mode shows that an IG mode can allow two IA modes to exchange energy in specific resonant triads. These ...

Climate Dynamics

A 21-yr climatology of Easterly Waves Disturbances (EWDs) over the Tropical South Atlantic (TSA) ... more A 21-yr climatology of Easterly Waves Disturbances (EWDs) over the Tropical South Atlantic (TSA) has been examined using data from the European Centers for Medium-Range Weather Forecasting (ECMWF) interim reanalysis (ERAI) and satellite data. This includes the frequency distribution of EWDs and their interannual variability. The largescale environment associated with EWDs has been investigated for the coastal region of Northeast Brazil (NEB) for the rainy (April-August) season using a composite analysis. EWDs were first identified in ERAI, resulting in 518 observed cases. These were found to show notable interannual variability with around 16-40 episodes each year and with an average lifetime of 4-6 days. Of the identified EWDs, 97% reached the coast of NEB, of which 64% were convective in nature and 14% moved across the NEB region and reached the Amazon. The annual occurrence of EWDs seems to be lower (higher) during El Niño (La Niña). The monthly occurrence of EWDs shows higher activity in the rainy season. EWDs originate in association with five types of system: cold fronts, convective clusters from the west coast of Africa, Intertropical Convergence Zone and Tropical Upper Tropospheric Cyclonic Vortices. The composite analysis indicates strong relative vorticity (RV) and divergence anomalies at low levels, as well as in the vertical profiles of relative humidity and vertical velocity (omega). The precipitation composites show that the EWDs propagate between the TSA and NEB and contribute at least 60% of the total rainfall over the east coast of NEB throughout the rainy season.

In this work, a restructuring of the calls of the direct model solver was carried out to remove r... more In this work, a restructuring of the calls of the direct model solver was carried out to remove redundant executions of the symbolic and numerical factorization stages present in the original implementation of the chemistry module from BRAMS regional numerical weather prediction. In the case study chosen, this change resulted in a gain of approximately 37.5% on average of the chemistry iteration serial time.

Climate responses to volcanic eruptions include changes in the distribution of temperature and pr... more Climate responses to volcanic eruptions include changes in the distribution of temperature and precipitation such as those associated with El Niño Southern Oscillation (ENSO). Recent studies suggest an ENSO-positive phase after a volcanic eruption. In the Atlantic Basin, a similar mode of variability is referred as the Atlantic Niño, which is related to precipitation variability in West Africa and South America. Both ENSO and Atlantic Niño are characterized in the tropics by conjoined fluctuations in sea surface temperature (SST), zonal winds, and thermocline depth. Here, we examine possible responses of the Tropical Atlantic to last millennium volcanic forcing via SST, zonal winds, and thermocline changes. We used simulation results from the National Center for Atmospheric Research Community Earth System Model Last Millennium Ensemble single-forcing experiment ranging from 850 to 1850 C.E. Our results show an SST cooling in the Tropical Atlantic during the post-eruption year accompanied by differences in the Atlantic Niño associated feedback. However, we found no significant deviations in zonal winds and thermocline depth related to the volcanic forcing in the first 10 years after the eruption. Changes in South America and Africa monsoon precipitation regimes related to the volcanic forcing were detected, as well as in the Intertropical Convergence Zone position and associated precipitation. These precipitation responses derive primarily from Southern and Tropical volcanic eruptions and occur predominantly during the austral summer and autumn of the post-eruption year.

