Prakki Satyamurty

Global Climatological Features in a Simulation Using the CPTEC–COLA AGCM

Abstract The Center for Weather Forecasting and Climate Studies–Center for Ocean–Land–Atmosphere Studies (CPTEC–COLA) atmospheric general circulation model (AGCM) is integrated with nine initial conditions for 10 yr to obtain the model climate in an ensemble mode. The global climatological characteristics simulated by the model are compared with observational data, and emphasis is given to the Southern Hemisphere and South America. Evaluation of the models performance is presented by showing systematic errors of several variables, and anomaly correlation and reproducibility are applied to precipitation. The model is able to simulate the main features of the global climate, and the results are consistent with analyses of other AGCMs. The seasonal cycle is reproduced well in all analyzed variables, and systematic errors occur at the same regions in different seasons. The Southern Hemisphere convergence zones are simulated reasonably well, although the model overestimates precipitation in the southern porti...

The Northwestern Argentinean Low: A Study of Two Typical Events

Abstract A low pressure system [known as the northwestern Argentinean low (NAL)] is commonly observed over northwestern Argentina near the Andean slopes. This study describes two NAL episodes for summer and winter, with emphasis on the characterization of their three-dimensional structure and temporal variability. With the aid of a high-resolution regional model [Eta/Centro de Previsao de Tempo e Estudos Climaticos (CPTEC)], the main mechanisms involved in the NAL life cycle were studied in order to examine how the thermal topographical processes influenced the system behavior. Surface pressure changes in the NAL are mostly dominated by the 600–900-hPa thickness variability, suggesting its thermal character. Based on this result, the temperature tendency equation has been used to quantify all the contributions to thermal changes. The summer NAL has a significant diurnal cycle that has been dominated by surface warming. This single mechanism can explain the low pressure system formation by itself, suggesti...

Analysis of Three Situations of the Foehn Effect over the Andes (Zonda Wind) Using the Eta–CPTEC Regional Model

Abstract The zonda is a warm and extremely dry wind that occurs east of the Andes Cordillera in the extratropical latitudes of South America. Its orographic origin is similar to the foehn that blows in Germany and Austria and the chinook that occurs east of the Rocky Mountains. Three typical zonda events of different categories (surface and elevated) are described, through observational and Eta–Centro de Previsao de Tempo e Estudos Climaticos (CPTEC) model output. During the events the temperature rises sharply by 10°–15°C and the dewpoint temperature drops by 15°–20°C in an interval of a few hours. The sustained wind strength at the surface increases to 30 kt, with gusts of more than 40 kt. The episodes generally start around midday and last for about 10 h. The Eta–CPTEC model was able to forecast several aspects of the three analyzed zonda cases, such as wind strength, temperature, and humidity changes, and their starting and ending times. Some relationships between the intensity of the windward static ...

Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil

Abstract The dynamical and synoptic characteristics that distinguish heavy rainfall episodes from nonheavy rainfall episodes in southern Brazil are discussed. A heavy rainfall episode is defined here as one in which the 50 mm day−1 isohyet encloses an area of not less than 10 000 km2 in the domain of southern Brazil. One hundred and seventy such events are identified in the 11-yr period of 1991–2001. The mean flow patterns in the period of 1–3 days preceding the episodes show some striking synoptic-scale features that may be considered forerunners of these episodes: (i) a deepening midtropospheric trough in the eastern South Pacific approaches the continent 3 days before, (ii) a surface low pressure center forms in northern Argentina 1 day before, (iii) a northerly low-level jet develops over Paraguay 2 days before, and (iv) a strong moisture flux convergence over southern Brazil becomes prominent 1 day before the episode. A parameter called rainfall quantity, defined as the product of the area enclosed b...

Trends in the Frequency of Intense Precipitation Events in Southern and Southeastern Brazil during 1960-2004

AbstractA new approach to define heavy and extreme rainfall events based on cluster analysis and area-average rainfall series is presented. The annual frequency of the heavy and extreme rainfall events is obtained for the southeastern and southern Brazil regions. In the 1960–2004 period, 510 (98) and 466 (77) heavy (extreme) rainfall events are identified in the two regions. Monthly distributions of the events closely follow the monthly climatological rainfall in the two regions. In both regions, annual heavy and extreme rainfall event frequencies present increasing trends in the 45-yr period. However, only in southern Brazil is the trend statistically significant. Although longer time series are necessary to ensure the existence of long-term trends, the positive trends are somewhat alarming since they indicate that climate changes, in terms of rainfall regimes, are possibly under way in Brazil.

