Ernesto Caetano

The NAME 2004 Field Campaign and Modeling Strategy

The North American Monsoon Experiment (NAME) is an internationally coordinated process study aimed at determining the sources and limits of predictability of warm-season precipitation over North America. The scientific objectives of NAME are to promote a better understanding and more realistic simulation of warm-season convective processes in complex terrain, intraseasonal variability of the monsoon, and the response of the warm-season atmospheric circulation and precipitation patterns to slowly varying, potentially predictable surface boundary conditions. During the summer of 2004, the NAME community implemented an international (United States, Mexico, Central America), multiagency (NOAA, NASA, NSF, USDA) field experiment called NAME 2004. This article presents early results from the NAME 2004 campaign and describes how the NAME modeling community will leverage the NAME 2004 data to accelerate improvements in warm-season precipitation forecasts for North America.

Cold surge activity over the Gulf of Mexico in a warmer climate1

Cold surges are a dominant feature of midlatitude tropical interaction. During the North Hemisphere (NH) winter, midlatitude waves propagating from the Rocky Mountains into the Gulf of Mexico result in cold surges, also known as Nortes or Tehuantepecers, associated with severe weather over the southern part of Mexico. The magnitude of their intense surface winds, precipitation and drops in surface temperature depends on the characteristics of the midlatitude wave propagating into the tropics. The high spatial resolution (20km X 20km) version of the TL959L60-AGC Model of the Meteorological Research Institute of Japan is used to examine changes in cold surge activity under the A1B greenhouse gas emission scenario for the 2080 - 2099 period. The model realistically reproduces the spatial and temporal characteristics of cold surges for the 1980 - 1989 control period. The effect of changes in baroclinicity, static stability and mean flow over North America suggest that in a warmer climate, increased cold surge activity over the Gulf of Mexico would occur. However, these systems would have shorter wavelength (higher phase speeds) and shorter lifespans that could reduce the total amount of winter precipitation. The increased frequency of cold surges over the Gulf of Mexico would be a consequence of weaker baroclinicity and static stability in the lower troposphere over the cold surge genesis region, along with more dominant westerly winds, resulting from ENSO-like conditions in the atmospheric circulations over North America.

A Procedure for Operational Use of Wave Hindcasts to Identify Landfall of Heavy Swell

AbstractThe wave pattern on the Brazilian coastline is composed of both wind waves and swell. The wave systems (WSs), extracted from the spectra near the coast produced by numerical wave models, reveal the occasional presence of intense swells, with small significant wave height (HS) and large average period (Ta). This kind of event has nearly no effect over deep water, but its landfall can be accompanied by inundation, mainly when coupled with favorable tides and storm surge. Since these events are not clearly evident in the bulk parameters, this study proposes a methodology (i) to identify intense swells simulated by a coarse grid resolution wave modeling system (CWS) and (ii) to evaluate their importance. In this methodology, monitoring sites are defined along a 100-m isobath contouring the Brazilian coast, where the CWS hindcasts the spectra for a 31-yr period, from 1979 to 2009, obtained by the WAVEWATCH wave model. The spectra are partitioned into WSs, which are used to build cumulative distribution...

An improved second generation wave model

Um modelo numerico de ondas oceânicas (SG) e apresentado e aplicado para eventos no Mar Mediterrâneo durante o mes de dezembro de 1992. A adveccao de energia utiliza um esquema semi-Lagrangeano. Os ventos em superficie sao gerados por modelos atmosfericos global ou de area limitada ou, ainda, por dados atmosfericos de analise global. Os termos fontes (de geracao, dissipacao e interacao nao-linear) sao ajustados a curva empirica de crescimento de duracao limitada, proposta por Sanders. Um esquema de relaxacao para situacoes de variacao de direcao de vento, que permite que a energia emigra lentamente a nova direcao do vento, e proposto. Este esquema combina o espectro real e aquele obtido por um esquema de relaxacao direcional rapido. Uma simulacao com o SG, para dezembro de 1992 no mar Mediterrâneo, foi realizada c os resultados comparados com observacoes de dados de boias. Os resultados mostram que o SG e capaz de simular eventos de agitacao maritima associados a sistemas frontais que durante o periodo analisado passaram pela regiao. Comparado com a simulacao feita pelo modelo WAM (Komen et. al., 1994) para os mesmos eventos, mostra que ambos modelos apresentam resultados similares. Portanto o modelo SG pode ser aplicado em estudos de casos e experimentos climaticos com a vantagem de ter um custo computacional relativamente baixo.

Forecasting Summertime Surface Temperature and Precipitation in the Mexico City Metropolitan Area: Sensitivity of the WRF Model to Land Cover Changes

Changes in the frequency and intensity of severe hydrometeorological events in recent decades in the Mexico City Metropolitan Area have motivated the development of weather warning systems. The weather forecasting system for this region was evaluated in sensitivity studies using the Weather Research and Forecasting Model (WRF) for July 2014, a summer time month. It was found that changes in the extent of the urban area and associated changes in thermodynamic and dynamic variables have induced local circulations that affect the diurnal cycles of temperature, precipitation, and wind fields. A newly implemented configuration (land cover update and Four-Dimensional Data Assimilation (FDDA)) of the WRF model has improved the adjustment of the precipitation field to the orography. However, errors related to the depiction of convection due to parameterizations and microphysics remains a source of uncertainty in weather forecasting in this region.

Use of Radar Precipitation Estimates in Urban Areas: A Case Study of Mexico City

Storm events have long been a menace to Mexico City. The main reason is related to the fact that in summer, many showers can reach intensities of more than 20 mm/hour, which makes difficult the management of the drainage system in various areas of the city. As instance discharges of large magnitudes in the western part of the city are an element of danger, as they lead to flash flood that inundate populated areas downstream in a matter of minutes. Recent flooding events in Mexico City have revealed its vulnerability to severe weather conditions. Although regularization programs and new urban land policies are been implemented by the council government, there are still many families living in high risk areas. These areas over hillsides, and irregular human settlements still proliferate. Usually, severe storms can cause hazard landslides because unstable landfills and deforested hill slopes. On the other hand in the flat parts of the city, faulty drainage systems usually cause sewage flooding after continuous rain events. The urban sprawl undergone in the last half century, has not kept pace with urban services such as drainage. In the rainy season, puddles arise, sometimes caused by the presence of silt and debris in the ducts and the drainage system capacity is exceeded, and in other cases there are no absorption wells in areas with problems in the drainage network. Additionally, the lack of maintenance of dams and channels can also result in severe flooding problems. In most cases, the intense rainfall events produce merely an emergency response of fire departments.