Bulletin of the American Meteorological Society

Journal of the Atmospheric Sciences

In the present study a simplified multiscale atmosphere–ocean coupled model for the tropical inte... more In the present study a simplified multiscale atmosphere–ocean coupled model for the tropical interactions among synoptic, intraseasonal, and interannual scales is developed. Two nonlinear equatorial β-plane shallow-water equations are considered: one for the ocean and the other for the atmosphere. The nonlinear terms are the intrinsic advective nonlinearity and the air–sea coupling fluxes. To mimic the main differences between the fast atmosphere and the slow ocean, suitable anisotropic multispace/multitime scalings are applied, yielding a balanced synoptic–intraseasonal–interannual–El Niño (SInEN) regime. In this distinguished balanced regime, the synoptic scale is the fastest atmospheric time scale, the intraseasonal scale is the intermediate air–sea coupling time scale (common to both fluid flows), and El Niño refers to the slowest interannual ocean time scale. The asymptotic SInEN equations reveal that the slow wave amplitude evolution depends on both types of nonlinearities. An...

Geoscientific Model Development Discussions, 2016

We present a new version of the Brazilian developments on the Regional Atmospheric Modeling Syste... more We present a new version of the Brazilian developments on the Regional Atmospheric Modeling System where different previous versions for weather, chemistry and carbon cycle were unified in a single integrated software system. The new version also has a new set of state-of-the-art physical parameterizations and greater computational parallel and memory usage efficiency. Together with the description of the main features are examples of the quality of the transport scheme for scalars, radiative fluxes on surface and model simulation of rainfall systems over South America in different spatial resolutions using a scale-aware convective parameterization. Besides, the simulation of the diurnal cycle of the convection and carbon dioxide concentration over the Amazon Basin, as well as carbon dioxide fluxes from biogenic processes over a large portion of South America are shown. Atmospheric chemistry examples present model performance in simulating near-surface carbon monoxide and ozone in A...

We present a methodology to reconstruct vertical profiles of chlorophyll-a pigment concentration ... more We present a methodology to reconstruct vertical profiles of chlorophyll-a pigment concentration in open-ocean waters based on radiance values at different depths. The inverse problem is formulated here as an optimization problem and iteratively solved by an Ant Colony System (ACS) meta-heuristic. An objective function is given by the square difference between computed and experimental radiances at each iteration. The Laplace transform discrete ordinate (LTSN) method is used to solve the radiative transfer equation (direct problem) in order to compute the radiances. In a first approach, this methodology was not able to reconstruct profiles with two or more peaks of chlorophyll-a concentration. This result can be partially explained by the relatively low number of sampling points (11 points), that limits the geometric resolution of the vertical profile to be reconstructed. Alternatively, we propose the reconstruction vertical profile using a higher geometric resolution, lower than one meter, in order to evaluate the ability of identifying any peak in chlorophyll-a concentration. A hybrid methodology is adopted: initially, the original inverse ACS methodology is employed to retrieve a high resolution profile (81 points), and then this result is used as an initial guess for the deterministic method of optimization Levenberg-Marquardt to refine the profile.

Meteorology and Atmospheric Physics, 2006

This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the... more This study is aimed to qualitatively analyze the impact of remote sources on air pollution in the Metropolitan Area of Sã ao Paulo (MASP). Air-mass back trajectories from June to August of 1999 were calculated using a three-dimensional kinematic trajectory model and grouped into trajectory clusters. Correlations of individual trajectory clusters with O 3 , CO and PM 10 concentrations were determined. In this model, trajectories were obtained using the means of the three wind velocity components (U, V and W). The threedimensional wind field was derived from the Regional Atmospheric Modeling System, and downscaling was employed. Coarse and fine nested grids (64-km and 16-km horizontal resolution, respectively) were used. Every 12 h (at 00 and 12 UTC), a back-trajectory ensemble, using the 64-km grid, was calculated for five defined endpoints at intervals of 0.5 N, S, E and W of the MASP (¼ 23 33 0 S, ' ¼ 46 45 0 W), that last endpoint being centered in the MASP. To analyze cluster trajectories, the five trajectory ensembles from each day were allocated into one of four clusters (northeast, southeast, southwest or northwest quadrant) based on the origin of the trajectory over 4 days. Days on which all five trajectories originated from the same quadrant were classified as ''core'' days. Core day concentrations of CO, O 3 and PM 10 during the study period were evaluated. The results show that, during the study period, air-mass back trajectories in the MASP originated from all four quadrants: northeast (32%), southeast (12%), southwest (19%) and northwest (37%). Our analysis of backtrajectory clusters in the MASP suggests a transport to ambient air of O 3 precursors and O 3 from the northeast region, which is associated with agricultural activities involving biomass burning.

