Jacyra Soares

Correlation models of diffuse solar-radiation applied to the city of São Paulo, Brazil

Measurements of global and diffuse solar-radiation, at the Earths surface, carried out from May 1994 to June 1999 in Sao Paulo City, Brazil, were used to develop correlation models to estimate hourly, daily and monthly values of diffuse solar-radiation on horizontal surfaces. The polynomials derived by linear regression fitting were able to model satisfactorily the daily and monthly values of diffuse radiation. The comparison with models derived for other places demonstrates some differences related mainly to altitude effects.

Annual and Diurnal Wind Patterns in the City of São Paulo

The major topographic, mesoscale, and urban influences on the wind patterns of the City of São Paulo are characterized using one year of surface wind velocity data observed at 11 surface stations within its urban limits. The data was used to study the diurnal and annual variations of wind velocity and horizontal wind divergence within the city. Results showed that the circulation over the investigated area is dominated by three major factors: sea breeze; mountain-valley circulations; and urban effects, such as roughness, building-barrier, and urban heat island. The sea breeze was found to be the dominant feature of the monthly-averaged diurnal variation of São Paulo surface winds during the eight warmest months of the year. The sea breeze front induces a velocity minimum at the time of its passage and a post-frontal afternoon velocity maximum. Mountain-valley thermal effects on the flow can be seen in the temporal divergence/convergence patterns. These thermal effects tend to be more important during colder months, at night, and when the wind velocities are low. Nighttime downslope convergent flows are present over the city during winter and spring and daytime upslope divergent flows are present over the city during summer months.

North northeast Brazil rainfall and its decadal-scale relationship to wind stress and sea surface temperature

In this study low-frequency variability of rainfall data for the North part of Northeast (NNE) Brazil is examined. The time scale dependence of NNE Brazil rainfall and the associated sea surface temperature (SST) field is also described. Area averaged monthly rainfall data for the NNE Brazil from 1911 to 1989 exhibits not only a distinct interannual behavior but also significant decadal variability. Examination of a 30 year data set of tropical Atlantic SST and wind stress show similar behavior. It was found that the relationships between SST, NNE Brazil rainfall and meridional pseudo-wind stress on the interdecadal time scale are very similar to those on the interannual and seasonal time scale. In both time scales, SST in the Tropical Atlantic are in phase with the meridional displacement of the Intertropical Convergence Zone and associated meridional pseudo-wind stress and out of phase with rainfall.

Radiation balance at the surface in the city of São Paulo, Brazil: diurnal and seasonal variations

The main goal of this work is to describe the diurnal and seasonal variations of the radiation balance components at the surface in the city of São Paulo based on observations carried out during 2004. Monthly average hourly values indicate that the amplitudes of the diurnal cycles of net radiation (Q*), downwelling and upwelling shortwave radiation (SWDW, SWUP), and longwave radiations (LWDW, LWUP) in February were, respectively, 37%, 14%, 19%, 11%, and 5% larger than they were in August. The monthly average daily values indicate a variation of 60% for Q*, with a minimum in June and a maximum in December; 45% for SWDW, with a minimum in May and a maximum in September; 50% for SWUP, with a minimum in June and a maximum in September; 13% for LWDW, with a minimum in July and a maximum in January; and 9% for LWUP, with a minimum in July and a maximum in February. It was verified that the atmospheric broadband transmissivity varied from 0.36 to 0.57; the effective albedo of the surface varied from 0.08 to 0.10; and the atmospheric effective emissivity varied from 0.79 to 0.92. The surface effective emissivity remained approximately constant and equal to 0.96. The albedo and surface effective emissivity for São Paulo agreed with those reported for urban areas in Europe and North America cities. This indicates that material and geometric effects on albedo and surface emissivity in São Paulo are similar to ones observed in typical middle latitudes cities. On the other hand, it was found that São Paulo city induces an urban heat island with daytime maximum intensity varying from 2.6°C in July (16:00 LT) to 5.5°C in September (15:00 LT). The analysis of the radiometric properties carried out here indicate that this daytime maximum is a primary response to the seasonal variation of daily values of net solar radiation at the surface.

