Dry spells occurrence in the northwest portion of Rio Grande do Sul state between the years 1978 and 2005 and its association to the climatic conditions in the atmosphere / Veranicos ocorridos na porção noroeste do estado do Rio Grande do Sul entre 1978 e 2005 e sua associação às condições climáticas na atmosfera

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Agriculture plays an extremely important role in the economy of Rio Grande do Sul state. The target region of the present work in its northwest portion is represented by six cities: São Luiz Gonzaga, Santa Rosa, Cruz Alta, Iraí, Passo Fundo e Marcelino Ramos. It constitute a national focus of soya production and thus depend heavily on atmospheric conditions not only in the synoptic scale but also in climatic. In dry spells periods (known as veranicos in portuguese), during growing to harvest and, comprehending the months from October to March, the frequent lack of rain brings great economic losses to the region. The aim of this work is to estimate the climatology of dry spells occurrence in the northwest portion of Rio Grande do Sul in the first and fourth quarters of the year, between 1978 and 2005. Related to extreme climatic periods and the greater occurrence of dry spells, we depicted atmospheric and oceanic patterns. In conclusion, it is stated that the number of dry spells that occur in the first quarter of the year is greater than that which take place in the fourth quarter what is directly related to the monthly precipitation climatology. Santa Rosa is the municipality which presents the greater number of dry spells, even with higher monthly climatologic average than the other locations. March and December present more events than the other months, what in this case is related to the low amount of precipitation. During dry and wet periods, there is the evidence of a dipole standard based on ROL data. During dry (wet) periods in the southern part of Brazil it is observed low (high) values of ROL, in relation to climatology. Over the northern region of Brazil, during the same periods, it is observed inverted ROL anomalies, figuring the dipole pattern. An anomalous convergence (divergence) region in high levels above part of the South Region and the adjacent South Atlantic is observed during dry (wet) periods. The circulation pattern in low atmospheric levels, during wet (dry) periods, shows the strengthening (weakening) of the meridional low levels jet, which contributes for the increase (decrease) of rain in the region. ENSO events are somehow connected to the occurrence of dry spells in the region of study. All the considered month during dry (wet) periods in climatic extremes are related to negative (positive) TSM anomalies in the Equatorial Pacific region, that is, to La Niña (El Niño) events. This strong relation between precipitation variability and surface temperature anomalies over South Atlantic is not so evident. In conclusion, the occurrence of dry spells periods is well related to extreme climatic conditions.

ASSUNTO(S)

padrões atmosféricos soya climatologia climatology dry spells precipitation standards atmospherics veranico precipitação soja

ACESSO AO ARTIGO

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