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Synoptic Scale Waves Associated with Heavy Rainfall Episodes in Southern Brazil
| Content Provider | Semantic Scholar |
|---|---|
| Author | Teixeira, Mateus Da Silva Satyamurty, Prakki |
| Copyright Year | 2006 |
| Abstract | Although the monthly distribution of rainfall in Southern Brazil is quite uniform (Rao and Hada 1990), day-to-day variability is high. The sources for rainfall in this region are mainly cold fronts and mesoscale convective complexes (MCC) (Velasco and Fritsch 1987). The extratropical cyclones approaching South America from the west move to east-southeast after crossing the Andes while the associated cold fronts move to north-northeast, producing convective activity in southern Brazil and further north (Kousky and Cavalcanti 1984). MCC develop over Paraguay and northern Argentina preferentially in the spring season (SON). They form during early morning hours and have a life cycle of less than one day (Velasco and Fritsch 1987). Interactions between low-level jet east of the Andes and the upper-level jet provide the instability for triggering the explosive development of the MCC in a moist ambient (Uccellini and Johnson 1979). MCC move eastward from their source region reaching Uruguay and southern Brazil causing, often, heavy rainfall. Other possible synoptic-scale systems responsible for heavy rainfall are the comma-cloud systems in the Atlantic (Bonatti and Rao 1987) and the midtropospheric cut-off lows approaching from the Pacific (Ramirez et al. 2000). Occasionally, the rainfall exceeds 100 mm day in some episodes causing serious problems to this region. The major economic activity of the region is agriculture and heavy rainfall may destroy entire crops over millions of hectares. The floods associated with these episodes are the worst natural disasters of southern Brazil. During some episodes loss of livestock and human lives are also reported. Heavy rainfall is a subjective term and its definition varies significantly. It is sometimes defined with reference to a single station rainfall and other times with reference to an average over a reasonably large area. ______________________ * Corresponding author address: Mateus da Silva Teixeira, CPTEC, INPE, São José dos Campos, 12227-010, e-mail: mateus@cptec.inpe.br However, it generally refers to a short period of time ranging from a few hours to one day. In many disastrously heavy rainfall episodes both intensity and duration of rain tend to be large. Harnack et al. (1999), for example, defined heavy rainfall episodes as those that had more than 51 mm of precipitation over an area of 10 000 km in a period of 1 to 2 days. As mentioned above, flood is one of the most dramatic consequences of heavy rainfall episodes both in the mountainous northeastern parts and in the southwestern pampas of southern Brazil. The possibility of a specific rainfall episode causing floods at a place is a function of many factors such as previous rainfall, regional topography, hydrological basin size, soil moisture saturation etc. But, the rainfall itself depends on convective instability, moisture convergence and its sustainability by synoptic-scale atmospheric conditions, which play a very important role in the maintenance of intense precipitation over sufficiently long intervals of time. Thus, the hypothesis we make here is that the small scale and mesoscale disturbances, which produce heavy rainfall over southern Brazil, develop when there is a favorable synoptic-scale situation over South America and the adjoining seas. The objective of this study is to establish the characteristics of the synoptic-scale patterns in the middle and lower troposphere associated with heavy rainfall episodes in southern Brazil within the period of 3 days prior to the occurrence of the episodes. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://mtc-m16b.sid.inpe.br/col/cptec.inpe.br/adm_conf/2005/10.06.13.40/doc/2067-2076.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