Patterns of Local Circulation in the Itaipu Lake Area: Numerical Simulations of Lake Breeze

Abstract The lake-breeze circulation in the Itaipu region was investigated numerically using a nonhydrostatic version of the Topographic Vorticity Model. The area of study corresponds to a 100 km × 180 km rectangle, located on the Brazil–Paraguay border, with Itaipu Lake in its center. The characteristics of the lake breeze generated by the numerical experiments were consistent with the observations available in the area. The numerical experiments have shown that the land use effect is important in the spatial distribution of the lake-breeze circulation and that the topography contributes to modulating the breeze intensity, with the daytime valley–mountain circulation intensifying the lake breeze. However, the circulation pattern observed during daytime over the region is mainly due to the Itaipu Lake presence. The numerical results indicated that Itaipu Lake is able to generate and sustain a lake breeze, with 3.5 m s−1 of maximum intensity and 1500-m depth, that propagates inland at 5.1 km h−1 under typi...

An Application of Neural Network Technique to Correct the Dome Temperature Effects on Pyrgeometer Measurements

Univ Sao Paulo, IAG, Dept Ciencias Atmosfericas, Grp Micrometeorol, BR-05508900 Sao Paulo, Brazil

The co-influence of the sea breeze and the coastal upwelling at Cabo Frio: a numerical investigation using coupled models

A coupled atmospheric-oceanic model was used to investigate whether there is a positive feedback between the coastal upwelling and the sea breeze at Cabo Frio - RJ (Brazil). Two experiments were performed to ascertain the influence of the sea breeze on the coastal upwelling: the first one used the coupled model forced with synoptic NE winds of 8 m s-1 and the sign of the sea breeze circulation was set by the atmospheric model; the second experiment used only the oceanic model with constant 8 m s-1 NE winds. Then, to study the influence of the coastal upwelling on the sea breeze, two more experiments were performed: one using a coastal upwelling representative SST initial field and the other one using a constant and homogeneous SST field of 26°C. Finally, two more experiments were conducted to verify the influence of the topography and the spatial distribution of the sea surface temperature on the previous results. The results showed that the sea breeze can intensify the coastal upwelling, but the coastal upwelling does not intensify the sea breeze circulation, suggesting that there is no positive feedback between these two phenomena at Cabo Frio.

Application of mass conservation method to investigate the wind patterns over an area of complex topography

The most basic mass conservation method is described here in detail. A simplified version of this method is then applied to estimate the wind field over a region of complex topography, the Metropolitan Region of Sao Paulo City, Brazil. The resulting adjusted wind field and its horizontal divergence patterns compare well with observed wind field, indicating that the topography has a major effect in the investigated area.

Dynamics of the equatorial undercurrent in a high-resolution ocean model

In this study, we investigate the sensitivity of the equatorial circulation simulated with the high-resolution World Ocean Circulation Experiment (WOCE) Community Modeling Effort (CME) model to the specification of eddy viscosity. In one of two simulations the coefficient of vertical viscosity is tripled. We focus on the dynamics associated with the anomalous eastward surface flow found in the simulation results. We find, in agreement with other studies, that close to the western boundary, the equatorial undercurrent is dominated by a large positive pressure gradient. In the top layer, for the low-viscosity case, the balance in the western part of the basin is everywhere between the horizontal pressure gradient and vertical viscosity with the advective terms playing a secondary role. In the high-viscosity zonal momentum budget analysis the advective terms are less significant in the surface layers in the west. Toward the east the advective terms become more important in the low-viscosity experiment, whereas in the high-viscosity case the balance is still predominantly between the horizontal pressure gradient and vertical diffusion terms. It is found that in the CME, horizontal viscosity plays a very minor role in the zonal momentum balance. Changes in the vertical viscosity lead to changes in the nonlinear advective terms. These, in turn, contribute to the unusual eastward surface flow.

Sea-Breeze and Topographic Influences on the Planetary Boundary Layer in the Coastal Upwelling Area of Cabo Frio (Brazil)

We use a fully coupled oceanic-atmospheric model to investigate the sources and sinks of turbulent kinetic energy in the Cabo Frio coastal area and to determine the role of topography and the sea breeze in planetary boundary-layer (PBL) development. The study area presents similar boundary-layer characteristics than other coastal upwelling areas with complex topography, such as increased stability and low-level jets. The results show that the major effect of upwelling, over the investigated area, is to maintain low temperatures in the lower atmosphere over the coastal zone, sustaining a strong temperature inversion that precludes the vertical PBL development. Therefore, the cooling effect reduces the horizontal thermal contrast between land and water, generating a negative feedback between the intensity of the sea breeze and the intensity of the upwelling. The topography at Cabo Frio prevents this cooling effect from propagating inland, since it limits the penetration of the sea-breeze circulation.