Abstract:The rainfall and the 850 hPa wind characteristic of the semiarid interior zone of the northeast Brazil (NEB) are analyzed. The database used are the daily mean u, v, z, T , q and θ , at 850 hPa, 500 hPa and 200 hPa, displayed on a 2.5°× 2.5°g rid, from the NCEP/NCAR reanalysis; the daily mean OLR data from the Climate Diagnostics Center, from June 1986 to December 1997; and the gridded daily precipitation (P) analysis data in Brazil (10°S-40°S and 30°W-80°W), produced by the Climate Prediction Center, from 1977 to 1997. Daily time series of the normalized rainfall index (RI) and the normalized 850 hPa wind indexes (i.e. zonal index (ZI), the meridional index (MI) and the u minus v index (UVI)) were calculated for northern (A1: 7°S-10°S and 37°W-44°W) and southern (A2: 10°S-15°S and 40°W-45°W) domains. The RI, ZI, MI and UVI were defined by area-average of P, u, v, and u minus v, divided by the number of grid points corresponding to each area, respectively. As for regional features this region presents a well-defined annual cycle of rainfall with rainy seasons from December to April in A1 and from November to March in A2, and a few extreme rainfall events (during a 20-year period, 26 cases occurred in A1 and 39 cases in A2). Several synoptic scale systems acting alone or simultaneously in the NEB could explain the occurrence of heavy rainfall in this region. The RI is correlated positively with both the ZI and the UVI, and negatively with the MI, which might indicate that when easterly and southerly winds intensify (weaken), the rainfall decreases (increases). From the statistical perspective the UVI appears to be more effective to describe the daily rainfall variability in the NEB semiarid interior region, compared to the ZI or MI.
An explosive cyclogenesis over the east coast of South America was simulated during the period from 28 to 30 May 1999, using a limited-area hydrostatic model with 100 km horizontal resolution. The simulations showed that surface heat flux had an important contribution in developing the explosive cyclogenesis, and that the latent heat flux (LHF) has a larger contribution than the sensible heat flux (SHF). In the absence of a total heat flux (THF, ie. LHF plus SHF), the cyclone was 6 hPa shallower than in the control simulation (with THF). Without LHF the cyclone was 4 hPa shallower, while without SHF the cyclone presented the same intensity as the control simulation. The sensitivity experiments show the following effects of surface heat fluxes: i) the magnitudes and extensions of the effects grew with simulation time; ii) the maximum effects appeared in the southeastern part of the cyclone (warm front sector); iii) the LHF effects were 2-3 times larger than the SHF ones; and iv) the LHF effects were observed in the neighborhood of the cyclone, while the SHF effects were more spread out over the domain. In the THF absent experiment, a drier and colder environment was generated, mainly in the lower troposphere over the ocean, decreasing the environmental potential instability, latent heat release and cyclone intensification. Although the THF effects became larger during the most rapid development phase, they must have been present before this period because they preconditioned the environment for explosive development. Thus, to simulate or forecast the explosive cyclogenes on the South American east coast, an adequate representation of the planetary boundary layer is necessary.
RESUMONeste estudo foram realizados experimentos numéricos com um modelo meteorológico regional a fim de verificar o impacto dos Fluxos de Calor Latente (FCL) e Calor Sensível (FCS) em superfície no desenvolvimento de um ciclone intenso ocorrido sobre a costa leste da região sudeste da América do Sul, entre os dias 24 e 26 de julho de 1998. A taxa de intensificação do ciclone foi reduzida em 6 hPa/24 h no experimento em que os FCL e FCS estavam ausentes. Verificou-se que a ausência do FCL apresentou maior impacto do que a ausência do FCS, fazendo com que a taxa de intensificação fosse reduzida em 6 hPa/24 h para o experimento sem FCL e permanecesse inalterada sem FCS, mas neste último a isóbara de menor valor no centro do ciclone ocupou uma área menor. A ausência dos FCL e FCS em superfície gerou uma camada mais seca e mais fria próxima à superfície oceânica, reduzindo a instabilidade potencial do ambiente e diminuindo a intensificação do ciclone. Concluiu-se, portanto que os FCL e FCS em superfície foram importantes antes da fase de mais rápido desenvolvimento do ciclone, agindo no sentido de preparar o ambiente para uma ciclogênese mais intensa, através do fornecimento de energia e umidade para a baixa troposfera. Na fase de mais rápido desenvolvimento, a energia e a umidade disponíveis nas camadas mais baixas da atmosfera (inseridos na fase anterior) também foram importantes, permitindo ao ciclone se desenvolver mais intensamente do que ocorreria em um ambiente mais seco e menos instável termicamente. Palavras-Chave: ciclogênese, fluxos de calor em superfície, modelo regional. ABSTRACT: ROLE OF SURFACE LATENT AND SENSIBLE HEAT FLUXES ASSOCIATED TO A SOUTH AMERICA EAST COAST CYCLOGENESIS CASENumeric experiments were run with meteorological regional model with the purpose to verify the impact of both latent and sensible surface heat fluxes (FCL and FCS, respectively) during the development of an intense east cost cyclone over southeastern region of South America from 24 to 26 July, 1998. The intensification rate of the cyclone was reduced by 6 hPa/24 h in the experiment where the FCL and FCS were absents. It was also verified that the absence of FCL presented more impact than without FCS. The intensification rate was reduced by 6 hPa/24h in the experiment without FCL and became unaltered in the experiment without FCS, but in the later the isobar with minimum value around the cyclone center occupied a smaller area. The absence of the FCL and FCS generated a drier and colder layer near the oceanic surface, reducing the environmental potential instability and decreasing the cyclone intensification. With these results it is possible to conclude that the FCL and FCS were important before the phase of most rapid cyclone development, preparing the environment to a more intense cyclogenesis, supplying both energy and moisture to the lower troposphere. In the phase of the most rapid development, the available energy and moisture (inserted in the previous phase) in the lower levels were also important, allowing the cyclo...
Abstract. We have investigated the energetics of the summer circulation over tropical and extratropical South America. The kinetic energy equations of divergent (Kχ ) and rotational (Kψ) motion are utilized. All the terms of these equations are calculated on each day for five summers (November-February 1985–1990), using global wind analysis from the National Meteorological Center (NMC), now National Centers for Environmental Prediction (NCEP). The regional kinetic energy balance showed that the energy cycle over South America during the summer is, A P E to Kχ through the term -χ∇2Φ,and Kχ to Kψ through the term f∇ψ ∙ ∇χ. In the literature, several dominant oscillation modes have been noted over South America, namely the annual cycle, inter-annual, seasonal, intraseasonal, and high frequency scales, as revised by Lima. Results of the power spectrum analysis of kinetic energy terms indicate several statistically significant peaks and these have been confirmed with a fouth-order Butterworth filter. A well-defined mode, with a period around 30 days, was detected in the terms -χ∇2Φ and f∇ψ ∙ ∇χ, likely associated with Madden-Julian Oscillation (MJO). Later, we discuss the local kinetic energy balance using Mak’s local energetics scheme. We attempted to verify how the intraseasonal component interacts with other dominant oscillations over South America, such as seasonal cycle and high frequency disturbances,. It is noted that the major interactions among the three temporal scales occur mainly close to the South Atlantic Convergence Zone (SACZ) region. The temporal scale interactions in the Bolivian High (BH) and Northeast Brazil Low (NL) are distinct, and the dominant temporal scales may change from year to year.Key words. Meteorology and atmospheric dynamics (climatology, general circulation, tropical meteorology)
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.