Atmospheric Environment, 2005

An in-line simplified photochemical module was coupled with RAMS, an atmopsheric mesoscale model,... more An in-line simplified photochemical module was coupled with RAMS, an atmopsheric mesoscale model, to produce an operational forecast of ozone and other constituent concentration for the Metropolitan Area of Sa˜o Paulo (MASP), Brazil. Comparisons between surface pollutants concentrations data, provided by automatic network stations for air quality monitoring and modeled values, show good agreement, with correlation coefficients greater than 0.7 for all stations considered. Mean values over all analyzed stations have an index of agreement higher than 0.8. An important feature observed during the simulations was the ability of the model to simulate nocturnal concentrations of ozone over MASP which are usually observed as a result of transport of this pollutant from other regions and from higher levels of the atmosphere, representing the close coupling between the micro scale process and the chemical reactions, although these nocturnal maximums are overestimated by the model in some cases. The computational efficiency of the model shows that it can be considered for operational procedures with relatively small PC-based clusters and used as a tool for emission control strategies by environmental agencies concerned with the improvement of air quality.

In this work, a new theoretical mechanism is presented in which equatorial Rossby and inertio-gra... more In this work, a new theoretical mechanism is presented in which equatorial Rossby and inertio-gravity wave modes may interact with each other through resonance with the diurnal cycle of tropical deep convection. We have adopted the two-layer incompressible equatorial primitive equations forced by a parametric heating that roughly represents deep convection activity in the tropical atmosphere. The heat source was parametrized in the simplest way according to the hypothesis that it is proportional to the lower-troposphere moisture convergence, with the background moisture state function mimicking the structure of the ITCZ. In this context, we have investigated the possibility of resonant interaction between equatorially trapped Rossby and inertio-gravity modes through the diurnal cycle of the background moisture state function. The reduced dynamics of a single resonant duo shows that when this diurnal variation is considered, a Rossby wave mode can undergo significant amplitude modulations when interacting with an inertio-gravity wave mode, which is not possible in the context of the resonant triad non-linear interaction. Therefore, the results suggest that the diurnal variation of the ITCZ can be a possible dynamical mechanism that leads the Rossby waves to be significantly affected by high frequency modes.

The dynamics of convectively coupled equatorial waves (CCEWs) is analyzed in an idealized model o... more The dynamics of convectively coupled equatorial waves (CCEWs) is analyzed in an idealized model of the large-scale atmospheric circulation. The model is composed of a linear rotating shallow-water system with a variable equivalent height, or equivalent gravity wave speed, which varies in space. This model is based on the hypothesis that moist convection acts to remove convective instability, therefore modulating the equivalent height of a shallow-water system. Asymptotic solutions are derived in the case of a small perturbation around a constant coefficient, which is assumed to be a mean moist equivalent height derived from satellite observations. The first-order solutions correspond to the free normal modes of the linear shallow-water system and the second-order flow is derived solving a perturbation eigenvalue problem. The asymptotic solutions are documented in the case of a zonally varying equivalent height and for wavenumbers and frequencies that are consistent with observations of CCEWs. This analysis shows that the dynamics of the secondary divergence and its impact on the full divergence varies mode by mode. For instance, for a negative equivalent height anomaly, which is interpreted as a moister background, the secondary divergence is nearly in phase with the primary divergence in the case of Kelvin waves-in contrast to mixed Rossby-gravity waves where the secondary divergence acts to attenuate the primary divergence. While highly idealized, the modeled waves share some features with observations, providing a mechanism for the relationship between CCEWs phase speed, amplitude, and horizontal structure.