DOWNWARD LONGWAVE RADIATION ESTIMATES FOR CLEAR-SKY CONDITIONS OVER NORTHEAST BRAZIL

The main objective of this paper is to assess the performance of nine downward longwave radiation equations for clear-sky condition and develop a locally adjusted equation using the observed vapor pressure and air temperature data. The radiation and atmospheric parameters were measured during the months of October 2005 to June 2006 at a micrometeorological tower installed at the experimental site in a banana orchard in the semiarid region of Northeast Brazil. The comparative statistics for the performance of the downward longwave radiation calculation models during daytime and nighttime compared to measured data have shown that the parameterizations with more physical foundations have the best results. The locally adjusted equation and Sugita and Brutsaert model developed in 1993 showed errors less than 1.0% in comparison with measured values. Downward longwave radiation is one of the most expensive and difficult component of the radiation budget to be monitored in micrometeorological studies. Hence, the locally adjusted equation can be used to estimate downward longwave energy, needed as input to some agricultural and hydrological models, in semi-arid regions of the Northeast Brazil, where this component is not monitored.

An early freeze in southern Brazil in April 1999 and its NWP guidance

A cold air outbreak occurred in the third week of April 1999 in southern Brazil. A synoptic study of this rare event is undertaken. A surface high pressure cell in the Pacific Ocean off the coast of Chile slowly built up and moved eastward on 14 April. It started crossing the Andes, acquiring the characteristic shape of a bean on 15th, and separated into two cells later in the day. The cell on the lee side of the mountains moved gradually northwards over central South America affecting northern Argentina, Paraguay, Uruguay, Bolivia and southern Brazil. The temperature fell in the state of Mato Grosso (about ). In southern Brazil temperatures below freezing were registered in some places on the 17th and 18th and frost occurred in many states. There was snowfall in the uplands of Santa Catarina on the 17th, and such an early snow had not been recorded for 30 years. Baroclinic synoptic wave intensification followed by surface low development in association with a cut-off low formation in the middle and upper troposphere were responsible for strong surface southerlies over Argentina on the 16th and 17th. Cold air advection by the southerlies in the eastern sector of the high-pressure centre was responsible for the northward projection of the high pressure cell east of the Andes. The whole event was well predicted by the Centro de Previsao de Tempo e Estudos Climaticos/Instituto Nacional de Pesquisas Espaciais (CPTEC/INPE) operational global and regional models with lead times of 120 and 60 hours respectively. Copyright

Tendências de índices de extremos climáticos para a região de Manaus-AM

Trends in the extreme climate indices based on precipitation data at three stations in and around the city of Manaus for the period 1971-2007 are studied. Based on the results obtained it can be observed that there was an increase of the annual total precipitation in the area studied. At the station located in the city of Manaus (INMET), the frequency of precipitation events with 50 mm (R50mm) or more, the amount precipitation in five consecutive days (Rx5day) and the number of wet days (R95p), showed an increase, with statistical significance, indicating that Manaus may suffer with the increase of the extreme rainfall events. An increase in the positive SST anomalies in the Equatorial Pacific Ocean induce an increase of the consecutive dry days and decrease of the extreme rainfall events and, consequently, in the total precipitation in the Amazon basin. The positive SST anomalies in the South Atlantic Ocean induce the displacement of ITCZ to the south of Equator causing an increase of the precipitation in the Manaus region. The results obtained here have potential for possible prediction of precipitation characteristics at Manaus.

REGIONAL CIRCULATION DIFFERENCES BETWEEN A RAINY EPISODE AND A NONRAINY EPISODE IN EASTERN SÃO PAULO STATE IN MARCH 2006

The differences between the regional flow characteristics of a rainy episode and a nonrainy episode in March 2006 in eastern Sao Paulo state are discussed. The surface humidity and temperature characteristics do not show significant differences between the two cases. The composites of the middle tropospheric geopotential field and the lower-tropospheric wind field show a short-wave trough in the Atlantic off southern Brazil during the rainy episode. In the upper troposphere, the Bolivian high is stronger during the rainy episode than during the nonrainy episode, indicating that the troposphere over tropical South America is warmer during the rainy episode. The low-level jet in the rainy case does not penetrate northern Argentina, and is more NW-SE oriented, indicating that the humidity transport is more toward the southeastern Brazil. The moisture flux convergence over the eastern Sao Paulo at the 850-hPa is fairly strong in the rainy case whereas it is divergent in the nonrainy case. The presence of a low pressure area in the South Atlantic with westward tilt in the vertical provides synoptic forcing for the rising motion over eastern Sao Paulo state. These differences seem to be useful indicators for distinguishing rainy and nonrainy episodes.

Aplicação do método Fuzzy na classificação da zona de convergência do Atlântico Sul no sul da Amazônia

The South Atlantic Convergence Zone (SACZ) influences the variability of precipitation in South Amazon Basin. In this sense, we applied the Fuzzy Logical Method in order to have a mechanism of warning for the precipitation above the climatological average due to the SACZ (classified as oceanic, coastal or Amazon) over the Southern Amazon region, during the months from November to March in the period from 1999 to 2010. An objective algorithm to identify the occurrence of SACZ is designed and the classification in linguistic terms allows categorizing the SACZ in different types. During the periods of SACZ, the possibility of daily heavy rains (> 20 mm) is twice greater than the climatology. Amazonian and coastal SACZ produce nearly 71.4% of the precipitation during the months from January to March, representing 64% of the active events in Southern Amazon.