In the present work we use an asymptotic approach to obtain the long wave equations. The shallow ... more In the present work we use an asymptotic approach to obtain the long wave equations. The shallow water equation is put as a function of an external parameter that is a measure of both the spatial scales anisotropy and the fast to slow time ratio. The values given to the external parameters are consistent with those computed using typical values of the perturbations in tropical dynamics. Asymptotically, the model converge toward the long wave model. Thus, it is possible to go toward the long wave approximation through intermediate realizable states. With this approach, the resonant nonlinear wave interactions are studied. To simplify, the reduced dynamics of a single resonant triad is used for some selected equatorial trios. It was verified by both theoretical and numerical results that the nonlinear energy exchange period increases smoothly as we move toward the long wave approach. The magnitude of the energy exchanges is also modified, but in this case depends on the particular triad used and also on the initial energy partition among the triad components. Some implications of the results for the tropical dynamics are disccussed. In particular, we discuss the implications of the results for El Niño and the Madden-Julian in connection with other scales of time and spatial variability.

This chapter is based on recent works from Atmosfera Massiva Research Group 1 on evaluating OLAM'... more This chapter is based on recent works from Atmosfera Massiva Research Group 1 on evaluating OLAM's performance and scalability in multi-core environments-single node and cluster. Large-scale simulations, as OLAM, need a high-throughput shared storage system so that the distributed instances can access their input data and store the execution results for later analysis. One characteristic of weather and climate forecast models is that data generated during the execution is stored on a large amount of small files. This has a large impact on the scalability of the system, especially when executing using parallel file systems: the large amount of metadata operations for opening and closing files, allied with small read and write operations, can transform the I/O subroutines in a significant bottleneck. General Purpose computation on Graphics Processing Units (GPGPU) is a trend that uses GPUs (Graphics Processing Units) for general-purpose computing. The modern GPUs' highly parallel structure makes them often more effective than general-purpose CPUs for a range of complex algorithms. GPUs are "many-core" processors, with hundreds of processing elements. In this chapter, we also present recent studies that evaluates a implementation of OLAM that uses GPUs to accelerate its computations. Therefore, this chapter presents an overview on OLAM's performance and scalability. We aim at exploiting all levels of parallelism in the architectures, and also at paying attention to important performance factors like I/O. The remainder of this chapter is structured as follows. Section 2 presents the Ocean-Land-Atmosphere Model, and Section 3 presents performance experiments and analysis. Related works are shown in Section 4. The last section closes the chapter with final remarks and future work.

One possible explanation for the relatively high signal of the mixed Rossby–gravity waves observe... more One possible explanation for the relatively high signal of the mixed Rossby–gravity waves observed in the tropical atmosphere is explored in this paper. This explanation is based on the nonlinear interactions among equatorial waves, and is made by adopting the nonlinear shallow water equations on the equatorial β plane. These equations are solved by a spectral method that uses the eigensolutions of the linear problem as the expansion basis. Numerical simulations are performed with a specified stationary mass source representative of the tropospheric heating associated with the typical convective activity over the Amazon Basin during the austral summer period. The numerical results show that the mixed Rossby–gravity waves are excited by a nonlinear mechanism in which the slow modes excited by the thermal forcing generate a quasigeostrophic basic state that supplies energy especially to the mixed Rossby–gravity waves with zonal wavenumbers 4 and 5, which have periods of the order of 4 days. The phase propagation of these unstable mixed modes leads to a periodic energy exchange between the mixed Rossby–gravity waves and the quasigeostrophic modes (Rossby and ultralong Kelvin modes). This regular nonlinear energy exchange implies a 4-day-cycle vacillation in the solution, which might be linked to the 4–6-day local oscillations in the dynamical field data throughout the Amazon region found in observational studies. Besides the importance of quasigeostrophic modes in the excitation of mixed Rossby–gravity waves, the numerical results also suggest that the predominance of the slow modes is crucial for maintaining the high signal of the unstable mixed modes, since these waves are strongly suppressed by the inclusion of the fast modes in the integration.

Resonant interactions among equatorial waves in the presence of a diurnally varying heat source a... more Resonant interactions among equatorial waves in the presence of a diurnally varying heat source are studied in the context of the diabatic version of the equatorial β-plane primitive equations for a motionless, hydrostatic, horizontally homogeneous and stably stratified background atmosphere. The heat source is assumed to be periodic in time and of small amplitude [i.e., O(ε)] and is prescribed to roughly represent the typical heating associated with deep convection in the tropical atmosphere. In this context, using the asymptotic method of multiple time scales, the free linear Rossby, Kelvin, mixed Rossby–gravity, and inertio-gravity waves, as well as their vertical structures, are obtained as leading-order solutions. These waves are shown to interact resonantly in a triad configuration at the O(ε) approximation, and the dynamics of these interactions have been studied in the presence of the forcing. It is shown that for the planetary-scale wave resonant triads composed of two first baroclinic equatorially trapped waves and one barotropic Rossby mode, the spectrum of the thermal forcing is such that only one of the triad components is resonant with the heat source. As a result, to illustrate the role of the diurnal forcing in these interactions in a simplified fashion, two kinds of triads have been analyzed. The first one refers to triads composed of a k = 0 first baroclinic geostrophic mode, which is resonant with the stationary component of the diurnal heat source, and two dispersive modes, namely, a mixed Rossby–gravity wave and a barotropic Rossby mode. The other class corresponds to triads composed of two first baroclinic inertio-gravity waves in which the highest-frequency wave resonates with a transient harmonic of the forcing. The integration of the asymptotic reduced equations for these selected resonant triads shows that the stationary component of the diurnal heat source acts as an “accelerator” for the energy exchanges between the two dispersive waves through the excitation of the catalyst geostrophic mode. On the other hand, since in the second class of triads the mode that resonates with the forcing is the most energetically active member because of the energy constraints imposed by the triad dynamics, the results show that the convective forcing in this case is responsible for a longer time scale modulation in the resonant interactions, generating a period doubling in the energy exchanges. The results suggest that the diurnal variation of tropical convection might play an important role in generating low-frequency fluctuations in the atmospheric circulation through resonant nonlinear interactions.

In this paper we explore some dynamical features on the non-linear interactions among equatorial ... more In this paper we explore some dynamical features on the non-linear interactions among equatorial waves. The shallowwater equation model with the equatorial β-plane approximation is used for this purpose. The Galerkin method is applied to the governing equations with the basis functions given by the eigensolutions of the linear problem. From the phase space expansion of two particular integrals of motion of the system, quadratic to lowest order, some constraints are obtained which the coupling coefficients must satisfy in order to ensure the invariance of such integrals. From the numerical evaluation of the coupling coefficients, these constraints are used to determine the possible resonant triads among equatorial waves. Numerical integrations of the resonant three-wave problem show that the energy of the waves in a resonant triad evolves periodically in time, with the period and amplitude of the energy oscillations dependent on the magnitude of the initial amplitudes of the waves and the way in which the initial energy is distributed among the triad components. The high-frequency modes are found to be energetically more active than the low-frequency modes. The latter tend to act as 'catalytic' components in a resonant triad. Integrations of the problem of two resonant triads coupled by a single mode point out the importance of gravity waves in the intertriad energy exchanges, suggesting the significance of these modes in the redistribution of energy throughout the atmospheric motion spectrum. The results also show that the intertriad energy exchanges provided by the highest frequency mode of two triads occur in a longer timescale than the intratriad interactions. Therefore, these results also suggest the importance of the high-frequency modes in the generation of the low-frequency variability (intraseasonal and even longer term) of the atmospheric flow.

Meteorology and Atmospheric …, 1986